The adhesion of evaporated metal films on glass

Abstract

The adhesion of films of a large number of metals deposited by vacuum techniques on to a glass surface have been examined. It has been found that the affinity of the metal for oxygen plays an important role in determining the adhesion and the results appear to confirm the theory that the formation of an intermediate oxide layer at the metal/glass interface is necessary for good adhesion. There has been some doubt as to how this intermediate oxide layer is formed and the present investigation has shown that the nature and pressure of the residual atmosphere during deposition determines the extent of the formation of the oxide layer during deposition and therefore the initial adhesion of the films. However, variations in adhesion with time have been observed with films of a number of metals and it would appear that if the formation of the oxide layer is not complete during deposition then diffusion of gas to the metal/glass interface can continue the formation of the oxide layer after deposition thus accounting for the variation in adhesion with time. Since the film structure would determine the rate and extent of the diffusion of gas to the interface, it can be an important factor affecting the adhesion. Electron-microscope examination of a number of the films has been made and confirms the importance of the film structure. Furthermore, certain anomalies such as the poor adhesion of films of the low melting point metals and aluminium can be explained on the basis of film structure.