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The molecular interaction between the organic and inorganic phases of vinyl polymer/silica colloidal nanocomposites is studied by using NMR spectroscopy. Results indicate that the molecular interaction between the polymer and silica phases involves hydrogen bond formation between the pyridine nitrogen and a surface hydroxyl proton for P4VP/silica nanocomposite particles.

The monolayer formation of even-numbered alkyltri-methylammonium bromides CnTAB (n = 6-16) at the graphite/water interface is studied by applying frontal-flow and pulsed-flow calorimetric methods. It is concluded that surface characterization of heterogeneous catalysts by the chemisorption of suitably elected probe molecules from inert solvents is promising.

The properties of a liquidlike layer (LLL) at the gold/frozen electrolyte interface are studied by using the quartz crystal microbalance (QCM). It was found that at temperatures well below the melting point of the electrolyte, in the range of -2 to -7 degree C, the QCM immersed in a frozen electrolyte shows detectable resonance, the parameters of which depends strongly on temperature.

A study is conducted to examine premelting at the ice/gold and the frozen electrolyte/golf interfaces with the help of quartz-crystal microbalance. The findings indicate that in a certain range of temperature the resonance of the QCM is readily detectable and the parameters of the resonance depend on temperature as well as the shape of the resonance is very different from that observed for the QCM in contact with liquids.

A device allowing direct optical measurement of the displacement was used to measure the thickness of the liquid-like layer. The results were correlated with the calculations of the thickness based on admittance data of quartz crystal microbalance, measured at the same time.

A comparison is made between the codeposition behavior of Zn with SiC nanoparticles (NPs) of two average sizes: 56 nm and 90 nm. The SiC NPs are first characterized using transmission electron microscopy (TEM) and X-ray diffraction (XRD). Dynamic light scattering (DLS) is used to compare the surface charge of both kinds of SiC NPs suspended in aqueous citrate electrolytes. The effect of applied current density, hydrodynamic conditions, and total charge passed on the SiC content in the coating and electrodeposition rate is studied. The electrodeposited Zn-SiC coatings are characterized by wavelength dispersive X-ray fluorescence (WDXRF), scanning electron microscopy (SEM), and XRD. The results obtained confirm that Cit-Zn complexes are adsorbed on the surface of the SiC NPs, which are transported to the cathode and are codeposited with Zn during reduction. Zn-SiC incorporation may proceed also by mechanical entrapment of SiC agglomerates in the cavities and pores that are formed in the deposit under condition of relatively fast Zn deposition, which is accompanied by fast hydrogen evolution. [ABSTRACT FROM AUTHOR]

Zn-SiC nanocomposite coatings are successfully produced by galvanostatic electrodeposition from aqueous citrate solutions, using SiC nanoparticles (NPs) with an average size of 56 nm. The optimal parameters of the zinc-citrate bath are chosen on the basis of analysis of a thermodynamic model. The effect of applied current density, bath composition, and hydrodynamic conditions are studied. The kinetics and mechanism of zinc reduction in the presence of SiC NPs are investigated using cyclic voltammetry. The surface charge of SiC NPs suspended in the electrolyte solutions is examined by the dynamic light scattering technique. The electrodeposited Zn-SiC coatings are characterized by wavelength dispersive X-ray fluorescence and scanning electron microscopy. It is shown that SiC codeposition with Zn proceeds through the entrapment of ceramic NPs during the reduction of citrate-zinc ions that are first adsorbed on the surface of the ceramic NPs. A maximal content of 6.4 wt% SiC incorporated into the Zn matrix is obtained at the lowest applied current density of j = -0.5 A dm-2, with a nearly constant faradaic efficiency of 90%. [ABSTRACT FROM AUTHOR]

Rhenium alloys exhibit a unique combination of chemical, physical, and mechanical properties that makes them attractive for a variety of applications. Herein, we present atomic-scale structural and atomic part-per-million level three-dimensional (3D) chemical characterization of a Re-Ni coating, combining aberration-corrected scanning transmission electron microscopy (STEM) and atom-probe tomography (APT). A unique combination of a columnar and multilayer structure is formed by singlebath dc-electroplating and is reported here for the first time. Alternating thicker Re-rich and thinner Ni-rich layers support a mechanism in which Ni acts as a reducing agent. The multilayers exhibit hetero-epitaxial growth resulting in high residual shear stresses that lead to formation of corrugated interfaces and an outer layer with mud-cracks. [ABSTRACT FROM AUTHOR]

Rhenium (Re), with its unique chemical and mechanical properties, has sparked a rising interest in many communities in recent years. Electrochemical deposition has proven to be a promising method for the manufacture of Re-based products, with pulse electrodepo-sition allowing for finer control of the deposit properties. In this work, the effects of a wide range of pulse-plating parameters on the composition and microstructure of Re-Ni alloys were studied. The samples were examined under a scanning electron microscope, and it was found that a nodular morphology was generated in all samples within the region of pulse parameters investigated. A surface morphology diagram was constructed, delineating the conditions leading to colonies that extend perpendicularly from the substrate vs. those that remain nearly flat on the substrate surface ('rough' vs. 'smooth' deposits, respectively). XPS analysis showed an increase in the rhenium oxide content relative to pure Re, both at higher on-times and at higher peak current densities. XRD analysis showed that all samples contained fee Ni, although certain fee Ni reflections were absent in the case of smooth samples. This absence was coupled with evidence of a solid solution of Re in an hcp Ni lattice, found exclusively in the smooth samples. [ABSTRACT FROM AUTHOR]

The Re-Ir system is of great interest for high-temperature applications and extreme environments. Here, Re-Ir-Ni alloy coatings were electroplated from aqueous solutions. The effects of pH and temperature on the faradaic efficiency (FE), chemical composition, surface morphology and crystallographic structure of the coatings were studied. The results show that the pH and temperature of electrolytes have a significant effect on the electrodeposition of Re-Ir-Ni. As the pH was increased from 2.0 to 8.0, the FE, partial current densities for deposition of the three metals, and deposition rate increased. The highest Re-content (82 at%) was obtained at pH = 2.5. At pH = 2.0, the coating consisted of an amorphous phase, and no cracking was observed. When raising the pH to 4.0 and above, crystalline phases (including hydrides) formed, and both columnar crystals and micro-cracks were observed. The bath temperature affected the surface crack density and the size of the grains that form the mesoscopic colonies. At the two lowest temperatures studied herein (50 and 60°C), no codeposition of Ir was observed. The phase composition of the coating changed from amorphous Re-Ni at 50°C; to amorphous Re-Ni, hcp-Ni and hexagonal Ni2H at 60°C; to hcp-Ir0.4Re0.6, hcp-Ni and hexagonal Ni2H at higher temperatures. [ABSTRACT FROM AUTHOR]

The effect of pulse electrodeposition parameters on the composition and microstructure of Ni–Re alloys were studied on a rotating cylinder electrode. Ni–Re alloys were deposited from a citrate bath where the nickel-to-rhenium ratio was 45:1. The composition of the deposited alloy was monitored by energy dispersive spectroscopy (EDS) and compared to a single component transport-based model describing the pulse limiting current of perrhenate. At long pulse times and high duty cycles, the partial current density of rhenium is predicted by the model, and rhenium inclusion into the alloy can therefore be described as being completely transport controlled. At shorter pulse times and low duty cycles, rhenium deposits under mixed or activation control. The morphology of the surface and cross-section were studied by SEM. The oxidation states and phases were studied by XPS and XRD, respectively, and discussed in view of the pulse parameters. By examining the effect of pulse parameters on composition and microstructure, we can deduce the practical range of pulse parameters for use in Ni–Re alloy film synthesis from dilute perrhenate electrolytes. [ABSTRACT FROM AUTHOR]

The transfer coefficient α is a quantity that is commonly employed in the kinetic investigation of electrode processes. An unambiguous definition of the transfer coefficient, independent of any mechanistic consideration and exclusively based on experimental data, is proposed. The cathodic transfer coefficient αc is defined as -( RT/ F)(dln| jc|/d E), where jc is the cathodic current density corrected for any changes in the reactant concentration on the electrode surface with respect to its bulk value, E is the applied electric potential, and R, T, and F have their usual significance. The anodic transfer coefficient αa is defined similarly, by simply replacing jc with the anodic current density and the minus sign with the plus sign. This recommendation aims at clarifying and improving the definition of the transfer coefficient reported in the 3rd edition of the IUPAC Green Book. [ABSTRACT FROM AUTHOR]

The transfer coefficient α is a quantity that is commonly employed in the kinetic investigation of electrode processes. In the 3rd edition of the IUPAC Green Book, the cathodic transfer coefficient αc is defined as -( RT/ nF)( dln kc/d E), where kc is the electroreduction rate constant, E is the applied potential, and R, T, and F have their usual significance. This definition is equivalent to the other, -( RT/ nF)( dln| jc|/d E), where jc is the cathodic current density corrected for any changes in the reactant concentration at the electrode surface with respect to its bulk value. The anodic transfer coefficient αa is defined similarly, by simply replacing jc with the anodic current density ja and the minus sign with the plus sign. It is shown that this definition applies only to an electrode reaction that consists of a single elementary step involving the simultaneous uptake of n electrons from the electrode in the case of αc, or their release to the electrode in the case of αa. However, an elementary step involving the simultaneous release or uptake of more than one electron is regarded as highly improbable in view of the absolute rate theory of electron transfer of Marcus; the hardly satisfiable requirements for the occurrence of such an event are examined. Moreover, the majority of electrode reactions do not consist of a single elementary step; rather, they are multistep, multi-electron processes. The uncritical application of the above definitions of αc and αa has led researchers to provide unwarranted mechanistic interpretations of electrode reactions. In fact, the only directly measurable experimental quantity is dln| j|/d E, which can be made dimensionless upon multiplication by RT/ F, yielding ( RT/ F)( dln| j|/d E). One common source of misinterpretation consists in setting this experimental quantity equal to αn, according to the above definition of the transfer coefficient, and in trying to estimate n from αn, upon ascribing an arbitrary value to α, often close to 0.5. The resulting n value is then identified with the number of electrons involved in a hypothetical rate-determining step or with that involved in the overall electrode reaction. A few examples of these unwarranted mechanistic interpretations are reported. In view of the above considerations, it is proposed to define the cathodic and anodic transfer coefficients by the quantities αc = -( RT/ F)( dln| jc|/d E) and αa = ( RT/ F)( dln ja/d E), which are independent of any mechanistic consideration. [ABSTRACT FROM AUTHOR]

Electrode reactions are characterized by charge transfer across the interface. The charge can be carried by electrons or by ions. It is shown here that when both mass and charge cross the interface, the charge must be carried by the ionic species, not by the electrons, as a result of the very large difference in the time scale for electron and ion transfer. A prime example of charge transfer by ions is metal deposition.It is proposed that ion transfer occurs by migration of the ions across the interface, under the influence of the high electrostatic field in the double layer. The rate constants observed for metal deposition are comparable to those for outer-sphere charge transfer. These unexpectedly high rate constants for metal deposition are explained by a model in which removal of the solvation shell and reduction of the effective charge on the metal ion occur in many small steps, and a make-before-break mechanism exists, which lowers the total Gibbs energy of the system as it moves along the reaction coordinate from the initial to the final state. [ABSTRACT FROM AUTHOR]

This article focuses on views of the author, who is the winner of 2003 Olin Palladium Award, on conducting research in the digital era. At the University of Pennsylvania, Philadelphia the author met Srinivasan Subramanian, called Srini for short, who has been his good friend ever since. When there was an equation to solve Srini would look at it, think a minute, and write down the solution. He was the mathematical wizard for students. They spend time for nearly three years, learned a lot from each other, wrote a few papers together, and consoled each other when the going got rough.

Investigates the effect of surface roughness on the response of quartz crystal microbalance (QCM). Models for the interpretation of QCM response at rough surfaces accounting for the multiscale nature of roughness; Dependencies of the real part of the admittance of the QCM on frequency at 25 degrees Celsius.

The development of a 3D electrochemical deposition system, which combines meniscus‐confined electrodeposition (MCED) with atomic force microscope (AFM) closed‐loop control and has a submicron resolution, is described. Thanks to the high rigidity of the hollow borosilicate glass (or quartz) tip and quartz crystal tuning fork (QTF), combined with the QTF's high force sensitivity, the use of a solution‐filled AFM tip in air is successful. The AFM control enables full automation and in situ growth control. Using this scheme, 3D printing of high‐quality, fully dense, uniform and exceptionally smooth, freestanding straight and overhang pure polycrystalline copper pillars, with diameters ranging from 1.5 µm to 250 nm, and an aspect ratio > 100, is demonstrated. This process may be useful for manufacturing of high‐frequency terahertz antennas, high‐density interconnects, precision sensors, micro‐ and nano‐electromechanical systems, batteries, and fuel cells, as well as for repair or modification of existing micro‐sized or nano‐sized features. [ABSTRACT FROM AUTHOR]

Zn–SiC nanocomposite coatings were electrodeposited from aqueous citrate electrolytes using either direct current deposition (DCD) or pulsed electrodeposition (PED). The effects of various surface-active organic compounds (SDS, gum arabic, gelatin, CTAB, PEG 20000, and Triton X–100) on the coatings' surface morphology and chemical composition were studied. The influence of pulse frequency and duty cycle on the percentage of the SiC nanoparticles (NPs) incorporated and on the quality of the deposits was also investigated. The amount of SiC NPs incorporated in the Zn matrix was similar for layers obtained by DCD compared to PED. The Zn–SiC coating deposited by PED exhibited a more fine-grained surface morphology. The percentage of SiC co-deposited with Zn was mainly affected by the type of surfactant used. The ionic surfactants (cationic gelatin and CTAB or anionic gum arabic) allowed the co-deposition of considerably higher amounts of SiC NPs with Zn, compared to the non-ionic compounds PEG 20000 and Triton X–100. However, the use of high molecular weight organic compounds such as gelatin and gum arabic led to aggregation of SiC NPs within the Zn matrix. [ABSTRACT FROM AUTHOR]

In this study, Re-Ni alloys with high Re content were electrodeposited on copper substrates from aqueous solutions containing additives with a combination of vanillin, sodium lauryl sulfate and gelatin. The bath additives were found to have a significant effect on the chemical composition, surface morphology and cracking pattern. The morphology of the alloy was changed from uniformly smooth without additives to relatively coarse-grained with three additives. The deposition rate and crack density decreased when additives were added to a bath containing 34 mM ReO 4 − , 124 mM Ni 2 + and 343 mM [Cit] 3 − . Almost pure Re films were formed at low Ni 2 + concentration of 30–50 mM due to the effect of additives; however, the deposited film was thin. A thin layer of Re oxide, a new Re-O-C-complex state and some organic residues from additives were formed at the surface of the Re film. Both the Re-rich alloy and the Re film were found to have an amorphous structure. [ABSTRACT FROM AUTHOR]

Abstract: Rhenium (Re) is a refractory metal which exhibits an extraordinary combination of properties. Thus, nanowires and other nanostructures of Re-alloys may possess unique properties resulting from both Re chemistry and the nanometer scale, and become attractive for a variety of applications, such as in catalysis, photovoltaic cells, and microelectronics. Rhenium–tin coatings, consisting of nanowires with a core/shell structure, were electrodeposited on copper substrates under galvanostatic or potentiostatic conditions. The effects of bath composition and operating conditions were investigated, and the chemistry and structure of the coatings were studied by a variety of analytical tools. A Re-content as high as 77at.% or a Faradaic efficiency as high as 46% were attained. Ranges of Sn-to-Re in the plating bath, applied current density and applied potential, within which the nanowires could be formed, were determined. A mechanism was suggested, according to which Sn nanowires were first grown on top of Sn micro-particles, and then the Sn nanowires reduced the perrhenate chemically, thus forming a core made of crystalline Sn-rich phase, and a shell made of amorphous Re-rich phase. The absence of mutual solubility of Re and Sn may be the driving force for this phase separation. [Copyright &y& Elsevier]

Abstract: In this study, rhenium–nickel (Re–Ni) films were formed by electroless deposition on conductive (Cu) and non-conductive (SiO2) substrates. Different bath compositions were evaluated, aiming to achieve high Re-content. Both sodium hypophosphite and dimethylamine-borane were used as reducing agents. Films containing up to 75at% Re were obtained. The influence of nickel concentration in the solution on alloy composition, deposition rate and surface morphology were determined. It is shown that Ni2+ acts as a catalyst for the in situ reduction of the perrhenate ion, in a manner similar to what was proposed for electroplating of the same alloy. The rate of electroless plating is similar to that found in electroplating at an applied current density of 50mAcm−2. While pure Re cannot be deposited from our electroless plating baths, the addition of even a very small amount of Ni2+ ions (0.25mM) is enough to start the induced codeposition of Re. Proper selection of the bath composition can lead to fine control of the alloy thickness and its Re-content, thus making it potentially attractive for thin barrier layers. [Copyright &y& Elsevier]

Abstract: The surface properties of any substance in the solid state differ from its bulk properties. This can give rise to the formation of a liquid-like layer (LLL) at the interface, at temperatures below the melting point. The phenomenon generated interest among both theoreticians and experimentalists for more than 150 years and was studied, employing different techniques. However, electrochemical techniques have not been implemented in studies of this phenomenon. We used, for the first time, the quartz crystal microbalance (QCM) to study the LLL at the ice/gold and the frozen electrolyte/gold interfaces. It was shown that the QCM in contact with ice or with frozen electrolyte at temperatures well below the melting point shows detectable resonance. The parameters of the resonance depend strongly on temperature, composition of the frozen phase, adsorption taking place at the gold surface (including gold surfaces modified by different thiol-derivates) and, in the case of electrolyte, on the potential applied across the interface. Corresponding theoretical models have been developed to understand the kind of information contained in the response of the QCM on the properties of the LLL. Independent data obtained with a device allowing direct optical measurement of the displacement show good agreement with the calculations of thickness of the LLL based on developed models. [Copyright &y& Elsevier]

Electrochemical removal of oxygen and hydrogen from aqueous solution in the vicinity of gold electrodes, with simultaneous measurements of the response of the quartz crystal microbalance, show no evidence of gas nano-bubbles attached to the surface, irrespective of its roughness and hydrophobicity. The contact between gold and frozen electrolyte, which forms a liquid-like layer between them, also does not contain gas bubbles. These statements could be extended to nano-bubbles with characteristic dimensions larger than a few nanometers.