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First-principles study the the ceramic material RBaCo_4O_7 and Pb thin film quantum size effect

Author: ChenWeiGuang
Tutor: HuXing；JiaZuo
School: Zhengzhou University
Course: Materials Physics and Chemistry
Keywords: First-principles Density functional theory Energy band Density of states Quantum size effect Surface energy Work function Lattice relaxation Thin film growth
CLC: TQ174
Type: Master's thesis
Year: 2007
Downloads: 107
Quote: 1
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Abstract


In this thesis, using first-principles density functional theory (DFT) or said on the nature of the material calculated. In the first part the novel perovskite composite material RBaCo 4 O 7 (R = Ca, Y, Yb, etc.) carried out research to optimize the lattice constant, and gives the band structure and the density of states in the ground state, to discuss the problems encountered in the calculation and solution ideas. The results show that: the low energy levels of some of the major Y-4p and O-2s, most of the band consisting of Ba, O atoms BaO 12 , Y, O atoms YO < sub> 8 and Co and O atoms CoO 4 group contribution; given Co 2, 3 valence state was the arbitrary ratio mixed valence electronic structure image, pointed out near the Fermi level electron is mainly dominated by the Co-3d electronic 3d locality and strong correlation DFT calculation of the band structure near the Fermi could not give the correct In the second part of this paper, we study the Pb film free substrate, the growth of different polarity of the GaAs (111) surface doped Bi quantum size effect (QSE), respectively, from the substrate and the film itself the angle of the surface of the different thickness of the energy, work function, and the lattice relaxation, etc. were calculated and comparing its effect. The free Pb films of different thickness calculations show that the surface energy, the work function and the lattice of the film near the two-tier Chi Henan with thickness change is a 9ML large period oscillations superimposed on top of the in 2ML small cycle mode, with the experimental and The other calculation results are consistent; reveal the role of the quantum size effect in the modulation of thin film growth. Pb atom growth on the GaAs (111) polar substrates include Ga and As on the top in the top bit of the two cases are calculated. The study showed that: the surface of the system, the work function of the lattice relaxation With the Pb film has a thickness appeared strong double oscillation free Pb films comparison, the inflection point of the position and the cycle vary with the substrate and the difference in polarity change, indicating that the substrate has a very important role in the regulation of the growth of Pb films. Finally, the Pb-Bi alloy films doped with Bi atoms quantum size effect. The results show that: the quantum size effect of the surface energy and other double oscillation phenomenon still exists, but this oscillation due to the interaction of the Bi-Bi decay rapidly after 20ML. Of addition also calculated the substrate Ge (111) and Si (111) on the role of the Pb-Bi thin films, these two substrates is almost has the same impact on the Pb-Bi alloy thin film, consistent with the results of the previous experiments.

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