Structures and defects of heterogeneous interfaces have been discussed using the concept of “coherency”which has been applied to interphase boundaries. Interfacial structures have been classified into three kinds, coherent, semicoherent and incoherent interfaces, depending on lattice mismatch. As a case study of the interface with great mismatch of about 10%, the structure of PtSi/ (111) Si interface has been discussed in detail on the basis of HRTEM images. The interface has been found to be atomically abrupt and has atomic steps which increases local coherency between PtSi and Si. (J. Cryst. Soc. Jpn. 28, 151 (1986) ) .
