Our Publications

  • Surface magnetism of gallium arsenide nanofilms. PHYSICAL REVIEW B. 2017

    Gallium arsenide (GaAs) is the most widely used second-generation semiconductor with a direct band gap, and it is being increasingly used as nanofilms. However, the magnetic properties of GaAs nanofilms have never been studied. Here we find by comprehensive density-functional-theory calculations that GaAs nanofilms cleaved along the 111 and 100 directions become intrinsically metallic films with strong surface magnetism and the magnetoelectric effect. Surface magnetism and electrical conductivity are realized via a combined effect of charge transfer induced by spontaneous electric polarization through the film thickness and spin-polarized surface states. The surface magnetism of 111 nanofilms can be significantly and linearly tuned by a vertically applied electric field, endowing the nanofilms with unexpectedly high magnetoelectric coefficients, which are tens of times higher than those of ferromagnetic metals and transition-metal oxides.

    ARTICLE LINK

  • Equation of state for charge-doping-induced deformation and hardening in cubic crystals. PHYSICAL REVIEW B. 2017

    Charge doping would inevitably induce strain, which can significantly influence device performance but cannot be directly predicted by classical mechanical laws. Here we present a set of equations of states for deformable cubic crystals subjected to charge doping by introducing the quantum electronic stress at fixed lattice as equivalent mechanical pressure into the classical hydrostatic pressure-vs-deformation equations. The equations are proved to be efficient for all the cubic crystals considered in this work (diamond, Si, Ge, GaAs, Al, and ZrO2) by first-principles calculations. The proposed method and presented equations should pave a convenient way to predict doping effects on device performance.

    ARTICLE LINK

  • Tunable bending stiffness of MoSe2/WSe2 heterobilayers from flexural wrinkling. Nanotechnology. 2017

    Understanding the mechanical behaviors of van der Waals heterogeneous 2D materials is important for their actual applications. Our extensive first-principles calculations and continuum mechanical modeling on the wrinkling of MoSe2/WSe2 heterobilayers caused by compression reveal that the bending stiffness of MoSe2/WSe2 wrinkles strongly depend on the wrinkle structures, which first increase and then decrease with increasing the compressive strain. The bending stiffness of MoSe2/WSe2 wrinkles could be effectively mediated and tuned by adjusting the wrinkle geometry and size. The underlying mechanisms are elucidated by the differences in electronic structures and bonding states at the top, middle and bottom parts of the wrinkles, and the relevance of the changes of bond lengths to flexural deformation. Our results suggest a feasible way to develop flexible devices and nanoelectromechanical systems by utilizing the correlation and coupling between the mechanical and electronic properties in MoSe2/WSe2 wrinkles.

    ARTICLE LINK

  • Two-Dimensional Boron Crystals: Structural Stability, Tunable Properties, Fabrications and Applications. Adv. Funct. Mater. 2017

    Boron, as a unique element nearest to carbon in the periodic table, has been predicted to form many distinctive two-dimensional (2D) structures that significantly differ from other well-studied 2D materials, owning to its exceptional ability to form strong covalent two-center-two-electron bonds as well as stable electron-deficient multi-center-two-electron bonds. Until recently, the successful syntheses of atomically thin crystalline 2D boron sheets (i.e., borophenes) provoked growing passion in 2D boron crystals. In this feature article, we present a survey of the latest achievements on 2D boron structures, starting from a concise introduction of the structures and properties of the bulk allotropes of boron, boron clusters, and especially potential building blocks for 2D boron crystals. Then we review important achievements and the current status of research on single-layered metallic borophene, and discuss 2D fewlayered boron sheets, from their possible structures to tunable properties and potential applications in electronics, spintronics, and photoelectronics. We also systematically investigate the stability and functionalization of 2D icosahedral boron sheets in comparison with borophenes through first-principles studies.
    Finally, we present an outlook on the advance in fabrications of 2D boron sheets, and the challenges and prospects in the realm of 2D boron crystals.

    ARTICLE LINK

  • Wettability of Supported Monolayer Hexagonal Boron Nitride in Air. Adv. Funct. Mater. 2017

    Hexagonal boron nitride (h-BN), a wide band gap monolayer crystal with structure similar to graphene, is optically transparent with exceptionally high thermal and chemical stability, and should be ideal to serve as an atomically thin coating. However, limited by the challenges in fabricating h-BN of high quality in large area, the wetting performance of h-BN has seldom been
    studied. Here, it is shown that the water contact angle of freshly grown h-BN film is nearly independent of the underlying materials as well as the h-BN layer number, but increases gradually to a saturated stable value in air due to the spontaneous adsorption of airborne hydrocarbon. First-principles calculations and molecular interaction modeling confirm that a monolayer
    h-BN coating does efficiently tune the interaction of a water molecule with different substrates to a converging level. The saturated wettability of h-BN coating is robust against variation of several factors, facilitating its practical applications.

    ARTICLE LINK

  • Layer Identification of Colorful Black Phosphorus. Small. 2017

    A quick method for estimating the layer number of black phosphorus is demonstrated by simple color-comparison using optical microscope in this paper. A thickness-dependent reflection model of black phosphorus/SiO2/Si is constructed and a colorbar confirmed by experiments is obtained for quick identifying layer number. The enhanced visibility affected by substrates or wavelength of light is further verified by calculating the contrast.

    ARTICLE LINK

  • Insertion of Neurotransmitters into a Lipid Bilayer Membrane and Its Implication on Membrane Stability: A Molecular Dynamics Study. ChemPhysChem. 2017

    The signaling molecules in neurons, called neurotransmitters, play an essential role in the transportation of neural signals, during which the neurotransmitters interact with not only specific receptors, but also cytomembranes, such as synaptic vesicle
    membranes and postsynaptic membranes. Through extensive molecular dynamics simulations, the atomic-scale insertion dynamics of typical neurotransmitters, including methionine enkephalin (ME), leucine enkephalin (LE), dopamine (DA), acetylcholine (ACh), and aspartic acid (ASP), into lipid bilayers is investigated. The results show that the first three neurotransmitters (ME, LE, and DA) are able to diffuse freely into both 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE) membranes, and are guided by the aromatic residues Tyr and Phe. Only a limited number of these neurotransmitters are allowed to penetrate into the membrane, which suggests an intrinsic mechanism by which the membrane is protected from being destroyed by excessive inserted neurotransmitters. After spontaneous insertion, the neurotransmitters disturb the surrounding phospholipids in the membrane, as indicated by the altered distribution of components in lipid leaflets and the disordered lipid tails. In contrast, the last two neurotransmitters (ACh and ASP) cannot enter the membrane, but instead always diffuse freely in solution. These findings provide an understanding at the atomic level of how neurotransmitters interact with the surrounding cytomembrane, as well as their impact on membrane behavior.

    ARTICLE LINK

  • Tunable Rashba spin splitting in quantum-spin Hall-insulator AsF bilayers. Nano Research. 2016

    Rashba spin splitting (RSS) in quantum-spin Hall (QSH) insulators is of special importance for fabricating spintronic devices. By changing the stacking order, a unique bilayered fluorinated arsenene (AsF) system is demonstrated to simultaneously possess RSS and non-trivial topological electronic states. We show by first-principle calculations that tunable RSS can be realized in bilayered AsF. Intrinsic RSS of 25 meV is obtained in the AA-stacked AsF bilayer by considering the spin-orbit coupling effect. The RSS can be tuned in the range of 0 to 50 meV by applying biaxial strains and can be significantly enhanced up to 186 meV in the presence of an external electric field. The AB-stacked AsF bilayer is shown to be a two-dimensional topological insulator with a sizable bulk bandgap of 140 meV (up to 240 meV), which originates from the spin-orbit coupling within the px,y–pz band inversion. Surprisingly, RSS up to 295 meV can be induced in the AB-stacked AsF bilayer by applying an external electric field, while the robust topology property without RSS can be retained under the applied strains. The AsF bilayers with tunable RSS and a nontrivial bandgap with AA- and AB-stacking orders can pave the way for designing spin field-effect transistors and new QSH devices.

    ARTICLE LINK

  • Oxygen-suppressed selective growth of monolayer hexagonal boron nitride on copper twin crystals. Nano Research. 2016

    Controlled growth of hexagonal boron nitride (h-BN) with desired properties is essential for its wide range of applications. Here, we systematically carried out the chemical vapor deposition of monolayer h-BN on Cu twin crystals. It was found that h-BN nucleated and grew preferentially and simultaneously on the narrow twin crystal strips present in the Cu substrates. The density functional theory calculations revealed that the introduction of oxygen could efficiently tune the selectivity. This is because of the reduction in the dehydrogenation barrier of the precursor molecules by the introduction of oxygen. Our findings throw light on the direct growth of functional h-BN nanoribbons on nano-twinned crystal strips and switching of the growth behavior of h-BN films by oxygen.

    ARTICLE LINK

  • Hydroelectric generator from transparent flexible zinc oxide nanofilms. Nano Energy. 2016

    Harvesting wave energy based on waving potential, a newly found electrokinetic effect, is attractive but limited mainly to monolayer graphene. Here we demonstrate that moving a transparent flexible ZnO nanofilm across the surface of ionic solutions can generate electricity. The generated electricity increases linearly with the moving velocity with an open-circuit voltage up to tens of millivolt and a short-circuit current at the order of microampere. The harvested electricity can be efficiently scaled up through series and parallel connections. Theoretical simulations show that it is the proper electrical property that endows the ZnO nanofilm with the outstanding capacity in harvesting the wave energy.

    ARTICLE LINK

  • Bending-induced extension in two-dimensional crystals. Acta Mech. Sin. 2017

    We find by ab initio simulations that significant overall tensile strain can be induced by pure bending in a wide range of two-dimensional crystals perpendicular to the bending moment, just like an accordion being bent to open. This bending-induced tensile strain increases in a power law with bent curvature and can be over 20% in monolayered black phosphorus and transition metal dichalcogenides at a moderate curvature of 2 nm−1 butmore than an order weaker in graphene and hexagon boron nitride. This accordion effect is found to be a quantum mechanical effect raised by the asymmetric response of chemical bonds and electron density to the bending curvature.

    ARTICLE LINK

  • Water-evaporation-induced electricity with nanostructured carbon materials. Nature Nanotechnology. 2017

    Water evaporation is a ubiquitous natural process that harvests thermal energy from the ambient environment. It has previously been utilized in a number of applications including the synthesis of nanostructures and the creation of energyharvesting devices. Here, we show that water evaporation from the surface of a variety of nanostructured carbon materials can be used to generate electricity. We find that evaporation from centimetre-sized carbon black sheets can reliably generate
    sustained voltages of up to 1 V under ambient conditions. The interaction between the water molecules and the carbon layers and moreover evaporation-induced water flow within the porous carbon sheets are thought to be key to the voltage generation. This approach to electricity generation is related to the traditional streaming potential, which relies on driving ionic solutions through narrow gaps, and the recently reported method of moving ionic solutions across graphene surfaces, but as it exploits the natural process of evaporation and uses cheap carbon black it could offer advantages in the development of practical devices.

    ARTICLE LINK