Characterization of the surface structure of CH3 and CF3 terminated n-alkanethiol monolayers self assembled on Au{111}

Abstract

Novel cyanoterphenyl self-assembly monolayers on Au(111) studied by ellipsometry, x-ray photoelectron spectroscopy, and vibrational spectroscopies Interaction of self-assembled monolayers of oligo(ethylene glycol)-terminated alkanethiols with water studied by vibrational sum-frequency generation Surface elemental and structural characterization of hexadecanethiol and heptadecanethiol (C 16 and C 17 for short͒ and 16,16,16-trifluorohexadecanethiol (FC 16 ) self-assembled monolayers ͑SAMs͒ on a Au͕111͖ surface have been obtained from time-of-flight scattering and recoiling spectrometry. The clean Au surface was also characterized in order to identify the azimuthal orientation of the SAMs with respect to the substrate. Classical ion trajectory simulations were used to relate the experimental scattering and recoiling data to the surface structure. The scattered and recoiled atoms originate from the outermost five-six atomic layers, and azimuthal anisotropy was observed in the measurements. The results provide a model for the SAMs in which the alkyl chains chemisorb with the S atoms situated above the face-centered-cubic ͑fcc͒ threefold sites of the Au͕111͖ surface to form a continuous film with a (ͱ3ϫͱ3)R30°structure that fully covers the Au surface. The orientation of the molecular axis azimuth of the SAMs relative to the Au azimuthal directions was determined. The data indicate that the molecular chains have specific tilt and twist angles relative to the Au surface and six coexisting domains resulting from the six equivalent tilt directions of the molecular axis. Dramatic changes in the anisotropic patterns of the ion scattering azimuthal scans from the surfaces of the SAMs with different terminations were observed. These phenomena result from the different tilt angles of the CH 3 and CF 3 groups. The data are consistent with free rotation of both the CH 3 and CF 3 groups. The C 16 SAM exhibited the best azimuthal features and was more resistant to radiation damage from the incident Ar ϩ scattering beam than the other films. Due to the tilt angle of the SAMs, an ''ion's eye view'' of the structure, i.e., the positions of the atomic cores as experienced by the incoming keV ions, reveals a regular array of sloping cavities within each unit cell.

Adsorbate Geometry Distinction in Arenethiols by Ion/Surface Reactive Collisions

“…Studies and molecular dynamics simulations have investigated the surface's role in the kinetic energy of the scattered ion beam resulting from changes in the self-assembled monolayer terminal group. [14][15][16] Surface-induced dissociation processes and hydrogen abstraction reactions are surfacemonolayer specific and thus can be employed to monitor the condition of self-assembled monolayer surfaces as well as to explore chain length effects on chain terminus orientation. 17 Self-assembled monolayers (SAMs) are widely used for the investigation of surface chemical and physical properties 18,19 and have potential applications in microelectronic device fabrication.…”

Of interfaces and spin transport across nanoscale layers

“…This reconstruction has a large effect on the calculated work function of a methane-thiolate SAM on Ag(111) [96]. Here we analyze the contributions to the work function and the interface dipole and contrast this analysis with the SAM/Au (111) case.…”

“…The initial structural models for these systems assumed an unreconstructed Ag(111) surface, similar to Au(111) [87,88,89]. Indeed, the structures of SAMs on unreconstructed Ag (111) and Au(111) surfaces are very similar. Yet the work function changes induced by SAM adsorption are quite different.…”

“…A persisting controversy surrounds the precise adsorption site of the sulfur headgroup on the Au(111) surface. Time of flight scattering and GXRD studies emphasize adsorption at (fcc and hcp) hollow sites [111,112], where the sulfur head-group binds to three Au surface atoms, while photoelectron diffraction (PED) and normal incidence x-ray standing wave (NIXSW) studies prefer on-top adsorption, where sulfur binds to one Au atom [113,114] . Computational studies offer a third possibility.…”

“…Thiol Alkyl Backbone Active Group Figure 1.1: Hexylthiol, a prototypical SAM assembling on Au (111). The SAM is anchored on the Au(111) surface by a thiol group (green), ordered by an alkyl backbone (black) and conferred a particular functionality by an active group (red).…”