The scattering of light by thin metallic films

Abstract

Observations on a new kind of light scattering shown by thin films of metals obtained by evaporation in vacuo and cathodic sputtering are described. The light scattered by such films exhibits anomalous depolarisation characteristic of metallic surfaces. It is thus essentially a surface effect and not the ordinary Rayleigh type of colloidal scattering. The portions of the film which are thin enough to show this effect are found to have no metallic reflection and either a large or else a practically infinite electrical resistance. It is suggested that the metallic film has three possible different states: a crystalline state with metallic properties, a two-dimensional gaseous state which is not metallic and is non-conducting, and thirdly an intermediate state with high electrical resistance. An evaporated silver film in the first state scatters little light and is black by scattered light. In the intermediate state, it scatters bright orange yellow light, and in the gaseous state, a bright green. Observations on the colours of the film by transmission and reflection examined with a nicol are also recorded. It is hoped that a more detailed quantitative investigation of the scattering of light by thin films of metals will throw light on their nature.