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

Huiwen Liu, Bharat Bhushan

Computer Microtribology and Contamination Laboratory
206 W. 18 th Avenue, The Ohio State University
Columbus, OH 43210-1107, USA

Recent studies have emphasized the use of biphenyl thiol (BPT) monolayers as a resist in electron lithography. In this paper, adhesion, friction and wear properties of biphenyl thiol (BPT) monolayers have been studied by atomic force microscopy (AFM). The BPT molecular chains have compliant features and can experience orientation under normal load, which in turn reduces the friction force. It is observed that after first several scans, the friction force of BPT is significantly reduced, but the surface height does not have any apparently change. These phenomena suggested 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. Through the wear resistance studies of a single BPT terrace, it is found that the wear lives of SAMs increase exponentially with terrace size.