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

The crystalline structure of hydroxy-functionalized hexanethiol self-a ssembled monolayers on Au(111) were characterized using gas-phase tran sport of molecular precursors and an ultrahigh vacuum scanning tunneli ng microscope. In the pristine state the monolayer exhibits a commensu rate lattice with an oblique primitive unit-cell of dimensions a=3, b= root 13, alpha=a tan(2 root 3); a structure that is fundamentally diff erent than the hexagonal lattice observed for methyl-terminated monola yers. Hydration of the monolayer results in conversion to a polymorphi c phase. These results demonstrate the importance of end-group chemica l bonding in the molecular packing of this widely studied class of mat erials.