A spectroscopic study of a copper surface under boundary lubrication: I. Chemisorbed stearic acid multilayers

The thickness of chemisorbed stearic acid films on copper surfaces was deduced by Fourier transform infrared (FTIR) spectroscopy and Auger electron spectroscopy (AES). The chemisorption was detected by FTIR from the carboxyl (COO) asymmetric stretching band at 1585 cm⁻¹. Multilayer growth was observed by monitoring the intensity increase in the asymmetric CH₂ stretching mode at 2915 cm⁻¹. The growth of the chemisorbed layer was found to depend on the concentration of the stearic acid/hexadecane solution. The chemisorption kinetic profile had a step-function due to the change in the number of layers. High carbon concentration in Auger spectroscopic characterisation indicated that the surface was coated with a stearic acid film. AES depth profiling analysis supports this step-function model and agrees well with the FTIR results.