Nanocrystalline titanium films deposited via thermal-emission-enhanced magnetron sputtering

Nanocrystalline titanium films were deposited at ultra-high current density by a direct-current closed-field unbalanced magnetron sputtering technique. The structures and properties of the films were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM) and nanoindentation microscratch. The Ti film deposited at target current density of 0.267 A/cm2 exhibited a polycrystalline microstructure with average grain size of 16 nm, fine columnar structure with no obvious voids and smooth surface, better film thickness uniformity in different parts, and excellent film-substrate adhesion. These results showed that the excellent film structure and performances were primarily achieved by using high ionization rate and energy of target atoms. As current density exceeded 0.175 A/cm2, ionization rate and energy of target atoms were greatly improved owing to the thermally-enhanced spontaneous emission of atoms and electrons from the target by Ar+ bombardment and Joule heating.