Elemental two-dimensional materials such as graphene and black phosphorus exhibit excellent physicochemical properties and are regarded as important candidate materials for the core functional units of electronic and optoelectronic devices in the future. A small amount of black phosphorus is the first elemental two-dimensional semi-monomer with many excellent properties. However, its poor air stability is prone to failure due to oxidation in cumbersome material preparation and device processing, as well as in subsequent harsh environments. Therefore, it has become a new and challenging problem to find a single-mass two-dimensional semiconductor that not only has outstanding physical and chemical properties, but also has good air stability and can be prepared by a convenient method.
[Introduction]
Recently, Prof. Ji Wei from the Department of Physics of Renmin University of China and Prof. Chai Yang from the Hong Kong Polytechnic University published a paper entitled “Few-layer Tellurium: one-dimensional-like layered elementary semiconductor with striking physical properties†on Science Bulletin. In this paper, the electrical, mechanical and optical properties of a novel elemental two-dimensional semiconductor α phase layer are studied systematically. They considered the structural stability of the three less layers of tantalum by first-principles calculations, and finally determined that the α-phase layer is the most stable phase from the double layer to the bulk phase. On this basis, they found that there is a kind of covalent-like quasi-bonding in the non-covalent direction between the layers and layers of the layer, and its nature is related to the black phosphorus and Pt transition metal sulfur. The inter-layer covalent quasi-bonds found in the family compounds are similar and result in a few layers of bismuth with many specific physical properties. Theoretical predictions show that the material has a band-dependent band gap from 0.31 eV (bulk phase) to 1.17 eV (double layer) and an abnormal high hole mobility of 105 cm 2 /Vs in the non-covalent direction in the layer. (about 1-2 orders of magnitude higher than black phosphorus), the valence top shape of the Mexican hat type (M type), and the significant double-to-body phase conduction band bottom/valence band top evolution relationship, novel interlaminar shear Numerical overlap with the vibrational force constant of the breathing mode and mode mixing, ideal intensity greater than 20%, near-isotropic strong light absorption in the near-infrared and visible-light regions (average visible light absorption of single layer up to ~9%) and far superior Air stability of black phosphorus. At the same time, the small layer of bismuth can be synthesized by solution chemistry, which has the advantages of convenience, rapid, low cost and large size preparation.
figure 1. Structural diagram and stability comparison of a few layers of elemental allotropes
(a) The most stable crystal structure of the 碲 single plastid phase (α phase);
(b) - (d) Top and side views of the 2-layer alpha phase ;;
(e), (f) Top view and side view of the 2-layer β phase ;;
(g), (h) Top view and side view of the 2-layer γ phase ;;
(i) α, β and γ phase enthalpy as a function of layer thermal stability;
(j) - (k) α phase 晶 with the lattice constants in both directions (b and c), the binding energy and the layer spacing curve.
figure 2. Electronic band structure of a few layers of α-phase elemental enthalpy
(a), (b) Schematic diagram of the Brillouin zone of the bulk phase and the minor alpha phase enthalpy;
(c), (d) the bulk band structure of the bulk phase and the two layers of alpha phase ;;
(e) - (l) Schematic diagram of the lowest conduction band and the highest valence band energy of the 2, 4, and 6 layers and the bulk phase α phase.
image 3. Interlayer interaction of a few layers of alpha phase
(a), (b) the α phase 碲 band gap and the conduction band bottom, the valence band top energy as a function of the number of layers;
(c) - (f) The differential charge density of the double helium atomic chain and the two alpha phase tantalum;
(g) - (i) Spatial distribution map of the visible wave function of the two-layer α phase 碲 near-valence band bond state (electronic state VB4 shown in Fig. 2(d)) and the inverse bond state (electronic state VB1) Xz plane and yz plane).
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