In the electrolytic dissolution of binary alloys the concepts of ionization and redeposition of a metal, coupling of the anodic reactions in accordance with the concepts of irreversible thermodynamics, and volume diffusion in the presence of given supersaturations of single and double vacancies are analyzed theoretically. The ionization‐redeposition mechanism is in principle possible but only if coupling of the anodic reactions occurs. Volume diffusion may be operative via divacancies. Results from x‐ray investigations and from measurements with a rotating disk‐ring electrode for copper‐gold alloy indicate that interdiffusion of the constituent metals in the alloy occurs to a significant extent and dissolution of Au does not take place. Electrochemical measurements with a Cu‐Zn alloy involving 30 a/o (atomic per cent) Zn give no indication of occurrence of the ionization‐redeposition mechanism.

The structure of C6o molecules adsorbed on the Cu(l 1 l)-(l x 1) surface has been investigated by scanning tunneling microscopy (STM). Bias voltage dependent STM images of individual C6o molecules in the monolayer film showed unique intramolecular structures with a threefold symmetry. The observed images agree well with those calculated using the local density approximation. With charge transfer from the Cu(l 11) substrate to the monolayer film, the €50 molecule ratchets to threefold hollow sites. PACS numbers: 68.35.Bs, 61.16.Ch, 61.46,+w, 68.65.+g The investigation on carbon fullerenes discovered by Kroto et al. [1] has been a growing exciting field, since Kratschmer et al. [2] succeeded in the extraction and purification of C60 and other fullerenes. Discovery of superconductivity by Hebard et al. [3] in a K-doped fullerene sample, K3C60, added further excitement with promising practical applications [4]. Scanning tunneling microscopy (STM) has been successfully used to reveal the geometric and electronic structure of the fullerenes with molecular resolution. The nucleation and growth of C60 film and its structure on various substrates, such as Au(100) [5], (111) and (110) [6], Ag(lll) [7], highly oriented pyrolytic graphite (0001) [8], GaAs(llO) [9], and Si(l 11) [10], and (100) [11] have been major interests in STM studies. Investigations on other fullerene films, such as C70 [12], Cu [13], and SCC74/SC2C74 [14], and Sc 2 C 8 4 [15] on the Si (100)-(2x 1) surface have been reported using the FI-STM (field ion scanning tunneling microscope), elucidating the growth kinetics and geometric structures.The Cu(l 11) surface is one of the ideal surfaces for the growth of C60 film similar to the bulk [16], since the lattice mismatch is small (2%) between the nearest neighbor (nn) distance (10.0 A) of the bulk Ceo crystal and 4 times of the Cu-Cu nn distance (10.2 A). A recent study of C 60 adsorption on the Cu(lll), (110), and (100) surfaces using x-ray photoemission spectroscopy (XPS) and high resolution electron energy loss spectroscopy (HREELS) and other techniques [17] concluded the following: (1) The Cu substrate donates charge to the lowest unoccupied molecular orbital (LUMO) band of C60 as K does in K x C6o films and (2) single-domain epitaxy with a (4x4) superlattice and successive layer-bylayer growth can be achieved on the Cu(l 11) surface.In this Letter, we report the intramolecular structure of C60 molecules on the Cudll)-(lxl) surface using the FI-STM [18]. C60 molecules ratchet to hollow sites and are ordered due to the substrate-C6o and C60-C60 interactions. Observed intramolecular structure with a unique threefold symmetry agrees well with the charge density around the molecule calculated using the local density approximation (LDA). It was confirmed in the STM images and calculated charge density that excess charge on the molecule is present on top of the pentagonal rings.The experimental details of the extraction and purification of high-purity C60 powder (purity of 99.95%, the rest being C70) [19], a...

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A mechanistic model has been developed which for the first time considers the effect of hydrogen entry into a metal on the kinetics of the hydrogen evolution reaction (h.e.r.). The model enables computation of (i) the hydrogen surface coverage and surface concentration; (ii) the hydrogen adsorption, absorption, discharge and recombination rate constants; and (iii) the h.e.r, coverage-dependent transfer coefficient, ~, and the exchange current density io, from a knowledge of the steady-state hydrogen permeation current, cathodic charging current, hydrogen overvoltage, and hydrogen diffusivity. The model predicts a linear relationship between the permeation flux and the square root of the hydrogen recombination flux, and provides an analytical method to determine the cathodic potential range for operation of a coupled dischargerecombination mechanism of the h.e.r. With modifications the model can treat permeation data for which (i) the mechanics of the discharge step involve a (proposed) selvedge reaction, and (ii) surface hydrogen coverages are relatively high as in the presence of poisons (e.g., H2S or As2OD. Some of the existing literature data for hydrogen permeation in iron and nickel in acid and alkaline solutions are successfully analyzed.Hydrogen is one of the most damaging species in metals, causing hydrogen assisted cracking, blisters, and similar phenomena. Hydrogen entry into metals from aqueous solutions has been studied extensively by hydrogen permeation experiments of thin samples using the DevanathanStachurski cell (1-7). Some studies carried out on iron in acid and alkaline solutions (2, 4, 6) reveal a coupled discharge-recombination mechanism for the hydrogen evolution reaction (h.e.r.) with diffusion of absorbed hydrogen into the metal being rate controlling for the permeation process. The models based on this mechanism predict a square-root relationship between the hydrogen charging current and the steady-state hydrogen permeation flux or current (2). In all of these models, it has been assumed that the hydrogen permeation flux is negligible. It has also been assumed that the hydrogen coverage (Os) is quite low, although the coverage itself is unknown. However, especially when poisons such as H2S or As~O3 are present in the solution, both the permeation current and the hydrogen coverage can be appreciable (8,9). If the steady-state permeation current (i~) is proportional to the square root of the charging current (and the Tafel slope is -120 mV decade -~ and d~l/d log i~ is -240 mV decade -~ where ~1 is the overpotential for the h.e.r.), the h.e.r, is generally considered to follow a coupled diseharge-reeombinati0n mechanism. Apart from these considerations which have not produced operative models yielding the relevant parameters, e.g., 0s, the current models also do not explain the mechanics of the intermediate reaction between adsorption and absorption of hydrogen in metals, which is probably correctly assumed in many eases, but perhaps not in all, to be in equilibrium at the cathode surface.T...