Investigation of spin injection and optical imaging with scanning probe microscopy techniques

The work presented in thesis focuses on two important applications of scanning probe microscopy. The first is the attempt at measuring spin-polarized current injection from a ferromagnet into a semiconductor in an ex-situ environment at room temperature. The interface current-voltage characteristics in scanning tunneling microscopy (STM) offer one of the few viable methods that can produce the current densities and contact resistances necessary to surmount the theoretical barriers to this type of spin injection. Surface passivation techniques for the semiconductors used in these experiments are also discussed. Experimental data with different ferromagnetic tips on two types of semiconductors are presented. The results obtained in this and other spin injection experiments are explained with an interfacial equilibrium drift-diffusion theory.; The second part focuses on the theory of the generally accepted contrast mechanism in scanning apertureless microscopy (SAM). Simulations are presented of a dipole-dipole interaction model between the tip and sample. These simulations show that the dipole coupling model does indeed predict optical discrimination on the nanometer scale. Simulated images are contrasted with experiment in order to test the validity of the model.