Laser-induced short time scale thermal chemistry of perfluoropolyether lubricant films

Abstract

We investigate the effect of heating a perfluoropolyether lubricant film in a localized area for relatively short time periods using laser irradiation versus conventional oven heating. These experiments help provide understanding on how flash temperatures generated at frictional contacts affect the thermal chemistry of lubricant films. In these experiments, a CO2 laser heats a 50 μm wide area of a silicon wafer for time periods ranging from 0.1 to 60 s. The surface temperature within the heated area (up to 280°C in these experiments) is monitored with a second laser by measuring the change in reflectivity near the center of the heated area. A major difference observed for laser heating compared to oven heating is that the effective evaporation rate is orders of magnitude higher for laser heating. If the lubricant film is heated for sufficiently long enough time at high temperatures, we are able to observe thermal bonding of the lubricant via its alcohol end groups to the silicon oxide surface, followed by thermal decomposition of the lubricant molecules. After laser heating, we are able to observe the diffusion of lubricant back into the localized heated area using a combination of optical microscopy and imaging ellipsometry.