Xuhui Yang

Bio: Xuhui Yang is an academic researcher from Fuzhou University. The author has contributed to research in topics: van der Waals force & Band gap. The author has an hindex of 5, co-authored 6 publications receiving 67 citations. Previous affiliations of Xuhui Yang include University of Nevada, Las Vegas.

Electric field-modulated data storage in bilayer InSe

Abstract: Recently, due to the unexpectedly high carrier mobility and strongly suppressed recombination of electron–hole pairs, exfoliated atomically thin InSe has exhibited potential applications in nanoscaled electronic devices. In this study, via first-principle calculations, we have systematically investigated the crystal and electronic structures of bilayer InSe with different stacking configurations. Interestingly, the five possible stacking configurations of bilayer InSe can be categorized into two groups: Group-S with a shorter vdW interlayer distance and smaller band gap and Group-L with a longer vdW interlayer distance and larger band gap. It is highlighted that the indirect band gap bilayer InSe can be transformed into its metallic type. We have unraveled that the electronic origin of the band gap transition is derived from the electric field-induced near free-electron gas. Furthermore, a prototype data storage device based on the bilayer InSe has been proposed; this study will shed light on the design and application of bilayer InSe as well as two-dimensional material-based electronic devices in the future.

Tunable Contacts in Graphene/InSe van der Waals Heterostructures

Abstract: In the wake of the considerable investigation of two-dimensional (2D) materials, van der Waals (vdW) heterostructures based on atomically thin 2D materials show large potential for functional elect...

Elastic Anisotropy and Optic Isotropy in Black Phosphorene/Transition-Metal Trisulfide van der Waals Heterostructures.

Abstract: Anisotropic two-dimensional materials with direction-dependent mechanical and optical properties have attracted significant attention in recent years. In this work, based on density functional theory calculations, unexpected elastic anisotropy and optical isotropy in van der Waals (vdW) heterostructures have been theoretically proposed by assembling the well-known anisotropic black phosphorene (BP) and transition-metal trisulfides MS3 (M = Ti, Hf) together. It is interesting to see that the BP/MS3 vdW heterostructures show anisotropic flexibility in different directions according to the elastic constants, Young's modulus, and Poisson's ratio. We have further unraveled their physical origin of the type-II band structure nature with their conduction band minimum and valence band maximum separated in different layers. In particular, our results on the optical response functions including the excitonic effects of the BP/MS3 vdW heterostructures suggest their unexpected optical isotropies together with the enhancements of the solar energy conversion efficiency.

Computational discovery of PtS2/GaSe van der Waals heterostructure for solar energy applications.

Abstract: 2D van der Waals (vdW) heterostructures as potential materials for solar energy-related applications have been brought to the forefront for researchers. Here, by employing first-principles calculations, we proposed that the PtS2/GaSe vdW heterostructure is a distinguished candidate for photocatalytic water splitting and solar cells. It is shown that the PtS2/GaSe heterostructure exhibits high thermal stability with an indirect band gap of 1.81 eV. We further highlighted the strain induced type-V to type-II band alignment transitions and band gap variations in PtS2/GaSe heterostructures. More importantly, the outstanding absorption coefficients in the visible light region and high carrier mobility further guarantee the photo energy conversion efficiency of PtS2/GaSe heterostructures. Interestingly, the natural type-V band alignments of PtS2/GaSe heterostructures are appropriate for the redox potential of water. On the other hand, the power conversion efficiency of ZnO/(PtS2/GaSe heterostructure)/CIGS (copper indium gallium diselenide) solar cells can achieve ∼17.4%, which can be further optimized up to ∼18.5% by increasing the CIGS thickness. Our present study paves the way for facilitating the potential application of vdW heterostructures as a promising photocatalyst for water splitting as well as the buffer layer for solar cells.

Tunable band gaps in bilayer graphene-BN heterostructures

Abstract: We investigate band gap tuning of bilayer graphene between hexagonal boron nitride sheets, by external electric fields. Using density functional theory, we show that the gap is continuously tunable from 0 to 0.2 eV and is robust to stacking disorder. Moreover, boron nitride sheets do not alter the fundamental response from that of free-standing bilayer graphene, apart from additional screening. The calculations suggest that graphene−boron nitride heterostructures could provide a viable route to graphene-based electronic devices.

Black Phosphorus Field-effect Transistors

Abstract: Two-dimensional crystals have emerged as a class of materials that may impact future electronic technologies. Experimentally identifying and characterizing new functional two-dimensional materials is challenging, but also potentially rewarding. Here, we fabricate field-effect transistors based on few-layer black phosphorus crystals with thickness down to a few nanometres. Reliable transistor performance is achieved at room temperature in samples thinner than 7.5 nm, with drain current modulation on the order of 10(5) and well-developed current saturation in the I-V characteristics. The charge-carrier mobility is found to be thickness-dependent, with the highest values up to ∼ 1,000 cm(2) V(-1) s(-1) obtained for a thickness of ∼ 10 nm. Our results demonstrate the potential of black phosphorus thin crystals as a new two-dimensional material for applications in nanoelectronic devices.

Single layer of MX3 (M=Ti, Zr; X=S, Se, Te): a new platform for nano-electronics and optics

Abstract: A serial of two dimensional titanium and zirconium trichalcogenides nanosheets MX3 (M=Ti, Zr; X=S, Se, Te) are investigated based on first-principles calculations. The evaluated low cleavage energy indicates that stable two dimensional monolayers can be exfoliated from their bulk crystals in experiment. Electronic studies reveal very rich electronic properties in these monolayers, including metallic TiTe3 and ZrTe3, direct band gap semiconductor TiS3 and indirect band gap semiconductors TiSe3, ZrS3 and ZrSe3. The band gaps of all the semiconductors are between 0.57~1.90 eV, which implies their potential applications in nano-electronics. And the calculated effective masses demonstrate highly anisotropic conduction properties for all the semiconductors. Optically, TiS3 and TiSe3 monolayers exhibit good light absorption in the visible and near-infrared region respectively, indicating their potential applications in optical devices. In particular, the highly anisotropic optical absorption of TiS3 monolayer suggests it could be used in designing nano optical waveguide polarizers.

III–VI van der Waals heterostructures for sustainable energy related applications

Abstract: van der Waals (vdW) heterostructures, achieved by binding various two-dimensional (2D) materials together via vdW interaction, expand the family of 2D materials and show fascinating possibilities. In this work, we have systematically investigated the geometrical structures, electronic structures, and optical properties of III-VI (MX, M = Ga, In and X = S, Se, Te) vdW heterostructures and their corresponding applications in sustainable energy related areas based on first principles calculations. It is highlighted that different heterostructure types can be achieved in spite of the similar electronic structures of MX monolayers. Meanwhile, the potential applications of the heterostructures for sustainable energy related areas have been further unraveled. For instance, type-II InS/GaSe and GaS/GaSe vdW heterostructures can separately produce hydrogen and oxygen at the opposite parts. On the other hand, a type-II GaSe/GaTe heterostructure with a direct band gap compatible with silicon has been proposed to be a potential solar cell material with a power conversion efficiency over 18%. Furthermore, a gapless type-IV semi-metallic InTe/GaS heterostructure has been predicted to be a Li-ion battery anode material based on three-step lithiated analysis. The present results will shed light on the sustainable energy applications of such remarkable artificial MX vdW heterostructures in the future.

Two-dimensional few-layer group-III metal monochalcogenides as effective photocatalysts for overall water splitting in the visible range

Abstract: Using first-principles calculations, the photocatalytic performances of two dimensional (2D) few-layer group-III metal monochalcogenides MXs (M = Ga, In; X= S, Se) towards overall water splitting reaction are systematically investigated. On the basis of two criteria, i.e., the band edge positions need to straddle the oxidation potential of H2O and the reduction potential of H2, and an optimal band gap of ∼2.0 eV is required to enhance absorption in the visible range, it was found that few-layer GaSe is the most appropriate photocatalyst for overall water splitting. Further calculations revealed that: (i) with the number of layers increasing, few-layer GaSe tends to evolve into a direct bandgap semiconductor, and meanwhile, energy conversion efficiency of sunlight increases; (ii) carrier mobilities of few-layer GaSe are estimated to be as high as 880–7000 cm2 V−1 s−1, and photogenerated electrons and holes tend to spatially separate; and (iii) few-layer GaSe is predicted to be highly stable at room temperature. In brief, few-layer GaSe is demonstrated to have high stabilities, suitable band edge positions, optimal band gap value, high carrier mobility, and effective spatial separation of photogenerated electron–hole pairs as well as excellent solar absorption, leading to its high promise as a next-generation 2D photocatalyst for overall water splitting in the visible range. Our results would motivate more experimental and theoretical research to further explore the potential of 2D few-layer GaSe as photocatalysts.