Thermally Activated Nucleation and Faceting in Immiscible Cu-Cr thin Films
The use of the electron microscope as an experimental chamber in which nucleation and growth observations can take place simultaneously has allowed in-situ studies to be performed on Cu-Cr thin films. Detailed investigations of the time-temperature sequence of events occurring during phase separation of two immiscible materials have been recorded on motion picture film. Each stage in the process of thermally induced phase separation of these thin films has been examined and characterized.Co-evaporation and deposition of Cu-Cr at ambient temperatures on freshly cleaved (100) NaCI substrates results in a polycrystalline two-component structure such as shown in Fig. I(a) where the average particle size was less than 100A. Microprobe data showed the composition of the co-evaporated film to be 59.4 Cu - 40.6 Cr. The advantage of working with unsupported nucle-ation of films of immiscible materials as compared to other techniques of substrate supported nucleation studies lies in the inherent nature of immiscible materials. Because surface diffusion is a controlling mechanism, nucleation, faceting and subsequent growth are more rapid. Exsolved parti-cles once nucleated are three dimensional with minimal constraints, and are on the surface of the thin film as compared to platelet geometries obtained from nucleation and growth on most substrate-type investigations.