Porphyrin wires for nanoelectronics

Collaborators: Harry Anderson (Oxford, UK), Colin Lambert and Iain Grace (Lancaster, UK), Martin Elliot and J. Emyr Macdonald (Cardiff, UK)

Oligo-porphyrins can mediate electron transmission over unusually long distances with low attenuation, making them attractive targets as molecular wires. Thus they could be utilised in the electrical "wiring" of sub-10-nm electronic devices and also in photo-voltaic systems for charge transport and separation. We have been examining charge transport in both linear and barrel-shaped oligo-porphyrins looking for unusual properties in the mechanism of conduction.

Relevant publications:
Nature Nanotechnology (2011)
Advanced Materials (2011)

Single-Molecule Photo-spintronics

Collaborators: Walther Schwarzacher (Bristol, UK)

Single-molecule spintronic measurements promise to yield a fundamental understanding of spin transport in organic systems and will help establish whether organic spintronic devices are a practical proposition. Our goal is to measure the photocurrent from a semiconductor (GaAs) to a metal through a single molecule and its dependence on the light polarization, the metal magnetization direction (for ferromagnetic electrodes) and the applied bias. A signal that depends only on the polarization relative to the magnetization direction will be evidence for spin-dependent tunnelling. We aim to understand the transport and magneto-transport properties of semiconductor-molecule junctions, focusing on molecules where the charge transfer is by coherent tunnelling, rather than hopping conduction.

Relevant publications:
Nano Letters (2017)

Organometallic molecular wires

Collaborators: Paul J. Low (Perth, Australia), Andrew Beeby (Durham, UK)

Metal complexes have proven to be valueble for evaluation of many properties of charge transport in molecular wires, and a wide range of metal ions can be incorporated. This allows a selection of physical and chemical properties relating the charge, size, and redox or magnetic properties of the complex and the ligand shell to be readily examined. We study such complexes to better understand these properties, and their redox behaviour can be used to gate molecular conductance, with a FET-like behaviour.

Relevant publications:
Nanoscale (2017)
Chemistry: A European Journal (2017)
Organometallics (2016)
Inorganic Chemistry (2016)
Inorganic Chemistry (2015)

Supramolecular Effects

Collaborators: Colin Lambert and Iain Grace (Lancaster, UK), Martin Elliot and J. Emyr Macdonald (Cardiff, UK), Bingqian Xu (Athens, USA)

Although an isolated molecule within a junction, and its contacts to the electrodes, must necessarily be affected by interactions with solvent molecules, and/or ambient water, this has provoked few detailed studies. The study of conductance behaviour of supramolecular assemblies of molecules, such as host-guest complexes or charge-transfer complexes, and of the solvation shell surrounding a metal-molecule-metal junction can lead to the use of single-molecule devices as sensors or chemFETs.

Relevant publications:
Journal of Chemical Physics (2017)
Nanoscale (2016)
ACS Nano (2016)
Nanoscale (2015)
Journal of Physical Chemistry C (2015)
Physical Review Letters (2008)

Electrochemical Gating

Collaborators: Martin Bryce (Durham, UK), Santiago Martin (Zaragoza, Spain), Colin Lambert and Iain Grace (Lancaster, UK)

We pioneered the measurement of single molecule conductance in electrochemical environments. This has enabled detailed investigation of charge transfer through molecules in electrochemical environments. Large changes in molecule conductance can occur with electrode potential, but the form of these changes is very sensitive to the molecule structure and redox properties of the molecular wire.

Relevant publications:
Faraday Discussions (2016)
Journal of the American Chemical Society (2015)
Journal of the American Chemical Society (2012)

Fundamental Molecular Electronics

Collaborators: Martin Bryce (Durham, UK), Santiago Martin (Zaragoza, Spain), Colin Lambert and Iain Grace (Lancaster, UK)

In a metal-molecule-metal junction a small modification of the molecular backbone can lead to a dramatic change in its behaviour. By synthesising families of archetypal molecular wires such as oligo-ynes, bipyridyls, alkanes, etc. and measuring their conductance and its decay with length we aim at a better understanding of the fundamental properties of charge transport through metal-molecule-metal junctions.

Relevant publications:
RSC Advances (2016)
Physical Review B (2015)
Journal of Physical Chemistry C (2015)
Journal of Physics: Condensed Matter (2012)
Journal of the American Chemical Society (2009)

Surface Electrochemistry and Electrodes

Collaborators: Trevor J. Davies (Chester, UK), Centre for Global Eco-Innovation (UK)

Carbon fibre based materials like graphite felts (GFs) are commonly used in redox flow batteries as electrodes due to their electrochemical activity, high permeability for liquids, high surface area and relatively low cost. Previous characterisation of GFs has involved flow systems, which can be complicated to replicate and expensive. Using pre-treatment techniques to ensure sufficient wetting, GFs can be used effectively in quiescent electrochemistry. Those electrodes show promising limit of detection values, with experiments suggesting these electrodes may have applications in electroanalysis.

Relevant publications:
Journal of Electroanalytical Chemistry (2015)
Electrochimica Acta (2016)