Co-reporter:Le Huang, Bo Li, Mianzeng Zhong, Zhongming Wei, and Jingbo Li
The Journal of Physical Chemistry C May 4, 2017 Volume 121(Issue 17) pp:9305-9305
Publication Date(Web):April 19, 2017
DOI:10.1021/acs.jpcc.7b00383
Transition-metal dichalcogenide monolayers have gained significant attention because of their excellent physical properties and promising applications as a channel material in the next-generation transistors. In this work, we focus on contacts at the surface of various metals and single-layer MoSe2. Partial Fermi level pinning is demonstrated by the first-principle calculations, which indicates modulation of the electron Schottky barrier. Upon inserting a VS2 layer between MoSe2 layer and metal electrodes, all the n-type contacts at MoSe2/metal interfaces turn into p-type, and the hole Schottky barrier can be tuned effectively by varying metal electrodes. The high work function of the VS2 layer exerts significant influence on the band realignment of MoSe2, making all the n-type contacts at MoSe2/metal interfaces become p-type contacts at MoSe2/VS2–metal interfaces. Variation of the Schottky barriers and band alignments with the work function of metal electrodes demonstrated a partial Fermi level pinning at the interfaces of MoSe2/metal and MoSe2/VS2–metal. The partial Fermi level pinning results from the low density of interfacial states, which can be reflected partly by the interaction between MoSe2 layer and metal electrodes. Our results would provide guidelines for designing novel 2D nanoelectronic devices with good performance.
Co-reporter:Zhaoqiang Zheng, Jiandong Yao, Bing Wang, Yibin Yang, Guowei Yang, and Jingbo Li
ACS Applied Materials & Interfaces December 20, 2017 Volume 9(Issue 50) pp:43830-43830
Publication Date(Web):December 1, 2017
DOI:10.1021/acsami.7b16329
The emergence of a rich variety of layered materials has attracted considerable attention in recent years because of their exciting properties. However, the applications of layered materials in optoelectronic devices are hampered by the low light absorption of monolayers/few layers, the lack of p–n junction, and the challenges for large-scale production. Here, we report a scalable production of β-In2Se3/Si heterojunction arrays using pulsed-laser deposition. Photodetectors based on the as-produced heterojunction array are sensitive to a broadband wavelength from ultraviolet (370 nm) to near-infrared (808 nm), showing a high responsivity (5.9 A/W), a decent current on/off ratio (∼600), and a superior detectivity (4.9 × 1012 jones), simultaneously. These figures-of-merits are among the best values of the reported heterojunction-based photodetectors. In addition, these devices can further enable the detection of weak signals, as successfully demonstrated with weak light sources including a flashlight, lighter, and fluorescent light. Device physics modeling shows that their high performance is attributed to the strong light absorption of the relatively thick β-In2Se3 film (20.3 nm) and the rational energy band structures of β-In2Se3 and Si, which allows efficient separation of photoexcited electron–hole pairs. These results offer a new insight into the rational design of optoelectronic devices from the synergetic effect of layered materials as well as mature semiconductor technology.Keywords: layered materials; photodetector array; p−n junction; weak signal detection; β-In2Se3/Si heterojunction;
Co-reporter:Yujue Yang;Nengjie Huo
Journal of Materials Chemistry C 2017 vol. 5(Issue 28) pp:7051-7056
Publication Date(Web):2017/07/20
DOI:10.1039/C7TC01806A
Two-dimensional (2D) material based photovoltaic devices have attracted attention due to their atomically thin profile, strong light–matter interaction and mechanical flexibility. van der Waals heterojunctions, assembled with different 2D materials and a homojunction, are achieved with a doping technique and have been demonstrated to have considerable photovoltaic properties. Here, a more facile approach is proposed to realise an in-plane MoSe2 homojunction with a gate tunable and highly efficient photovoltaic effect. By applying a negative back gate, the device can exhibit a current rectification ratio as high as 105 and a significant Voc of 0.24 V under illumination. The high power conversion efficiency of 1.9% and high photo-responsivity of 550 A W−1 with a fast temporal response of 10 ms indicate that our MoSe2 homojunction based device is a promising candidate in photovoltaic and photodetection applications.
Co-reporter:Jimin Shang;Shuai Zhang;Xuerui Cheng;Zhongming Wei
RSC Advances (2011-Present) 2017 vol. 7(Issue 24) pp:14625-14630
Publication Date(Web):2017/03/03
DOI:10.1039/C6RA28383G
By using first-principles calculations, we investigate the electronic properties of a ZrS2/HfS2 heterostructure modulated by an external electric field. An intrinsic type-I band alignment with an indirect band gap is demonstrated, which can be tuned to become type-II by applying an electric field. The spatial distribution of electron–hole pairs with the lowest energy is accordingly separated between different layers of the heterostructure. Moreover, the band gap exhibits linear variation and a semiconductor-to-metal transition can be realized. The underlying mechanism can be attributed to the linear shifts of band edges along with the quasi-Fermi levels splitting of the respective layers, induced by the charge transfer between layers of the heterostructure driven by the external electric field. Our results provide great application potential of the ZrS2/HfS2 heterostructure in optoelectronic devices.
Co-reporter:Qiang Gao;Congxin Xia;Wenqi Xiong;Juan Du;Tianxing Wang;Zhongming Wei
Journal of Materials Chemistry C 2017 vol. 5(Issue 47) pp:12629-12634
Publication Date(Web):2017/12/07
DOI:10.1039/C7TC03779A
The van der Waals (vdW) heterostructure is attracting intensive attention as a unique building block in the construction of future nano-devices. In this work, through first-principle calculations, we systemically predict the stability, electronic structures, band alignment, interface charge transfer and optical absorption of a Ca(OH)2/α-MoTe2 vdW heterostructure, considering stacking patterns and electric field (E-field) effects. The studies show that the heterostructure possesses the outstanding characteristics of direct band structures, type-I alignment, high ultraviolet absorption strength (∼105 cm−1) and broadband spectrum. Moreover, the external E-fields can tune the band alignment transformation from type I to type II. These results indicate that the Ca(OH)2/α-MoTe2 vdW heterostructure will be a promising candidate for ultraviolet optoelectronic device applications.
Co-reporter:Yujue Yang;Nengjie Huo
Journal of Materials Chemistry C 2017 vol. 5(Issue 44) pp:11614-11619
Publication Date(Web):2017/11/16
DOI:10.1039/C7TC03476H
Monolayer MoS2 photodetectors have been extensively investigated; however, their responsivity and sensitivity are highly limited due to the monolayer thin profile. Herein, we proposed a sensitized-MoS2 photodetector consisting of a monolayer MoS2 transport channel sensitizing with few-layer MoS2 on top; this photodetector exhibited a very high responsivity of ∼104 A W−1 (at negative Vg) and ∼105–106 A W−1 (at zero and positive Vg) due to improved photon absorption and enhanced mobility, more than one order of magnitude higher than that of the pure monolayer MoS2. Moreover, the sensitivity D* as high as ∼1013 Jones was achieved by operating our sensitized device in the depletion mode, where there was very low noise. This device design and the simple approach proposed herein can open up new ways towards high-performance 2D material-based photodetectors.
Co-reporter:Yujue Yang;Nengjie Huo
RSC Advances (2011-Present) 2017 vol. 7(Issue 65) pp:41052-41056
Publication Date(Web):2017/08/18
DOI:10.1039/C7RA07672J
Van der Waals heterojunctions, stacked with different two-dimensional materials, have enabled novel optoelectronic functionalities with high performances for various applications such as in photodetectors, solar cells and light-emitting diodes. Herein, we fabricated MoSe2 and CVD-grown MoS2 heterojunctions with significant gate modulated photovoltaic effect with an open-circuit voltage of 0.16 V and power conversion efficiency of ∼0.5% due to the type-II band alignment and gate tunable band slope. Moreover, the photo-responsivity was dramatically improved to ∼350 A W−1, which is two orders of magnitude larger than that of the isolated components (MoSe2 or MoS2), and the temporal response was as fast as ∼10 ms at negative back gate. All these results indicate the vast potential applications of heterojunctions, with facile procedure, in photovoltaic cells and photodetectors.
Co-reporter:Yan Wang;Le Huang;Bo Li;Jimin Shang;Congxin Xia;Chao Fan;Hui-Xiong Deng;Zhongming Wei
Journal of Materials Chemistry C 2017 vol. 5(Issue 1) pp:84-90
Publication Date(Web):2016/12/22
DOI:10.1039/C6TC03751H
Efficient bandgap engineering is a significant strategy for the utilization of widely concerned two-dimensional (2D) layered materials in versatile devices such as nanoelectronics, optoelectronics, and photonics. Alloying transition-metal dichalcogenides (TMDs) with different components has been proved as a very effective way to get 2D nanostructured semiconductors with artificially designed tunable bandgaps. Here we report a systematically study of chemical vapor transport (CVT) grown SnSe2(1−x)S2x alloys with continuously bandgaps ranging from 1.37 eV (SnSe2) to 2.27 eV (SnS2). The carrier mobility of 2D SnSe2(1−x)S2x nanosheets can be tuned from 2.34 cm2 V−1 s−1 (SnS2) to 71.30 cm2 V−1 s−1 (SnSe2) by controlling the S composition in the alloy. Furthermore, the carrier mobility of SnSeS increase from 10.34 to 12.16 cm2 V−1 s−1 under illumination, showing excellent optoelectronic properties. Our study suggests that SnSe2(1−x)S2x nanosheets is a highly qualified 2D materials for next-generation nanoelectronics and optoelectronics application.
Co-reporter:Congxin Xia;Qiang Gao;Wenqi Xiong;Juan Du;Xu Zhao;Tianxing Wang;Zhongming Wei
Journal of Materials Chemistry C 2017 vol. 5(Issue 29) pp:7230-7235
Publication Date(Web):2017/07/27
DOI:10.1039/C7TC02288C
Based on first-principles calculations, we study the electronic structures of 2D alkaline-earth metal hydroxide X(OH)2/graphene (X = Ca, Mg) heterostructures. The results show that the characteristics of the band gap size of X(OH)2 and Dirac cone of graphene are preserved well, and p-type Schottky barriers with a small Schottky barrier height (SBH) are formed in the hetero-multilayers. Moreover, double Dirac cones are also found in the X(OH)2/bilayer graphene (X(OH)2/BLG) cases. Interestingly, negative electric fields can easily induce the transition from p-type Schottky to Ohmic contact, while the p-type to n-type Schottky transition can be realized by positive electric fields. In addition, the electric field-modulations of the Schottky barrier are more sensitive in the X(OH)2/BLG systems. These studies may open the possibility of using X(OH)2/graphene as building blocks in the fabrication of Schottky devices.
Co-reporter:Qingtian Zhang;K. S. Chan
Physical Chemistry Chemical Physics 2017 vol. 19(Issue 9) pp:6871-6877
Publication Date(Web):2017/03/01
DOI:10.1039/C6CP06972J
We study the spin-dependent transport properties of graphene nanoribbons with Rashba spin–orbit interaction (SOI). It is found that highly spin polarized electrical currents can be produced in asymmetrically-notched graphene nanoribbons, and the polarization components are found to be along the x, y and z directions. The spin polarization is largely enhanced by breaking the spatial symmetries of ideal graphene nanoribbons with Rashba SOI, and the spin polarized electrical currents with higher flexibility in the orientation of the polarization can be generated. This offers new possibilities for the generation of high spin polarization in graphene nanoribbons without external magnetic fields.
Co-reporter:Mianzeng Zhong;Shuai Zhang;Le Huang;Jingbi You;Zhongming Wei;Xinfeng Liu
Nanoscale (2009-Present) 2017 vol. 9(Issue 11) pp:3736-3741
Publication Date(Web):2017/03/17
DOI:10.1039/C6NR07924E
Large-scale PbI2 monolayers and few layers with high crystallinity and a uniform hexagonal shape were synthesized via a facile physical vapour deposition (PVD) method. The transition from a direct band-gap in the bulk to an indirect band-gap in the monolayer is verified by photoluminescence (PL) spectra, optoelectronic properties, and first principle calculations.
Co-reporter:Juan Du;Congxin Xia;Wenqi Xiong;Tianxing Wang;Yu Jia
Nanoscale (2009-Present) 2017 vol. 9(Issue 44) pp:17585-17592
Publication Date(Web):2017/11/16
DOI:10.1039/C7NR06473J
The lack of ferromagnetic (FM) van der Waals (vdW) heterostructures hinders the application of two-dimensional (2D) materials in spintronics, information memories and storage devices. Herein, we find theoretically that 2D transition-metal dichalcogenides-based vdW heterostructures, such as MoS2/VS2 and WS2/VS2, possess excellent characteristics of stable stacking configurations, FM semiconducting ground states, high Curie temperatures, staggered band alignment and a large band offset. Fortunately, 100% spin-polarized currents at the Fermi level can be achieved under certain positive external electric fields, which can filter the current into a single spin channel. Moreover, the majority channel undergoes the transition from type-II to type-I (type-III) band alignment under the negative (positive) electric field; while the band alignment of the minority channel is robust to the electric field. Our results provide a feasible way to realize 2D TMDs-based FM semiconducting heterostructures for spintronic devices.
Co-reporter:Xiaoting Wang, Le Huang, Xiang-Wei Jiang, Yan Li, Zhongming Wei and Jingbo Li
Journal of Materials Chemistry A 2016 vol. 4(Issue 15) pp:3143-3148
Publication Date(Web):09 Mar 2016
DOI:10.1039/C6TC00254D
We present the scalable synthesis of large scale (up to 30 μm in lateral size), single-crystalline, atomically thin hexagonal ZrS2 nanoflakes via an optimized chemical vapor deposition (CVD) method on traditional substrates (silica, sapphire). The Vienna ab initio simulation package (VASP) was employed to calculate the adhesion energy and provided an exact theoretical account for the substrate and temperature dependent growth process of ZrS2 nanoflakes. Photodetectors based on ZrS2 nanoflakes were fabricated and displayed a remarkable photoconductivity under visible light. Field-effect transistors based on ZrS2 monolayers exhibited obvious n-type transport characteristics with relatively high mobility.
Co-reporter:Mianzeng Zhong, Le Huang, Hui-Xiong Deng, Xiaoting Wang, Bo Li, Zhongming Wei and Jingbo Li
Journal of Materials Chemistry A 2016 vol. 4(Issue 27) pp:6492-6499
Publication Date(Web):09 May 2016
DOI:10.1039/C6TC00918B
As a precursor of perovskites, lead iodide (PbI2) is a typical layered material with a direct bandgap. Perovskites are widely utilized in highly efficient photovoltaics, but the low-dimensional PbI2 nanostructures and their (opto)electronic properties are rarely reported. Herein, single-crystalline PbI2 nanosheets (phase I) and nanowires (phase II) are controllably synthesized via a facile physical vapor deposition method. Their different crystal morphology and crystallographic symmetry show obvious phase dependence. The corresponding photodetectors on both SiO2/Si and flexible polyethylene terephthalate (PET) substrates are investigated systematically. Compared with PbI2 nanowire based photodetectors, PbI2 nanosheet based photodetectors exhibit a relatively high sensitivity (with a high photoresponsivity of 147.6 A W−1 and fast response time) to the 450 nm laser. Both the PbI2 nanosheet and nanowire devices with flexible PET substrates exhibit comparable performance to their photodetectors fabricated on SiO2/Si, and also show excellent mechanical stability and durability. At the same time, the photoelectric properties vary greatly with different bending angles for such flexible PbI2 photodetectors. By modeling the band structures under different compressive strains, the theoretical simulations fit very well with experimental results. These findings provide a scientific basis for exploiting high-performance flexible photodetectors based on low-dimensional PbI2 single crystals.
Co-reporter:Yongtao Li, Yan Wang, Le Huang, Xiaoting Wang, Xingyun Li, Hui-Xiong Deng, Zhongming Wei, and Jingbo Li
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 24) pp:15574-15581
Publication Date(Web):June 3, 2016
DOI:10.1021/acsami.6b02513
Two-dimensional (2D) materials and their related van der Waals heterostructures have attracted considerable interest for their fascinating new properties. There are still many challenges in realizing the potential of 2D semiconductors in practical (opto)electronics such as signal transmission and logic circuit, etc. Herein, we report the gate-tunable anti-ambipolar devices on the basis of few-layer transition metal dichalcogenides (TMDs) heterostructures to gain higher information storage density. Our study shows that carrier concentration regulated by the gate voltage plays a major role in the “anti-ambipolar” behavior, where the drain-source current can only pass through in specific range of gate voltage (Vg) and it will be restrained if the Vg goes beyond the range. Several improved strategies were theoretically discussed and experimentally adopted to obtain higher current on/off ratio for the anti-ambipolar devices, such as choosing suitable p-/n-pair, increasing carrier concentration by using thicker-layer TMDs, and so on. The modified SnS2/WSe2 device with the current on/off ratio exceeding 200 and on-state Vg ranging from −20 to 0 V was successfully achieved. On the basis of the anti-ambipolar field-effect transistors (FETs), we also reveal the potential of three-channel device unit for signal processing and information storage. With the equal quantity N of device units, 3N digital signals can be obtained from such three-channel devices, which are much larger than 2N ones obtained from traditional two-channel complementary metal oxide semiconductors (CMOS).
Co-reporter:Chao Fan, Yan Li, Fangyuan Lu, Hui-Xiong Deng, Zhongming Wei and Jingbo Li
RSC Advances 2016 vol. 6(Issue 1) pp:422-427
Publication Date(Web):01 Dec 2015
DOI:10.1039/C5RA24905H
2D layered materials have attracted increasing interest, owing to their unique properties and large potential for versatile applications. As one of the 2D layered semiconductors, tin disulfide (SnS2) is rarely reported compared with other 2D materials like molybdenum disulfide (MoS2). Herein, high quality SnS2 flakes were grown by a facile and low-cost path, and photodetectors based on thin SnS2 flakes were fabricated and characterized. These flakes are of high quality according to the results of XRD, Raman and TEM measurements, and present hexagonal and half-hexagonal forms with an average diameter of 100 μm. The devices based on these SnS2 flakes showed wavelength dependent photo-responsive characteristics as the illuminating wavelength varied in the UV-Vis range (from 100 to 800 nm). They also showed excellent photo-responsive characteristics under monochromic illumination using three different wavelengths (533, 405 and 255 nm) with high photo-responsivity and high external quantum efficiency (EQE). The experimental results agree well with the first-principles calculated band structure and optical absorption coefficient curve.
Co-reporter:Yongtao Li, Le Huang, Bo Li, Xiaoting Wang, Ziqi Zhou, Jingbo Li, and Zhongming Wei
ACS Nano 2016 Volume 10(Issue 9) pp:8938
Publication Date(Web):August 29, 2016
DOI:10.1021/acsnano.6b04952
Heterostructures constructed by low-dimensional (such as 0D, 1D, and 2D) materials have opened up opportunities for exploring interesting physical properties and versatile (opto)electronics. Recently, 2D/2D heterostructures, in particular, atomically thin graphene and transition-metal dichalcogenides, including graphene/MoS2, WSe2/MoS2, and WS2/WSe2, were efficiently prepared (by transfer techniques, chemical vapor deposition (CVD) growth, etc.) and systematically studied. In contrast, investigation of 1D/2D heterostructures was still very challenging and rarely reported, and the understanding of such heterostructures was also not well established. Herein, we demonstrate the one-step growth of a heterostructure on the basis of a 1D-Bi2S3 nanowire and a 2D-MoS2 monolayer through the CVD method. Multimeans were employed, and the results proved the separated growth of a Bi2S3 nanowire and a MoS2 sheet in the heterostructure rather than forming a BixMo1–xSy alloy due to their large lattice mismatch. Defect-induced co-nucleus growth, which was an important growth mode in 1D/2D heterostructures, was also experimentally confirmed and systematically investigated in our research. Such 1D/2D heterostructures were further fabricated and utilized in (opto)electronic devices, such as field-effect transistors and photodetectors, and revealed their potential for multifunctional design in electrical properties. The direct growth of such nanostructures will help us to gain a better comprehension of these specific configurations and allow device functionalities in potential applications.Keywords: 1D/2D; Bi2S3; CVD growth; heterostructure; MoS2
Co-reporter:Shengxue Yang, Cong Wang, Hasan Sahin, Hui Chen, Yan Li, Shu-Shen Li, Aslihan Suslu, Francois M. Peeters, Qian Liu, Jingbo Li, and Sefaattin Tongay
Nano Letters 2015 Volume 15(Issue 3) pp:1660-1666
Publication Date(Web):February 2, 2015
DOI:10.1021/nl504276u
Creating materials with ultimate control over their physical properties is vital for a wide range of applications. From a traditional materials design perspective, this task often requires precise control over the atomic composition and structure. However, owing to their mechanical properties, low-dimensional layered materials can actually withstand a significant amount of strain and thus sustain elastic deformations before fracture. This, in return, presents a unique technique for tuning their physical properties by “strain engineering”. Here, we find that local strain induced on ReSe2, a new member of the transition metal dichalcogenides family, greatly changes its magnetic, optical, and electrical properties. Local strain induced by generation of wrinkle (1) modulates the optical gap as evidenced by red-shifted photoluminescence peak, (2) enhances light emission, (3) induces magnetism, and (4) modulates the electrical properties. The results not only allow us to create materials with vastly different properties at the nanoscale, but also enable a wide range of applications based on 2D materials, including strain sensors, stretchable electrodes, flexible field-effect transistors, artificial-muscle actuators, solar cells, and other spintronic, electromechanical, piezoelectric, photonic devices.
Co-reporter:Nengjie Huo, Zhongming Wei, Xiuqing Meng, Joongoo Kang, Fengmin Wu, Shu-Shen Li, Su-Huai Wei and Jingbo Li
Journal of Materials Chemistry A 2015 vol. 3(Issue 21) pp:5467-5473
Publication Date(Web):27 Apr 2015
DOI:10.1039/C5TC00698H
Unique optoelectronic properties and interlayer coupling are observed in the artificial two-dimensional (2D) heterostructures based on graphene, MoS2 and WS2 monolayers. In the graphene–WS2 heterostructures, substantial photoluminescence (PL) quenching and significant stiffening phonon modes emerge due to strong interlayer coupling. Such hybrid systems also exhibit gate-tunable current rectification behavior with a maximum rectification ratio of 103. In addition, the ambipolar properties originating from their constituents and enhanced photo-switching properties with a maximum on/off ratio of 103 were also observed. The MoS2–WS2 heterostructures exhibit light emission quenching of WS2 while unchanged emission of MoS2. Such a phenomenon is due to the weak interlayer coupling and inefficient charge transfer process. The enhanced optoelectronic performances suggest that the ultrathin 2D heterostructures have great potential in the future architectural design of novel optoelectronic devices.
Co-reporter:Sijie Liu, Nengjie Huo, Sheng Gan, Yan Li, Zhongming Wei, Beiju Huang, Jian Liu, Jingbo Li and Hongda Chen
Journal of Materials Chemistry A 2015 vol. 3(Issue 42) pp:10974-10980
Publication Date(Web):11 Sep 2015
DOI:10.1039/C5TC01809A
The crystalline thin layer of black phosphorus (BP) has emerged as a new category of two-dimensional (2D) materials very recently, due to its tunable direct bandgap, promising physical properties, and potential applications in optoelectronics. Herein, the Raman scattering properties of the few layers of BP including the frequency shift and the intensity of the A1g, B2g and A2g modes have been studied in detail and they show obvious dependence on thickness and light polarization. The optoelectronic performances of few-layer black phosphorus including field-effect properties and photosensitivity to laser light with different wavelengths are also investigated. The optoelectronic parameters including the current modulation, mobility, photoresponsivity and response time vary distinctly with the layer thickness. At room temperature, the obvious bipolar transport properties are obtained (with the hole and electron mobility as high as 240 and 2 cm2 V−1 s−1, respectively) in the thicker (15 nm) BP devices, while the thinner (9 nm) BP only shows P-type transportation. The photoresponsivity of BP devices under different laser light illumination reaches several tens of mA W−1, which demonstrates their excellent photo-responsive properties and broadband detection. The thinner (9 nm) BP shows a high photoresponsivity of 64.8 mA W−1 at the communication band of 1550 nm, which is much larger than that of the thicker sample. Our findings reveal that the charge transport and infrared photo-response properties of BP are excellent, and diverse and can be intentionally designed through the thickness control. Such results also suggest BP's great potential in nanoelectronic devices and photodetection from the visible light up to the communication band (infrared light).
Co-reporter:Fangyuan Lu, Juehan Yang, Renxiong Li, Nengjie Huo, Yongtao Li, Zhongming Wei and Jingbo Li
Journal of Materials Chemistry A 2015 vol. 3(Issue 6) pp:1397-1402
Publication Date(Web):08 Dec 2014
DOI:10.1039/C4TC02574A
SnS nanoparticles were synthesized with a facile hydrothermal method and characterized by X-ray diffraction (XRD), Raman, transmission electron microscope (TEM) and scanning electron microscope (SEM). The red light photoresponse of the SnS-based devices in different gas environments were also systematically investigated, and revealed that the adsorbed gas molecules play important roles in the photosensitive properties. Compared with that in vacuum, the photosensitivity was enhanced in O2 (or air) and reduced in NH3. The dynamic response time was much longer in a gas environment. These influences were ascribed to the charge transfer between the adsorbed gas molecules and SnS.
Co-reporter:Mianzeng Zhong, Zhongming Wei, Xiuqing Meng, Fengmin Wu and Jingbo Li
RSC Advances 2015 vol. 5(Issue 4) pp:2429-2433
Publication Date(Web):01 Dec 2014
DOI:10.1039/C4RA13398F
ZnSb2O4 nanoparticles with an average size of about 53 nm are synthesized by a facile hydrothermal method. The humidity sensing characteristics of the devices based on our ZnSb2O4 nanoparticles are investigated systematically. Such humidity sensors show excellent performance with ultra-high sensitivity, fast response/recovery speed, a wide range of relative humidity (RH) response, and excellent stability and reversibility. The responsive mechanisms in the low and high humidity ranges are also analyzed and simulated.
Co-reporter:Mianzeng Zhong, Zhongming Wei, Xiuqing Meng, Fengmin Wu, Jingbo Li
Journal of Alloys and Compounds 2015 Volume 619() pp:572-575
Publication Date(Web):15 January 2015
DOI:10.1016/j.jallcom.2014.09.070
•β-Ga2O3 micro/nano-sheets were synthesized via chemical vapor deposition method.•β-Ga2O3 micro/nano-sheets based Schottky UV photodetector was fabricated.•This device shows excellent optoelectronic performance.High quality β-Ga2O3 single crystals were synthesized via chemical vapor deposition (CVD) method. Such single crystals of β-Ga2O3 are grown along the [1 1 0] direction to form micro/nano-sheets. Based on this micro/nano-sheet, we fabricate single crystalline Ga2O3 UV photodetector which is composed of an Au Schottky contact and a Cr contact. This device shows excellent optoelectronic performance with high sensitivity, fast response speed, excellent stability and reversibility, and an open circuit voltage of 0.33 V. The excellent β-Ga2O3 micro/nano-sheet Schottky barrier UV photodetector will enable significant advancements of the next-generation photodetection and photosensing applications.
Co-reporter:Mianzeng Zhong, Xiuqing Meng, Jingbo Li
Applied Surface Science 2015 Volume 332() pp:76-79
Publication Date(Web):30 March 2015
DOI:10.1016/j.apsusc.2015.01.125
Highlights
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ZnSb nanorods have been synthesized by surfactant-assisted solvothermal method.
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The diameter of ZnSb nanorods is about 20 nm.
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The ZnSb nanorods have single-crystalline structure with a growth direction of [0 0 1].
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The final morphologies of ZnSb nanostructures can be controlled by CTAB.
Co-reporter:Hui Chen, Yan Li, Le Huang and Jingbo Li
RSC Advances 2015 vol. 5(Issue 63) pp:50883-50889
Publication Date(Web):26 May 2015
DOI:10.1039/C5RA08329J
The electronic and magnetic properties of native point defects, including vacancies (VGa and VS), antisites (GaS and SGa) and interstitials (Gai and Si) in monolayer and bulk GaS, were systemically studied using the density functional theory method. For the monolayer, the impurity states appeared in the band gaps of all defect structures except interstitial Si. Half-metallic behavior can be obtained in the presence of VGa and Gai. Monolayers with VGa, GaS, SGa and Gai had a total magnetic moment of 1.0 μB, as did the bulk samples with VGa, GaS and SGa, whereas the monolayers with VS and Si and bulk sample with Gai were spin-unpolarized. In addition, n- and p-type GaS monolayers were obtained under Ga-rich and S-rich conditions, respectively. GaS and SGa were identified as suitable n- and p-type defects, respectively.
Co-reporter:Bo Li, Le Huang, Mianzeng Zhong, Zhongming Wei and Jingbo Li
RSC Advances 2015 vol. 5(Issue 111) pp:91103-91107
Publication Date(Web):19 Oct 2015
DOI:10.1039/C5RA16918F
The properties of nanomaterials are always connected with their crystal morphologies of the crystals. Here, we report the synthesis of square-like high crystalline iron pyrite (FeS2) and chalcopyrite (CuFeS2) nanoplates with an average dimension of 70 nm by a developed hydrothermal process. TEM, XRD and Raman spectra characterization indicate that the nanoplates are high crystalline and pure phase. The optical band gaps of the FeS2 and CuFeS2 nanoplates are 0.97 and 0.52 eV, respectively. The electrical measurements indicate that the nanoplates have good electrical conductivity. With the dangling bonds at interface, the as-made nanoplates exhibit abnormal strong ferromagnetic behavior both at room temperature and low temperature (5 K). These nanoplates with unique morphology, high quality and good performance show huge potential in inexpensive nanoelectronics, such as solar cells and magnetic area.
Co-reporter:Le Huang, Zhanghui Chen and Jingbo Li
RSC Advances 2015 vol. 5(Issue 8) pp:5788-5794
Publication Date(Web):11 Dec 2014
DOI:10.1039/C4RA12107D
First-principles calculations have been performed to study the mechanical and electronic properties of two-dimensional monolayer GaX (X = S, Se, Te) under strain. It was found that the in-plane stiffness decreases from 86 N m−1 for GaS and 68 N m−1 for GaSe to 57 N m−1 for GaTe, which is in good agreement with experimental results and is attributed to the weakening interactions between Ga and X atoms with the increasing atomic number of the X atoms. The band gaps of the GaX monolayers decrease approximately linearly with increasing tensile strain, while the variation in their band gaps with compressive strain does not show linearity, because the conduction band maximum is transferred among several high symmetry k-points. The effective masses of electrons and holes also exhibit strong anisotropy and can be modulated by applying both compressive and tensile strains, which indicates that monolayer GaX could be very useful for device modeling.
Co-reporter:Yan Li; Hui Chen; Le Huang
The Journal of Physical Chemistry Letters 2015 Volume 6(Issue 6) pp:1059-1064
Publication Date(Web):March 9, 2015
DOI:10.1021/acs.jpclett.5b00139
The dielectric properties of multilayer GaS films have been investigated using a Berry phase method and a density functional perturbation theory approach. A linear relationship has been observed between the number of GaS layers and slab polarizability, which can be easily converged at a small supercell size and has a weak correlation with different stacking orders. Moreover, the intercoupling effect of the stacking pattern and applied vertical field on the electronic properties of GaS bilayers has been discussed. The band gaps of different stacking orders show various downward trends with the increasing field, which is interpreted as giant Stark effect. Our study demonstrates that the slab polarizability as the substitution of conventional dielectric constant can act as an independent and reliable parameter to elucidate the dielectric properties of low-dimensional systems and that the applied electric field is an effective method to modulate the electric properties of nanostructures.
Co-reporter:Le Huang; Nengjie Huo; Yan Li; Hui Chen; Juehan Yang; Zhongming Wei; Jingbo Li;Shu-Shen Li
The Journal of Physical Chemistry Letters 2015 Volume 6(Issue 13) pp:2483-2488
Publication Date(Web):June 13, 2015
DOI:10.1021/acs.jpclett.5b00976
The structural and electronic properties of black phosphorus/MoS2 (BP/MoS2) van der Waals (vdW) heterostructure are investigated by first-principles calculations. It is demonstrated that the BP/MoS2 bilayer is a type-II p-n vdW heterostructure, and thus the lowest energy electron–hole pairs are spatially separated. The band gap of BP/MoS2 can be significantly modulated by external electric field, and a transition from semiconductor to metal is observed. It gets further support from the band edges of BP and MoS2 in BP/MoS2 bilayer, which show linear variations with E⊥. BP/MoS2 bilayer also exhibits modulation of its band offsets and band alignment by E⊥, resulting in different spatial distribution of the lowest energy electron–hole pairs. Our theoretical results may inspire much interest in experimental research of BP/MoS2 vdW heterostructures and would open a new avenue for application of the heterostructures in future nano- and optoelectronics.
Co-reporter:Juehan Yang;Nengjie Huo;Yan Li;Xiang-Wei Jiang;Tao Li;Renxiong Li;Fangyuan Lu;Chao Fan;Bo Li;Kasper Nørgaard;Bo W. Laursen;Zhongming Wei;Shu-Shen Li
Advanced Electronic Materials 2015 Volume 1( Issue 10) pp:
Publication Date(Web):
DOI:10.1002/aelm.201500267
2D materials heterostructures are built by vertical stacking of solution-processed reduced graphene oxide (rGO) film and few-layer MoS2. The Raman and photoluminescence of the MoS2/rGO heterostructures show more significant peak shift compared to individual MoS2 or rGO film. The field-effect transistors (FETs) based on such MoS2/rGO heterostructures show ambipolar behavior in the dark but n-type behavior under illumination. This phenomenon provides a way to investigate the charge transport in valence band of MoS2. Due to charge separation caused by built-in potential at MoS2/rGO interface, the recombination of photoexcited electron–hole pairs is effectively suppressed, leading to high photoresponsivity (≈2.4 × 104 A W−1) and photogain (≈4.7 × 104) of the MoS2/rGO heterostructures in ambient air with modulation of gate bias and drain–source bias.
Co-reporter:Fangyuan Lu;Renxiong Li;Yan Li;Nengjie Huo;Juehan Yang;Yongtao Li;Bo Li;Dr. Shengxue Yang;Dr. Zhongming Wei; Jingbo Li
ChemPhysChem 2015 Volume 16( Issue 1) pp:99-103
Publication Date(Web):
DOI:10.1002/cphc.201402594
Abstract
High-quality Bi2S3 nanowires are synthesized by chemical vapor deposition and their intrinsic photoresponsive and field-effect characteristics are explored in detail. Among the studied Au–Au, Ag–Ag, and Au–Ag electrode pairs, the device with stepwise band alignment of asymmetric Au–Ag electrodes has the highest mobility. Furthermore, it is shown that light can cause a sevenfold decrease of the on/off ratio. This can be explained by the photoexcited charge carriers that are more beneficial to the increase of Ioff than Ion. The photoresponsive properties of the asymmetric Au–Ag electrode devices were also explored, and the results show a photoconductive gain of seven with a rise time of 2.9 s and a decay time of 1.6 s.
Co-reporter:Bo Li, Le Huang, Mianzeng Zhong, Nengjie Huo, Yongtao Li, Shengxue Yang, Chao Fan, Juehan Yang, Wenping Hu, Zhongming Wei, and Jingbo Li
ACS Nano 2015 Volume 9(Issue 2) pp:1257
Publication Date(Web):January 13, 2015
DOI:10.1021/nn505048y
Synthesis of large-scale highly crystalline two-dimensional alloys is significant for revealing properties. Here, we have investigated the vapor growth process of high-quality bilayer CoxMo1–xS2 (x = 0.16) hexagonal nanosheets systematically. As the initial loading of the sulfur increases, the morphology of the CoxMo1–xS2 (0 < x ≤ 1) nanosheets becomes hexagons from David stars step by step at 680 °C. We find that Co atoms mainly distribute at the edge of nanosheets. When the temperature increases from 680 to 750 °C, high-quality cubic pyrite-type crystal structure CoS2 grows on the surface of CoxMo1–xS2 nanosheet gradually and forms hexagonal film induced by the nanosheet. Electrical transport measurements reveal that the CoxMo1–xS2 nanosheets and CoS2 films exhibit n-type semiconducting transport behavior and half-metallic behavior, respectively. Theoretical calculations of their band structures agree well with the experimental results.Keywords: band structure; CoxMo1−xS2; transition-metal dichalcogenides; transport property; two-dimensional alloy;
Co-reporter:Hui Chen
The Journal of Physical Chemistry C 2015 Volume 119(Issue 52) pp:29148-29156
Publication Date(Web):December 10, 2015
DOI:10.1021/acs.jpcc.5b09635
The structural, electronic, and magnetic properties of the GaS monolayer doped by 12 different kinds of atoms were investigated systemically using first-principles calculations. N is found to be the most promising candidate for p-type doping among dopants at the S site, including nonmetal atoms H, B, C, N, O, and F and transition metal atoms V, Cr, Mn, Fe, Co, and Ni. Transition metal atoms appear to be hardly incorporated in the GaS monolayer under either S- or Ga-rich conditions. While the net magnetic moments of doped GaS by nonmetal atoms are either 0 or 1 μB, the value of transition metal dopants decreases from 5 to 0 μB by adding the number of valence electrons from V to Ni. In the case of transition metal dopants at the Ga site, the majority spin states of Cr and Co are located closest to the conduction band minimum and valence band maximum, respectively. Magnetic ground states exist in all of the monolayers doped by these impurities. Indirect band gap of the pristine GaS monolayer is regulated to be direct from one type of spin channel by introducing B and Mn in the S site and V, Fe, Co, and Ni in the Ga site.
Co-reporter:Nengjie Huo;Jun Kang;Zhongming Wei;Shu-Shen Li;Su-Huai Wei
Advanced Functional Materials 2014 Volume 24( Issue 44) pp:7025-7031
Publication Date(Web):
DOI:10.1002/adfm.201401504
Van der Waals heterostructures designed by assembling isolated two-dimensional (2D) crystals have emerged as a new class of artificial materials with interesting and unusual physical properties. Here, the multilayer MoS2–WS2 heterostructures with different configurations are reported and their optoelectronic properties are studied. It is shown that the new heterostructured material possesses new functionalities and superior electrical and optoelectronic properties that far exceed the one for their constituents, MoS2 or WS2. The vertical transistor exhibits a novel rectifying and bipolar behavior, and can also act as photovoltaic cell and self-driven photodetector with photo-switching ratio exceeding 103. The planar device also exhibits high field-effect ON/OFF ratio (>105), high electron mobility of 65 cm2/Vs, and high photoresponsivity of 1.42 A/W compared to that in isolated multilayer MoS2 or WS2 nanoflake transistors. The results suggest that formation of MoS2–WS2 heterostructures could significantly enhance the performance of optoelectronic devices, thus open up possibilities for future nanoelectronic, photovoltaic, and optoelectronic applications.
Co-reporter:Juehan Yang, Fangyuan Lu, Yan Li, Shengxue Yang, Renxiong Li, Nengjie Huo, Chao Fan, Zhongming Wei, Jingbo Li and Shu-Shen Li
Journal of Materials Chemistry A 2014 vol. 2(Issue 6) pp:1034-1040
Publication Date(Web):13 Nov 2013
DOI:10.1039/C3TC32142H
α-MoO3 nanosheets were synthesized by a water bath method using ammonium heptamolybdenum tetrahydrate and concentrated nitric acid as precursors. Hydrogen was doped by a chemical reduction in aqueous acidic media, with hydrazine hydrate used as the reducing agent. Temperature dependent resistance showed that the low temperature Peierls transition of H-doped MoO3 nanosheets breaks below 50 K, and its resistance is satisfied at temperatures lower than 37 K (37–10 K). This phenomenon was induced by thermal disturbance and the dominance of defects in low temperature transport, which was confirmed by photoresponse measurements taken before and after the break of the new phase.
Co-reporter:Chao Fan, Tao Li, Zhongming Wei, Nengjie Huo, Fangyuan Lu, Juehan Yang, Renxiong Li, Shengxue Yang, Bo Li, Wenping Hu and Jingbo Li
Nanoscale 2014 vol. 6(Issue 24) pp:14652-14656
Publication Date(Web):13 Oct 2014
DOI:10.1039/C4NR05111D
Recently, molybdenum disulfide (MoS2) has become a popular material due to its unique electrical and chemical properties, and its use as a potential substitute for graphene. Herein, we report a new two-step method by utilizing thermal evaporation–sulfurization to synthesize MoS2 which possesses an innovative micro-ring structure. The average statistical values of the height, width and external diameter were 69 nm, 0.3 μm and 5.0 μm, respectively. Then the mechanism for the growth of such MoS2 micro-rings was proposed. A device based on the MoS2 micro-ring was prepared by electron beam lithography, and its electrical transport properties were determined at different temperatures.
Co-reporter:Shengxue Yang, Yan Li, Xiaozhou Wang, Nengjie Huo, Jian-Bai Xia, Shu-Shen Li and Jingbo Li
Nanoscale 2014 vol. 6(Issue 5) pp:2582-2587
Publication Date(Web):05 Dec 2013
DOI:10.1039/C3NR05965K
Layered GaS nanosheets have been attracting increasing research interests due to their highly anisotropic structural, electrical, optical, and mechanical properties, which are useful for many applications. However, single-layer or few-layer GaS-based photodetectors have been rarely reported. Here a few-layer GaS two-terminal photodetector with a fast and stable response has been fabricated. It shows different photo-responses in various gas environments. A higher photo-response (64.43 A W−1) and external quantum efficiency (EQE) (12621%) is obtained in ammonia (NH3) than in air or oxygen (O2). A theoretical investigation shows that the charge transfer between the adsorbed gas molecules and the photodetector leads to the different photo-responses.
Co-reporter:Juehan Yang, Renxiong Li, Nengjie Huo, Wen-Long Ma, Fangyuan Lu, Chao Fan, Shengxue Yang, Zhongming Wei, Jingbo Li and Shu-Shen Li
RSC Advances 2014 vol. 4(Issue 91) pp:49873-49878
Publication Date(Web):24 Sep 2014
DOI:10.1039/C4RA08557D
A MoO3 nanoflakes/graphene heterocomposite synthesized by a water bath method showed unusual photoelectric behavior. Its resistance increased under visible light irradiation in air. The behavior arises from the physical contact between the two materials, which leads to hole doping in graphene. Thus, the increase of electrons in the MoO3 nanoflakes induced by desorption of oxygen molecules from its surface under visible light was probably the main reason for the change in resistance. This was confirmed by the resistance of the heterocomposite in a vacuum being 102 times larger than that in air, and by the photoelectric measurements under Ar. The MoO3 nanoflakes/graphene heterocomposite exhibits great potential for use in oxygen gas sensing.
Co-reporter:Yan Li, Jun Kang and Jingbo Li
RSC Advances 2014 vol. 4(Issue 15) pp:7396-7401
Publication Date(Web):22 Nov 2013
DOI:10.1039/C3RA46090H
The elastic, electronic and optical properties of the ZrS2 monolayer and the effects of different kinds of in-plane strains on its electronic structure are investigated using first-principles method. By analyzing the strain–energy relationship we show that the ZrS2 monolayer has a Poisson's ratio of 0.22 and an in-plane stiffness of 75.74 N m−1. The band structures of the ZrS2 monolayer calculated using both generalized gradient approximation and hybrid functional present an indirect band gap feature. The optical properties of the ZrS2 monolayer exhibit strong anisotropy. In the low-energy region, the perpendicular dielectric function dominates while in the high-energy range both perpendicular and parallel polarizations contribute. Moreover, strain has significant influence on the band structure. It is found that the band gap of the ZrS2 monolayer can be continuously modified from zero to 2.47 eV always with an indirect band gap under symmetrical strain in the elastic regime. Remarkably, an indirect-to-direct band gap transition has been observed when the uniaxial strain is applied to the monolayer along either the zigzag or armchair directions.
Co-reporter:Chao Fan, Zhongming Wei, Shengxue Yang and Jingbo Li
RSC Advances 2014 vol. 4(Issue 2) pp:775-778
Publication Date(Web):30 Jul 2013
DOI:10.1039/C3RA42564A
Novel MoSe2 flower-like nanostructures were produced by a facile hydrothermal method. Devices containing such nanostructures were also fabricated and reveal obvious photo-responsive characteristics. SEM and HRTEM images show that the as-prepared products have a flower-like structure, and the diameter of a single particle is about 500 nm. The average atomic ratio between Se and Mo is 2.68 according to the results of the EDS measurements. The photo-responsive characteristics responding to red illumination of a device with MoSe2 flower-like nanostructures were investigated for the first time and a mechanism for the photoresponse was proposed. Our findings reveal that such nanostructures have excellent electric conductivity and new photo-responsive properties.
Co-reporter:Shengxue Yang, Qu Yue, Fengmin Wu, Nengjie Huo, Zhanghui Chen, Juehan Yang, Jingbo Li
Journal of Alloys and Compounds 2014 Volume 597() pp:91-94
Publication Date(Web):5 June 2014
DOI:10.1016/j.jallcom.2014.02.006
This study reports a simple thiourea reduction method to prepare nanostructured Cd4GeS6 with direct band gap. Samples were characterized by X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), high resolution transmission electron microscopy (HRTEM), and UV–Vis diffuse reflectance spectra (UV–Vis). The photocatalytic activity of the Cd4GeS6 was evaluated by the degradation of methylene blue (MB) aqueous under visible light irradiation. The enhanced activities of Cd4GeS6 can be attributed to the direct band gap and large surface area, which is favorable for degradation of reactants, enhancement of photo-adsorption and transfer of photogenerated carriers.
Co-reporter:Fangyuan Lu, Renxiong Li, Nengjie Huo, Juehan Yang, Chao Fan, Xiaozhou Wang, Shengxue Yang and Jingbo Li
RSC Advances 2014 vol. 4(Issue 11) pp:5666-5670
Publication Date(Web):18 Dec 2013
DOI:10.1039/C3RA46283H
Bi2S3–Bi2O3 composites were synthesized by a facile hydrothermal method with surfactant as template. The structure and morphology of the as-synthesized products were characterized in detail. The photosensitive behavior of the Bi2S3–Bi2O3 composites was investigated carefully. Under the illumination of a 650 nm laser in air or vacuum, the device displayed enhanced photosensitive performance compared to the pure Bi2S3, pure Bi2O3 and mechanical mixture of Bi2S3 and Bi2O3 based devices. The photoswitch ratio (Iphoto/Idark) was as high as 30 in a vacuum with fast photoresponse speed, which indicated their potential applications in manufacturing photodetectors and optoelectronic devices. The possible mechanism of enhanced photosensitivity was also proposed.
Co-reporter:Mianzeng Zhong;Zhongming Wei;Xiuqing Meng;Fengmin Wu
European Journal of Inorganic Chemistry 2014 Volume 2014( Issue 20) pp:3245-3251
Publication Date(Web):
DOI:10.1002/ejic.201402079
Abstract
Flowerlike MoS2 microspheres were synthesized through a hydrothermal method. 2H-MoS2 nanoparticles, MoS2/MoO3 heterojunctions, and α-MoO3 nanoplates were prepared by annealing the MoS2 microspheres under different reaction conditions. The formation and growth mechanism of the samples from flowerlike MoS2 microspheres to α-MoO3 nanoplates is explained in detail. The photocatalytic properties of the four samples for the degradation of rhodamine B (RhB) under visible-light irradiation were studied. The results showed that the flowerlike MoS2 microspheres, MoS2/α-MoO3 heterojunctions, and α-MoO3 nanoplates all have excellent photocatalytic activities. In particular, the flowerlike MoS2 microspheres exhibit the highest photocatalytic activity for the degradation of RhB.
Co-reporter:Mianzeng Zhong, Yan Li, Qinglin Xia, Xiuqing Meng, Fengmin Wu, Jingbo Li
Materials Letters 2014 Volume 124() pp:282-285
Publication Date(Web):1 June 2014
DOI:10.1016/j.matlet.2014.03.110
•VS2 nanoflowers and nanosheets are synthesized by a simple hydrothermal synthesis.•Experimental results show that VS2 nanostructures have ferromagnetism in low temperature.•As the number of layers is increased from nanosheets to nanoflowers, the Curie temperature will decrease from 72 K to 10 K.We present a hydrothermal synthesis of VS2 nanoflowers with the average thicknesses of about 150 nm. The ultrathin nanosheets with the average thicknesses of about 8 nm are achieved by a simple chemical exfoliation method. We examine the ferromagnetic property of the two samples. The Low temperature ferromagnetism of the samples is found. We find that as the number of layers is increased from nanosheets to nanoflowers, the Curie temperature will decrease from 72 K to 10 K.
Co-reporter:Renxiong Li;Juehan Yang;Nengjie Huo;Chao Fan;Fangyuan Lu;Tengfei Yan;Dr. Zhongming Wei; Jingbo Li
ChemPhysChem 2014 Volume 15( Issue 12) pp:2510-2516
Publication Date(Web):
DOI:10.1002/cphc.201402201
Abstract
Bi2S3 single-crystalline nanowires are synthesized through a hydrothermal method and then fabricated into single nanowire photodetectors. Due to the different contact barrier between the gold electrode and Bi2S3 nanowires, two kinds of devices with different electrical contacts are obtained and their photoresponsive properties are investigated. The non-ohmic contact devices show larger photocurrent gains and shorter response times than those of ohmic contact devices. Furthermore, the influence of a focused laser on the barrier height between gold and Bi2S3 is explored in both kinds of devices and shows that laser illumination on the AuBi2S3 interface can greatly affect the barrier height in non-ohmic contact devices, while keeping it intact in ohmic contact devices. A model based on the surface photovoltage effect is used to explain this phenomenon.
Co-reporter:Yan Li ; Shengxue Yang
The Journal of Physical Chemistry C 2014 Volume 118(Issue 41) pp:23970-23976
Publication Date(Web):September 24, 2014
DOI:10.1021/jp506881v
The structural and electronic properties of the bulk and ultrathin black phosphorus and the effects of in-plane strain and out-of-plane electrical field on the electronic structure of phosphorene are investigated using first-principles methods. The computed results show that the bulk and few-layer black phosphorus from monolayer to six-layer demonstrates inherent direct bandgap features ranging from 0.5 to 1.6 eV. Interestingly, the band structures of the bulk and few-layer black phosphorus from X point via A point to Y point present degenerate distribution, which shows totally different partial charge dispersions. Moreover, strong anisotropy in regard to carrier effective mass has been observed along different directions. The response of phosphorene to in-plane strain is diverse. The bandgap monotonically decreases with increasing compressive strain, and semiconductor-to-metal transition occurs for phosphorene when the biaxial compressive reaches −9%. Tensile strain first enlarges the gap until the strain reaches around 4%, after which the bandgap exhibits a descending relationship with tensile strain. The bandgaps of the pristine and deformed phosphorene can also be continuously modulated by the electrical field and finally close up at about 15 V/nm. Besides, the electron and hole effective mass along different directions exhibits different responses to the combined impact of strain and electrical field.
Co-reporter:Nengjie Huo, Shengxue Yang, Zhongming Wei and Jingbo Li
Journal of Materials Chemistry A 2013 vol. 1(Issue 25) pp:3999-4007
Publication Date(Web):18 Apr 2013
DOI:10.1039/C3TC30527A
Tungsten oxide (WO3) nanostructures such as nanowires, nanorod bundles and nanotube bundles are synthesized by a facile hydrothermal method. The ultraviolet (UV) photoresponse characteristics of devices containing these WO3 nanostructures are investigated for the first time and new photosensitive mechanisms involving both photo-generated electron–hole pairs and reversible electrochemical reactions are proposed. We find that h-WO3 nanowires with large specific surface areas and fewer defects exhibit excellent UV photoresponse properties with switch ratios (defined as Iphoto/Idark) as high as 60, which is due to the existing large tunnels serving as channels and intercalation sites for mobile ions and active electrochemical reactions, and our findings provide a new family and more selectivity for UV photosensitive nanomaterials in the future.
Co-reporter:Xiuqing Meng, Sefaattin Tongay, Jun Kang, Zhanghui Chen, Fengmin Wu, Shu-Shen Li, Jian-Bai Xia, Jingbo Li, Junqiao Wu
Carbon 2013 Volume 57() pp:507-514
Publication Date(Web):June 2013
DOI:10.1016/j.carbon.2013.02.028
ZnMg and NbCl5 were intercalated in graphite and the presence of such molecules between the graphene sheets results in n- and p-type doping, respectively. The doping effect is confirmed by Hall and Raman measurements and the intercalation process is monitored by scanning tunneling microscopy. After intercalation the carrier concentration increase almost an order of magnitude and reaches values as high as 1019and 1018 cm−3 for p- and n-type doping, respectively. For higher intercalation times, the intercalated graphite turns back to be as ordered as pristine one as evidenced by the reduction in the D peak in Raman measurements. Intercalation compounds show remarkable stability allowing us to permanently tune the physical properties of few-layer graphite. Our study has provided a new route to produce stable and functional graphite intercalation compounds and the results can be applied to other graphitic structures such as few-layer graphene on SiC.
Co-reporter:Nengjie Huo;Qu Yue;Juehan Yang;Dr. Shengxue Yang; Jingbo Li
ChemPhysChem 2013 Volume 14( Issue 18) pp:4069-4073
Publication Date(Web):
DOI:10.1002/cphc.201300680
Co-reporter:Qu Yue, Shengli Chang, Jun Kang, Shiqiao Qin, and Jingbo Li
The Journal of Physical Chemistry C 2013 Volume 117(Issue 28) pp:14804-14811
Publication Date(Web):June 20, 2013
DOI:10.1021/jp4021189
Using the first-principles calculations, we investigate the mechanical and electronic properties of graphyne and its family under strain. It is found that the in-plane stiffness decreases with increasing the number of acetylenic linkages, which can be characterized by a simple scaling law. The band gap of the graphyne family is found to be modified by applying strain through various approaches. While homogeneous tensile strain leads to an increase in the band gap, the homogeneous compressive strain as well as uniaxial tensile and compressive strains within the imposed range induce a reduction in it. Both graphyne and graphyne-3 under different tensile strains possess direct gaps at either M or S point of Brillouin zone, whereas the band gaps of graphdiyne and graphyne-4 are always direct and located at the Γ point, irrespective of strain types. Our study suggests a potential direction for fabrication of novel strain-tunable nanoelectronic and optoelectronic devices.
Co-reporter:Chong Li, Shengxue Yang, Shu-Shen Li, Jian-Bai Xia, and Jingbo Li
The Journal of Physical Chemistry C 2013 Volume 117(Issue 1) pp:483-488
Publication Date(Web):December 13, 2012
DOI:10.1021/jp310746m
First-principles calculations have been performed to study Au-decorated silicene (Au/silicene) as a high-activity catalyst for CO oxidation. The high binding strength of the Au/silicene system and the high diffusion-energy barrier of Au adsorbates, as well as the assisted Coulomb repulsion effect, jointly prevent the formation of Au clusters. Au/silicene transfers many more electrons to O2 than to CO, thus facilitating CO oxidation first by the Langmuir–Hinshelwood (LH) mechanism (CO + O2 → OOCO → CO2 + O) and then by Eley–Rideal (ER) mechanism (CO + O → CO2). The two reaction processes have quite low catalytic energy barriers of 0.34 and 0.32 eV, respectively. The underlying mechanism of high catalytic oxidation of CO can be attributed to electronic-state hybridization among Au d orbitals and CO and O2 2π* antibonding states around the Fermi energy. These findings enrich the applications of Si-based materials to the high-activity catalytic field.
Co-reporter:Meili Wang;Yan Wang
Journal of Sol-Gel Science and Technology 2012 Volume 61( Issue 3) pp:613-619
Publication Date(Web):2012 March
DOI:10.1007/s10971-011-2667-5
Porous TiO2 nanoparticles coated on ZnO nanowire arrays (TiO2 NP/ZnO NW) as photoanode for dye-sensitized solar cell (DSSC) has been fabricated and investigated to improve the power conversion efficiency. The TiO2 NP/ZnO NW photoanode consists of single crystalline ZnO NWs synthesized via hydrothermal method and porous TiO2 NP film covered on the surface of ZnO NW arrays by screen printing technique. The effect of TiO2 NPs thickness of the bi-filmed photoanode on the cell performance has been investigated, and TiO2 NP/ZnO NW DSSC with NP thickness of ~5 μm exhibits the best efficiency of 4.68%, higher than 1.16% of ZnO NW DSSC and 3.18% of TiO2 NPs DSSC, prepared and tested under identical conditions. The efficiency increase is attributed to the enlarged photocurrent, due to the greatly enhanced surface area for dye absorption and light harvesting efficiency resulted from TiO2 NPs, and improved open-circuit voltage, due to reduced electron recombination by providing direct conduction pathway along ZnO NWs.
Co-reporter:Jun Kang, Fengmin Wu, Shu-Shen Li, Jian-Bai Xia, and Jingbo Li
The Journal of Physical Chemistry C 2012 Volume 116(Issue 39) pp:20765-20768
Publication Date(Web):September 6, 2012
DOI:10.1021/jp3067525
A method to calculate the band alignment between materials with different structures using passivated quantum dots is proposed. By using this method, the rutile/anatase titanium dioxide band offset is determined. The valence band maxima of anatase and rutile are close to each other, whereas the conduction band minimum of anatase is found to be about 0.2 eV higher than that of rutile, which is in agreement with the experimental fact that anatase has higher photocatalytic activity. The reliability of this method is further tested on several semiconductors, and reasonable results are obtained for most cases.
Co-reporter:Jing Wang ; Shu-Shen Li ; Ying Liu
The Journal of Physical Chemistry C 2012 Volume 116(Issue 39) pp:21039-21045
Publication Date(Web):September 5, 2012
DOI:10.1021/jp3048778
Using the first-principles band structure method, the electronic properties and optical properties of cupric iodide (CuI) quantum dots (QDs) are studied for the first time. A model is proposed to passivate the surface atoms of CuI QDs. In this model, pseudohydrogen atoms are used to passivate the dangling surface bonds, which remove the localized in-gap surface states. The size dependence of the QD gaps is obtained and is found to evolve as ΔEg = 1.60/d0.84 as the effective diameter d decreases. The energy of the calculated absorption peak is shifted higher with the decreasing d and the full width at half-maximum of the peak becomes larger as d increases, which are in good agreement with previous experiments. It is confirmed, although the local density approximation (LDA) calculations underestimate the band gap, that they give the trend of band gap shift as much as that obtained by the hybrid PBE0 for CuI QDs. These results provide understanding of the effects of the dimensionality of CuI nanocrystals, and it is expected that the method used in this work will be a practical approach to the study of other I–VII semiconductor nanocrystals.
Co-reporter:Chong Li, Fengmin Wu, Jingbo Li, and Lin-Wang Wang
The Journal of Physical Chemistry C 2012 Volume 116(Issue 46) pp:24824-24828
Publication Date(Web):October 30, 2012
DOI:10.1021/jp3088034
Using first-principles calculations, we study on the energetics, kinetics, and electronic properties of transition metal atoms Ti, Mn, and Au on zigzag graphene nanoribbons (ZGNRs) with one edge saturated by two H atoms C(2H), while the other one by one H atom C(H). Because of the larger magnetic bearded edge states on the C(2H) edge, all these three adatoms prefer adsorbing on the C(2H) edge, but Ti binds stronger to ZGNRs on the C(2H) edge than both Mn and Au atoms. The saturated C(2H) edge not only dramatically enhances the Ti mobility from the center to C(2H) edge but also weakens the diffusion isotropy; thus, Ti quantum wire is formed readily along the C(2H) edge. Along Ti atomic wire there is a spin-up conducting channel contributed by pure Ti 3d state, indicating spin-dependent charge transport properties. This may open new avenues in fabricating metal quantum wires.
Co-reporter:Meili Wang, Yan Wang and Jingbo Li
Chemical Communications 2011 vol. 47(Issue 40) pp:11246-11248
Publication Date(Web):19 Sep 2011
DOI:10.1039/C1CC15310B
A novel composite photoanode with ZnO nanowire arrays coating on the top of TiO2 nanoparticles is fabricated, and an efficiency of 4.52% is achieved for the composite cell, far higher than both 0.90% of the ZnO nanowire cell and 3.56% of the TiO2 nanoparticle cell. The improved efficiency is resulted from the high surface area of nanoparticles, as well as fast electron transport and light scattering effect of nanowires.
Co-reporter:Xiuqing Meng, Chaoren Liu, Fengmin Wu, Jingbo Li
Journal of Colloid and Interface Science 2011 Volume 358(Issue 2) pp:334-337
Publication Date(Web):15 June 2011
DOI:10.1016/j.jcis.2011.03.036
ZnO:Er3+ and ZnO:Er3+–Yb3+ nanoparticles (NPs) are fabricated by a sol–gel method, afterwards parts of which are separated and surface modified in Mo(NO3)3 solution. Analyses on phase and structure based on X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) techniques indicate that Er3+ and Yb3+ are incorporated into the ZnO lattice successfully and after Mo treatment, a thin layer of MoO3 forms on the NPs surface, forming core/shell structures. Raman scattering spectra reveal the existence of ZnMoO4 in the shell part. Visible up-conversion (UC) is observed in all the samples, with Mo treated and untreated ZnO:Er3+ emitting dominant but relatively weak red light, corresponding to 4F9/2–4I15/2 transition of Er3+. In Yb3+-codoping systems, the integral UC intensity is enhanced obviously though red emission still dominates the UC spectra before surface modification. In the Mo treated system, ZnO:Er3+–Yb3+/MoO3, green emission is increased while the red is suppressed in comparison to ZnO:Er3+–Yb3+, with the intensity of green to red ratio (GRR) changing from 0.25 to 8. A novel phenomenon is discovered that the green emissions in our samples involve three-photon processes.Graphical abstractRoom temperature up-conversion PL properties from sample B to C1, which indicates that the green emission of sample C enhanced greatly after MoO3 surface modification.Highlights► ZnO:Er3+/MoO3 and ZnO:Er3+Yb3+/MoO3 core/shell structures. ► Core/shell structures obtained by surface modified ZnO:Er3+ and ZnO:Er3+Yb3+ NPs. ► Core/shell structures improve green up conversion (UC) emissions greatly in the NPs. ► Green UC emissions in ZnO: Er3+Yb3+/MoO3 involve three-photon processes.
Co-reporter:Xiuqing Meng ; Fengmin Wu
The Journal of Physical Chemistry C 2011 Volume 115(Issue 15) pp:7225-7229
Publication Date(Web):March 29, 2011
DOI:10.1021/jp1101847
SnO2/ZnS one-dimensional core/shell nanowires have been synthesized by a two-step growth process. Phase and structural analyses reveal that the core has a single crystalline phase, whereas the shell has a polycrystalline phase covering the surface of the core. The optical properties of SnO2 nanowires change as a function of the ZnS shell thickness. The increase in photoluminescence intensity at the stage when the shell is very thin is attributed to the surface modification by the ZnS shell. When the shell gets thicker, the intensity of the photoluminescence decreases because a type-II band alignment is formed between the core and shell. The changes are also detected in the Raman spectra: new lines caused by surface optical phonons emerge when the shell is very thin, and their intensities decrease with the increase of the shell thickness.
Co-reporter:Jun Kang ; Jingbo Li ; Fengmin Wu ; Shu-Shen Li ;Jian-Bai Xia
The Journal of Physical Chemistry C 2011 Volume 115(Issue 42) pp:20466-20470
Publication Date(Web):September 13, 2011
DOI:10.1021/jp206751m
The elastic, electronic, and optical properties of the 2D graphyne sheet, which consists of hexagonal carbon rings and acetylenic linkages, are investigated from first-principles calculations. Graphyne has a Poisson’s ratio of 0.417 and an in-plane stiffness of 10.36 eV/Å2. Compared with graphene, graphyne is much softer because of its relatively smaller number of bonds. The band structure of graphyne is calculated using both generalized gradient approximation and hybrid functional, and the band gap predicted by the latter is twice as much as that given by the former. It is also shown that the energy bands of graphyne can be divided into several regions according to bonding character. The optical property of graphyne is found to be strongly anisotropic. For electric field parallel to the graphyne plane, strong optical adsorption is observed in low-energy region, whereas for the electric field perpendicular to the graphyne plane, the adsorption in the low-energy region is very weak. What’s more, the response of the band gap of graphyne to uniform strain is also studied, and we show that the band gap can be continuously modified under the strain.
Co-reporter:Chong Li ; Jingbo Li ; Fengmin Wu ; Shu-Shen Li ; Jian-Bai Xia ;Lin-Wang Wang
The Journal of Physical Chemistry C 2011 Volume 115(Issue 46) pp:23221-23225
Publication Date(Web):October 14, 2011
DOI:10.1021/jp208423y
Ca decorated carbon allotropes have a potential for high density hydrogen storage, except that the Ca–graphene and Ca–fullerenes binding is not strong enough to prevent the formation of a Ca cluster. Using first-principles calculations, we show that Ca can bind strongly to s–p and s–p2 bonded graphyne without the formation of a Ca cluster. This enhanced binding energy is due to the additional in-plane π states which do not exist in the s–p2 bonded graphene and fullerenes. The H2 binding to the Ca–graphyne system is similar to the Ca–fullerenes system with a maximum of six H2 molecules per Ca atom and a 0.2 eV per H2 binding energy which is optimal as hydrogen storage materials. With two Ca atoms per unit cell, this leads to 9.6 wt % hydrogen storage capacity in theory.
Co-reporter:X. Q. Meng, Haowei Peng, Y. Q. Gai and Jingbo Li
The Journal of Physical Chemistry C 2010 Volume 114(Issue 3) pp:1467-1471
Publication Date(Web):December 30, 2009
DOI:10.1021/jp909176p
By sequential growth of the core and shell of different materials, ZnO/ZnS and ZnO/MgO core/shell nanowire arrays are fabricated. Photoluminescence properties of these samples with different shell thicknesses are studied in detail. The results indicate that the ZnS shell thickness as a function of treatment time will noticeably change the photoluminescence intensity of the ZnO nanowires, whereas the MgO shell will not change the photoluminescence intensity any more after it saturates the surface dangling bonds of ZnO core. Large-scale first-principles calculations indicate that, unlike the ZnO/MgO core/shell nanowires, the electrons and holes of which are both confined in the core of the nanowires (type-I heterostructures), the ZnO/ZnS core/shell nanowires are type-II heterostructures, the electrons and holes of which are respectively confined in the core and the shell; as a result, the separation of electrons and holes in the ZnO/ZnS core/shell nanowires will reduce the spatial overlap between them, leading to the decrease of the photoluminescence intensity in this system. The experimental observations are in good agreement with first-principles calculations (PACS: 62.23.Hj, 71.55.Gs, 73.40.Lq, 74.25.Gz, 73.43.Cd).
Co-reporter:Hui-Xiong Deng, Shu-Shen Li and Jingbo Li
The Journal of Physical Chemistry C 2010 Volume 114(Issue 11) pp:4841-4845
Publication Date(Web):March 1, 2010
DOI:10.1021/jp911035z
On the basis of the density functional theory (DFT) within local density approximations (LDA) approach, we calculate the band gaps for different size SnO2 quantum wires (QWs) and quantum dots (QDs). A model is proposed to passivate the surface atoms of SnO2 QWs and QDs. We find that the band gap increases between QWs and bulk evolve as ΔEgwire = 1.74/d1.20 as the effective diameter d decreases, while being ΔEgdot = 2.84/d1.26 for the QDs. Though the ∼d1.2 scale is significantly different from ∼d2 of the effective mass result, the ratio of band gap increases between SnO2 QWs and QDs is 0.609, very close to the effective mass prediction. We also confirm, although the LDA calculations underestimate the band gap, that they give the trend of band gap shift as much as that obtained by the hybrid functional (PBE0) with a rational mixing of 25% Fock exchange and 75% of the conventional Perdew−Burke−Ernzerhof (PBE) exchange functional for the SnO2 QWs and QDs. The relative deviation of the LDA calculated band gap difference ΔEg compared with the corresponding PBE0 result is only within 5%. Additionally, it is found the states of valence band maximum (VBM) and conduction band minimum (CBM) of SnO2 QWs or QDs have a mostly p- and s-like envelope function symmetry, respectively, from both LDA and PBE0 calculations.
Co-reporter:Xiuqing Meng ; Liming Tang
The Journal of Physical Chemistry C 2010 Volume 114(Issue 41) pp:17569-17573
Publication Date(Web):September 16, 2010
DOI:10.1021/jp106767n
Co-doped In2O3 nanocrystals showing room-temperature ferromagnetism have been successfully prepared by a simple sol−gel synthesis route. The sample displays a clear ferromagnetism behavior above 300 K. Phase and structure analyses reveal that the nanocrystals are crystallized with Co ions substituted for In ions in the In2O3 matrix, and no trace of secondary phases or clusters is detected. The experimental results are explained theoretically by first-principles calculations based on density functional theory, which indicate that the native ferromagnetic behavior of Co-doped In2O3 could be mainly ascribed to the strong d−d coupling of the magnetic ions.
Co-reporter:Yanqin Gai, Haowei Peng and Jingbo Li
The Journal of Physical Chemistry C 2009 Volume 113(Issue 52) pp:21506-21511
Publication Date(Web):December 2, 2009
DOI:10.1021/jp905868f
The electronic properties of PbSe quantum dots containing a nonstoichiometric Pb:Se ratio are investigated by ab initio density functional theory. We take five nearly spherical PbSe nanocrystals with effective diameters ranging from 11.22 to 31.86 Å into account and compare their electronic properties before and after passivations. We find that despite the strong ionic character of the Pb−Se bond, their dangling bonds at the surface of nonstoichiometric PbSe nanocrystals introduce in-gap states, which are quite different from those of the stoichiometric PbSe nanocrystals. The same phenomenon is also observed for bare PbSe (011) and (111) surfaces. Compared with that of the self-passivated (001) surface, there is large surface relaxation and rumpling at the unsaturated (011) and (111) surfaces. We expect this might also be the origin of surface states in nonstoichiometric PbSe nanocrystals. We observed the almost recovery of structures and at the same time the elimination of in-gap states by passivating the dangling bonds with pseudo-hydrogen atoms. Meanwhile, the size dependencies of the QDs’ gaps are obtained, which are in accordance with experimental measurement and other theoretical calculations.
Co-reporter:Zhiguo Wang, Shengjie Wang, Jingbo Li, Fei Gao and William J. Weber
The Journal of Physical Chemistry C 2009 Volume 113(Issue 44) pp:19281-19285
Publication Date(Web):October 9, 2009
DOI:10.1021/jp907657z
The atomic and electronic structures of saturated and unsaturated GaN nanotubes along the [001] direction with (100) lateral facets are studied using first-principles calculations. Atomic relaxation of nanotubes shows that appreciable distortion occurs in the unsaturated nanotubes. All the nanotubes considered, including saturated and unsaturated ones, exhibit semiconducting, with a direct band gap. Surface states arisen from the 3-fold-coordinated N and Ga atoms at the lateral facets exist inside the bulklike band gap. When the nanotubes are saturated with hydrogen, these dangling bond bands are removed from the band gap, but the band gap decreases with increasing the wall thickness of the nanotubes.
Co-reporter:Haowei Peng, Jingbo Li, Shu-Shen Li and Jian-Bai Xia
The Journal of Physical Chemistry C 2008 Volume 112(Issue 36) pp:13964-13969
Publication Date(Web):2017-2-22
DOI:10.1021/jp8042973
The electronic structure of rutile TiO2 quantum dots (QDs) are investigated via the first-principles band structure method. We first propose a model to passivate the rutile TiO2 surfaces for the local density approximation calculations. In this model pseudohydrogen atoms are used to passivate the surface dangling bonds, which remove the localized in-gap surface states in the TiO2 QDs. As the size of the QD decreases, the band gap evolves as Eg(dot) = Eg(bulk) + 73.70/d1.93, where Eg(dot) and d are the band gap and diameter of the QD, and Eg(bulk) is the band gap of the bulk rutile TiO2. The valence band maximum and the conduction band minimum states of the QDs are distributed mostly in the interior of the QDs, and they well inherit the atomic characteristics of those states of the bulk rutile TiO2.
Co-reporter:Haowei Peng and Jingbo Li
The Journal of Physical Chemistry C 2008 Volume 112(Issue 51) pp:20241-20245
Publication Date(Web):2017-2-22
DOI:10.1021/jp807439q
The quantum confinement effect, electronic properties, and optical properties of TiO2 nanowires in rutile structure are investigated via first-principles calculations. We calculate the size- and shape-dependent band gap of the nanowires and fit the results with the function Eg = Egbulk + β/dα. We find that the quantum confinement effect becomes significant for d < 25 Å, and a notable anisotropy exists that arises from the anisotropy of the effective masses. We also evaluate the imaginary part of the frequency-dependent dielectric function [ε2(ω)] within the electric-dipole approximation, for both the polarization parallel [ε2∥(ω)] and the perpendicular [ε2⊥(ω)] to the axial (c) direction. The band structure of the nanowires is calculated, with which the fine structure of ε2∥(ω) has been analyzed.
Co-reporter:Nengjie Huo, Zhongming Wei, Xiuqing Meng, Joongoo Kang, Fengmin Wu, Shu-Shen Li, Su-Huai Wei and Jingbo Li
Journal of Materials Chemistry A 2015 - vol. 3(Issue 21) pp:NaN5473-5473
Publication Date(Web):2015/04/27
DOI:10.1039/C5TC00698H
Unique optoelectronic properties and interlayer coupling are observed in the artificial two-dimensional (2D) heterostructures based on graphene, MoS2 and WS2 monolayers. In the graphene–WS2 heterostructures, substantial photoluminescence (PL) quenching and significant stiffening phonon modes emerge due to strong interlayer coupling. Such hybrid systems also exhibit gate-tunable current rectification behavior with a maximum rectification ratio of 103. In addition, the ambipolar properties originating from their constituents and enhanced photo-switching properties with a maximum on/off ratio of 103 were also observed. The MoS2–WS2 heterostructures exhibit light emission quenching of WS2 while unchanged emission of MoS2. Such a phenomenon is due to the weak interlayer coupling and inefficient charge transfer process. The enhanced optoelectronic performances suggest that the ultrathin 2D heterostructures have great potential in the future architectural design of novel optoelectronic devices.
Co-reporter:Xiaoting Wang, Le Huang, Xiang-Wei Jiang, Yan Li, Zhongming Wei and Jingbo Li
Journal of Materials Chemistry A 2016 - vol. 4(Issue 15) pp:NaN3148-3148
Publication Date(Web):2016/03/09
DOI:10.1039/C6TC00254D
We present the scalable synthesis of large scale (up to 30 μm in lateral size), single-crystalline, atomically thin hexagonal ZrS2 nanoflakes via an optimized chemical vapor deposition (CVD) method on traditional substrates (silica, sapphire). The Vienna ab initio simulation package (VASP) was employed to calculate the adhesion energy and provided an exact theoretical account for the substrate and temperature dependent growth process of ZrS2 nanoflakes. Photodetectors based on ZrS2 nanoflakes were fabricated and displayed a remarkable photoconductivity under visible light. Field-effect transistors based on ZrS2 monolayers exhibited obvious n-type transport characteristics with relatively high mobility.
Co-reporter:Congxin Xia, Qiang Gao, Wenqi Xiong, Juan Du, Xu Zhao, Tianxing Wang, Zhongming Wei and Jingbo Li
Journal of Materials Chemistry A 2017 - vol. 5(Issue 29) pp:NaN7235-7235
Publication Date(Web):2017/06/26
DOI:10.1039/C7TC02288C
Based on first-principles calculations, we study the electronic structures of 2D alkaline-earth metal hydroxide X(OH)2/graphene (X = Ca, Mg) heterostructures. The results show that the characteristics of the band gap size of X(OH)2 and Dirac cone of graphene are preserved well, and p-type Schottky barriers with a small Schottky barrier height (SBH) are formed in the hetero-multilayers. Moreover, double Dirac cones are also found in the X(OH)2/bilayer graphene (X(OH)2/BLG) cases. Interestingly, negative electric fields can easily induce the transition from p-type Schottky to Ohmic contact, while the p-type to n-type Schottky transition can be realized by positive electric fields. In addition, the electric field-modulations of the Schottky barrier are more sensitive in the X(OH)2/BLG systems. These studies may open the possibility of using X(OH)2/graphene as building blocks in the fabrication of Schottky devices.
Co-reporter:Juan Du, Congxin Xia, Tianxing Wang, Wenqi Xiong and Jingbo Li
Journal of Materials Chemistry A 2016 - vol. 4(Issue 39) pp:NaN9302-9302
Publication Date(Web):2016/09/09
DOI:10.1039/C6TC02469F
The band structures and optical characteristics of group IV (Si, Ge) and V (P, As) element-alloyed C2N monolayers are investigated by means of first-principles methods. The results indicate that C2N1−xPx and C2N1−xAsx alloys are easier to fabricate than C2−xSixN and C2−xGexN alloys. Moreover, it is feasible to construct mixed C2N1−xPx and C2N1−xAsx alloys with tunable composition and band gap. When the doping concentration increases, the band gap shows a decreasing tendency, and the absorption edges exhibit a red shift in these alloys. These obtained results predicate that C2N1−xPx and C2N1−xAsx alloys may be promising candidates for optoelectronic applications.
Co-reporter:Fangyuan Lu, Juehan Yang, Renxiong Li, Nengjie Huo, Yongtao Li, Zhongming Wei and Jingbo Li
Journal of Materials Chemistry A 2015 - vol. 3(Issue 6) pp:NaN1402-1402
Publication Date(Web):2014/12/08
DOI:10.1039/C4TC02574A
SnS nanoparticles were synthesized with a facile hydrothermal method and characterized by X-ray diffraction (XRD), Raman, transmission electron microscope (TEM) and scanning electron microscope (SEM). The red light photoresponse of the SnS-based devices in different gas environments were also systematically investigated, and revealed that the adsorbed gas molecules play important roles in the photosensitive properties. Compared with that in vacuum, the photosensitivity was enhanced in O2 (or air) and reduced in NH3. The dynamic response time was much longer in a gas environment. These influences were ascribed to the charge transfer between the adsorbed gas molecules and SnS.
Co-reporter:Yan Wang, Le Huang, Bo Li, Jimin Shang, Congxin Xia, Chao Fan, Hui-Xiong Deng, Zhongming Wei and Jingbo Li
Journal of Materials Chemistry A 2017 - vol. 5(Issue 1) pp:NaN90-90
Publication Date(Web):2016/11/17
DOI:10.1039/C6TC03751H
Efficient bandgap engineering is a significant strategy for the utilization of widely concerned two-dimensional (2D) layered materials in versatile devices such as nanoelectronics, optoelectronics, and photonics. Alloying transition-metal dichalcogenides (TMDs) with different components has been proved as a very effective way to get 2D nanostructured semiconductors with artificially designed tunable bandgaps. Here we report a systematically study of chemical vapor transport (CVT) grown SnSe2(1−x)S2x alloys with continuously bandgaps ranging from 1.37 eV (SnSe2) to 2.27 eV (SnS2). The carrier mobility of 2D SnSe2(1−x)S2x nanosheets can be tuned from 2.34 cm2 V−1 s−1 (SnS2) to 71.30 cm2 V−1 s−1 (SnSe2) by controlling the S composition in the alloy. Furthermore, the carrier mobility of SnSeS increase from 10.34 to 12.16 cm2 V−1 s−1 under illumination, showing excellent optoelectronic properties. Our study suggests that SnSe2(1−x)S2x nanosheets is a highly qualified 2D materials for next-generation nanoelectronics and optoelectronics application.
Co-reporter:Cong Wang, Shengxue Yang, Wenqi Xiong, Congxin Xia, Hui Cai, Bin Chen, Xiaoting Wang, Xinzheng Zhang, Zhongming Wei, Sefaattin Tongay, Jingbo Li and Qian Liu
Physical Chemistry Chemical Physics 2016 - vol. 18(Issue 40) pp:NaN27753-27753
Publication Date(Web):2016/09/02
DOI:10.1039/C6CP04752A
Vertically stacked van der Waals (vdW) heterojunctions of two-dimensional (2D) transition metal dichalcogenides (TMDs) have attracted a great deal of attention due to their fascinating properties. In this work, we report two important gate-tunable phenomena in new artificial vdW p–n heterojunctions created by vertically stacking p-type multilayer ReSe2 and n-type multilayer WS2: (1) well-defined strong gate-tunable diode-like current rectification across the p–n interface is observed, and the tunability of the electronic processes is attributed to the tunneling-assisted interlayer recombination induced by majority carriers across the vdW interface; (2) the distinct ambipolar behavior under gate voltage modulation both at forward and reverse bias voltages is found in the vdW ReSe2/WS2 heterojunction transistors and a corresponding transport model is proposed for the tunable polarity behaviors. The findings may provide some new opportunities for building nanoscale electronic and optoelectronic devices.
Co-reporter:Meili Wang, Yan Wang and Jingbo Li
Chemical Communications 2011 - vol. 47(Issue 40) pp:NaN11248-11248
Publication Date(Web):2011/09/19
DOI:10.1039/C1CC15310B
A novel composite photoanode with ZnO nanowire arrays coating on the top of TiO2 nanoparticles is fabricated, and an efficiency of 4.52% is achieved for the composite cell, far higher than both 0.90% of the ZnO nanowire cell and 3.56% of the TiO2 nanoparticle cell. The improved efficiency is resulted from the high surface area of nanoparticles, as well as fast electron transport and light scattering effect of nanowires.
Co-reporter:Mianzeng Zhong, Le Huang, Hui-Xiong Deng, Xiaoting Wang, Bo Li, Zhongming Wei and Jingbo Li
Journal of Materials Chemistry A 2016 - vol. 4(Issue 27) pp:NaN6499-6499
Publication Date(Web):2016/05/09
DOI:10.1039/C6TC00918B
As a precursor of perovskites, lead iodide (PbI2) is a typical layered material with a direct bandgap. Perovskites are widely utilized in highly efficient photovoltaics, but the low-dimensional PbI2 nanostructures and their (opto)electronic properties are rarely reported. Herein, single-crystalline PbI2 nanosheets (phase I) and nanowires (phase II) are controllably synthesized via a facile physical vapor deposition method. Their different crystal morphology and crystallographic symmetry show obvious phase dependence. The corresponding photodetectors on both SiO2/Si and flexible polyethylene terephthalate (PET) substrates are investigated systematically. Compared with PbI2 nanowire based photodetectors, PbI2 nanosheet based photodetectors exhibit a relatively high sensitivity (with a high photoresponsivity of 147.6 A W−1 and fast response time) to the 450 nm laser. Both the PbI2 nanosheet and nanowire devices with flexible PET substrates exhibit comparable performance to their photodetectors fabricated on SiO2/Si, and also show excellent mechanical stability and durability. At the same time, the photoelectric properties vary greatly with different bending angles for such flexible PbI2 photodetectors. By modeling the band structures under different compressive strains, the theoretical simulations fit very well with experimental results. These findings provide a scientific basis for exploiting high-performance flexible photodetectors based on low-dimensional PbI2 single crystals.
Co-reporter:Juehan Yang, Fangyuan Lu, Yan Li, Shengxue Yang, Renxiong Li, Nengjie Huo, Chao Fan, Zhongming Wei, Jingbo Li and Shu-Shen Li
Journal of Materials Chemistry A 2014 - vol. 2(Issue 6) pp:NaN1040-1040
Publication Date(Web):2013/11/13
DOI:10.1039/C3TC32142H
α-MoO3 nanosheets were synthesized by a water bath method using ammonium heptamolybdenum tetrahydrate and concentrated nitric acid as precursors. Hydrogen was doped by a chemical reduction in aqueous acidic media, with hydrazine hydrate used as the reducing agent. Temperature dependent resistance showed that the low temperature Peierls transition of H-doped MoO3 nanosheets breaks below 50 K, and its resistance is satisfied at temperatures lower than 37 K (37–10 K). This phenomenon was induced by thermal disturbance and the dominance of defects in low temperature transport, which was confirmed by photoresponse measurements taken before and after the break of the new phase.
Co-reporter:Sijie Liu, Nengjie Huo, Sheng Gan, Yan Li, Zhongming Wei, Beiju Huang, Jian Liu, Jingbo Li and Hongda Chen
Journal of Materials Chemistry A 2015 - vol. 3(Issue 42) pp:NaN10980-10980
Publication Date(Web):2015/09/11
DOI:10.1039/C5TC01809A
The crystalline thin layer of black phosphorus (BP) has emerged as a new category of two-dimensional (2D) materials very recently, due to its tunable direct bandgap, promising physical properties, and potential applications in optoelectronics. Herein, the Raman scattering properties of the few layers of BP including the frequency shift and the intensity of the A1g, B2g and A2g modes have been studied in detail and they show obvious dependence on thickness and light polarization. The optoelectronic performances of few-layer black phosphorus including field-effect properties and photosensitivity to laser light with different wavelengths are also investigated. The optoelectronic parameters including the current modulation, mobility, photoresponsivity and response time vary distinctly with the layer thickness. At room temperature, the obvious bipolar transport properties are obtained (with the hole and electron mobility as high as 240 and 2 cm2 V−1 s−1, respectively) in the thicker (15 nm) BP devices, while the thinner (9 nm) BP only shows P-type transportation. The photoresponsivity of BP devices under different laser light illumination reaches several tens of mA W−1, which demonstrates their excellent photo-responsive properties and broadband detection. The thinner (9 nm) BP shows a high photoresponsivity of 64.8 mA W−1 at the communication band of 1550 nm, which is much larger than that of the thicker sample. Our findings reveal that the charge transport and infrared photo-response properties of BP are excellent, and diverse and can be intentionally designed through the thickness control. Such results also suggest BP's great potential in nanoelectronic devices and photodetection from the visible light up to the communication band (infrared light).
Co-reporter:Nengjie Huo, Shengxue Yang, Zhongming Wei and Jingbo Li
Journal of Materials Chemistry A 2013 - vol. 1(Issue 25) pp:NaN4007-4007
Publication Date(Web):2013/04/18
DOI:10.1039/C3TC30527A
Tungsten oxide (WO3) nanostructures such as nanowires, nanorod bundles and nanotube bundles are synthesized by a facile hydrothermal method. The ultraviolet (UV) photoresponse characteristics of devices containing these WO3 nanostructures are investigated for the first time and new photosensitive mechanisms involving both photo-generated electron–hole pairs and reversible electrochemical reactions are proposed. We find that h-WO3 nanowires with large specific surface areas and fewer defects exhibit excellent UV photoresponse properties with switch ratios (defined as Iphoto/Idark) as high as 60, which is due to the existing large tunnels serving as channels and intercalation sites for mobile ions and active electrochemical reactions, and our findings provide a new family and more selectivity for UV photosensitive nanomaterials in the future.
Co-reporter:Yujue Yang, Nengjie Huo and Jingbo Li
Journal of Materials Chemistry A 2017 - vol. 5(Issue 28) pp:NaN7056-7056
Publication Date(Web):2017/06/29
DOI:10.1039/C7TC01806A
Two-dimensional (2D) material based photovoltaic devices have attracted attention due to their atomically thin profile, strong light–matter interaction and mechanical flexibility. van der Waals heterojunctions, assembled with different 2D materials and a homojunction, are achieved with a doping technique and have been demonstrated to have considerable photovoltaic properties. Here, a more facile approach is proposed to realise an in-plane MoSe2 homojunction with a gate tunable and highly efficient photovoltaic effect. By applying a negative back gate, the device can exhibit a current rectification ratio as high as 105 and a significant Voc of 0.24 V under illumination. The high power conversion efficiency of 1.9% and high photo-responsivity of 550 A W−1 with a fast temporal response of 10 ms indicate that our MoSe2 homojunction based device is a promising candidate in photovoltaic and photodetection applications.
Co-reporter:Qingtian Zhang, K. S. Chan and Jingbo Li
Physical Chemistry Chemical Physics 2017 - vol. 19(Issue 9) pp:NaN6877-6877
Publication Date(Web):2017/02/08
DOI:10.1039/C6CP06972J
We study the spin-dependent transport properties of graphene nanoribbons with Rashba spin–orbit interaction (SOI). It is found that highly spin polarized electrical currents can be produced in asymmetrically-notched graphene nanoribbons, and the polarization components are found to be along the x, y and z directions. The spin polarization is largely enhanced by breaking the spatial symmetries of ideal graphene nanoribbons with Rashba SOI, and the spin polarized electrical currents with higher flexibility in the orientation of the polarization can be generated. This offers new possibilities for the generation of high spin polarization in graphene nanoribbons without external magnetic fields.
