An electrodeposition study of the nucleation and growth of silver on boron-doped diamond electrodes

A study is reported of the electrochemical nucleation of silver on boron-doped diamond from aqueous solutions of silver nitrate, using a single-pulse potentiostatic technique. Data are obtained for the nucleation rate by interpretation of the deposition voltammetry, and by inspection of in situ optical microscopic images. The distribution of nearest neighbours is determined as a function of time and also the first to fifth nearest-neighbour distributions are examined at specific times. The distribution of nucleus areas is found and a simple stochastic model of nucleation and growth developed in order to understand qualitatively the nearest neighbour and nucleus area results. © 2003 Elsevier B.V. All rights reserved

Formate adsorption on Pt nanoparticles during formic acid electro-oxidation: insights from in situ infrared spectroscopy

Adsorbed formate is observed on a supported Pt nanoparticle for the first time during formic acid electro-oxidation. Bands assigned to OCO stretching and CH bending reveal some OCO but little CH bond weakening on adsorption compared to the free anion. The formate potential dependence is similar to polycrystalline electrodes while adsorbed CO persists up to +1.2 V, 0.5 V higher than on polycrystalline Pt

Formate adsorption on Pt nanoparticles during formic acid electro-oxidation: insights from in situ infrared spectroscopy

Adsorbed formate is observed on a supported Pt nanoparticle for the first time during formic acid electro-oxidation. Bands assigned to OCO stretching and CH bending reveal some OCO but little CH bond weakening on adsorption compared to the free anion. The formate potential dependence is similar to polycrystalline electrodes while adsorbed CO persists up to +1.2 V, 0.5 V higher than on polycrystalline Pt

Monitoring potassium metal electrodeposition from an ionic liquid using in situ electrochemical-X-ray photoelectron spectroscopy

The real time electrodeposition of potassium has been monitored for the first time in an ionic liquid using in situ electrodeposition-X-ray photoelectron spectroscopy (XPS). The ionic liquid used was N-butyl-N- methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([C4mpyrr] [NTf2]), and electrodeposition occurred at a nickel mesh electrode. Potassium electrochemistry was monitored at the ionic liquid-vacuum-electrode interface using a novel cell design. © 2011 Elsevier B.V. All rights reserved

Interaction of tyrosine-, tryptophan-, and lysine-containing polypeptides with single-wall carbon nanotubes and its relevance for the rational design of dispersing agents

The polypeptides poly-L-(Trp,Lys·HBr) (Trp/Lys·HBr = n/m) and poly-L-(Tyr,Lys·HBr) (Tyr/Lys·HBr = n/m) were tested as dispersing agents for single-wall carbon nanotubes (SWCNTs) for n/(n+m) values of 0, 0.2, and 1. Best results were obtained for the two copolymers, illustrating the importance of using amphiphilic dispersing agents. The dispersion effect is 3.5 times higher for the copolymer containing tryptophan, indicating a stronger interaction of the tryptophan residue with the SWCNTs compared to tyrosine. The degrees of debundling of the SWCNTs and the apparent binding of the polypeptides with the SWCNTs are analyzed by atomic force microscopy for the different dispersions. The interactions of the aromatic amino acid residues with the SWCNTs are further probed by using optical absorbance and fluorescence spectroscopy. © 2007 American Chemical Society

On the Stability of Oligo(ethylene glycol) (C(11)EG(6)OMe) SAMs on Gold: Behavior at Elevated Temperature in Contact with Water

In this study the temperature dependent confor-mation of hexa(ethylene glycol) self-assembling monolayers (SAMs) under aqueous conditions (in situ) is investigated. To this end characteristic absorption modes in the fingerprint region (1050-1500 cm(-1)) were monitored with real-time polarization modulation infrared spectroscopy. We found a temperature induced conformational change from predominantly helical to helical/all-trans. The process may be divided into two temperature regimes. Up to 40 °C the process is reversible after drying the monolayers in air and successive reimmersion in water, indicating a strong binding of the water molecules to the SAM. At higher temperatures, the conformational change is irreversible. Additionally, a rapid change to a larger mode width and a shift of the mode position to higher wavenumbers (blue-shift) at about 50 °C indicates structural changes caused by decreasing crystallinity of the SAM. While the conformational changes up to 40 °C are supposed to originate from an increased conformational freedom in combination with a stronger interaction with water molecules, the irreversibility and rapid change of mode characteristics at higher temperatures indicate chemical degradation. Complementary measurements in air show a fast and virtually complete reversibility up to 40 °C underlining the effect of the interaction of the ethylene glycol moiety with water. At temperatures above 50 °C modes indicating ester and formate groups appear, supporting the idea of chemical degeneration. Moreover, the temperature behavior is coverage dependent. At incomplete coverage the structural order of the SAM starts decreasing at lower temperatures. This study shows, that the conformational and structural change of hexa(ethylene glycol) SAMs at elevated temperature is an interplay of conformational changes of the SAM, its interaction with water and at higher temperatures its chemical degradation. Our experiments also underline the importance of the in situ analysis on the film structure

In situ electrochemical-X-ray Photoelectron Spectroscopy: Rubidium metal deposition from an ionic liquid in competition with solvent breakdown

The electrodeposition of rubidium from an ionic liquid (IL) N-butyl-N-methylpyrrolidium bis(trifluoromethylsulfonyl)imide ([C 4mpyrr][NTf2]) has been performed and monitored at a Nickel mesh electrode by using in situ electrochemical-X-ray Photoelectron Spectroscopy (XPS) measurements. At extremely high current values during the deposition of the metal, the solvent breakdown was also observed. By choosing suitable low current values, electrodeposition of Rb can be promoted over the IL degradation. IL degradation was characterised by carbonisation of the electrode-IL-vacuum interface, with the loss of fluorine being relatively pronounced, consistent with reduction of the [NTf2]- anion. © 2011 Elsevier B.V. All rights reserved

Structural, optical and electrical properties of In4Sn3O12 films prepared by pulsed laser deposition

Highly conducting (σ ∼ 2.6 × 103 Ω-1 cm-1) In4Sn3O12 films have been deposited using pulsed laser deposition (PLD) on glass and quartz substrates held at temperatures between 350 and 550 °C under chamber pressures of between 2.5 and 15 mTorr O2. The crystallinity and the surface roughness of the films were found to increase with increasing substrate temperature. Electron concentrations of the order of 5 × 1020 cm-3 and mobilities as high as 30 cm2 V-1 s-1 were determined from Hall effect measurements performed on the films. Fitting of the transmission spectral profiles in the ultra-violet-visible spectrum has allowed the determination of the refractive index and extinction coefficient for the films. A red-shift in the frequency of plasmon resonance is observed with both increasing substrate temperature and oxygen pressure. Effective masses have been derived from the plasma frequencies and have been found to increase with carrier concentration indicating a non-parabolic conduction band in the material In4Sn3O12. The optical band-gap has been determined as 3.8 eV from the analysis of the absorption edge in the UV. These results highlight the potential of these films as lower In-content functional transparent conducting materials. © 2010 Elsevier B.V. All rights reserved

Reverse Micelle Synthesis of Co-Al LDHs: Control of Particle Size and Magnetic Properties

Nanoplatelet Co - Al layered double hydroxides (LDHs) {Co 1.8Al1.1(OH)6(DDS)x•yH 2O (DDS = dodecyl sulfate; x ≈ 0.9; y = 2 - 6)} have been prepared using a homogeneous precipitation approach in water pools formed by a water-in-oil reverse microemulsion. The size of the LDH particles is controlled by adjusting the water to surfactant ratio (ω). The particle sizes vary from about 60 × 60 × 13 nm3 to 160 × 160 × 40 nm3 with increasing ω. This contrasts with platelets of Co1.89Al(OH)6(DDS)0.8•4.3H2O prepared by conventional homogeneous precipitation which had dimensions about 2 - 3 μm wide and 0.5 - 1 μm thick. All the Co - Al LDH samples were paramagnetic above 50 K. The molar magnetic susceptibilities of each sample were very similar and they could all be fitted to the Curie - Weiss law with μeff ca. 5.2 μB per Co2+ and θca. 6 K. Below 50 K, we observed a rapid rise in χMT indicative of cooperative ferromagnetic interactions. At very low temperature the LDH nanoplatelets show magnetic behavior which is different to Co 1.8Al1.1(OH)6(DDS)x•yH2O made by conventional homogeneous precipitation. The nanoplatelets show bifurcation in their field-cooled (FC) and zero-field-cooled (ZFC) magnetizations and also a frequency dependence of the in-phase (χ′) and out-of-phase (χ″) ac susceptibilities, which is dependent on the size of the nanoplatelets. © 2010 American Chemical Society