Microstructure and electrical properties of thin films of ReSi1.75 produced by co-sputtering

Microstructural evolution and changes in electrical resistivity of ReSi_1.75 thin films produced by co-sputtering has been investigated as a function of annealing temperature. Crystallization of amorphous ReSi_1.75 thin films occurs at 600 °C without forming any metastable phases. The crystallization temperature for ReSi_1.75 is considerably higher than those observed for other transition-metal disilicides. The crystal structure as well as the domain (twinned) structure observed for crystallites in ReSi_1.75 thin films annealed above 600 °C are essentially the same as those observed in bulk crystals of ReSi_1.75. Although the grain size of crystallites increases with the increase in annealing temperature, thin films annealed below 650 °C exhibit a nano-crystalline structure. Thin films of amorphous and crystalline ReSi_1.75 and bulk polycrystalline ReSi_1.75 all exhibit electrical resistivity values decreasing with the increase in temperature, indicating the semiconducting nature. Values of electrical resistivity for crystallized thin films are systematically higher than those for amorphous ReSi_1.75 thin films and bulk polycrystalline ReSi_1.75 and increase with the decrease in annealing temperature, exhibiting a peak at just above the crystallization temperature. The high values of electrical resistivity around the crystallization temperature are discussed in terms of the formation of the nano-crystalline structure in thin films, for which the effective medium approximation is not valid.