Studies and applications of molecular beam epitaxy

Single crystal Nb samples have been prepared with stepped surfaces to investigate the effect of surface steps on nucleation and growth in molecular beam epitaxy (MBE). Studies of the critical temperature between two-dimensional and three-dimensional growth are completed by means of reflection high energy diffraction. These critical temperatures are observed to depend on the density of surfaces steps as well as the deposition rate. A perturbed step-flow-growth model is formulated and applied to the results to determine a critical cluster size for growth. The analysis reveals that the growth is dominated by mobility changes associated with the formation of adatom pairs, and that the densities of adatoms on the terraces at such critical conditions are typically as low as 10$\sp{-3}.$ Activation energies for surface diffusion and cluster binding energies are determined.In addition to the experiments on growth and nucleation, studies of Dy/Lu superlattices, Dy/Lu and Er/Lu films synthesized by methods of MBE are undertaken. These experiments investigate the effect of epitaxial strain, in particular compression, on the magnetic properties of rare earth metals. The structural and magnetic properties are characterized using x-ray diffraction analysis, bulk magnetization measurement and elastic neutron scattering method. Long range magnetic order is observed in the Dy/Lu superlattices probably owing to an RKKY-like exchange mechanism. The rare earth metal samples exhibit ferromagnetic transitions at temperatures that are very enhanced seen over that seen in bulk. This behavior is the opposite of that reported for Dy/Y and Er/Y samples studied in previous experiments. In these systems the ferromagnetic transition is completely suppressed. The difference is undoubtedly caused by the opposite types of epitaxial strain in these two cases.U of I OnlyETDs are only available to UIUC Users without author permissio