title: Crystalline phases of alkyl-thiol monolayers on liquid mercury.
abstract: The structure of octadecanethiol monolyers on liquid Hg surfaces, measured with subangstrom resolution, evolves with increasing coverage from a laterally disordered phase of surface-parallel molecules to ordered rotator phases of surface-normal molecules. For the latter, an abrupt transition is found at 19 A(2)/molecule from a rectangular packing of molecules tilted by 27 degrees in the nearest-neighbor direction to a hexagonal unit cell of untilted molecules. The unit cell of the tilted phase is centered for the chains and noncentered for the headgroups. The thiol headgroups associate in pairs with a single Hg atom, and the bonds form long-range orientational order. The different order of thiols on Au(111) and on Hg highlights the subphase's role in determining the overlayer's structure.
authors.affiliation: Department of Physics, Brookhaven National Laboratory, Upton, NY 11973, USA. ocko@bnl.gov
authors.forename: B M
authors.initials: BM
authors.lastname: Ocko
authors.forename: H
authors.initials: H
authors.lastname: Kraack
authors.forename: P S
authors.initials: PS
authors.lastname: Pershan
authors.forename: E
authors.initials: E
authors.lastname: Sloutskin
authors.forename: L
authors.initials: L
authors.lastname: Tamam
authors.forename: M
authors.initials: M
authors.lastname: Deutsch