2. Material and methods
Films were prepared using an FCVA deposition system [17], operating with an arc current of 100 A. A magnetic double bend filter connecting the source and deposition chambers minimized the deposition of macroparticles. Polished silicon wafer substrates were cleaned with acetone and ethanol and mounted on a bias-compatible, resistive filament, substrate heater/holder within the FCVA system prior to deposition. The FCVA was then pumped to a base pressure of less than 10− 3 Pa. The nano-composite films of HSS/TiN were all deposited from the HSS/Ti cathode in a 0.29 Pa N2 and 0.013 Pa Ar atmosphere (Ar/N2 flow rates 5/60 sccm). For comparison purposes, a TiN film was deposited using a Ti cathode under similar conditions and a HSS/Ti film was deposited in an inert 0.30 Pa Ar atmosphere. The ion beam current density at the substrate (measured using an electrometer built into the bias power supply) was less than 1.0 mA/cm2 during all depositions. A schematic of the HSS/Ti cathode is shown in Fig. 1(a). Concentric channels of depth 5 mm were cut into a Ti solid cathode and subsequently filled with cold-sprayed HSS, resulting in the cathode shown in the upper part of the photograph shown in Fig. 1(b). The surface areas of the HSS and Ti sections were approximately equal. A series of films was prepared using different substrate bias and heater temperatures, as shown in Table 1. The surface temperature of the substrate measured during deposition using a thermocouple mounted on a separate silicon substrate was less than 35 °C during all depositions. The cathode exhibited uniform erosion during our depositions. After all depositions were complete, some preferential erosion of the HSS was observed at the edges of the tracks as shown in the lower part of Fig. 1(b).