Scanning Tunneling Microscopy Studies of Ir on Ge(111), Ag on Ge(110), and the Effects of Sputtering Energy on Pyramids formed on Ge(110)

Metal-semiconductor junctions are a basic component of many modern electronic devices. In an effort to increase component speed and reduce thermal emission, much effort has been put into the miniaturization of device elements. The research I have performed investigates a bottom-up approach towards achieving miniaturization by creating reproducible nanoscale features on surfaces. Using scanning tunneling microscopy (STM), we have characterized the surfaces of Ir/Ge(111), Ag/Ge(110), and clean Ge(110) sputtered with various energies of Ar+ ions.;We dosed cleaned Ge(111) samples with between 0.66 and 2.0 monolayers (ML) of Ir and then annealed them to a temperature between 550 K and 750 K. After the samples cooled to a temperature between room temperature (RT) and 400 K, we imaged them using STM. We observed a broad range of surface formations. Islands with winding, wormy shapes formed around 580 K. As the annealing temperature was increased towards 650 K, these wormy islands broke apart into smaller components. Above 650 K, round islands formed which were interconnected by narrow pathways; in addition many small clusters of Ir adatoms dotted the Ge surface. We present a model consistent with our XPS and LEEM data that suggests that each Ir adatom cluster observed in STM corresponds to 3 Ir adatoms.;We also studied one-dimensional (1D) Ag islands on Ge(110) using STM. These islands formed after depositing many MLs of Ag and were very tall with steep walls. We obtained sufficient resolution to both distinguish the Ag from the Ge and to identify the orientation and lattice structure of the islands. 1D Ag island growth primarily nucleated from defects and the islands had widths dependent on the defect size. These defects appeared with increasing frequency as the Ge(110) substrate went through more cleaning cycles.;We performed a group of experiments to study the defects because of their potential value in controlling the locations of 1D island growth. We observed the characteristics of the defect formations which formed at various sputtering energies and ion fluence. At low sputtering energies, the defects formed into four-sided pyramids. The slope, density, and size of the pyramids changed depending on the sputtering parameters. The pyramids appeared to nucleate due to protective caps which formed on the surface. The caps are likely to be formed of trace contaminants, or unintentionally co-sputtered materials, and are found at the apex of pyramid structures.;In addition to our analysis of STM data, we have performed a number of Monte Carlo simulations, which provide additional support for models presented for our data. The discussion of the research presented in this dissertation deepens our understanding of these systems and provides promise for possible applications.