English: "a Schematic illustration of the device structure. b Photograph of the devices fabricated as an array on a flexible substrate. c TEM image of SnO2 nanoparticles. d High-resolution TEM of MoS2 nanoflakes showing that the measured lattice spacing can be indexed to (100) plane. Inset shows the TEM image of an individual MoS2 nanoflake. e UV–visible absorption spectra of MoS2 nanoflakes showing four absorption peaks, which are characteristics of transition metal dichalcogenides that have trigonal prismatic structure (2H phase). f XRD patterns of SnO2-nanoparticle/MoS2-nanoflake film. g Optical microscopy of the film. Inset shows Raman mapping acquired at a MoS2 peak of 408 cm−1 (scale bar: 10 μm). h SEM image of the film. Inset shows a close-up SEM image (scale bar: 500 nm). i Transfer curve of the device. Id, Ig, and Vth represent drain current, gate leakage current, and threshold voltage, respectively. j Spike-number dependent plasticity of the device. PSC represents postsynaptic current. k spike-rate dependent plasticity of the device. l Cycle-to-cycle variation of the device. m BCM rule implemented by applying positive spike trains (7 V) with various frequencies to the device. ΔPSC represents a change in postsynaptic current. n Inhibition of the BCM rule by applying a negative spike train (−2.5 V) after each of the four positive spike trains to reset the device. Measurements in i–n were performed by applying voltage spikes to a single-gate (Gate1) of the device under a bias of 0.75 V."