Martin E. Zoloff Michoff

Quantitative Study of Non‐Covalent Interactions at the Electrode–Electrolyte Interface Using Cyanide‐Modified Pt(111) Electrodes

Cations at the outer Helmholtz plane (OHP) can interact through non-covalent interactions with species at the inner Helmholtz plane (IHP), which are covalently bonded to the electrode surface, thereby affecting the structure and the properties of the electrochemical double layer. These non-covalent interactions can be studied quantitatively using cyanide-modified Pt(111) electrodes.

Configurational Behavior and Conductance of Alkanedithiol Molecular Wires from Accelerated Dynamics Simulations

An accelerated dynamics scheme is employed to sample the configurational space of a system consisting of an alkanedithiol molecule confined to the gap between a metal tip and a perfect metal surface. With this information and by means of nonequilibrium green functions techniques (NEGF), conductance calculations are performed. The present results show that even for this system, which is one of the most simple conceivable because of the perfectness of the surface, a complex behavior appears due to the occurrence of an unexpected tip-molecule-surface arrangement, where the insertion of one of the molecular ends into the tip-surface gap generates configurations with strongly enhanced conductance. Estimates are also made for the time required to generate the molecular junction, indicating that it should depend on the tip-surface distance, thus opening the way to new experiments in this direction.

Effects of the alkyl substituent in the π-donor heteroatom on the kinetic and thermodynamic acidities of Fischer thiocarbene complexes

Rate constants for the proton transfer reaction from Fischer thiocarbene complexes (CO)5MC(SR1)CH3 (M = Cr or W; R1 = n-butyl, isopropyl, tert-butyl, cyclohexyl) to OH– and various primary and secondary amines were determined in 50% acetonitrile–50% water at 25 °C. These measurements allowed the determination of the thermodynamic and kinetic acidities for these substrates. The results obtained show that there is a slight effect of the substituent on the thermodynamic acidity, which is governed by its hydrophobicity; whereas the effect on the kinetic acidity is more noticeable and is due to the steric effect of the substituent.

Computational Tools to Study and Predict the Long-Term Stability of Nanowires.

held in 2007, Gordon Moore recognized that by about 2020, his law would come up against the laws of physics. Furthermore, he recognized a change in a paradigm: the replacement of the top-down approach currently used for building circuits by a bottom-up procedure, where chips would be assembled using individual atoms or molecules. This is nothing but the realm of nanotechnology, while there is some consensus that the elementary switches of these circuits should be molecules with some feature allowing for the on/off status required for the components of logical devices, many questions remain concerning their stability. In the case of micrometric circuit components temperature may be an issue, but in the case of single molecules thermal effects may be overwhelming, since current flow occurs across a single bond. The lifetime of this bond, will determine the lifetime of the circuit component. Under these conditions, circuit engineering will be coming unexpectedly close to chemical kinetics. It still is far from clear which will be the technological procedure for the massive production of these molecular circuits. However, there are a number of experimental techniques for the study of their properties that are well established. These are shown schematically in Fig. 1. Fig. 1d shows a method devised to study the structure of monatomic nanowires (NWs). It has been developed by Kondo and Takayanagi (Kondo & Takayanagi, 1997) using High Resolution Transmission Electronic Microscopy (HRTEM) and allows the generation of suspended NWs. In this approach nanowires are generated in situ by focusing an electron beam on adjacent sites of a self-supported metal thin film (ca. 3 nm), making holes and allowing them to grow until a nanometric bridge is formed inside or between grains. The

On the effect of the carbonaceous substrate in the nucleation of Sn nanoparticles for Li-ion anodes: experiments and first principles calculations

AbstractThe nucleation of Sn nanoparticles by chemical reduction was studied using three different carbonaceous substrates, to obtain Sn/C composites. When used as active materials in anodes for lithium-ion batteries, these composites displayed higher capacities than commercially used graphite, and showed a good cyclability. The differences in morphology, capacity, cyclability, and diffusion between the resulting materials are highlighted. The resulting materials were characterized by charge-discharge cycling, voltammetry, EIS, SEM, and TEM microscopy. It was found that the substrate has a determinant effect on the deposition of Sn. This effect is interpreted in terms of the relative adsorption energies of a single Sn atom obtained from DFT calculations. Graphical abstractᅟ