STRUCTURE AND GROWTH OF HEXYL AZOBENZENE THIOL SAMS ON AU(111)

The structure and growth of functionalized thiol self-assembled monola yers (SAMs) on Au(lll) derived from a new compound, 12-(4-((4-hexylphe nyl)azo)phenoxy)dodecane-1-thiol (''hexyl azobenzene thiol''), were ex amined by atomic force microscopy (AFM), X-ray photoelectron spectrosc opy (XPS), dynamic contact angles, Fourier transform infrared-reflecti on absorption spectroscopy (FTIR-RAS), and reflection UV-vis absorptio n spectroscopy. The hexyl azobenzene thiol SAM showed adsorption kinet ics comparable to that of alkanethiols. At the initial stage of SAM gr owth, formation of nanosize domains resulting from the rearrangement o f molecules on the surface was confirmed in a similar manner as for al kanethiol SAMs with long alkyl chains. The hexyl azobenzene thiol SAM exhibited a unique molecular ordering due to the intermolecular intera ction between tail groups. Molecular resolution AFM images revealed an expanded lattice (nearest neighbor spacings, a = 5.3 +/- 0.1 Angstrom , b = 5.6 +/- 0.1 Angstrom; angle between the two axes, phi = 85 +/- 1 degrees) relative to that of simple azobenzene-terminated SAMs, due t o the influence of the hexyl-terminal groups attached to the para-posi tion of the azobenzene moieties. Average molecular tilt and twist angl es (alpha = 14 degrees, beta = 42 degrees) were determined by quantita tive analysis of C-H stretching mode for FTIR-RAS data. The reflection UV-vis absorption spectra implied that the long axes of the trans-azo benzene moieties were aligned normal to the plane of surface in fully covered SAMs, while those were more tilted (aligned more parallel to t he surface plane) in the submonolayers.