Structural investigation of Au(111)/butylthiolate adsorption phases

The structures of the high-coverage ('standing-up') and low-coverage ('ying-down') phases of butylthiolate on Au(111) have been investigated by a range of experimental methods. Normal incidence X-ray standing waves, photoelectron diffraction and near-edge X-ray absorption. ne structure results all identify the local S headgroup site as atop a surface Au atom in a bulk continuation site for both high-and low-coverage phases. Low energy electron diffraction shows the low-coverage phase to have a (12 x root 3) rect. surface mesh with glide-line symmetry (pmg space group), the long dimension of this mesh being approximately four times the length of the butylthiolate molecule. A structural model is proposed for this phase based on two different enantiomers of an Au-adatom-dithiolate species that is consistent with these results and with recent finding for propylthiolate on this surface using low-temperature scanning tunnelling microscopy (O. Voznyy, J. J. Dubowski, J. T. Yates Jr. and P. Maksymovych, J. Am Chem. Soc., 2009, 131, 12989)