**2.4. Thin film diagnostics**

Confirmation of thin film composition and thickness prior to RCF testing can give insight and predictability to the test results. RCF test results may be confounded due to unknown and unwanted constituents within the coating. Auger Electron Spectroscopy (AES) may be used to measure and sample atoms within the coating. The AES process uses a high energy electron beam to bore a small diameter hole, on the order of 1 – 2 nm, into the coating and ball surface. The material that is removed during the process is analyzed using an in-situ mass spectrometer to determine its species. Figure 3 presents constituent information related to a thin film of silver that was deposited onto a 7.94 mm diameter ANSI T5 steel ball. Starting from the left, which correlates to the surface of the coated-ball, carbon, oxygen, and silver are present in the coating. Moving to the far right in Figure 3, there is a strong transition from silver to iron and chromium, which are two constituents of T5. Based on the known composition of T5 and the AES results of Figure 3 the coating thickness may be approximated as 190 nm. More interesting however is the composition of the coating through its thickness, specifically, the iron, oxygen, and nickel present throughout the silver layer. The results of Figure 4 illustrate element composition of a nickel-copper-silver coating deposited on to a Si3N4 ball using a physical vapor deposition ion plating process. Referring to Figure 4, there is a high concentration of nickel and iron near the ball-coating interface at about 120 nm. Since the ball itself does not contain Ni or Fe, the presence of those elements and their concentrations suggest that contamination occurred during the deposition process. The results of Figures 3 and 4 suggest interlayer mixing and coating contamination during the deposition process which is likely to influence the lubrication properties of the film, and ultimately the RCF life. For more information concerning thin film diagnostics and deposition plasma diagnostics related to RCF life, see (Danyluk and Dhingra, 2012b).

**Figure 3.** Auger electron spectroscopy depth profile of a silver film deposited on a 7.94 mm diameter ANSI T5 steel ball.

**Figure 4.** Auger electron spectroscopy depth profile of a nickel-copper-silver film deposited on a 7.94 mm diameter Si3N4 ball.
