Ordered phases and temperature behaviour ofCH3S self-assembled monolayers on Au(111)

Abstract

We present the results of an experimental characterization of the ordered phases ofCH3S chemisorbed on Au(111) and of their temperature dependence. TheCH3S self-assembled monolayer has been grown by dosing dimethyl disulfide (DMDS) in ultrahighvacuum at different substrate temperatures between 200 and 320 K and has been characterizedby means of low energy He atom scattering (HAS) with time of flight detection and lowenergy electron diffraction (LEED) in a temperature range between 150 and 320 K. Uponfollowing an appropriate dosing–annealing procedure, two ordered coexisting phases, i.e. a(3 × 4) and a periodicity, have been observed using HAS, in agreement with previous findings.Moreover, a new protocol consisting of a single-step dosing of DMDS at higher pressures(10−5 mbar range) has been found to produce both coexisting phases without any need ofthe annealing step. The temperature behaviour of the ordered phases has beenstudied using LEED, showing that a first-order phase transition occurs at∼320 K.