Phase transformation of thin sputter-deposited tungsten films at room temperature

Thin W films, deposited by magnetron sputtering, were deposited on silicon-dioxide surfaces at near-room temperature at thicknesses from 3 to 150 nm. As such, films below 45 nm thickness showed evidence of metastable beta-phase W which changed to alpha phase in a period of hour to days at room temperature, and faster at elevated temperature. Films >45 nm thickness, when deposited with better cooling, showed evidence of beta-phase W which then changed to alpha phase in tens of hours with an average activation energy of 1.1±0.2 eV.