Fig. 4: Multistate resistive modulation through probe-induced hydrogen evolution.

a Maps of local current at an identical region through successive writing (hydrogenation) and erasing (dehydrogenation). The biased voltages of +4 V and −4 V at a scanning rate of 9.8 Hz were employed for the hydrogenation and dehydrogenation processes, respectively. The scale bar shows a 2 μm length. b A summary of conductance modulation through multiple successive writing and erasing processes. The inset shows the normalized conductance change among different voltages, in which the normalizations were performed against the maximum current value of each set of data. The nearly identical writing and erasing sequences for these voltages nicely mimic the set/reset process for artificial synapse functions. The scan number indicates the number of scan times at the same area: 1–10 are successive writing scans and 11–20 are successive erasing scans. c Multiple (200) I–V curves obtained at a fixed point with the AFM probe as the top contact. The voltage sweeping rate is 20 V/s. d Endurance test of multiple-state resistive switching obtained at a fixed point. The biased voltages of +4 V/−4 V were used to set and reset between a high-resistance state (HRS) and a low-resistance state (LSR), as shown in the red curves; while +2 V/−2 V was employed to set the resistance between the HRS and an intermediate-resistance state (IRS).