Stress Formation During Self-Assembly of Alkanethiols on Differently Pre-Treated Gold Surfaces

Micromachined cantilevers can be applied as highly sensitive surface stress sensors and have been used to study the stress formation in self-assembled aJkanethiollayers on gold. We have investigated ways of cleaning the gold surface befare adsorption of gaseous hexanethiol in arder to optimise the rate and reproducibility of the adsorption process. Further objectives have been to maximise the stress signal during adsorption and to develop a method for removing sulphur immobilised molecules. Before each adsorption experiment the gold surface was cleaned in aqua regia, or in oxygen plasma. Adsorption of alkanethiols caused changes in surface stress, which closely followed Langmuir type kinetics. Cleaning with aqua regia generally provides higher adsorption rates and a larger stress change than cleaning with oxygen plasma. Based on AFM imaging, we propose that this is related to a larger surface roughness induced by aqua regia etching, resulting in a higher density of adsorption sites. Surfaces cleaned willi oxygen plasma, however, give more reproducible stress change curves. The stress change curves of surfaces cleaned with aqua regia become less stable af ter three subsequent cleanings, exhibiting oscillatory stress curves.