In Situ Observation of Low-Power Nano-Synaptic Response in Graphene Oxide Using Conductive Atomic Force Microscopy

Abstract
Multiple studies have reported the observation of electro-synaptic response in different metal/insulator/metal devices. However, most of them analyzed large (>1 µm2 ) devices that do not meet the integration density required by industry (1010  devices/mm2 ). Some studies emploied a scanning tunneling microscope (STM) to explore nano-synaptic response in different materials, but in this setup there is a nanogap between the insulator and one of the metallic electrodes (i.e., the STM tip), not present in real devices. Here, it is demonstrated how to use conductive atomic force microscopy to explore the presence and quality of nano-synaptic response in confined areas <50 nm2 . Graphene oxide (GO) is selected due to its easy fabrication. Metal/GO/metal nano-synapses exhibit potentiation and paired pulse facilitation with low write current levels <1 µA (i.e., power consumption ≈3 µW), controllable excitatory post-synaptic currents, and long-term potentiation and depression. The results provide a new method to explore nano-synaptic plasticity at the nanoscale, and point to GO as an important candidate for the fabrication of ultrasmall (<50 nm2 ) electronic synapses fulfilling the integration density requirements of neuromorphic systems.

Citation
Hui, F., Liu, P., Hodge, S. A., Carey, T., Wen, C., Torrisi, F., … Lanza, M. (2021). In Situ Observation of Low-Power Nano-Synaptic Response in Graphene Oxide Using Conductive Atomic Force Microscopy. Small, 2101100. doi:10.1002/smll.202101100

Acknowledgements
The authors acknowledge funding by the Ministry of Science and Technology of China (grant no. 2018YFE0100800, 2019YFE0124200), the National Natural Science Foundation of China (grant no. 61874075), the Ministry of Finance of China (grant no. SX21400213), the Jiangsu Planned Projects for Postdoctoral Research Funds of China (grant No. 7131712019), the 111 Project from the State Administration of Foreign Experts Affairs of China, the Collaborative Innovation Centre of Suzhou Nano Science & Technology, the Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, the Priority Academic Program Development of Jiangsu Higher Education Institutions, the Isaac Newton Trust, the EU project CareRAMM, EU Graphene Flagship, ERC grants Hetero2D and MINERGRACE, EPSRC grants EP/K01711X/1, EP/K017144/1, EP/N010345/1, EP/M507799/1, EP/L016087/1, EP/R511547/1, EP/P02534X/2, EP/T005106/1, and a Technion-Guangdong Fellowship.

Publisher
Wiley

Journal
Small

DOI
10.1002/smll.202101100

PubMed ID
34081416

Additional Links
https://onlinelibrary.wiley.com/doi/10.1002/smll.202101100

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