Ocko, B. M.Kraack, H.Pershan, PeterSloutskin, E.Tamam, L.Deutsch, M.2013-02-282005Ocko, B. M., H. Kraack, Peter S. Pershan, E. Sloutskin, L. Tamam, and M. Deutsch. 2005. Crystalline phases of alkyl-thiol monolayers on liquid mercury. Physical Review Letters 94(017802).0031-9007http://nrs.harvard.edu/urn-3:HUL.InstRepos:10354244The 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  Å\(^2\)/molecule from a rectangular packing of molecules tilted by 27\(^\circ\) 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.en-USJournal Article10.1103/PhysRevLett.94.017802