Thermodynamics and Kinetics of Defects at Surfaces

Fundamental understanding of the various electronic and structural properties at surfaces is a prerequisite for improved control of nanometer-scale patterning of surfaces for potential technological applications. In this dissertation, we have used multi-scale theoretical approaches to investigate the thermodynamic and kinetic properties of a few elemental types of surface defects. The multi-scale approaches range from first-principles calculations within density functional theory to empirical embedded atom method (EAM) to statistical analysis to kinetic Monte Carlo simulations. In studying the thermodynamic properties of intrinsic line defects on a vicinal TaC(910) surface, our Monte Carlo simulations in comparison with scanning tuning microscope (STM) images have established the existence of long-range attractive interaction between the steps. For extrinsic point defects underneath a GaAs surface, we have established through our theoretical analysis in comparison with STM observations that many-body effects in a system with purely repulsive interactions can give rise to an effective attractive interaction between the dopants at high dopant densities. In the study of the morphological evolution of monatomiclayer- high islands grown on metal surfaces, we have carried out Kinetic Monte Carlo simulations to demonstrate the importance of the island corner barriers. Our study has shown that if the island corner barrier effect is operational in preventing adatoms v located at an island edge to reach a neighboring edge defining the island corner, the islands thus formed must be non-compact, and develop fractal or dendritic shapes. Based on our EAM calculations of the diffusion barriers for various atomic processes and rate equation analysis, we have explained why fractal islands have rarely been observed on metal fcc(100) surfaces. For ideal surfaces, we have investigated the various driving forces for lattice relaxation based on first-principles calculations, and have proposed a new approach that has the promise to predict the direction of relaxation of the atoms in the surface layer strictly based on bulk properties of the given system. Finally, our fist-principles based interpretation of STM images within the framework of the Tersoff-Hamann theory has resulted in good agreement with STM experiments in revealing the anisotropy of electron density corrugations on several open metallic surfaces.