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Thermoelectrical properties of self-assembled molecular-scale junctions enhanced by quantum interference effects

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Room-temperature quantum interference (QI) can be used to enhance the thermal and electrical properties of arrays of organic molecules to create ultra-thin-film thermoelectric materials with an unprecedented ability to convert waste heat to electricity using the Seebeck effect and to cool at the nanoscale via the Peltier effect. The realisation of self-assembled molecular-electronic films, whose room-temperature transport properties are controlled by QI, is an essential step in the scale-up of QI effects from single molecules to parallel arrays of molecules. Here I will report on our recent progress such enhanced self-assembled monolayers (SAMs). I will focus on experimental aspects of the work using and discuss the key role that scanning probe microscopy takes in the characterisation of SAMs. Recently, the effect of destructive QI (DQI) on the electrical conductance of self-assembled monolayers (SAMs) has been investigated. Here, I will show that we have demonstrated chemical control of different forms of constructive QI (CQI) in cross-plane transport through SAMs and its influence on cross-plane thermoelectricity in SAMs. It is known that the electrical conductance of single molecules can be controlled deterministically by chemically varying their connectivity to external electrodes. Here, by employing synthetic methodologies to vary the connectivity of terminal anchor groups around aromatic anthracene cores, and by forming SAMs of the resulting molecules, it can be clearly demonstrated that this signature of CQI can be translated into SAM -on-gold molecular films [1]. Furthermore, I will discuss the role that the chemical anchor of the SAM plays in the transport properties of the film [2] and how thermoelectric power harvesting can be controlled by the pressure applied to molecular junctions [3]. Finally, I will discuss the role of ‘slippery’ porphyrin anchors [4] and multilayer films and how these offer exciting design strategies for future SAMs. 1. Wang, et al., Journal of the American Chemical Society 142 (19) 8555–8560 (2020) 2. Ismael, et al., Chemical Science, 11, 6836-6841 (2020) 3. Wang, et al., Chemical Science 12 (14), 5230-5235 (2021) 4. Wang, et al., Journal of Physics: Energy, 4 (2), 24002 (2022)

This talk is part of the Semiconductor Physics Group series.

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