Amorphous phase forming ability in(W–C)-based sputtered films

Abstract

The effect of adding transition metals, Me, to the structure of (W–C)-based films obtained by sputtering has been studied by the means of electron probe microanalysis (EPMA), secondary ion mass spectrometry (SIMS), low angle X-ray diffraction (XRD), hot stage transmission electron microscopy (TEM), Mössbauer spectroscopy, extended X-ray absorption fine structure (EXAFS), magnetic measurements and differential thermal analysis (DTA). The results obtained for the films in the as-deposited conditions show two types of structures with different degrees of structural order. Films with Ti, Cr or Au are crystalline with a metastable structure of β-(W,Me)C 1- x with 1- x extending from near unity down to about 0.6. In opposition to these, films with Me=Group VIIIA transition metal, show crystalline→amorphous state transitions for Me percentages in the range 5–10 at.%. The structure of these films consists of small β-MC 1- x crystallites with a size of a few unity cells, surrounded by a disordered phase rich in element Me. Concerning the results obtained at increasing temperatures, the chemical and structural behaviour of the W–Me–C films depend on the affinity of carbon for the element Me. Strong or moderate carbide-forming elements (Ti or Cr) improve the stability of the crystalline phase at high temperatures; the films formed by W, C and a weak or non carbide-forming metal (Fe, Co, Ni, Pd or Au) change structurally in the temperature range studied.