Low-Energy Ion-Induced Tensile Stress of Self-Assembled Alkanethiol Monolayers

Monolayers of alkanethiols on gold have been exposed to low energy Ar ion. A micromechanical cantilever sensor technique was used to determine in situ the influence of the ion dose on the surface stress in the monolayers. In contrast to compressive surface stress during self-assembled monolayer growth, a strong tensile surface stress of about −0.7 N/m was found when the sensor is exposed to Ar ions. This value is 3–4 times larger than the compressive surface stress. We attribute this stress to a reaction between the alkyl chains in the molecules of the alkanethiol monolayer.