CRITICAL GRAIN-SIZE FOR STRUCTURAL TRANSFORMATION IN VACUUM-DEPOSITEDMOLYBDENUM FILMS

Nanometer-grained polycrystalline films were prepared by vacuum deposi tion of molybdenum (Mo) by using electron-beam heating. The structure and composition of the grains were analyzed by high-resolution electro n microscopy and Auger electron spectroscopy, respectively. The concen tration of carbon in the films was measured in relation to reduction o f the grain size to nanometer scale. The grains had a bcc structure wh en the grain size was larger than 4 nm. On the other hand, the grains smaller than 4 nm for films had a fee structure. Large amount of carbo n was included in the grains with the fee structure in comparison with the grains of bcc structure, although amount of other impurities such as nitrogen and oxygen was similar in both grains. It was found that the structure was transformed from bcc to fee below the critical grain size, 4 nm, and the grains with the fee structure were cubic Mo-C.