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Register a new userPulling gold nanowires with a hydrogen clamp
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In this paper an experimental study of the interaction of hydrogen molecules with gold nanowires is presented. Our results show, that chains of Au atoms can also be pulled in hydrogen environment, however in this case the conductance of the chain is strongly reduced compared to the perfect transmission of pure Au chains. The comparison of our experiments with recent theoretical prediction for the hydrogen welding of Au nanowires implies that a hydrogen molecule can even be incorporated in the gold nanocontact, and this hydrogen clamp is strong enough to pull a chain of gold atoms.
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We report quantitative electrical admittance measurements of diffusive superconductor--normal-metal--superconductor (SNS) junctions at gigahertz frequencies and millikelvin temperatures. The gold-palladium-based SNS junctions are arranged into a chain of superconducting quantum interference devices. The chain is coupled strongly to a multimode microwave resonator with a mode spacing of approximately 0.6 GHz. By measuring the resonance frequencies and quality factors of the resonator modes, we extract the dissipative and reactive parts of the admittance of the chain. We compare the phase and temperature dependence of the admittance near 1 GHz to theory based on the time-dependent Usadel equations. This comparison allows us to identify important discrepancies between theory and experiment that are not resolved by including inelastic scattering or elastic spin-flip scattering in the theory.
The vibrations of gold nanowires and nanorods are investigated numerically in the framework of continuum elasticity using the Rayleigh-Ritz variational method. Special attention is paid to identify the vibrations relevant in Raman scattering experiments. A comprehensive description of the vibrations of nanorods is proposed by determining their symmetry, comparing with standing waves in the corresponding nanowires and estimating their Raman intensity. The role of experimentally relevant parameters such as the anisotropic cubic lattice structure, the presence of faceted lateral surfaces and the shape of the ends of the nanorods is evaluated. Elastic anisotropy is shown to play a significant role contrarily to the presence of facets. Localized vibrations are found for nanorods with flat ends. Their evolution as the shape of the ends is changed to half-spheres is discussed.
Atomic nanowires on semiconductor surfaces induced by the adsorption of metallic atoms have attracted a lot of attention as possible hosts of the elusive, Tomonaga-Luttinger liquid. The Au/Ge(100) system in particular is the subject of controversy as to whether the Au-induced nanowires do indeed host exotic, 1D metallic states. We report on a thorough study of the electronic properties of high quality nanowires formed at the Au/Ge(100) surface. High resolution ARPES data show the low-lying Au-induced electronic states to possess a dispersion relation that depends on two orthogonal directions in k-space. Comparison of the E(k$_x$,k$_y$) surface measured using ARPES to tight-binding calculations yields hopping parameters in the two different directions that differ by a factor of two. We find that the larger of the two hopping parameters corresponds, in fact, to the direction perpendicular to the nanowires (t$_{perp}$). This, the topology of the $E$=$E_F$ contour in k$_{||}$, and the fact that $t_{||}$/$t_{perp}sim 0.5$ proves that the Au-induced electron pockets possess a 2D, closed Fermi surface, this firmly places the Au/Ge(100) nanowire system outside being a potential hosts of a Tomonaga-Luttinger liquid. We combine these ARPES data with STS measurements of the spatially-resolved electronic structure and find that the spatially straight conduction channels observed up to energies of order one electron volt below the Fermi level do not originate from the Au-induced states seen in the ARPES data. The former are more likely to be associated with bulk Ge states that are localized to the subsurface region. Despite our proof of the 2D nature of the Au-induced nanowire and sub-surface Ge-related states, an anomalous suppression of the density of states at the Fermi level is observed in both the STS and ARPES data, this phenomenon is discussed in the light of the effects of disorder.
We extend our previous shell effect observation in gold nanowires at room temperature under ultra high vacuum to the other two noble metals: silver and copper. Similar to gold, silver nanowires present two series of exceptionally stable diameters related to electronic and atomic shell filling. This observation is in concordance to what was previously found for alkali metal nanowires. Copper however presents only electronic shell filling. Remarkably we find that shell structure survives under ambient conditions for gold and silver.
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.
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