Biomedical subjects

J M van Ruitenbeek

Publications and source records attributed to J M van Ruitenbeek.

9 recordsLinked to original sources

PubMed2006

Vibrationally induced two-level systems in single-molecule junctions.

Single-molecule junctions are found to show anomalous spikes in dI/dV spectra. The position in energy of the spikes is related to local vibration mode energies. A model of vibrationally induced two-level systems reproduces the data very well. This mechanism is expected to be quite general for single-molecule junctions. It acts as an intrinsic amplification mechanism for local vibration mode features and may be exploited as a new spectroscopic tool.

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PubMed2006

Oxygen-enhanced atomic chain formation.

We report experimental evidence for atomic chain formation during stretching of atomic-sized contacts for gold and silver, that is strongly enhanced due to oxygen incorporation. While gold has been known for its tendency to form atomic chains, for silver this is only observed in the presence of oxygen. With oxygen the silver chains are as long as those for gold, but the conductance drops with chain length to about 0.1 conductance quantum. A relation is suggested with previous work on surface reconstructions for silver (110) surfaces after chemisorption of oxygen.

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PubMed2006

Shot noise measurements on a single molecule.

We report measurements of shot noise in the current through a single D2 molecule. The molecular junctions were formed by means of the mechanically controllable break junction technique. The configuration of the D2 molecule bridging the gap between two Pt tips is verified by use of point contact spectroscopy. Maintaining the same junction shot noise measurements were performed and the observed quantum suppression shows that conductance is carried dominantly by a single, almost fully transparent conductance channel. This observation allows us to decide between conflicting model calculations for this system, and this may serve as a benchmark for further computations on molecular junctions.

Deuterium↗

PubMed2005

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

Nanowires of different natures have been shown to self-assemble as a function of stress at the contact between two macroscopic metallic leads. Here we demonstrate for Au 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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PubMed2003

Observation of a parity oscillation in the conductance of atomic wires.

Using a scanning tunnel microscope or mechanically controllable break junctions atomic contacts for Au, Pt, and Ir are pulled to form chains of atoms. We have recorded traces of conductance during the pulling process and averaged these for a large number of contacts. An oscillatory evolution of conductance is observed during the formation of the monoatomic chain suggesting a dependence on the numbers of atoms forming the chain being even or odd. This behavior is not only observed for the monovalent metal Au, as was predicted, but is also found for the other chain-forming metals, suggesting it to be a universal feature of atomic wires.

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PubMed2002

Measurement of the conductance of a hydrogen molecule.

Recent years have shown steady progress towards molecular electronics, in which molecules form basic components such as switches, diodes and electronic mixers. Often, a scanning tunnelling microscope is used to address an individual molecule, although this arrangement does not provide long-term stability. Therefore, metal-molecule-metal links using break-junction devices have also been explored; however, it is difficult to establish unambiguously that a single molecule forms the contact. Here we show that a single hydrogen molecule can form a stable bridge between platinum electrodes. In contrast to results for organic molecules, the bridge has a nearly perfect conductance of one quantum unit, carried by a single channel. The hydrogen bridge represents a simple test system in which to understand fundamental transport properties of single-molecule devices.

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PubMed2001

Common origin for surface reconstruction and the formation of chains of metal atoms.

During the fracture of nanocontacts gold spontaneously forms freely suspended chains of atoms, which is not observed for the isoelectronic noble metals Ag and Cu. Au also differs from Ag and Cu in forming reconstructions at its low-index surfaces. Using mechanically controllable break junctions we show that all the 5d metals that show similar reconstructions (Ir, Pt, and Au) also form chains of atoms, while both properties are absent in the 4d neighbor elements (Rh, Pd, and Ag), indicating a common origin for these two phenomena. A competition between s and d bonding is proposed as an explanation.

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PubMed2001

Crossover from electronic to atomic shell structure in alkali metal nanowires.

After making a cold weld by pressing two clean metal surfaces together, upon gradually separating the two pieces a metallic nanowire is formed, which progressively thins down to a single atom before contact is lost. In previous experiments we have observed that the stability of such nanowires is influenced by electronic shell filling effects, in analogy to shell effects in metal clusters. For sodium and potassium at larger diameters there is a crossover to crystalline wires with shell closings corresponding to the completion of additional atomic layers. This observation completes the analogy between shell effects observed for clusters and nanowires.

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PubMed2001

Atomic-size metallic conductors.

A number of newly developed experimental techniques and theoretical insights have made it possible to investigate the electronic transport properties of conductors at the atomic scale. Although the field is still rapidly evolving, a number of new discoveries, concepts and insights have been clearly established. The central theme of this brief review will be the electronic conductance of a single atom. This conductance can be described in terms of a number of quantum modes, where the number of these modes is determined by the valence orbitals of the metal atom. I first present some elements of the theoretical basis for these concepts, and discuss the various experimental tools that have been used to verify it. Electronic conductance at the atomic scale cannot be separated from the problem of the energetics and dynamics of atomic-scale configurations. Investigations in this area have produced a number of surprising discoveries, and of these I will discuss the spontaneous formation of a conducting chain of single gold atoms, and the enhanced stability of nanowires of alkali metals at 'magic' radii determined by shell structure of the conductance modes.

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