Self-Assembled Monolayers of Small Aromatic Disulfide and Diselenide Molecules on Polycrystalline Gold Films:  A Comparative Study of the Geometrical Constraint Using Temperature-Dependent Surface-Enhanced Raman Spectroscopy, X-ray Photoelectron Spectroscopy, and Electrochemistry

Abstract

A detailed investigation of the self-assembled monolayers of diphenyl disulfide (DDS), diphenyl diselenide (DDSe), and naphthalene disulfide (NDS) on polycrystalline gold films using surface-enhanced Raman spectroscopy (SERS), X-ray photoelectron spectroscopy (XPS), and electrochemistry is presented. Whereas DDS dissociatively chemisorbs on Au, in both DDSe and NDS, the Se−Se and S−S bonds, respectively, are preserved upon adsorption. All of the molecules adsorb with the molecular plane perpendicular to the surface. Temperature-dependent SERS studies suggest that the DDS monolayer is by far the most stable one and is stable up to a temperature of 423 K. Both DDSe and NDS desorb without breaking the diselenide and disulfide bonds. None of the monolayers show any structural change upon heating. XPS investigations show the presence of beam-induced damage upon X-ray exposure to DDS and NDS monolayers, and the damage is greater in the latter. Electrochemical investigations support the SERS and XPS data. Number of pinholes and defects are much less in the DDS monolayer than in NDS and DDSe. The impedance parameters such as double-layer capacitance, charge-transfer resistance, and diffusion coefficients measured at different frequencies support the above conclusion. It is suggested that the geometric constraint imposed by the rigid naphthalene ring inhibits the cleavage of the S−S bond, and consequently, the adsorption sites for sulfurs are not strongly bonded. For DDSe, it appears that the Se−Se distance is such that appropriate binding sites are available, thus leading to a more ordered monolayer. For DDS, the facile cleavage of the S−S bond leads to strong binding of the adsorbate molecules at the preferred surface sites, resulting in a rather well-ordered self-assembled structure.

Comparative Behavior of Aromatic Disulfide and Diselenide Monolayers on Polycrystalline Gold Films Using Cyclic Voltammetry, STM, and Quartz Crystal Microbalance

“…This could be due to the easy relaxation appearing from bond cleavage for DDSe and DDS, while for NDS, the fused ring may impose constraints for side movement and a lesser interaction affinity of DDSe than for the corresponding disulfides. These results underline the importance of intramolecular conformational changes in controlling the monolayer packing density and is in agreement with the results of surface-enhanced Raman spectroscopy (SERS) investigations (17).…”

“…All other chemicals used in this work were purchased from Aldrich Co. and were used as received. Before the SAMs were deposited, the substrates were cleaned by the standard cleaning procedure described earlier (17). After repeated cleaning cycles using sulfochromic acid, aqueous HF, and deionized water, the substrates were blown dry with pure argon and were immediately transferred into a deaerated 1 mM solution of the appropriate compound in acetonitrile.…”

Structure and dynamics of monolayers on planar and cluster surfaces

“…SAMs of dialkyl chalcogenides on Au(111) have been studied by Nakamura et al, and they found that selenides form ordered monolayers on Au(111) with long exposure time, whereas tellurides form disordered monolayers [34]. A detailed investigation of the selfassembled monolayers of diphenyl disulfide (DDS), diphenyl diselenide (DDSe), and naphthalene disulfide (NDS) on polycrystalline gold films was performed recently [35]. Whereas DDS dissociatively chemisorbs on Au, in both DDSe and NDS, the Se-Se and S-S bonds, respectively, are preserved upon adsorption.…”

Characteristics of Cl‐ and Au‐Containing Nanocomplex and Its Effect on the Following Electrodeposition of Polypyrrole

“…Numerous methods can be used to obtain rough metals substrates, including plasma treatment [11], sputtering coating [3,15], mechanically polishing by using abrasives [16] and vacuum evaporation deposition [4,9,12,17,18]. However, a controllable and reproduced surface roughness can be generated through control of the electrochemical oxidation-reduction cycles (ORC) procedure [19].…”

“…In chemical enhancement, most studies [1,3,5,11,22] were devoted to molecules adsorbed on activated metals surfaces, especially to pyridine adsorbed on roughened silver [14,18,23,24]. Plays et al [20] studied the oxidation behavior of poly-1,8-diaminonaphthalene thin film, preparing by a cyclic voltammetry method, deposited on electrochemically roughened metals via SERS spectrum.…”