A microscopic picture of heteroepitaxy on silicon is obtained using surface techniques such as photoelectron spectroscopy. From core level measurements, the bonding at the interface is established. Furthermore, it is possible to detect the valence orbitals that hold the interface together. Dramatic changes in the electronic properties (e.g., the bandgap) are seen for the layer adjacent to the interface. Using such microscopic information, the effect of various surface treatments (passivation by overlayers, activation by irradiation) on epitaxial growth is understood. Examples include the CaF2/Si, Si02/Si, and SrO/Si interfaces. © 1988, The Electrochemical Society, Inc. All rights reserved.