Influence of Sputtering Parameters on Structural, Electrical and Thermoelectric Properties of Mg-Si Coatings

Mg-Si thin films (23 <= at.% Si <= 43) were deposited by co-sputtering of Mg and Si targets in an argon atmosphere. Two groups of samples were prepared with respect to sputtering parameters. The first Group I was synthesized while residual pressure in the reactor was lower than 7 x 10(-4) Pa and the second Group II when reactor was pumped down to pressure higher than 7 x 10(-4) Pa. The Mg2Si phase appeared for all as-deposited films of Group I around the stoichiometric composition region (29 <= at.% Si <= 37) and in the Mg-rich region (at.% Si <= 29) the Mg2Si and Mg phases coexisted. An amorphous structure was obtained for all as-deposited films of Group II no matter their composition (34 <= at.% Si <= 38) and the Mg2Si structure was achieved after post annealing under air at temperature >= 140 degrees C. Thermal stability of Mg2Si thin films was investigated by annealing treatments under air. Superficial Mg2Si structural decomposition began at T > 500 degrees C and layer morphology and structure damaged while annealing temperature increased up to 700 degrees C. The films' electrical resistivity, free carrier concentration and mobility as well as Seebeck coefficient were measured and thermoelectric power factors were discussed vs. composition.