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We report the results of low energy helium atom scattering studies of the surface structure of n-alkane thiol overlayers on gold surfaces. We show that the primitive unit mesh of conventionally prepared self-assembled monolayers is not a simple ((root)3X(root)3)R30deg hexagonal mesh but is in fact a 8.65X9.99 $angstrom rectangle [corresponding to a c(4(root)3X2(root)3)R30deg overlayer]. We also discuss the results of recent molecular-beam-deposition experiments which produce ordered (5(root)3X(root)3)R30deg and rectangular (root)3Xn (n$AP10) overlayers, structures quite distinct from the solution-grown c(4(root)3X2(root)3)R30deg structure. Finally, we report thermally-induced reorganization of conventionally prepared self-assembled c(4(root)3X2(root)3)R30deg monolayers into (5(root)3X(root)3)R30deg and (root)3Xn (n$AP10)lattices. These experiments suggest that the variety of structures observed results from dependence of the molecular packing upon coverage. Our observations demonstrate that the ordering of thiols on gold is not as simple as early studies have proposed; rather, adsorption of these molecules on gold results in a rich variety of structures, depending upon the coverage and, possibly, the means of preparation.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only. |
