| Summary: | 碩士 === 淡江大學 === 物理學系 === 87 === Work function is one of the fundamental important surface properties of material and it important application can be derived from the control of work function. We can control work function to change photoelectron current by deposition on surface with other element. Spin polarised photoelectron current can be used to study surface surface system to obtain more information. In recent years, physical experimentalists and theoretician are interested in how to get bigger and more stable photoelectron current. Experimentalists found that depositing Cs on GaAs surface make work function reduced and produce bigger spin polarization photoelectron current. However, over-deposited Cs makes photoelectron current smaller. Experiments demonstrat that alternating adsorption of Cs and O, known as yo-yo process, can lower the work function even further.
In this paper, We report the results of ab initio self-consistent electronic structure calculations for absorbtion induced work function change. We use DFT (Density Functional Theory) with CASTEP (Cambridge Serial Total Energy Package) do a series simulant caculation and anaylse the results. We also succeed caculate material system work function by CASTEP. The reason of work function chage due to different surface reconstruction of will be discussed. We found that dangling bond electron move towards solid while surface recontruct form dimer, this will reduce work function by electron transfer. Different surface reconstruct therefore form different dimer and makes work function not to be the same. We found that the main reason of work function decrease is Cs 6S Orbital electron move to solid when low coverage Cs adsorpt on GaAs (100) surface. At higher coverage of Cs, the metalic state formed doesn't reduce work function. We also simulate yo yo process and prove that the dipole change analytic method allow us to study the contribution of work function change due to the variation of electronic structure within specific region in real space.
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