Surface structure and thermal motion of n-alkane thiols self-assembled on Au(111) studied by low energy helium diffraction
- 15 June 1991
- journal article
- research article
- Published by AIP Publishing in The Journal of Chemical Physics
- Vol. 94 (12), 8493-8502
- https://doi.org/10.1063/1.460082
Abstract
Low energy helium diffraction has been used to study the packing and thermal motion of the terminal CH3 groups of monolayers of n‐alkane thiols self‐assembled on Au(111)/mica films and a Au(111) single crystalsurface. At low temperatures (<100 K), the terminal CH3 groups are arranged in domains containing a hexagonal lattice with a lattice constant of 5.01 Å. As the length of the carbon chain is shortened, an abrupt decrease in the diffraction peak intensities is observed for CH3(CH2)9SH/Au(111)/mica, and no diffraction is observed for CH3(CH2)5SH/Au(111)/mica. This is indicative of a sudden decrease in surface order at around ten carbon atoms per chain. A semi‐quantitative estimation of the average domain size of each monolayersurface shows a maximum of 46 Å at intermediate chain length [CH3(CH2)13SH/Au(111)/mica], decreasing to 26 Å at longer [CH3(CH2)21SH/Au(111)/mica] and 41 Å at shorter [CH3(CH2)9SH/Au(111)/mica] chain lengths. No phase transitions could be detected at the surfaces of these monolayers from 35 K to 100 K, but as expected for a soft material, the thermal motion of the n‐alkane thiol molecules increases with increasing surface temperature and reduces the diffraction intensities to zero at around 100 K. The relative mean square displacements of the surface CH3 groups along the directions perpendicular and parallel to the surface have been calculated from the temperature dependence of the diffraction peak intensities using the standard Debye–Waller formalism. The measured values are in good agreement with the results from a recent molecular dynamics simulation. [J. Hautman and M. Klein, J. Chem. Phys. 9 3, 7483 (1990).]Keywords
This publication has 39 references indexed in Scilit:
- Helium diffraction from overlayers physisorbed on a self-assembled organic monolayerLangmuir, 1990
- Molecular dynamics simulation of the effects of temperature on a dense monolayer of long-chain moleculesThe Journal of Chemical Physics, 1990
- Formation of monolayers by the coadsorption of thiols on gold: variation in the head group, tail group, and solventJournal of the American Chemical Society, 1989
- Modeling Organic Surfaces with Self‐Assembled MonolayersAngewandte Chemie-International Edition, 1989
- Formation of monolayer films by the spontaneous assembly of organic thiols from solution onto goldJournal of the American Chemical Society, 1989
- Structure and dynamics of periodic and randomly distributed surface features by high resolution helium atom scatteringJournal of Vacuum Science & Technology A, 1987
- Tilt and splay of surfactants on surfacesPhysical Review A, 1986
- Very low-energy scattering of helium atoms from crystal surfaces. A quantitative comparison between experiment and theoryFaraday Discussions of the Chemical Society, 1985
- Atom scattering as a quantitative surface probe: Noble-gas monolayer and bilayer adsorbed on graphitePhysical Review B, 1984
- Selective adsorption resonances in the scattering of helium atoms from xenon coated graphite: Close-coupling calculations and potential dependenceThe Journal of Chemical Physics, 1983