Face-centred cubic modification in sputtered films of tantalum, molybdenum, tungsten, rhenium, hafnium and zirconium

Abstract

Stable face-centred cubic modifications of tantalum, molybdenum, tungsten, rhenium, hafnium and zirconium have been observed in sputtered films of these metals deposited at ˜200-400°C. The f.c.c. structure has been found in films as thick as 2 microns, and on substrates of glass, mica and rock salt. A mixture of f.c.c. and the normal structure appears in thicker films. Perfect epitaxial growth of the f.c.c. phase with parallel orientation with respect to rock salt is observed in Ta, Mo and Zr films. The densities of the observed f.c.c. structures are lower than those of the normal structures, with a maximum decrease of 29.1% for Hf. At deposition temperatures exceeding 400°c, the normal structures are obtained in all cases. The transformation of the f.c.c. to the normal structure is obtained by subsequent annealing at higher temperatures (˜700°c). Thermally evaporated films also assume f.c.c. structures which change readily to the normal structures with the increase of the film thickness and the substrate temperature. Stability of the f.c.c. structure in sputtered films may be the result of the nucleation of this phase due to the high kinetic energy and the electrostatic charges carried by the sputtered atoms. Definitive evidence is presented to show that the observed F.C.C. structures are metallic modifications rather than certain F.C.C. nitride compounds.