Orientation and relocation of biphenyl thiol self-assembled monolayers under sliding

Recent studies have emphasized the use of biphenyl thiol (BPT) monolayers as a resist in electron lithography. In this paper, friction and wear properties of BPT monolayers have been studied by atomic force microscopy. The BPT molecular chains are compliant and experience orientation under normal load, which in turn reduces the friction force. During sliding it is observed that after the first several scans, the friction force of BPT is significantly reduced, but the surface height does not show any apparent change. These observations suggest that the orientation is reversible and can be facilitated by initial sliding. Relocation and accumulation of BPT occurs during the first several scans, which lead to the formation of larger terrace. Based on the wear studies of a single BPT terrace, it is found that the wear lives of self-assembled monolayers increase exponentially with terrace size.