Nanomechanics of bidentate thiolate ligands of gold surfaces

The effect of the chain length separating sulfur atoms in bidentate thiols attached to defective gold surfaces on the rupture of the respective molecule-gold junctions has been studied computationally. Thermal desorption always yields cyclic disulfides. In contrast, mechanochemical desorption leads to cyclic gold complexes, where metal atoms are extracted from the surface and kept in tweezer-like arrangements by the sulfur atoms. This phenomenon is rationalized in terms of directional mechanical manipulation of Au-Au bonds and Au-S coordination numbers. Moreover, the flexibility of the chain is shown to crucially impact on the mechanical strength of the junction

Selective nanomechanics of aromatic versus aliphatic thiolates on gold surfaces

Thiolated gold nanointerfaces play a key role in numerous fields of science, technology, as well as modern medicine to coat, functionalize, and protect. Our computational study reveals that the mechanical vs thermal stabilities of aliphatic thiolates on gold surfaces are strikingly different from those of aromatic thiolates. The aliphatic thiolates feature, at the same time, a higher thermal desorption energy but a lower mechanical rupture force than thiophenolates. Our analysis discloses that this most counterintuitive property is due to different mechanochemical detachment mechanisms. Electronic structure analyses along the detachment pathways trace this back to the distinct electronic properties of the S─Au bond in stretched nanojunctions. The discoveries that it is a higher thermal stability that entails a lower mechanical stability and that mechanical loads generate different local nanostructures depending on the nature of the thiolate are highly relevant for the rational design of improved thiol-gold nanocontacts

Super-Nernstian Shifts of Interfacial Proton-Coupled Electron Transfers : Origin and Effect of Noncovalent Interactions

The support of the University of Aberdeen is gratefully acknowledged. C.W. acknowledges a summer studentship from the Carnegie Trust for the Universities of Scotland. E.P.M.L. acknowledges SeCYT (Universidad Nacional de Cordoba), ́ CONICET- PIP 11220110100992, Program BID (PICT 2012-2324), and PME 2006-01581 for financial support.Peer reviewedPostprin

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

The 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.Facultad de Ciencias ExactasInstituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Nanomechanics of bidentate thiolate ligands of gold surfaces

The effect of the chain length separating sulfur atoms in bidentate thiols attached to defective gold surfaces on the rupture of the respective molecule-gold junctions has been studied computationally. Thermal desorption always yields cyclic disulfides. In contrast, mechanochemical desorption leads to cyclic gold complexes, where metal atoms are extracted from the surface and kept in tweezer-like arrangements by the sulfur atoms. This phenomenon is rationalized in terms of directional mechanical manipulation of Au-Au bonds and Au-S coordination numbers. Moreover, the flexibility of the chain is shown to crucially impact on the mechanical strength of the junction

A Reversible Molecular Switch Based on the Biphenyl Structure

DFT calculations were performed on a biphenyl-based molecule bonded to gold nanoleads in order to evaluate its potential as a reversible molecular switch. The torsion angle (φ) between the aromatic rings may be controlled by means of reducing a disulfide functionality that bridges the two rings, giving rise to a “closed” species (disulfide bridge oxidized, φ ∼ 28°) and an “opened” species (disulfide bridge reduced, φ ∼ 65°). The mechanical properties of the nanojunction formed by this molecular species sandwiched between gold cluster pyramids mimicking metallic electrodes were determined. The thermodynamics of the reduction reaction was studied on the disulfide bridge as well as on the potentially competing anchoring sulfur atoms. A highly favorable product ratio toward the disulfide bridge reduction was found. Conductance values were calculated by means of non-equilibrium Green functions techniques. Interestingly, a significant difference between the closed (high conductance) and opened (low conductance) species was found