Grain size in evaporated nickel-aluminium films

Nickel-aluminium films with compositions ranging from pure nickel to 50 at.% Al were prepared by co-evaporation from two electron-beam-heated crucibles at a substrate temperature of 570 K. The grain size and the microstructure were investigated in a transmission electron microscope. The grain size decreases rapidly when small amounts of aluminium are added. For higher concentrations the presence of intermetallic phases determines the growth and the grain size. In the range between 33 and 50 at.% Al the films are covered with surface outgrowths similar to those found on films deposited at low substrate temperatures. The formation of these outgrowths is suggested to be due to the difference in the heat of formation between the nickel and the NiAl phase.