To study the mode of action of lubricant oil additives usually tribometer tests were performed to determine the friction and wear properties of different systems. Following the experiment, analytics will be carried out in more in-depth investigations, to give information about the chemical composition of the tribofilms. These types of tests are so called post-mortem and ex-situ studies - therewith the determination of the initial processes is almost impossible.
In order to investigate exactly those initial processes we use an integrated in-vacuum measurement set-up, including an effusion cell, a tribometer and a photoelectron spectrometer (XPS). In the effusion cell the lubricant additives were deposited on an iron oxide substrate with a certain film thickness. The adsorbed layer(s) (chemisorbed and/or physisorbed) were investigated by XPS-analyses. This allows us to determine the fundamental chemical bindings of additive molecules and the substrate. In a next step we perform tribometer tests in vacuum to investigate the influence of the ultra –thin additive layer(s) on the coefficient of friction. Following the tribometer tests, again XPS- analyses were done to determine the influence of pressure and shear on the adsorbed additive layer.