Xiangyang Peng

Xiangtan University, Siangtan, Hunan, China

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Publications (28)86.61 Total impact

  • Wenliang Liu · Xiangyang Peng · Hong Yang · Xiaolin Wei · Jianxin Zhong
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    ABSTRACT: The Fermi level of the topological insulators (TIs) Bi2Se3 and Bi2Te3 is usually well above the Dirac points, which is ascribed to the intrinsic donor defects, such as antisites and anion vacancies. We show here by first-principles calculations that the substrates can modulate the Fermi level of TIs considerably. It is found that in Bi2Se3/graphene and Bi2Te3/Si(1 1 1), the substrates play the role of electron donor due to their lower workfunctions and push up the Fermi level of the TIs. Thicker TI films are found to have larger density of states and hence the charge transferred to TI leads to a smaller Fermi level shift, in good agreement with experiments. We propose to use high workfunction substrates to counterbalance the upward shift of the Fermi level due to the donor defects. Our calculations found that the fluorinated substrates F-graphene and F-Si(1 1 1) have very high workfunction and become electron acceptors, leading to a downward shift of the Fermi level of TIs.
    No preview · Article · Sep 2015 · Journal of Physics Condensed Matter
  • Chaoyu He · Jin Li · xiangyang Peng · Lijun Meng · Chao Tang · Jianxin Zhong
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    ABSTRACT: In our present work, five previously proposed sp$^3$ carbon crystals were suggested as silicon allotropes and their stabilities, electronic and optical properties were investigated by first-principles method. We find that these allotropes with direct or quasi-direct band gaps in range of 1.2-1.6 eV are very suitable for applications in thin-film solar cells. They display strong adsorption coefficients in the visible range of the sunlight in comparison with diamond silicon. These five silicon allotropes are confirmed possessing positive dynamical stability and remarkable themodynamical stability close to that of diamond silicon. Especially, the direct band gap M585-silicon possessing energy higher than diamond silicon only 25 meV per atom is expected to be experimentally produced for thin-film solar cells.
    No preview · Article · Jun 2015
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    ABSTRACT: Based on first-principles calculations in the framework of van der Waals density functional theory, we investigate the structural, electronic properties and band-gap tuning of the h-BN/MoS2/h-BN sandwich heterostructure under an external electric field. We find that, different from the suspended monolayer MoS2 with a direct band-gap, h-BN/MoS2/h-BN has an indirect band-gap. Particular attention has been focused on the engineering of the band-gap of the h-BN/MoS2/h-BN heterostructure via application of an external electric field. With the increase of electric field, the band-gap of the h-BN/MoS2/h-BN heterostructure undergoes an indirect-to-direct band-gap transition. Once the electric field intensity is larger than 0.1 V Å−1, the gap value of direct band-gap shrinks almost linearly with the field-strength, which indicates that the h-BN/MoS2/h-BN heterostructure is a viable candidate for optoelectronic applications.
    No preview · Article · May 2015 · Journal of Physics D Applied Physics
  • Wenliang Liu · Zhen Zhang · Xiangyang Peng · Jianxin Zhong
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    ABSTRACT: Based on first‐principles calculations, it is found that the Dirac cone of Bi2Te3 film, which is buried in the bulk valence bands, can be tuned by the substitutional nonmagnetic atoms. It is found that substituting the Bi layer at the two ends of Bi2Te3 films with group III atoms Al, Ga, In and Tl, which have lower electronegativity than Bi atoms, can lead to an isolated Dirac cone with the Dirac point shifted into the bulk band gap and located on the Fermi level. Substituting the more electronegative Se, S and O atoms for Te atoms at the top and bottom layers of Bi2Te3 film, only the most electronegative O atoms give rise to a nearly ideal Dirac cone. The charge distribution of the resulting isolated Dirac point state is concentrated at the Te layers facing the van der Waals layers and vanishes in the middle of the quintuple layers.
    No preview · Article · Jan 2015 · Physica B Condensed Matter
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    ABSTRACT: Adsorption of hydrogen and hydrocarbon molecules on semiconductor surfaces plays a key role in surface science and technology. Most studies have employed silicon (Si) as a substrate because of its paramount technological importance and scientific interest. However, other semiconductor substrates are gaining an increasing interest as well. Silicon carbide (SiC), which is a material with very special properties allowing developments of novel devices and applications, offers particularly fascinating new degrees of freedom for exceptional adsorption behaviour. For example, a very unusual hydrogen-induced metallization of a SiC(001) surface has been reported and hydrogen molecules show very different adsorption behaviour on different SiC(001) reconstructions although the latter exhibit very similar surface dimers. In marked contrast to the Si(001) surface, the adsorption of hydrocarbon molecules on SiC(001) can yield structurally well-defined adlayers in favourable cases which may have large potential for organic functionalization. We review and discuss theoretical ab initio results on conceivable adsorption scenarios of atomic and molecular hydrogen as well as acetylene, ethylene, butadiene, benzene and cyclohexadiene on various reconstructions of the SiC(001) surface. The main emphasize is on a detailed understanding of these adsorption systems and on identifying the physical origin of the particular adsorption behaviour. The results will be discussed in the light of related adsorption events on the Si(001) surface and in comparison with available experimental data.
    Full-text · Article · Sep 2014 · Surface Science Reports
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    ABSTRACT: Based on first-principles calculations in the framework of van der Waals density functional theory, we find that giant, Rashba-like spin splittings can be induced in both the surface states and quantum well states of thin Bi2Se3 films by application of an external electric field. The charge is redistributed so that the Dirac cones of the upper and lower surfaces become nondegenerate and completely gapless. Interestingly, a momentum-dependent spin texture is developed on the two surfaces of the films. Some of the quantum well states, which reside in the middle of the Bi2Se3 film under zero field, are driven to the surface by the electric field. The Rashba splitting energy has a highly non-linear dependence on the momentum and the electric field due to the large contribution of the high-order Rashba terms, which suggests complex spin dynamics in the thin films of Bi2Se3 under an electric field.
    No preview · Article · Aug 2014 · Journal of Physics Condensed Matter
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    ABSTRACT: By performing density functional theory calculations, we studied the quantum confinement in charged graphene quantum dots (GQDs), which is found to be clearly edge and shape dependent. It is found that the excess charges have a large distribution at the edges of the GQD. The resulting energy spectrum shift is very nonuniform and hence the Coulomb diamonds in the charge stability diagram vary irregularly, in good agreement with the observed nonperiodic Coulomb blockade oscillation. We also illustrate that the level statistics of the GQDs can be described by a Gaussian distribution, as predicted for chaotic Dirac billiards. The charge stability diagram (left) and the Gaussian distribution of the width of the Coulomb diamonds (right), indicating the nonperiodic Coulomb blockade oscillation in GQD due to quantum confinement. ((c) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    No preview · Article · May 2014 · physica status solidi (RRL) - Rapid Research Letters
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    ABSTRACT: Ultrathin topological insulator Bi2Te3 nanoplates with well-defined orientations have been fabricated on few-layer MoS2 films via van der Waals epitaxial growth. Electrostatic properties of the epitaxial heterostructures were systematically investigated by Kelvin probe force microscopy under ambient conditions. Experimental results demonstrate that charge exchange exists at the interface, resulting in doping to ultrathin Bi2Te3 nanoplates from few-layer MoS2 substrate. These results may provide a route to investigate the electronic and spintronic properties of topological insulators.
    No preview · Article · Feb 2014 · Science of Advanced Materials
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    ABSTRACT: We have carried out first-principles calculations and theoretical analysis to explore the structural and electronic properties of MoS2/n-h-BN heterostructures consisting of monolayer MoS2 on top of h-BN substrates with one to five layers. We find that the MoS2/n-h-BN heterostructures show indirect bandgap features with both of CBM (in the K point) and VBM (in the Γ point) localized on the monolayer MoS2. Difference charge density and surface bands indicate there is no obvious charge exchange in the heterostructure systems. We show that the changes from a direct bandgap in monolayer free-stranding MoS2 to an indirect bandgap in MoS2/n-h-BN heterostructure is induced by the strain. Moreover, we find that the bandgaps of MoS2/n-h-BN heterostructures decrease with increasing number of h-BN layers, which is proposed to result from the different strain distributions in MoS2 due to the varieties of lattice mismatch rates between MoS2 and h-BN layers. Our results suggest that the MoS2/n-h-BN heterostructure could serve as a prototypical example for band structure engineering of 2D crystals with atomic layer precision.
    No preview · Article · Jan 2014 · Journal of Physics D Applied Physics
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    ABSTRACT: Functionalization of MoS2 sheet (monolayer and bilayer) by the adsorption of transition metal Fe adatom to its surface and interlayer has been investigated computationally using first-principles calculations based on the density functional theory. We found that the systems with absorption of Fe adatoms on the surfaces of both monolayer and bilayer MoS2 sheets are still semiconductors, without spin polarization at the Fermi level. However, for the system with absorption of Fe adatom in the interlayer of bilayer MoS2 sheet, its electronic structure exhibits half-metal behavior, with 100% spin polarization at the Femi level, which provides a promising material for spintronic devices.
    No preview · Article · Aug 2013 · Journal of Applied Physics
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    ABSTRACT: We have carried out first-principles calculations and theoretical analysis to explore the structural, spin-polarized electronic and magnetic properties of bi-layered MoS2 with transition-metal (TM) atoms (Cr, Mn, Fe, Co and Ni) doped in the interlayer. The charge density distribution indicates that the doping TM atoms and the nearest S atoms in the lower and upper planes display a clear covalent-bonding feature. The local moments of the doping TM atoms are smaller than the magnetic moments of their free states. Also, the spin polarization is found to be 100% at the Fermi level or HOMO level for interlayer doping with Cr, Mn, Fe and Co.
    No preview · Article · Aug 2013 · RSC Advances
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    ABSTRACT: Based on van der Waals density functional calculations, we have studied few-quintuple-layer (QL) films of Bi2Se3 and Bi2Te3. The separation between the QLs near the surface is found to have a large increase after relaxation, whereas, the separation between the inner QLs is smaller and approaches the bulk value as the thickness grows, showing a two-dimensional to three-dimensional structural crossover. Accordingly, the surface Dirac cone of the Bi2Se3 film is evidently gapped for small thicknesses (two to four QLs), and the gap is reduced and, finally, is closed with the increasing thickness, agreeing well with the experiments. We further studied the substrate effect by investigating the Bi2Se3/graphene system. It is found that the underlying graphene induces a giant thickness-dependent Rashba splitting and Dirac point shift. Because Bi2Te3 films have smaller relative inter-QL expansion and stronger spin-orbit coupling, the topological features start to appear in the film as thin as two QLs in good accord with the experiments.
    No preview · Article · May 2013 · Physical review. B, Condensed matter
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    ABSTRACT: Two-dimensional MoS2-based materials are considered to be one of the most attractive materials for next-generation nanoelectronics. The electrostatic properties are important in designing and understanding the performance of MoS2-based devices. By using Kelvin probe force microscopy, we show that few-layer MoS2 sheets exhibit uniform surface potential and charge distributions on their surfaces but have relatively lower surface potentials on the edges, folded areas as well as defect grain boundaries.
    Full-text · Article · Apr 2013 · AIP Advances
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    Xinjun Tan · Jian Wu · Kaiwang Zhang · Xiangyang Peng · Lizhong Sun · Jianxin Zhong
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    ABSTRACT: We studied the nanoindentation of monolayer graphene by molecular dynamics simulations. It is found that the response of graphene to indentation is deflection dependent. In small deflection range, the response obeys point load model, while large-deflection indentation follows the sphere load model. Hence, we proposed to make sectional fittings and use different response models in different deflection ranges. In this way, a consistent Young's modulus is obtained that is almost independent of the size ratio of intender to graphene and the pretensions of graphene. The calculated Young's modulus is about 1.00 TPa, in good agreement with the experiments.
    Full-text · Article · Feb 2013 · Applied Physics Letters
  • Guolin Hao · Xiang Qi · Yinping Fan · Lin Xue · Xiangyang Peng · Xiaolin Wei · Jianxin Zhong
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    ABSTRACT: Sb2Te3 nanoplates synthesized by vapor phase deposition method have been systemically investigated employing atomic force microscopy, which exhibit regular spiral structures on the surface. The height of spiral steps is determined to be 1 nm corresponding to one quintuple layer, with an inter-step separation ranging from 500 nm to 1 μm. Growth mechanism of spiral structures on the Sb2Te3 nanoplate surface is elucidated, which can be applied to other layered materials with van der Waals epitaxy growth. The electrostatic properties of Sb2Te3 nanoplates with spiral structures are also simultaneously characterized.
    No preview · Article · Jan 2013 · Applied Physics Letters
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    ABSTRACT: Based on the first-principle calculations performed by Vienna Ab initio simulation package (VASP), we report the size limitation of half-metallic properties in hybrid zigzag BCN nanoribbons. Both boron–carbon (B–C) and nitrogen–carbon (N–C) interfacial hybrid zigzag BCN nanoribbons are considered. We find that all hybrid systems establish antiferromagnetic ground states. Moreover their electronic properties are mainly determined by the carbon rather than boron nitride segments. Transitions between semiconductor, half-metal and metal can be realized in both systems as the width of the carbon segment increases. However, the half-metallic property can only exist in the systems for which the zigzag carbon chain is less than 6 and 9 for B–C and N–C interfacial systems, respectively. As long as the carbon segment is wider than the above sizes, the systems behave as metals. This effect derives from the electron or hole doping of carbon on the BN segment.
    No preview · Article · Dec 2012 · Physica B Condensed Matter
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    ABSTRACT: Based on first-principles calculations within density functional theory, we find that Pb adlayers can induce a giant Rashba spin splitting in the quantum well states of an underlying Bi2Se3 film. As the thickness of the Pb adlayers varies, the distance between the Pb adlayer and the Bi2Se3 film, the charge density at the interface, and the binding between the Pb adlayers exhibit an oscillatory behavior due to the quantum size effects, which in turn modulates the magnitude of the Rashba spin splitting of the quantum well states in the Bi2Se3 film.
    No preview · Article · Oct 2012 · Physical review. B, Condensed matter
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    ABSTRACT: Sb2Te3-based nanomaterials are predicted to be one of the topological insulators promising in future spintronics and topological quantum computation. Few-layer Sb2Te3 nanoplates on different substrates forming heterostructures were fabricated via the vapor phase deposition method. The electrostatic properties of Sb2Te3 nanoplates were characterized by Kelvin probe force microscopy. It was found that Sb2Te3 nanoplates exhibit uniform surface potential and charge distribution. The work function was determined to be 5.016 eV for Sb2Te3 nanoplates grown on highly oriented pyrolytic graphite. These results pave a route to explore the exotic topological properties of Sb2Te3-based nanoelectronic devices.
    No preview · Article · Oct 2012 · RSC Advances
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    ABSTRACT: A superhard boron nitride phase dubbed as Z-BN is proposed as a possible intermediate phase between h-BN and zinc blende BN (c-BN), and investigated using first-principles calculations within the framework of density functional theory. Although the structure of Z-BN is similar to that of bct-BN containing four-eight BN rings, it is more energetically favorable than bct-BN. Our study reveals that Z-BN, with a considerable structural stability and high density comparable to c-BN, is a transparent insulator with an indirect band gap of about 5.27 eV. Amazingly, its Vickers hardness is 55.88 GPa which is comparable to that of c-BN. This new BN phase may be produced in experiments through cold compressing AB stacking h-BN due to its low transition pressure point of 3.3 GPa.
    No preview · Article · Jul 2012 · Physical Chemistry Chemical Physics
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    N Jiao · Chaoyu He · C. X. Zhang · Xiangyang Peng · K. W. Zhang · L. Z. Sun
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    ABSTRACT: Using first-principles calculations within the framework of density-functional theory, we studied the modulation effect of hydrogen/fluorine chemical decoration on the surface work function of BN sheets. We found that the difference in the work function (ΔWBN) between two surfaces of the chair structure varies with the different decoration. Geometric distortion and chemical effects cause opposite modulation effects, and the chemical effect plays a leading role by inducing charge redistribution in the system.
    Full-text · Article · May 2012 · AIP Advances