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Studying conductivity at the single molecule level

Recent advances in scanning probe microscopy (SPM) have enabled investigation of a number of processes at the single molecule level. In addition to biological importance such as understanding DNA-enzyme reactions, single molecule interactions are of interest for studying and developing new electrical behaviours at the single molecule level with potential relevance to the electronics industry.

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The ‘Single-molecule studies of photo-conductance on photosynthetic molecular systems by SPM break-junction measurements’ (Photosyn-STM) project studied various methodologies enabling characterisation of single metal-molecule-metal electric contacts and their charge transport behaviours. Among these technologies are scanning tunnelling microscopy (STM) break-junction techniques. During the initial phase of the project, the researchers developed new designs for the STM break-junction setup to evaluate novel electrical behaviours as related to photoconductance, or increased electrical conductivity in response to exposure to photons emitted by electromagnetic radiation. Using these tools, they demonstrated diode behaviour of a single-molecule junction, achieved an electrochemical gate effect directly applicable to single molecule field effect transistors (FETs) and designed a single-molecule electromechanical device that mechanically modulates current flow. They also obtained preliminary single-molecule photoemission data related to the previously mentioned diode behaviour. Project members successfully implemented two STM break-junction setups to study single molecule junctions and charge transport in molecular systems with biological relevance. Specifically, the investigators characterised charge transport in single-protein junctions using the redox protein blue Cu-azurin to produce the first single-azurin electrical contact between two metallic electrodes. The results produced by Photosyn-STM have had significant impact on the field of molecular electronics. Continued research should pave the way for commercial applicability of the new generation of single-molecule devices.

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Scientific advances
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9 October 2020