Co-reporter:P. Liu;C. X. Wang;X. Y. Chen;G. W. Yang
The Journal of Physical Chemistry C September 4, 2008 Volume 112(Issue 35) pp:13450-13456
Publication Date(Web):Publication Date (Web): August 8, 2008
DOI:10.1021/jp802529r
We have developed a unique technique, the facile electrical-field-assisted laser ablation in liquid (EFLAL) without any catalyst or organic additives, to controllably fabricate the mass production of GeO2 micro- and nanoparticles with various shapes. By adjusting the applied electrical field, we synthesized the high-index facets GeO2 micro- and nanocubes and spindles, and propose the growth mechanisms of nanostructures upon EFLAL. On the basis of the cathodoluminescence measurements of dispersive GeO2 nanoparticles, we observed a shape-dependent red-shift of emission wavelength when the shape of GeO2 nanostructures transforms into spindle from cube, and then we established the physical model to address the anomalous red-shift of emission wavelength. Accordingly, we expecte EFLAL to be a general route to synthesize the micro- and nanostructures with metastable structures or metastable shapes.
Co-reporter:N. W. Wang;Y. H. Yang;G. W. Yang
The Journal of Physical Chemistry C September 3, 2009 Volume 113(Issue 35) pp:15480-15483
Publication Date(Web):Publication Date (Web): August 12, 2009
DOI:10.1021/jp906924w
In2O3−ZnO one-dimensional nanosized heterostructures constructed by In2O3 quadrangular columns and ZnO hexagonal disks have been fabricated by thermal chemical vapor transport and condensation with Au catalysts, and the cathodeluminescence of the as-prepared heterostructures are characterized. It was found that there is basically no luminescence emission from In2O3 quadrangular columns, while there is the intense luminescence emission from ZnO hexagonal disks, which are attributed to the whispering gallery mode from the optical resonator of ZnO hexagonal disks.
Co-reporter:X. W. Zhang;G. W. Yang
The Journal of Physical Chemistry C March 19, 2009 Volume 113(Issue 11) pp:4662-4668
Publication Date(Web):2017-2-22
DOI:10.1021/jp810483r
Using an empirical linear combination of atomic orbitals method (LCAO) based on the sp3 tight-binding scheme, we studied the band structures of graphene nanoribbons with armchair edges terminated by H atoms and found that the band gap exhibits the size dependence and the ‘family’ behaviors, in which a metallic graphene nanoribbon and two semiconducting graphene nanoribbons coexist in a ‘family’. On the basis of Pichard’s transfer matrix technique, we calculated the conductance of the graphene nanoribbons and interestingly found that the steplike curves of conductance display conductance plateaus in the integer multiples of G0 = 2e2/h and the conductance gap emerges in the semiconducting graphene nanoribbon. Meanwhile, a side needle is located on the conductance curve at zero energy in the metallic graphene nanoribbon, which is attributed to degeneration of eigenstates at zero energy. Additionally, we showed that edge states do not have a notable contribution to the conductance because of the strong localization.
Co-reporter:Zhaoqiang Zheng;Jiandong Yao
ACS Applied Materials & Interfaces March 1, 2017 Volume 9(Issue 8) pp:7288-7296
Publication Date(Web):February 9, 2017
DOI:10.1021/acsami.6b16323
Layered materials have been found to be promising candidates for next-generation microelectronic and optoelectronic devices due to their unique electrical and optical properties. The p–n junction is an elementary building block for microelectronics and optoelectronics devices. Herein, using the pulsed-laser deposition (PLD) method, we achieve pure In2Se3-based photodetectors and In2Se3/CuInSe2-based photodetectors with a lateral p–n heterojunction. In comparison to that of the pure In2Se3-based photodetector, the photodetectors based on the In2Se3/CuInSe2 heterojunction exhibit a tremendous promotion of photodetection performance and obvious rectifying behavior. The photoresponsivity and external quantum efficiency of the fabricated heterojunction-based device under 532 nm light irradiation are 20.1 A/W and 4698%, respectively. These values are about 7.5 times higher than those of our fabricated pure In2Se3-based devices. We attribute this promotion of photodetection to the suitable band structures of In2Se3 and CuInSe2, which greatly promote the separation of photoexcited electron–hole pairs. This work suggests an effective way to form lateral p–n junctions, opening up a new scenario for designing and constructing high-performance optoelectronic devices.Keywords: CuInSe2; In2Se3; lateral junction; layered materials; photodetectors;
Co-reporter:Pu Liu;Chengxin Wang;Ningsheng Xu;Ning Ke;Jianbin Xu;Jian Chen
The Journal of Physical Chemistry C July 16, 2009 Volume 113(Issue 28) pp:12154-12161
Publication Date(Web):2017-2-22
DOI:10.1021/jp901359b
The phase transformation from amorphous carbon to nanodiamond has been achieved by pulsed-laser irradiation of amorphous carbon films in a confined liquid at room temperature and ambient pressure. Nanocrystalline diamonds (NCDs) with size of about 4−7 nm were generated in the surface layer of amorphous carbon films by the amorphous carbon-to-diamond transition. It was found that the embedded NCDs microstructure array considerably improve the field emission performance of the treated amorphous carbon films. The physical and chemical mechanisms of the amorphous carbon-to-diamond transition induced by laser irradiation in liquid and the enhanced field emission caused by NCDs embedded in amorphous carbon films were pursued.
Co-reporter:Zhaoyong Lin;Lihua Li;Lili Yu;Weijia Li
Journal of Materials Chemistry A 2017 vol. 5(Issue 11) pp:5235-5259
Publication Date(Web):2017/03/14
DOI:10.1039/C6TA10497E
Converting abundant solar energy into precious and clean hydrogen energy through photocatalytic water splitting is a highly promising way to address energy shortages. Solar H2 evolution is a practical technology in the environmental and energy fields. The electron is the protagonist in solar H2 evolution and the electron behavior determines performance. Three pivotal steps, electron generation, electron survival and electron utilization, are involved in this photocatalytic process. This review discusses some typical cases from the last two years of improving the performance of solar H2 evolution through elaborately manipulating the electron behavior. The manipulation can be accomplished by modifying the photocatalyst itself (self-modification) and with the assistance of foreign materials (extra-modification). It is expected that the main ideas behind these strategies can be extracted and used when designing efficient and robust photocatalytic systems in the future.
Co-reporter:Churong Ma;Jiahao Yan;Yingcong Huang
Advanced Optical Materials 2017 Volume 5(Issue 24) pp:
Publication Date(Web):2017/12/01
DOI:10.1002/adom.201700761
AbstractPrevious designs of photonic nanoantennas are based on noble metal plasmonic structures, suffering from large ohmic loss and only possessing dipolar plasmon modes. This has driven the intense search for all-dielectric materials (ADMs) beyond noble metals. Here, for the first time, a strong scattering anisotropy in a Ge nanosphere is demonstrated in the visible and near-infrared regions. The forward-to-backward scattering ratio for an individual Ge nanosphere (150 nm) can reach a maximum value of ≈20 theoretically and ≈8 experimentally. This scattering behavior derives from the special real part and imaginary part of refractive index of Ge. Differing form other high-index ADMs such as Si and GaAs, the electric dipole and magnetic dipole resonances of Ge nanospheres are closer to each other in the spectrum due to the non-negligible imaginary part of refractive index. The spectral overlap between electric dipole and magnetic dipole resonances endows Ge nanospheres with efficient directional scattering near the scattering peak. Fano resonances with strong directivity are observed in Ge nanosphere dimers, which is the result of a broad electric gap mode coupled with a hybrid magnetic mode. These findings make Ge nanospheres a promising candidate for nanoantennas, directional sources, and optical switches.
Co-reporter:Jiong Yao;Zhaoqiang Zheng
Advanced Functional Materials 2017 Volume 27(Issue 33) pp:
Publication Date(Web):2017/09/01
DOI:10.1002/adfm.201701823
Nanoelectronics is in urgent demand of exceptional device architecture with ultrathin thickness below 10 nm and dangling-bond-free surface to break through current physical bottleneck and achieve new record of integration level. The advance in 2D van der Waals materials endows scientists with new accessibility. This study reports an all-layered 2D Bi2Te3-SnSe-Bi2Te3 photodetector, and the broadband photoresponse of the device from ultraviolet (370 nm) to near-infrared (808 nm) is demonstrated. In addition, the optimized responsivity reaches 5.5 A W−1, with the corresponding eternal quantum efficiency of 1833% and detectivity of 6 × 1010 cm Hz1/2 W−1. These figures-of-merits are among the best values of the reported all-layered 2D photodetectors, which are several orders of magnitude higher than those of the previous SnSe photodetectors. The superior device performance is attributed to the synergy of highly conductive surface state of Bi2Te3 topological insulator, perfect band alignment between Bi2Te3 and SnSe as well as small interface potential fluctuation. Meanwhile, the all-layered 2D device is further constructed onto flexible mica substrate and its photoresponse is maintained roughly unchanged upon 60 bending cycles. The findings represent a fundamental scenario for advancement of the next generation high performance and high integration level flexible optoelectronics.
Co-reporter:J. Xiao, P. Liu, C.X. Wang, G.W. Yang
Progress in Materials Science 2017 Volume 87(Volume 87) pp:
Publication Date(Web):1 June 2017
DOI:10.1016/j.pmatsci.2017.02.004
Laser ablation in liquid (LAL) has received considerable attention over the last decade, and is gradually becoming an irreplaceable technique to synthesize nanocrystals and fabricate functional nanostructures because it can offer effective solutions to some challenges in the field of nanotechnology. The goal of this review is to offer a comprehensive summary of recent developments of LAL in nanocrystal synthesis and nanostructure fabrication. First, we will introduce the fundamental processes of microsecond, nanosecond, and femtosecond LAL, and how the active species act differently in plasma, cavitation bubbles, and droplets in the different LAL processes. Second, a variety of LAL-based techniques for nanomaterials synthesis and processing are presented, such as electric-, magnetic-, and temperature-field LAL, as well as electrochemically assisted LAL, pulsed laser deposition in liquid, and laser writing of nanopatterns in liquid. Third, new progress in LAL-generated nanomaterials is described. Fourth, we emphasize five applications of LAL-generated nanomaterials that have emerged recently in the fields of optics, magnetism, environment, energy, and biomedicine. Finally, we consider the core advantages of LAL, the limitations of LAL and corresponding solutions, and the future directions in this promising research area.
Co-reporter:Zhaoyong Lin;Lihua Li;Lili Yu;Weijia Li
Physical Chemistry Chemical Physics 2017 vol. 19(Issue 12) pp:8356-8362
Publication Date(Web):2017/03/22
DOI:10.1039/C7CP00250E
Realization of hydrogen economy requires an environmental and economic method for hydrogen (H2) evolution. Dual-functional photocatalysis, that is, producing H2 from industrial wastewaters, may be the most ideal. However, it seems almost impossible to achieve dual-functional photocatalysis because of the difficulty in the simultaneous existence of photocatalytic pollutant degradation (PDR) and H2 evolution reactions (HER) in one system. All previous designs show that either HER or PDR is inhibited due to the insufficient management of the photo-generated electrons (e−) and holes (h+). To overcome this issue, we consider that both PDR and HER could be improved simultaneously by employing a suitable photocatalyst whose main active species in PDR are h+. In this case, e− and h+ can play their own roles in accomplishing HER and PDR, respectively, via the charge spatial separation in the selected photocatalyst. Herein, Cu2O polyhedrons are constructed as a proof-of-concept example. A favorable dual-functional photocatalytic performance is achieved by the Cu2O cubooctahedrons. Furthermore, an appropriate pollutant concentration is significant for the optimization of both HER and PDR performances due to the competition between H atom adsorption and pollutant molecule adsorption on the surfaces of the photocatalyst. This advance provides the H2 evolution technology with a more environmental and economic method.
Co-reporter:J. D. Yao;Z. Q. Zheng;G. W. Yang
Nanoscale (2009-Present) 2017 vol. 9(Issue 42) pp:16396-16403
Publication Date(Web):2017/11/02
DOI:10.1039/C7NR04374K
The fresh water crisis has emerged as one of the most urgent bottlenecks hindering the rapid development of modern industry and society. Solar energy-driven water evaporation represents a potential green and sustainable solution to address this issue. Herein, for the first time, centimeter-scale BiInSe3-coated nickel foam (BiInSe3@NF) as an efficient solar-enabled evaporator was successfully achieved and exploited for solar energy-driven water evaporation. Benefitting from multiple scattering-induced light trapping of the rough substrate, strong light–matter interaction and intermediate band (IB)-induced efficient phonon emission of BiInSe3, the BiInSe3@NF device achieved a high evaporation rate of 0.83 kg m−2 h−1 under 1 sun irradiation, which is 2.5 times that of pure water. These figures-of-merit are superior to recently reported state-of-the-art photothermal conversion materials, such as black titania, plasmonic assembly and carbon black. In addition, superior stability over a period of 60 days was demonstrated. In summary, the current contribution depicts a facile scenario for design, production and application of an economical and efficient solar-enabled BiInSe3@NF evaporator. More importantly, the phonon engineering strategy based on alloying induced IB states can be readily applied to other analogous van der Waals materials and a series of superior vdWM alloys toward photothermal applications can be expected in the near future.
Co-reporter:T. M. Chen;X. J. Wu;J. X. Wang;G. W. Yang
Nanoscale (2009-Present) 2017 vol. 9(Issue 32) pp:11806-11813
Publication Date(Web):2017/08/17
DOI:10.1039/C7NR03179C
As one of the transition metal dichalcogenide materials, WSe2 in the form of a few layers (nanosheets) have received much attention due to their unique physical, optical and electrical properties. Herein, we demonstrate that WSe2 nanosheets possess intrinsic enzyme mimic activity. Under acidic conditions, they exhibit pronounced peroxidase-like property. The Michaelis–Menten kinetics indicate that the catalytic activity of WSe2 nanosheets is comparable to that of horseradish peroxidase. Based on the color reaction, a platform of WSe2 nanosheets was constructed to detect glucose concentration and it showed high sensitivity and high selectivity, which means that WSe2 nanosheets with peroxidase-like property can be used to develop a highly sensitive and selective colorimetric method for glucose detection. Moreover, due to the electron-transferring and antioxidant properties of WSe2 few layers, the peroxidase-like catalysis is proposed. These findings pave the way for further application of WSe2 nanosheets in nano-biomedicine.
Co-reporter:Weijia Li;Zhaoyong Lin
Nanoscale (2009-Present) 2017 vol. 9(Issue 46) pp:18290-18298
Publication Date(Web):2017/11/30
DOI:10.1039/C7NR06755K
Semiconductor photocatalysis for hydrogen production is a promising route to address current energy demands. It is still a great challenge to spatially separate photogenerated electrons and holes in bulk photocatalysts because of the long carrier transport pathway from the bulk to the surface. 2D heterostructured photocatalysts with the type II band alignment can not only shorten the carrier transport pathway, but also create an electric field at the interface to suppress the carrier recombination. However, ultrathin and intimate-contact 2D heterostructured photocatalysts have rarely been achieved so far. Herein, we reported that ZnIn2S4 nanosheets were self-assembled on few-layer MoS2 nanosheets to fabricate ultrathin and intimate-contact 2D heterostructured photocatalysts. This 2D heterostructure was formed thanks to the strong electrostatic adsorption between MoS2 and ZnIn2S4. Under visible light irradiation, the H2 evolution rate of 2D MoS2/ZnIn2S4 heterostructured photocatalysts can reach 8898 μmol g−1 h−1, which is almost 16 times higher than that of the pure ZnIn2S4 photocatalysts. The dramatically enhanced photocatalytic performance was ascribed to the better charge separation and the accelerated surface reaction due to the heterostructure and more active sites provided by MoS2. These results provided a new insight for the design and development of 2D heterostructured photocatalysts.
Co-reporter:T. M. Chen;X. M. Tian;L. Huang;J. Xiao;G. W. Yang
Nanoscale (2009-Present) 2017 vol. 9(Issue 40) pp:15673-15684
Publication Date(Web):2017/10/19
DOI:10.1039/C7NR05629J
Nanodiamonds (NDs) have recently become a focus of interest from the viewpoints of both science and technology. Their intriguing properties make them suitable as biologically active substrates, in biosensor applications as well as diagnostic and therapeutic biomedical imaging probes. Here, we demonstrate that NDs, as oxidation and reduction catalysts, possess intrinsic enzyme mimetic properties of oxidase, peroxidase and catalase, and these behaviors can be switched by modulating the pH value. NDs not only catalyze the reduction of oxygen (O2) and hydrogen peroxide (H2O2) at acidic pH, but also catalyze the dismutation decomposition of H2O2 to produce O2 at alkaline pH. It was proposed that the molecular mechanism of their peroxidase-like activity is electron-transfer acceleration, the source of which is likely derived from oxygen containing functional groups on their surface. Based on the color reaction, a nanodiamond-based enzyme linked immunosorbent assay (ELISA) was established for the detection of immunoglobulin G (IgG). Surprisingly, NDs display an excellent antioxidant activity due to the protective effect against H2O2-induced cellular oxidative damage. These findings make NDs a promising enzyme mimetic candidate and expand their applications in biocatalysis, bioassays and nano-biomedicine.
Co-reporter:Churong Ma;Jiahao Yan;Yuming Wei;Pu Liu
Journal of Materials Chemistry C 2017 vol. 5(Issue 19) pp:4810-4819
Publication Date(Web):2017/05/18
DOI:10.1039/C7TC00650K
Although previous designs of nonlinear optical (NLO) nanostructures have focused on photonic crystals and metal plasmonic nanostructures, complex structures, large ohmic loss, and Joule heating greatly hinder their practical applications. Beyond photonic crystals and metal plasmonic nanostructures, all-dielectric materials (ADMs) offer new ways to generate NLO behavior at subwavelength scales. Herein, we report enhancement in the tunable second harmonic generation (SHG) reflected from individual mid-refractive ADM nanoparticles, BaTiO3 nanoparticles (BTO NPs). Multipole decomposition, as observed in the linear spectra, demonstrated that the SHG enhancement originated from an overlap between the magnetic dipole or quadrupole resonance and the second harmonic wavelength of the pump source. In the vicinity of magnetic resonances, the localized field inside the nanoparticles could be increased by more than one order of magnitude. Compared with the spectral-separated electric and magnetic resonances in high-refractive all-dielectric nanostructures, an overlap of resonances was observed in the mid-refractive all-dielectric nanostructures and it resulted in electromagnetic (EM) mode coupling. A broad spectral characteristic results in moderate EM field enhancements over a wide wavelength range, which is conducive to the tunability of the SHG responses. Our study revealed the relationship between the linear and nonlinear optics at the nanoscale and helped in the design of efficient nonlinear optical devices based on ADMs.
Co-reporter:Zhaoyong Lin;Jiling Li;Lihua Li;Lili Yu;Weijia Li
Journal of Materials Chemistry A 2017 vol. 5(Issue 2) pp:773-781
Publication Date(Web):2017/01/03
DOI:10.1039/C6TA09169E
The supply of clean hydrogen energy through photocatalysis in the future requires the finding of low-cost, efficient and durable cocatalysts to replace noble metal Pt. Cu and Ni are believed to be two promising materials. However, their cocatalytic performance is still limited. The theory of the hydrogen evolution pathway on Cu and Ni surfaces reveals that Cu can release H2 molecules easily but capture H atoms and photoelectrons with difficulty, while Ni performs inversely. To overcome this issue, we consider that improved cocatalytic performance could be achieved by the substitution of Ni atoms into a Cu crystal lattice to form a CuNi alloy. Here, we reported that CuNi alloy nanoparticles were prepared by a process of laser ablation in liquid (LAL). Their compositions could be tuned by varying the concentration of the isopropanol aqueous solution, which is novel in LAL. We demonstrated that the photocatalytic H2 evolution performance of TiO2 nanorods can be greatly improved by loading these CuNi nanoalloys on them to act as cocatalysts. Furthermore, these cocatalysts present favorable stability. The best cocatalytic performance was achieved by Cu63Ni37 alloy nanoparticles, even better than Pt. First-principles calculations demonstrated that the Cu63Ni37 alloy nanoparticles possess a high H atom adsorption energy, a large work function and a small H2 molecule adsorption energy, resulting in the rational manipulation of the hydrogen evolution pathway and the optimal cocatalytic performance. This work provided a strategy to design cheap, robust and durable cocatalysts for photocatalytic H2 evolution.
Co-reporter:Zhaoyong Lin;Jun Xiao;Lihua Li;Pu Liu;Chengxin Wang
Advanced Energy Materials 2016 Volume 6( Issue 4) pp:
Publication Date(Web):
DOI:10.1002/aenm.201501865
Copper(I) oxide (Cu2O) is an attractive photocatalyst because of its abundance, low toxicity, environmental compatibility, and narrow direct band gap, which allows efficient light harvesting. However, Cu2O exhibits poor photocatalytic performance and photostability because of its short electron diffusion length and low hole mobility. Here, it is demonstrated that nanodiamond (ND) can greatly improve the photocatalytic hydrogen evolution reaction (HER) of the p-type photocatalyst Cu2O nanocrystals by nanocomposition. Compared with pure Cu2O nanocrystals, this composite shows a tremendous improvement in HER performance and photostability. HER rates of 100.0 mg NDs-Cu2O nanocrystals are 1597 and 824 under the simulated solar light irradiation (AM 1.5, 100 mW cm−2) and visible light irradiation (420–760 nm, 77.5 mW cm−2), respectively. The solar-to-hydrogen conversion efficiency of this composite is 0.85%, which is nearly ten times higher than that of pure Cu2O. The quantum efficiency of the composite is high, with values of 0.17% at and 0.23% at . The broad spectral response of ND provides numerous carriers for the subsequent reactions. The electron-donating ability of ND and suitable band structures of the two components promote electron injection from ND to Cu2O. These results suggest the broad applicability of ND to ameliorate the photoelectric properties of semiconductors.
Co-reporter:Zhaoyong Lin;Jiling Li;Zhaoqiang Zheng;Lihua Li;Lili Yu;Chengxin Wang
Advanced Energy Materials 2016 Volume 6( Issue 15) pp:
Publication Date(Web):
DOI:10.1002/aenm.201600510
Solar photocatalytic water splitting has been a promising way to provide clean hydrogen energy. There are two weaknesses in the typical photocatalytic process in which photocatalysts are generally dispersing in water under stir. One is the inadequate utilization of light energy and the other one is the cumbersome operation in the recycling procedure. This study demonstrates an efficient solar photocatalytic water splitting using a floating sheet with a novel WSe2 cocatalyst. The sheet is fabricated by laser-depositing WSe2 film on a carbon foam (CF) substrate and drop-casting of the synthesized nanodiamond-embedded Cu2O (NEC) photocatalysts. This is a new-type artificial photocatalytic system that overcomes the above-mentioned weaknesses of a powder-dispersing system. The WSe2 cocatalyst acts as an electron sink to promote electron–hole separation, resulting in the further improvement of photocatalytic performance. This floating NEC/WSe2/CF structure achieves efficient water splitting upon simulated solar irradiation with an increased H2 evolution rate, which is 13.2 times that of the powder-dispersing system. This study offers a strategy for the design of new-type photocatalytic system and discovery of alternative noble metal-free cocatalysts.
Co-reporter:Jiahao Yan, Zhaoyong Lin, Churong Ma, Zhaoqiang Zheng, Pu Liu and Guowei Yang
Nanoscale 2016 vol. 8(Issue 32) pp:15001-15007
Publication Date(Web):18 Jul 2016
DOI:10.1039/C6NR04857A
Hot carriers, generated via the non-radiative decay of localized surface plasmon, can be utilized in photovoltaic and photocatalytic devices. In recent years, most studies have focused on conventional plasmon materials like Au and Ag. However, they suffer from several drawbacks like low energy of the generated hot carriers and a high charge-carrier recombination rate. To resolve these problems, here, we propose the plasmon resonances in heavily self-doped titanium oxide (TiO1.67) to realize effective hot carrier generation. Since the plasmon resonant energy of TiO1.67 nanoparticles (2.56 eV) is larger than the bandgap (2.15 eV), plasmon resonances through interband transition can realize both the generation and separation of hot carriers and bring a new strategy for visible-light photodegradation. The photodegradation rate for methyl orange was about 0.034 min−1. More importantly, the combination of plasmonic and catalytic properties makes it feasible to investigate the degradation process of different materials and different structures at the single particle level in situ. By detecting the scattering shift, we demonstrated that the TiO1.67 dimer (Δλ/ΔλRIU = 0.16) possesses a higher photodegradation rate than an individual nanoparticle (Δλ/ΔλRIU = 0.09). We hope this finding may be a beginning, paving the way toward the development of semiconductor plasmonic materials for new applications beyond noble metals.
Co-reporter:Jiahao Yan, Pu Liu, Churong Ma, Zhaoyong Lin and Guowei Yang
Nanoscale 2016 vol. 8(Issue 16) pp:8826-8838
Publication Date(Web):25 Mar 2016
DOI:10.1039/C6NR01295G
Through the excitation of plasmon resonance, the energy of plasmonic nanoparticles either reradiates through light scattering or decays into energetic electrons (absorption). The plasmon-induced absorption can greatly enhance the efficiency of solar energy harvesting, local heating, photodetection and photocatalysis. Here, we demonstrate that heavily self-doped titanium oxide nanoparticles (TiO1.67 analogue arising from oxygen vacancies in rutile TiO2) with the plasmon resonance dominated by an interband transition shows strong absorption to build a broadband perfect absorber in the wavelength range from 300 to 2000 nm covering the solar irradiation spectrum completely. The absorptivity of the fabricated array is greater than 90% in the whole spectral range. And the broadband and strong absorption is due to the plasmon hybridization and hot spot generation from near-touching TiO1.67 nanoparticles with different sizes. What is more, the local heating of a TiO1.67 nanoparticle layer is fast and effective. The temperature increases quickly from 30 °C to 80 °C within 200 seconds. This local heating can realize rapid solar-enabled evaporation which can find applications in large-scale distillation and seawater desalination. These findings actually open a pathway for applications of these newly developed plasmonic materials in the energy and environment fields.
Co-reporter:Jiahao Yan, Pu Liu, Zhaoyong Lin and Guowei Yang
Nanoscale 2016 vol. 8(Issue 11) pp:5996-6007
Publication Date(Web):17 Feb 2016
DOI:10.1039/C5NR07871G
Sensing is regarded as one of the most important applications of noble metal-based nanoplasmonics. However, all previous designs have been based on the wavelength-shift of the localized surface plasmon resonance, in which the sensitivity is intrinsically limited by the low quality factors induced by metal losses, and meanwhile the large ohmic loss, high cost and inevitable toxicity and biofouling for detection in vivo greatly hinder their further applications in biosensors. Beyond noble metals, high-refractive index dielectric materials (HRDMs) like silicon with low-loss and strong magnetic response have drawn more attention. Here, for the first time, we proposed a HRDM nanosphere as a new nanosensor for biomolecule detection, and experimentally demonstrated a HRDM sensor working on the intensity-shift but not wavelength-shift of the scattering. The sensing mechanism based on the synergistic effect of the broadening electric mode shift of HRDMs and the Kerker's scattering intensity-shift is beneficial to achieve higher sensitivity. We validated the efficacy of our sensor to detect refractive index changes and trace amounts of streptavidin molecules, and the sensitivity can reach 27 times as high as the highest sensitivity reported to date for nanoplasmonic structures. These findings showed that monitoring the change of the scattering intensity of HRDM nanostructures is superior to monitoring the wavelength-shift of nanoplasmonic structures, as is widely used in nanoplasmonic sensors, for biosensing, meaning HRDM nanosensors could be an important tool in biomolecule detection.
Co-reporter:Y. Q. Gao, X. Y. Liu and G. W. Yang
Nanoscale 2016 vol. 8(Issue 9) pp:5015-5023
Publication Date(Web):02 Feb 2016
DOI:10.1039/C5NR08989A
The design of highly efficient, durable, and earth-abundant catalysts for the oxygen evolution reaction (OER) is crucial in order to promote energy conversion and storage processes. Here, we synthesize amorphous mixed-metal (Ni–Fe) hydroxide nanostructures with a homogeneous distribution of Ni/Fe as well as a tunable Ni/Fe ratio by a simple, facile, green and low-cost electrochemical technique, and we demonstrate that the synthesized amorphous nanomaterials possess ultrahigh activity and super long-term cycle stability in the OER process. The amorphous Ni0.71Fe0.29(OH)x nanostructure affords a current density of 10 mA cm−2 at an overpotential of a mere 0.296 V and a small Tafel slope of 58 mV dec−1, while no deactivation is detected in the CV testing even up to 30000 cycles, which suggests the promising application of these amorphous nanomaterials in electrochemical oxidation. Meanwhile, the distinct catalytic activities among these amorphous Ni–Fe hydroxide nanostructures prompts us to take notice of the composition of the alloy hydroxides/oxides when studying their catalytic properties, which opens an avenue for the rational design and controllable preparation of such amorphous nanomaterials as advanced OER electrocatalysts.
Co-reporter:X. Y. Liu, Y. Q. Gao and G. W. Yang
Nanoscale 2016 vol. 8(Issue 7) pp:4227-4235
Publication Date(Web):26 Jan 2016
DOI:10.1039/C5NR09145D
Flexible and transparent supercapacitors, as advanced energy storage devices, are essential for the development of innovative wearable electronics because of their unique optical and mechanical qualities. However, all previous designs are based on carbon-based nanostructures like carbon nanotubes and graphene, and these devices usually have poor or short cycling lives. Here, we demonstrate a high-performance, flexible, transparent, and super-long-life supercapacitor made from ultrafine Co3O4 nanocrystals synthesized using a novel process involving laser ablation in liquid. The fabricated flexible and transparent pseudocapacitor exhibits a high capacitance of 177 F g−1 on a mass basis and 6.03 mF cm−2 based on the area of the active material at a scan rate of 1 mV s−1, as well as a super-long cycling life with 100% retention rate after 20000 cycles. An optical transmittance of up to 51% at a wavelength of 550 nm is achieved, and there are not any obvious changes in the specific capacitance after bending from 0° to 150°, even after bending over 100 times. The integrated electrochemical performance of the Co3O4-based supercapacitor is greatly superior to that of the carbon-based ones reported to date. These findings open the door to applications of transition metal oxides as advanced electrode materials in flexible and transparent pseudocapacitors.
Co-reporter:Jiandong Yao, Zhaoqiang Zheng and Guowei Yang
Journal of Materials Chemistry A 2016 vol. 4(Issue 33) pp:7831-7840
Publication Date(Web):19 Jul 2016
DOI:10.1039/C6TC01453D
Transition metal dichalcogenides (TMDs) manifest excellent phonon-limited mobility and strong light–matter interaction, which, however, conflict with the long response time and low responsivity of TMD-based photodetectors. The extreme susceptibility of TMDs' electronic qualities to the large density of unscreened disturbances from the SiO2 substrate accounts for such inconformity. Here, we evaluated the potential of WS2 for photodetectors by passivating SiO2 substrates with layered Bi2Te3, a representative three dimensional topological insulator. Comparative photoswitching measurements of the WS2/Bi2Te3 photodetector demonstrated its stable and broadband photoresponse from 370 to 1550 nm. Meanwhile, WS2 and Bi2Te3 allied a high responsivity of 30.7 A W−1, a pronounced detectivity of 2.3 × 1011 cm Hz1/2 W−1 as well as a short response time of 20 ms, which make the device stand out among previously reported WS2 photodetectors. In fact, the responsivity and detectivity are comparable to those of state-of-the-art commercial Si and Ge photodetectors (R ∼ 0.5 to 0.85 A W−1, D* ∼ 3 × 1011 to 3 × 1012 cm Hz1/2 W−1), suggesting its great potential for practical applications. In addition, we also established that the excellent device performance is attributed to the synergy of the passivation of the SiO2 substrate, efficient carrier separation at the WS2/Bi2Te3 heterointerface and excellent carrier transport along the time-reversal-symmetry protected surface channel of Bi2Te3. In summary, these findings suggest that the WS2/Bi2Te3 photodetector will launch a significant advance in next-generation photodetection. Moreover, the interface engineering strategy depicts a universal scenario for development of TMD devices in the future.
Co-reporter:C. R. Ma, J. H. Yan, P. Liu, Y. M. Wei and G. W. Yang
Journal of Materials Chemistry A 2016 vol. 4(Issue 25) pp:6063-6069
Publication Date(Web):01 Jun 2016
DOI:10.1039/C6TC01635A
Nonlinear optical (NLO) nanostructures have played important roles in frequency conversion, optical switching, information storage and biomedical imaging. Although previous designs have focused on photonic crystals and metal plasmonic nanostructures, complex structure, large ohmic loss and Joule heating greatly hinder their practical applications. Beyond photonic crystals and metal plasmonic nanostructures, all-dielectric materials (ADMs) bring new ways to generate NLO behavior at subwavelength scales. We, for the first time to our knowledge, demonstrate irregular-geometry induced second harmonic generation (SHG) enhancement from an individual all-dielectric SiC nanoparticle. SHG conversion efficiency of single irregular-geometry SiC nanoparticles increases to 10−5 under an average excitation power of 6 mW at 880 nm excitation, thirtyfold higher than that of SiC nanosphere. We also establish that not only electric dipole mode but also magnetic dipole mode can exist in the vicinity of nanoparticles in mid-refractive (2 < n < 3) ADMs, and the stronger enhancement of the magnetic response induced by the irregular-geometry makes a great contribution to the SHG enhancement. A modified formula that includes electric and magnetic contributions is proposed to predict the SHG enhancement from ADMs. This discovery makes geometry-tuning all-dielectric nanoparticles promising in NLO nanostructures of nanophotonics in the future.
Co-reporter:C. R. Ma, J. Xiao and G. W. Yang
Journal of Materials Chemistry A 2016 vol. 4(Issue 21) pp:4692-4698
Publication Date(Web):11 Apr 2016
DOI:10.1039/C6TC00648E
Carbyne, the third allotrope of carbon with alternating single and triple bonds, consists of sp-hybridized carbon atoms. Theoretically, with two degenerate π-electron bands in one monomer, carbyne exhibits stronger nonlinear optical responses than graphene and it is acknowledged as a superior nonlinear optical material with just one π-electron band. Very recently, carbyne has been synthesized in the laboratory. Here, we demonstrate the giant nonlinear optical responses of carbyne. By employing the Z-scan technique using a femtosecond laser, we show that carbyne exhibits a large nonlinear absorption coefficient β and a refractive index n2 of 3.53 × 10−13 m W−1 and −1.40 × 10−13 esu at 800 nm excitation, respectively. Excellent broadband optical limiting responses of carbyne to femtosecond laser pulses at 800 and 400 nm were observed, respectively. We also establish that extensive π-electron delocalization and electron resonance enhancement of carbyne have made significant contributions to these nonlinear optical responses. These findings open the door to exploring the optical and technological applications of carbyne.
Co-reporter:Lihua Li, Lili Yu, Zhaoyong Lin, and Guowei Yang
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 13) pp:8536
Publication Date(Web):March 17, 2016
DOI:10.1021/acsami.6b00966
The reduced TiO2-graphene oxide heterostructure as an alternative broad spectrum-driven efficient water splitting photocatalyst has become a really interesting topic, however, its syntheses has many flaws, e.g., tedious experimental steps, time-consuming, small scale production, and requirement of various additives, for example, hydrazine hydrate is widely used as reductant to the reduction of graphene oxide, which is high toxicity and easy to cause the second pollution. For these issues, herein, we reported the synthesis of the reduced TiO2-graphene oxide heterostructure by a facile chemical reduction agent-free one-step laser ablation in liquid (LAL) method, which achieves extended optical response range from ultraviolet to visible and composites TiO2–x (reduced TiO2) nanoparticle and graphene oxide for promoting charge conducting. 30.64% Ti3+ content in the reduced TiO2 nanoparticles induces the electronic reconstruction of TiO2, which results in 0.87 eV decrease of the band gap for the visible light absorption. TiO2–x-graphene oxide heterostructure achieved drastically increased photocatalytic H2 production rate, up to 23 times with respect to the blank experiment. Furthermore, a maximum H2 production rate was measured to be 16 mmol/h/g using Pt as a cocatalyst under the simulated sunlight irradiation (AM 1.5G, 135 mW/cm2), the quantum efficiencies were measured to be 5.15% for wavelength λ = 365 ± 10 nm and 1.84% for λ = 405 ± 10 nm, and overall solar energy conversion efficiency was measured to be 14.3%. These findings provided new insights into the broad applicability of this methodology for accessing fascinate photocatalysts.Keywords: H2 production; laser ablation in liquid; reduced graphene oxide; reduced TiO2; water splitting
Co-reporter:Jiandong Yao, Zhaoqiang Zheng, and Guowei Yang
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 20) pp:12915-12924
Publication Date(Web):May 6, 2016
DOI:10.1021/acsami.6b03691
The successful peeling of graphene heralded the era of van der Waals material (vdWM) electronics. However, photodetectors based on semiconducting transition metal dichalcogenides (TMDs), formulated as MX2 (M = Mo, W; X = S, Se), often suffer either poor responsivity or long response time because of their high density of deep-level defect states (DLDSs). Alloy engineering, which can shift the DLDSs to shallow-level defect states, is proposed to be an efficient strategy to solve this problem. However, proof-of-concept is still lacking, which is probably because of the absence of a facile technology to grow high-quality alloyed TMDs. Here, we report the growth of large-scale and high-quality Mo0.5W0.5S2 alloy films via pulsed laser deposition (PLD). We demonstrate that the resulting Mo0.5W0.5S2 photodetector possesses a stable photoresponse from 370 to 1064 nm. The photocurrent exhibits positive dependence on both the source–drain voltage and incident power density, providing good tunability for multifunctional photoelectrical applications. We also establish that, because of the suppression of DLDSs with alloy engineering, the Mo0.5W0.5S2 photodetector achieves a good responsivity of 5.8 A/W and a response time shorter than 150 ms. The working mechanism for the suppression of DLDSs in Mo0.5W0.5S2 is unveiled by qualitatively analyzing the alloying-dressed band structure. In conclusion, the excellent performance of the PLD-grown Mo0.5W0.5S2 photodetector may pave the way for next-generation photodetection. The approach shown here represents a fundamental and universal scenario for the development of alloyed TMDs.
Co-reporter:Zhaoqiang Zheng, Jiandong Yao, Jun Xiao, and Guowei Yang
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 31) pp:20200
Publication Date(Web):July 20, 2016
DOI:10.1021/acsami.6b06531
Layered materials have rapidly established themselves as intriguing building blocks for next-generation photodetection platforms in view of their exotic electronic and optical attributes. However, both relatively low mobility and heavier electron effective mass limit layered materials for high-performance applications. Herein, we employed nanodiamonds (NDs) to promote the performance of multilayer In2Se3 photodetectors for the first time. This hybrid NDs–In2Se3 photodetector showed a tremendous promotion of photodetection performance in comparison to pristine In2Se3 ones. This hybrid devices exhibited remarkable detectivity (5.12 × 1012 jones), fast response speed (less than 16.6 ms), and decent current on/off ratio (∼2285) simultaneously. These parameters are superior to most reported layered materials based photodetectors and even comparable to the state-of-the-art commercial photodetectors. Meanwhile, we attributed this excellent performance to the synergistic effect between NDs and the In2Se3. They can greatly enhance the broad spectrum absorption and promote the injection of photoexcited carrier in NDs to In2Se3. These results actually open up a new scenario for designing and fabricating innovative optoelectronic systems.Keywords: In2Se3; layered materials; nanodiamonds; photodetectors; synergistic effect
Co-reporter:Jiandong Yao, Zexiang Deng, Zhaoqiang Zheng, and Guowei Yang
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 32) pp:20872
Publication Date(Web):July 26, 2016
DOI:10.1021/acsami.6b06222
Photoelectric conversion is of great importance to extensive applications. However, thus far, photodetectors integrated with high responsivity, excellent detectivity, large phototo-dark current ratio, fast response speed, broad spectral range, and good stability are rarely achieved. Herein, we deposited large-scale and high-quality polycrystalline indium sesquitelluride (α-In2Te3) films via pulsed-laser deposition. Then, we demonstrated that the photodetectors made of the prepared α-In2Te3 films possess stable photoswitching behavior from 370 to 1064 nm and short response time better than ca. 15 ms. At a source-drain voltage of 5 V, the device achieves a high responsivity of 44 A/W, along with an outstanding detectivity of 6 × 1012 cm H1/2 W–1 and an excellent sensitivity of 2.5 × 105 cm2/W. All of these figures-of-merit are the best among those of the reported α-In2Te3 photodetectors. In fact, they are comparable to the state-of-the-art commercial Si and Ge photodetectors. For the first time, we established the theoretical evidence that α-In2Te3 possesses a direct bandgap structure, which reasonably accounts for the superior photodetection performances above. Importantly, the device exhibits a good stability against the multiple photoswitching operation and ambient environment, along with no obvious voltage-scan hysteresis. These excellent figures-of-merit, together with the broad spectral range and good stability, underscore α-In2Te3 as a promising candidate material for next-generation photodetection.Keywords: broadband; direct bandgap; indium sesquitelluride; photodetection; pulsed-laser deposition
Co-reporter:Pu Liu, Jiahao Yan, Curong Ma, Zhaoyong Lin, and Guowei Yang
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 34) pp:22468
Publication Date(Web):August 9, 2016
DOI:10.1021/acsami.6b05123
Nanoantennas have found many applications in ultrasmall sensors, single-molecule detection, and all-optical communication. Conventional nanoantennas are based on noble-metal plasmonic structures, but suffer from large ohmic loss and only possess dipolar plasmon modes. This has driven an intense search for all-dielectric materials beyond noble metals. Here, we propose midrefractive nanospheres as a novel all-dielectric material to realize broadband unidirectional radiation and effective radiative tailoring in the visible region. Midrefractive all-dielectric materials such as boron nanospheres possess broad and overlapping electric and magnetic dipole modes. The internal interaction between these two modes can route the radiation almost on the one side covering the whole visible range. Unlike the elaborate design in plasmonic nanostructures to obtain strong coupled broad and narrow modes, the bright mode in boron nanospheres is intrinsic, independent, and easily coupled with adjacent narrow modes. So the strong interaction in boron-based heterodimer is able to realize an independent and precise tailoring of the radiant and subradiant states by simply changing the particle sizes, respectively. Our findings imply midrefractivity materials like boron are excellent building blocks to support electromagnetic coupling operation in nanoscale devices, which will lead to a variety of emerging applications such as nanoantennas with directing exciton emission, ultrasensitive nanosensors, or even potential new construction of photonic metamaterials.Keywords: broadband; midrefractive dielectric; radiative tailoring; unidirectional scattering; visible region
Co-reporter:T. M. Chen, J. Xiao and G. W. Yang
RSC Advances 2016 vol. 6(Issue 74) pp:70124-70132
Publication Date(Web):19 Jul 2016
DOI:10.1039/C6RA14856E
Inorganic artificial enzymes have been developed as potential candidates to naturally occurring enzymes, and three inorganic enzyme mimics, noble metals, metal oxides and carbon materials, have been reported so far. Here, we reported the inorganic enzyme mimic of nitride-based materials. We demonstrated that cubic boron nitride (c-BN) as an enzyme mimic showed intrinsic peroxidase-like activity towards classical colorimetric substrates in the presence of hydrogen peroxide (H2O2). The Michaelis–Menten kinetics studies indicated that the catalytic efficiency of c-BN is superior to its natural peroxidase counterparts. We also established that the peroxidase-like activity of c-BN is induced by catalyzing the decomposition of H2O2 and generating hydroxyl radicals (˙OH). Based on the color reaction, a strategy was developed for H2O2 and glucose quantitative detection with high sensitivity. A reactor was constructed by entrapping c-BN in a porous platform and the peroxidase mimic immobilization for removal of organic pollutants was successfully conducted. Additionally, c-BN can be re-used up to 5 times and retain its catalytic activity after incubation at extremes of pH and temperature. These findings open the door for the application of c-BN as a catalyst and the development of nitride-based materials in the enzyme-mimics field.
Co-reporter:Lihua Li, Zexiang Deng, Lili Yu, Zhaoyong Lin, Weiliang Wang, Guowei Yang
Nano Energy 2016 Volume 27() pp:103-113
Publication Date(Web):September 2016
DOI:10.1016/j.nanoen.2016.06.054
•We, for the first time, demonstrated that amorphous transitional metal borides (TMBs) are a great substitute for noble metals (Pt) as cocatalysts for superior H2 production via water splitting under visible light irradiation....Cocatalysts for H2 production are often made from noble metals, which are expensive and rare. Cocatalysts made from cheap and abundant elements are therefore highly desirable for economically viable H2 production. Here, we demonstrate that amorphous transitional metal borides (TMBs)—made from abundant materials and costing less than 0.1% of the price of Pt cocatalysts—are effective substitutes for Pt-based cocatalysts and result in superior H2 production via water-splitting under visible light irradiation. Under visible-light driven photocatalytic water-splitting, using TMBs as cocatalysts for nanostructured NiCoB/CdS composites achieved an extraordinary H2 production of 144.8 mmol h−1 g−1, up to 36 times greater than that observed when using CdS alone. The apparent quantum efficiency was measured as 97.42% at 500 nm, which is the highest value reported for CdS photocatalysts. The hydrogen atom adsorption energy (ΔE(H)) and hydrogen molecule adsorption energy (ΔE(H2)) of NiB, NiCoB and Pt have been calculated for the first time. Compared with Pt cocatalyst, amorphous TMBs cocatalysts more readily adsorb hydrogen protons and desorb molecular hydrogen during the photocatalytic process. Superior performance of TMBs as cocatalyst, much better than Pt, can be attributed to its powerful trapping electrons ability and highly adsorption of protons. These findings provide a straightforward and effective route to produce cheap and efficient cocatalysts for large-scale water splitting.Figure optionsDownload full-size imageDownload as PowerPoint slide
Co-reporter:Hongbo Li;Yuqian Gao;Chengxin Wang
Advanced Energy Materials 2015 Volume 5( Issue 6) pp:
Publication Date(Web):
DOI:10.1002/aenm.201401767
Supercapacitors or electrochemical capacitors, as energy storage devices, require very stable positive electrode materials for useful applications. Although most positive electrodes are based on crystalline mixed-metal hydroxides, their pseudocapacitors usually perform poorly or have a short cycle life. High activities can be achieved with amorphous phases. Methods to produce amorphous materials are also not typically amenable towards mixed-metal compositions. It is demonstrated that electrochemistry in an ambient environment can be used to produce a series of amorphous mixed-metal hydroxides with a homogeneous distribution of metals for use as positive electrode materials in a supercapacitor. The integrated performance of the amorphous ternary mixed-metal hydroxide pseudocapacitor is superior to that of crystalline materials. The amorphous Ni-Co-Fe hydroxide supercapacitor is characterized by a long-term cycling stability that retained 94% of its capacity after 20 000 cycles. This is much higher than the cycle life of crystalline devices. These results show the broad applicability of this methodology towards new electrode materials for high-performance supercapacitors, especially amorphous mixed-metal hydroxides, as advanced electrode materials.
Co-reporter:Jiandong Yao, Jianmei Shao, Yingxin Wang, Ziran Zhao and Guowei Yang
Nanoscale 2015 vol. 7(Issue 29) pp:12535-12541
Publication Date(Web):19 Jun 2015
DOI:10.1039/C5NR02953H
Broadband photodetection is central to various technological applications including imaging, sensing and optical communications. On account of their Dirac-like surface state, Topological insulators (TIs) are theoretically predicted to be promising candidate materials for broadband photodetection from the infrared to the terahertz. Here, we report a vertically-constructed ultra-broadband photodetector based on a TI Bi2Te3–Si heterostructure. The device demonstrated room-temperature photodetection from the ultraviolet (370.6 nm) to terahertz (118 μm) with good reproducibility. Under bias conditions, the visible responsivity reaches ca. 1 A W−1 and the response time is better than 100 ms. As a self-powered photodetector, it exhibits extremely high photosensitivity approaching 7.5 × 105 cm2 W−1, and decent detectivity as high as 2.5 × 1011 cm Hz1/2 W−1. In addition, such a prototype device without any encapsulation suffers no obvious degradation after long-time exposure to air, high-energy UV illumination and acidic treatment. In summary, we demonstrate that TI-based heterostructures hold great promise for addressing the long lasting predicament of stable room-temperature high-performance broadband photodetectors.
Co-reporter:Zhaoyong Lin, Pu Liu, Jiahao Yan and Guowei Yang
Journal of Materials Chemistry A 2015 vol. 3(Issue 28) pp:14853-14863
Publication Date(Web):09 Jun 2015
DOI:10.1039/C5TA02958A
Coupling TiO2 with other semiconductors is a route to extend the optical response range of TiO2 and to improve the efficiency of its photon quantum. α-Fe2O3 seems compatible with TiO2 and possesses a high solar-light-harvesting capability that is fifteen times as large as that of TiO2. However, there is an energy level mismatch between TiO2 and α-Fe2O3. The photocatalytic performance of TiO2 would be inhibited when compositing with α-Fe2O3 due to the α-Fe2O3-induced photo-generated carriers trapping and dissipation. The composite acts like a one-way valve, in which photo-generated carriers flow from a thick pipe to a thin one and then jam up. Herein, we achieved the goal of matching the energy levels between TiO2 and α-Fe2O3 in a core–shell nanoparticle for enhancing visible-light photocatalysis. Heterostructured TiO2@α-Fe2O3 core–shell nanoparticles were fabricated by the long-pulsed laser ablation of a titanium target in water followed by a hydrothermal reaction. A well-matched interface between TiO2 and α-Fe2O3 was observed, which promoted photo-generated electrons and holes migration and separation. The energy band of the TiO2 nanoparticle was demonstrated to be matched with that of α-Fe2O3, resulting from the upward shift of its valence band due to the abundant oxygen vacancies and bridging hydroxyls on its surface. In this situation, the “blocked pipe” seems to be dredged effectively and the visible-light photocatalytic methyl orange dyes degradation performance of the TiO2@α-Fe2O3 nanoparticles is improved by a factor of two over that of the as-synthesized TiO2 nanoparticles. These findings provide new insights into TiO2 nanostructure photocatalysts and energy band engineering for visible-light photocatalysis.
Co-reporter:Z. Y. Lin, J. Xiao, J. H. Yan, P. Liu, L. H. Li and G. W. Yang
Journal of Materials Chemistry A 2015 vol. 3(Issue 14) pp:7649-7658
Publication Date(Web):20 Feb 2015
DOI:10.1039/C5TA00942A
Among numerous visible-light photocatalysts, plasmonic structure is a promising photocatalyst for photodegradation and energy generation. Ag/AgCl composite as an alternative visible-light photocatalyst has attracted extensive interests; however, its syntheses has many visible flaws, e.g. high temperature environment, requirement of various templates or additives, complicated synthetic procedures and impurities in the final products. For these issues, herein, we report, for the first time, a simple, facile, rapid and green technique to synthesize Ag/AgCl heterostructured cubes using a one-step process of laser irradiation in liquids. The fabricated Ag/AgCl cubes possess some active {111} facets and a high visible-light utilization efficiency induced by the localized surface plasmon resonance (SPR) from the Ag/AgCl heterostructure. As plasmonic photocatalysts, these Ag/AgCl cubes exhibited excellent photodegrading performance for dye molecules of methyl orange, Rhodamine B and methylene blue, and the photodegradation rates were about 0.268, 0.057, and 0.094 min−1, which are considerably higher than that of commercial Ag3PO4 by a factor of 29.8, 3.8 and 6.7, respectively. The high photo-stability of the Ag/AgCl cubes was also demonstrated. The SPR-mediated photocatalytic mechanism was proposed to address the ultrahigh activity of the Ag/AgCl heterostructure as an advanced visible-light photocatalyst. These results showed the broad applicability of the developed technique for accessing a new plasmonic photocatalyst with high-performance.
Co-reporter:Z. Q. Zheng, B. Wang, J. D. Yao and G. W. Yang
Journal of Materials Chemistry A 2015 vol. 3(Issue 27) pp:7067-7074
Publication Date(Web):09 Jun 2015
DOI:10.1039/C5TC01024A
We have experimentally demonstrated a visible light-controlled sensing response of the Au–ZnO nanowires for C2H2 gas at room temperature by plasmon-enhanced sensitivity, in which Au nanoparticles were coated on the surface of ZnO nanowires. The ZnO nanowires without Au nanoparticles showed a normal n-type response, whereas the Au coated ZnO nanowires exhibited a concentration-dependent and time-dependent p–n transition response for the sensing response to C2H2 gas at room temperature. This unconventional sensing behavior can be explained by the formation of a surface inversion layer. Meanwhile, this sensing can be modulated and the response was significantly enhanced at room temperature under visible light illumination. This light-controlled sensing response from the Au–ZnO nanowires was attributed to the fact that the visible light excites the surface plasmon resonance of Au nanoparticles on the surface of ZnO nanowires, and it can inject hot electrons into the conduction band of ZnO. These results hinted the potential application of the as-fabricated sensor in monitoring C2H2 gas at room temperature, and opened up new approaches for developing a new generation of visible light modulated gas sensors.
Co-reporter:J. D. Yao, Z. Q. Zheng, J. M. Shao and G. W. Yang
Nanoscale 2015 vol. 7(Issue 36) pp:14974-14981
Publication Date(Web):17 Aug 2015
DOI:10.1039/C5NR03361F
The progress in the field of graphene has aroused a renaissance of keen research interest in layered transition metal dichalcogenides (TMDs). Tungsten disulfide (WS2), a typical TMD with favorable semiconducting band gap and strong light–matter interaction, exhibits great potential for highly-responsive photodetection. However, WS2-based photodetection is currently unsatisfactory due to the low optical absorption (2%–10%) and poor carrier mobility (0.01–0.91 cm2 V−1 s−1) of the thin WS2 layers grown by chemical vapor deposition (CVD). Here, we introduce pulsed-laser deposition (PLD) to prepare multilayered WS2 films. Large-area WS2 films of the magnitude of cm2 are achieved. Comparative measurements of a WS2-based photoresistor demonstrate its stable broadband photoresponse from 370 to 1064 nm, the broadest range demonstrated in WS2 photodetectors. Benefiting from the large optical absorbance (40%–85%) and high carrier mobility (31 cm2 V−1 s−1), the responsivity of the device approaches a high value of 0.51 A W−1 in an ambient environment. Such a performance far surpasses the CVD-grown WS2-based photodetectors (μA W−1). In a vacuum environment, the responsivity is further enhanced to 0.70 A W−1 along with an external quantum efficiency of 137% and a photodetectivity of 2.7 × 109 cm Hz1/2 W−1. These findings stress that the PLD-grown WS2 film may constitute a new paradigm for the next-generation stable, broadband and highly-responsive photodetectors.
Co-reporter:J. Xiao, P. Liu and G. W. Yang
Nanoscale 2015 vol. 7(Issue 14) pp:6114-6125
Publication Date(Web):03 Mar 2015
DOI:10.1039/C4NR06186A
Coal is the most abundant energy resource, but it is only useful for producing energy via combustion due to its structural characteristics. However, coal is also inexpensive and is the most plentiful and readily available carbon source material for the production of nanodiamonds compared with the most widely used solid carbon source, high-purity graphite, and the high-purity hydrocarbon gas precursor, methane. Here, we report a simple and green top-down strategy for synthesizing nanodiamonds with a cubic phase and a mean size of 3 nm from various types of coal at atmospheric pressure and room temperature using a novel process involving laser ablation in liquid. Furthermore, we have systematically studied the process of phase transformation from coal to nanodiamonds using nucleation thermodynamics, growth kinetics and structural stability. The synthesized nanodiamonds have turned out to be soluble monodisperse colloids that exhibit strong and stable fluorescence both in alcohol and in water. These results provide a route for producing nanodiamonds from inexpensive and abundant coal.
Co-reporter:Jiandong Yao, Zhaoqiang Zheng, Jianmei Shao, and Guowei Yang
ACS Applied Materials & Interfaces 2015 Volume 7(Issue 48) pp:26701
Publication Date(Web):November 12, 2015
DOI:10.1021/acsami.5b08677
Layered transition metal dichalcogenides (TMDs) have been proven to be essential building blocks for the high-performance optoelectronic devices as a result of their favorable bandgaps, extraordinary light absorption, and closed surface electronic structures. However, the in-depth exploration of their operating mechanism as insertion layers in heterojunction photodetectors is scarce. Here, we demonstrate that a Bi/Si heterojunction photodetector can achieve a superior performance by inserting a WS2 layer. A high photosensitivity of 1.4 × 108 cm2/W and an outstanding detectivity of 1.36 × 1013 cm Hz1/2 W–1 are obtained, which are comparable or even surpass those of state-of-art commercial photodetectors. The working mechanism of the Bi/WS2/Si sandwich-structured photodetector is unveiled, including the efficient passivation of the interface, enhancement of light absorption, and selective carrier blocking. Finally, a good voltage tunability of the photoresponse is also demonstrated. These findings are significant to the deep understanding on the integration of layered TMDs with conventional semiconductors, and they provide an attractive methodology to develop layered TMDs in a multi-junction system.Keywords: 2D materials; Bi; heterojunction; photodetector; WS2
Co-reporter:Yuqian Gao, Hongbo Li, and Guowei Yang
Crystal Growth & Design 2015 Volume 15(Issue 9) pp:4475-4483
Publication Date(Web):July 23, 2015
DOI:10.1021/acs.cgd.5b00752
Good conductivity is conventionally considered as a typical reference standard in terms of selecting water electrolysis catalysts. Electrocatalyst research so far has focused on crystal rather than amorphous due to poor conductivity. Here, we demonstrate that the amorphous electrocatalyst made of 3D honeycomb-like amorphous nickel hydroxide (Ni(OH)2) nanosheets synthesized by a simple, facile, green, and low-cost electrochemistry technique possesses ultrahigh activity and super-long-term cycle stability in the oxygen evolution reaction (OER). The amorphous Ni(OH)2 affords a current density of 10 mA cm–2 at an overpotential of a mere 0.344 V and a small Tafel slope of 46 mV/dec, while no deactivation is detected in the CV cycles even up to 5000 times. We also establish that the short-range order, i.e., nanophase, of amorphous creates a lot of active sites for OER, which can greatly promote the electrochemical performance of amorphous catalysts. These findings show that the conventional understanding of selecting electrocatalysts with conductivity as a typical reference standard seems out of date for developing new catalysts at the nanometer, which opens a door ever closed to applications of amorphous nanomaterials as advanced catalysts for water oxidation.
Co-reporter:H. B. Li, Y. Q. Gao and G. W. Yang
RSC Advances 2015 vol. 5(Issue 56) pp:45359-45367
Publication Date(Web):30 Apr 2015
DOI:10.1039/C4RA14370A
A series of amorphous mixed-metal hydroxide nanospheres with a homogeneous distribution of metals in compositions, including binary Fe–Co, Fe–Ni and Co–Ni hydroxides and ternary Ni–Co–Fe hydroxides, have been for the first time prepared via a simple, facile and green electrochemical technique. The morphology, structure and element distribution of the as-prepared amorphous nanophases were characterized in detail. The magnetic measurements showed that all the as-prepared amorphous nanophases exhibit similar magnetic behaviors for their clear magnetic hysteresis loops and well saturated magnetization, and the amorphous Fe–Co hydroxide nanospheres have the highest saturation magnetization (160.7 emu g−1) at room temperature among four amorphous nanophases. These findings pave a way for the applications of amorphous metal hydroxides nanomaterials as magnetic materials.
Co-reporter:Jiahao Yan, Pu Liu, Zhaoyong Lin, Hao Wang, Huanjun Chen, Chengxin Wang, and Guowei Yang
ACS Nano 2015 Volume 9(Issue 3) pp:2968
Publication Date(Web):February 15, 2015
DOI:10.1021/nn507148z
Fano resonance arising from the interaction between a broad “bright” mode and a narrow “dark” mode has been widely investigated in symmetry-breaking structures made of noble metals such as plasmonic asymmetric oligomers or other well-designed nanostructures. However, Fano resonance in nanoscale all-dielectric dimers has not been experimentally demonstrated so far. We report the first experimental observation of directional Fano resonance in silicon nanosphere dimers (both homodimer and heterodimer) and clarify that the coupling between magnetic and electric dipole modes can easily generate Fano resonance in all-dielectric oligomers, distinctly differing from conventional Fano resonances based on electric responses or artificial optical magnetism. A silicon nanosphere dimer, exhibiting a strong magnetic response inside and an electric enhancement in the gap, is an excellent structure to support magnetic-based Fano scattering. Interactions between magnetic and electric dipoles can suppress backward scattering and enhance forward scattering at Fano wavelengths. This directional scattering is much more prominent than that from a single silicon sphere and shows promising applications in areas such as directional nanoantenna or optical switching, opening up avenues for developing all-dielectric low-loss metamaterials or nanophotonic devices at visible wavelengths.Keywords: all-dielectric; directional scattering; Fano resonace; magnetic response; silicon sphere dimer;
Co-reporter:Jiling Li
The Journal of Physical Chemistry C 2015 Volume 119(Issue 34) pp:19681-19688
Publication Date(Web):August 14, 2015
DOI:10.1021/acs.jpcc.5b06164
Recently, a novel boron monolayer with the “hexagon holes” density of η = 1/8 was repeatedly predicted to be the most stable boron sheet in different literatures. Its fascinating porous characteristic structure and sufficient surface space seem attractive and motivate researchers to perform further investigation about it. Herein, we demonstrated that the Li-decorated 1/8-boron monolayer is a kind of ultrahigh capacity hydrogen storage medium. We also established that Li atoms can be attached above the centers of the hexagonal holes in the novel 1/8-boron monolayer due to the charge transfer from Li atoms to boron atoms, and the electric field induced by the positive charged Li atoms attracts and polarizes the H2 molecules and makes the binding strong enough for potential applications to store H2 molecules but not dissociate them. Detailed calculations showed that the two-sided Li-decorated 1/8-boron monolayer has an ultrahigh hydrogen storage capacity averagely to bind up to four H2 molecules for each Li atom with an ideal binding energy of 0.23 eV/H2, which is just in the ideal binding energy scope (0.2–0.4 eV/H2) for reversible hydrogen storage and corresponding to a hydrogen uptake of 15.26 wt %. These findings suggested a possible method of engineering a new structure for ultrahigh-capacity hydrogen storage materials with the reversible adsorption and desorption of hydrogen molecules, and they were expected to motivate an active line of experimental efforts.
Co-reporter:Pu Liu
The Journal of Physical Chemistry C 2015 Volume 119(Issue 2) pp:1234-1246
Publication Date(Web):December 26, 2014
DOI:10.1021/jp5111482
Nanoparticles of noble metals are typically plasmonic materials, but the pure metals have high nonirradiative ohmic losses at optical frequencies, leading to large absorption and unwanted heating effects. Additionally, spherical silicon nanoparticles (NPs) have a unique optical system with a high-refractive-index dielectric nanostructure. Combining these two components in one functional core/shell NP nanostructure of Si/M, where M represents a noble metal, to produce resonant optical electronic and magnetic responses has been rare. Herein, an approach for the assembly of Si/M core/shell NPs is developed on the basis of double-beam laser ablation in liquid, thereby fabricating a series of Si/M (M = Au, Ag, Pd, and Pt) core/shell NPs and characterizing the intense visible-light scattering modes from the as-fabricated Si/Au NPs as a nanoplasmonic structure. Dark-field optical measurements show that these Si/Au NPs have a strong electromagnetic response in the visible-light region, and the resonant frequencies can be modulated by NP size and morphology. The dispersed NPs are used as a highly sensitive surface-enhanced Raman scattering (SERS) active probe for detecting monolayer molecules, as proven herein using 4-MBT molecules. A SERS plasmonic enhancement factor of ∼108 is found for these Si/Au NPs by correlating the SERS measurement with scanning electron microscopy analysis. These findings present the possibility of confining light in ubiquitous silicon-based semiconductor technologies and manipulating the optical properties of nontraditional plasmonic nanostructures, while also opening new perspectives. This technique can be extended to other noble metals to form similar structures and fabricate low-loss metamaterials and nanophotonic devices.
Co-reporter:Jun Xiao
The Journal of Physical Chemistry C 2015 Volume 119(Issue 4) pp:2239-2248
Publication Date(Web):January 5, 2015
DOI:10.1021/jp512188x
Despite extensive work on the fluorescence behavior of graphite and graphene quantum dots, reports on the luminescence of nanodiamonds are so far much fewer. In fact, nanodiamonds are distinctly different from carbon quantum dots with nondiamond phases in both crystalline structure and electronic structure. Here, we report that fluorescent nanodiamond colloids exhibit strong visible fluorescence emissions and that their characteristics can be summarized as follows: (i) the fluorescence is unrelated to the size effect and (ii) obviously the excitation-dependent fluorescence, (iii) the maximum emission peak shows a giant red shift of 100 nm after heat treatment, and (iv) the red shift of fluorescence excited by a certain wavelength is out of sync with that of the strongest fluorescent peak. Based on these experimental observations above, the origin of nanodiamonds fluorescence is proposed to be the functional groups residing on the nanodiamonds, such as OH, ketone C═O, and ester C═O groups. These deductions are confirmed by the evolutions of the microscopic Fourier transform infrared spectrum. For a more specific aspect, the red shift and excitation dependence of the fluorescence in nanodiamonds is ascribed to the combined effect of the relative intensity changes of various types of oxygenous groups and low-lying effects resulting from n(OH) → π*(CO) interactions between the hydroxyl groups and carbonyl groups. Accordingly, both excitation-dependent fluorescence and excitation-independent fluorescence can be achieved by engineering the surface functional groups of nanodiamonds, which verifies the proposed mechanism. Overall, the essence of the fluorescence in nanodiamonds is the collaboration and competition of the functional groups. The collaboration is reflected in excitation-dependent fluorescence, whereas the competition is reflected in the change of the optimum excitation and emission wavelengths. Therefore, these results provide other guidelines for the design of carbon nanomaterials, not only nanodiamonds but also graphite and graphene quantum dots, for application in the field of biomedical labeling.
Co-reporter:Jiling Li;Pu Liu;Bitao Pan;Jun Xiao;Chengxin Wang
Science Advances 2015 Volume 1(Issue 9) pp:e1500857
Publication Date(Web):30 Oct 2015
DOI:10.1126/sciadv.1500857
Carbyne with one-dimensional sp-hybridized carbon atoms is synthesized under ambient conditions in the laboratory.
Co-reporter:Zhaoyong Lin, Jiling Li, Zhaoqiang Zheng, Jiahao Yan, Pu Liu, Chengxin Wang, and Guowei Yang
ACS Nano 2015 Volume 9(Issue 7) pp:7256
Publication Date(Web):June 10, 2015
DOI:10.1021/acsnano.5b02077
α-Ag2WO4 (AWO) has been studied extensively due to its H2 evolution and organic pollution degradation ability under the irradiation of UV light. However, the band gap of AWO is theoretically calculated to be 3.55 eV, resulting in its sluggish reaction to visible light. Herein, we demonstrated that, by using the electronic reconstruction of AWO nanorods upon a unique process of laser irradiation in liquid, these nanorods performed good visible-light photocatalytic organics degradation and H2 evolution. Using commercial AWO powders as the starting materials, we achieved the electronic reconstruction of AWO by a recrystallization of the starting powders upon laser irradiation in liquid and synthesized AWO nanorods. Due to the weak bond energy of AWO and the far from thermodynamic equilibrium process created by laser irradiation in liquid, abundant cluster distortions, especially [WO6] cluster distortions, are introduced into the crystal lattice, the defect density increases by a factor of 2.75, and uneven intermediate energy levels are inset into the band gap, resulting in a 0.44 eV decrease of the band gap, which modified the AWO itself by electronic reconstruction to be sensitive to visible light without the addition of others. Further, the first-principles calculation was carried out to clarify the electronic reconstruction of AWO, and the theoretical results confirmed the deduction based on the experimental measurements.Keywords: H2 evolution; organics degradation; visible-light photocatalysis;
Co-reporter:X.L. Li, C.X. Wang, G.W. Yang
Progress in Materials Science 2014 Volume 64() pp:121-199
Publication Date(Web):July 2014
DOI:10.1016/j.pmatsci.2014.03.002
Self-assembled nanostructures, such as quantum dots (QDs), quantum rings (QRs) and nanowires (NWs), have been extensively studied because of their physical properties and promising device applications. To improve their physical properties and device applications, the fabrication of nanostructures with a uniform size, proper shape and regular position is desired in nanotechnology. Therefore, investigations of the growth process of nanostructures are highly important to control the self-assembly and synthesis processes of nanostructures flexibly. Thermodynamic theory as a universal approach to investigate material growth has been widely used to study the growth of nanostructures. This review covers the thermodynamic theoretical treatments of the growth of nanostructures, including QDs by epitaxy, QRs by droplet epitaxy, and NWs by the vapor–liquid–solid (VLS) mechanism. First, we introduce the thermodynamic models of the growth mechanisms of QDs by self-assembled epitaxy. The formation, stability, shape and position of QDs are discussed. Second, we introduce the nucleation thermodynamics and the growth kinetics of QRs by droplet epitaxy, and we present a simulation method employing the shape evolution of QRs based on a kinetic model. Third, several theoretical tools are introduced to address the nucleation and growth of NW by the VLS process. Finally, we introduce a thermodynamic treatment including the thermal fluctuations within the context of a statistical mechanical and quantum mechanical model for the temperature-dependent growth of nanostructures.
Co-reporter:J. Xiao, G. Ouyang, P. Liu, C. X. Wang, and G. W. Yang
Nano Letters 2014 Volume 14(Issue 6) pp:3645-3652
Publication Date(Web):May 13, 2014
DOI:10.1021/nl5014234
Because of their considerable science and technical interest, nanodiamonds (3–5 nm) are often used as a model to study the phase transformation between graphite and diamond. Here we demonstrated that a reversible nanodiamond-carbon onion phase transformation can become true when laser irradiates colloidal suspensions of nanodiamonds at the ambient temperature and pressure. Nanodiamonds are first transformed to carbon onions driven by the laser-induced high temperature in which an intermediary bucky diamond phase is observed. Sequentially, carbon onions are transformed back to nanodiamonds driven by the laser-induced high temperature and high pressure from carbon onions as nanoscaled temperature and pressure cell upon the laser irradiation process in liquid. Similarly, the same bucky diamond phase serving as an intermediate phase is found during the carbon onion-to-nanodiamond transition. To have a clear insight into the unique phase transformation the thermodynamic approaches on the nanoscale were proposed to elucidate the reversible phase transformation of nanodiamond-to-carbon onion-to-nanodiamond via an intermediary bucky diamond phase upon the laser irradiation in liquid. This reversible transition reveals a series of phase transformations between diamond and carbon allotropes, such as carbon onion and bucky diamond, having a general insight into the basic physics involved in these phase transformations. These results give a clue to the root of meteoritic nanodiamonds that are commonly found in primitive meteorites but their origin is puzzling and offers one suitable approach for breaking controllable pathways between diamond and carbon allotropes.
Co-reporter:J. Xiao, J. L. Li, P. Liu and G. W. Yang
Nanoscale 2014 vol. 6(Issue 24) pp:15098-15106
Publication Date(Web):13 Oct 2014
DOI:10.1039/C4NR05246C
The investigation of carbon allotropes such as graphite, diamond, fullerenes, nanotubes and carbon onions and mechanisms that underlie their mutual phase transformation is a long-standing problem of great fundamental importance. New diamond (n-diamond) is a novel metastable phase of carbon with a face-centered cubic structure; it is called “new diamond” because many reflections in its electron diffraction pattern are similar to those of diamond. However, producing n-diamond from raw carbon materials has so far been challenging due to n-diamond's higher formation energy than that of diamond. Here, we, for the first time, demonstrate a new phase transformation path from nanodiamond to n-diamond via an intermediate carbon onion in the unique process of laser ablation in water, and establish that water plays a crucial role in the formation of n-diamond. When a laser irradiates colloidal suspensions of nanodiamonds at ambient pressure and room temperature, nanodiamonds are first transformed into carbon onions serving as an intermediate phase, and sequentially carbon onions are transformed into n-diamonds driven by the laser-induced high temperature and high pressure from the carbon onion as a nanoscaled temperature and pressure cell upon the process of laser irradiation in a liquid. This phase transformation not only provides new insight into the physical mechanism involved, but also offers one suitable opportunity for breaking controllable pathways between n-diamond and carbon allotropes such as diamond and carbon onions.
Co-reporter:J. M. Shao, H. Li and G. W. Yang
Nanoscale 2014 vol. 6(Issue 7) pp:3513-3517
Publication Date(Web):27 Feb 2014
DOI:10.1039/C3NR06506E
Strong optical absorbance makes topological insulator (TI) surfaces a promising high-performance photodetector in the terahertz (THz) to infrared frequency range. Here, we study the optical absorbance of more realistic TI films with hexagonal warping effect using the Fermi's golden rules. It was found that when the warping term is λ ≠ 0, the absorbance is no longer a universal value as that of graphene or ideal Dirac cone, but increases monotonously with the photon energy. The increment is positively correlated with the parameter λ/vF3 where vF is the Fermi velocity. The relative signal-to-noise ratio (SNR) of the TI film working as a photoresistor-type photodetector is significantly enhanced by the warping effect-induced absorbance increment. These investigations provide useful information for developing TI-based photodetectors with high SNR in the range of THz to infrared frequency.
Co-reporter:H. Li, J. M. Shao, H. B. Zhang and G. W. Yang
Nanoscale 2014 vol. 6(Issue 6) pp:3127-3137
Publication Date(Web):03 Jan 2014
DOI:10.1039/C3NR05828J
Considering that topological insulator (TI) ultrathin films (UTFs) provide an ideal platform for the transport measurement of topologically protected surface states, we have investigated the transport properties of the three-dimensional (3D) TI UTFs through an array of potential barriers. The 3D TI UTF was considered to be thin enough (5 nm) that the top and bottom surface states of the UTF can hybridize to create an energy gap at the Dirac point, which results in a hyperbola-like energy dispersion. It was found that the Klein tunneling effect disappears due to the interaction between the top and bottom surface states. By tuning the barrier strength or the incident energy, three kinds of transport processes can be realized, and the conditions of the transport processes were determined. The oscillatory characters of the transmission (conductance) spectra without a decaying envelope are due to the novel surface states of TIs, which are quite different from that observed for a conventional two-dimensional electron gas. For the structure consisting of two anti-parallel potential barriers, the conductance spectra exhibit a perfect on/off switching effect by tuning the barrier strength, which is favorable for electrically controllable device applications. In the case of a superlattice (SL) structure, due to the mini-gaps induced by the SL geometry, some additional resonant peaks and valleys can be observed in the transmission spectra, and similar characters are also reflected in the conductance spectra. Owing to the Dirac characters of the charge carriers therein, the transmission (conductance) spectra never decay with increasing barrier strength, which is distinguished from that observed for semiconductor SLs. These findings were not only meaningful for understanding the basic physical processes in the transport of TIs, but also useful for developing nanoscaled TI-based devices.
Co-reporter:H. B. Li, M. H. Yu, X. H. Lu, P. Liu, Y. Liang, J. Xiao, Y. X. Tong, and G. W. Yang
ACS Applied Materials & Interfaces 2014 Volume 6(Issue 2) pp:745
Publication Date(Web):January 3, 2014
DOI:10.1021/am404769z
Cobalt hydroxide (Co(OH)2) has received extensive attention for its exceptional splendid electrical properties as a promising supercapacitor electrode material. Co(OH)2 study so far prefers to crystal instead of amorphous, in spite of amorphous impressive electrochemical properties including the ability to improve the electrochemical efficiency based on the disorder structure. The amorphous Co(OH)2 nanostructures with excellent electrochemical behaviors were successfully synthesized by a simple and green electrochemistry. Our as-prepared Co(OH)2 electrode exhibited ultrahigh capacitance of 1094 F g–1 and super long cycle life of 95% retention over 8000 cycle numbers at a nominal 100 mV s–1 scan rate. The united pseudo-capacitive performances of the amorphous Co(OH)2 nanostructures in electrochemical capacitors are totally comparable to those of the crystalline Co(OH)2 nanomaterials. These findings actually open a door to applications of amorphous nanomaterials in the field of energy storage as superior electrochemical pseudocapacitors materials.Keywords: amorphous cobalt hydroxide; electrochemical performance; high capacitance; super long-life;
Co-reporter:Hai Li, Jianmei Shao, Daoxin Yao, and Guowei Yang
ACS Applied Materials & Interfaces 2014 Volume 6(Issue 3) pp:1759
Publication Date(Web):January 13, 2014
DOI:10.1021/am4047602
Two-dimensional (2D) materials are extensively explored due to the remarkable physical property and the great potential for post-silicon electronics since the landmark achievement of graphene. The monolayer (ML) MoS2 with a direct energy gap is a typical 2D material and promising candidate for a wide range of device applications. The extensive efforts so far have focused on the optical valley control applications of ML MoS2 rather than the electrical control of spin and valley transport. However, the electrical manipulation of spin injection and transport is essential to realize practical spintronics applications. Here, we theoretically demonstrated that the valley and spin transport can be electrically manipulated by a gate voltage in a normal/ferromagnetic/normal monolayer MoS2 junction device. It was found that the fully valley- and spin-polarized conductance can be achieved due to the spin–valley coupling of valence-band edges together with the exchange field, and both the amplitude and direction of the fully spin-polarized conductance can be modulated by the gate voltage. These findings not only provided deep understanding to the basic physics in the spin and valley transport of ML MoS2 but also opened an avenue for the electrical control of valley and spin transport in monolayer dichalcogenide-based devices.Keywords: MoS2; polarization; spin; spintronics; valley; valleytronics;
Co-reporter:Haimei Dong, Yuhua Yang, and Guowei Yang
ACS Applied Materials & Interfaces 2014 Volume 6(Issue 5) pp:3093
Publication Date(Web):February 19, 2014
DOI:10.1021/am4058869
Lots of theories and experiments have so far tried to acquire the directional emission with whispering-gallery modes (WGMs) from micro- and nanostructures, which will enhance the applications of micro- and nanoscaled whispering-gallery resonators in optoelectronic devices. Here for the first time we report a series of directional emission patterns with WGMs from the single ZnO hexagonal micro- and nanodisk. Based on the cathodeluminescence technique, we observed far-field emissions from ZnO hexagonal micro- and nanodisks in four geometries with different deformations. Mechanisms of directional emissions above were suggested. These investigations facilitated the applications of ZnO hexagonal micro- and nanodisks in photonic devices.Keywords: cathodeluminescence; deformation; directional emissions; geometry; whispering-gallery modes; ZnO micro- and nanodisk;
Co-reporter:Ying Liang, Pu Liu, and Guowei Yang
Crystal Growth & Design 2014 Volume 14(Issue 11) pp:5847-5855
Publication Date(Web):October 9, 2014
DOI:10.1021/cg501079a
One-dimension (1D) chains of magnetic nanoparticles (MNPs) are attractive due to their wide applications in new materials and devices. The fabrication of 1D chains of MNPs especially for bimetallic alloys such as iron-based bimetallic alloys MNPs is still a challenge considering the difficulty in the formation of alloying MNPs and the self-assembly process. Herein, we reported that a novel technique [i.e., the magnetic field assisted laser ablation in liquid (MF-LAL)], has been used to fabricate 1D chains of MNPs of iron-based bimetallic alloys of FePt, FeCo, and FeNi within one-step, taking a significant step toward the fabrication of functional nanomaterials and nanostructures. These 1D chains of alloying MNPs are ferromagnetic with high saturation magnetizations, low coercivity, and remanent magnetization, implying they are useful in the areas of magnetotransporters, micromechanical sensors, magnetic memory materials, DNA separation materials, and so on. A thermodynamic model has been established to address the assembly mechanism of 1D chains of alloying MNPs upon the MF-LAL process and the results showed that MF-LAL is a general, facile, and green strategy for fabricating 1D chains of alloying MNPs. These studies are useful for researchers to choose target materials and liquid mediums for the fabrication of 1D chains of MNPs for purpose of fundamental issues and applications via the MF-LAL technique.
Co-reporter:Y. Y. Cao, G. Ouyang, C. X. Wang, and G. W. Yang
Nano Letters 2013 Volume 13(Issue 2) pp:436-443
Publication Date(Web):January 8, 2013
DOI:10.1021/nl303702w
As a promising and typical semiconductor heterostructure at the nanoscale, the radial Ge/Si NW heterostructure, that is, the Ge-core/Si-shell NW structure, has been widely investigated and used in various nanodevices such as solar cells, lasers, and sensors because of the strong changes in the band structure and increased charge carrier mobility. Therefore, to attain high quality radial semiconductor NW heterostructures, controllable and stable epitaxial growth of core–shell NW structures has become a major challenge for both experimental and theoretical evaluation. Surface roughening is usually undesirable for the epitaxial growth of high quality radial semiconductor NW heterostructures, because it would destroy the core–shell NW structures. For example, the surface of the Ge-core/Si-shell NWs always exhibits a periodic modulation with island-like morphologies, that is, surface roughening, during epitaxial growth. Therefore, the physical understanding of the surface roughening behavior during the epitaxial growth of core–shell NW structures is essential and urgent for theoretical design and experimentally controlling the growth of high quality radial semiconductor NW heterostructures. Here, we proposed a quantitative thermodynamic theory to address the physical process of epitaxial growth of core–shell NW structures and surface roughening. We showed that the transformation from the Frank–van der Merwe mode to the Stranski–Krastanow mode during the epitaxial growth of radial semiconductor NW heterostructures is the physical origin of surface roughening. We deduced the thermodynamic criterion for the formation of the surface roughening and the phase diagram of growth and showed that the radius of the NWs and the thickness of the shell layer can not only determine the formation of the surface roughening in a core–shell NW structure, but also control the periodicity and amplitude of the surface roughness. The agreement between the theoretical results and the experimental data of the Ge-core/Si-shell NW structure implied that the established approach could be applicable to the understanding and design of various semiconductor core–shell NW structures. Consequentially, we used the established theoretical model to study the epitaxial growth of the InAs-core/GaAs-shell NW structure and predict the surface roughening formation, as well as the periodicity and amplitude of the surface roughness, which provided useful information to theoretically design and experimentally control the epitaxial growth of the radial InAs-core/GaAs-shell NW structure.
Co-reporter:J. Xiao, P. Liu, Y. Liang, H. B. Li and G. W. Yang
Nanoscale 2013 vol. 5(Issue 3) pp:899-903
Publication Date(Web):07 Dec 2012
DOI:10.1039/C2NR33484D
Ultrafine tungsten nanocrystals (average size of 3 nm) with a metastable phase (beta-tungsten with A15 structure, β-W) have been prepared by laser ablation of tungsten in liquid nitrogen. The as-prepared metastable nanocrystals exhibited super-stablity, and can keep the same metastable structure over a period of 6 months at room temperature. This super-stability is attributed to the nanosized confinement effect of ultrafine nanocrystals. The magnetism measurements showed that the β-W nanocrystals have weak ferromagnetic properties at 2 K, which may arise from surface defects and unpaired electrons on the surface of the ultrafine nanocrystals. These findings provided useful information for the application of ultrafine β-W nanocrystals in microelectronics and spintronics.
Co-reporter:H. B. Zhang, H. Li, J. M. Shao, S. W. Li, D. H. Bao, and G. W. Yang
ACS Applied Materials & Interfaces 2013 Volume 5(Issue 22) pp:11503
Publication Date(Web):October 30, 2013
DOI:10.1021/am403634u
Topological insulators with the nanoscaled metallic surface state (3–5 nm) are actually of typical functional nanostructures. Significant efforts have been devoted to study new families of topological insulators and identifications of topological surface state, as well as fundamental physics issues relating to spin-polarized surface electronic states in the past few years. However, transport investigations that can provide direct experimental evidence for potentially practical applications of topological insulators are limited, and realization of functional devices based on topological insulators is still under exploration. Here, using the Sn-doping Bi2Te3 polycrystalline topological insulator films, we fabricated high-performance current-controlled magnetic field detectors. When a parallel magnetic field is applied, the as-fabricated device exhibits a stable and reproducible magneto-resistance (MR) switching behavior, and the corresponding MR ratio can be modulated by the applied current. Even under such a low magnetic field (0.5 kG), the device still shows a distinguishable MR switching performance, suggesting that topological insulator devices are very sensitive to external stimulation and potentially applicable to weak magnetic field detection.Keywords: magnetic-field detector; topological insulator;
Co-reporter:Y. Liang, L. F. Zhu, P. Liu, H. B. Li, J. Xiao, X. W. Ji and G. W. Yang
CrystEngComm 2013 vol. 15(Issue 31) pp:6131-6135
Publication Date(Web):05 Jun 2013
DOI:10.1039/C3CE40787J
Ag2V4O11 brush-like nanostructures with a large specific surface area have been synthesized by a unique electrochemistry assisted laser ablation in liquids without any template or surfactant in an ambient environment. Considering the large surface-to-volume ratio of the as-synthesized nanostructures, an Ag2V4O11 brush-like nanostructured gas sensor was fabricated and exhibited an excellent performance in sensor response to ethanol concentrations in the range of 10 to 600 ppm under low working temperature. This high response was attributed to the highly crystalline and brush-like surface, which leads to the effective adsorption and desorption, and provides more active sites for gas molecules reacting. These findings show our desire to encourage the synthesis of new nanomaterials, e.g. ternary transition metal oxides, as gas sensors prepared by novel means.
Co-reporter:H. B. Li, P. Liu, Y. Liang, J. Xiao and G. W. Yang
CrystEngComm 2013 vol. 15(Issue 20) pp:4054-4057
Publication Date(Web):18 Mar 2013
DOI:10.1039/C3CE40120K
The amorphous nickel hydroxide nanospheres have been prepared by a simple and green electrochemistry technique, and the magnetism measurements of the products show that the prepared amorphous nickel hydroxide nanospheres present ferromagnetism below the Curie temperature of 16.5 K, accompanied by high magnetization of 50 emu g−1 and high coercivity of 630 Oe at 5 K. These findings pave a way to applications of amorphous nickel hydroxide nanostructures as magnetic materials.
Co-reporter:Hong Bin Zhang;Hai Lin Yu;Ding Hua Bao;Shu Wei Li;Cheng Xin Wang ;Guo Wei Yang
Advanced Materials 2012 Volume 24( Issue 1) pp:132-136
Publication Date(Web):
DOI:10.1002/adma.201103530
Co-reporter:J. L. Li, T. He and G. W. Yang
Nanoscale 2012 vol. 4(Issue 5) pp:1665-1670
Publication Date(Web):01 Feb 2012
DOI:10.1039/C2NR11808D
We have theoretically shown that the boron nitride fullerene cage B12N12 is an all-purpose building block for fabricating multifarious BN nanotubes. Firstly, we investigated the stability and structural of the boron nitride fullerene cage B12N12 and the polymerized derivatives obtained from it. Interestingly we found out that two B12N12 cages can spontaneously form one BN nanotube with two closed ends through the structural transformation when one cage meets another. These results indicated that the fullerene B12N12 can be polymerized to build various remarkable polymers through the spontaneous structural transformation when they are together, which all have planer or tridimensional shapes with a hollow tubular structure, even at the juncture of the coalesced B12N12. Simultaneously, after the structure optimization, the quadrangles at the juncture of the coalesced B12N12 disappear to form a perfect surface only composed of hexagons. Then, we calculated the energy of all the considered nanostructures. The polymerization of the fullerene B12N12 is exothermic and thus can form very stable derivative polymers. These theoretical conclusions stimulate us to use the fullerene B12N12 as an all-purpose building block to construct various BN nanostructures for purpose of fundamental research and potential applications.
Co-reporter:H. B. Li, P. Liu, Y. Liang, J. Xiao and G. W. Yang
Nanoscale 2012 vol. 4(Issue 16) pp:5082-5091
Publication Date(Web):14 Jun 2012
DOI:10.1039/C2NR30761H
We have developed simple and green electrochemistry to synthesize Ag nanostructures with high purity, good crystallinity and smooth surface for applications as super-SERS (surface-enhanced Raman scattering), SERS-active substrates and with highly effective antimicrobial activities. This synthesis takes place in a clean and slow reaction environment without any chemical additives, which ensures an ultrahigh active surface of the as-synthesized Ag nanostructures owing to their purity, good crystallinity and smooth morphology. Using this method, we synthesized nearly perfect Ag nanodendrites (NDs), which exhibit super-SERS sensitivity when they are used to detect the SERS spectra of rhodamine 6G at concentrations as low as 5 × 10−16 M, and have an ultrahigh electromagnetic (EM) enhancement factor of the order of 1013, breaking through the theoretical limit of EM enhancement. Meanwhile, the as-synthesized Ag NDs possess highly effective antimicrobial activities for Escherichia coli, Candida albicans and Staphylococcus aureus, which are over 10 times that of silver nanoparticles. Additionally, the basic physics and chemistry involved in the fabrication of Ag nanostructures are pursued. These investigations show that silver nanostructures with highly active surfaces can make the most of Ag nanostructures functioning as super-SERS-active substrates and multiple antibiotics.
Co-reporter:J. Xiao, P. Liu, Y. Liang, H. B. Li and G. W. Yang
Nanoscale 2012 vol. 4(Issue 22) pp:7078-7083
Publication Date(Web):25 Sep 2012
DOI:10.1039/C2NR32078A
Porous tungsten oxide (WO3) nanoflakes have been synthesized by a simple and green approach in an ambient environment. As a precursor solution a polycrystalline hydrated tungstite (H2WO4·H2O) nanoparticles colloid was first prepared by pulsed-laser ablation of a tungsten target in water. The H2WO4·H2O nanoflakes were produced by 72 h aging treatment at room temperature. Finally, porous WO3 nanoflakes were synthesized by annealing at 800 °C for 4 h. Considering the large surface-to-volume ratio of porous nanoflakes, a porous WO3 nanoflake gas sensor was fabricated, which exhibits an excellent sensor response performance to alcohol concentrations in the range of 20 to 600 ppm under low working temperature. This high response was attributed to the highly crystalline and porous flake-like morphology, which leads to effective adsorption and desorption, and provides more active sites for the gas molecules’ reaction. These findings showed that the porous tungsten oxide nanoflake has great potential in gas-sensing performance.
Co-reporter:G. Ouyang and G. W. Yang
ACS Applied Materials & Interfaces 2012 Volume 4(Issue 1) pp:210
Publication Date(Web):December 7, 2011
DOI:10.1021/am201270r
We establish an analytic model to illustrate the energy bandgap of ZnO hollow quantum dots (HQDs) with negative curvature surface from the perspective of nanothermodynamics. It was found that the bandgap of ZnO HQDs shows a pronounced blue-shift as comparable to those of bulk counterpart and free nanocrystals. Furthermore, the photoelectric properties of ZnO HQDs can be effectively modulated by three independent dimensions, including the outer surface, the inner surface and the shell thickness. Strikingly, the emission wavelength of ZnO HQDs can be extended into the deep-ultraviolet (DUV) region, which suggests this kind of nanostructure could be expected to be applicable for the new-generation, compact, and environmentally friendly alternative DUV light emitter.Keywords: bandgap; deep-ultraviolet; hollow quantum dot; negative curvature; size effect; surface energy;
Co-reporter:T. He, J. L. Li, and G. W. Yang
ACS Applied Materials & Interfaces 2012 Volume 4(Issue 4) pp:2192
Publication Date(Web):April 2, 2012
DOI:10.1021/am300193d
Titanium oxide (TiO2) nanostructures have been attracting consistent focus in the past few years because of their enhanced power in solar-energy conversion. Surface and interface play a crucial role in the determination of thermodynamic stability and electronic structure of TiO2 nanostructures. The rutile (110) nanoslab (NS) has been used as a common subject to investigate the surface relaxation, defect characters, molecule adsorption, and chemically dynamic reaction of TiO2 nanostructures. Up to date, a long-time standing issue in TiO2 NS, i.e., the general oscillation of structure, surface energy and electronic property with changing of NS thickness, has not been clear. We have presented a comprehensive investigation on the relationship between surface and oscillation behavior in the TiO2 (110) NS by the first-principles calculations accompanied with the wave function analysis. We clearly, for the first time, pointed out that the dipoles and surface states bonding induced by the surface–surface interactions are the physical origin of general oscillations in the TiO2 (110) NS. Our findings not only have a new insight into the basic interactions between surfaces in TiO2 nanostructures, but also provide useful information for tuning the photocatalytic and photovoltaic properties by surface design.Keywords: band gap; first-principles; oscillation; surface energy; surface−surface interaction; TiO2 nanoslab;
Co-reporter:Y. Liang, P. Liu, H. B. Li, and G. W. Yang
Crystal Growth & Design 2012 Volume 12(Issue 9) pp:4487
Publication Date(Web):August 7, 2012
DOI:10.1021/cg3006629
Electrochemistry-assisted laser ablation in liquids (ECLAL) is a chemically “simple and clean” synthesis of nanoparticles. Using ECLAL, we have synthesized zinc molybdate nanoplates and nanorods with two different phases. These two nanostructures are characterized carefully by scanning electron microscopy, transmission electron microscopy, X-ray diffraction analysis, Fourier transform infrared spectroscopy, Raman scattering spectroscopy, and UV–vis spectrophotometry. On the basis of the cathodoluminescence measurements, we observe that the nanoplates emit no light, while the nanorods give out green light before annealing. The optical properties of both get much better after annealing, which indicates their potential applications in photoelectric nanodevices. The basic physics and chemistry involved in the ECLAL fabrication and the luminescence mechanism for products before and after annealing are discussed.
Co-reporter:Y. Liang, P. Liu, H. B. Li and G. W. Yang
CrystEngComm 2012 vol. 14(Issue 9) pp:3291-3296
Publication Date(Web):08 Mar 2012
DOI:10.1039/C2CE06347F
Transition metal vanadates MxVyOn (M = Cu, Ag, Zn, Co, Mo) have been studied extensively due to their fascinating structures and electronic, optical, and magnetic properties. Scientists have thus developed many methods for the synthesis of the nanostructures of these materials in recent years. However, these techniques have many visible flaws, e.g. high temperature or high pressure environment, various templates or additives, demanding complicated synthetic procedures, impurities in final products, and so on. In this contribution, we develop a facile synthesis for fabricating transition metal vanadates nanostructures, i.e., the electrochemistry assisted laser ablation in liquid (ECLAL). This is a green, simple, and catalyst-free approach under an ambient environment. Using ECLAL, we have synthesized copper vanadate nanostructures with various phases, and characterized the morphology and structure of the as-synthesized products by scanning electron microscope, transmission electron microscope, X-ray diffraction analysis, Fourier transform infrared spectroscopy and Raman scattering spectroscopy. Additionally, we have measured the optical multi-absorption properties of the as-synthesized products by a UV-vis spectrophotometer, which was attributed to the co-existing behavior of various phases in the as-synthesized nanostructures. The physical and chemical mechanisms of the synthesis of the copper vanadate nanostructures were pursued upon ECLAL.
Co-reporter:J.L. Li, Z.S. Hu, G.W. Yang
Chemical Physics 2012 Volume 392(Issue 1) pp:16-20
Publication Date(Web):2 January 2012
DOI:10.1016/j.chemphys.2011.08.017
Abstract
By theoretical analysis, we have explored the feasibility of functionalizing boron fullerene (B80) by adsorbing Mg atoms for the application as hydrogen storage nanomaterials. Our results show that due to the charge transfer from Mg to B atoms Mg atoms reside above the pentagonal faces of the B80 cage. The electric field induced around the positive charged Mg atoms polarizes H2 molecules, and the resulting binding is strong enough to adsorb H2 without dissociation. Further calculations indicated that the 12Mg-decorated-B80 has a high hydrogen storage capacity storing up to 96 H2 molecules with an ideal binding energy of 0.20 eV/H2 according to the approximation of GGA and 0.5 eV/H2 according to LDA, corresponding to a hydrogen uptake of 14.2%. This suggested a possible method of engineering new structure for high-capacity hydrogen storage materials with the reversible adsorption and desorption of hydrogen molecules.
Co-reporter:Y. Y. Cao and G. W. Yang
The Journal of Physical Chemistry C 2012 Volume 116(Issue 10) pp:6233-6238
Publication Date(Web):February 23, 2012
DOI:10.1021/jp210659g
We have established a theoretical model to address quantitatively the temperature-dependent growth of nanowire orientation and growth from substrates upon the vapor–liquid–solid (VLS) process by introducing thermal fluctuations. It was found that there is a critical temperature, depending on the Gibbs free energy of the nanowire nucleus, and that the nanowires with higher critical temperature tend to align horizontally to the substrate. Moreover, nanowires are vertically aligned on the substrate, or their growth direction is angled from the substrate, varying between 90 and 40°, if the critical temperature is lower. The critical temperatures of nanowires can be enormously dissimilar, which accounts for the fact that growth directions can be modulated by temperature. The developed theory explains the findings from a recent set of experiments on the temperature-dependent orientation of nanowires grown by the VLS process. These investigations concluded that thermal fluctuations play a crucial role in the VLS nanowire growth, and the preferred nanowire growth directions can be produced by temperature regulation, which would provide useful physical criteria in other types of experiments.
Co-reporter:Y. H. Yang, Y. Zhang, N. W. Wang, C. X. Wang, B. J. Li and G. W. Yang
Nanoscale 2011 vol. 3(Issue 2) pp:592-597
Publication Date(Web):15 Nov 2010
DOI:10.1039/C0NR00592D
ZnO semiconductors at the micro- and nanometre scales are attractive in optical, magnetic, and electronic applications because of their particular features and excellent properties. The whispering gallery mode (WGM) is a general and effective type to amplify the intensity of the luminescence emission, and has gained extensive application in lasing and microcavities. In this contribution, we reported that the smallest whispering gallery optical resonator has been achieved in an individual ZnO nanocone whose diameter gradually reduces from bottom to top in the range of 700 to 50 nm. Using the monochromatic cathodoluminescence (CL) equipment attached at a scanning electron microscopy, we observed the alternating patterns of bright and dark rings from the monochromatic CL image of an individual ZnO nanocone, which is attributed to the WGM-like enhanced luminescence emission when the ZnO nanocone is considered as an optical resonator. The smallest mode number of WGM, N = 0, was observed in the ZnO nanocone with a radius of 55 nm for the considered light wavelength of 380 nm, and with a radius of 81 nm for the considered light wavelength of 500 nm, respectively. These results showed that the smallest whispering gallery optical resonator from an individual ZnO nanocone has been fabricated. Experiments are in good agreement with both theoretical predictions and computer simulations based on the finite-difference time domain method with perfectly matched layer boundary conditions. These findings provided valuable information for applications of ZnO micro- and nanostructures in optoelectronic devices.
Co-reporter:T. He ; Z. S. Hu ; J. L. Li ;G. W. Yang
The Journal of Physical Chemistry C 2011 Volume 115(Issue 28) pp:13837-13843
Publication Date(Web):June 22, 2011
DOI:10.1021/jp203843j
We have presented a comprehensive investigation for the geometric, energetic, and electronic structures of the rutile TiO2 nanowire (NW) and nanotube (NT) by the first-principles calculations accompanied with the crystal orbital overlap population and the wave function analysis. Taking into account the surface interactions, we found that the geometry and stability of TiO2 NWs and NTs greatly depend on the surface structure with the size decreasing, which demonstrates the forming shape and structure. The competition between the surface-bonding effect and the quantum-confinement effect induces the oscillation behavior and the direct–indirect transition of the band gap of TiO2 NWs and NTs. These findings not only provide a new insight into the fundamental understanding of TiO2 nanostructures but also provide useful information to design TiO2 nanostructures for different applications.
Co-reporter:Pu Liu, Ying Liang, Xianzhong Lin, Chengxin Wang, and Guowei Yang
ACS Nano 2011 Volume 5(Issue 6) pp:4748
Publication Date(Web):May 25, 2011
DOI:10.1021/nn2007282
Polyoxometalate nanostructures have attracted much attention because of significant technical demands in applications such as catalysts, sensors, and smart windows. Therefore, researchers have recently developed many methods for the synthesis of these nanomaterials. However, these techniques have many visible flaws such as high temperatures or high pressure environments, various templates or additives, demanding and complicated synthesis procedures as well as the presence of impurities in the final products. We therefore propose a general strategy for the fabrication of particular polyoxometalate nanostructures by electrochemically assisted laser ablation in liquid (ECLAL). These polyoxometalates are usually simple as they typically contain two metals and are not soluble in water. This approach is a green, simple, and catalyst-free approach under an ambient environment. Apart from these merits, this novel technique allows researchers to choose and design interesting solid targets and to use an electrochemical approach toward the fabrication of polyoxometalate nanostructures for the purpose of fundamental research and for potential applications. Using the synthesis of Cu3Mo2O9 nanorods as an example, we substantiate the validity of the proposed strategy. For the fabrication of Cu3Mo2O9 nanostructures, we chose molybdenum as a solid target for laser ablation in liquid copper electrodes for the electrochemical reaction and water as a solvent for the ECLAL synthesis. We successfully fabricated Cu3(OH)2(MoO4)2 nanorods with magnetic properties. Interestingly, we obtained well-defined Cu3Mo2O9 nanorods by annealing the Cu3(OH)2(MoO4)2 nanostructures at 500 °C. Additionally, the basic physics and chemistry involved in the ECLAL fabrication of nanostructures are discussed.Keywords: electrochemistry; fabrication; laser ablation in liquid; polyoxometalate nanostructures
Co-reporter:P. Liu, H. Cui, C. X. Wang and G. W. Yang
Physical Chemistry Chemical Physics 2010 vol. 12(Issue 16) pp:3942-3952
Publication Date(Web):12 Mar 2010
DOI:10.1039/B918759F
Although nanomaterials investigations have been carried over the recent decades, researchers still face a fundamental challenge: how to control the phase, size and shape of nanocrystals in the synthesis of nanomaterials, i.e., how to achieve the transformation from nanocrytsal synthesis to functional nanostructure fabrication. For this issue, we, in this review, introduce recent developments in laser ablation in liquid (LAL) for the synthesis and fabrication of novel nanostructures with metastable phases and shapes. Laser ablation of solid targets in liquid has actually opened a door toward to synthesize nanocrystals and fabricate nanostructures due to these advantages as follows: (i) LAL is a chemically “simple and clean” synthesis due to the process with reduced byproduct formation, simpler starting materials, no need for catalyst, etc. (ii) Under ambient conditions, not extreme temperature and pressure, a variety of metastable phases that may not usually be attainable, can be generated by mild preparation methods. (iii) New phase formation involves in both liquid and solid upon LAL, which allows researchers to choose and combine interesting solid target and liquid to synthesize nanocrystals and fabricate nanostructures of new compounds for purpose of fundamental research and potential applications. (iv) The phase, size and shape of the synthesized nanocrystals can be readily controlled by tuning laser parameters and applying assistances such as inorganic salts or electrical field upon LAL. For example, we have synthesized the micro- and nanocubes of carbon with C8-like structures by the inorganic salts assisted LAL, and the micro- and nanocubes and spindles of GeO2 by the electrical field assisted LAL. Additionally, we have developed a new technique to fabricate functional nanopatterns on the basis of the pulsed-laser deposition in liquid. Accordingly, LAL could greatly extend its application in fabrication of functional nanostructures in the future.
Co-reporter:Y.H. Yang, G.W. Yang
Chemical Physics Letters 2010 Volume 494(1–3) pp:64-68
Publication Date(Web):9 July 2010
DOI:10.1016/j.cplett.2010.05.074
Abstract
ZnO nanowires have been self-assembled on amorphous carbon using the thermal chemical vapor transport and condensation without any metal catalysts. The temperature dependence of the growth rate of ZnO nanowires is characterized, and the growth activation energy is estimated to be 234 kJ/mol based on the experimental data. It is found that the growth rate of the thin ZnO nanowire is smaller than that of the thick one. A size-dependent kinetic model is proposed to address the unusual growth behaviors of ZnO nanowires. The theoretical predictions are consistent with experiments.
Co-reporter:S. Li and G. W. Yang
The Journal of Physical Chemistry C 2010 Volume 114(Issue 35) pp:15054-15060
Publication Date(Web):August 18, 2010
DOI:10.1021/jp1056545
The phase transition is fundamental for understanding physical and chemical properties of materials. The phase transition at the nanometer scale is usually distinguished from that of the bulk counterpart. It is essential to pursue the basic physics involved in the phase transition on nanoscale for applications of nanomaterials. Herein, we have established an analytical thermodynamic model at the nanometer scale to study the phase transition of II−VI semiconductor nanocrystals, and revealed the size-dependent polymorphism behaviors of the phase transition. The physical origin of the size effects on the polymorphism behaviors of II−VI semiconductor nanocrystals was addressed on the basis of the contributions of surface energy and surface stress of nanocrystals to the total Gibbs free energy. It was found that the low surface energy and the small surface stress always predominate the thermal stability of nanostructures with the metastable phase. These results provided new insight into the fundamental understanding of the phase transition of II−VI semiconductor nanocrystals.
Co-reporter:Nengwen Wang, Y. H. Yang, Jian Chen, Ningsheng Xu and Guowei Yang
The Journal of Physical Chemistry C 2010 Volume 114(Issue 7) pp:2909-2912
Publication Date(Web):January 29, 2010
DOI:10.1021/jp910802z
One-dimensional (1D) Zn-doped In2O3−SnO2 superlattice nanostructures have been fabricated on single-crystal silicon substrates by the layer-by-layer growth mode via the thermal chemical vapor transport and condensation with Au catalysts. The morphology, structure, and composition of the as-synthesized 1D superlattice were analyzed in detail. To exploit the potential applications of the fabricated nanostructures, the field emission properties of samples were characterized. The growth mechanism of the 1D Zn-doped In2O3−SnO2 superlattice nanostructures was discussed on the basis of the vapor−liquid−solid process.
Co-reporter:G. Ouyang, C. X. Wang and G. W. Yang
Chemical Reviews 2009 Volume 109(Issue 9) pp:4221
Publication Date(Web):August 11, 2009
DOI:10.1021/cr900055f
Co-reporter:P Liu, Y. L. Cao, X. Y. Chen and G. W. Yang
Crystal Growth & Design 2009 Volume 9(Issue 3) pp:1390
Publication Date(Web):December 30, 2008
DOI:10.1021/cg800633j
The high-pressure nanophase, that is, the metastable tetragonal structure, of germanium is trapped by a facile technique named electrical-field assisted pulsed laser ablation in liquid at ambient pressure and temperature. On the basis of X-ray diffraction, transmission electron microscopy, and Raman scattering analyses, the trapped Ge nanophase is identified to be the tetragonal structure rather than the diamond structure of bulk germanium. First-principles calculations are used to clarify the physical and chemical mechanisms of the tetragonal Ge formation upon laser ablation in liquid.
Co-reporter:J. L. Li and G. W. Yang
The Journal of Physical Chemistry C 2009 Volume 113(Issue 42) pp:18292-18295
Publication Date(Web):September 28, 2009
DOI:10.1021/jp9064592
We have theoretically performed that Fe endohedral-doped boron fullerene (B80) is a potential single molecular device with tunable electronic and magnetic properties. Both the energy gap and magnetic moment of the Fe endohedral-doped B80 can be greatly tuned, simultaneously by changing the position of the Fe atom inside the hollow cage of B80. In comparison with that of the Fe endohedral-doped B80 with Fe atom located at center-at, the energy gap decreases half and the magnetic moment decreases zero for the case of the Fe endohedral-doped B80 with the Fe atom located at hexagon-in in the hollow cage. These fascinating findings imply that the Fe endohedral-doped B80 with tunable electronic and magnetic properties can be expected to be applicable as a single molecular device.
Co-reporter:Xin Tan and Guowei Yang
The Journal of Physical Chemistry C 2009 Volume 113(Issue 46) pp:19926-19929
Publication Date(Web):October 23, 2009
DOI:10.1021/jp905619a
The self-assembly of the extended supramolecular nanowires on the stepped Ag(110) surfaces has been simulated by the kinetic Monte Carlo (KMC) method. The KMC simulations predict an optimal temperature and an optimal deposition flux for the formation of the longest supramolecular nanowire at the mesoscale. The kinetic instabilities of supramolecular nanowires self-assembly were elucidated, as were the physical and chemical mechanisms of formation of the extended supramolecular nanowires forming on the stepped Ag(110) surfaces.
Co-reporter:Xinlei Li and Guowei Yang
The Journal of Physical Chemistry C 2009 Volume 113(Issue 28) pp:12402-12406
Publication Date(Web):June 16, 2009
DOI:10.1021/jp9019766
The self-assembly of one-dimensional semiconductor heterostructures including core−shell structures and quantum dots (QDs) on nanowires (NWs) has attracted considerable interest because heterostructures as basic functional units play a key role in device physics. Herein, we theoretically revealed that a new physical mechanism, the self-relaxation of an epitaxial layer originated from a nanosized curve surface, works well in heteroepitaxial growth on the surface of NWs. The competition between the relaxation of islands and the self-relaxation of an epitaxial layer determines the epitaxial mode on the surface of NWs, i.e., core−shell or QD heterostructures. The agreement between theoretical predictions and experiments indicated that the proposed theory could be highly expected to be applicable to the controllable fabrication of NW heterostructures.
Co-reporter:P. Liu, Y. L. Cao, C. X. Wang, X. Y. Chen and G. W. Yang
Nano Letters 2008 Volume 8(Issue 8) pp:2570-2575
Publication Date(Web):July 24, 2008
DOI:10.1021/nl801392v
Micro- and nanocubes of carbon have been synthesized by laser ablation in liquid. The morphology and structure analyses indicated that these micro- and nanocubes are single crystals with a body-centered cubic structure with a lattice constant of 5.46 Å, which is so-called C8-like structure, and they have a slightly truncated shape bounded mainly by {200} facets. A blue-purple luminescence at room temperature was observed in the cathodoluminescence spectrum of the synthesized single micro- and nanocube of carbon, which exhibited that this unique carbon nanomaterial is a new semiconductor with blue luminescence. The physical and chemical mechanisms of the synthesis of carbon micro- and nanocubes were pursued upon laser ablation in liquid.
Co-reporter:P. Liu, Y. L. Cao, H. Cui, X. Y. Chen and G. W. Yang
Chemistry of Materials 2008 Volume 20(Issue 2) pp:494
Publication Date(Web):December 19, 2007
DOI:10.1021/cm7027178
Micro- and nanocubes of single-crystalline silicon with the zinc-blende structure have been synthesized by pulsed-laser-induced liquid–solid interface reaction. Raman scattering, scanning electron microscopy, transmission electronic microscopy equipped with energy dispersive X-ray spectrometer, selected area electron diffraction, and electron energy-loss spectroscopy are employed to characterize the morphology and structure of the as-synthesized samples. The first-principles calculations are employed to theoretically analyze the data of experiments. The synthesis mechanisms of silicon cubes upon PLIIR are pursued in physical and chemical mechanisms.
Co-reporter:X. Y. Chen, H. Cui, P. Liu and G. W. Yang
Chemistry of Materials 2008 Volume 20(Issue 5) pp:2035
Publication Date(Web):January 19, 2008
DOI:10.1021/cm703271m
A high-pressure phase of iron, double-layer hexagonal close-packed (DHCP) structure, is observed upon pulsed-laser ablation of an iron target in liquid under the conditions of room temperature and ambient pressure, and meanwhile DHCP iron nanocrystals with 10–20 nm diameter are prepared. The magnetism measurements of the prepared nanocrystals indicate that DHCP iron nanocrystals are nonferromagnetic. The stability of DHCP iron nanocrystals under normal temperature and pressure is attributed to the nanosized confinement effect of nanocrystals.
Co-reporter:P. Liu, Y. L. Cao, H. Cui, X. Y. Chen and G. W. Yang
Crystal Growth & Design 2008 Volume 8(Issue 2) pp:559
Publication Date(Web):January 19, 2008
DOI:10.1021/cg0705963
The phase transition from hexagonal to cubic GaN has been observed upon pulsed-laser ablation of hexagonal GaN powders in a liquid at room temperature and ambient pressure. At the same time, GaN nanocrystals are synthesized through this hexagonal-to-cubic phase transition. Cathodoluminescence spectroscopy is employed to characterize the luminescence of the synthesized GaN nanocrystals. First-principle calculations are used to clarify the physical and chemical mechanisms of the phase transition from hexagonal to cubic GaN upon pulsed-laser induced solid–liquid interface reaction.
Co-reporter:P. Liu, H. Cui and G. W. Yang
Crystal Growth & Design 2008 Volume 8(Issue 2) pp:581
Publication Date(Web):January 12, 2008
DOI:10.1021/cg7006777
A kind of carbon nanocrystals with body-centered cubic (bcc) structure has been synthesized by using a pulsed-laser induced liquid–solid interface reaction (PLIIR). Scanning electron microscopy, Raman spectra, transmission electron microscopy with energy dispersive X-ray spectrometry, selected area electronic diffraction, and high-resolution analysis are employed to characterize the morphology, composition, and structure of the synthesized nanocrystals. The experimental analyses show that the synthesized nanocrystals are single crystals with a bcc structure, the so-called C8, which was theoretically predicted by Johnston and Hoffmann. Carbon with a bcc structure has potential applications in mechanical engineering and electronics, because it is superdense and superhard. The synthesis mechanisms of bcc carbon nanocrystals by PLIIR are studied.
Co-reporter:X. L. Li ;G. W. Yang
The Journal of Physical Chemistry C 2008 Volume 112(Issue 20) pp:7693-7697
Publication Date(Web):April 15, 2008
DOI:10.1021/jp801528r
A thermodynamic approach has been proposed to address the quantum rings (QRs) self-assembly upon droplet epitaxy. It is found that the selective nucleation on the droplet skirt induced by the high surface energy density of droplet leads to the QR formation at the initial deposition stage, and then the QR growth is controlled by the diffusion of the droplet atoms and the trapping of the deposited atoms, which determines the final size and shape of QRs. Taking the GaAs/AlGaAs system as an example, the established theory nicely elucidates the physical mechanisms of the self-assembly of GaAs nanostructures including the single and double QRs and the holed nanostructure upon droplet epitaxy. Theoretical predictions are consistent with experiments, implying that the proposed thermodynamic model could be expected to be a general approach to pursue the nanostructural self-assembly upon droplet epitaxy.
Co-reporter:Juncong She, Zhiming Xiao, Yuhua Yang, Shaozhi Deng, Jun Chen, Guowei Yang and Ningsheng Xu
ACS Nano 2008 Volume 2(Issue 10) pp:2015
Publication Date(Web):September 12, 2008
DOI:10.1021/nn800283u
Both electrical and field emission measurements were carried out to study the correlation between resistance and field emission performance of individual one-dimensional (1D) ZnO nanostructures. Three types of 1D ZnO nanostructures were investigated (i.e., agave-like shape, pencil-like shape, and hierarchical structure) and were prepared by thermal chemical vapor transport and condensation without using any catalyst. The 1D ZnO nanostructures have obvious differences in resistance and thus conductivity from type to type. In addition, in the same type of 1D ZnO nanostructure, each individual emitter may also have variation in resistance and thus in conductivity. The field emission performance of the ZnO emitters was found to be strongly correlated with the resistance of each individual ZnO nanostructure: (i) a ZnO emitter with low resistance will have better emission; (ii) a high resistance region in a ZnO nanostructure is liable to the initiation of a vacuum breakdown event. The results indicate that, besides the uniformity in the geometrical structure, the uniformity in conductivity of the emitters in an array should be ensured, in order to meet the requirement of device application.Keywords: anode probe; field emission; resistance; single ZnO nanostructure; vacuum breakdown
Co-reporter:M. Q. Cai, X. Tan, G. W. Yang, L. Q. Wen, L. L. Wang, W. Y. Hu and Y. G. Wang
The Journal of Physical Chemistry C 2008 Volume 112(Issue 42) pp:16638-16642
Publication Date(Web):2017-2-22
DOI:10.1021/jp801889b
We theoretically show that the giant magneto-optical Kerr effects are induced by the electronic structure of half-metallic ferromagnetism in the perovskite BiNiO3 with the orthorhombic structure by first-principles calculation. A Kerr rotation is up to 1.28° at 1.87 eV, which is comparative to the recognized maximum polar Kerr rotation of 1.35° at 1.75 eV in the Heusler compound PtMnSb. The strong p−d exchange interaction causes the half-metallic ferromagnetism, i.e., the majority-spin electrons are semiconducting and the minority-spin electrons are metallic, which finally leads to the large Kerr rotation in the half-metallic ferromagnetic perovskite BiNiO3.
Co-reporter:G.W. Yang
Progress in Materials Science 2007 Volume 52(Issue 4) pp:648-698
Publication Date(Web):May 2007
DOI:10.1016/j.pmatsci.2006.10.016
This work presents a survey on the recent progress in laser ablation of a solid target in a confining liquid for the synthesis of nanocrystals with focus on the mechanism of nanocrystal growth. The effects of liquid confinement, thermodynamic nucleation, phase transition, and kinetic growth of the nanostructures are discussed in detail. Besides, a variety of applications of the laser ablation is reviewed, including surface patterning, surface cleaning, and surface coating. Experimental results and theoretical analysis indicate that laser ablation of a solid target in a confining liquid provides an effective means to synthesize nanocrystals, especially for the metastable nanocrystals such as diamond and carbon related materials, immiscible alloys, etc. The laser ablation in liquids has demonstrated the following advantages: (i) a chemically “simple and clean” synthesis, (ii) an ambient conditions not extreme temperature and pressure, and (iii) the new phase formation of nanocrystals may involve in both liquid and solid. These advantages allow us to combine selected solid targets and liquid to fabricate compound nanostructures with desired functions.
Co-reporter:Meng-Qiu Cai, Ji-Cheng Liu, Guo-Wei Yang, Xin Tan, Yun-Lun Cao, Wang-Yu Hu, Ling-Ling Wang, Yan-Guo Wang
Surface Science 2007 Volume 601(Issue 5) pp:1345-1350
Publication Date(Web):1 March 2007
DOI:10.1016/j.susc.2006.12.076
The rumpled relaxation and the core-level shift of full-relaxed BaTiO3 (0 0 1) surface have been investigated by first-principles calculation. Based on the work function and the electric-field gradient, the right size of vacuum and the slab have been evaluated. The large displacements of ions deviated from their crystalline sites to lead to the formation of the surface rumples have been found. Some fully occupied surface oxygen p states at the top M point of the valance band and the empty surface titanium d states at the edge of the bulk conduction band are observed on the TiO2-terminated surface. In contrast, on the BaO-terminated surface, two different core levels of the Ba 5p states shifted about 1.29 eV are induced by the bulk perovskite Ba atoms and the relaxation of surface Ba atoms, respectively. Our calculations are consistent with the experimental data.
Co-reporter:P. Liu, H. Cui, C. X. Wang and G. W. Yang
Physical Chemistry Chemical Physics 2010 - vol. 12(Issue 16) pp:NaN3952-3952
Publication Date(Web):2010/03/12
DOI:10.1039/B918759F
Although nanomaterials investigations have been carried over the recent decades, researchers still face a fundamental challenge: how to control the phase, size and shape of nanocrystals in the synthesis of nanomaterials, i.e., how to achieve the transformation from nanocrytsal synthesis to functional nanostructure fabrication. For this issue, we, in this review, introduce recent developments in laser ablation in liquid (LAL) for the synthesis and fabrication of novel nanostructures with metastable phases and shapes. Laser ablation of solid targets in liquid has actually opened a door toward to synthesize nanocrystals and fabricate nanostructures due to these advantages as follows: (i) LAL is a chemically “simple and clean” synthesis due to the process with reduced byproduct formation, simpler starting materials, no need for catalyst, etc. (ii) Under ambient conditions, not extreme temperature and pressure, a variety of metastable phases that may not usually be attainable, can be generated by mild preparation methods. (iii) New phase formation involves in both liquid and solid upon LAL, which allows researchers to choose and combine interesting solid target and liquid to synthesize nanocrystals and fabricate nanostructures of new compounds for purpose of fundamental research and potential applications. (iv) The phase, size and shape of the synthesized nanocrystals can be readily controlled by tuning laser parameters and applying assistances such as inorganic salts or electrical field upon LAL. For example, we have synthesized the micro- and nanocubes of carbon with C8-like structures by the inorganic salts assisted LAL, and the micro- and nanocubes and spindles of GeO2 by the electrical field assisted LAL. Additionally, we have developed a new technique to fabricate functional nanopatterns on the basis of the pulsed-laser deposition in liquid. Accordingly, LAL could greatly extend its application in fabrication of functional nanostructures in the future.
Co-reporter:Z. Q. Zheng, B. Wang, J. D. Yao and G. W. Yang
Journal of Materials Chemistry A 2015 - vol. 3(Issue 27) pp:NaN7074-7074
Publication Date(Web):2015/06/09
DOI:10.1039/C5TC01024A
We have experimentally demonstrated a visible light-controlled sensing response of the Au–ZnO nanowires for C2H2 gas at room temperature by plasmon-enhanced sensitivity, in which Au nanoparticles were coated on the surface of ZnO nanowires. The ZnO nanowires without Au nanoparticles showed a normal n-type response, whereas the Au coated ZnO nanowires exhibited a concentration-dependent and time-dependent p–n transition response for the sensing response to C2H2 gas at room temperature. This unconventional sensing behavior can be explained by the formation of a surface inversion layer. Meanwhile, this sensing can be modulated and the response was significantly enhanced at room temperature under visible light illumination. This light-controlled sensing response from the Au–ZnO nanowires was attributed to the fact that the visible light excites the surface plasmon resonance of Au nanoparticles on the surface of ZnO nanowires, and it can inject hot electrons into the conduction band of ZnO. These results hinted the potential application of the as-fabricated sensor in monitoring C2H2 gas at room temperature, and opened up new approaches for developing a new generation of visible light modulated gas sensors.
Co-reporter:Jiandong Yao, Zhaoqiang Zheng and Guowei Yang
Journal of Materials Chemistry A 2016 - vol. 4(Issue 33) pp:NaN7840-7840
Publication Date(Web):2016/07/19
DOI:10.1039/C6TC01453D
Transition metal dichalcogenides (TMDs) manifest excellent phonon-limited mobility and strong light–matter interaction, which, however, conflict with the long response time and low responsivity of TMD-based photodetectors. The extreme susceptibility of TMDs' electronic qualities to the large density of unscreened disturbances from the SiO2 substrate accounts for such inconformity. Here, we evaluated the potential of WS2 for photodetectors by passivating SiO2 substrates with layered Bi2Te3, a representative three dimensional topological insulator. Comparative photoswitching measurements of the WS2/Bi2Te3 photodetector demonstrated its stable and broadband photoresponse from 370 to 1550 nm. Meanwhile, WS2 and Bi2Te3 allied a high responsivity of 30.7 A W−1, a pronounced detectivity of 2.3 × 1011 cm Hz1/2 W−1 as well as a short response time of 20 ms, which make the device stand out among previously reported WS2 photodetectors. In fact, the responsivity and detectivity are comparable to those of state-of-the-art commercial Si and Ge photodetectors (R ∼ 0.5 to 0.85 A W−1, D* ∼ 3 × 1011 to 3 × 1012 cm Hz1/2 W−1), suggesting its great potential for practical applications. In addition, we also established that the excellent device performance is attributed to the synergy of the passivation of the SiO2 substrate, efficient carrier separation at the WS2/Bi2Te3 heterointerface and excellent carrier transport along the time-reversal-symmetry protected surface channel of Bi2Te3. In summary, these findings suggest that the WS2/Bi2Te3 photodetector will launch a significant advance in next-generation photodetection. Moreover, the interface engineering strategy depicts a universal scenario for development of TMD devices in the future.
Co-reporter:Zhaoyong Lin, Pu Liu, Jiahao Yan and Guowei Yang
Journal of Materials Chemistry A 2015 - vol. 3(Issue 28) pp:NaN14863-14863
Publication Date(Web):2015/06/09
DOI:10.1039/C5TA02958A
Coupling TiO2 with other semiconductors is a route to extend the optical response range of TiO2 and to improve the efficiency of its photon quantum. α-Fe2O3 seems compatible with TiO2 and possesses a high solar-light-harvesting capability that is fifteen times as large as that of TiO2. However, there is an energy level mismatch between TiO2 and α-Fe2O3. The photocatalytic performance of TiO2 would be inhibited when compositing with α-Fe2O3 due to the α-Fe2O3-induced photo-generated carriers trapping and dissipation. The composite acts like a one-way valve, in which photo-generated carriers flow from a thick pipe to a thin one and then jam up. Herein, we achieved the goal of matching the energy levels between TiO2 and α-Fe2O3 in a core–shell nanoparticle for enhancing visible-light photocatalysis. Heterostructured TiO2@α-Fe2O3 core–shell nanoparticles were fabricated by the long-pulsed laser ablation of a titanium target in water followed by a hydrothermal reaction. A well-matched interface between TiO2 and α-Fe2O3 was observed, which promoted photo-generated electrons and holes migration and separation. The energy band of the TiO2 nanoparticle was demonstrated to be matched with that of α-Fe2O3, resulting from the upward shift of its valence band due to the abundant oxygen vacancies and bridging hydroxyls on its surface. In this situation, the “blocked pipe” seems to be dredged effectively and the visible-light photocatalytic methyl orange dyes degradation performance of the TiO2@α-Fe2O3 nanoparticles is improved by a factor of two over that of the as-synthesized TiO2 nanoparticles. These findings provide new insights into TiO2 nanostructure photocatalysts and energy band engineering for visible-light photocatalysis.
Co-reporter:Z. Y. Lin, J. Xiao, J. H. Yan, P. Liu, L. H. Li and G. W. Yang
Journal of Materials Chemistry A 2015 - vol. 3(Issue 14) pp:NaN7658-7658
Publication Date(Web):2015/02/20
DOI:10.1039/C5TA00942A
Among numerous visible-light photocatalysts, plasmonic structure is a promising photocatalyst for photodegradation and energy generation. Ag/AgCl composite as an alternative visible-light photocatalyst has attracted extensive interests; however, its syntheses has many visible flaws, e.g. high temperature environment, requirement of various templates or additives, complicated synthetic procedures and impurities in the final products. For these issues, herein, we report, for the first time, a simple, facile, rapid and green technique to synthesize Ag/AgCl heterostructured cubes using a one-step process of laser irradiation in liquids. The fabricated Ag/AgCl cubes possess some active {111} facets and a high visible-light utilization efficiency induced by the localized surface plasmon resonance (SPR) from the Ag/AgCl heterostructure. As plasmonic photocatalysts, these Ag/AgCl cubes exhibited excellent photodegrading performance for dye molecules of methyl orange, Rhodamine B and methylene blue, and the photodegradation rates were about 0.268, 0.057, and 0.094 min−1, which are considerably higher than that of commercial Ag3PO4 by a factor of 29.8, 3.8 and 6.7, respectively. The high photo-stability of the Ag/AgCl cubes was also demonstrated. The SPR-mediated photocatalytic mechanism was proposed to address the ultrahigh activity of the Ag/AgCl heterostructure as an advanced visible-light photocatalyst. These results showed the broad applicability of the developed technique for accessing a new plasmonic photocatalyst with high-performance.
Co-reporter:Zhaoyong Lin, Jiling Li, Lihua Li, Lili Yu, Weijia Li and Guowei Yang
Journal of Materials Chemistry A 2017 - vol. 5(Issue 2) pp:NaN781-781
Publication Date(Web):2016/11/29
DOI:10.1039/C6TA09169E
The supply of clean hydrogen energy through photocatalysis in the future requires the finding of low-cost, efficient and durable cocatalysts to replace noble metal Pt. Cu and Ni are believed to be two promising materials. However, their cocatalytic performance is still limited. The theory of the hydrogen evolution pathway on Cu and Ni surfaces reveals that Cu can release H2 molecules easily but capture H atoms and photoelectrons with difficulty, while Ni performs inversely. To overcome this issue, we consider that improved cocatalytic performance could be achieved by the substitution of Ni atoms into a Cu crystal lattice to form a CuNi alloy. Here, we reported that CuNi alloy nanoparticles were prepared by a process of laser ablation in liquid (LAL). Their compositions could be tuned by varying the concentration of the isopropanol aqueous solution, which is novel in LAL. We demonstrated that the photocatalytic H2 evolution performance of TiO2 nanorods can be greatly improved by loading these CuNi nanoalloys on them to act as cocatalysts. Furthermore, these cocatalysts present favorable stability. The best cocatalytic performance was achieved by Cu63Ni37 alloy nanoparticles, even better than Pt. First-principles calculations demonstrated that the Cu63Ni37 alloy nanoparticles possess a high H atom adsorption energy, a large work function and a small H2 molecule adsorption energy, resulting in the rational manipulation of the hydrogen evolution pathway and the optimal cocatalytic performance. This work provided a strategy to design cheap, robust and durable cocatalysts for photocatalytic H2 evolution.
Co-reporter:Z. Q. Zheng, J. D. Yao and G. W. Yang
Journal of Materials Chemistry A 2016 - vol. 4(Issue 34) pp:NaN8103-8103
Publication Date(Web):2016/08/09
DOI:10.1039/C6TC02296K
High-sensitivity photodetectors are of great importance to extensive applications. However, thus far, photodetectors integrating transparency, flexibility, broadband response and competitive responsivity are quite rare. Herein, we demonstrate that photodetectors fabricated with pulsed-laser deposition (PLD) grown centimeter-scale high quality In2Se3 films on various substrates are capable of superior photoresponse. In particular, the fabricated device on a transparent polyimide (PI) substrate possesses flexible and transparent properties. In addition, it exhibits broadband photoresponse ranging from 254 to 1064 nm and a high detectivity reaching 6.02 × 1011 cm Hz1/2 W−1 at 532 nm. The responsivity and the external quantum efficiency are 20.5 A W−1 and 4784%, respectively, plus it shows a fast response time of 24.6 ms for the rise and 57.4 ms for the decay. Importantly, the responsivity of the device exhibits a linear dependence on the bias voltage, providing smooth modulation for multifunctional photoelectrical applications. We establish that the direct bandgap nature of In2Se3 and good Ohmic contact between In2Se3 and indium tin oxide (ITO) electrodes are responsible for such excellent performance. This study unambiguously reveals that these PLD-grown In2Se3 films possess the potential to be applied for versatile optoelectronic systems.
Co-reporter:Churong Ma, Jiahao Yan, Yuming Wei, Pu Liu and Guowei Yang
Journal of Materials Chemistry A 2017 - vol. 5(Issue 19) pp:NaN4819-4819
Publication Date(Web):2017/04/22
DOI:10.1039/C7TC00650K
Although previous designs of nonlinear optical (NLO) nanostructures have focused on photonic crystals and metal plasmonic nanostructures, complex structures, large ohmic loss, and Joule heating greatly hinder their practical applications. Beyond photonic crystals and metal plasmonic nanostructures, all-dielectric materials (ADMs) offer new ways to generate NLO behavior at subwavelength scales. Herein, we report enhancement in the tunable second harmonic generation (SHG) reflected from individual mid-refractive ADM nanoparticles, BaTiO3 nanoparticles (BTO NPs). Multipole decomposition, as observed in the linear spectra, demonstrated that the SHG enhancement originated from an overlap between the magnetic dipole or quadrupole resonance and the second harmonic wavelength of the pump source. In the vicinity of magnetic resonances, the localized field inside the nanoparticles could be increased by more than one order of magnitude. Compared with the spectral-separated electric and magnetic resonances in high-refractive all-dielectric nanostructures, an overlap of resonances was observed in the mid-refractive all-dielectric nanostructures and it resulted in electromagnetic (EM) mode coupling. A broad spectral characteristic results in moderate EM field enhancements over a wide wavelength range, which is conducive to the tunability of the SHG responses. Our study revealed the relationship between the linear and nonlinear optics at the nanoscale and helped in the design of efficient nonlinear optical devices based on ADMs.
Co-reporter:Lihua Li, Zhaoyong Lin, Lili Yu, Weijia Li and Guowei Yang
Journal of Materials Chemistry A 2016 - vol. 4(Issue 41) pp:NaN15928-15928
Publication Date(Web):2016/09/26
DOI:10.1039/C6TA06450G
Water finding, collection and retention are important issues in drylands because of the rareness and high evaporation of water. Efficiently and fully utilizing water for photocatalytic hydrogen production is thus a challenge in desert areas. Inspired by the decent water absorption and retention properties of super absorbent polymers (SAPs), it is a bracing idea to use SAPs for water storage and hydrogen production reactors to enable full use of precious water for light-driven water splitting. Herein, for the first time, we have prepared a self-assembling solid-state hydrogen source (SHS) for photocatalytic hydrogen evolution. In the SHS, Pt/TiO2 and NiB/CdS nanocomposites were used as solar-driven and visible-light driven hydrogen production model catalysts, respectively, integrated with commercial agricultural acrylamide-acrylate copolymerized crosslinked SAP (AAC). It exhibits hydrogen production comparable to that of a typical suspension system, is reusable, and can be more readily recycled than conventional powdery catalysts, because of its monolithic structure. All water molecules in the SHS can be used to produce hydrogen. Accordingly, the SHS developed in this work offers a strategy for integrating SAPs with catalysts that would be practical in water-efficient photocatalytic hydrogen evolution in drought regions.
Co-reporter:Zhaoyong Lin, Lihua Li, Lili Yu, Weijia Li and Guowei Yang
Journal of Materials Chemistry A 2017 - vol. 5(Issue 11) pp:NaN5259-5259
Publication Date(Web):2017/02/07
DOI:10.1039/C6TA10497E
Converting abundant solar energy into precious and clean hydrogen energy through photocatalytic water splitting is a highly promising way to address energy shortages. Solar H2 evolution is a practical technology in the environmental and energy fields. The electron is the protagonist in solar H2 evolution and the electron behavior determines performance. Three pivotal steps, electron generation, electron survival and electron utilization, are involved in this photocatalytic process. This review discusses some typical cases from the last two years of improving the performance of solar H2 evolution through elaborately manipulating the electron behavior. The manipulation can be accomplished by modifying the photocatalyst itself (self-modification) and with the assistance of foreign materials (extra-modification). It is expected that the main ideas behind these strategies can be extracted and used when designing efficient and robust photocatalytic systems in the future.
Co-reporter:C. R. Ma, J. Xiao and G. W. Yang
Journal of Materials Chemistry A 2016 - vol. 4(Issue 21) pp:NaN4698-4698
Publication Date(Web):2016/04/11
DOI:10.1039/C6TC00648E
Carbyne, the third allotrope of carbon with alternating single and triple bonds, consists of sp-hybridized carbon atoms. Theoretically, with two degenerate π-electron bands in one monomer, carbyne exhibits stronger nonlinear optical responses than graphene and it is acknowledged as a superior nonlinear optical material with just one π-electron band. Very recently, carbyne has been synthesized in the laboratory. Here, we demonstrate the giant nonlinear optical responses of carbyne. By employing the Z-scan technique using a femtosecond laser, we show that carbyne exhibits a large nonlinear absorption coefficient β and a refractive index n2 of 3.53 × 10−13 m W−1 and −1.40 × 10−13 esu at 800 nm excitation, respectively. Excellent broadband optical limiting responses of carbyne to femtosecond laser pulses at 800 and 400 nm were observed, respectively. We also establish that extensive π-electron delocalization and electron resonance enhancement of carbyne have made significant contributions to these nonlinear optical responses. These findings open the door to exploring the optical and technological applications of carbyne.
Co-reporter:C. R. Ma, J. H. Yan, P. Liu, Y. M. Wei and G. W. Yang
Journal of Materials Chemistry A 2016 - vol. 4(Issue 25) pp:NaN6069-6069
Publication Date(Web):2016/06/01
DOI:10.1039/C6TC01635A
Nonlinear optical (NLO) nanostructures have played important roles in frequency conversion, optical switching, information storage and biomedical imaging. Although previous designs have focused on photonic crystals and metal plasmonic nanostructures, complex structure, large ohmic loss and Joule heating greatly hinder their practical applications. Beyond photonic crystals and metal plasmonic nanostructures, all-dielectric materials (ADMs) bring new ways to generate NLO behavior at subwavelength scales. We, for the first time to our knowledge, demonstrate irregular-geometry induced second harmonic generation (SHG) enhancement from an individual all-dielectric SiC nanoparticle. SHG conversion efficiency of single irregular-geometry SiC nanoparticles increases to 10−5 under an average excitation power of 6 mW at 880 nm excitation, thirtyfold higher than that of SiC nanosphere. We also establish that not only electric dipole mode but also magnetic dipole mode can exist in the vicinity of nanoparticles in mid-refractive (2 < n < 3) ADMs, and the stronger enhancement of the magnetic response induced by the irregular-geometry makes a great contribution to the SHG enhancement. A modified formula that includes electric and magnetic contributions is proposed to predict the SHG enhancement from ADMs. This discovery makes geometry-tuning all-dielectric nanoparticles promising in NLO nanostructures of nanophotonics in the future.
Co-reporter:Zhaoyong Lin, Lihua Li, Lili Yu, Weijia Li and Guowei Yang
Physical Chemistry Chemical Physics 2017 - vol. 19(Issue 12) pp:NaN8362-8362
Publication Date(Web):2017/02/21
DOI:10.1039/C7CP00250E
Realization of hydrogen economy requires an environmental and economic method for hydrogen (H2) evolution. Dual-functional photocatalysis, that is, producing H2 from industrial wastewaters, may be the most ideal. However, it seems almost impossible to achieve dual-functional photocatalysis because of the difficulty in the simultaneous existence of photocatalytic pollutant degradation (PDR) and H2 evolution reactions (HER) in one system. All previous designs show that either HER or PDR is inhibited due to the insufficient management of the photo-generated electrons (e−) and holes (h+). To overcome this issue, we consider that both PDR and HER could be improved simultaneously by employing a suitable photocatalyst whose main active species in PDR are h+. In this case, e− and h+ can play their own roles in accomplishing HER and PDR, respectively, via the charge spatial separation in the selected photocatalyst. Herein, Cu2O polyhedrons are constructed as a proof-of-concept example. A favorable dual-functional photocatalytic performance is achieved by the Cu2O cubooctahedrons. Furthermore, an appropriate pollutant concentration is significant for the optimization of both HER and PDR performances due to the competition between H atom adsorption and pollutant molecule adsorption on the surfaces of the photocatalyst. This advance provides the H2 evolution technology with a more environmental and economic method.
