When a gold film is evaporated on Si and the Au/Si Schottky contact is exposed to air, outdiffusion of Si to the Au surface takes place even at room temperature. A similarly enhanced outdiffusion in Au films has been observed for GaAs and many metals at elevated temperatures in air over those in vacuum or inert ambients. We have investigated the interactions between metal and semiconductor, and between metal and metal in different ambients and found a similarity between these two systems: The observed ambient effects can be commonly correlated by the consideration of two factors—the electronegativity difference between the overcoating metal and the underlying species, and the ambient-induced surface potential change of the former which is a polycrystalline film in all the systems studied, thus enabling the ambient species to diffuse to the interface to affect the interactions there. These correlations have led to the prediction of a reduced diffusion of a less electronegative species in Au films by CO, and, more significantly, of a similarly reduced diffusion in Pt films by oxygen. We have confirmed these predicted effects for many systems including both semiconductors and metals. The application of this work to the fabrication of Schottky contacts for stable operation in air is also discussed.