3He + ISS of 11-mercaptoundecanoic acid self-assembled monolayers onto gold

Abstract

ISS and XPS spectra were recorded before and after forming an organized molecular assembly (OMA) of HS(CH 2) 10COOH, 11-mercaptoundecanoic acid (MUA) on 20 nm thick gold thin films on a silicon substrate. The MUA/OMA is attached to gold via the thiol (SH) group, and the acid group (CO 2H) becomes the outer monolayer. At low current densities, l keV 3e + ISS showed no detectable amount of gold on the surface, indicating the gold film was completely covered by the OMA. XPS signals acquired from the OMA showed carbon, oxygen, sulfur, gold, and a trace of silicon. When using ISS at higher current densities to sputter the OMA, the same elements were detected. The presence of silicon at the Au/OMA interface is attributed to silicon diffusion from the substrate through 20 nm of gold at 22°C. Some potential uses of ISS for studying well-characterized OMAs are also suggested. The primary purpose of this work is to use the surface-monolayer sensitive ISS technique on a well-characterized OMA on gold to confirm conclusions reached in prior work about the coverage of gold films by the OMA. ISS of self-assembled MUA on gold has not been previously reported, and our results have provided additional interesting information.