Abstract
Up to date, 2D topological insulators found are limited to the quantum well systems which have small band gaps and do not survive at room temperature. A recent theoretical calculation shows that GaBi and InBi films of one or two bilayer thick are 2D topological insulators with large band gaps. This finding encourages us to proceed this experimental study. Growth of (In,Bi) thin film study was initially accomplished by Denisov et al. So far, Growth of GaBi thin film has not been carried out experimentally. Because the lattice constant of Ge(111)-(2×2) is very close to that of the calculated GaBi-(√3×√3), we chose the Ge(111) wafer as the substrate in this study. After the growth, we use scanning tunneling microscopy to observe the evolution of the surface morphology, and X-ray photoemission spectroscopy to analyze the chemical shift of various surface species. These two techniques are complementary to each other, allowing us to understand the phenomenon on the sample surface during growth. Three growth method are employed in this experiment:1. Deposit Bi on Ga/Ge(111).”, “2. Deposit Ga on Bi/Ge(111).”, “3. Co-deposit Ga and Bi on Ge(111).” In method 1, the surface exhibits (√3×√3) structure after annealing to 400 ℃. The (√3×√3) domains prefer to grow along the steps. With further investigation, we find this structure is not the GaBi thin film. Instead, it consists Bi adatoms that replace the Ga atoms and bond with Ge substrate. In other words, the Ga-Ge bonds is replaced by Bi-Ge ones upon Bi adsorption. The structure of Bi thin film on Ge(111) is more stable, but it is difficult to for Ga adsorption. Subsequential Ga adsorption form many 3D islands upon 200-250℃ annealing and large clusters at enen higher temperature. Finally, we discuss the evolution in three growth method and organize them to simple models. In summary, neither of these three growth methods succeeded to form GaBi films. In this thesis, we discussed some phenomenon in the process of growth, including “the Bi atom replace the Ga atom”, “the Ga 3D islands formed”, “phase transition in Ga/Ge(111)”, and “Ge(111) substrate etched by Ga”. We realized more details about properties of Bi and Ga atoms on the surface. The knowledge acquired herein could help further investigation of this new material. .