Nanoscale friction and wearing of octadecyltrichlorosilane covered silicon surface

Abstract

Silicon wafers were silanized by plasma hydroxylation and chemical vapour deposition of octadecyltrichlorosilane [OTS, CH3(CH2)17SiCl3]. Then, the OTS covered silicon samples were used in atomic force microscopy (AFM) measurements of wearing and friction at nanoscale. Wearing experiment performed by 1000 cycles of forwards and backwards movements of sharp AFM tip revealed formation of a wearing track with a depth that was much smaller than the thickness of OTS coating, which confirmed a very good wearing property of OTS coating. Friction versus normal loading force experiments performed with the same AFM tip revealed a nonlinear dependence of friction force on the normal loading force in agreement with prediction of Bowden and Tabor’s theory of friction and an increase of friction with the moving speed. Dependence of friction force on the sliding speed is attributed to a transfer of kinetic energy from the moving AFM tip to individual molecules of OTS coating.