Study of the Hyperthermal Proton Bombardment Effects on Self-Assembled Monolayers of

Proton bombardment on self-assembled monolayers (SAMs) of dodecanethiol formed on a gold surface is performed and its effect is studied by scanning tunneling microscope (STM) and time-of-flight secondary ion mass spectrometry (TOF-SIMS). STM gives clear evidence that a relatively uniform layer of organic nanoclusters with different sizes and densities can be created on the surface. Analysis of the mass spectra collected from the SAM samples reveals that large hydrocarbon fragments from the bombarded sample area show higher intensity than those from the virgin area, which is a strong indication that selective C-H bond cleavage and cross-linking are induced by the proton beam bombardment. We demonstrate that the size and density of the clusters can be harnessed by controlling the proton beam energy and fluence. The clusters grow bigger, at the expense of a decreasing number density, with increasing proton energy or fluence