Experimental Confirmation of Precipitation and Oxidation in Evanohm Condensate Thin Films

BY ELECTRON and optical microscopic techniques, the precipitation out of the original solid solution of a phase based on Ni3Al has been observed in the metal films condensed from the alloy Evanohm. A precipitation clustering of solute atoms causes a slight increase in the film resistivity. This is followed by a large decrease in resistivity as the solute content of the solvent or matrix is depleted by the growth of the solute rich precipitates. The rate of these processes has been observed to depend on the thickness of the film, with the thinnest films aging fastest. The oxidation of these films has been studied using electron microscopy to identify the reaction and using a quartz crystal microbalance to determine the reaction kinetics. Prior to precipitation, a uniform Cr2O3 oxide layer grows with a limiting thickness, saturating form of kinetics. This is typical of a case where a retarding electric field is created in the oxide layer by the migration of the charged species which eventually halts the diffusion or oxidation process. Later, after clustering and precipitati6n has occurred, a particulate oxide identified as NiO grows with kinetics proportional to the cube of time. This particulate oxide grows in the solute-depleted portion of the matrix.