Co-reporter:Feng Wang;Zhenxing Wang;Tofik Ahmed Shifa;Yao Wen;Fengmei Wang;Xueying Zhan;Qisheng Wang;Kai Xu;Yun Huang;Lei Yin;Chao Jiang
Advanced Functional Materials 2017 Volume 27(Issue 19) pp:
Publication Date(Web):2017/05/01
DOI:10.1002/adfm.201603254
Holding novel physical properties, high flexibility and strong integration ability with Si-based electronic devices, two-dimensional (2D) non-layered materials have received considerable attentions in recent years. To achieve the 2D anisotropic growth, various strategies have been developed. And a variety of applications have been demonstrated. This review provides an overview on the recent progress of this material family. The scope will cover the preparation strategies, including dry methods and wet chemical approaches, as well as the applications in catalysis, energy conversion and storage, optoelectronic devices and topological crystalline insulators. Conclusion and future perspectives are also given.
Co-reporter:Ruiqing Cheng;Yao Wen;Lei Yin;Fengmei Wang;Feng Wang;Kaili Liu;Tofik Ahmed Shifa;Jie Li;Chao Jiang;Zhenxing Wang
Advanced Materials 2017 Volume 29(Issue 35) pp:
Publication Date(Web):2017/09/01
DOI:10.1002/adma.201703122
Due to the novel physical properties, high flexibility, and strong compatibility with Si-based electronic techniques, 2D nonlayered structures have become one of the hottest topics. However, the realization of 2D structures from nonlayered crystals is still a critical challenge, which requires breaking the bulk crystal symmetry and guaranteeing the highly anisotropic crystal growth. CdTe owns a typical wurtzite crystal structure, which hinders the 2D anisotropic growth of hexagonal-symmetry CdTe. Here, for the first time, the 2D anisotropic growth of ultrathin nonlayered CdTe as thin as 4.8 nm via an effective van der Waals epitaxy method is demonstrated. The anisotropic ratio exceeds 103. Highly crystalline nanosheets with uniform thickness and large lateral dimensions are obtained. The in situ fabricated ultrathin 2D CdTe photodetector shows ultralow dark current (≈100 fA), as well as high detectivity, stable photoswitching, and fast photoresponse speed (τrising = 18.4 ms, τdecay = 14.7 ms). Besides, benefitting from its 2D planar geometry, CdTe nanosheet exhibits high compatibility with flexible substrates and traditional microfabrication techniques, indicating its significant potential in the applications of flexible electronic and optoelectronic devices.
Co-reporter:Junwei Chu;Fengmei Wang;Lei Yin;Le Lei;Chaoyi Yan;Feng Wang;Yao Wen;Zhenxing Wang;Chao Jiang;Liping Feng;Jie Xiong;Yanrong Li
Advanced Functional Materials 2017 Volume 27(Issue 32) pp:
Publication Date(Web):2017/08/01
DOI:10.1002/adfm.201701342
2D materials, represented by transition metal dichalcogenides (TMDs), have attracted tremendous research interests in photoelectronic and electronic devices. However, for their relatively small bandgap (<2 eV), the application of traditional TMDs into solar-blind ultraviolet (UV) photodetection is restricted. Here, for the first time, NiPS3 nanosheets are grown via chemical vapor deposition method. The nanosheets thinning to 3.2 nm with the lateral size of dozens of micrometers are acquired. Based on the various nanosheets, a linearity is found between the Raman intensity of specific Ag modes and the thickness, providing a convenient method to determine their layer numbers. Furthermore, a UV photodetector is fabricated using few-layered 2D NiPS3 nanosheets. It shows an ultrafast rise time shorter than 5 ms with an ultralow dark current less than 10 fA. Notably, this UV photodetector demonstrates a high detectivity of 1.22 × 1012 Jones, outperforming some traditional wide-bandgap UV detectors. The wavelength-dependent photoresponsivity measurement allows the direct observation of an admirable cut-off wavelength at 360 nm, which indicates a superior spectral selectivity. The promising photodetector performance, accompanied with the controllable fabrication and transfer process of nanosheet, lays the foundation of applying 2D semiconductors for ultrafast UV light detection.
Co-reporter:Kaili Liu;Fengmei Wang;Tofik Ahmed Shifa;Zhenxing Wang;Kai Xu;Yu Zhang;Zhongzhou Cheng;Xueying Zhan
Nanoscale (2009-Present) 2017 vol. 9(Issue 11) pp:3995-4001
Publication Date(Web):2017/03/17
DOI:10.1039/C7NR00460E
Developing earth-abundant and efficient bifunctional electrocatalysts for realizing the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) under alkaline conditions is an intriguing challenge. Here, ternary necklace-like CoP2xSe2(1−x) nanowire arrays are synthesized via simultaneously phosphorizing and selenizing Co(OH)2 nanowires. Owing to the substitution of the P atom in the ternary system, the optimal electronic structure of CoP2xSe2(1−x) can be obtained and the stability can also be enhanced for hydrogen evolution. Thus, the ternary CoP2xSe2(1−x) NWs are highly active for electrochemical hydrogen evolution in both acidic and alkaline media, achieving a current density of 10 mA cm −2 at overpotentials of 70 mV and 98 mV, respectively. To realize the overall water splitting, we further performed the experiment using the CoP2xSe2(1−x) NWs as a cathode and Co(OH)2 NWs as an anode, which requires a cell voltage of 1.65 V to afford a water splitting current density of 10 mA cm −2 in strong alkaline media (1.0 M KOH).
Co-reporter:Yu Zhang;Kaili Liu;Fengmei Wang;Tofik Ahmed Shifa;Yao Wen;Feng Wang;Kai Xu;Zhenxing Wang;Chao Jiang
Nanoscale (2009-Present) 2017 vol. 9(Issue 17) pp:5641-5647
Publication Date(Web):2017/05/04
DOI:10.1039/C7NR00895C
Two-dimensional transition-metal dichalcogenides (TMDs) have attracted much research interest in the hydrogen evolution reaction (HER) due to their superior electrocatalytic properties. Beyond binary TMDs, ternary TMD alloys, as electrocatalysts, were also gradually acknowledged for their remarkable efficiency in HER. Herein, we successfully synthesized monolayer dendritic ternary WS2(1−x)Se2x flakes possessing abundant active edge sites on a single crystalline SrTiO3 (STO(100)). And the obtained dendritic WS2(1−x)Se2x flakes could be transferred intact to arbitrary substrates, for example, SiO2/Si and Au foils. Intriguingly, the transferred dendritic WS2(1−x)Se2x flakes on Au foil demonstrate a significant HER performance, reflected by a rather lower Tafel slope of ∼69 mV dec−1 and a much higher exchange current density of ∼50.1 μA cm−2 outshining other CVD-grown two-dimensional TMD flakes. Furthermore, our new material shows excellent stability in electro-catalyzing the HER, suggestive of its robustness for being an excellent electrocatalyst. We believe that this work broadens the outlook for the synthesis of two-dimensional TMDs toward satisfying the applications in electrocatalysis.
Co-reporter:Ji Dong;Fengjing Liu;Feng Wang;Jiawei Wang;Molin Li;Yao Wen;Liang Wang;Gongtang Wang;Chao Jiang
Nanoscale (2009-Present) 2017 vol. 9(Issue 22) pp:7519-7525
Publication Date(Web):2017/06/08
DOI:10.1039/C7NR01822C
Recently, van der Waals heterostructures (vdWHs) have trigged intensive interest due to their novel electronic and optoelectronic properties. The vdWHs could be achieved by stacking two dimensional layered materials (2DLMs) on top of another and vertically kept by van der Waals forces. Furthermore, organic semiconductors are also known to interact via van der Waals forces, which offer an alternative for the fabrication of organic–inorganic p–n vdWHs. However, the performances of organic–inorganic p–n vdWHs produced so far are rather poor, owing to the unmatched electrical property between the 2DLMs and organic polycrystalline films. To make improvements in such novel heterostructure architectures, here we adopt high quality organic single crystals instead of polycrystalline films to construct a pentacene/MoS2 p–n vdWH. The vdWHs show a much higher current density and better anti-ambipolar characteristics with a highest transconductance of 211 nS. Moreover, device configuration-dependent transfer characteristics are demonstrated and a mechanism of a gate bias modulated vertical space charge zone existing at the vertical p–n vdWHs interface is proposed. These findings provide a new route to optimize the organic–inorganic p–n vdWHs and a guideline for studying the intrinsic properties of vdWHs.
Co-reporter:Kai Xu, Dongxue Chen, Fengyou Yang, Zhenxing Wang, Lei Yin, Feng Wang, Ruiqing Cheng, Kaihui LiuJie Xiong, Qian Liu, Jun He
Nano Letters 2017 Volume 17(Issue 2) pp:
Publication Date(Web):January 16, 2017
DOI:10.1021/acs.nanolett.6b04576
Two-dimensional materials (2DMs) are competitive candidates in replacing or supplementing conventional semiconductors owing to their atomically uniform thickness. However, current conventional micro/nanofabrication technologies realize hardly ultrashort channel and integration, especially for sub-10 nm. Meanwhile, experimental device performance associated with the scaling of dimension needs to be investigated, due to the short channel effects. Here, we show a novel and universal technological method to fabricate sub-10 nm gaps with sharp edges and steep sidewalls. The realization of sub-10 nm gaps derives from a corrosion crack along the cleavage plane of Bi2O3. By this method, ultrathin body field-effect transistors (FETs), consisting of 8.2 nm channel length, 6 nm high-k dielectric, and 0.7 nm monolayer MoS2, exhibit no obvious short channel effects. The corresponding current on/off ratio and subthreshold swing reaches to 106 and 140 mV/dec, respectively. Moreover, integrated circuits with sub-10 nm channel are capable of operating as digital inverters with high voltage gain. The results suggest our technological method can be used to fabricate the ultrashort channel nanopatterns, build the experimental groundwork for 2DMs FETs with sub-10 nm channel length and 2DMs integrated circuits, and offer new potential opportunities for large-scale device constructions and applications.Keywords: 2D materials; field-effect transistors; nanopatterns; Sub-10 nm; very-large-scale integration;
Co-reporter:Fengmei Wang, Tofik Ahmed Shifa, Peng He, Zhongzhou Cheng, Junwei Chu, Yang Liu, Zhenxing Wang, Feng Wang, Yao Wen, Lirong Liang, Jun He
Nano Energy 2017 Volume 40(Volume 40) pp:
Publication Date(Web):1 October 2017
DOI:10.1016/j.nanoen.2017.09.017
•Large-scale ultrathin (≤ 3.5 nm)hexagonal NiPS3 nanosheets are successfully synthesized through chemical vapor deposition (CVD) method.•The synthesized NiPS3 nanosheets can act as a novel photocatalyst to decompose water for H2 generation under solar light irradiation without any co-catalyst or sacrificial agents.•The band structure of the 2D ultrathin NiPS3 was systematically studied via using ultraviolet photoelectron spectrometer and electrochemical impedance spectroscopy.The development and utilization of photocatalysts to realize water-splitting without any external bias or sacrificial agents has received the limelight. As a novel two-dimensional layered material, metal phosphorus trichalcogenides (MPTs) cause wide research interest, presently. However, the growth of ultrathin two-dimensional MPT crystals is a great challenge to hinder their application. Here, we initially grow few-atomic layered nickel phosphorus trisulfide (NiPS3) as promising photocatalyst for hydrogen evolution. The as-prepared NiPS3 hexagonal nanosheet, as thin as few atomic layers (≤ 3.5 nm), has lateral size of larger than 15 µm. These ultrathin NiPS3 crystals can directly generate hydrogen gas from pure water without any sacrificial agents under sunlight. With ultraviolet photoelectron spectrometer and electrochemical impedance spectroscopy, we show that the attractive photocatalytic activity of the ultrathin NiPS3 crystals arise from their appropriate positions of the band edges. This discovery is expected to make a contribution to develop next generation solar-fuel conversion catalysts for H2 production.Large-scale ultrathin nickel phosphorus trisulfide (NiPS3) hexagonal nanosheets are successfully synthesized through chemical vapor deposition (CVD) method in this work. The lateral size of the NiPS3 nanosheet, as thin as 3.5 nm, is larger than 15 µm. Notably, these NiPS3 nanosheets demonstrate high crystal quality and intriguing solar-driven water splitting photocatalysis in pure water.Download high-res image (336KB)Download full-size image
Co-reporter:Qisheng Wang;Kaiming Cai;Jie Li;Yun Huang;Zhenxing Wang;Kai Xu;Feng Wang;Xueying Zhan;Fengmei Wang;Kaiyou Wang
Advanced Materials 2016 Volume 28( Issue 4) pp:617-623
Publication Date(Web):
DOI:10.1002/adma.201504630
Co-reporter:Qisheng Wang;Jie Li;Yin Lei;Yao Wen;Zhenxing Wang;Xueying Zhan;Feng Wang;Fengmei Wang;Yun Huang;Kai Xu
Advanced Materials 2016 Volume 28( Issue 18) pp:3596-3601
Publication Date(Web):
DOI:10.1002/adma.201506338
Co-reporter:Qisheng Wang;Yao Wen;Peng He;Lei Yin;Zhenxing Wang;Feng Wang;Kai Xu;Yun Huang;Fengmei Wang;Chao Jiang
Advanced Materials 2016 Volume 28( Issue 30) pp:6497-6503
Publication Date(Web):
DOI:10.1002/adma.201601071
Co-reporter:Yao Wen, Lei Yin, Peng He, Zhenxing Wang, XianKun Zhang, Qisheng Wang, Tofik Ahmed Shifa, Kai Xu, Fengmei Wang, Xueying Zhan, Feng Wang, Chao Jiang, and Jun He
Nano Letters 2016 Volume 16(Issue 10) pp:6437-6444
Publication Date(Web):September 29, 2016
DOI:10.1021/acs.nanolett.6b02881
Molybdenum disulfide (MoS2) has attracted a great deal of attention in optoelectronic applications due to its high mobility, low off-state current and high on/off ratio. However, its intrinsic large bandgap limits its application in infrared detection. Here, we have developed a high-performance infrared photodetector by integrating nonlayered PbS and layered MoS2 nanostructures via van der Waals epitaxy. Density functional theory (DFT) calculations indicate that PbS nanoplates are in contact with MoS2 edges through strong chemical hybridization, which is expected to offer a fast transmission path for carriers that enhances the response speed. The phototransistor exhibits a fast response (τrising = τdecay = 7.8 ms) as well as high photoresponsivity (4.5 × 104 A·W–1) and Ilight/Idark (1.3 × 102) in the near-infrared spectral region at room temperature. In particular, the detectivity (D*) is as high as 3 × 1013 Jones, which is even better than that of commercial Si and InGaAs photodetectors. Furthermore, by controlling the growth and microfabrication patterning, periodic device arrays of PbS–MoS2 that are capable of infrared detection are achieved on Si/SiO2 substrates. Our work provides a possible method for the integration of photodetector arrays on Si-based electronic devices and lays a solid foundation for the practical applications of MoS2-based devices in the future.Keywords: edge contact; infrared phototransistor; integration; nonlayered PbS−MoS2 heterostructure;
Co-reporter:Feng Wang;Lei Yin;Zhen Xing Wang;Kai Xu;Feng Mei Wang;Tofik Ahmed Shifa;Yun Huang;Chao Jiang
Advanced Functional Materials 2016 Volume 26( Issue 30) pp:5499-5506
Publication Date(Web):
DOI:10.1002/adfm.201601349
Van der Waals heterostructures (vdWHs), obtained by artificially stacking 2D layered material (2DLM) plains upon each other, are brand new structures that have exhibited novel electronic and optoelectronic properties and attracted a great deal of attention. So far, the results are only based on devices with symmetrical configurations: devices predominated by vdWH parts, or cross-like configurations combined with both vdWHs and extra individual 2DLM layers. Quite different gate tunable phenomena have been observed for these two configurations even though 2DLMs with similar band alignments were used, which may be due to the different device configurations utilized. For a deeper understanding, rational investigation on configuration-dependent properties of vdWHs is needed. Here, using MoTe2/MoS2 as an example, vdWH device is artificially designed with two asymmetrical configurations. Through comparing the respective results, it is found that the properties that stem only from the vdWH, i.e., the rectification behavior and open voltage in photovoltaic effect, are independent of the device structures. However, other properties, i.e., drain currents, short circuit currents, and photoreponse performances, strongly depend on the configuration used. These results give a guideline on studying the intrinsic properties of vdWHs and optimizing the device structures for better performances.
Co-reporter:Zhenxing Wang, Feng Wang, Lei Yin, Yun Huang, Kai Xu, Fengmei Wang, Xueying Zhan and Jun He
Nanoscale 2016 vol. 8(Issue 27) pp:13245-13250
Publication Date(Web):13 Jun 2016
DOI:10.1039/C6NR02231F
Because of their ultimate thickness, layered structure and high flexibility, pn junctions based on layered two-dimensional semiconductors have been attracting increasing attention recently. In this study, for the first time, we fabricated lateral pn junctions (LPNJs) based on ultrathin MoTe2 by introducing two separated electrostatic back gates, and investigated their electronic and photovoltaic performance. Pn, np, nn, and pp junctions can be easily realized by modulating the conductive channel type using gate voltages with different polarities. Strong rectification effects were observed in the pn and np junctions and the rectification ratio reached ∼5 × 104. Importantly, we find a unique phenomenon that the parameters for MoTe2 LPNJs experience abrupt changes during the transition from p to n or n to p. Furthermore, a high performance photovoltaic device with a filling factor of above 51% and electrical conversion efficiency (η) of around 0.5% is achieved. Our findings are of importance to comprehensively understand the electronic and optoelectronic properties of MoTe2 and may further open up novel electronic and optoelectronic device applications.
Co-reporter:Kaili Liu, Fengmei Wang, Kai Xu, Tofik Ahmed Shifa, Zhongzhou Cheng, Xueying Zhan and Jun He
Nanoscale 2016 vol. 8(Issue 8) pp:4699-4704
Publication Date(Web):22 Jan 2016
DOI:10.1039/C5NR07735D
Binary transition metal dichalcogenides (TMDs) have emerged as efficient catalysts for the hydrogen evolution reaction (HER). Co-based TMDs, such as CoS2 and CoSe2, demonstrate promising HER performance due to their intrinsic metallic nature. Recently, the ternary electrocatalysts were widely acknowledged for their prominent efficiency as compared to their binary counterparts due to increased active sites caused by the incorporation of different atoms. Herein, we successfully grew the ternary CoS2xSe2(1−x) (x = 0.67) nanowires (NWs) on a flexible carbon fiber. As a superior electrocatalyst, ternary CoS2xSe2(1−x) NWs arrays demonstrated excellent catalytic activity for electrochemical hydrogen evolution in acidic media, achieving current densities of 10 mA cm−2 and 100 mA cm−2 at overpotentials of 129.5 mV and 174 mV, respectively. Notably, the high stability of CoS2xSe2(1−x) NWs suggested that the ternary CoS2xSe2(1−x) NWs are a scalable catalyst for electrochemical hydrogen evolution.
Co-reporter:Fengmei Wang; Yuanchang Li;Tofik Ahmed Shifa;Kaili Liu;Feng Wang; Zhenxing Wang;Peng Xu;Qisheng Wang; Jun He
Angewandte Chemie 2016 Volume 128( Issue 24) pp:7033-7038
Publication Date(Web):
DOI:10.1002/ange.201602802
Abstract
To address the urgent need for clean and sustainable energy, the rapid development of hydrogen-based technologies has started to revolutionize the use of earth-abundant noble-metal-free catalysts for the hydrogen evolution reaction (HER). Like the active sites of hydrogenases, the cation sites of pyrite-type transition-metal dichalcogenides have been suggested to be active in the HER. Herein, we synthesized electrodes based on a Se-enriched NiSe2 nanosheet array and explored the relationship between the anion sites and the improved hydrogen evolution activity through theoretical and experimental studies. The free energy for atomic hydrogen adsorption is much lower on the Se sites (0.13 eV) than on the Ni sites (0.87 eV). Notably, this electrode benefits from remarkable kinetic properties, with a small overpotential of 117 mV at 10 mA cm−2, a low Tafel slope of 32 mV per decade, and excellent stability. Control experiments showed that the efficient conversion of H+ into H2 is due to the presence of an excess of selenium in the NiSe2 nanosheet surface.
Co-reporter:Fengmei Wang; Yuanchang Li;Tofik Ahmed Shifa;Kaili Liu;Feng Wang; Zhenxing Wang;Peng Xu;Qisheng Wang; Jun He
Angewandte Chemie International Edition 2016 Volume 55( Issue 24) pp:6919-6924
Publication Date(Web):
DOI:10.1002/anie.201602802
Abstract
To address the urgent need for clean and sustainable energy, the rapid development of hydrogen-based technologies has started to revolutionize the use of earth-abundant noble-metal-free catalysts for the hydrogen evolution reaction (HER). Like the active sites of hydrogenases, the cation sites of pyrite-type transition-metal dichalcogenides have been suggested to be active in the HER. Herein, we synthesized electrodes based on a Se-enriched NiSe2 nanosheet array and explored the relationship between the anion sites and the improved hydrogen evolution activity through theoretical and experimental studies. The free energy for atomic hydrogen adsorption is much lower on the Se sites (0.13 eV) than on the Ni sites (0.87 eV). Notably, this electrode benefits from remarkable kinetic properties, with a small overpotential of 117 mV at 10 mA cm−2, a low Tafel slope of 32 mV per decade, and excellent stability. Control experiments showed that the efficient conversion of H+ into H2 is due to the presence of an excess of selenium in the NiSe2 nanosheet surface.
Co-reporter:Kai Xu;Zhenxing Wang;Feng Wang;Yun Huang;Fengmei Wang;Lei Yin;Chao Jiang
Advanced Materials 2015 Volume 27( Issue 47) pp:7881-7887
Publication Date(Web):
DOI:10.1002/adma.201503864
Co-reporter:Qisheng Wang, Kai Xu, Zhenxing Wang, Feng Wang, Yun Huang, Muhammad Safdar, Xueying Zhan, Fengmei Wang, Zhongzhou Cheng, and Jun He
Nano Letters 2015 Volume 15(Issue 2) pp:1183-1189
Publication Date(Web):January 20, 2015
DOI:10.1021/nl504258m
Despite great progress in synthesis and application of graphene-like materials, it remains a considerable challenge to prepare two-dimensional (2D) nanostructures of nonlayered materials that may bring us surprising physical and chemical properties. Here, we propose a general strategy for the growth of 2D nonlayered materials by van der Waals epitaxy (vdWE) growth with two conditions: (1) the nonlayered materials satisfy 2D anisotropic growth and (2) the growth is implemented on the van der Waals substrates. Large-scale ultrathin 2D Pb1–xSnxSe nanoplates (∼15–45 nm) have been produced on mica sheets by applying this strategy. Benefiting from the 2D geometry of Pb1–xSnxSe nanoplates and the flexibility of mica sheet, flexible photodetectors that exhibit fast, reversible, and stable photoresponse and broad spectra detection ranging from UV to infrared light (375, 473, 632, 800, and 980 nm) are in situ fabricated based on Pb1–xSnxSe nanoplates. We anticipate that more nonlayered materials will be developed into 2D nanostructures through vdWE, enabling the exploitation of novel electronic and optoelectronic devices.
Co-reporter:Muhammad Safdar, Qisheng Wang, Zhenxing Wang, Xueying Zhan, Kai Xu, Fengmei Wang, Misbah Mirza, and Jun He
Nano Letters 2015 Volume 15(Issue 4) pp:2485-2490
Publication Date(Web):March 2, 2015
DOI:10.1021/nl504976g
Pb1–xSnxTe is a unique topological crystalline insulator (TCI) that undergoes a topological phase transition from topological trivial insulator to TCI with the change of Sn content and temperature. Meanwhile, the surface states properties of Pb1–xSnxTe are strongly dependent on crystallographic plane orientation. In this work, we first reported controllable synthesis of rectangular prismatic PbxSn1–xTe nanowires by vapor deposition method. Rectangular prismatic PbxSn1–xTe nanowires exhibits distinct {100} surfaces. Furthermore, The Sn composition of Pb1–xSnxTe nanowires can be continuously controlled from 0 to 1. Low temperature magnetotransport shows that PbTe nanowire exhibits weak localization (WL) effect, whereas Pb0.5Sn0.5Te and Pb0.2Sn0.8Te nanowires display pronounced weak antilocalization (WAL) effect. This transition is explained by the topological phase transform of Pb1–xSnxTe from trivial to nontrivial insulator with Sn content (x) exceeding 0.38. PbxSn1–xTe nanowires synthesized in this work lay a foundation for probing spin-correlated electron transport and show great potentials for future applications of tunable spintronic devices.
Co-reporter:Feng Wang, Zhenxing Wang, Kai Xu, Fengmei Wang, Qisheng Wang, Yun Huang, Lei Yin, and Jun He
Nano Letters 2015 Volume 15(Issue 11) pp:7558-7566
Publication Date(Web):October 15, 2015
DOI:10.1021/acs.nanolett.5b03291
P-n junctions based on vertically stacked van der Waals (vdW) materials have attracted a great deal of attention and may open up unforeseen opportunities in electronics and optoelectronics. However, due to the lack of intrinsic p-type vdW materials, most previous studies generally adopted electrical gating, special electrode contacts, or chemical doping methods to realize p-n vdW junctions. GaTe is an intrinsic p-type vdW material with a relatively high charge density, and it has a direct band gap that is independent of thickness. Here, we report the construction of ultrathin and tunable p-GaTe/n-MoS2 vdW heterostructure with high photovoltaic and photodetecting performance. The rectification ratio, external quantum efficiency, and photoresponsivity are as high as 4 × 105, 61.68%, and 21.83 AW–1, respectively. In particular, the detectivity is up to 8.4 × 1013 Jones, which is even higher than commercial Si, InGaAs photodetectors. This study demonstrates the promising potential of p-GaTe/n-MoS2 heterostructures for next-generation electronic and optoelectronic devices.
Co-reporter:Fengmei Wang;Jinshan Li;Feng Wang;Tofik Ahmed Shifa;Zhongzhou Cheng;Zhenxing Wang;Kai Xu;Xueying Zhan;Qisheng Wang;Yun Huang;Chao Jiang
Advanced Functional Materials 2015 Volume 25( Issue 38) pp:6077-6083
Publication Date(Web):
DOI:10.1002/adfm.201502680
As an effective alternative to noble platinum electrocatalyst, earth abundant and inexpensive layered transition metal dichalcogenides (TMDs) are investigated for the hydrogen evolution reaction (HER). Compared with binary TMDs, the tunably composed ternary TMDs have hitherto received relatively little attention. Here, few-layered ternary WS2(1−x)Se2x nanoribbons (NRs) with metallic 1T phases, much more catalytically active in HER, are prepared for the first time. The favorable ΔGHo introduced by the tensile region on the surface, along with the presence of local lattice distortions of the WS2(1−x)Se2x nanoribbons with metallic 1T phases, greatly promotes the HER process. These ternary NRs achieve the lowest overpotential of ≈0.17 V at 10 mA cm−2 and a Tafel slope of ≈68 mV dec−1 at a low catalyst loading (≈0.30 ± 0.02 mg cm−2). Notably, the long-term durability suggests the potential of practical applications in acid electrolytes. The results here suggest that the ternary WS2(1−x)Se2x NRs with 1T phases are prominent alternatives to platinum-based HER electrocatalysts.
Co-reporter:Fengmei Wang, Tofik Ahmed Shifa, Xueying Zhan, Yun Huang, Kaili Liu, Zhongzhou Cheng, Chao Jiang and Jun He
Nanoscale 2015 vol. 7(Issue 47) pp:19764-19788
Publication Date(Web):06 Nov 2015
DOI:10.1039/C5NR06718A
The desire for sustainable and clean energy future continues to be the concern of the scientific community. Researchers are incessantly targeting the development of scalable and abundant electro- or photo-catalysts for water splitting. Owing to their suitable band-gap and excellent stability, an enormous amount of transition-metal dichalcogenides (TMDs) with hierarchical nanostructures have been extensively explored. Herein, we present an overview of the recent research progresses in the design, characterization and applications of the TMD-based electro- or photo-catalysts for hydrogen and oxygen evolution. Emphasis is given to the layered and pyrite-phase structured TMDs encompassing semiconducting and metallic nanomaterials. Illustrative results and the future prospects are pointed out. This review will provide the readers with insight into the state-of-the-art research progresses in TMD based nanomaterials for water splitting.
Co-reporter:Yun Huang, Kai Xu, Zhenxing Wang, Tofik Ahmed Shifa, Qisheng Wang, Feng Wang, Chao Jiang and Jun He
Nanoscale 2015 vol. 7(Issue 41) pp:17375-17380
Publication Date(Web):21 Sep 2015
DOI:10.1039/C5NR05989E
Layered chalcogenide materials (LCMs) are emerging materials in recent years for their great potential in applications of electronics and optoelectronics. As a member of LCMs, SnSe2, an n-type semiconductor with a band gap of ∼1.0 eV, is of great value to explore. In this paper, we develop a facile CVD method, for the first time, to synthesize diverse shaped SnSe2 and square SnSe nanosheets (NSs) on SiO2/Si substrates. To the best of our knowledge, the thickness of as-grown SnSe2 is among the thinnest ones synthesized by CVD methods on various substrates. What's more, photodetectors are fabricated to investigate the optoelectronic properties of SnSe2. The on/off ratio of photoswitches reaches 100 under the illumination of an 800 nm laser. This work will pave a new pathway to synthesize LCM nanostructures, shed light on the shape evolution during the growth process and expand the candidates for high performance optoelectronic devices.
Co-reporter:Kai Xu, Hui-Xiong Deng, Zhenxing Wang, Yun Huang, Feng Wang, Shu-Shen Li, Jun-Wei Luo and Jun He
Nanoscale 2015 vol. 7(Issue 38) pp:15757-15762
Publication Date(Web):26 Aug 2015
DOI:10.1039/C5NR04625D
Rhenium disulphide (ReS2) is a recently discovered new member of the transition metal dichalcogenides. Most impressively, it exhibits a direct bandgap from bulk to monolayer. However, the growth of ReS2 nanosheets (NSs) still remains a challenge and in turn their applications are unexplored. In this study, we successfully synthesized high-quality ReS2 NSs via chemical vapor deposition. A high-performance field effect transistor of ReS2 NSs with an on/off ratio of ∼105 was demonstrated. Through both electrical transport measurements at varying temperatures (80 K–360 K) and first-principles calculations, we find sulfur vacancies, which exist intrinsically in ReS2 NSs and significantly affect the performance of the ReS2 FET device. Furthermore, we demonstrated that sulfur vacancies can efficiently adsorb and recognize oxidizing (O2) and reducing (NH3) gases, which electronically interact with ReS2 only at defect sites. Our findings provide experimental groundwork for the synthesis of new transition metal dichalocogenides, supply guidelines for understanding the physical nature of ReS2 FETs, and offer a new route toward tailoring their electrical properties by defect engineering in the future.
Co-reporter:Tofik Ahmed Shifa, Fengmei Wang, Zhongzhou Cheng, Xueying Zhan, Zhenxing Wang, Kaili Liu, Muhammad Safdar, Lianfeng Sun and Jun He
Nanoscale 2015 vol. 7(Issue 35) pp:14760-14765
Publication Date(Web):05 Aug 2015
DOI:10.1039/C5NR03704B
Electrocatalytic hydrogen production at low overpotential is a promising route towards a clean and sustainable energy. Layered transition metal dichalcogenides (LTMDs) have attracted copious attention for their outstanding activities in hydrogen evolution reaction (HER). However, the horizontally laid nanosheets suffer from a paucity of active edge sites. Herein, we report the successful synthesis of vertical-oriented WS2 nanosheets through a hydrothermal method followed by a facile sulfurization process. Furthermore, the surface of synthesized WS2 nanosheets was decorated by ultrathin reduced graphene oxide (rGO) nanoplates. This is achieved for the first time by bringing the rGO on the surface of vertical-oriented WS2 nanosheets, which is conducive to rapid electron transport during the HER process. Significantly, the as-synthesized rGO/WS2 nanosheets exhibit improved HER activity as compared to the undecorated ones. It needs a low overpotential of only 229 mV vs. RHE to afford a current density of 10 mA cm−2. We believe that this hybrid structure demonstrated remarkable HER activity brought about by a compatible synergism between rGO and WS2.
Co-reporter:Yun Huang, Hui-Xiong Deng, Kai Xu, Zhen-Xing Wang, Qi-Sheng Wang, Feng-Mei Wang, Feng Wang, Xue-Ying Zhan, Shu-Shen Li, Jun-Wei Luo and Jun He
Nanoscale 2015 vol. 7(Issue 33) pp:14093-14099
Publication Date(Web):28 Jul 2015
DOI:10.1039/C5NR04174K
A facile and fruitful CVD method is reported for the first time, to synthesize high-quality hexagonal SnS2 nanosheets on carbon cloth via in situ sulfurization of SnO2. Moreover, highly sensitive phototransistors based on SnS2 with an on/off ratio surpassing 106 under ambient conditions and a rising time as short as 22 ms under vacuum are fabricated, which are superior than most phototransistors based on LMDs. Electrical transport measurements at varied temperatures together with theoretical calculations verify that sulfur vacancies generated by the growth process would induce a defect level near the bottom of the conduction band, which significantly affects the performance of the SnS2 device. These findings may open up a new pathway for the synthesis of LMDs, shed light on the effects of defects on devices and expand the building blocks for high performance optoelectronic devices.
Co-reporter:Zhenxing Wang, Muhammad Safdar, Misbah Mirza, Kai Xu, Qisheng Wang, Yun Huang, Fengmei Wang, Xueying Zhan and Jun He
Nanoscale 2015 vol. 7(Issue 16) pp:7252-7258
Publication Date(Web):19 Mar 2015
DOI:10.1039/C4NR07313D
2D layered GaTe materials have attracted a great deal of attention for optoelectronic applications due to their direct band structure, whether in bulk or as a single layer. In this paper, for the first time, we have synthesized high quality, single crystalline GaTe nanosheets by employing a facile CVD method. The size of the GaTe nanosheets reached several tens of micrometers, and some of them even exceeded 100 μm. In particular, planar GaTe nanosheets were achieved on a mica substrate following a van der Waals epitaxial growth mechanism. Further, through a systematic comparison of the performances under various conditions, we found that adsorbates on the GaTe surface under ambient conditions strongly deteriorated the GaTe photodetector device performance. After removing the adsorbates in a ∼7 × 10−5 torr vacuum, a flexible, fast response GaTe photodetector with a high photoresponse, high mechanical stability and an excellent linear input–output relationship was obtained. The results presented in this study suggest that the GaTe nanosheets grown by a CVD method are promising candidates for optoelectronic applications in the future.
Co-reporter:Zhongzhou Cheng, Xueying Zhan, Fengmei Wang, Qisheng Wang, Kai Xu, Quanlin Liu, Chao Jiang, Zhenxing Wang and Jun He
RSC Advances 2015 vol. 5(Issue 99) pp:81723-81727
Publication Date(Web):18 Sep 2015
DOI:10.1039/C5RA14188E
CuInS2 has attracted much attention for application in solar energy due to its small and tunable band gap. It has demonstrated high photoelectric conversion efficiency as a photocathode for solar cells, and it is also suitable for hydrogen generation under visible light (ECBM = −0.44 eV, EVBM = 1.06 eV, vs. NHE). However, there are rare reports of water splitting based on CuInS2. In this work, a simple solution method was designed to decorate a ZnO nanowire (NW) array grown on a FTO substrate with Ag and CuInS2 nanoparticles (NPs). The photoelectrochemical (PEC) activities and hydrogen generation performances were studied. Compared with a bare ZnO NW array, a steady photocurrent increases 100-fold for the ZnO/Ag/CIS system (ZAC) under visible illumination. The solar-to-chemical energy conversion efficiency reaches up to 0.05% with excellent stability. It is expected that this conversion efficiency may be further enhanced several times by increasing the length of the ZnO NWs and controlling the distribution of CuInS2 and Ag NPs on the ZnO NWs.
Co-reporter:Fengmei Wang;Xueying Zhan;Zhongzhou Cheng;Qisheng Wang;Zhenxing Wang;Feng Wang;Kai Xu;Yun Huang;Muhammad Safdar
Advanced Electronic Materials 2015 Volume 1( Issue 4) pp:
Publication Date(Web):
DOI:10.1002/aelm.201400053
Co-reporter:Yajun Wang, Xueying Zhan, Fengmei Wang, Qisheng Wang, Muhammad Safdar and Jun He
Journal of Materials Chemistry A 2014 vol. 2(Issue 43) pp:18413-18419
Publication Date(Web):05 Sep 2014
DOI:10.1039/C4TA04293J
ZnO/ZnSxSe1−x core–shell nanowire arrays on a silicon substrate were successfully prepared via a hydrothermal method followed by chemical vapor deposition (CVD) of the ZnSxSe1−x shell. By optimizing the CVD growth conditions, a crystalline ZnSxSe1−x shell and well-aligned ZnO/ZnSxSe1−x interface were achieved, which plays an important role towards the enhanced performance of photocatalytic activity. The introduction of the crystalline, lattice-matched ZnSxSe1−x shell to ZnO nanowires significantly enhances the photocatalytic and photoelectrocatalytic activity under UV light irradiation. More attractively, after being combined with the ZnSxSe1−x shell, the visible light photoelectrocatalytic activity of the ZnO/ZnSxSe1−x core–shell nanowires is observed. The performance enhancement of ZnO/ZnSxSe1−x core–shell nanowires under irradiation is mainly due to matching lattice and band energy level alignment between the crystalline ZnSxSe1−x shell and ZnO nanowire core. The high crystal quality of the ZnSxSe1−x shell and the band alignment of the ZnO/ZnSxSe1−x core–shell greatly enhance the charge separation efficiency and prolong the life-time of photogenerated charge carriers. Our finding is expected to provide a new insight into the fabrication of novel and high performance nanowire based core–shell photocatalysts.
Co-reporter:Xueying Zhan, Qisheng Wang, Fengmei Wang, Yajun Wang, Zhenxing Wang, Jinli Cao, Muhammad Safdar, and Jun He
ACS Applied Materials & Interfaces 2014 Volume 6(Issue 4) pp:2878
Publication Date(Web):January 27, 2014
DOI:10.1021/am4054332
For highly efficient photoelectrodes, the materials used must have both a broad absorption range and large separation efficiency of photogenerated electron–hole pairs. Type II heterostructures with a ternary shell meet these two requirements and thus are recognized as being an ideal materials system for application in photocatalytic hydrogen production. Here, a ZnO/ZnxCd1–xTe core/shell nanowires array with a broad absorption edge from UV (380 nm) to NIR (855 nm) was fabricated via a chemical vapor-deposition method. More importantly, the ZnO/ZnxCd1–xTe core/shell nanowires array are highly single crystalline, and the composition can be continuously tuned by optimizing the deposition temperature, making the design of the desired photocatalyst possible. As expected, the single-crystalline ternary ZnxCd1–xTe shell greatly enhances the charge separation efficiency and prolongs the lifetime of photogenerated charge carriers, which contribute to the high photocatalytic and photoelectrocatalytic activity under light irradiation. In addition, ZnO/ZnxCd1–xTe core/shell structure show remarkable photocatalytic H2-production activity and high H2-production capability because of the synergistic light absorption of the ternary ZnxCd1–xTe shell and the formation of a type II heterostructure at the interface between the ZnO core and ZnxCd1–xTe shell. This work provides a new material platform for the design of highly efficient solar-fuel devices that demonstrate a broad and controllable absorption from the UV to NIR wavelengths.Keywords: broad absorption; controllable band gap; hydrogen production; type II heterostructure; ZnO/ZnxCd1−xTe nanowires array;
Co-reporter:Fengmei Wang, Yuanchang Li, Zhongzhou Cheng, Kai Xu, Xueying Zhan, Zhenxing Wang and Jun He
Physical Chemistry Chemical Physics 2014 vol. 16(Issue 24) pp:12214-12220
Publication Date(Web):17 Apr 2014
DOI:10.1039/C4CP01200C
3D semiconductor nanostructures have proved to be a rich system for the exploring of high-performance pseudocapacitors. Herein, a novel 3D WO3 nanotree on W foil is developed via a facile and green method. Both capacitance and conductivity of the WO3 nanotree electrode are greatly improved after hydrogenation treatment (denoted as H-WO3). First-principles calculation based on the experiments reveals the mechanism of the hydrogenation treatment effect on the 3D WO3 nanotrees. The surface O of 3D WO3 nanotrees gains electrons from the adsorbed H, and consequently certain electrons are back-donated to the neighboring W, thus providing the conducting channel on the surface. Ultrathin V2O5 films were coated on the H-WO3 nanotrees via a simple, low-cost, environmentally friendly electrochemical technique. This V2O5/H-WO3 electrode exhibited a remarkable specific capacitance of 1101 F g−1 and an energy density of 98 W h kg−1. The solid-state device based on the V2O5/H-WO3 electrodes shows excellent stability and practical application. Our work opens up the potential broad application of hydrogenation treatment of semiconductor nanostructures in pseudocapacitors and other energy storage devices.
Co-reporter:Muhammad Safdar, Qisheng Wang, Misbah Mirza, Zhenxing Wang, and Jun He
Crystal Growth & Design 2014 Volume 14(Issue 5) pp:2502-2509
Publication Date(Web):March 21, 2014
DOI:10.1021/cg5002122
Since different high-symmetrical crystal planes of topological crystalline insulator possess their own topological electronic structure, manipulating crystal shapes with distinct facets of SnTe nanostructures is crucial for the realization of desired topological surface properties. Here, we developed crystal shapes engineering for the controllable synthesis of SnTe microcrystals and nanowires with specific exposed surfaces by optimizing experimental parameters in the chemical vapor deposition process. Crystal shapes of SnTe microcrystals are tailored from {100} surface-covered cubes, {100} and {111} surface-coated truncated octahedron, to a {111} surface-terminated octahedron. Significantly, with gold nanoparticles as the catalyst, two novel SnTe nanowires, octahedron-attached SnTe nanowires, and truncated octahedron-assisted SnTe nanowires, are achieved. The requirement of minimizing the overall surface energy drives the formation of various crystal shapes of SnTe microcrystals and nanowires. In addition, SnTe nanowires possess a huge thermal activation energy gap (350 ± 17 meV), 14 times larger than the energy scale of room temperature. This huge thermal activation energy gap can protect topological surface states of SnTe nanowires against the disturbance of thermal excitation. Our work provides the building block for the realization of unique topological surface effects on specific facets and novel spintronic devices.
Co-reporter:Fengmei Wang, Yajun Wang, Xueying Zhan, Muhammad Safdar, Jianru Gong and Jun He
CrystEngComm 2014 vol. 16(Issue 7) pp:1389-1394
Publication Date(Web):01 Nov 2013
DOI:10.1039/C3CE41826J
One-dimensional semiconductor nanomaterials are considered to be promising photocatalysts due to their large surface-to-volume ratio and high charge separation efficiency. Here, a Pt nanoparticle and CdS quantum dot (QD) co-decorated one-dimensional WO3 heterostructure was fabricated on flexible carbon fibers for water oxidation via a facile method. WO3 nanowires (NWs), with their advantage of resilience to photo-corrosion effects in aqueous solution, serve as the main photocatalyst; Pt nanoparticles and CdS QDs act as the co-photocatalyst. It was found that the photocurrent density of this novel nanostructure is about 5 times higher than that of pure WO3 under visible light irradiation. Significantly, the yield of O2 after the 5.5 h reaction time with the assistance of AgNO3 reaches 1 μmol. This work not only provides a conceptual blueprint for the design of a one dimensional heterostructure photocatalyst on flexible substrate to ameliorate its recyclability but also offers an excellent alternative material for application in renewable energy.
Co-reporter:Zhenxing Wang, Kai Xu, Yuanchang Li, Xueying Zhan, Muhammad Safdar, Qisheng Wang, Fengmei Wang, and Jun He
ACS Nano 2014 Volume 8(Issue 5) pp:4859
Publication Date(Web):April 3, 2014
DOI:10.1021/nn500782n
We report a high-performance field-effect transistor (FET) and phototransistor based on back-gated multilayer GaTe nanosheets. Through both electrical transport measurements at variable temperatures and first-principles calculations, we find Ga ion vacancy is the critical factor that causes high off-state current, low on/off ratio, and large hysteresis of GaTe FET at room temperature. By suppressing thermally activated Ga vacancy defects at liquid nitrogen temperature, a GaTe nanosheet FET with on/off ratio of ∼105, off-state current of ∼10–12 A, and negligible gate hysteresis is successfully demonstrated. Furthermore, a GaTe phototransistor with high photogain above 2000 and high responsivity over 800 AW–1 is achieved, as well. Our findings are of scientific importance to understand the physical nature of intrinsic GaTe transistor performance degradation and also technical significance to unlock the hurdle for practical applications of GaTe transistors in the future.Keywords: gallium telluride; layered materials; transistor; two-dimensional; vacancy
Co-reporter:Qisheng Wang, Muhammad Safdar, Kai Xu, Misbah Mirza, Zhenxing Wang, and Jun He
ACS Nano 2014 Volume 8(Issue 7) pp:7497
Publication Date(Web):July 2, 2014
DOI:10.1021/nn5028104
Van der Waals epitaxy (vdWE) is of great interest due to its extensive applications in the synthesis of ultrathin two-dimensional (2D) layered materials. However, vdWE of nonlayered functional materials is still not very well documented. Here, although tellurium has a strong tendency to grow into one-dimensional nanoarchitecture due to its chain-like structure, we successfully realize 2D hexagonal tellurium nanoplates on flexible mica sheets via vdWE. Chemically inert mica surface is found to be crucial for the lateral growth of hexagonal tellurium nanoplates since it (1) facilitates the migration of tellurium adatoms along mica surface and (2) allows a large lattice mismatch. Furthermore, 2D tellurium hexagonal nanoplates-based photodetectors are in situ fabricated on flexible mica sheets. Efficient photoresponse is obtained even after bending the device for 100 times, indicating 2D tellurium hexagonal nanoplates-based photodetectors on mica sheets have a great application potential in flexible and wearable optoelectronic devices. We believe the fundamental understanding of vdWE effect on the growth of 2D tellurium hexagonal nanoplate can pave the way toward leveraging vdWE as a useful channel to realize the 2D geometry of other nonlayered materials.Keywords: 2D tellurium nanoplate; flexible device; mica substrate; photodetector; van der Waals epitaxy
Co-reporter:Kai Xu, Fengmei Wang, Zhenxing Wang, Xueying Zhan, Qisheng Wang, Zhongzhou Cheng, Muhammad Safdar, and Jun He
ACS Nano 2014 Volume 8(Issue 8) pp:8468
Publication Date(Web):August 11, 2014
DOI:10.1021/nn503027k
Owing to the excellent potential for fundamental research and technical applications in optoelectronic devices and catalytic activity for hydrogen evolution reaction (HER), transition metal dichalcogenides have recently attracted much attention. Transition metal sulfide nanostructures have been reported and demonstrated promising application in transistors and photodetectors. However, the growth of transition metal selenide nanostructures and their applications has still been a challenge. In this work, we successfully synthesized high-quality WSe2 nanotubes on carbon fibers via selenization. More importantly, through optimizing the growth conditions, ternary WS2(1–x)Se2x nanotubes were synthesized and the composition of S and Se can be systematically controlled. The as-grown WS2(1–x)Se2x nanotubes on carbon fibers, assembled as a working electrode, revealing low overpotential, high exchange current density, and small series resistance, exhibit excellent electrocatalytic properties for hydrogen evolution reaction. Our study provides the experimental groundwork for the synthesis of low-dimensional transition metal dichalcogenides and may open up exciting opportunities for their application in electronics, photoelectronics, and catalytic electrochemical reactions.Keywords: carbon fiber; chemical vapor deposition; hydrogen evolution reaction; WS2(1−x)Se2x nanotube; WSe2 nanotube
Co-reporter:Qisheng Wang;Muhammad Safdar;Zhenxing Wang
Advanced Materials 2013 Volume 25( Issue 28) pp:3915-3921
Publication Date(Web):
DOI:10.1002/adma.201301128
Abstract
Low-dimensional Te-based nanomaterials have attracted intense attention in recent years due to their novel physical properties including surface-state effects, photoelectricity, phase changes, and thermoelectricity. The recent development of synthesis methods of low-dimensional Te-based nanostructures is reviewed, such as van der Waals expitaxial growth and template-assisted solution-phase deposition. In addition, the unique properties of these materials, such as tunable surface states, high photoresponsivity, fast phase change, and high thermoelectricity figure of merit, are reviewed. The potential applications of low-dimensional Te-based nanostructures are broad but particularly promising for nanoscale electronic and photoelectronic devices.
Co-reporter:Muhammad Safdar, Qisheng Wang, Misbah Mirza, Zhenxing Wang, Kai Xu, and Jun He
Nano Letters 2013 Volume 13(Issue 11) pp:5344-5349
Publication Date(Web):October 31, 2013
DOI:10.1021/nl402841x
SnTe has attracted worldwide interest since its theoretical predication as topological crystalline insulator. Because of promising applications of one-dimensional topological insulator in nanoscale electronics and spintronics device, it is very important to realize the observation of topological surface states in one-dimensional SnTe. In this work, for the first time we successfully synthesized high-quality single crystalline SnTe nanowire via gold-catalyst chemical vapor deposition method. Systematical investigation of Aharonov-Bohm and Shubnikov-de Haas oscillations in single SnTe nanowire prove the existence of Dirac electrons. Further analysis of temperature-dependent Shubnikov-de Haas oscillations gives valuable information of cyclotron mass, mean-free path, and mobility of Dirac electrons in SnTe nanowire. Our study provides the experimental groundwork for research in low-dimensional topological crystalline insulator materials and paves the way for the application of SnTe nanowire in nanoelectronics and spintronics device.
Co-reporter:Jinli Cao, Muhammad Safdar, Zhenxing Wang and Jun He
Journal of Materials Chemistry A 2013 vol. 1(Issue 34) pp:10024-10029
Publication Date(Web):24 Jun 2013
DOI:10.1039/C3TA12012K
We utilize high-conductivity Te nanowire arrays grown on flexible carbon fibre to fabricate a hybrid Te/Au/MnO2 core–shell nanostructure as a supercapacitor electrode. Electrochemical measurements show that a very high specific capacitance of 930 F g−1 (based on the mass of MnO2) is obtained for Te/Au/MnO2 core–shell nanostructures. In addition, our Te nanowire array-based supercapacitor exhibits excellent rate capability and long term cycling stability. Uniquely, high-density Te nanowire arrays offer a high specific surface area to the hybrid Te/Au/MnO2 core–shell nanostructure which profoundly increases the specific capacitance. These results indicate that Te nanowire array/Au/MnO2 core–shell nanostructures show promising applications as electrode materials for energy storage.
Co-reporter:Muhammad Safdar, Zhenxing Wang, Misbah Mirza, Faheem K. Butt, Yajun Wang, Lianfeng Sun and Jun He
Journal of Materials Chemistry A 2013 vol. 1(Issue 4) pp:1427-1432
Publication Date(Web):12 Nov 2012
DOI:10.1039/C2TA00470D
We report for the first time the synthesis of single crystalline In2Te3 nanosheets. Te nanorods were first produced by controlling the reaction kinetics and then In2Te3 nanosheets nucleated at the body of Te nanorods in the presence of organic surfactant. The self-assembly and the certain directional growth process of In2Te3 on the body of Te nanorods resulted in an ordered nanostring-cluster which subsequently gave split In2Te3 nanosheets. The transformation can be attributed to the developed facets and organic surfactants which can greatly enlarge the lateral dimensions and produce nanosheets. The morphology evolution from nanorods to nanosheets is demonstrated with experimental evidence collected via SEM, TEM and XRD studies. The synthesis of nanorods/nanosheets will supply additional opportunities for the exploration of novel fundamental properties of telluride based chalcogenides materials. Initial hydrogen storage results pave the way for utilizing telluride-based nanostructures for gas storage and gas sensing properties. Also, the photoresponse properties of indium telluride offers good knowledge for the fabrication of nanoscale electronic and optoelectronic devices.
Co-reporter:Yajun Wang, Fengmei Wang and Jun He
Nanoscale 2013 vol. 5(Issue 22) pp:11291-11297
Publication Date(Web):05 Sep 2013
DOI:10.1039/C3NR03969B
A novel ZnO/reduced graphene oxide (RGO)/CdS heterostructure was successfully synthesized via a facile three-step solution method. RGO serves as an interlayer between ZnO nanowires and CdS quantum dots (QDs), which provides a high speed charge transfer channel, leading to an enhanced charge separation efficiency. Under UV light irradiation, the photocatalytic activity of the ZnO/RGO/CdS heterostructure is 4.0 times and 1.9 times as high as those of pure ZnO and ZnO/RGO, respectively. Under visible light irradiation, the ZnO/RGO/CdS heterostructure shows a dramatic visible light photocatalytic activity which is 2.3 times higher than that of the ZnO/CdS photocatalyst. The photocurrent of the ZnO/RGO/CdS heterostructure under UV light irradiation was greatly enhanced and a photocurrent under visible light irradiation was observed. The enhanced photocatalytic activity and the extended light adsorption spectrum originate from the type-II ZnO/CdS band alignment and the introduction of RGO as a charge mediator. Our results might open up a promising way to develop novel and highly efficient RGO-based heterostructure photocatalysts.
Co-reporter:Minjiang Chen, Haiqing Zhou, Fang Yu, Huaichao Yang, Gang Wang, Jun He and Lianfeng Sun
Nanoscale 2013 vol. 5(Issue 18) pp:8359-8362
Publication Date(Web):10 Jun 2013
DOI:10.1039/C3NR02055J
In this work, the doping of n-layer graphenes with C60 is investigated via Raman spectroscopy. The results indicate that C60 can induce hole doping in graphenes, and that the doping level is closely related to the layer number of the graphenes. Moreover, the level of doping in the hybrid of C60 on graphene (C60/G) is more significant than that in the hybrid of graphene on C60 (G/C60).
Co-reporter:Yajun Wang, Qisheng Wang, Xueying Zhan, Fengmei Wang, Muhammad Safdar and Jun He
Nanoscale 2013 vol. 5(Issue 18) pp:8326-8339
Publication Date(Web):21 May 2013
DOI:10.1039/C3NR01577G
Considerable efforts have been devoted to enhancing the photocatalytic activity and solar energy utilization of photocatalysts. The fabrication of type II heterostructures plays an important role in photocatalysts modification and has been extensively studied. In this review, we briefly trace the application of type II heterostructured semiconductors in the area of environmental remediation and water splitting, summarize major fabrication methods, describe some of the progress and resulting achievements, and discuss the future prospects. The scope of this review covers a variety of type II heterostructures, focusing particularly on TiO2 and ZnO based visible light driven type II 0D and 1D heterostructured photocatalysts. Some other low dimensional nanomaterials which have shown high-performance photocatalysis are also presented. We expect this review to provide a guideline for readers to gain a clear picture of fabrication and application of type II heterostructures.
Co-reporter:Qisheng Wang, Muhammad Safdar, Xueying Zhan and Jun He
CrystEngComm 2013 vol. 15(Issue 42) pp:8475-8482
Publication Date(Web):04 Sep 2013
DOI:10.1039/C3CE41534A
Controllable wettability is significant for fundamental research and practical applications such as smart and fluid-controllable devices, cell proliferation and inkjet printing. In this work, four one-dimensional Te micro–nanostructures have been fabricated by one-step physical vapor deposition method on the surface of the widely used engineering material FeCoCr alloy. The top morphology and framework of the one-dimensional Te micro–nanostructures can be precisely controlled by the source and deposition temperature, which enables us to design the desired wettability of a solid surface. The wettability of the FeCoCr alloy surface dramatically changes from the near-superhydrophilicity of a Te microscale triangle array to the complete superhydrophobicity of a random-oriented Te nanoscale needle array. Significantly, a complete non-stick superhydrophobic surface with a contact angle of 171° is achieved, for the first time, by adjusting the framework of Te micro–nanostructures from needle microrod arrays to random-oriented needle nanowire networks, which form a special three dimensional (3D) nanoporous network structure. The controllable wettability is suggested to arise from the synergy between the roughness and the framework of Te micro–nanostructures. Our finding not only opens an avenue for the application of Te micro–nanostructures but also paves a way towards the design for controlling the wettability of one-dimensional micro–nanostructure arrays.
Co-reporter:Zhenxing Wang, Muhammad Safdar, Chao Jiang, and Jun He
Nano Letters 2012 Volume 12(Issue 9) pp:4715-4721
Publication Date(Web):August 21, 2012
DOI:10.1021/nl302142g
For the first time, high quality In2Te3 nanowires were synthesized via a chemical vapor deposition (CVD) method. The synthesized In2Te3 nanowires are single crystals grown along the [132] direction with a uniform diameter of around 150 nm and an average length of tens of micrometers. Further, two kinds of photodetectors made by 1D In2Te3 nanostructures synthesized by CVD and solvothermal (ST) methods respectively were fabricated. To our best knowledge, this is the first time photoresponse properties of In2Te3 nanowire have been studied. The CVD grown nanowire device shows better performance than the ST device, which demonstrates a fast, reversible, and stable photoresponse and also a broad light detection range from 350 nm to 1090 nm, covering the UV–visible–NIR region. The excellent performance of the In2Te3 nanowire photodetectors will enable significant advancements of the next-generation photodetection and photosensing applications.
Co-reporter:Zhenxing Wang, Xueying Zhan, Yajun Wang, Safdar Muhammad, Ying Huang and Jun He
Nanoscale 2012 vol. 4(Issue 8) pp:2678-2684
Publication Date(Web):06 Mar 2012
DOI:10.1039/C2NR30354J
A low-cost, compatible with flexible electronics, high performance UV sensor has been achieved from a reduced graphene oxide (RGO) decorated hydrangea-like ZnO film on a PDMS substrate. The hydrangea-like ZnO UV sensor has the best UV sensing performance among devices made of three kinds of ZnO nanostructures synthesized by a hydrothermal method, and demonstrated a dramatic enhancement in on/off ratio and photoresponse current by introducing an appropriate weight ratio of RGO. The on/off ratio of the 0.05% RGO/ZnO sensor increases almost one order of magnitude compared to that of a pristine hydrangea-like ZnO UV sensor. While for the 5% RGO decorated ZnO sensor, the photoresponse current reaches as high as ∼1 μA and exceeds 700 times that of a ZnO UV sensor. These results indicate that RGO is an appropriate material to enhance the performance of ZnO nanostructure UV sensors based on its unique features, especially the high optical transparency and excellent electronic conductivity. Our findings will make RGO/ZnO nanohybrids extraordinarily promising in optoelectronics, flexible electronics and sensor applications.
Co-reporter:Muhammad Safdar, Zhenxing Wang, Misbah Mirza, Chao Jiang and Jun He
Journal of Materials Chemistry A 2012 vol. 22(Issue 36) pp:19228-19235
Publication Date(Web):02 Aug 2012
DOI:10.1039/C2JM33760F
In the present work, we report for the first time the growth of uniform single crystalline In2Te3 nanowires via the chemical vapor deposition (CVD) method. The CVD grown In2Te3 nanowires are single crystals along [132] growth direction with a uniform diameter of around 150 nm and an average length of tens of microns. In addition, polycrystalline hierarchical nanostructures of In2Te3 are also fabricated via a solvothermal method under low temperature conditions. The morphology and crystal structures are systematically studied using SEM and TEM. Optical characterization by Raman spectroscopy provides further information of the achieved products, and UV-vis spectroscopy helped to investigate the bandgap of these nanostructures. By surfactant and solvent effects, the morphologies of the nanostructure are controllable. The electrical properties of the two kinds of nanowire are compared. The morphology controllable nanostructure offers the possibility of controlling the properties of In2Te3 and this opens up new means for achieving high performance nanodevices based on these nanostructures.
Co-reporter:Yajun Wang, Zhenxing Wang, Safdar Muhammad and Jun He
CrystEngComm 2012 vol. 14(Issue 15) pp:5065-5070
Publication Date(Web):08 May 2012
DOI:10.1039/C2CE25517K
Graphite-like C3N4 hybridized ZnWO4 photocatalyst is synthesized via a facile chemisorption. The C3N4/ZnWO4 photocatalysts show high efficiency for the degradation of methylene blue (MB) under UV light and visible light irradiation. A loading amount of 5% C3N4 over ZnWO4 leads to an 80% increase in the photocatalytic activity under UV light irradiation. The enhanced photocatalytic performance under UV light irradiation could be attributed to the high separation efficiency of the photogenerated electron-hole pairs. The visible light activity of C3N4/ZnWO4 originates from the injection of excited electrons from the lower unoccupied molecular orbital (LUMO) of C3N4 to the conduction band (CB) of ZnWO4.
Co-reporter:Fengmei Wang, Yuanchang Li, Zhongzhou Cheng, Kai Xu, Xueying Zhan, Zhenxing Wang and Jun He
Physical Chemistry Chemical Physics 2014 - vol. 16(Issue 24) pp:NaN12220-12220
Publication Date(Web):2014/04/17
DOI:10.1039/C4CP01200C
3D semiconductor nanostructures have proved to be a rich system for the exploring of high-performance pseudocapacitors. Herein, a novel 3D WO3 nanotree on W foil is developed via a facile and green method. Both capacitance and conductivity of the WO3 nanotree electrode are greatly improved after hydrogenation treatment (denoted as H-WO3). First-principles calculation based on the experiments reveals the mechanism of the hydrogenation treatment effect on the 3D WO3 nanotrees. The surface O of 3D WO3 nanotrees gains electrons from the adsorbed H, and consequently certain electrons are back-donated to the neighboring W, thus providing the conducting channel on the surface. Ultrathin V2O5 films were coated on the H-WO3 nanotrees via a simple, low-cost, environmentally friendly electrochemical technique. This V2O5/H-WO3 electrode exhibited a remarkable specific capacitance of 1101 F g−1 and an energy density of 98 W h kg−1. The solid-state device based on the V2O5/H-WO3 electrodes shows excellent stability and practical application. Our work opens up the potential broad application of hydrogenation treatment of semiconductor nanostructures in pseudocapacitors and other energy storage devices.
Co-reporter:Muhammad Safdar, Zhenxing Wang, Misbah Mirza, Chao Jiang and Jun He
Journal of Materials Chemistry A 2012 - vol. 22(Issue 36) pp:NaN19235-19235
Publication Date(Web):2012/08/02
DOI:10.1039/C2JM33760F
In the present work, we report for the first time the growth of uniform single crystalline In2Te3 nanowires via the chemical vapor deposition (CVD) method. The CVD grown In2Te3 nanowires are single crystals along [132] growth direction with a uniform diameter of around 150 nm and an average length of tens of microns. In addition, polycrystalline hierarchical nanostructures of In2Te3 are also fabricated via a solvothermal method under low temperature conditions. The morphology and crystal structures are systematically studied using SEM and TEM. Optical characterization by Raman spectroscopy provides further information of the achieved products, and UV-vis spectroscopy helped to investigate the bandgap of these nanostructures. By surfactant and solvent effects, the morphologies of the nanostructure are controllable. The electrical properties of the two kinds of nanowire are compared. The morphology controllable nanostructure offers the possibility of controlling the properties of In2Te3 and this opens up new means for achieving high performance nanodevices based on these nanostructures.
Co-reporter:Jinli Cao, Muhammad Safdar, Zhenxing Wang and Jun He
Journal of Materials Chemistry A 2013 - vol. 1(Issue 34) pp:NaN10029-10029
Publication Date(Web):2013/06/24
DOI:10.1039/C3TA12012K
We utilize high-conductivity Te nanowire arrays grown on flexible carbon fibre to fabricate a hybrid Te/Au/MnO2 core–shell nanostructure as a supercapacitor electrode. Electrochemical measurements show that a very high specific capacitance of 930 F g−1 (based on the mass of MnO2) is obtained for Te/Au/MnO2 core–shell nanostructures. In addition, our Te nanowire array-based supercapacitor exhibits excellent rate capability and long term cycling stability. Uniquely, high-density Te nanowire arrays offer a high specific surface area to the hybrid Te/Au/MnO2 core–shell nanostructure which profoundly increases the specific capacitance. These results indicate that Te nanowire array/Au/MnO2 core–shell nanostructures show promising applications as electrode materials for energy storage.
Co-reporter:Muhammad Safdar, Zhenxing Wang, Misbah Mirza, Faheem K. Butt, Yajun Wang, Lianfeng Sun and Jun He
Journal of Materials Chemistry A 2013 - vol. 1(Issue 4) pp:NaN1432-1432
Publication Date(Web):2012/11/12
DOI:10.1039/C2TA00470D
We report for the first time the synthesis of single crystalline In2Te3 nanosheets. Te nanorods were first produced by controlling the reaction kinetics and then In2Te3 nanosheets nucleated at the body of Te nanorods in the presence of organic surfactant. The self-assembly and the certain directional growth process of In2Te3 on the body of Te nanorods resulted in an ordered nanostring-cluster which subsequently gave split In2Te3 nanosheets. The transformation can be attributed to the developed facets and organic surfactants which can greatly enlarge the lateral dimensions and produce nanosheets. The morphology evolution from nanorods to nanosheets is demonstrated with experimental evidence collected via SEM, TEM and XRD studies. The synthesis of nanorods/nanosheets will supply additional opportunities for the exploration of novel fundamental properties of telluride based chalcogenides materials. Initial hydrogen storage results pave the way for utilizing telluride-based nanostructures for gas storage and gas sensing properties. Also, the photoresponse properties of indium telluride offers good knowledge for the fabrication of nanoscale electronic and optoelectronic devices.
Co-reporter:Yajun Wang, Xueying Zhan, Fengmei Wang, Qisheng Wang, Muhammad Safdar and Jun He
Journal of Materials Chemistry A 2014 - vol. 2(Issue 43) pp:NaN18419-18419
Publication Date(Web):2014/09/05
DOI:10.1039/C4TA04293J
ZnO/ZnSxSe1−x core–shell nanowire arrays on a silicon substrate were successfully prepared via a hydrothermal method followed by chemical vapor deposition (CVD) of the ZnSxSe1−x shell. By optimizing the CVD growth conditions, a crystalline ZnSxSe1−x shell and well-aligned ZnO/ZnSxSe1−x interface were achieved, which plays an important role towards the enhanced performance of photocatalytic activity. The introduction of the crystalline, lattice-matched ZnSxSe1−x shell to ZnO nanowires significantly enhances the photocatalytic and photoelectrocatalytic activity under UV light irradiation. More attractively, after being combined with the ZnSxSe1−x shell, the visible light photoelectrocatalytic activity of the ZnO/ZnSxSe1−x core–shell nanowires is observed. The performance enhancement of ZnO/ZnSxSe1−x core–shell nanowires under irradiation is mainly due to matching lattice and band energy level alignment between the crystalline ZnSxSe1−x shell and ZnO nanowire core. The high crystal quality of the ZnSxSe1−x shell and the band alignment of the ZnO/ZnSxSe1−x core–shell greatly enhance the charge separation efficiency and prolong the life-time of photogenerated charge carriers. Our finding is expected to provide a new insight into the fabrication of novel and high performance nanowire based core–shell photocatalysts.
