Significantly improved stability of n-octadecyltrichlorosilane self-assembled monolayer by plasma pretreatment on mica

It has been well known that plasma pretreatment can stabilize the hydrocarbon silane monolayer self-assembled on a mica surface. However, the extent of this improvement is not well known. To explore this issue, n-octadecyltrichlorosilane (OTS) monolayers were self-assembled on both untreated and plasma-treated mica surfaces, and their interfacial properties were investigated and compared at various physical conditions (temperature, relative humidity, contact time, high stress, and contact repetition) through the use of surface force measurements. This study revealed that in highly humid conditions (> 90% relative humidity) there is a substantial difference of stability between untreated and plasma-treated surfaces, the OTS monolayer on plasma-treated mica surface being much more stable. In particular, protrusion behavior in the monolayer was always observed in untreated samples, but never in plasma-treated samples during contact repetition experiments. This directly demonstrates that the significantly improved stability directly comes from extensive chemical bonds between OTS molecules and the plasma-treated mica surface.