Face-centered-cubic titanium in Ti/Al multilayer thin films synthesized by magnetron sputtering technique

TL;DR

This study reports the synthesis of Ti/Al multilayer thin films with precise layer control, revealing the presence of face-centered cubic titanium, a phase not typically stable in bulk titanium, influenced by deposition conditions.

Contribution

It demonstrates the formation of fcc-Ti in multilayer films via magnetron sputtering and provides thermodynamic insights into phase stability at the nanoscale.

Findings

Unmixed multilayer structure with sharp interfaces

Detection of fcc-Ti phase in as-deposited films

Fcc-Ti formation influenced by deposition parameters

Abstract

Ti/Al multilayer thin films with precise thickness have been deposited using a combination of dc and rf magnetron sputtering techniques. Cross-sectional transmission electron microscopy (TEM) revealed unmixed fifteen parallel and alternate layers of Ti and Al with sharp interfaces, each measuring 27 nm and 15 nm in thickness, respectively. The Ti layer was composed of hcp and fcc phases while the Al layer was fcc. Both x-ray diffraction (XRD) and selected area electron diffraction (SAED) analysis confirmed the identity of these phases. Detection of fcc-Ti in as-deposited the Ti/Al multilayer thin film by XRD established that the fcc-Ti phase is not an artifact of TEM sample preparation, as have been envisaged by some of the previous researchers. The fcc-Ti phase appeared when dual rf guns were used for Ti deposition and the diffraction peak intensity corresponding to fcc phase increased when the gun power was raised. A modified equation of state based thermodynamic analysis confirmed that the formation of hcp phase as opposed to the thermodynamically stable fcc phase of pure Ti is due to crystallite size reduction and not impurity driven.