Direct in situ surface X-ray scattering studies of electrochemical dissolution at technologically relevant rates are presented using Au(111) electrodes in acidic chloride-containing solutions as an example. The dissolution process was investigated with high time resolution by monitoring the time-dependent X-ray intensity at selected positions in reciprocal space and by simultaneously recording high-quality electrochemical data. With increasing electrode potential, transitions from step-flow to layer-by-layer dissolution, manifesting as layering oscillations in the X-ray intensity as well as in electrochemical current time transients, are observed prior to surface passivation. A quantitative analysis based on an atomic-scale structural model reveals that the dissolution process proceeds via progressive vacancy island nucleation in the whole active dissolution regime with next-layer nucleation occurring at comparatively low critical coverages between theta(c) = 0.29 and theta(c) = 0.44. This dissolution behavior shows the same characteristics as the intermediate "smooth multilayer growth" regime recently introduced in kinetic growth theories.

Au(111) electrodes have been modified with self-assembled rnonolayers (SAM) of 3-mercapto-1-propanesulfonic acid (MPS) and used as a substrate for Cu electrodeposition. Aqueous plating solutions contained 0.1 M H2SO4, low Cu concentrations (<= 80 mu M), and, optionally, 1.4 mM Cl ions. The deposition process was characterized by cyclic voltarnmetry (CV) and in-situ scanning tunneling microscopy (STM) as a function of the electrode potential. At potentials positive of Cu growth (>= 0.7 V-RHE), freshly modified electrodes are covered by an ordered (5 root 3 x root 21) MPS adlayer (alpha) both in Cl-free and Cl-containing electrolytes. The alpha adlayer becomes disordered at more negative potentials prior to the onset of Cu deposition (<= 0.65 V-RHE). In the potential regime of Cu underpotential deposition (UPD) (approximate to 0.2-0.65 V-RHE), the surface morphology strongly depends on the presence of Cl. In the absence of Cl, a transient, ordered Cu/MPS adlayer phase (delta) forms via 2D growth and covers the entire Au(111) surface. Subsequently, the delta phase transforms into a disordered Cu/MPS phase (sigma c(u)) with small, embedded Cu islands. In Cl-containing electrolyte, a disordered Cu/MPS/Cl phase (gamma) nucleates at Au step edges or surface defects and spreads laterally. Cu islands form simultaneously within the gamma phase. Two-dimensional growth of these islands results in a pure Cu-UPD layer. Overpotential deposition (OPD) proceeds via layer-by-layer mode with second layer nucleations at surprisingly small critical coverages (theta(c) << 0.5). Our observations differ significantly from those in previous studies, demonstrating that the Cu growth behavior critically depends on the concentrations of MPS, Cu, and Cl at the interface.

A novel approach to construct organized structures and tunable electronic properties of poly(3-hexylthiophene) (P3HT) monolayers on Au(111) surfaces was developed based on a self-assembly process in a liquid phase. On a bare Au(111) surface, P3HT adsorbs as a monolayer with a randomly oriented and curvy-wire morphology. When the gold surface was pre-modified by an iodine adlayer (I-Au(111)), the passivation effect of iodine decreases the substrate-adsorbate interaction. As a result, P3HT adsorbs as linear chains, stacking and folding into regular arrays of a polymer bundle. By controlling the electrode at more negative potentials, it is able to desorb the iodine adlayer from the substrate. The remaining P3HT adsorbs onto the Au(111) surface directly, retaining a linear and regular arrangement. However, a different electronic structure is imaged by scanning tunneling microscopy (STM). The scanning tunneling spectroscopy (STS) analysis reveals that this molecular image is associated with a 0.16 eV shift of the Fermi level toward HOMO position, indicating a stronger p-doping characteristic of the adlayer. The phenomenon is ascribed to an iodine-induced p-doping reaction which occurs during the desorption of iodine. This work demonstrates that electrode potential and pre-adsorbed halide adlayers can be effectively used to regulate the arrangement and electronic properties of adsorbed molecules on metallic substrates.

The adsorption behavior of an Cu electroplating additive, 3,3 thiobis-(1-propanesulfonic acid sodium salt) (TBPS) in a process of Cu deposition onto a single crystalline Au(111) surface is studied by an in-situ Surface-Enhanced Infrared Absorption Spectroscopy (SEIRAS). The SEIRAS spectra of the TBPS adlayer on a Cu film is investigated first and compared to that on an Au film. These results are utilized to evaluate the characteristics of TBPS adlayer on the electrode surface during the Cu deposition and stripping processes. The results show that the SEIRAS spectra of TBPS adsorbed on the Cu film resembles closely to that on the Au film, and the most pronounced peaks are symmetric S-O (ss-SO) and asymmetric S-O (as-SO) stretching modes. However, the as-SO band is sharper with a higher intensity on the Cu film. Since the ss-SO and as-SO peaks correspond to the molecular with upright and lie-down orientations, respectively, it implies that the TBPS molecules have higher ratio of lie-down orientation on the Cu film. In the Cu electrodeposition process, the cyclic voltammetry (CV) result shows that the presence of the TBPS in the HClO4 solution can decrease the inhibition effect of HClO4 to the Cu deposition. For the spectra measured at various potential during cathodic and anodic sweeping, an obvious change of the spectra occurs at ca. 0.6 V, the initiation of Cu underpotential deposition (Cu-UPD). For potentials higher and lower than 0.6 V, the spectra are similar, respectively, to those measured for the Au and Cu films. This result indicates that the TBPS molecules originally adsorbing on the Au film transfer to the surface of deposited Cu layer. This inference is also confirmed by the variation in wavenumber and peak intensity of ss-SO and as-SO peaks during the potential sweeping.

Direct in situ surface X-ray scattering studies of electrochemical dissolution at technologically relevant rates are presented using Au(111) electrodes in acidic chloride-containing solutions as an example. The dissolution process was investigated with high time resolution by monitoring the time-dependent X-ray intensity at selected positions in reciprocal space and by simultaneously recording high-quality electrochemical data. With increasing electrode potential, transitions from step-flow to layer-by-layer dissolution, manifesting as layering oscillations in the X-ray intensity as well as in electrochemical current time transients, are observed prior to surface passivation. A quantitative analysis based on an atomic-scale structural model reveals that the dissolution process proceeds via progressive vacancy island nucleation in the whole active dissolution regime with next-layer nucleation occurring at comparatively low critical coverages between theta(c) = 0.29 and theta(c) = 0.44. This dissolution behavior shows the same characteristics as the intermediate "smooth multilayer growth" regime recently introduced in kinetic growth theories.

Detailed X-ray diffraction studies that allow us to monitor the solid-liquid interface structure during electrodeposition with high time resolution are demonstrated using as an example the homoepitaxial growth on Au(100) electrodes in HCl solution at a deposition rate of similar to 4.2 ML/min. By measuring X-ray intensity curves I(t) after a potential step at different diffraction index L, time-dependent crystal truncation rods (CTR) can be obtained. In the potential regime of the unreconstructed Au(100) surface (0.35 V), the initial stages are well described by nucleation and growth of Au monolayer islands. For deposition onto the reconstructed surface at -0.2 V, CTRs and complementary grazing incidence diffraction studies reveal rapid formation of the hex reconstruction within the first 4 s after the potential step, followed by layer-by-layer growth.

Self-assembled monolayers (SAMs) of 3,3'-thiobis(1-propane-sulfonic acid, sodium salt) (TBPS) on Au(111) electrodes have been characterized by scanning tunneling microscopy and cyclic voltammetry in aqueous perchloric acid solutions. TBPS exhibits an adsorption behavior typically observed for dialkyl sulfides including intact adsorption and low coverage phases with molecules predominantly lying flat on the surface. On the other hand, an untypical chemical bond and well domains were determined which resemble the characteristics of alkenethiol SAMs. When the adlayer was prepared at its open circuit potential (OCP), a (6 x 3 root 3) TBPS adlayer phase was observed at potentials E > 0.7 V(RHE) in TBPS-free electrolyte. At more cathodic potentials, the adlayer transforms irreversible to a disordered phase. In contrast, in situ STM studies in TBPS-containing electrolyte reveal a very complex, potential-dependent adsorption behavior. With increasing electrode potential, the structure of the adlayer transforms in sequence from a disordered phase sigma, to a low coverage stripe phase alpha, to a high coverage stripe phase beta, and finally to a disordered aggregate phase sigma(a). The re verse cathodic sweep shows transitions from sigma(a) to beta, back to sigma(a), and to an ordered adlayer phase gamma. All of these phases significantly differ from the (6 x 3 root 3) phase oil are not transient phases at OCP. This behavior is attributed to the influence of the electrode potential on intermolecular and molecule - substrate interaction, as well is on the TBPS coverage Furthermore, the cathodic deposition of Au-TBPS complexes results in the formation of Au islands with fractal morphology.

A combined structural and electrochemical study of self-assembled monolayers of the azobenzene-containing alkane thiol N-(2-mercaptoethyl)-4-phenylazobenzamide on Au(111) by scanning tunneling microscopy, synchrotron X-ray reflectivity, and cyclic voltammetry is presented. Densely packed monolayers are observed, in which the molecules are arranged in chains forming an ordered (root 13 x root 3) structure with a coverage of 2/7 ML. The molecules are tilted by 40 degrees relative to the surface normal, resulting in a monolayer thickness of 13.7 angstrom. A total charge of 65.2 +/- 4.3 mu C/cm(2) corresponding to 1(e-) per molecule and apparent electron transfer coefficients of approximate to 0.5 are found. (C) 2008 Elsevier B.V. All rights reserved.

The impact of 3,3'-thiobis(1-propanesulfonic acid, sodium salt) (TBPS) on Cu/Au(111) electrodeposition has been investigated by electrochemical methods and scanning tunneling microscopy (STM). Cyclic voltammetry and galvanostatic experiments indicate that Cu growth on Au(111) - which is known to be strongly kinetically hindered in additive-free, aqueous perchloric acid solutions - proceeds significantly faster in the presence of TBPS. The TBPS molecules either "float" on top of the growing film or become incorporated into the deposit. Complementary in situ STM studies show that Cu underpotential deposition (UPD) proceeds via two distinct mechanisms. One-dimensional growth of Cu stripes was observed between 0.05 and 0.35 V-RHE for TBPS-modified Au(111) electrodes. Each stripe is composed of two or three parallel rows of Cu atoms oriented along the main crystallographic directions of the Au(111) substrate. An increase of the TBPS concentration near the solid/liquid interface restricts the Cu stripe growth to a narrow potential regime between 0.3 and 0.35 V-RHE and two-dimensional Cu island growth becomes the favored growth mechanism. The latter fully dominates in TBPS-containing electrolyte. Cu growth in the overpotential deposition (OPD) regime results in a smooth Cu film with low surface roughness, in contrast to defect-mediated 3D island growth in additive-free electrolytes. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.057202jes] All rights reserved.