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

beta-W is a metastable, topologically close-packed phase with the A15 structure. The deposition of beta-W, using N-2 as the impurity gas introduced into the sputtering chamber, is reported and a mechanism for beta-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 beta-W. The proposed mechanism is supported by the dependence of beta-W phase fraction in sputter deposited films on pressure of N-2 and on substrate temperature. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.