Transmission Electron Microscopy Studies of Bismuth Films

We have studied the structure of Bi films grown on BaF₂ substrates as a function of the distance from the interface with the substrate. Close to the interface the films show a polycrystalline structure and probably contain some amorphous regions. The crystallite size increases as the distance from the interface increases. At distances ≥90 nm the film becomes single crystalline and has the (111) trigonal direction normal to the film surface. Our structural data relate very well to mobility measurements performed on samples grown under the same conditions. Our results suggest that the carrier mobility is higher at distances ≥90 nm from the interface, where the film is single crystalline, than close to the interface, where it is polycrystalline.