Characteristics of microstructure and mechanical properties of Sc films as a function of substrate temperature

Scandium films were deposited on molybdenum (Mo) substrates, at different substrate temperatures (100–650 °C) by electron-beam evaporation. The oxidation behavior was investigated by X-ray photoelectron spectroscopy (XPS). Hardness and elastic modulus of Sc films were measured by the nano-indentation technique. XPS depth profile results demonstrate that Sc films deposited at lower substrate temperatures are oxidized easier than those at higher temperatures. Besides the effect of thermodynamics, the easier oxidation at lower temperatures may be attributed to the smaller grain size and lower diffusibility of oxygen in the inner film. Increasing substrate temperature first decreases the hardness and elastic modulus due to the increased grain size and decreased degree of oxidation. Then, when the temperature increases from 450 °C to 550 °C, the hardness and elastic modulus are improved owing to the higher texture coefficient and densification, as well as the abnormally decreased grain size. However, when the temperature further increases to 650 °C, the hardness and elastic modulus decrease again.