Molecular packing changes of alkanethiols monolayers on Au(111)under applied pressure

摘要

A study of the changes of molecular packing in self-assembled monolayers of alkylthiols on Au(111) induced by external pressure is presented. Atomic force microscopy (AFM) is used to measure the height of islands of alkanethiols partially convering the gold surface. The islands are made of ordered straight chain alkyltinol molecules tilted from the surface norma. Their height was found to decrease in a stepwise manner as a function of the load applied by the tip. Simulatneous stepwise increases in friction force were observed. A simple geometrical model involving the interlocking of alkyl chains at specific molecular tilt angles can explain the observation. According to the model. tilts in both the neares neighbor and the next-nearest neighbor directionsare necessary.