ON THE POSSIBILITY OF TAILORING A COMPOSITIONAL GRADIENT IN THIN-FILMS SPUTTERED FROM A MOSI2+XSIC COMPOSITE TARGET

To protect molybdenum against high temperature oxidation, a prototype coating system will consist of a molybdenum substrate followed by a si licon diffusion barrier layer, a functionally-graded layer of MoSi2+XS iC (X is the mole fraction), and a thick layer of MoSi2 to provide the reservoir of silicon for oxidation resistance. A critical element in the coating system is the ability to tailor the compositional gradient in the composite layer (i.e., vary X in the MoSi2 + XSiC layer). This paper will examine both the possibility of directly depositing compos ite films by r.f. magnetron sputtering, as well as the feasibility of synthesizing a ''functionally-graded'' thin him, by varying process pa rameters such as the applied power, substrate bias, and argon pressure . In this context, the role of the sputter yields for Mo, Si and C wil l be explored, with respect to the ability to vary the composition of as-deposited films. In addition, the modifications which were required to sputter 58.4 mm diameter composite targets (produced in-house, by different synthesis reactions, as well as commercially supplied), usin g a 127 x 381 mm Vac Tec cathode will be discussed. Details of Auger e lectron spectroscopy, scanning electron microscopy and X-ray diffracti on analyses of the as-deposited films will be presented.