Abstract
In this thesis, low energy electron diffraction (LEED) and angle-resolved photoemission (ARPES) were used to study the interfacial phenomena and electronic structure of Pb film grown on the reconstructed surfaces, Pb/Ge(111)-β phase and Au/Ge(111)-(√3×√3)R30˚. Lattice match is an important factor for epitaxial growth. The lattice mismatch between the Pb (a = 4.95 Å) and Ge (a = 5.65 Å), is 13%. Such large lattice mismatch between Pb and Ge causes a strong strain on the Pb adlayer, which should hinder the layer-by-layer growth of Pb films. On the contrary, we succeeded to produce atomically uniform Pb films on Pb/Ge(111)-β phase and Au/Ge(111)-(√3×√3)R30˚, respectively. However, we found that the lattice structures grown on these two wetting layers are different. For Pb films on Pb/Ge(111)-β phase, initially at 1 ML, Pb films grow in the same direction as the Ge(111) substrate, forming a Moiré superstructures as revealed by LEED pattern. The periodicity of the Moiré structure determined from LEED pattern is 25 Å, differed from the value 28 Å derived from the bulk lattices of Pb and Ge, indicating a 10% strain. For Pb films grown on Au/Ge(111)-(√3×√3) R30˚, the corresponding LEED patterns showed the one-domain Pb (1×1) structure, being independent of Pb films thickness. This is different from Pb films on Pb/Ge(111)-β phase which has one more different lattice structure, Pb(1×1)- R30˚, as the thickness increases above 2 ML. In addition, we found that Pb films would interdiffuse with Au to form a unique alloy phase after being annealed to room temperature from 140 K, as revealed by the distinct LEED pattern and ARPES spectrums. The band dispersions were measured along two symmetry directions, ΓK and ΓM. At the surface zone center,Γ, we observed two Dirac-cone-like bands. And unusually, two parabolic bands cross each other at the surface zone boundary of Ge(111),M, implying a giant Rashba splitting