(a) The optical image of the device (top) and the schematic of the memristor device (bottom). (b) AFM image of GaO_x stacked on few layer graphene. (c), (d) Measured I–V characteristics of the memristor. (e) The current and voltage data plotted against time for the device in (c) and (d), indicating the variation trend in current in sequential voltage sweeps. (f) The current was obtained after a series of 20 set pulses (2 V, 100 ms, black dots) followed by 20 reset pulses (−2 V, 100 ms, red dots), showing the respective potentiation and depression of the synaptic weight. The reading voltage is 1 V.