The initial growth state ofCaF2/Si(111)has been investigated in the high-temperature regime(700 °C).At these growth temperatures the interface betweenCaF2and Si consists of CaF with the Ca atoms bound to the Si. Using friction force microscopy it is possible to distinguish between the interfacial CaF layer and the overgrowingCaF2with high lateral resolution: the CaF layer has a higher friction coefficient than the bulklikeCaF2.This material contrast has been used to investigate theCaF2nucleation on the interfacial CaF layer. ©1998 American Institute of Physics.