Effect of sputtering pressure on the structure and solid-state reaction of titanium-nickel compositionally modulated film

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Abstract
The structure and annealing behavior of compositionally modulated nickel-titanium films is a function of the sputter deposition pressure. Films with a composition modulation wavelength of 20 close-packed atomic planes of each constituent per layer were prepared with argon sputter deposition pressures of 2, 5, and 10.2 mTorr. The structure was studied with x-ray diffraction in symmetric reflecting, and transmission geometries, and by x-ray rocking curves. Anneals of 1 h at 300 °C were performed to access the effect of the structure on solid-state formation of an amorphous alloy. Samples prepared under low deposition pressure exhibited textured, relatively high quality crystalline layers resulting from layer nucleation and growth. These films were not transformed to an amorphous phase by an anneal. Higher deposition pressures resulted in island nucleation and growth, random orientation, and a higher degree of disorder. Amorphous phase growth was observed during the anneal of the sample prepared at 10.2 mTorr of Ar. Increase in deposition pressure will result in lower impact energy of the deposited species, which will result in lower atomic mobility. Higher mobility with the negative surface tension between nickel and titanium will result in layer nucleation and growth. The disorder in the high deposition pressure samples may be acting as a nucleus for amorphous phase growth.