Aluminium Nanowires: Influence of Work Hardening on Conductance Histograms

Conductance histograms of work-hardened Al show a series up to 11 equidistant peaks with a period of 1.15 +/- 0.02 of the quantum conductance unit G_0 = 2e^2/h. Assuming the peaks originate from atomic discreteness, this agrees with the value of 1.16 G_0 per atom obtained in numerical calculations by Hasmy et al.Comment: 4 pages, 4 figure

Conductance of Pd-H nanojunctions

Results of an experimental study of palladium nanojunctions in hydrogen environment are presented. Two new hydrogen-related atomic configurations are found, which have a conductances of ~0.5 and ~1 quantum unit (2e^2/h). Phonon spectrum measurements demonstrate that these configurations are situated between electrodes containing dissolved hydrogen. The crucial differences compared to the previously studied Pt-H_2 junctions, and the possible microscopic realizations of the new configurations in palladium-hydrogen atomic-sized contacts are discussed.Comment: 4 pages, 4 figure

Atomic size oscillations in conductance histograms for gold nanowires and the influence of work hardening

Nanowires of different nature have been shown to self-assemble as a function of stress at the contact between two macroscopic metallic leads. Here we demonstrate for gold wires that the balance between various metastable nanowire configurations is influenced by the microstructure of the starting materials and we discover a new set of periodic structures, which we interpret as due to the atomic discreteness of the contact size for the three principal crystal orientations.Comment: This version corrects an error in attributing the three observed periods, and includes a comparison with recent model calculation

Dielectric constants of Ir, Ru, Pt, and IrO2: Contributions from bound charges

We investigated the dielectric functions $\epsilon$($\omega$) of Ir, Ru, Pt, and IrO$_2$, which are commonly used as electrodes in ferroelectric thin film applications. In particular, we investigated the contributions from bound charges $\epsilon^{b}$($\omega$), since these are important scientifically as well as technologically: the $\epsilon_1^{b}$(0) of a metal electrode is one of the major factors determining the depolarization field inside a ferroelectric capacitor. To obtain $\epsilon_1^{b}$(0), we measured reflectivity spectra of sputtered Pt, Ir, Ru, and IrO2 films in a wide photon energy range between 3.7 meV and 20 eV. We used a Kramers-Kronig transformation to obtain real and imaginary dielectric functions, and then used Drude-Lorentz oscillator fittings to extract $\epsilon_1^{b}$(0) values. Ir, Ru, Pt, and IrO$_2$ produced experimental $\epsilon_1^{b}$(0) values of 48$\pm$10, 82$\pm$10, 58$\pm$10, and 29$\pm$5, respectively, which are in good agreement with values obtained using first-principles calculations. These values are much higher than those for noble metals such as Cu, Ag, and Au because transition metals and IrO$_2$ have such strong d-d transitions below 2.0 eV. High $\epsilon_1^{b}$(0) values will reduce the depolarization field in ferroelectric capacitors, making these materials good candidates for use as electrodes in ferroelectric applications.Comment: 26 pages, 6 figures, 2 table

Quantum interference structures in the conductance plateaus of gold nanojunctions

The conductance of breaking metallic nanojunctions shows plateaus alternated with sudden jumps, corresponding to the stretching of stable atomic configurations and atomic rearrangements, respectively. We investigate the structure of the conductance plateaus both by measuring the voltage dependence of the plateaus' slope on individual junctions and by a detailed statistical analysis on a large amount of contacts. Though the atomic discreteness of the junction plays a fundamental role in the evolution of the conductance, we find that the fine structure of the conductance plateaus is determined by quantum interference phenomenon to a great extent.Comment: 4 pages, 4 figure

Keijsers, Shklyarevskii and van Kempen Reply

Answer to the Comment on ``Point-Contact Study of Fast and Slow Two-Level Fluctuators in Metallic Glasses'' by Jan von Delft et al.Comment: 3 pages, no figures, accepted Phys. Rev. Letter

Electron scattering effects at physisorbed hydrogen molecules on break-junction electrodes and nanowires formation in hydrogen environment

The physisorption of hydrogen molecules on the surface of gold and other coinage metals was studied using distance tunneling spectroscopy. We observed strong N-shaped deviation of the tunnel current (resistance) vs distance dependences from the exponential one. Such deviations are difficult to explain in the framework of the Tersoff–Hamann approximation. We suggest the scattering of the tunneling electrons by H₂ molecules as origin for observed effect. We found that this phenomenon is also common for strongly adsorbed organic molecules with one anchoring group. Pulling Au, Cu and Pt nanowires at 22 K in hydrogen environment show that the electrodes of break junctions are still connected up to very low conductances of 10⁻⁴–10⁻⁶ G₀ through hydrogen–metal one-atom chains