Topologically close-packed phases: Deposition and formation mechanism of metastable β-W in thin films

β-W is a metastable, topologically close-packed phase with the A15 structure. The deposition of β-W, using N2 as the impurity gas introduced into the sputtering chamber, is reported and a mechanism for β-W formation is proposed. Molecules of the impurity gas in the chamber are adsorbed onto the surface during the deposition process and act as nucleation sites for the formation of β-W. The proposed mechanism is supported by the dependence of β-W phase fraction in sputter deposited films on pressure of N2 and on substrate temperature.

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