Fig. 17

a Construction diagrams of biological and artificial neural networks. b Working principle of the MXene-based artificial neural network. c Characteristic information of letter ‘A’ extracted by optoelectronic synapse. d Feature dictionary of different letters. e Handwritten word ‘ESKIN’, and its feature dictionary. f Reduced vector dimensionality for learning and recognition of the handwritten word ‘APPLE’. g Recognition of different handwritten words by artificial neural network after training [24]. Copyright 2020, Springer Nature