Graphene-contacted single molecular junctions with conjugated molecular wires

In this study, we have determined the electrical properties of amine- and thiol-terminated poly(p-phenylene) molecular wires bound either between two gold electrode contacts (Au/Au) or between a gold contact and a graphene electrode (Au/graphene). These different junctions were studied using a scanning tunneling microscopy (STM) and a noncontact method for forming the molecular bridges (the I(s) technique, where I = current and s = distance). We show that for these molecular targets, junctions formed with Au/Au electrodes have higher conductance than those formed with Au/graphene electrodes. The measured conductance decays exponentially with an increase in the number of phenyl rings, giving a decay constant that is similar for amine- and thiol-terminated molecular junctions with the Au/graphene system. This work reveals that poly(p-phenylene) chains present similar electronic properties when coupled to either gold or graphene electrodes, independently of whether the anchoring group is amine or thiol(ate), and that the transport properties are essentially dominated by the intrinsic molecular properties

Nanostructural origin of blue fluorescence in the mineral karpatite

The colour of crystals is a function of their atomic structure. In the case of organic crystals, it is the spatial relationships between molecules that determine the colour, so the same molecules in the same arrangement should produce crystals of the same colour, regardless of whether they arise geologically or synthetically. There is a naturally-occurring organic crystal known as karpatite which is prized for its beautiful blue fluorescence under ultra-violet illumination. When grown under laboratory conditions however, the crystals fluoresce with an intense green colour. For 20 years, this difference has been thought to be due to chemical impurities in the laboratory-grown material. Using electron microscopy coupled with fluorescence spectroscopy and X-Ray diffraction, we report here that this disparity is instead due to differences in the structure of the crystals at the nanoscale. The results show that in nature, karpatite has a nanotexture that is not present in the synthetic crystals, which enables different photonic pathways and therefore a blue, rather than green colour whilst undergoing fluorescence.</p

Band Engineering of Dangling-Bond Wires on the Si(100)H Surface

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Enabling Materials By Dimensionality: From 0D to 3D Carbon-Based Nanostructures

This chapter is aimed at analysing the influence that dimensional scaling exerts on the electronic, optical, transport and mechanical properties of materials using both experiments and computer simulations. In particular, to climb the “dimensional ladder” from 0D to 3D, we analyse a specific set of all-carbon allotropes, making the best use of the versatility of this element to combine in different bonding schemes, such as sp2 and sp3, resulting in architectures as diverse as fullerenes, nanotubes, graphene, and diamond. Owing to the central role of carbon in future emerging technologies, we will discuss a variety of physical observables to show how novel characteristics emerge by increasing or decreasing the dimensional space in which particles can move, ranging from the charge transport in semiconductor (diamond) and semimetallic (graphite) samples to the stress-strain characteristics of several 2D carbon-based materials, to the gas absorption and selectivity in pillared structures and to the thermal diffusion in foams. In this respect, our analysis uses ab initio, multiscale and Monte Carlo (MC) methods to deal with the complexity of physical phenomena at different scales. In particular, the response of the systems to external electromagnetic fields is described using the effective dielectric model of the plasma losses within a Monte Carlo framework, while pressure fields are dealt with the ab initio simulation of the stress-strain relationships. Moreover, in this chapter we present recent theoretical and experimental investigations aimed at producing graphene and other carbon-based materials using supersonic molecular beam epitaxy on inorganic surfaces, starting from fullerene precursors. We mostly focus on the computational techniques used to model various stages of the process on multiple length and time scales, from the breaking of the fullerene cage upon impact to the rearrangement of atoms on the metal surface used to catalyse graphene formation. The insights obtained by our computational modelling of the impact and of the following chemical-physical processes underlying the materials growth have been successfully used to set up an experimental procedure that ended up in the production of graphene flakes by C60 impact on copper surfaces