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Molecular 'Click-tronics': Surface-based synthesis of single-molecule electronic components

Periodic Reporting for period 2 - MOLCLICK (Molecular 'Click-tronics': Surface-based synthesis of single-molecule electronic components)

Reporting period: 2017-10-01 to 2018-09-30

How can we best utilize single-molecules in electronics? The smallest features of circuits used inside computer chips will reach the size of a single molecule in 10-20 years (following Moore’s Law). So far, researchers have typically studied molecular-scale electronic components using a common iterative process. First the molecules are prepared and isolated elsewhere (ex situ), then their properties are measured. In this project I am taking a different approach, by preparing and measuring the molecular components in the same place (in situ). This can make them easier to construct, and provide insights into new strategies for ‘wiring up’ molecules into more complicated circuits. Specifically, I am (i) exploring new ways to make the molecular electronic components in situ, and (ii) developing new techniques using the ‘scanning tunnelling microscope’ (STM) to assess whether I have successfully constructed the desired molecular circuit(s). My approach can be used to rapidly screen novel single-molecule wires and devices (e.g. diodes or switches), improving important properties such as how well they conduct electricity (for a switch they should conduct well when ‘on’ and not at all when ‘off’). It also provides a mechanism to test the properties of single-molecule electronic components comprising weakly-bound species. These typically fall apart while they are being tested using existing methods. This research has broad applications and far-reaching impact in data storage and computation (‘wiring-up’ molecules in circuits), and will open up exciting possibilities in other areas of surface chemistry (e.g. sensing and catalysis).
We have developed general, robust methodologies to wire up molecules into simple circuits on surfaces, using synthetic chemistry to modify and extend surface-bound molecular materials. We have demonstrated that the success of surface reactions can be probed at the single-molecule level using the scanning tunnelling microscope-based break-junction (STM-BJ) technique, by comparing the single-molecule conductance of molecules prepared in situ to the conductance of identical molecules prepared ex situ. Multiple different reactions, and even reversible, multi-step reactions have now been identified as suitable for modifying molecules in situ, where the STM-BJ has proved a remarkably sensitive and precise tool for surface analysis. Though efforts have been focused on thiol-based self-assembled monolayers on gold surfaces, they have also led us to explore the conductance of molecules terminated by other notable surface-binding linkers such as N-heterocyclic carbenes. To date, research supported by this fellowship has been disseminated through 7 articles in international, peer-review journals, as well as through presentation at over 10 scientific conferences and meetings.
Efforts are underway to utilise the in situ reactions and STM-BJ techniques developed in this work to build and interrogate the properties of more complex surface-bound molecular structures, to understand the physical processes involved in their construction, and to improve our understanding of associated fundamental charge transport processes on the nanoscale. This work charts a clear path for the further development of surface-based reactions and the exploitation of different surface substrates in this context, and has already helped to improve our understanding of how to control, develop, and exploit bottom-up techniques in molecular nanotechnology.