Utilization of Raman spectroscopy in tribochemistry studies

Abstract

Raman spectroscopy is used to investigate the tribochemistry of thin film solid lubricants. The development of an in situ tribotester (pin-on-disk), to be used in conjunction with a Raman spectrometer, is described in detail and its utility is demonstrated in several MoS2-based thin film systems. The films studied include two commercial films and two films generated in-house by pulsed laser deposition (PLD). The commercial films were MoS2-PbO-graphite and MoS2-Sb2O3. The PLD films were MoS2 and MoS2-PbO. Wear test studies on the commercial films generally produced MoO3 as a reaction product. PLD films were deposited at room temperature and 300 °C. The PLD films formed at room temperature are amorphous and do not exhibit Raman scattering. The 300 °C films contain enough crystalline domains to exhibit Raman scattering. Initial rubbing of the room-temperature PLD films imparts enough crystallinity to support Raman scattering. Wear tests on the PLD films produce reaction products containing MoO3 and PbMoO4. These crystalline oxides have a large Raman scattering cross section, making them easily detectable. These data provide a unique insight into the tribochemical interactions of MoS2-based materials.