Identification of Surface Debye Temperature of an Alkanethiol Self Assembled Monolayer on Au(111) by Low Energy Helium Diffraction

Using Low Energy Atomic Diffraction (LEAD), a nonperturbative and totally unpenetrating surface characterization technique, we have conducted measurements on the surface of self assembling monolayers (SAMs) of decanethiol on a Au(111) surface. Debye-Waller attenuation measurements were taken for substrate temperatures from 14.5~K to 110~K. For the lowest substrate temperatures, thermal Debye-Waller attenuation decreased consistent with a surface Debye temperature of about 100~K. The excellent order demonstrated by these particular data provided high resolution to six orders of the hexagonal peak (corresponding to the rt3 x rt3 thiol mesh). These data from higher order diffraction peaks allows us to more precisely measure the \underline {lateral} thermal vibration of the terminal methyl groups, which is considerably less than previously reported