NiTi thin films prepared by biased target ion beam deposition co-sputtering from elemental Ni and Ti targets

NiTi thin films are fabricated using biased target ion beam deposition technique. By design, the technique operates over a broad range of processing pressures; enables control of adatom energies; facilitates low energy bombardment; and promotes uniformity and repeatability. Thus, the technique is advantageous for preparing smooth and dense ultrathin films. Typically NiTi shape memory alloy thin films are deposited using the magnetron-sputtering technique and alloy targets. In this work films are co-sputtered from pure Ti and pure Ni targets and the technique is contrast with magnetron co-sputtering. Approximately 100 nm thick NiTi thin films are prepared with Ni-rich (> 50.5 at.% Ni), near equiatomic, and Ti-rich (< 49.5 at.% Ni) compositions. Atomic force microscopy reveals that films are consistently ultra-smooth over the broad range of compositions. The current findings confirm that biased target ion beam deposition can facilitate the preparation of high quality ultrathin NiTi films. After heat-treatment, the films deposited exhibit B2 and B19′ crystal structures and thus possess potential for martensitic phase transformation, which is the prerequisite for functional shape memory behavior.