CRYSTALLINE-STRUCTURES OF PRISTINE AND HYDRATED MERCAPTOHEXANOL SELF-ASSEMBLED MONOLAYERS AN AU(111)

The crystalline structures of hydroxy-functionalized hexanethiol self- assembled monolayers on Au(111) were characterized using gas-phase tra nsport of molecular precursors and an ultrahigh vacuum scanning tunnel ing microscope. In the pristine state the monolayer exhibits a commens urate lattice with an oblique primitive unit-cell of dimensions a = 3, b = root 13, alpha = a tan(2 root 3); a structure that is fundamental ly different than the hexagonal lattice observed for methyl-terminated monolayers. Hydration of the monolayer results in conversion to a pol ymorphic phase. These results demonstrate the importance of end-group chemical bonding in the molecular packing of this widely studied class of materials.