In this review, the following epitaxial systems are adopted: GaAs on Si, SiC on Si, GaAs on CaF2 and Ni-silicide on Si studied by photoemission spectroscopy using synchrotron radiation, medium energy ion scattering, low energy electron loss spectroscopy, and X-ray standing wave method, respectively. Importance of fundamental studies is emphasized for the development of reliable and useful devices with new functions.
