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The Properties of Superconductor, Reconstruction and Surface Alloy of Semiconductor Surface

Author: LiChong
Tutor: JiaZuo
School: Zhengzhou University
Course: Theoretical Physics
Keywords: First-principles Anti - perovskite structure Surface reconstruction Surface vacancy formation energy ab initio atomic thermodynamics Structural phase transition Surface alloy
CLC: TN304.01
Type: Master's thesis
Year: 2010
Downloads: 68
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Abstract


The first part of the paper-based first-principles density range of functional theory (DFT), anti-perovskite structure of Ni-based N-containing low-temperature superconductors lattice constant ZnNNi3, body modulus cubic crystal elastic constants ( C11, C12, C44), the effective charge and electronic structure; study the the same charge the same structure MgNNi3 and CdNNi3 materials to for comparison and ZnNNi3. The results show that the lattice constant of the three compounds have the following relationship: a (ZnNNi3) lt; a (MgNNi3) lt; a (CdNNi3), exactly contrary to the bulk modulus relationship B (ZnNNi3) gt; of B (MgNNi3) gt ; B (CdNNi3), and tetrahedral relationship of the shear modulus G 'and the body becomes modulus relationship. The nearest neighbor Ni atoms and N atoms tend to form a covalent bond, M / Ni (M = Zn, Mg or Cd), however, prefer to form an ionic bond. The nature of the electronic structure of the 3d states of Ni and Ni 3d and N 2p states hybrid largest contribution to the density of states at the Fermi level (N (EF)). M on the Fermi level at the density of states (N (EF)) contribute little, but it may lead to the Fermi level at the energy band moved, and therefore may decide ZnNNi3 TC ≈ 3 K superconducting . The second part of the first-principles calculation focuses on semiconductor Cu20 (111) oxygen truncated surface different vacancy defects on the surface morphology. The results show that the availability of copper (CuCUS) and oxygen (OCUS) are excited large surface relaxation, and is formed of two different types of projection facet. Simulated STM images and experimental STM images. Both surfaces of the copper or oxygen voids rendering the magnetic moment of approximately (-1.0μB). The calculation results show that these two surface defects than the ideal O-terminated (1 × 1) surface stabilization vacancy formation energy, the results obtained by the result and using ab initio atoms thermodynamic method. The third portion of semiconductor Si (111) - (?) × (?)-Pb surface under low coverage (θ) (θ ≤ 2/3) adsorption of the precious metals Au atomic structural phase transition occurs, the formation of (3 × 3) of PbAu of surface alloy. Adsorption of Ag and Cu atoms when the adsorption characteristics were also studied in order to compare and Au. The results showed that Although the coverage of the Au and Cu atoms in the θ = 1/3 system the most stable, but three Au atom clusters in the Pb triangular plane, forming an Au: PB = 1:1 alloy system was Semiconductor Properties, bandgap; Cu atoms due to the smaller atomic radius and embedded into the Si substrate, the surface alloy is not formed; Ag atoms coverage θ4 / 9 of system when the most stable, corresponding to the four Ag atoms Pb triangular plane the formation of clusters of tetrahedral structure.

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