Nanotribology: an UHV-SFM study on thin films of AgBr(001)

We performed scanning force microscopy (SFM) in ultrahigh vacuum (UHV) on AgBr thin films which were in situ deposited on NaCl(001) substrates. The morphology of the initial growth stage and the nanotribological properties of these thin films are characterized and discussed. The lateral (frictional) forces are measured as a function of normal load. The local friction coefficients are extracted by means of the two-dimensional histogram technique. In the low load regime, friction coefficients of 0.33 ± 0.07 and <0.03 are found between probing SiO_x tip and AgBr and NaCl, respectively. The two-dimensional histogram reveals the transition from the force regime of wearless friction to the initial stage of wear on this thin film system. High-resolution SFM images of AgBr(001) are presented which reveal the atomic-scale periodicity of an unreconstructed AgBr(001) surface. The stick-slip nature of the frictional force is demonstrated.