Visualization of gold clusters deposited on a dithiol self-assembled monolayer by tapping mode atomic force microscopy

Tapping mode atomic force microscopy (TM-AFM) was used to characterize individual gold clusters deposited on a 1,4-benzenedimethanethiol layer. Aun (n=1–500) clusters were produced with a laser vaporization source and deposited with low kinetic energy (0.4 eV/atom). The free thiol group of the 1,4-benzenedimethanethiol layer gives rise to a large attractive force that inhibits reliable AFM probing of the sample with standard silicon tips. After etching the tip with hydrogen fluoride this interaction becomes repulsive and the image quality drastically improves. Tip–surface interaction measurements combined with an analysis of the cluster sizes reveal a configuration where clusters grow on top of the dithiol layer. The clusters are slightly deformed after impact and due to a strong sulfur–gold binding the cluster mobility on the layer is negligible.