Zhongming Wei

IT University of Copenhagen, København, Capital Region, Denmark

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Publications (66)409.3 Total impact

  • Le Huang · Yan Li · Zhongming Wei · Jingbo Li ·

    Scientific Reports 11/2015; 5:16448. DOI:10.1038/srep16448 · 5.58 Impact Factor
  • Sijie Liu · Nengjie Huo · Sheng Gan · Yan Li · Zhongming Wei · Beiju Huang · Jian Liu · Jingbo Li · Hongda Chen ·
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    ABSTRACT: 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).
    Journal of Materials Chemistry C 09/2015; 3(42). DOI:10.1039/C5TC01809A · 4.70 Impact Factor
  • Yan Li · Zhongming Wei · Jingbo Li ·
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    ABSTRACT: The electronic properties of wrinkled phosphorene and its response to charge injection and external vertical electric field have been studied using first-principles calculations. It is found that small-size wrinkle systems have lower energy than wrinkle-free monolayer, suggesting that free-standing phosphorene spontaneously forms small protrusion on its nanosheet. The ratio of wrinkle height to curvature radius increases with enlarging height, indicating a promotion of field enhancement factor. Furthermore, the injected charges mostly distribute at peak and valley. Direct-to-indirect band-gap transition has been found for zigzag wrinkle with height of 14.81-Å. The band gaps of wrinkled nanosheets decrease almost linearly with increasing field, which is caused by charge separation of valence band maximum and conduction band minimum.
    Applied Physics Letters 09/2015; 107(11). DOI:10.1063/1.4931119 · 3.30 Impact Factor
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    ABSTRACT: D 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.
    09/2015; DOI:10.1002/aelm.201500267
  • Nengjie Huo · Juehan Yang · Le Huang · Zhongming Wei · Shu-Shen Li · Su-Huai Wei · Jingbo Li ·
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    ABSTRACT: Van der Waals (vdW) p-n heterojunctions consisting of various 2D layer compounds are fascinating new artificial materials that can possess novel physics and functionalities enabling the next-generation of electronics and optoelectronics devices. Here, it is reported that the WSe2 /WS2 p-n heterojunctions perform novel electrical transport properties such as distinct rectifying, ambipolar, and hysteresis characteristics. Intriguingly, the novel tunable polarity transition along a route of n-"anti-bipolar"-p-ambipolar is observed in the WSe2 /WS2 heterojunctions owing to the successive work of conducting channels of junctions, p-WSe2 and n-WS2 on the electrical transport of the whole systems. The type-II band alignment obtained from first principle calculations and built-in potential in this vdW heterojunction can also facilitate the efficient electron-hole separation, thus enabling the significant photovoltaic effect and a much enhanced self-driven photoswitching response in this system. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    Small 08/2015; 11(40). DOI:10.1002/smll.201501206 · 8.37 Impact Factor
  • Le Huang · Nengjie Huo · Yan Li · Hui Chen · Juehan Yang · Zhongming Wei · Jingbo Li · Shu-Shen Li ·
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    ABSTRACT: 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.Keywords: work function; electron−hole pairs separation; semiconductor-to-metal transition; band alignment
    Journal of Physical Chemistry Letters 07/2015; 6(13):2483-2488. DOI:10.1021/acs.jpclett.5b00976 · 7.46 Impact Factor
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    ABSTRACT: Molecular electronics describes a field that seeks to implement electronic components made of molecular building blocks. To date, few studies have used conjugated polymers in molecular junctions despite the fact that they potentially transport charge more efficiently than the extensively investigated small-molecular systems. Here we report a novel type of molecular tunnelling junction exploring the use of conjugated polymers, which are self-assembled into ultrathin films in a distinguishable 'planar' manner from the traditional vertically oriented small-molecule monolayers. Electrical measurements on the junctions reveal molecular-specific characteristics of the polymeric molecules in comparison with less conjugated small molecules. More significantly, we decorate redox-active functionality into polymeric backbones, demonstrating a key role of redox centre in the modulation of charge transport behaviour via energy level engineering and external stimuli, and implying the potential of employing tailor-made polymeric components as alternatives to small molecules for future molecular-scale electronics.
    Nature Communications 06/2015; 6:7478. DOI:10.1038/ncomms8478 · 11.47 Impact Factor
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    ABSTRACT: 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 the 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 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 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 future architectural design of novel optoelectronic devices.
    Journal of Materials Chemistry C 06/2015; 3(21). DOI:10.1039/C5TC00698H · 4.70 Impact Factor
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    ABSTRACT: Vertically stacked Van der Waals heterojunctions of atomically thin transition metal dichalcogenides (TMDs) offer new physical properties and new strategies for designing novel device functionalities that are vastly different from homostructured TMDs. The Raman intensity is strongest and frequency difference is largest in monolayer WSe2 compared with that in few-layers, which is opposite to MoS2 and WS2. In the WSe2/MoS2 bilayer heterostructures, inefficient charge transfer quenches light emission of monolayer WSe2 but strengthens those of MoS2 monolayer. Interestingly, rectification and ambipolar effects emerge due to tunneling-assisted interlayer recombination and dual conducting channels of p-WSe2 and n-MoS2 in the heterojunctions system. Gate-induced holes tunneling also leads to a novel “anti-bipolar” behavior with a sharp current peak. Under light illumination, charge transfer competes with the holes tunneling between the WSe2 and MoS2 layers, which can greatly influence the electrical transport leading to the disappeared rectifying and “anti-bipolar” properties.
    05/2015; 1(5). DOI:10.1002/aelm.201400066
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    ABSTRACT: Electrical transport properties of molecular junctions are fundamentally affected by the energy alignment between molecular frontier orbitals (highest occupied molecular orbital (HOMO) or lowest unoccupied molecular orbital (LUMO)) and Fermi level (or work function) of electrode metals. Dithiafulvene (DTF) is used as substituent group to the oligo(phenylene ethynylene) (OPE) molecular wires and different molecular structures based on OPE3 backbone (with linear to cruciform framework) are achieved, with viable molecular orbitals and HOMO–LUMO energy gaps. OPE3, OPE3–DTF, and OPE3–tetrathiafulvalene (TTF) can form good self-assembled monolayers (SAMs) on Au substrates. Molecular heterojunctions based on these SAMs are investigated using conducting probe–atomic force microscopy with different tips (Ag, Au, and Pt) and Fermi levels. The calibrated conductance values follow the sequence OPE3–TTF > OPE3–DTF > OPE3 irrespective of the tip metal. Rectification properties (or diode behavior) are observed in case of the Ag tip for which the work function is furthest from the HOMO levels of the OPE3s. Quantum chemical calculations of the transmission qualitatively agree with the experimental data and reproduce the substituent effect of DTF. Zero-bias conductance, and symmetric or asymmetric couplings to the electrodes are investigated. The results indicate that improved fidelity of molecular transport measurements may be achieved by systematic studies of homologues series of molecular wires applying several different metal electrodes.
    Advanced Functional Materials 02/2015; 25(11). DOI:10.1002/adfm.201404388 · 11.81 Impact Factor
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    ABSTRACT: 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.
    ACS Nano 01/2015; 9(2). DOI:10.1021/nn505048y · 12.88 Impact Factor
  • Mianzeng Zhong · Zhongming Wei · Xiuqing Meng · Fengmin Wu · Jingbo Li ·
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    ABSTRACT: 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.
    Journal of Alloys and Compounds 01/2015; 619:572-575. DOI:10.1016/j.jallcom.2014.09.070 · 3.00 Impact Factor
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    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.
    ChemPhysChem 01/2015; 16(1). DOI:10.1002/cphc.201402594 · 3.42 Impact Factor
  • Bo Li · Le Huang · Mianzeng Zhong · Zhongming Wei · Jingbo Li ·
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    ABSTRACT: 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. This journal is
    RSC Advances 01/2015; 5(111):91103-91107. DOI:10.1039/C5RA16918F · 3.84 Impact Factor
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    Fangyuan Lu · Juehan Yang · Renxiong Li · Nengjie Huo · Yongtao Li · Zhongming Wei · Jingbo Li ·
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    ABSTRACT: 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) in details. The red light photoresponse of the SnS based devices in different gas environments were also systematically investigated, which revealed that the adsorbed gas molecules play important roles in photosensitive properties. Compared with that in vacuum, the photosensitivity were enhanced in O2 (or air) and reduced in NH3. The dynamic response time was much longer in gas environment. These influences were ascribed to the charge transfer between the adsorbed gas molecules and SnS.
    12/2014; 3(6). DOI:10.1039/C4TC02574A
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    Mianzeng Zhong · Zhongming Wei · Xiuqing Meng · Fengmin Wu · Jingbo Li ·
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    ABSTRACT: 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.
    RSC Advances 12/2014; 5(4). DOI:10.1039/C4RA13398F · 3.84 Impact Factor
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    ABSTRACT: The triazatriangulene (TATA) ring system was investigated as binding group for tunnel junctions of molecular wires on gold surfaces. Self-assembled monolayers (SAMs) of TATA platforms with three different lengths of phenylene wires were fabricated and their electrical conductance recorded by both conducting probe-atomic force microscopy (CP-AFM) and scanning tunneling microscopy (STM). Similar measurements were performed for phenylene SAMs with thiol anchoring groups as references. It was found that despite the presence of a sp3 hybridized carbon atom in the conduction path, the TATA platform, displays a contact resistance only slightly larger than the thiols. This surprising finding has not been reported before and was analyzed by theoretical computations of the transmission functions of the TATA anchored molecular wires. The relatively low contact resistance of the TATA platform along with its high stability and directionality makes this binding group very attractive for molecular electronic measurements and devices.
    Langmuir 11/2014; DOI:10.1021/la504056v · 4.46 Impact Factor
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    ABSTRACT: Cruciform-like molecules with two orthogonally placed π-conjugated systems have in recent years attracted significant interest for their potential use as molecular wires in Molecular Electronics. Here we present synthetic protocols for a large selection of cruciform molecules based on oligo(phenyleneethynylene) (OPE) and tetrathiafulvalene (TTF) scaffolds, end-capped with acetyl-protected thiolates as electrode anchoring groups. The molecules were subjected to a comprehensive study of their conducting properties as well as their photophysical and electrochemical properties in solution. The complex nature of the molecules and their possible binding in different configurations in junctions called for different techniques of conductance measurements, 1) conducting-probe atomic force microscopy (CP-AFM) measurements on self-assembled monolayers (SAMs), 2) mechanically controlled break-junction (MCBJ) measurements, and 3) scanning tunneling microscopy break-junction (STM-BJ) measurements. The CP-AFM measurements showed structure-property relationships: from SAMs of series of OPE3 and OPE5 cruciform molecules, the conductance of the SAM increased with the number of dithiafulvene (DTF) units (0, 1, 2) along the wire, and it increased when substituting two arylethynyl end-groups of the OPE3 backbone with two DTF units. The MCBJ and STM-BJ stud-ies on single molecules both showed that DTFs decreased the junction formation probability, but, in contrast, no significant influ-ence on the single-molecule conductance was observed. We suggest that the origins of the difference between SAM and single-molecule measurements lie in the nature of the molecule|electrode interface as well as in effects arising from molecular packing in the SAMs. This comprehensive study shows that for complex molecules care should be taken when directly comparing single-molecule measurements and measurements of SAMs and solid-state devices thereof.
    Journal of the American Chemical Society 11/2014; 136(47). DOI:10.1021/ja509937k · 12.11 Impact Factor

Publication Stats

735 Citations
409.30 Total Impact Points


  • 2012-2015
    • IT University of Copenhagen
      København, Capital Region, Denmark
  • 2008-2015
    • Chinese Academy of Sciences
      • • State Key Laboratory for Superlattices and Microstructures
      • • Key Laboratory of Organic Solids
      • • Institute of Chemistry
      • • Graduate School
      Peping, Beijing, China
  • 2009
    • Fudan University
      • Department of Chemistry
      Shanghai, Shanghai Shi, China
    • Technical Institute of Physics and Chemistry
      Peping, Beijing, China