Alloying Behavior of Thin Bimetal Films, Simultaneously or Successively Deposited

Abstract

Studies of the alloying of thin bimetal films of 20 metal pairs have been conducted by measurement of changes in the properties of the films before and after heating to successively higher temperatures in vacuo. Films consisted of layers of about 1000 angstroms of each metal consecutively deposited or of a single layer of 2000 angstroms formed of two metals deposited simultaneously. Techniques of study included visual examination of color changes, measurements of changes in electrical resistivity and temperature coefficient of resistance, metallography, x‐ray diffraction, electron microscopy and diffraction, and measurement of frequency changes of piezoelectric resonators coated with a metal pair. Regardless of the method of coating, i.e., evaporation, sputtering, or electroplating, films were found to interdiffuse or alloy at or below the temperature of recrystallization of the metal of higher melting point. The order of deposition of the films affected their subsequent behavior. Films of aluminum formed an oxide coating during a few minutes storage in vacuo; the oxide appreciably retarded diffusion between the layers until a temperature of about 400°C was reached. Simultaneous evaporation produced films which alloyed readily at relatively low temperatures or, in the absence of intrinsic alloying affinities of the metal pair, films of highly imperfect structure. The imperfection of the latter was exhibited by reductions of up to 90% in the electrical resistance of the films upon annealing. By the methods outlined valuable studies of the properties of metals can be conducted with microquantities of the metals at temperatures below 0.40°K_m (melting point °K); and alloys unavailable commercially can be prepared in the laboratory at minimum expense.