Improvements in the Characterization of the Crystalline Structure of Acid-Terminated Alkanethiol Self-Assembled Monolayers on Au(111) (original) (raw)
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Self-assembled monolayers of alkanethiols on Au(111): surface structures, defects and dynamics
Physical Chemistry Chemical Physics, 2005
The surface structures, defects and dynamics of self-assembled monolayers (SAMs) on Au(111) are reviewed. In the case of the well-known c(4 Â 2) and O3 Â O3 R301 surface structures, the present discussion is centered on the determination of the adsorption sites. A more complex scenario emerges for the striped phases, where a variety of surface structures that depends on surface coverage are described. Recently reported surface structures at non-saturation coverage show the richness of the self-assembly process. The study of surface dynamics sheds light on the relative stability of some of these surface structures. Typical defects at the alkanethiol monolayer are shown and discussed in relation to SAMs applications.
Surface structure and interface dynamics of alkanethiol self-assembled monolayers on Au(111)
The journal of physical chemistry. B, 2006
Scanning tunneling microscopy (STM) and high-resolution electron energy loss spectroscopy (HREELS) were used to examine the structural transitions and interface dynamics of octanethiol (OT) self-assembled monolayers (SAMs) caused by long-term storage or annealing at an elevated temperature. We found that the structural transitions of OT SAMs from the c(4 x 2) superlattice to the (6 x square root 3) superlattice resulting from long-term storage were caused by both the dynamic movement of the adsorbed sulfur atoms on several adsorption sites of the Au(111) surface and the change of molecular orientation in the ordered layer. Moreover, it was found that the chemical structure of the sulfur headgroups does not change from monomer to dimer by the temporal change of SAMs at room temperature. Contrary to the results of the long-term-stored SAMs, it was found that the annealing process did not modify either the interfacial or chemical structures of the sulfur headgroups or the two-dimension...
Langmuir, 2010
A characterization of the 1,8-octanedithiol (ODT) self-assembled monolayer (SAM) formed from a Triton X-100 lyotropic medium has been conducted by electrochemical techniques. It is found that an ODT layer of standing-up molecules is obtained at short modification time without removing oxygen from the medium. The electrochemical study shows that the ODT layer formed after 15 min of modification time has similar electron-transfer blocking properties to the layers formed from organic solvents at much longer modification times. On the basis of XPS data, it is demonstrated that the inability to bind gold nanoparticles (AuNPs) is due to the presence of extra ODT molecules either interdigited or on top of the layer. Treatment consisting of an acid washing step following the formation of the ODT-Au(111) SAM produces a layer that is able to attach AuNPs as demonstrated by electrochemical techniques and atomic force microscopy (AFM) images.
Electrochemical STM investigation of 1,8-octanedithiol monolayers on Au(111)
Surface Science, 2006
The surface structure of Au(1 1 1) electrodes covered by 1,8-octanedithiol self-assembled monolayers (SAMs) was studied with in situ scanning tunnelling microscopy (STM) as a function of the electrode potential in acidic and alkaline electrolytes. We investigated the correlation between the dynamics of the SAM and the underlying gold atoms during the reductive desorption and oxidative readsorption processes. The reductive desorption of 1,8-octanedithiol is characterized by a transition from a compact monolayer with an upright molecular configuration to a striped phase with flat lying dithiol molecules, whereas during the oxidative readsorption process the surface first becomes increasingly covered by the striped phase until the transition to the compact phase occurs. We also considered under equivalent conditions 1-octanethiol/Au(1 1 1) SAMs which were used as a reference to evaluate the influence of the-SH terminal group on the structure and stability of dithiol SAMs. The desorption and readsorption of both the dithiol and the monothiol have a considerable influence on the substrate morphology which is manifested in the dynamics of vacancy islands, gold islands and indentation of step edges. Quantum mechanical calculations in the framework of density functional theory (DFT) show that adsorbed thiols greatly facilitate the detachment of gold atoms from step edges. The high mobility of gold atoms observed experimentally is compatible with the presence of a defected layer of gold atoms. The DFT results suggest that the formation of a monolayer may involve the diffusion and self assembly of thiolate-Au moieties rather than the diffusion of the bare thiolates across the surface. This mechanism explains the formation of a defected layer of gold atoms.
Journal of Electroanalytical Chemistry, 2011
Self-assembled adlayers of alkanedithiols (DTs) on Au(1 1 1) are studied with electrochemical techniques (reductive desorption experiments, redox couples cyclic voltamperometry and electrochemical impedance spectroscopy) in order to characterize adlayer structures. The formation of intralayer and interlayer disulphide bonds (S-S) strongly affects the structure of the layers. We considered different variables which influence the amount of S-S bonds: the length of the alkyl chain (from 2 to 9 C atoms), the polarity of the solvent of the forming solution (ethanol, n-hexane and toluene), the O 2 level and the use of a postdeposition treatment with mild reducing agents. Optimal experimental conditions for the formation of DT monolayers with controlled amount of S-S bonds for both short and long alkyl chains are precisely identified. According to our results, short chain DTs form multilayer structures (interlayer S-S bonds) under typical procedures; whereas long chain DTs present intralayer S-S bonds. The use of low polarity solvents during the layer formation as well as the use of reducing agents after deposition favours the formation of good quality DT monolayers.
Direct observation of sulfur dimers in alkanethiol self-assembled monolayers on Au(111)
Physical Review B, 1999
High-resolution electron-energy-loss spectra of octadecanethiol self-assembled monolayers ͑SAM's͒ on Au thin films have been obtained after annealing the sample to various temperatures. Annealing to 375 K results in the appearance of the S-S stretch at 530 cm Ϫ1 , a direct observation of sulfur dimers for alkanethiol SAM's adsorbed on Au. The appearance of dimers following annealing is explained by the presence of an activation barrier to the formation of gauche defects at the S-C bond. ͓S0163-1829͑99͒51016-3͔ RAPID COMMUNICATIONS
Using alkanethiol dense packing as a starting point, we have found six prototypical packing structures commensurate with the (3 Â 2 √ 3) supercell of the Au (111) surface. Five of the six structures are not compatible with the flat surface conditions but can be fitted to a reconstructed surface. Combined with density functional theory calculations and simulations of grazing incidence X-ray diffraction maps and of scanning tunneling microscopy images, this allowed us to refine and assess the recently proposed models of the c(4 Â 2) self-assembled monolayers involving thiolate-adatom and thiolate-adatom-thiolate species and to propose a new model with four gold adatoms per unit cell. Langmuir 2009, 25(13), 7353-7358 Voznyy and Dubowski Article (52) Torrelles, X.; Vericat, C.; Vela, M. E.; Fonticelli, M. H.; Millone, M. A. D.; Felici, R.; Lee, T. L.; Zegenhagen, J.; Munoz, G.; Martin-Gago, J. A.; Salvarezza, R. C.