Logic and memory functions in molecular tunnelling junctions

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• Hippolyte Astier (AMAT-NUS Corp Lab / National University of Singapore)
• Wednesday 05 July 2023, 11:00-12:00
• Mott Seminar Room, Cavendish Laboratory.

If you have a question about this talk, please contact Chris Ford.

The field of molecular electronics proposes to use molecules as electronic components and was initially envisaged as a route towards extreme circuit miniaturisation. The challenge in integrating these molecules into circuits in a scalable and reliable manner motivated intense research efforts and the proposal of several experimental approaches, notably eutectic GaIn and graphene. Functionalities beyond standard tunnelling junctions are being sought using bespoke molecular structures. One such functionality is that of switches and memory devices, whereby, by utilising chemical reactions within the molecule probed, its electronic structure can be changed to produce several distinct conductance states. In this presentation, I will discuss two such structures. Methyl viologen is a molecule that offers two very distinct states depending on the presence of a counter-ion balancing charge in the junction [1]. When biased, this counterion can be caused to migrate, leading to a complete rearrangement of the molecule and a dramatic change in conduction properties, with a high ratio between high and low conductance states of 6,700, and a diode behaviour (rectification ratio 250,000), producing a one-diode-one-resistor (1D1R) component, useful for logic crossbar arrays. I will also discuss molecular junctions containing hexaazatrinaphthylene (HATNA) [2]. These combine electron transport with proton exchange with their environment to produce intricate transport properties including multi-state memory, and negative differential resistance with peak-to-valley ratios of ~14. I will explain how these properties can produce artificial synapses for neuromorphic computing, as they demonstrate plasticity in relation to signal amplitude, duration, and frequency. I will give examples of simplified networks showing their utilisation. Finally, I will present a new experimental approach to probe molecular junctions by manipulating micro-sized EGaIn droplets with a conductive AFM [3]. This approach offers an easy way to probe molecular junctions of known geometry and produces extremely robust junctions capable of withstanding large electric fields. 1. Han, Y., Nickle, C., Zhang, Z., Astier, H. P. A. G., et al., Electric-field-driven dual-functional molecular switches in tunnel junctions. Nature Materials, 19, 843 (2020). 2. Wang, Y., Zhang, Q., Astier, H. P. A. G., et al., Dynamic molecular switches with hysteretic negative differential conductance emulating synaptic behaviour. Nature Materials 21, 1403 (2022). 3. Soh, E. J. H., Astier, H. P. A. G., et al., AFM Manipulation of EGaIn Microdroplets to Generate Controlled, On-Demand Contacts on Molecular Self-Assembled Monolayers. ACS Nano, 16, 14370 (2022).

This talk is part of the Semiconductor Physics Group series.

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• Mott Seminar Room, Cavendish Laboratory

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