Some optical properties of thin films of silver and other metals

Abstract

In the last fifteen years there has been a considerable increase in the knowledge of the optical properties of metal layers less than 1000 A thick, and the use of layers produced by evaporation or cathodic sputtering has become increasingly common for the determination of the optical constants of metals. In this work the interferometric method, originally due to Tolansky, for the determination of the relative phase changes occurring on reflexion at the surface of a metal layer has been further developed, and, coupled with a simple photoelectric device for the measurement of intensity changes, has been applied to the study of reflexion at a number of surfaces. The method requires slightly transparent layers of the metal to form a transmission interferometer, and it is therefore of particular importance to determine within what thickness limits the optical properties of these layers can be taken as characteristic of the metal in bulk form. To this end, a study of the variation with thickness of the characteristics of non-normal reflexion at thin silver layers has been made for thicknesses between 100 and 1000 A. Measurements have also been made using the technique of the optical constants of copper, tin, speculum, and a new tin-nickel alloy. Some interesting anomalies in the opticalproperties of evaporated layers of tin have been observed. The thesis commences with a treatment of the theory of reflexion at metal surfaces and layers, and the previous work in this field is reviewed, with particular reference to measurements on evaporated layers, and the variation of their properties with thickness. The evaporation equipment and procedure used are described, and the measurement of layer thicknesses critically discussed. The optical techniques are then described, the interferometric technique being analysed in detail. Finally the results of the experiments are mentioned and discussed.