Study of the variation of the optical constants of the aluminum-based multilayer thin films

The effective optical constants of aluminum-based multilayer metallic thin films (Ti/Al bilayer and Ag/Ti/Al trilayer) annealed at low temperature in air were determined by using the Krestchmann configuration in the attenuated total reflection (ATR) angular scan experiment. The theoretical reflectivity functions with and without the inclusion of the aluminum oxide layer correction were used in the data fitting procedure. The actual film thicknesses were also measured by an A-scope interferometer. The analysis of the penetration depths suggested that the ATR approach is more suitable than the normal incidence reflectivity for studying the effective multilayer optical constants. Good agreement with the reflectivity data as well as the actual film thicknesses also suggested that the optical properties of these multilayer metallic thin films can be properly represented by one set of effective optical constants. The effective optical constants of Ti/Al bilayer and Ag/Ti/Al trilayer films obtained from fitting the data were shown to have a non-linear functional dependence on the atomic fractions of Ti and Al. The results of the Rutherford backscattering spectroscopy (RBS) confirmed the compositions of the bilayer and trilayer films as well as the existence of the oxide layer. The calculated atomic fractions of Ti for Ti/Al bilayer and Ag/Ti/Al trilayer films were close to those obtained from the RBS spectra. During the crystallization of thin metal films, there is a stronger tendency for Ag rather than Al to form the FCC crystal structure during the formation of an ultra-thin film.