Yichun Liu

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Organization: Northeast Normal University

Department: Center for Advanced Optoelectronic Functional Materials Research

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Material Chemistry

Perovskite Solar Cells

Polymer

Stimuli Responsive Polymers Stimuli Responsive Polymers Photo Responsive Polymers

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References

Fabrication of efficient PbS colloidal quantum dot solar cell with low temperature sputter-deposited ZnO electron transport layer

Co-reporter:Shuaipu Zang, Yinglin Wang, Meiying Li, Wei Su, Hancheng Zhu, Xintong Zhang, Yichun Liu

Solar Energy Materials and Solar Cells 2017 Volume 169(Volume 169) pp:

Publication Date(Web):1 September 2017

DOI:10.1016/j.solmat.2017.05.026

•Pinhole free sputtered ZnO film was used as ETL of PbS CQDSCs.•Sputtered ZnO ETL generated higher PCE than that with traditional ZnO ETL.•Sputtered ZnO ETL facilitated performance consistency of large-area cell.•High bending tolerance of flexible cell with sputtered ZnO ETL.Preparation of electron transport layer (ETL) with high uniformity by convenient and low-temperature process is of essential importance for the future development of colloidal quantum dot solar cells (CQDSCs) into large-area and flexible devices. Herein we utilized magnetron sputtering technique to deposit ZnO thin film as the ETL of PbS CQDSCs. The ZnO film deposited at ambient temperature displayed preferential growth along (001) direction, pinhole free morphology, and good optical transmittance. On rigid SnO2:F (FTO) conductive glass substrates, PbS CQDSCs with sputtered ZnO ETL achieved a power conversion efficiency of 6.47% under AM 1.5 G simulated solar irradiation, which was higher than the 6.02% efficiency of the CQDSC fabricated on the benchmarked ZnO nanocrystals ETL. The good uniformity of sputtered ZnO film also facilitated the consistency of photovoltaic parameters of big-sized CQDSCs, as demonstrated by the similar output of four series-connected CQDSC units fabricated in one batch with a total active area of 14.4 cm2. Flexible PbS CQDSCs was also fabricated on the sputtered ZnO ETL, using In2O3:Sn-coated polyethylene terephthalate (ITO-PET) as the substrate, which achieved a power conversion efficiency of 3.87% and displayed negligible decline of the photovoltaic parameters after 100-time bending treatment. Our research demonstrates that the magnetron-sputtered ZnO film, with favorable features of low-temperature process, large-area continuity, and high bending tolerance, presents promising potential for the future development of PbS CQDSCs.

Pectinate nanofiber mat with high absorbency and antibacterial activity: A potential superior wound dressing to alginate and chitosan nanofiber mats

Co-reporter:Sainan Chen, Sisi Cui, Junli Hu, Yifa Zhou, Yichun Liu

Carbohydrate Polymers 2017 Volume 174(Volume 174) pp:

Publication Date(Web):15 October 2017

DOI:10.1016/j.carbpol.2017.06.096

•The properties of pectinate, alginate and chitosan nanofiber mats were compared.•The three mats had comparable mechanical strength and vapour permeability.•The pectinate nanofiber mat could absorb more exudates faster.•The pectinate nanofiber mat could suppress bacteria’s growth more effectively.Polysaccharides including pectin, alginate and chitosan are fabricated into dressings of micrometer-scaled architecture (micro- fiber or particle) and widely applied in wound treatments clinically. This work characterized and compared the properties of electrospun nanofibrous dressings of these polysaccharides. We found that although the three polysaccharide nanofiber mats had comparable mechanical strength and vapour permeability, the pectinate nanofiber mat could absorb 1.2 times and 3.6 times more exudates than the alginate and chitosan nanofiber mats, respectively, within less time. Moreover, the pectinate nanofiber mat showed much higher antibacterial activity (73.1%) than the alginate and chitosan nanofiber mats (11.8% and 17.1%, respectively). Further examinations demonstrated that the superior absorbency and antibacterial activity of the pectinate nanofiber mat were associated with the moderate extent of swelling of pectinate nanofibers under hydrated conditions. All these results suggest that the pectinate nanofiber mat might be a superior wound dressing to the alginate and chitosan nanofiber mats.

Highly stable copper wire/alumina/polyimide composite films for stretchable and transparent heaters

Co-reporter:Peng Li, Jiangang Ma, Haiyang Xu, Xiaodan Xue and Yichun Liu

Journal of Materials Chemistry A 2016 vol. 4(Issue 16) pp:3581-3591

Publication Date(Web):22 Mar 2016

DOI:10.1039/C5TC04276C

Transparent heaters, which are capable of withstanding a high dynamic strain, in contrast with those made of brittle indium tin oxide films, are increasingly needed for heating of next-generation flexible and stretchable electronics, such as artificial skins, touch screens, displays, and sensors. This work provides a new approach for the fabrication of a transparent heater that is made of a Cu wire/alumina/polyimide composite film. The advantages of this film include a high transparency, low operating voltage, unprecedented stability against harsh environmental conditions, and repeated bending or stretching. A highly conductive Cu wire network was prepared via thermal evaporation of low-cost Cu on electrospun polymer nanofibers. Atomic layer deposition was used to conformably deposit an alumina film on the Cu wire network to suppress the diffusion and oxidation of Cu. The solution casted polyimide film that was introduced acts as a binder and can successfully improve the adhesion strength between the Cu wire and its substrate. After delicate optimization of the layered structure, we fabricated a transparent heater that exhibits a low sheet resistance of 8 Ω sq−1 and a high visible light transmittance of up to 91.4%, and it demonstrated an unprecedented ability to resist temperatures as high as 300 °C. Furthermore, the Cu wire/alumina/polyimide-based transparent heater can endure 100 cycles of stretching–releasing at a strain of 30% with an exceptionally high stability and reversibility. Thus, these copper wire/alumina/polyimide composite films have extremely high potential for applications in heating of future wearable optoelectronic devices.

Effect of SiO2 Spacer-Layer Thickness on Localized Surface Plasmon-Enhanced ZnO Nanorod Array LEDs

Co-reporter:Weizhen Liu, Haiyang Xu, Siyi Yan, Cen Zhang, Lingling Wang, Chunliang Wang, Liu Yang, Xinhua Wang, Lixia Zhang, Jiannong Wang, and Yichun Liu

ACS Applied Materials & Interfaces 2016 Volume 8(Issue 3) pp:1653

Publication Date(Web):January 7, 2016

DOI:10.1021/acsami.5b08382

Localized surface plasmon (LSP)-enhanced ultraviolet LEDs have been constructed via spin-coating Ag nanoparticles onto ZnO/SiO2 core/shell nanorod array/p-GaN heterostructures. Different from the previous reports where the dielectric spacer-layer thickness was determined only through photoluminescence (PL) characterization, the SiO2 shell thickness in this work is also optimized by actual electroluminescence (EL) measurements to maximize the enhancement. It is interesting to find that the enhancement ratios derived from PL and EL measurements demonstrate different thickness dependences on SiO2 shell: an optimal 3.5-fold PL enhancement was obtained at the SiO2 thickness of 16 nm, while an “abnormal” 7-fold EL enhancement was achieved at the thickness of 12 nm. Time-resolved spectroscopy studies, as well as theoretical estimations and numerical simulations, reveal that the higher-ratio EL enhancement stems from joint contributions, both internal-quantum-efficiency improvement induced by exciton-LSP coupling and light-extraction-efficiency improvement aroused by photon-LSP coupling.Keywords: exciton-LSP coupling; localized surface plasmon; luminescence enhancement; photon-LSP coupling; ultraviolet LED; ZnO/SiO2 core/shell nanorod array

Flexible transparent heaters based on silver nanotrough meshes

Co-reporter:P. Li, J.G. Ma, H.Y. Xu, D. Lin, X.D. Xue, X.Z. Yan, P. Xia, Y.C. Liu

Journal of Alloys and Compounds 2016 Volume 664() pp:764-769

Publication Date(Web):15 April 2016

DOI:10.1016/j.jallcom.2015.12.216

•Ag NTR was achieved via thermal evaporation of silver on the nanofiber template.•Ag NTR mesh exhibited flexibility and strong adhesion to its substrate.•Ag NTR mesh-based heater exhibited rapid thermal response at low operation voltage.Flexible transparent heaters based on silver nanotrough mesh were prepared by thermal evaporation of silver on sacrificial nanofiber templates fabricated by electrospinning. Due to the specific preparation process, the heaters have many advantages like large area uniformity, low resistance, high transparency, mechanical flexibility and strong adhesion to substrates. A rapid and effective heating (rising from 25 °C to 100 °C in 50 s) is obtained at a DC input of 7 V with a visible light transmittance as high as 87%, which results in a relatively high figure of merit for transparent heaters. Therefore, silver nanotrough mesh can be a promising candidate for transparent heating applications.

Individual single-crystal nanowires as electrodes for organic single-crystal nanodevices

Co-reporter:Guorui Wang, Qingxin Tang, Yanhong Tong, Wenping Hu and Yichun Liu

Journal of Materials Chemistry A 2015 vol. 3(Issue 37) pp:9534-9539

Publication Date(Web):05 Aug 2015

DOI:10.1039/C5TC01920F

Conductive, transparent, and flexible SnO2:Sb single-crystal nanowires are shown as electrodes for F16CuPc single-crystal nanowire devices on flexible plastic, which includes anisotropic-transport OFETs, electrode-movable OFETs, and p–n junction photovoltaic devices. The SnO2:Sb nanowires provide a good energy level match and excellent soft contact with F16CuPc nanowires, leading to multifaceted applications of the SnO2:Sb nanowire in nanowire electronics and optoelectronics, as well as high device performance. Combined with their good size compatibility, these results show that the conductive SnO2:Sb single-crystal nanowire opens a window into the fundamental understanding of the intrinsic properties of highly ordered organic semiconductors, optimization and miniaturization of organic nanocircuits, and development of new-generation flexible organic nanodevices.

Enhanced waveguide-type ultraviolet electroluminescence from ZnO/MgZnO core/shell nanorod array light-emitting diodes via coupling with Ag nanoparticles localized surface plasmons

Co-reporter:Cen Zhang, Claire Elizabeth Marvinney, Hai Yang Xu, Wei Zhen Liu, Chun Liang Wang, Li Xia Zhang, Jian Nong Wang, Jian Gang Ma and Yi Chun Liu

Nanoscale 2015 vol. 7(Issue 3) pp:1073-1080

Publication Date(Web):21 Nov 2014

DOI:10.1039/C4NR04966G

Localized surface plasmon (LSP) enhanced waveguide-type ultraviolet light-emitting diodes (LEDs) were fabricated by sputtering Ag nanoparticles (Ag-NPs) onto ZnO/MgZnO core/shell nanorod array (CS-NRA)/p-GaN heterostructures. A ∼9-fold enhancement of ZnO ultraviolet electroluminescence (EL) was demonstrated by the Ag-NPs decorated LED compared with the device without Ag-NPs. Angle-dependent EL measurements, as well as finite-difference time-domain simulations of the EL intensity spatial distribution, confirmed the waveguide-type EL transmission mode along the NR's axial direction. The increased spontaneous emission rate observed in time-resolved spectroscopy suggested that the ZnO EL enhancement was attributed to LSP–exciton/polariton coupling. However, a direct coupling is very difficult to achieve between Ag-LSPs and electron–hole pairs in the active region due to their “remote” separation. Thereby, two possible models involving the dynamic process of interactions among excitons, photons, and LSPs, were established to understand the selective enhancement of ZnO EL.

Correction: Individual single-crystal nanowires as electrodes for organic single-crystal nanodevices

Co-reporter:Guorui Wang, Qingxin Tang, Yanhong Tong, Wenping Hu and Yichun Liu

Journal of Materials Chemistry A 2015 vol. 3(Issue 37) pp:9749-9749

Publication Date(Web):02 Sep 2015

DOI:10.1039/C5TC90164B

Correction for ‘Individual single-crystal nanowires as electrodes for organic single-crystal nanodevices’ by Guorui Wang et al., J. Mater. Chem. C, 2015, DOI: 10.1039/c5tc01920f.

Nonvolatile/volatile behaviors and quantized conductance observed in resistive switching memory based on amorphous carbon

Co-reporter:Xiaoning Zhao, Haiyang Xu, Zhongqiang Wang, Lei Zhang, Jiangang Ma, Yichun Liu

Carbon 2015 Volume 91() pp:38-44

Publication Date(Web):September 2015

DOI:10.1016/j.carbon.2015.04.031

Coexistence of nonvolatile and volatile resistive switching behaviors was demonstrated in Cu/amorphous carbon/Pt sandwich-structure memory devices by adjusting compliance currents (CCs) to control the size of Cu conductive filament (CF). It was observed that the retention time of the volatile switching strongly depends on the CF’s size, and can be tuned in a wide range from hundreds of milliseconds to tens of seconds. When the nanoscale CF contains only a small number of Cu atoms, the conductance quantization occurs in the relaxation process of resistance state. By quantitatively studying the dependence of relaxation time on CF’s size and temperature, the volatile behavior can be well understood within the framework of the Rayleigh instability, where the Cu-CF spontaneously dissolves to minimize the surface energy. The observed nonvolatile/volatile behaviors, as well as the spontaneous relaxation effect, bear many resemblances to the long-term/short-term plasticity of biological synapses, and thus can be fully utilized to develop artificial synaptic devices.

Improved resistive switching characteristics by introducing Ag-nanoclusters in amorphous-carbon memory

Co-reporter:Lei Zhang, Haiyang Xu, Zhongqiang Wang, Xiaoning Zhao, Jiangang Ma, Yichun Liu

Materials Letters 2015 Volume 154() pp:98-102

Publication Date(Web):1 September 2015

DOI:10.1016/j.matlet.2015.04.052

•A special sputtering method was applied to deposit the Ag active electrode.•The Ag-nanoclusters (Ag-NCs) can be introduced into the a-C film.•The embedded Ag-NCs in the a-C film favor the formation tip electrode.•The embedded Ag-NCs can locally enhance and concentrate the electric field.•Embedding Ag-NCs with a proper concentration can improve RS characteristics.Bipolar resistive-switching (RS) memories were demonstrated based on an Ag/amorphous-carbon (a-C)/Pt sandwich structure. Here, the Ag-nanoclusters (NCs) were embedded into the a-C film via the sputtering deposition and thermal agglomeration. Versus the device without Ag-NCs, the embedding of the Ag-NCs in the a-C film favors the formation of incomplete Ag conducting filaments (CFs). This can act as tip electrodes for the RS. Therein, the local electric field can be enhanced and concentrated and lead to a simplified CF structure. Therefore, embedding Ag-NCs with a proper concentration into the electrolyte layer can effectively decrease the forming/switching voltages and improve the RS uniformity.

Two-wavelength exposure enhancement in holographic data storage of spirooxazine-doped polymers

Co-reporter:Xin Xie, Meiling Zheng, Shencheng Fu, Xiuli Wang, Ye Li, Yichun Liu

Optics Communications 2015 Volume 338() pp:269-276

Publication Date(Web):1 March 2015

DOI:10.1016/j.optcom.2014.10.061

Spirooxazine could be used as optical storage medium due to the excellent photochromic characteristic. In this paper, dynamics of holographic grating recording in spirooxazine-doped PMMA polymers was investigated using two coherent green beams (532 nm) and auxiliary blue-violet beam (405 nm) of various powers. The diffraction efficiency and growth rate of holographic gratings as well as the production rate of H-aggregation of merocyanine were strongly dependent on the auxiliary light power. In terms of these effects, an Aggregation Model was proposed, which was found to be in good agreement with the measurements. The corresponding dynamic parameters were obtained by fitting the experimental results, indicating that both the thermal rate constant and the aggregating rate constant increase exponentially versus the auxiliary light power. With the help of this model, the maximum brightness of reconstruction images was calculated and proved experimentally at the blue-violet light power of 57 mW. The results present a new approach to enhance the efficiency in spirooxazine-based films for holographic storage.

Interplay between Static and Dynamic Energy Transfer in Biofunctional Upconversion Nanoplatforms

Co-reporter:Yadan Ding; Fei Wu; Youlin Zhang; Xiaomin Liu; Elinore M. L. D. de Jong; Tom Gregorkiewicz; Xia Hong; Yichun Liu; Maurice C. G. Aalders; Wybren Jan Buma;Hong Zhang

The Journal of Physical Chemistry Letters 2015 Volume 6(Issue 13) pp:2518-2523

Publication Date(Web):June 15, 2015

DOI:10.1021/acs.jpclett.5b00999

Clarification of the energy-transfer (ET) mechanism is of vital importance for constructing efficient upconversion nanoplatforms for biological/biomedical applications. Yet, most strategies of optimizing these nanoplatforms were casually based on a dynamic ET assumption. In this work, we have modeled quantitatively the shell-thickness-dependent interplay between dynamic and static ET in nanosystems and validated the model in a typical biofunctional upconversion nanoplatform composed of NaYF4:Er, Yb/NaYF4 upconversion nanoparticles (UCNPs), and energy-acceptor photosensitizing molecule Rose Bengal (RB). It was determined that with a proper thickness shell, the energy transferred via dynamic ET as well as static ET in this case could be significantly improved by ∼4 and ∼9 fold, respectively, compared with the total energy transferred from bare core UCNPs. Our results shall form the bedrock in designing highly efficient ET-based biofunctional nanoplatforms.

Polarization-Controlled Bicolor Recording Enhances Holographic Memory in Ag/TiO2 Nanocomposite Films

Co-reporter:Shencheng Fu

The Journal of Physical Chemistry C 2015 Volume 119(Issue 32) pp:18559-18566

Publication Date(Web):July 17, 2015

DOI:10.1021/acs.jpcc.5b04409

Ag/TiO2 nanocomposite films present a stable optical memory based on localized surface plasmon resonance but still suffer from the problem of the low efficiency of holographic storage. Here, we report that the response time and diffraction efficiency of the high-density holographic storage of Ag/TiO2 nanocomposite films at 403.4 nm can be improved significantly and further modulated by introducing the auxiliary 532 nm irradiation with s or p linear polarization state. Absorbance at ∼600 nm, contrast of holographic fringes, and brightness of reconstruction image were all enhanced under the bicolor excitation. The observations were explained by Ag+ ions migration, Ag nanoparticle dissolution, and their redeposition, with the help of concentration and electronic-field gradient forces. Taking these factors in account, a phenomenological model describing the growth of two competitive-phase gratings is proposed. The localized surface plasmon resonance with the composite wave provides new possibilities for Ag/TiO2 nanocomposite films in application of long-life and high-density optical memory.

Wafer-Scale Coplanar Electrodes for 3D Conformal Organic Single-Crystal Circuits

Co-reporter:Xiaoli Zhao;Yanhong Tong;Qingxin Tang

Advanced Electronic Materials 2015 Volume 1( Issue 12) pp:

Publication Date(Web):

DOI:10.1002/aelm.201500239

Conformal organic single-crystal circuit on 3D curved surfaces, which can provide sensory and scanning features for monitoring, biofeedback, and tracking of physiological function, presents one of the most promising technologies for high-performance wearable and implantable electronics. However, the present organic single-crystal circuits remain limited on rigid planar substrates, by the lack of fabrication techniques for mechanically elastic and flexible electrodes to conform to 3D curved surfaces. Here, a novel electrode design for the formation of a wafer-scale coplanar electrode, together with only one individual flexible rubrene nanobelt, to achieve the 3D conformal single-crystal transistors and circuits for the first time is proposed. Excellent electrical properties with device yield as high as 93.2%, field-effect mobility up to 23.9 cm² V⁻¹ s⁻¹, near-zero threshold voltage, inverter gain over 23, and the extreme circuit stability with zero hysteresis are shown. The results open up the capability of organic single crystals for conformal circuits and reveal the strong potential of the new-type electrode for future large-scale wearable and implantable electronics.

Coexistence of an anatase/TiO2(B) heterojunction and an exposed (001) facet in TiO2 nanoribbon photocatalysts synthesized via a fluorine-free route and topotactic transformation

Co-reporter:Changhua Wang, Xintong Zhang and Yichun Liu

Nanoscale 2014 vol. 6(Issue 10) pp:5329-5337

Publication Date(Web):04 Mar 2014

DOI:10.1039/C4NR00236A

In this work, we report a novel approach to fabricate hierarchical TiO2 microspheres (HTMS) assembled by ultrathin nanoribbons where an anatase/TiO2(B) heterojunction and high energy facet coexist. The as-adopted approach involves (1) nonaqueous solvothermal treatment of a mixture of tetrabutyl titanate and acetic acid and (2) topotactical transformation into HTMS via thermal annealing. By this approach, the TiO2(B) phase usually synthesized from an alkaline treatment route could be initially formed. Subsequently, phase transition from TiO2(B) to anatase TiO2 occurs upon thermal treatment. It is demonstrated that such phase transition is accompanied by crystallographic orientation along the c-axis of anatase and TiO2(B) crystals, resulting in not only a coherent interface between two phases but also oriented attachment of anatase mesocrystals along the [001] direction, and finally high-energy (001) facet exposure. Interestingly, this work provides an alternative fluorine-free route for the synthesis of TiO2 crystals with high-energy (001) facet exposure. The structural analysis reveals that lattice-match induced topotactic transformation from TiO2(B) to anatase is the sole reason for the (001) facet exposure of anatase TiO2. The photocatalytic test for acetaldehyde decomposition shows that HTMS with anatase/TiO2(B) heterojunction and high-energy (001) facet exhibits superior photocatalytic efficiency compared with the relevant commercial product P25, which can be ascribed to the synergistic effect of large surface area, anatase/TiO2(B) heterojunction as well as high-energy facet exposure.

Waveband-dependent photochemical processing of graphene oxide in fabricating reduced graphene oxide film and graphene oxide–Ag nanoparticles film

Co-reporter:Bing Li, Xintong Zhang, Peng Chen, Xinghua Li, Lingling Wang, Ceng Zhang, Weitao Zheng and Yichun Liu

RSC Advances 2014 vol. 4(Issue 5) pp:2404-2408

Publication Date(Web):22 Nov 2013

DOI:10.1039/C3RA45355C

Waveband-dependent photochemical reduction properties of graphene oxide (GO) were investigated. The ratio of oxygenated carbon to graphitic carbon of the GO film was reduced to 39% and 28% by 400–800 nm and 350–800 nm irradiation, respectively from the initial value of 47%, while this ratio changed negligibly by 520–800 nm irradiation. This waveband-dependent photoreduction is closely related to the wide size distribution of sp2 carbon clusters with different band gaps within the GO sheet, which play the role of the photochemical reacting centers. In addition, the photochemical activity of GO was also demonstrated by photoreduction of Ag+ in water. Our research suggests the possibilities of tuning the microstructure of GO by careful selection of irradiation conditions and of preparing noble metal nanoparticles with a neat surface on GO sheets.

Ultraviolet electroluminescence from Au/MgO/MgxZn1−xO heterojunction diodes and the observation of Zn-rich cluster emission

Co-reporter:C.Y. Liu, H.Y. Xu, Y. Sun, C. Zhang, J.G. Ma, Y.C. Liu

Journal of Luminescence 2014 Volume 148() pp:116-120

Publication Date(Web):April 2014

DOI:10.1016/j.jlumin.2013.12.005

•A series of Au/MgO/MgxZn1−xO heterojunction diodes with multiple Mg compositions are fabricated and ultraviolet electroluminescence is achieved.•EL mechanism and laser forming process are discussed based on energy band diagram, impact-ionization process and disordered optical structure.•The transition from spontaneous to stimulated emission is observed in these heterojunctions, and the lasing mode is random laser.•In high Mg-content MgZnO devices, the emission from self-formed Zn-rich clusters is observed, which are thermally stable luminescence centers.In this work, ultraviolet (UV) electroluminescence (EL) is achieved from Au/MgO/MgxZn1−xO heterojunction diodes. The EL mechanism and laser forming process are discussed based on the energy band diagram, impact-ionization process and disordered optical structure. For ZnO and low Mg-content MgZnO devices, their EL spectra show single near-band-edge (NBE) emission. While in high Mg-content MgZnO devices, the emission from self-formed Zn-rich MgZnO clusters is observed and also contribute to the UV EL band. These Zn-rich clusters can act as thermally-stable luminescence centers, suggesting a promising route for developing MgZnO-based UV light-emitting devices.

Polarization-dependent and rewritable holographic gratings in Ag/TiO2 nanocomposite films

Co-reporter:Shencheng Fu, Shiyu Sun, Xintong Zhang, Xiuli Wang, Yichun Liu

Optics Communications 2014 Volume 318() pp:1-6

Publication Date(Web):1 May 2014

DOI:10.1016/j.optcom.2013.12.040

TiO2 nanoporous films loaded with Ag nanoparticles exhibited distinctive photochromism and photoanisotropy under the visible linearly polarized irradiation. Based on such properties, a pure polarization holographic grating was recorded in the photochromic film using two orthogonal circularly polarized green beams (532 nm) and reconstructed with a red beam (632.8 nm). The diffraction efficiency of the holographic grating and the brightness of the reconstruction image were strongly dependent on the polarization state of the probe beam. The hologram can be erased simply by the irradiation of single green beam. This recording–erasing process can be repeated with little loss, which may be benefited from the reciprocating mobility of Ag+ ions, reversible deformation and re-growth of Ag nanoparticles under the alternate irradiation of linearly and circularly polarized light. The novel nanocomposite system with photoanisotropy makes a new range of applications in the field of high-density optical memory media.

Recent progress in ZnO-based heterojunction ultraviolet light-emitting devices

Co-reporter:Yichun Liu;Haiyang Xu;Chunyang Liu;Weizhen Liu

Science Bulletin 2014 Volume 59( Issue 12) pp:1219-1227

Publication Date(Web):2014 April

DOI:10.1007/s11434-014-0206-9

Wide bandgap (3.37 eV) and high exciton-binding energy of ZnO (60 meV) make it a promising candidate for ultraviolet light-emitting diodes (LEDs) and low-threshold lasing diodes (LDs). However, the difficulty in producing stable and reproducible high-quality p-type ZnO has hindered the development of ZnO p–n homojunction LEDs. An alternative strategy for achieving ZnO electroluminescence is to fabricate heterojunction devices by employing other available p-type materials (such as p-GaN) or building new device structures. In this article, we will briefly review the recent progress in ZnO LEDs/LDs based on p–n heterostructures and metal–insulator-semiconductor heterostructures. Some methods to improve device efficiency are also introduced in detail, including the introduction of Ag localized surface plasmons and single-crystalline nanowires into ZnO LEDs/LDs.

Enhanced ultraviolet emission and improved spatial distribution uniformity of ZnO nanorod array light-emitting diodes via Ag nanoparticles decoration

Co-reporter:Wei Zhen Liu, Hai Yang Xu, Chun Liang Wang, Li Xia Zhang, Cen Zhang, Shi Yu Sun, Jian Gang Ma, Xin Tong Zhang, Jian Nong Wang and Yi Chun Liu

Nanoscale 2013 vol. 5(Issue 18) pp:8634-8639

Publication Date(Web):11 Jul 2013

DOI:10.1039/C3NR02844E

Localized surface plasmon (LSP) enhanced ultraviolet (UV) light-emitting diodes (LEDs) were fabricated by embedding a ZnO nanorod array/p-GaN film heterostructure into a Ag-nanoparticles/PMMA composite. By optimizing the concentration of Ag nanoparticles in PMMA, two distinct changes in electroluminescence (EL) spectra were observed: (1) the UV EL component from ZnO excitons was selectively enhanced more than 13-fold and the entire spectral lineshape was changed and (2) the spatial uniformity of the output photon intensity was improved and the linewidth of an angular distribution curve was increased by ∼2 times. These observations can be attributed to near-field optical coupling between Ag LSPs and ZnO excitons. Time-resolved luminescence measurements and a model calculation reveal that the optical coupling results in the increase of the spontaneous emission rate and internal quantum efficiency of Ag-nanoparticles-decorated ZnO nanorod arrays. Moreover, the LSP–exciton interaction allows the device's EL to be coupled out of the nanorod waveguide and to be isotropically scattered into every direction, thus broadening the angular distribution of the EL intensity.

Performance improvement of resistive switching memory achieved by enhancing local-electric-field near electromigrated Ag-nanoclusters

Co-reporter:Z. Q. Wang, H. Y. Xu, L. Zhang, X. H. Li, J. G. Ma, X. T. Zhang and Y. C. Liu

Nanoscale 2013 vol. 5(Issue 10) pp:4490-4494

Publication Date(Web):15 Mar 2013

DOI:10.1039/C3NR33692A

By introducing Ag nanoclusters (NCs), ZnO-based resistive switching memory devices offer improved performance, including improved uniformity of switching parameters, and increased switching speed with excellent reliability. These Ag NCs are formed between the top-electrode (cathode) and the switching layer by an electromigration process in the initial several switching cycles. The electric field can be enhanced around Ag NCs due to their high surface curvature. The enhanced local-electric-field (LEF) results in (1) the localization of the switching site near Ag NCs, where oxygen-vacancy-based conducting filaments have a simple structure, and tend to connect Ag NCs along the LEF direction; (2) an increase in migration and recombination rates of oxygen ions and oxygen vacancies. These factors are responsible for the improvement in device performance.

Ultrafast Li-ion battery anode with superlong life and excellent cycling stability from strongly coupled ZnO nanoparticle/conductive nanocarbon skeleton hybrid materials

Co-reporter:G.Z. Yang, H.W. Song, H. Cui, Y.C. Liu, C.X. Wang

Nano Energy 2013 Volume 2(Issue 5) pp:579-585

Publication Date(Web):September 2013

DOI:10.1016/j.nanoen.2013.06.013

•We fabricated novel ZnO/C nanospheresvia a hierarchical bottom-up assembly route.•ZnO nanograins were tightly sandwiched in the conductive nanocarbon skeleton.•Final products can be controlled by simply adjusting the reaction temperatures.•The unique nanostructures lead to superior capacity and excellent cycle stability.Ultrafast rechargeable lithium-ion batteries made from low-cost and abundant electrode materials would satisfy the increasing demands for energy storage worldwide. Herein, we demonstrate a large-scale hierarchical bottom-up assembly route for the formation of lithium-ion battery anode with excellent electrochemical properties by creating composites based on embedding ZnO nanoparticles into nanocarbon matrix which uniformly dispersed on the outer and inner surfaces of a porous creased carbon bubble host, which serves to hold them tightly by the pores and creases during battery operation and sandwich them between rapid ion and electron transport pathways. We successfully increase the charging and discharging rates by nearly 300-fold over the highest rate yet reported while attaining high power density and energy density which represents the best performance for long-cycle ZnO anode so far.

Synaptic Learning and Memory Functions Achieved Using Oxygen Ion Migration/Diffusion in an Amorphous InGaZnO Memristor

Co-reporter:Zhong Qiang Wang;Hai Yang Xu;Xing Hua Li;Hao Yu;Yi Chun Liu;Xiao Juan Zhu

Advanced Functional Materials 2012 Volume 22( Issue 13) pp:2759-2765

Publication Date(Web):

DOI:10.1002/adfm.201103148

Abstract

A single synaptic device with inherent learning and memory functions is demonstrated based on an amorphous InGaZnO (α-IGZO) memristor; several essential synaptic functions are simultaneously achieved in such a single device, including nonlinear transmission characteristics, spike-rate-dependent and spike-timing-dependent plasticity, long-term/short-term plasticity (LSP and STP) and “learning-experience” behavior. These characteristics bear striking resemblances to certain learning and memory functions of biological systems. Especially, a “learning-experience” function is obtained for the first time, which is thought to be related to the metastable local structures in α-IGZO. These functions are interrelated: frequent stimulation can cause an enhancement of LTP, both spike-rate-dependent and spike-timing-dependent plasticity is the same on this point; and, the STP-to-LTP transition can occur through repeated “stimulation” training. The physical mechanism of device operation, which does not strictly follow the memristor model, is attributed to oxygen ion migration/diffusion. A correlation between short-term memory and ion diffusion is established by studying the temperature dependence of the relaxation processes of STP and ion diffusion. The realization of important synaptic functions and the establishment of a dynamic model would promote more accurate modeling of the synapse for artificial neural network.

Memristors: Synaptic Learning and Memory Functions Achieved Using Oxygen Ion Migration/Diffusion in an Amorphous InGaZnO Memristor (Adv. Funct. Mater. 13/2012)

Co-reporter:Zhong Qiang Wang;Hai Yang Xu;Xing Hua Li;Hao Yu;Yi Chun Liu;Xiao Juan Zhu

Advanced Functional Materials 2012 Volume 22( Issue 13) pp:

Publication Date(Web):

DOI:10.1002/adfm.201290076

MgZnO/MgO strained multiple-quantum-well nanocolumnar films: Stress-induced structural transition and deep ultraviolet emission

Co-reporter:L. Wang, H.Y. Xu, C. Zhang, X.H. Li, Y.C. Liu, X.T. Zhang, Y. Tao, Y. Huang, D.L. Chen

Journal of Alloys and Compounds 2012 Volume 513() pp:399-403

Publication Date(Web):5 February 2012

DOI:10.1016/j.jallcom.2011.10.056

MgZnO/MgO strained multiple-quantum-wells (S-MQWs) with different structures are grown by pulsed laser deposition. The S-MQW films are composed of closely arranged, vertically oriented nanocolumns. Z-contrast scanning transmission electron microscopy observations and line-scan compositional analysis reveal that the nanocolumns are compositionally modulated along their length and have a MQW structure. A coherent epitaxial relationship with a sharp interface is established between MgZnO and MgO layers with large lattice mismatch. It is worth noting that the MgZnO layer undergoes a structural transition from hexagonal to cubic phase with its thickness decreasing. The calculations reveal that a large in-plane compressive stress dominates such an interesting phase transition process, stabilizes the low Mg-content MgZnO alloy in the anomalous cubic phase, and also leads to a broadening of the band gap. As a result, the wavelength-tunable deep-ultraviolet emission in the range of 261–314 nm is obtained from these S-MQW nanocolumnar films. The 261 nm is known to be the shortest emission wavelength ever reported for MgZnO material.Highlights► MgZnO/MgO strained multiple-quantum-wells nanocolumnar films are achieved. ► A epitaxial relationship with high-quality interface is established between MgZnO and MgO layers with large lattice mismatch. ► Stress-induced structural transition of MgZnO layers is observed. ► The wavelength-tunable deep-ultraviolet emission is obtained, and the 261 nm is known to be the shortest emission wavelength ever reported for MgZnO material.

Up-Conversion Luminescence of NaYF4:Yb3+/Er3+ Nanoparticles Embedded into PVP Nanotubes with Controllable Diameters

Co-reporter:Peng Zou, Xia Hong, Yadan Ding, Zhenyi Zhang, Xueying Chu, Talgar Shaymurat, Changlu Shao, and Yichun Liu

The Journal of Physical Chemistry C 2012 Volume 116(Issue 9) pp:5787-5791

Publication Date(Web):February 9, 2012

DOI:10.1021/jp2114863

NaYF4:Yb3+/Er3+/polyvinylpyrrolidone (PVP) up-conversion (UC) luminescent nanotubes were synthesized by the electrospinning technique. The diameters of the nanotubes were controllable by changing the electrospinning voltages. The structure and the optical properties were studied by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), photoluminescence (PL) spectra, and fluorescence microscope. The NaYF4:Yb3+/Er3+/PVP nanocomposites simultaneously possessed UC luminescent property, active surfaces and tubular structure. PVP molecules were found to have an important influence on the UC luminescence of NaYF4:Yb3+/Er3+/PVP nanotubes. Compared with those in pure NaYF4:Yb3+/Er3+ nanoparticles, the relative intensities of violet, blue, and green to red emissions were increased in NaYF4:Yb3+/Er3+/PVP nanotubes. It is owing to the existence of PVP molecules, which might produce the passivation on NaYF4:Yb3+/Er3+ nanoparticles and reduce the nonradiative relaxation of Er3+ ion. The luminescent nanotubes with desirable UC properties are expected to be applied in biomedicine.

Superhydrophobic and Ultraviolet-Blocking Cotton Textiles

Co-reporter:Lingling Wang, Xintong Zhang, Bing Li, Panpan Sun, Jikai Yang, Haiyang Xu, and Yichun Liu

ACS Applied Materials & Interfaces 2011 Volume 3(Issue 4) pp:1277

Publication Date(Web):March 20, 2011

DOI:10.1021/am200083z

Cotton textile was coated with ZnO@SiO2 nanorods in order to obtain superhydrophobic and ultraviolet (UV)-blocking properties. The coating process was conducted in mild conditions, which involved the low-temperature preparation of ZnO seeds, hydrothermal growth of ZnO nanorods, bioinspired layer-by-layer deposition of a SiO2 shell on the surface of ZnO nanorods, and hydrophobic modification of ZnO@SiO2 nanorods with octadecyltrimethoxysilane. Despite the highly curved morphology of cotton fibers, the ZnO@SiO2 nanorods coated the textile densely and uniformly. The treated cotton textile was found to have a large UV protection factor (UPF = 101.51) together with UV-durable superhydrophobicity, as determined by contact-angle measurement under long-term UV irradiation. The good UV-blocking property can be ascribed to the high UV absorbance and scattering properties of ZnO nanorods, and the UV-durable superhydrophobicity is a result of suppression of the photoactivity of ZnO nanorods by a SiO2 shell.Keywords: cotton textile; superhydrophobicity; surface modification; ultraviolet blocking; ZnO@SiO2 core−shell nanorod

Rutile TiO2 nanowires on anatase TiO2 nanofibers: A branched heterostructured photocatalysts via interface-assisted fabrication approach

Co-reporter:Changhua Wang, Xintong Zhang, Changlu Shao, Yanli Zhang, Jikai Yang, Panpan Sun, Xueping Liu, Hong Liu, Yichun Liu, Tengfeng Xie, Dejun Wang

Journal of Colloid and Interface Science 2011 Volume 363(Issue 1) pp:157-164

Publication Date(Web):1 November 2011

DOI:10.1016/j.jcis.2011.07.035

A water–dichloromethane interface-assisted hydrothermal method was employed to grow rutile TiO2 nanowires (NWs) on electrospun anatase TiO2 nanofibers (NFs), using highly reactive TiCl4 as precursor. The water–dichloromethane interface inhibited the formation of rutile NWs in water phase, but promoted the selective radial growth of densely packed rutile NWs on anatase NFs to form a branched heterojunction. The density and length of rutile NWs could be readily controlled by varying reaction parameters. A formation mechanism for the branched heterojunction was proposed which involved (1) the entrapment of rutile precursor nanoparticles at water–dichloromethane interface, (2) the growth of rutile NWs on anatase NFs via Ostwald ripening through the scavengering of interface-entrapped rutile nanoparticles. The heterojunction formed at anatase NF and rutile NW enhanced the charge separation of both under ultraviolet excitation, as evidenced by photoluminescence and surface photovoltage spectra. The branched TiO2 heterostructures showed higher photocatalytic activity in degradation of rodamine B dye solution than anatase NFs, and the mixture of anatase NFs, and P25 powders, which was discussed in terms of the synergistic effect of enhanced charge separation by anatase–rutile heterojunction, high activity of rutile NWs, and increased specific area of branched heterostructures.Graphical abstractA water–oil interface assisted fabrication approach was employed to fabricate rutile TiO2 nanowires-anatase TiO2 nanofibers heterostructures. The as-fabricated branched heterostructures display higher photocatalytic activities than pure TiO2 nanofibers as well as P25 powders.Highlights► We employ water–oil interface assisted hydrothermal technique to TiO2 based heterostructure fabrication. ► The as-fabricated heterostructure displayed interesting branched morphology. ► The branched heterostructure showed higher photocatalytic activity than pristine TiO2 nanofibers and P25 powders.

Red-emitting LiEuMo2−xSixO8 phosphors for white light-emitting diodes

Co-reporter:Pengpeng Dai, Xintong Zhang, Xinghua Li, Guorui Wang, Chengjiu Zhao, Yichun Liu

Journal of Luminescence 2011 Volume 131(Issue 4) pp:653-656

Publication Date(Web):April 2011

DOI:10.1016/j.jlumin.2010.11.010

Si4+ was introduced to the lattice of LiEuMo2O8 by solid-state reaction to prepare a new kind of red-emitting LiEuMo2−xSixO8 (0

Hydrothermal Growth of Layered Titanate Nanosheet Arrays on Titanium Foil and Their Topotactic Transformation to Heterostructured TiO2 Photocatalysts

Co-reporter:Changhua Wang ; Xintong Zhang ; Yanli Zhang ; Yan Jia ; Jikai Yang ; Panpan Sun

The Journal of Physical Chemistry C 2011 Volume 115(Issue 45) pp:22276-22285

Publication Date(Web):October 17, 2011

DOI:10.1021/jp2093719

Layered titanate nanostructures have been recognized as an important intermediate in preparing TiO2 nanostructures due to their availability in various morphologies, among which ultrathin nanosheets have attracted particular attention due to their unique properties arising from their high surface area and confined thickness in nanoscale. Herein, we report a simple approach to fabricate heterostructured TiO2 nanosheet array film by (1) hydrothermal growth of sodium trititanate nanosheet array on Ti foil in alkaline solution, (2) ion exchange of Na+ in titanate naosheet with H+, and (3) topotactical transformation into TiO2 nanosheet via thermal annealing. XRD and Raman as well as HRTEM analyses proved the formation of a novel anatase/TiO2(B) heterostructured nanosheet array with coherent interface between the two phases, which exhibited superior photocatalytic efficiency under UV illumination as compared with the relevant commercial products P25 and anode oxidized TiO2 nanotube film of the same thickness but with greater mass of photocatalyst. The high photocatalytic activity of the TiO2 nanosheet array film can be ascribed to the synergistic effect of large surface area and high crystallinity as well as heterojunction between TiO2(B) and anatase phase.

Heteroepitaxial Growth and Spatially Resolved Cathodoluminescence of ZnO/MgZnO Coaxial Nanorod Arrays

Co-reporter:Weizhen Liu ; Yao Liang ; Haiyang Xu ; Lingling Wang ; Xintong Zhang ; Yichun Liu ;Suikong Hark

The Journal of Physical Chemistry C 2010 Volume 114(Issue 39) pp:16148-16152

Publication Date(Web):September 15, 2010

DOI:10.1021/jp102395t

Vertically aligned, single-crystalline ZnO/MgZnO coaxial nanorod arrays were epitaxially grown on GaN substrates by hydrothermal synthesis combined with pulsed laser deposition. Well-defined core/shell heterostructures with high-quality interfaces and coherent epitaxial relationship were confirmed by Z-contrast scanning transmission electron microscopy and line-scan compositional analyses. It is interesting to note that the MgZnO shell thickness gradually decreases from the tip to the base of the nanorods, due to a shadow effect during the deposition. The nonuniform coating allows us to study the carrier confinement and surface passivation effects on a single nanorod. Spatially resolved cathodoluminescence measurements reveal that the band-edge emission intensity of ZnO cores is variable along their length, and depends strongly on the shell thickness. A model, which involves carrier tunneling, surface trapping, and radiative/nonradiative recombination processes, was developed to understand this phenomenon. However, a high-temperature thermal treatment may lead to the stress relaxation and the formation of interfacial defects, and enhance the interdiffusion of interfacial atoms. These degrade the optical quality of coaxial nanorods.

Water−Dichloromethane Interface Controlled Synthesis of Hierarchical Rutile TiO2 Superstructures and Their Photocatalytic Properties

Co-reporter:Changhua Wang ; Changlu Shao ; Yichun Liu ;Xinghua Li

Inorganic Chemistry 2009 Volume 48(Issue 3) pp:1105-1113

Publication Date(Web):January 7, 2009

DOI:10.1021/ic8018138

A water−dichloromethane interface is used for synthesis and assembly of rutile TiO2 nanorods. By hydrothermal treatment of a dichloromethane solution of TiCl4 at the interface of water−dichloromethane, turning to no surfactant or template, hierarchical rutile TiO2 superstructures are developed. By tuning the molar ratio of reactants rw (H2O/TiCl4), the size and shape of the samples significantly change. At a low value of rw, highly extended, robust, porous, and thick titania film with ordered rutile nanorod bundles are deposited at the interface. At a high value of rw, powders consisting of hierarchical rutile nanorod spheres together with disordered nanorods are obtained. A rational formation mechanism is proposed on the basis of a range of experiments. The main factors influencing the morphologies of the samples may be attributed to the acidity of the reaction system and the adsorption ability of the precursor nanoparticles to the water−dichloromethane interface. The as-obtained rutile TiO2 hierarchical superstructures show higher photocatalytic property to decompose methylene blue (MB) dye compared with that of commercial P25, which can be ascribed to the contribution of high surface area and high crystallinity. Other applications, such as solar energy conversion, environmental remediation, and advanced optical/electric nanodevices may also benefit from the unique properties of the hierarchically rutile TiO2 superstructures.

SnO2 Nanostructures-TiO2 Nanofibers Heterostructures: Controlled Fabrication and High Photocatalytic Properties

Co-reporter:Changhua Wang, Changlu Shao, Xintong Zhang and Yichun Liu

Inorganic Chemistry 2009 Volume 48(Issue 15) pp:7261-7268

Publication Date(Web):July 9, 2009

DOI:10.1021/ic9005983

Combining the versatility of the electrospinning technique and hydrothermal growth of nanostructures enabled the fabrication of hierarchical SnO2/TiO2 composite nanostructures. The results revealed that not only were secondary SnO2 nanostructures successfully grown on primary TiO2 nanofiber substrates but also the SnO2 nanostructures were uniformly distributed without aggregation on TiO2 nanofibers. By adjusting fabrication parameters, the morphology as well as coverage density of secondary SnO2 nanostructures could be further controlled, and then SnO2/TiO2 heterostructures with SnO2 nanoparticles or nanorods were facilely fabricated. The photocatalytic studies suggested that the SnO2/TiO2 heterostructures showed enhanced photocatalytic efficiency of photodegradation of Rhodamine B (RB) compared with the bare TiO2 nanofibers under UV light irradiation.

Electrospinning preparation, characterization and photocatalytic properties of Bi2O3 nanofibers

Co-reporter:Changhua Wang, Changlu Shao, Lianjia Wang, Lina Zhang, Xinghua Li, Yichun Liu

Journal of Colloid and Interface Science 2009 Volume 333(Issue 1) pp:242-248

Publication Date(Web):1 May 2009

DOI:10.1016/j.jcis.2008.12.077

Bi2O3 nanofibers with diameter of 70–200 nm were successfully prepared by electrospinning a precursor mixture of polyacrylonitrile (PAN)/bismuth nitrate, followed by calcination treatment of the electrospun polymer/inorganic composite fibers. The resulting Bi2O3 nanofibers were characterized with X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, FT-IR spectra and UV–vis diffuse reflectance spectroscopy. The Bi2O3 nanofibers calcined at 500 °C exhibited β phase, and whereas the nanofibers calcined at 550 and 600 °C both exhibited dominant β phase together with a trace amount of α phase. Photocatalytic experiments indicated that the obtained Bi2O3 nanofibers calcined at 500 °C were highly active for photodegradation of organic pollutants Rhodamine B (RB). Furthermore, the Bi2O3 nanofibers could be easily recycled without decrease of the photocatalytic activity.The Bi2O3 nanofibers with diameters of 70–200 nm are fabricated by electrospinning. The Bi2O3 nanofibers calcined at 500 °C possess high photocatalytic properties and can be conveniently fixed and reclaimed.

Hexamethylenediamine-assisted hydrothermal preparation of uniform ZnO particles and their morphology-dependent photoluminescent properties

Co-reporter:Lingling Wang, Xintong Zhang, Changlu Shao, Xia Hong, Qian Qiao, Yichun Liu

Materials Chemistry and Physics 2009 Volume 115(2–3) pp:547-550

Publication Date(Web):15 June 2009

DOI:10.1016/j.matchemphys.2008.12.002

Uniform ZnO particles with ellipsoidal, needle-like and branched morphologies were prepared by a hexamethylenediamine (HMDA)-assisted hydrothermal method. The morphology of ZnO particles was simply controlled by the molar ratio of zinc nitrate to HMDA, that is, ellipsoidal particles were prepared at a [Zn2+]/[HMDA] ratio larger than 0.5, needle-like particles were prepared at a ratio of 0.1, and branched particles were prepared at a ratio of 0.02. These ZnO particles were all of well-crystallized wurtzite structure despite of their different morphologies. However, they showed interesting morphology-dependent photoluminescent properties, with the branched particles showing the most intense near-band edge ultraviolet photoluminescence (PL) and the greatest ratio of ultraviolet (UV) to visible (Vis) photoluminescence. These phenomena were discussed by considering the role of the HMDA in the growth process of ZnO particles.

Bioinspired Preparation of Ultrathin SiO2 Shell on ZnO Nanowire Array for Ultraviolet-Durable Superhydrophobicity

Co-reporter:Lingling Wang, Xintong Zhang, Yang Fu, Bing Li and Yichun Liu

Langmuir 2009 Volume 25(Issue 23) pp:13619-13624

Publication Date(Web):July 16, 2009

DOI:10.1021/la901998p

ZnO nanowire (NW) array was conformally coated with an ultrathin SiO2 shell by a bioinspired layer-by-layer deposition in order to obtain ultraviolet (UV)-durable superhydrophobic property. Uniform SiO2 shell was prepared on ZnO NW by alternative reactive deposition of polyethylenimine and silicic acid. Despite the highly curved morphology of ZnO NW array, the thickness of SiO2 shell increased linearly with the number of deposition cycles, with a thickness increment being of ∼4.17 nm per deposition cycle. The SiO2 shell only had a slight influence on the superhydrophobic property of ZnO NW array after modification with a monolayer of octadecyltrimethoxysilane (OTS). However, it greatly improved the UV durability of the superhydrophobic property of ZnO NW array due to the confinement effect of insulating SiO2 layer on the photogenerated electron−hole pairs in ZnO NW.

Size-Controlled Synthesis and Optical Properties of Small-Sized ZnO Nanorods

Co-reporter:Y.W. Chen, Q. Qiao, Y.C. Liu and G.L. Yang

The Journal of Physical Chemistry C 2009 Volume 113(Issue 18) pp:7497-7502

Publication Date(Web):April 9, 2009

DOI:10.1021/jp809778w

One-dimensional ZnO nanorods with very small diameters in the range of 10 ± 2 nm were fabricated by facile sol−gel and hydrothermal methods. The structural, morphologic and optical properties of ZnO nanorods were investigated using X-ray diffraction, electron microscopy, and photoluminescence (PL). A strong ultraviolet (UV) near-band-edge emission peak at 373 nm (3.32 eV) was observed, while the deep-level emission band was too weak to observe at room temperature. The UV emission peak has an obvious blue shift compared to the samples with a larger size, which was attributed to the size-decreased nanorods. The large ratio of the UV emission to visible emissions in PL spectra can be obtained in small-sized ZnO nanorods. Furthermore, the morphologic and optical properties of ZnO nanorods can be adjusted by controlling the reactant concentration and reaction time. The possible growth mechanism of the nanorods is proposed.

Heterostructured ZnO/Au Nanoparticles-Based Resonant Raman Scattering for Protein Detection

Co-reporter:Guiye Shan, Shuang Wang, Xiaofang Fei, Yichun Liu and Guoliang Yang

The Journal of Physical Chemistry B 2009 Volume 113(Issue 5) pp:1468-1472

Publication Date(Web):January 12, 2009

DOI:10.1021/jp8046032

A new method of protein detection was explored on the resonant Raman scattering signal of ZnO nanoparticles. A probe for the target protein was constructed by binding the ZnO/Au nanoparticles to secondary protein by eletrostatic interaction. The detection of proteins was achieved by an antibody-based sandwich assay. A first antibody, which could be specifically recognized by target protein, was attached to a solid silicon surface. The ZnO/Au protein probe could specifically recognize and bind to the complex of the target protein and first antibody. This method on the resonant Raman scattering signal of ZnO nanoparticles showed good selectivity and sensitivity for the target protein.

The synthesis and optical properties of the heterostructured ZnO/Au nanocomposites

Co-reporter:Guiye Shan, Mingya Zhong, Shuang Wang, Yajun Li, Yichun Liu

Journal of Colloid and Interface Science 2008 Volume 326(Issue 2) pp:392-395

Publication Date(Web):15 October 2008

DOI:10.1016/j.jcis.2008.06.027

ZnO/Au heterostructured nanoparticles were formed through epitaxial growth of Au on the ZnO seeds. The morphology and structure of ZnO/Au nanocomposites were investigated by TEM and XRD analysis. The nanocontact between Au and ZnO results in red-shift of surface plasmon of the Au and increase the intensity of Raman signals of ZnO. Heterostructured ZnO/Au nanocomposites also enhance chemical stability of ZnO in aqueous solution.HRTEM image shows that single ZnO nanoparticle has been connected with Au nanoparticle. The resonant Raman scattering spectra of ZnO/Au nanocomposites with increasing the amount of Au were changed. The enhancement is predominant for the first-order LO phonon mode of ZnO. The enhancement of surface optical phonons in RRS experiments can be rationalized by the fact that surface optical phonons execute vibrational motion only within a few atomic layers near the surface, and the Raman scattering volume of this mode can entirely be subjected to the electromagnetic interaction with the Au surface plasmon.

Photocatalytic properties BiOCl and Bi2O3 nanofibers prepared by electrospinning

Co-reporter:Changhua Wang, Changlu Shao, Yichun Liu, Lina Zhang

Scripta Materialia 2008 Volume 59(Issue 3) pp:332-335

Publication Date(Web):August 2008

DOI:10.1016/j.scriptamat.2008.03.038

A simple electrospinning method was used to fabricate polymer/inorganic composite fibers from solutions containing polyacrylonitrile (PAN) and BiCl3, and PAN and Bi(NO3)3, respectively. By performing a calcining process for the composite fibers at 500 °C for 10 h, BiOCl and Bi2O3 nanofibers were successfully prepared. The as-prepared BiOCl and Bi2O3 nanofibers exhibit tetragonal and β phase, respectively. The photocatalytic test shows that BiOCl and Bi2O3 nanofibers possess photocatalytic properties with regard to decomposing rhodamine B under ultraviolet light.

Preparation, structure and photoluminescence properties of SiO2/ZnO nanocables via electrospinning and vapor transport deposition

Co-reporter:X.H. Li, C.L. Shao, Y.C. Liu, X.T. Zhang, S.K. Hark

Materials Letters 2008 Volume 62(Issue 14) pp:2088-2091

Publication Date(Web):15 May 2008

DOI:10.1016/j.matlet.2007.11.021

SiO2/ZnO nanocables were prepared by the combination of electrospinning technology and vapor transport deposition procedure. X-ray diffraction patterns indicated that ZnO with wurtzite structure was deposited on SiO2 nanofibers templates successfully. Field emission scanning electron microscopy and transmission electron microscopy showed that the products were core/shell nanocables with a narrow distribution of the core/shell diameters. The nanocables showed a strong near band edge emission in ultraviolet region and a weak deep level emission at room temperature in their photoluminescence (PL) spectra. The anomalous temperature characteristic of integrated PL intensity in temperature-dependent PL spectra was discussed by considering carrier injection across the interface of SiO2/ZnO nanocables.

Heterostructures of ZnO Microrods Coated with Iron Oxide Nanoparticles

Co-reporter:X. Y. Chu, X. Hong, X. T. Zhang, P. Zou and Y. C. Liu

The Journal of Physical Chemistry C 2008 Volume 112(Issue 41) pp:15980-15984

Publication Date(Web):2017-2-22

DOI:10.1021/jp804590y

Heterostructured composites of ZnO/Fe3O4 and ZnO/Fe2O3 were respectively prepared by depositing magnetic nanoparticles on ZnO microrod templates through low-temperature hydrothermal procedures. The formation of the heterostructures was evidenced by high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and Raman scattering analysis. Hexamethylenetetramine, a pH adjustor, was found to have important influence on the crystal phase of iron oxide in the heterostructured composites and greatly influenced the properties of the heterostructured composites. The heterostructured composites simultaneously possessed the magnetic properties of iron oxides and the optical properties of ZnO.

Biocompatible ZnO/Au Nanocomposites for Ultrasensitive DNA Detection Using Resonance Raman Scattering

Co-reporter:Yichun Liu, Mingya Zhong, Guiye Shan, Yajun Li, Baiqu Huang and Guoliang Yang

The Journal of Physical Chemistry B 2008 Volume 112(Issue 20) pp:6484-6489

Publication Date(Web):April 30, 2008

DOI:10.1021/jp710399d

A novel method for identifying DNA microarrays based on ZnO/Au nanocomposites functionalized with thiol-oligonucleotide as probes is descried here. DNA labeled with ZnO/Au nanocomposites has a strong Raman signal even without silver acting as a surface-enhanced Raman scattering promoter. X-ray photoelectron spectra confirmed the formation of a three-component sandwich assay, i.e., constituted DNA and ZnO/Au nanocomposites. The resonance multiple-phonon Raman signal of the ZnO/Au nanocomposites as a spectroscopic fingerprint is used to detect a target sequence of oligonucleotide. This method exhibits extraordinary sensitivity and the detection limit is at least 1 fM.

Growth and optical properties of ZnO nanostructures by vapor transport process

Co-reporter:Y.H. Tong, Y.C. Liu, L. Dong, L.X. Lu, D.X. Zhao, J.Y. Zhang, Y.M. Lu, D.Z. Shen, X.W. Fan

Materials Chemistry and Physics 2007 Volume 103(Issue 1) pp:190-194

Publication Date(Web):15 May 2007

DOI:10.1016/j.matchemphys.2007.02.015

ZnO nanorods and ZnO nanotubes have been fabricated by thermally evaporating the metal Zn powder. The ZnO nanorod obtained on the ITO substrate located above the Zn source has the uneven diameter with the abrupt change in its middle, which may originate from the decrease of the Zn vapor in the system. The ZnO nanotubes with the rough surfaces were obtained in the upstream region. The negative thermal quenching of the photoluminescence can be observed in the ZnO nanotubes. This is related with the abundant surface/interface defects which can introduce a large number of middle states in the band gap. According to Shibata's model, the activation energy of the electrons from the middle states to the initial states can be obtained by fitting the experimental data of the temperature dependence of the ultraviolet photoluminescence intensity. The fitting energy values are as high as ∼100 meV, which may be responsible for the negative thermal quenching in a high-temperature range from 163.5 to 205.6 K.

Intense luminescence of amorphous Eu2O3 prepared by aqueous sol–gel method

Co-reporter:S.X. Lu, Y.C. Liu

Journal of Non-Crystalline Solids 2007 Volume 353(11–12) pp:1037-1040

Publication Date(Web):1 May 2007

DOI:10.1016/j.jnoncrysol.2007.01.015

Amorphous Eu2O3 was prepared by an aqueous sol–gel method. Emission due to the 5D0 → 7FJ (J = 0, 1, 2) transitions of Eu3+ ions were observed. The dominant transition was the 5D0 → 7F2 red emission of Eu3+. The properties of the as-prepared samples were different with changes in the annealing temperature. To investigate the luminescence properties of the amorphous Eu2O3, the temperature-dependent photoluminescence (PL) spectra of samples annealed at 600 °C were measured in the temperature range 77–300 K. PL peak positions were unchanged with the change of temperature.

Synthesis and luminescence properties of Eu3+-doped ZnO nanocrystals by a hydrothermal process

Co-reporter:Mingya Zhong, Guiye Shan, Yajun Li, Guorui Wang, Yichun Liu

Materials Chemistry and Physics 2007 Volume 106(2–3) pp:305-309

Publication Date(Web):15 December 2007

DOI:10.1016/j.matchemphys.2007.06.007

Trivalent europium ions doped zinc oxide (ZnO:Eu3+) nanocrystals were prepared by a hydrothermal process. The obtained samples were characterized using X-ray diffraction (XRD) and photoluminescence (PL) spectra. The XRD patterns indicate that Eu3+ ions are successfully doped into the crystal lattice of ZnO matrix. The ZnO:Eu3+ nanocrystals exhibit a sharp red luminescence emission, which is from the intra-4f transitions of Eu3+ ions. The 5D0–7F2 emission comes from an allowed electric-dipole transition and its intensity is the strongest. This implies that Eu3+ ions are mainly in a large transition probability in the crystal field with inversion antisymmetry. The PL peaks of Eu3+ ions can be observed even under the nonresonant excitation of 325 nm. It is explained by an energy transfer mechanism in which the energy is transferred from the defect state of ZnO matrix to Eu3+ ions in ZnO:Eu3+ nanocrystals.

Growth and optical properties of ZnO nanorods by introducing ZnO sols prior to hydrothermal process

Co-reporter:Yanhong Tong, Lin Dong, Yichun Liu, Dongxu Zhao, Jiying Zhang, Youming Lu, Dezhen Shen, Xiwu Fan

Materials Letters 2007 Volume 61(Issue 17) pp:3578-3581

Publication Date(Web):July 2007

DOI:10.1016/j.matlet.2006.11.125

ZnO nanorods of 25 nm with quite homogeneous size and shape have been fabricated by introducing ZnO sols as nucleation centers prior to the hydrothermal reaction. The samples were characterized by scanning electron microscope, transmission electron microscope, X-ray diffraction, photoluminescence and resonant Raman spectra. After ZnO sols are introduced, the width of the resulting nanorods decreases above an order of magnitude and the aspect ratio increases 5 times. The increase of the intensity ratio of ultraviolet to visible emissions in room-temperature photoluminescence spectrum and the decrease of the Raman linewidths show the improvement in the quality of ZnO nanorods. Influences of the number of seed nuclei and the aging time of ZnO sols on the morphology of ZnO nanorods are discussed.

Structural and photoluminescent properties of ZnO hexagonal nanoprisms synthesized by microemulsion with polyvinyl pyrrolidone served as surfactant and passivant

Co-reporter:Xiaomeng Sui, Yichun Liu, Changlu Shao, Yuxue Liu, Changshan Xu

Chemical Physics Letters 2006 Volume 424(4–6) pp:340-344

Publication Date(Web):24 June 2006

DOI:10.1016/j.cplett.2006.04.053

ZnO hexagonal prisms have been successfully synthesized in large scale by microemulsion method with polyvinyl pyrrolidone (PVP) used as surfactant to form the template for the growth of ZnO and passivant for the modification of ZnO prisms surface, simultaneously. The as-prepared prisms show high crystal quality and Raman spectra indicate that the ZnO prisms are in wurtzite phase. In the presence of adsorbed PVP, the ZnO hexagonal prisms show an intensive near-band-edge emission. Our protocol provides an effective method to synthesize ZnO nanomaterials with perfect morphology, pure crystal quality and intensive UV emission.ZnO hexagonal prisms was synthesized in large scale by microemulsion ethod with polyvinyl pyrrolidone (PVP) served as surfactant and passivant. The as-prepared ZnO hexagonal prisms exhibit perfect morphology and high crystal quality. The PVP-assisted ZnO prisms show enhanced near-band-edge UV emission and reduced defect-relate gree emission

Structural and Optical Properties of Uniform ZnO Nanosheets

Co-reporter:S. J. Chen;Y. C. Liu;C. L. Shao;R. Mu;Y. M. Lu;J. Y. Zhang;D. Z. Shen;X. W. Fan

Advanced Materials 2005 Volume 17(Issue 5) pp:

Publication Date(Web):3 MAR 2005

DOI:10.1002/adma.200401263

ZnO nanosheets (see Figure) are fabricated by a physical vapor-transport technique. Temperature-dependent microphotoluminescence spectroscopy is conducted from 80–857 K. A surprisingly strong high-temperature (857 K) photon emission is observed. A brief discussion is given in an attempt to understand the physical mechanisms. Technically, this finding demonstrates that the ZnO nanostructure has a potential for high-temperature optoelectronic applications.

The effect of surface properties on visible luminescence of nanosized colloidal ZnO membranes

Co-reporter:Z.Y. Xiao, Y.C. Liu, L. Dong, C.L. Shao, J.Y. Zhang, Y.M. Lu, D.Z. Zhen, X.W. Fan

Journal of Colloid and Interface Science 2005 Volume 282(Issue 2) pp:403-407

Publication Date(Web):15 February 2005

DOI:10.1016/j.jcis.2004.08.111

Luminescence properties of nanosized zinc oxide (ZnO) colloids depend greatly on their surface properties, which are in turn largely determined by the method of preparation. ZnO nanoparticles in the size range from 3 to 9 nm were prepared by addition of tetramethylammonium hydroxide ((CH3)4NOH) to an ethanolic zinc acetate solution. X-ray diffraction (XRD) indicates nanocrystalline ZnO membranes with polycrystalline hexagonal wurtzite structure. The ZnO membranes have a strong visible-emission intensity and the intensity depends upon hydrolysis time. The infrared spectra imply a variety of forms of zinc acetate complexes present on the surface of ZnO particles. The effect of the ZnO membrane surface properties on photoluminescence is discussed.

Preparation of ZnO colloids by aggregation of the nanocrystal subunits

Co-reporter:L. Dong, Y.C. Liu, Y.H. Tong, Z.Y. Xiao, J.Y. Zhang, Y.M. Lu, D.Z. Shen, X.W. Fan

Journal of Colloid and Interface Science 2005 Volume 283(Issue 2) pp:380-384

Publication Date(Web):15 March 2005

DOI:10.1016/j.jcis.2004.09.044

Colloidal ZnO particles with narrow size distribution were prepared via a sol–gel process by base-catalyzed hydrolysis of zinc acetate. The morphology of ordered arrays of the particles was recorded by SEM. SEM also reveals that these uniform particles were composed of tiny ZnO subunits (singlets) sized of several nanometers. The size of the singlets, which is confirmed by X-ray diffraction and UV–vis absorption spectra, increases as the aging time is prolonged. The size-selective formation of colloids by aggregation of nanosized subunits is proposed to consist of two-stage growth by nucleation of nanosized crystalline primary particles and their subsequent aggregation into polycrystalline secondary colloids. The aggregates are all spherical because the internal rearrangement processes are fast enough. The ZnO colloids, i.e., the aggregates, tend to self-assemble into well-ordered hexagonal close-packed structures. Room-temperature photoluminescence was characterized for green and aged ZnO.

Effects of thermal annealing on the structural and optical properties of MgxZn1−xO nanocrystals

Co-reporter:J.H. Li, Y.C. Liu, C.L. Shao, X.T. Zhang, D.Z. Shen, Y.M. Lu, J.Y. Zhang, X.W. Fan

Journal of Colloid and Interface Science 2005 Volume 283(Issue 2) pp:513-517

Publication Date(Web):15 March 2005

DOI:10.1016/j.jcis.2004.09.011

MgxZn1−xO ternary alloy nanocrystals with hexagonal wurtzite structures were fabricated by using the sol–gel method. X-ray diffraction patterns, UV–vis absorption spectra, and photoluminescence spectra were used to characterize the structural and optical properties of the nanocrystals. For as-prepared nanocrystals, the band gap increases with increasing Mg content. Weak excitonic emission with strong deep-level emission related to oxygen vacancy and interface defects is observed in the photoluminescence spectra at room temperature. Thermal annealing in oxygen was used to decrease the number of defects and to improve the quality of the nanocrystals. In terms of XRD results, the grain sizes of nanocrystals increase with increasing annealing temperature and the lattice constants of alloy are smaller than those of pure ZnO. The band gap becomes narrower with increasing annealing temperature. For MgxZn1−xO nanocrystals (x=0.03–0.15x=0.03–0.15) annealed at temperatures ranging from 500 to 1000 °C, intense near-band-edge (NBE) emissions and weak deep-level (DL) emissions are observed. Consequently, the quality of MgxZn1−xO nanocrystals can be improved by thermal annealing.

Real-time holographic gratings recorded by He–Ne laser in polymer films containing spirooxazine compounds pre-irradiated by UV light

Co-reporter:Shencheng Fu, Yichun Liu, Zifeng Lu, Lin Dong, Weilin Hu, Minggui Xie

Optical Materials 2005 Volume 27(Issue 10) pp:1567-1570

Publication Date(Web):September 2005

DOI:10.1016/j.optmat.2004.10.012

Real-time holographic gratings were optically recorded with a pair of interferential He–Ne laser beams (632.8 nm) in poly(methylmethacrylate) (PMMA) film containing 6′-piperidino-1,3,3-trimethylspiro[indolino-2,3′-[3H]naphtha-[2,1-b][1,4]oxazine] (SO-1) pre-irradiated by ultraviolet light. The transformation from SO-1 to photomerocyanine (PMC) was studied in detail. PMC was observed in two forms. The holographic characteristics of the recorded gratings were dependent on the polarization direction of the recording beams. Reversible holograms were recorded in the medium by modulating UV light.

The structure and character of CdSe nanocrystals capped ZnO layer for phase transfer from hexane to ethanol solution

Co-reporter:Guiye Shan, Xianggui Kong, Xin Wang, Yichun Liu

Surface Science 2005 Volume 582(1–3) pp:61-68

Publication Date(Web):10 May 2005

DOI:10.1016/j.susc.2005.02.055

A new method for the preparation of CdSe/ZnO core–shell structure nanoparticles is described, where as-prepared CdSe nanocrystals in hexane were mixed with zinc acetate ethanol solution under ultrasonic. UV–visible absorption spectra, photoluminescence spectra and X-ray diffraction spectra were used to analyze the change of surface and structure of CdSe/ZnO core–shell nanocrystals by comparing with bare CdSe nanocrystals. The transmission electron microscopic images of CdSe/ZnO core–shell nanocrystals show that CdSe capped by ZnO is spherical or rod shape. The mechanism of the formation of CdSe/ZnO core–shell nanocrystals was discussed. During ZnO capping CdSe, the ligands of ZnO grown on the surface of CdSe nanocrystals provide a bridge for the CdSe nanocrystals transfer from hexane solution to ethanol solution. This experiment presents a simple, effective synthetic route for phase transfer of CdSe nanocrystals.

The structure and optical properties of AlN nanocrystals prepared by Schlenk techniques at atmospheric pressure and low temperature

Co-reporter:S.X. Lu, Y.H. Tong, Y.C. Liu, C.S. Xu, Y.M. Lu, J.Y. Zhang, D.Z. Shen, X.W. Fan

Journal of Physics and Chemistry of Solids 2005 Volume 66(Issue 10) pp:1609-1613

Publication Date(Web):October 2005

DOI:10.1016/j.jpcs.2005.06.007

AlN nanocrystals were prepared in organic solvent at atmospheric pressure and low temperature by the Schlenk technique. Both hexagonal and cubic AlN nanocrystals were obtained. The hexagonal nano-AlN powder possessed a wurtzite structure with a=3.124 Å, c=5.024 Å, the average grain size was about 2 nm. The lattice constant of the cubic nano-AlN was a=9.171 Å, the average grain size was about 4 nm. The structural and optical properties of the obtained AlN were analyzed. The emission related to deep-level defects was investigated by using temperature-dependent photoluminescence.

A control on the photoluminescence properties in P-passivated nanocrystalline ZnO films

Co-reporter:S.J. Chen, Y.C.Liu, C.L. Shao, Y.M. Lu, J.Y. Zhang, D.Z. Shen, X.W. Fan

Chemical Physics Letters 2004 Volume 397(4–6) pp:360-363

Publication Date(Web):21 October 2004

DOI:10.1016/j.cplett.2004.08.142

Abstract

P-passivated nanocrystalline ZnO films on InP substrates were prepared by thermal oxidation of Zn films. By a simple thermal annealing cycle process, uniform photoluminescence (PL) samples with controllable visible emission and intense UV emission were obtained at different annealing conditions. Through a detailed study of the photoluminescence spectra of P-passivated nano-ZnO films vs the annealing-temperature and annealing-time, it is shown that applying different annealing time or temperatures provides a very practical technique to control the deep-level defect emission. A core-shell structure model of the surface passivation was helpfully used to discuss the P-passivation mechanism.

Photo-induced birefringence and polarization holography in polymer films containing spirooxazine compounds pre-irradiated by UV light

Co-reporter:Shencheng Fu, Yichun Liu, Zifeng Lu, Lin Dong, Weilin Hu, Minggui Xie

Optics Communications 2004 Volume 242(1–3) pp:115-122

Publication Date(Web):26 November 2004

DOI:10.1016/j.optcom.2004.08.022

Photo-induced birefringence of spirooxazine (6′-piperidino-1,3,3-trimethylspiro[indolino-2,3′-[3H]naphtha-[2,1-b][1,4]oxazine] in poly(methyl methacrylate) films pre-irradiated by ultraviolet light was investigated as a function of He–Ne laser (632.8 nm) pumping-beam intensity. A phenomenological model, taking photo-orientation and photo-isomerization into account, is in good agreement with the measurements. This material exhibited a competing process between photo-orientation and photo-isomerization. The photo-orientation is predominant when the power density of He–Ne beam is lower; while the photo-isomerization is dominant at relatively high power density of He–Ne beam. In terms of these effects, a comparison between (s,s) and (s,p) holographic gratings optically recorded by He–Ne laser of 632.8 nm in this composite film pre-irradiated by UV light was also investigated.

Photochromism and holographic recording in polymer film containing chiral azo molecules derived from amino acid

Co-reporter:Yanjie Zhang, Zifeng Lu, Xuefeng Deng, Yichun Liu, Changhui Tan, Yingying Zhao, Xianggui Kong

Optical Materials 2003 Volume 22(Issue 3) pp:187-192

Publication Date(Web):May 2003

DOI:10.1016/S0925-3467(02)00243-4

A kind of chiral azo molecule derived from amino acid, N-[4-(4-octyloxyphenylazo)benzoyl]-l-glutamic acid (C8-Azo-l-Glu), was synthesized and the photochromism, photoinduced birefringence, and holographic recording in C8-Azo-l-Glu doped poly(methyl methacrylate) (PMMA) films were studied. C8-Azo-l-Glu underwent a reversible trans–cis–trans isomerization in the polymer matrix. The photoinduced birefringence was investigated at various intensities of Ar laser (488 nm) beam. A reversible hologram was recorded in this media and the dependence of the first order diffraction efficiency on the recording beam intensities was also presented.

Influence of surface hydrophobicity of substrates on the self-organization of chiral molecule

Co-reporter:Yanjie Zhang, Ran Lu, Qingsheng Liu, Yanlin Song, Lei Jiang, Yichun Liu, Yingying Zhao, Tie Jin Li

Thin Solid Films 2003 Volume 437(1–2) pp:150-154

Publication Date(Web):1 August 2003

DOI:10.1016/S0040-6090(03)00615-1

The interfacial-dependent self-organization of a chiral amino acid amphiphile was observed on various substrates with different surface hydrophobicity. Three kinds of organizations are induced at different substrates, which appear as helical aggregates on hydrophobic surface (e.g. highly oriented pyrolytic graphite), molecular flat layer on hydrophilic surface, (e.g. mica) and a transition state between them on silicon wafer. The strength of the interactions between the helical aggregates formed in solution and the substrate is the key factor to the self-organization of the chiral molecule. The results reported here provide insight into how the surface hydrophobicity of substrates affects the self-organization of chiral molecules.

Preferred orientation of ZnO nanoparticles formed by post-thermal annealing zinc implanted silica

Co-reporter:Y.X. Liu, Y.C. Liu, D.Z. Shen, G.Z. Zhong, X.W. Fan, X.G. Kong, R. Mu, D.O. Henderson

Solid State Communications 2002 Volume 121(9–10) pp:531-536

Publication Date(Web):7 March 2002

DOI:10.1016/S0038-1098(02)00006-6

High quality zinc oxide nanoparticles with (002) preferred orientation were prepared by post-thermal annealing zinc implanted silica at 700 °C using two methods. One method was annealing zinc implanted silica at 700 °C for 2 h in oxygen ambient; the other method was sequentially annealing zinc implanted silica at 700 °C in nitrogen and oxygen ambient for 1 h, respectively. X-ray diffraction (XRD), absorption and microphotoluminescence (micro-PL) results indicated that the latter method could create high quality ZnO nanoparticles with (002) preferred orientation and narrow size-distribution. X-ray photoelectron spectra (XPS) showed the formation of ZnO nanoparticles on a silica surface, where the ZnO nanoparticle content increased with increasing oxidation time in an oxygen environment. The processes of the transformation from Zn to ZnO are discussed.

Room-temperature blue luminescence from ZnO:Er thin films

Co-reporter:X.T Zhang, Y.C Liu, J.G Ma, Y.M Lu, D.Z Shen, W Xu, G.Z Zhong, X.W Fan

Thin Solid Films 2002 Volume 413(1–2) pp:257-261

Publication Date(Web):24 June 2002

DOI:10.1016/S0040-6090(02)00356-5

In this paper, room-temperature blue cathodoluminescence from ZnO:Er thin films has been studied using different electron beam currents. The ZnO:Er thin films used in our experiment were prepared by simultaneous evaporation from ZnO and Er sources. The X-ray diffraction spectra showed that the thin films had a strong preferential c-axis (0002) orientation with a hexagonal crystalline structure. The blue light emission at 455 nm originating from the intra-4f shell transition (4F5/2→4I15/2) in Er3+ ions was observed at room temperature. This is because many Er ions in the ground states resonantly absorb the energy from the emission related to deep-level defects and cathode ray, then fill in the 2H11/2 state, the non-radiative relaxation rates from the 4F5/2 state to the 2H11/2 state are completely suppressed. The non-linear dependence of the cathodoluminescence intensity on the electron beam current showed a blue light emission above the threshold electron beam current (Ith) of 0.6 μA, which was attributed to the phonon bottleneck effect. Furthermore, the near infrared luminescence at 1.54 μm was obtained at room temperature.

Effect of the growth temperature on ZnO thin films grown by plasma enhanced chemical vapor deposition

Co-reporter:B.S. Li, Y.C. Liu, Z.Z. Zhi, D.Z. Shen, Y.M. Lu, J.Y. Zhang, X.G. Kong, X.W. Fan

Thin Solid Films 2002 Volume 414(Issue 2) pp:170-174

Publication Date(Web):22 July 2002

DOI:10.1016/S0040-6090(02)00491-1

A preferred oriented (0 0 2) ZnO thin films have been grown on Si (1 0 0) substrate via plasma enhanced chemical vapor deposition using diethylzinc and carbon dioxide as reactant sources. In this paper, the dependence of the quality of the ZnO thin film on the growth temperature is studied. A polycrystalline ZnO thin film with a c-axis-orientated wurtize structure is obtained at a growth temperature of 230 °C. X-ray diffraction shows that the full width at half maximum (FWHM) of (0 0 2) ZnO, located at 34.42°, is approximately 0.26°. A pronounced exciton absorption peak is observed in the absorption spectrum. The photoluminescence (PL) spectra show a strong ultraviolet (UV) band emission approximately 3.26 eV with a weak emission related to deep-level defects, implying that the ZnO thin films are nearly stoichiometric. The FWHMs of the PL spectra become narrower with increasing growth temperature. The origin of the UV band is from free exciton recombination, testified by the temperature dependent PL spectra in the range of 81–581 K.

TiO2 nanoparticle-based electron transport layer with improved wettability for efficient planar-heterojunction perovskite solar cell

Co-reporter:Peng Chen, Yinglin Wang, Meiqi Wang, Xintong Zhang, ... Yichun Liu

Journal of Energy Chemistry (November 2015) Volume 24(Issue 6) pp:717-721

Publication Date(Web):1 November 2015

DOI:10.1016/j.jechem.2015.10.014

The electron transport layer (ETL) plays an important role in planar heterojunction perovskite solar cell (PSCs), by affecting the light-harvesting, electron injection and transportation processes, and especially the crystallization of perovskite absorber. In this work, we utilized a commercial TKD-TiO2 nanoparticle with a small diameter of 6 nm for the first time to prepare a compact ETL by spin coating. The packing of small-size particles endowed TKD-TiO2 ETL an appropriate surface-wettability, which is beneficial to the crystallization of perovskite deposited via solution-processed method. The uniform and high-transmittance TKD-TiO2 films were successfully incorporated into PSCs as ETLs. Further careful optimization of ETL thickness gave birth to a highest power conversion efficiency of 11.0%, which was much higher than that of PSC using an ETL with the same thickness made by spray pyrolysis. This TKD-TiO2 provided a universal solar material suitable for the further large-scale production of PSCs. The excellent morphology and the convenient preparation method of TKD-TiO2 film gave it an extensive application in photovoltaic devices.Description portion: Highly transparent TiO2 nanoparticle (∼ 6 nm) electron transport layer with improved wettability for DMF solvent were successfully used to fabricate planar-heterojunction PSCs with a PCE of 11.0%.Download high-res image (140KB)Download full-size image

Red-emitting LiEuMo2−xSixO8 phosphors for white light-emitting diodes

Co-reporter:Pengpeng Dai, Xintong Zhang, Xinghua Li, Guorui Wang, Chengjiu Zhao, Yichun Liu

Journal of Luminescence (April 2011) Volume 131(Issue 4) pp:653-656

Publication Date(Web):1 April 2011

DOI:10.1016/j.jlumin.2010.11.010

Si4+ was introduced to the lattice of LiEuMo2O8 by solid-state reaction to prepare a new kind of red-emitting LiEuMo2−xSixO8 (0

Interspace modification of titania-nanorod arrays for efficient mesoscopic perovskite solar cells

Co-reporter:Peng Chen, Zhixin Jin, Yinglin Wang, Meiqi Wang, Shixin Chen, Yang Zhang, Lingling Wang, Xintong Zhang, Yichun Liu

Applied Surface Science (30 April 2017) Volume 402() pp:

Publication Date(Web):30 April 2017

DOI:10.1016/j.apsusc.2017.01.037

•The fabrication of perovskite solar cells utilizing TiO2 NR arrays.•Investigation of the interspace effect of TiO2 NR on perovskite layer.•Understanding of the balance between perovskite capping layer and pore filling.Morphology of electron transport layers (ETLs) has an important influence on the device architecture and electronic processes of mesostructured solar cells. In this work, we thoroughly investigated the effect of the interspace of TiO2 nanorod (NR) arrays on the photovoltaic performance of the perovskite solar cells (PSCs). Along with the interspace in TiO2-NR arrays increasing, the thickness as well as the crystal size of perovskite capping layer are reduced accordingly, and the filling of perovskite in the channel becomes incomplete. Electrochemical impedance spectroscopy measurements reveal that this variation of perovskite absorber layer, induced by interspace of TiO2 NR arrays, causes the change of charge recombination process at the TiO2/perovskite interface, suggesting that a balance between capping layer and the perovskite filling is critical to obtain high charge collection efficiency of PSCs. A power conversion efficiency of 10.3% could be achieved through careful optimization of interspace in TiO2-NR arrays. Our research will shed light on the morphology control of ETLs with 1D structure for heterojunction solar cells fabricated by solution-deposited method.

Effects of pectin structure and crosslinking method on the properties of crosslinked pectin nanofibers

Co-reporter:Sisi Cui, Bing Yao, Meijiao Gao, Xue Sun, Dongxia Gou, Junli Hu, Yifa Zhou, Yichun Liu

Carbohydrate Polymers (10 February 2017) Volume 157() pp:

Publication Date(Web):10 February 2017

DOI:10.1016/j.carbpol.2016.10.052

•Electrospun nanofibers of three representative pectins were crosslinked.•Three feasible crosslinking methods were established.•Pectin structure affected properties of Ca2+-crosslinked nanofibers remarkably.•ADH crosslinking enhanced mechanical strength and inhibited degradation.•ADH crosslinking and high DM facilitated cell adhesion and proliferation.We reported crosslinking of electrospun nanofibers of three representative pectins (high-methoxylated, low-methoxylated, low-methoxylated and amidated pectin) and characterization of the crosslinked nanofibers. One mono-crosslinking strategy and two dual-crosslinking strategies were developed. Mono-crosslinking is achieved using calcium ions (Ca2+) to crosslink carboxylate ions in galacturonic acid residues. Dual-crosslinking is achieved using covalent crosslinking reagents glutaraldehyde (GLU) or adipic acid dihydrazide (ADH) to further crosslink hydroxyl groups or carboxylate ions after Ca2+ crosslinking. Mechanical tests and degradation experiments indicated pectin structure affected mechanical and degradation properties of Ca2+-crosslinked nanofibers remarkably. Subsequent GLU crosslinking improved their mechanical strength moderately but did not inhibit their degradation, while subsequent ADH crosslinking improved their mechanical strength and slowed down their degradation dramatically. Cell studies demonstrated that most crosslinked pectin nanofibers were of no obvious cytotoxicity, and both ADH crosslinking and high degree of methoxylation facilitated cell adhesion and proliferation on pectin nanofiber mats.

Correction: Individual single-crystal nanowires as electrodes for organic single-crystal nanodevices

Co-reporter:Guorui Wang, Qingxin Tang, Yanhong Tong, Wenping Hu and Yichun Liu

Journal of Materials Chemistry A 2015 - vol. 3(Issue 37) pp:NaN9749-9749

Publication Date(Web):2015/09/02

DOI:10.1039/C5TC90164B

Correction for ‘Individual single-crystal nanowires as electrodes for organic single-crystal nanodevices’ by Guorui Wang et al., J. Mater. Chem. C, 2015, DOI: 10.1039/c5tc01920f.

Individual single-crystal nanowires as electrodes for organic single-crystal nanodevices

Co-reporter:Guorui Wang, Qingxin Tang, Yanhong Tong, Wenping Hu and Yichun Liu

Journal of Materials Chemistry A 2015 - vol. 3(Issue 37) pp:NaN9539-9539

Publication Date(Web):2015/08/05

DOI:10.1039/C5TC01920F

Highly stable copper wire/alumina/polyimide composite films for stretchable and transparent heaters

Co-reporter:Peng Li, Jiangang Ma, Haiyang Xu, Xiaodan Xue and Yichun Liu

Journal of Materials Chemistry A 2016 - vol. 4(Issue 16) pp:NaN3591-3591

Publication Date(Web):2016/03/22

DOI:10.1039/C5TC04276C