High resolution electron energy loss Spectroscopy (HREELS) in conjunction with a number of other surface analytical techniques has been applied to study semiconductor and insulator surfaces and interfaces of technological importance. Results are presented for HREELS applied to characterize single-crystalline SiO2; surfaces, CaF2/Si(111) interfaces, as well as thin film SiO2/Si(100) grown in-situ by thermal oxidation or by chemical vapor deposition. Interface phonons can be identified for thin epitaxial insulator films and thin film properties (dielectric function) can be obtained for thin amorphous films. The mechanisms of hydrocarbon removal from Si wafers by H F and ultraviolet-ozone cleaning, processes crucial for Si technology, are revealed. © 1990.