<div class="htmlview paragraph">The Focused Ion Beam (FIB) technique combined with Transmission Electron Microscopy (TEM) was used here for the first time to reveal the microstructure of thin surface layers on brake pads and rotors after a run-in period during which a stable coefficient of friction had developed. Generally the outermost layers of both, pad and rotor, comprise a complicated structure of nanocrystalline metal and metal oxide particles embedded in an amorphous matrix. Obviously oxidation plays a major role and the third body seems to behave like a granular medium. The contact areas were no protuberant plateaus in the regarded case. Therefore the flow of the granular third body layer seems to control friction force rather than ploughing of asperities.</div>