Surface Evolution of NiTi and NiTiHf Thin Films

Abstract

AbstractThe microstructure evolution of Ti-rich NiTi thin films and (TiHf)-rich NiTiHf thin films containing 9at% Hf was investigated. These films were deposited from single NiTi and NiTiHf targets using a DC magnetron sputtering system. Free-standing films were obtained by using single crystal silicon substrates. The thickness of these films was controlled between 10-12 μm. In this investigation, the effects of deposition temperature on the surface and cross-sectional microstructures of these films were studied. Substrate temperature during deposition was varied between 300°C to 700°C at 100°C intervals. The influence of post deposition heat treatment (HT) temperature on the microstructure of these films was also studied. The post deposition HT temperature was varied between 300°C and 800°C at 100°C intervals. Both surface and cross- sectional microstructures were examined using a scanning electron microscope (SEM). The crystallinity and the phases present were determined using x-ray diffractometry. All the as- deposited films were found to be crystalline, even when the substrate temperature was as low as 300°C. Results from the microstructure analysis show that all the films have a relatively fine grain size ranging from 0.2 μm to 2.5 μm, and the grain size increases with increasing substrate deposition temperature. The effect of post deposition HT on grain size was found to be minimal.