COLL 515 |
| Benjamin M. Ocko1, Henning Kraack2, E Sloutskin2, M Deutsch2, and Peter Pershan3. (1) Physics Department, Brookhaven National Laboratory, Upton, NY 11973, (2) Physics Department, Bar-Ilan University, Ramat Gan, Israel, (3) Physics Dept, Harvard University, Cambridge, MA |
| Self assembled monolayers of n-alkanethiols on crystalline surfaces have been studied extensively and it is well known that the substrate plays an important role in determining their structural properties. Here we report surface x-ray scattering, grazing angle diffraction and reflectivity measurements, and surface-pressure isotherms results for n-alkanethiols, n=18 and 22, on the liquid mercury surface. At room temperature, with increasing coverage, the surface undergoes a sequence of phases, where the molecules form a (1) 2D Gas, (2) ordered lying down monolayer, (3) tilted standing-up monolayer with orthorhombic packing, and (4) and untilted standing up monolayer with hexagonal packing. The lying down phase is smectic-like, having long-range order normal to the chains but not along the chains. For the standing up phases, the unit cell is not body-centered and has a herringbone ordering. The structure suggests the possibility of sulfur dimerization, in the absence of a crystalline subphase. Our results will be compared with those on the crystalline metal surfaces of Ag and Au. |
|
Adamson Award Symposium Honoring Dave Allara and Ralph Nuzzo
Division of Colloid and Surface Chemistry |