Giving electrons a ride: nanomechanical electron shuttles

Nanomechanical shuttles transferring small groups of electrons or even individual electrons from one electrode to another offer a novel approach to the problem of controlled charge transport. Here, we report the fabrication of shuttle-junctions consisting of a 20 nm diameter gold nanoparticle embedded within the gap between two gold electrodes. The nanoparticle is attached to the electrodes through a monolayer of flexible organic molecules which play the role of springs so that when a sufficient voltage bias is applied, then nanoparticle starts to oscillate transferring electrons from one electrode to the other. Current-voltage characteristics for the fabricated devices have been measured and compared with the results of our computer simulations.Comment: 11 pages, 4 figure

Fabrication of shuttle-junctions for nanomechanical transfer of electrons

We report on the fabrication of nanomechanical devices for shuttling of electrons from one electrode to another. Each device consists of a 20 nm diameter gold nanoparticle embedded within the gap between two gold electrodes. In two different kinds of shuttle-junctions the nanoparticle is attached to the electrodes through either (i) a single layer of 1,8-octanedithiol or (ii) a multilayer of 1-octanethiol molecules. The thiol layers play the role of 'damped springs', such that when a sufficient voltage bias is applied to the junction, the nanoparticle is expected to start oscillating and thereby transferring electrons from one electrode to the other. For both kinds of shuttle-junctions we observed an abrupt increase in the transmitted current above a threshold voltage, which can be attributed to a transition from the stationary to the oscillating regime. The threshold voltage was found to be lower for single-layer shuttle-junctions

Mesoscopic phenomena in the electromechanics of suspended nanowires

Over the last two decades nanotechnology has been a very active field of scientific research, both from fundamental perspectives as well as for applications in technology and consumer goods. In this thesis, theoretical work on quantum mechanical effects on charge transport in nanoelectromechanical systems is presented. In particular, the effects of electron-vibron interactions in suspended nanowire structures are analysed and discussed. The thesis is structured around the appended scientific publications by the author. Also included is an introductory section where the underlying theory and motivation is presented. This introduction forms the basis on which the subsequent material and appended papers is based. The work presented in the appended papers considers systems comprising suspended oscillating nanowires, primarily in the form of carbon nanotubes. Central to these studies is the interaction between the charge transport and the mechanical motion of the nanowires. For the systems analysed in this thesis, these interactions are mediated through transverse magnetic fields, the effect of which is studied in various system setups. In particular, three topics of mesoscopic phenomena are presented; i) a temperature-independent current deficit due to interference effects between different electronic tunnelling paths over the nanowire-junction, ii) pumping of the mechanical vibrations in a low transparency superconducting junction, and iii) cooling of the mechanical vibrations in both current- and voltage-biased superconducting junctions. The outcome of the presented work is a number of interesting physical predictions for the electromechanics of suspended nanowires. These results are shown to be experimentally observable in systems with high mechanical resonance frequencies and if sufficiently strong electromechanical coupling can be achieved. Once these conditions are fulfilled, the predicted results are of interest both from a fundamental perspective in that they probe the underlying quantum nature of the systems, but also for sensing applications where quantum limited resolution could be experimentally achievable

Syntheses and Structures of Buta-1,3-Diynyl Complexes from ‘On Complex’ Cross-Coupling Reactions

The Pd(PPh3)4/CuI-cocatalyzed reaction of Ru(C≡CC≡CH)(PPh3)2Cp (2) with aryl iodides, Ar–I (3, Ar = C6H4CN-4 (a); C6H4Me-4 (b); C6H4OMe-4 (c); 2,3-dihydrobenzo[b]thiophene (d); C5H4N (e)) proceeds smoothly in diisopropylamine and under an inert atmosphere to give the substituted buta-1,3-diynyl complexes Ru(C≡CC≡CAr)(PPh3)2Cp (4a–e) in moderate to good yield. The procedure allows the rapid preparation of a range of metal complexes of arylbuta-1,3-diynyl ligands without necessitating the prior synthesis of the individual buta-1,3-diynes as ligand precursors. Similar reaction of 2 with half an equivalent of 1,4-diiodobenzene affords the bimetallic derivative {Ru(PPh3)2Cp}2(μ-C≡CC≡C-1,4-C6H4–C≡CC≡C) (5). In the presence of atmospheric oxygen, homocoupling of the diynyl reagent 2 takes place to provide the octa-1,3,5,7-tetrayndiyl complex {Ru(PPh3)2Cp}2(μ-C≡CC≡CC≡CC≡C) (6). Crystallographically determined molecular structures are reported for five complexes (4a, 4b, 4d, 5, and 6). Quantum chemical calculations indicate that the HOMOs are mainly located on the C4–C6H4–C4 and C8 bridges for 5 and 6, respectively, while spectroelectrochemical (UV–vis–NIR and IR) studies on 6 establish that oxidation takes place at the C8 bridge, likely followed by cyclodimerization reactions of the bridging ligand