Ordered phases and temperature behaviour of CH3S self-assembled monolayers on Au(111)

We present the results of an experimental characterization of the ordered phases of CH3S chemisorbed on Au(111) and of their temperature dependence. The CH3S self-assembled monolayer has been grown by dosing dimethyl disulfide (DMDS) in ultrahigh vacuum at different substrate temperatures between 200 and 320 K and has been characterized by means of low energy He atom scattering (HAS) with time of flight detection and low energy electron diffraction (LEED) in a temperature range between 150 and 320 K. Upon following an appropriate dosing-annealing procedure, two ordered coexisting phases, i.e. a (3 x 4) and a (root 3 x root 3) 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 of the annealing step. The temperature behaviour of the ordered phases has been studied using LEED, showing that a first-order phase transition occurs at similar to 320 K.