Effects of Cr Concentration on the Structure and the Electrical and Optical Properties of Ti-Al-Cr-N Thin Films Prepared by Means of Reactive Co-Sputtering

Abstract

Thin films of Ti-Al-Cr-N were deposited onto glass substrates by means of the reactive magnetron co-sputtering of pure Cr and TiAl alloy targets in an atmosphere of Ar and N2. This investigation was carried out by adjusting the Cr-target power in order to increase the Cr amount in the films. The crystal structure of the films was investigated via X-ray diffraction (XRD). The elemental composition of the coatings was determined using Auger electron spectroscopy (AES). The electrical resistivity was measured using the four-point probe method, and the optical properties were characterized via ultraviolet/visible (UV/Vis) spectroscopy. The experimental results showed that, with a Cr concentration between 0 at% and 11.6 at%, a transition between phases from a single-phase hexagonal wurtzite-type structure to a single-phase cubic NaCl-type structure took place. The addition of Cr increased the crystallite size and, with it, the roughness of the coatings. All of the coatings exhibited an ohmic behavior at room temperature, and their surface electrical resistivity decreased from 490.1 ± 43.4 Ωcm to 1.5 ± 0.1 Ωcm as the chromium concentration increased. The transmittance of the coatings decreased, and the optical band gap (Egap) went from 3.5 eV to 2.3 eV with the addition of Cr. These electrical and optical properties have not been previously reported for these films.