A new kinetic model for homoepitaxial growth on a singular surface is presented. The model combines the familiar rate equations approach and the concept of a feeding zone that allows connection between the growth processes occuring in neighbouring monolayers. The model involves the irreversible 2D nucleation, growth and coalescence of islands in each growing monolayer and consists of an infinite set of coupled rate equations for the adatom and island densities and coverage in successive monolayers. The temporal evolution of the surface morphology (rms roughness and RHEED intensity) is studied with this model. It is shown that the growth mode is fully determined by a single dimensionless parameter μ = D/J where D and J are the normalized surface diffusion coefficient and deposition flux, respectively. There exist five regions of μ corresponding the different growth regimes varying from smooth 2D layer-by-layer growth at sufficiently high values of μ (>108) to very rough Poisson-like random deposition growth at μ <10−4. The extension of the model to the case of heteroepitaxy is also discussed.

We have investigated transport processes on a stepped Ag(111) surface in an aqueous electrolyte by analyzing the equilibrium step fluctuations as a function of the electrode potential. No influence of the electrolyte and the potential was found in the regime of negative potentials with respect to the saturated calomel electrode. As the potential becomes positive and approaches the dissolution limit, the increasing magnitude of the step fluctuations and the change in the time dependence indicate a rapid exchange of silver atoms with the electrolyte long before the silver begins to dissolve.

The deposition of Cu onto Au(100) and of Pb onto n- Si(111) electrodes from aqueous solutions has been monitored in situ by scanning tunneling microscopy. In the first case, a bcc structure of the Cu overlayer is observed, which allows pseudomorphic growth on Au(100) up to the 10th layer. Then a slow structural transition to fee begins. In contrast, Pb on Si(111) is shown to deposit as 3D crystallites with flat (111) terminated surfaces.

We develop an embedded-atom-model (EAM) for simulations of metallic film growth under electrodeposition. The surface charge induced by the electric field is handled as an addition to the electron density to be used in the EAM. Parameters relating the shift in electron density to the electrolytic potential are calibrated to measurements of the capacitance and of surface stress versus potential for Au. For Ag the calibration is to capacitance and local density approximation calculations of surface energy. The resulting parameters are physically realistic for the experiments performed. The model is then applied to calculating migration and step edge barriers for Ag electrodeposited on Au (111) as an explanation of the observed Stranski-Krastanov growth.

Cantilevers developed for atomic force microscopy can be used to construct sensitive thermal and stress sensors. We have shown how the stress changes which accompany deposition and desorption may be measured on single crystal electrodes. In this work we describe the surface stress changes associated with three processes: the electrodeposition of Pb and I and desorption of self assembled thiol monolayers on the Au(111) surface.

An in-situ STM study of the initial stages of Ni electrodeposition on Au and Cu single-crystals is presented. On reconstructed Au(111) a complex, potential-dependent nucleation and growth process is found, involving selective Ni island formation at specific surface sites and growth of two types (compact and needle-like) of Ni monolayer islands. At higher coverages (1 ML ≤ θ ≤ 5 ML) an almost perfect layer-by-layer growth of a metallic Ni(111)-film was observed. Considerably rougher films were found on Au(100) and Cu(100).

We report in situ time-resolved surface x-ray scattering measurements of the underpoten-tial deposition of Cu2+ on Pt(111) in the presence of Cl− in HClO4 solution. Chronoamperometric (current vs. time) measurements indicate that after a potential step, the electrode-position current decays to 1/e of its initial value in at most 0.12 seconds. In contrast, our simultaneous time-resolved surface x-ray scattering data reveal that the overlayer requires on the order of two seconds to develop long-range periodic order. These results demonstrate that the kinetics of surface ordering can be significantly different from the kinetics of charge-transfer and illustrate the power of time-resolved surface x-ray scattering for in situ studies of electrodeposition.

The structure and phase behavior of halides have been investigated on single crystals of Ag and Au using synchrotron x-ray scattering techniques. The adlayer coverages are potential dependent. For all halides studied we found that with increasing potential, at a critical potential, a disordered adlayer transforms into an ordered structure. Often these ordered phases are incommensurate and exhibit potential-dependent lateral separations (electrocom-pression). We have analyzed the electrocompression in terms of a model which includes lateral interactions and partial charge. A continuous compression is not observed for Br on Ag(100). Rather, we find that the adsorption is site-specific (lattice gas) in both the ordered and disordered phases. The coverage increases with increasing potential and at a critical potential the disordered phase transforms to a well-ordered commensurate structure.

We discuss applications of statistical-mechanical lattice-gas models to electrochemical adsorption. Our strategy to describe specific systems includes microscopic model formulation, calculation of zero-temperature phase diagrams, numerical simulation of thermody-namic and structural quantities at nonzero temperatures, and estimation of effective, lateral interactions. We report applications to adsorption on single-crystal electrodes, presenting simulated and experimental coverages and voltammetric currents for urea on Pt(100) and the underpotential deposition of Cu on Au(111) in sulfuric acid. We also discuss an extension of the method to study time-dependent phenomena far from equilibrium.

In situ STM has been used to examine the influence of anion adsorption and metal underpotential deposition on the structure and dynamics of steps on copper surfaces. Chloride is shown to form potential dependent adlayer structures on Cu(100) and Cu(111) which strongly affects the orientation of the surface steps. The adlayer acts as a template guiding step evolution during metal deposition and dissolution. Metal underpotential deposition (upd) exhibits similar effects on step structure. This is demonstrated for Pb upd on Cu(lll). In this instance the Pb monolayer displaces chloride from the surface and leads to a reorientation of the steps and an alteration of the step dynamics.

The etching of single crystal and polycrystalline Cu surfaces by halogens was studied using temperature programmed desorption (TPD), low energy electron diffraction (LEED), and scanning tunneling microscopy (STM). For Br2 and Cl2 on Cu(100) and polycrystalline Cu, the etching mechanism could be characterized as a two step process: 1) formation of a bulk Cu(I) halide, and 2) removal of the halide by sublimation. In all cases the first step was found to be adsorption rate limited. Halide formation was observed to consume Cu atoms from the step edge and thus etching can be considered the reverse of step flow growth. While STM showed that Cl2 reacts isotropically with steps on Cu(100), the rate of CuBr formation was observed to be sensitive to the local adsorbate structure at the step edge. For Cl2, it was found that halide removal could be characterized as a simple bulk sublimation process independent of the structure of the underlying Cu. In contrast, a CuBr desorption peak at temperatures lower than anticipated from bulk vapor pressure data was observed. The presence of narrowly spaced steps on the Cu surface was observed to stabilize this low-temperature desorption peak.

Preparation of giant magnctorcsistancc Co/Cu multilayers by electrodeposition has been discussed on the basis of a nucleation- growth mechanism and experimental observations. Reflection electron microscopy (REM- RHEED) studies of clectrodcpositcd Co, Cu/Pt(111) ultrathin layers and bilayers have revealed a simultaneous multinuclcar multilayer growth (pseudo layer- by- layer growth). REM- RHEED observations have also suggested the formation of an additional (2×2) superstructure on an epitaxially grown Cu/Co/Pt(111) bilayer surface. “Giant” magnctorcsistancc and oscillatory antifcrramagnetic intcrlaycr coupling have been observed in a (111) textured Co/Cu multilayered nanostructurc, prepared by electrodeposition under potential control in the presence of a very slight amount of CrO3. Such a multilayered structure containing a nominal nonmagnetic Cu spacer layer thickness of 3.2 nm exhibits a large saturation magnctorcsistancc of more than 18% at room temperature.

In situ small angle neutron scattering (SANS) was used to characterize the formation of the random 3-dimensional porous structure created during the dealloying of a Ag0.7Au0.3 alloy under potential control. Using a model developed by N.F. Berk (Phys. Rev. Lett., 58 (1987) 2718) for the scattering properties of random porous media, we were able to characterize the average ligament width as a function of time during the dealloying process. We find that the coarsening of the average ligament width is strongly dependent upon the value of the applied potential. Our results represent the first in situ nanoscale characterization of the 3-dimensional formation of porosity in a dealloying system under potential control.

α-Dodecatungstosilicate (α-SiW12O404−) anions form ordered monolayers on Ag(111) and Au(111) surfaces. In-situ STM images reveal that the silicotungstate ion forms a square adlattice with an intermolecule spacing of 10.2 ± 0.5 Å on both Ag and Au surfaces. Additional structures exhibiting either row or rhombic motifs are observed on Au electrodes. The structure of the adlattices can be modeled using a simple model which maximizes the coordination of the silicotungstate ion to the electrode while maintaining van der Waals contacts between terminal oxygens of adjacent silicotungstates.

We study a system in which a monolayer of atoms of one kind are deposited epitaxialy onto a (111) surface of an FCC crystal using the Tight Binding approximation. First, we obtain an analytical expression for the energy spectrum of the system. This turns out to be an interesting result from the mathematical standpoint due to its simplicity, and to the fact that no artificial boundary conditions (like periodic or vanishing) were imposed on the wave functions. All the spectral information is shown to be contained in the roots of a quadratic polynomial. Then, for Cu on Au, we study the density of states and wave function decay out from the outer layer. This is done at zero and finite voltage applied between an electrode and bulk Gold, immersed in an electrolyte. This problem is of interest in electrochemistry.

Molecular dynamics simulations are reported for the atomic motion of adsorbates at a liquid-solid interface. The rate for physical desorption is analyzed using the potential of mean force to describe adsorbate and transition state energies.

Electrochemical processes hold great promise as flexible and effective tools for synthesis and processing of a wide range of materials from fractal electrodes to epitaxial nanostructures. The key to successful application of electrochemical techniques is in understanding the kinetic processes which control the evolution and the morphology of the surface at the solid-liquid interface. This paper provides a review of recent advances made by different electrochemical communities in recent years in studies of the growth and modification of a wide variety of materials. The topics covered include studies of pattern formation and growth of dendritic and fractal structures in electrode-position, kinetic roughening and dynamic scaling of surfaces fluctuations during electrochemical deposition and dissolution, as well as recent progress in electrochemical growth of epitaxial layers and nanostructures.

The quasi-two-dimensional electrodeposition of several metals (zinc, copper, silver and lithium) of varying levels of anisotropy has been investigated. The morphologies are very diverse for the different metals and the morphology selection depends on the degree of anisotropy. The fast propagation of the quasi-two-dimensional deposit is due to the lack of convection in the confined electrolyte. The velocity of the deposit is determined by the drift velocity of the anions, as the system is attempting to maintain electroneutrality and reduce the electric field in the space charge region. The effects of impurities and natural convection on the morphology are investigated as well.

Recent work demonstrates the relevant influence of convection during growth pattern formation in thin-layer electrochemical deposition. Convection is driven mainly by coulombic forces due to local charges at the tip of the aggregation and by buoyancy forces due to concentration gradients. Here we study through physical experiments and numerical modeling the regime under which coulombic forces are important. In the experimental measurements fluid motion near the growing tips of the deposit is visualized with neutrally buoyant latex spheres and its speed measured with videomicroscope tracking techniques and image processing software. The numerical modeling consists in the solution of the 2D dimensionless Nernst-Planck equations for ion concentrations, the Poisson equation for the electric field and the Navier-Stokes equations for the fluid flow, and a stochastic growth rule for ion deposition. A new set of dimensionless numbers governing electroconvection dominated flows is introduced. Preliminary experimental measurements and numerical results indicate that in the electroconvection dominated regime coulombic forces increase with the applied voltage, and their influence over growth pattern formation can be assessed with the magnitude of the dimensionless electric Froude number. It is suggested that when this number decreases the deposit morphology changes from fractal to dense branching.

This paper describes a new family of organized molecular assemblies that are produced by the spontaneous adsorption of alkanethiols onto gold surfaces that have been modified by the underpotential deposition of copper or silver. The system has the flexibility associated with the formation of self-assembled monolayers by the adsorption of thiols onto gold with the advantage of improved stability. The use of these systems as modified electrodes is also addressed.