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SUMMARY:Logic and memory functions in molecular tunnelling junctions - Hip
 polyte Astier (AMAT-NUS Corp Lab / National University of Singapore)
DTSTART:20230705T100000Z
DTEND:20230705T110000Z
UID:TALK202900@talks.cam.ac.uk
CONTACT:Chris Ford
DESCRIPTION:The field of molecular electronics proposes to use molecules a
 s electronic components and was initially envisaged as a route towards ext
 reme circuit miniaturisation. The challenge in integrating these molecules
  into circuits in a scalable and reliable manner motivated intense researc
 h efforts and the proposal of several experimental approaches\, notably eu
 tectic GaIn and graphene. Functionalities beyond standard tunnelling junct
 ions are being sought using bespoke molecular structures. One such functio
 nality is that of switches and memory devices\, whereby\, by utilising che
 mical reactions within the molecule probed\, its electronic structure can 
 be changed to produce several distinct conductance states. In this present
 ation\, I will discuss two such structures. Methyl viologen is a molecule 
 that offers two very distinct states depending on the presence of a counte
 r-ion balancing charge in the junction [1]. When biased\, this counterion 
 can be caused to migrate\, leading to a complete rearrangement of the mole
 cule and a dramatic change in conduction properties\, with a high ratio be
 tween high and low conductance states of 6\,700\, and a diode behaviour (r
 ectification ratio 250\,000)\, producing a one-diode-one-resistor (1D1R) c
 omponent\, useful for logic crossbar arrays. \nI will also discuss molecul
 ar junctions containing hexaazatrinaphthylene (HATNA) [2]. These combine e
 lectron transport with proton exchange with their environment to produce i
 ntricate 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 comp
 uting\, as they demonstrate plasticity in relation to signal amplitude\, d
 uration\, and frequency. I will give examples of simplified networks showi
 ng their utilisation. Finally\, I will present a new experimental approach
  to probe molecular junctions by manipulating micro-sized EGaIn droplets w
 ith a conductive AFM [3]. This approach offers an easy way to probe molecu
 lar junctions of known geometry and produces extremely robust junctions ca
 pable of withstanding large electric fields.\n1.	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). \n2.	Wang\, Y.\, Zhang\, Q.\, Astier\, H. P. A. G.\, _et al._
 \, Dynamic molecular switches with hysteretic negative differential conduc
 tance emulating synaptic behaviour. Nature Materials 21\, 1403 (2022). \n3
 .	Soh\, E. J. H.\, Astier\, H. P. A. G.\, _et al._\, AFM Manipulation of E
 GaIn Microdroplets to Generate Controlled\, On-Demand Contacts on Molecula
 r Self-Assembled Monolayers. ACS Nano\, 16\, 14370 (2022). \n
LOCATION:Mott Seminar Room\, Cavendish Laboratory
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