Microstructure and mechanical properties of ta-C films by pulse-enhanced cathodic arc evaporation: Effect of pulsed current

Abstract

The ta-C films were fabricated using direct-current cathodic arc evaporation (DC-CAE) and pulse-enhanced cathodic arc evaporation (PE-CAE). The effect of peak currents (Ip) on arc discharge, microstructure and mechanical properties of the films was focused on. The enhanced discharge process, microstructure and mechanical properties of the ta-C films were investigated by means of optical emission spectra (OES), Raman spectroscopy, Nano-indentation, etc. With the same average current, the Ip of 300 A of PE-CAE produced the substrate current of 1.14 A, but a markedly low current (0.82A) was observed for the DC-CAE. The plasma emission intensity of Ar II, C I and C II also increased by about 86%, 66% and 630% at pulse mode. This evidently indicated an enhanced arc discharge by PE-CAE. The highest ratio of CII/ArII (2.98) and electron excitation temperature (1.38 eV) was observed. DC-CAE led to a lower concentration of sp3 bonding (47.3%, ID/IG = 0.39) of ta-C films with a thickness of 171 nm. In contrast, the ta-C films fabricated by PE-CAE (Ip = 300 A) possessed the smallest ID/IG (0.22) as well as the highest concentration of sp3 bonding (65.1%). The thickness increased by about 30% in comparison with that by DC-CAE. The largest thickness (330 nm) was obtained at the peak current of 200A, mainly relating to the increased evaporation of carbon atom/ions. The hardness evaluated from the ta-C films fabricated by DC-CAE was about 29 GPa. However, the hardness increased significantly to 57 GPa by PE-CAE (Ip = 300 A), and the preferable toughness (H/E* of 0.11 and H3/E*2 of 0.68) was simultaneously achieved.