(a) Schematic of biological synapses and an array of Si-NC-based synaptic devices. (b) EPSC induced by a 375 nm laser spike. (c) PPF behavior induced by two successive 375 nm laser spikes. (d) Transition from STP to LTP by 375 nm laser spiking at the frequencies of 0.05 Hz and 0.25 Hz. (e) Variation of the STDP-induced synaptic-weight change (ΔS) with respect to Δt_pre-post for the 375 nm laser spiking. Δt_pre-post is the interval time of two identical laser spikes applied to the presynaptic and postsynaptic neurons. (f) The STS result for the Si-NC film measured at 77 K. The inset schematically shows the STS measurement. (g) Schematic model for the electronic structure and carrier behavior of Si NCs. Reproduced with permission from Ref. [93]. Copyright 2018, Elsevier Ltd.