Electric-field control of interfering transport pathways in a single-molecule anthraquinone transistor

It is understood that molecular conjugation plays an important role in charge transport through single-molecule junctions. Here, we investigate electron transport through an anthraquinone based single-molecule three-terminal device. With the use of an electric-field induced by a gate electrode, the molecule is reduced resulting into a ten-fold increase in the off-resonant differential conductance. Theoretical calculations link the change in differential conductance to a reduction-induced change in conjugation, thereby lifting destructive interference of transport pathways.Comment: Nano Letters (2015

Particle-stabilized oscillating diver: a self-assembled responsive capsule

We report the experimental discovery of a self-assembled capsule, with density set by interfacial glass beads and an internal bubble, that automatically performs regular oscillations up and down a vial in response to a temperature gradient. Similar composites featuring interfacial particles and multiple internal compartments could be the solution to a variety of application challenges.Comment: 7 pages, 3 figure

Formation and properties of metal-oxygen atomic chains

Suspended chains consisting of single noble metal and oxygen atoms have been formed. We provide evidence that oxygen can react with and be incorporated into metallic one-dimensional atomic chains. Oxygen incorporation reinforces the linear bonds in the chain, which facilitates the creation of longer atomic chains. The mechanical and electrical properties of these diatomic chains have been investigated by determining local vibration modes of the chain and by measuring the dependence of the average chain-conductance on the length of the chain. Additionally, we have performed calculations that give insight in the physical mechanism of the oxygen-induced strengthening of the linear bonds and the conductance of the metal-oxygen chains.Comment: 10 pages, 9 fig

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.Comment: 4 pages, 4 figure

Opportunities and limitations of transition voltage spectroscopy: a theoretical analysis

In molecular charge transport, transition voltage spectroscopy (TVS) holds the promise that molecular energy levels can be explored at bias voltages lower than required for resonant tunneling. We investigate the theoretical basis of this novel tool, using a generic model. In particular, we study the length dependence of the conducting frontier orbital and of the 'transition voltage' as a function of length. We show that this dependence is influenced by the amount of screening of the electrons in the molecule, which determines the voltage drop to be located at the contacts or across the entire molecule. We observe that the transition voltage depends significantly on the length, but that the ratio between the transition voltage and the conducting frontier orbital is approximately constant only in strongly screening (conjugated) molecules. Uncertainty about the screening within a molecule thus limits the predictive power of TVS. We furthermore argue that the relative length independence of the transition voltage for non-conjugated chains is due to strong localization of the frontier orbitals on the end groups ensuring binding of the rods to the metallic contacts. Finally, we investigate the characteristics of TVS in asymmetric molecular junctions. If a single level dominates the transport properties, TVS can provide a good estimate for both the level position and the degree of junction asymmetry. If more levels are involved the applicability of TVS becomes limited.Comment: 8 pages, 12 figure

Dynamics of hard-sphere suspension using Dynamic Light Scattering and X-Ray Photon Correlation Spectroscopy: dynamics and scaling of the Intermediate Scattering Function

Intermediate Scattering Functions (ISF's) are measured for colloidal hard sphere systems using both Dynamic Light Scattering (DLS) and X-ray Photon Correlation Spectroscopy (XPCS). We compare the techniques, and discuss the advantages and disadvantages of each. Both techniques agree in the overlapping range of scattering vectors. We investigate the scaling behaviour found by Segre and Pusey [1] but challenged by Lurio et al. [2]. We observe a scaling behaviour over several decades in time but not in the long time regime. Moreover, we do not observe long time diffusive regimes at scattering vectors away from the peak of the structure factor and so question the existence of a long time diffusion coefficients at these scattering vectors.Comment: 21 pages, 11 figure

Image effects in transport at metal-molecule interfaces

We present a method for incorporating image-charge effects into the description of charge transport through molecular devices. A simple model allows us to calculate the adjustment of the transport levels, due to the polarization of the electrodes as charge is added to and removed from the molecule. For this, we use the charge distributions of the molecule between two metal electrodes in several charge states, rather than in gas phase, as obtained from a density-functional theory-based transport code. This enables us to efficiently model level shifts and gap renormalization caused by image-charge effects, which are essential for understanding molecular transport experiments. We apply the method to benzene di-amine molecules and compare our results with the standard approach based on gas phase charges. Finally, we give a detailed account of the application of our approach to porphyrin-derivative devices recently studied experimentally by Perrin et al. [Nat. Nanotechnol. 8, 282 (2013)], which demonstrates the importance of accounting for image-charge effects when modeling transport through molecular junctions