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. 2023 Dec 20;14:8489. doi: 10.1038/s41467-023-43944-2

Fig. 2. Multimodal analogue resistive memory: electrical resistive switching (ERRAM mode) and pure optically controlled NPM/PPM switching (ORRAM mode).

Fig. 2

a Schematic diagram of the multimodal-multifunction MSFP-based resistive memory. The right inset is a cross-sectional FE-SEM image. b Fibroin extracted from cocoon-LG2 and the chemical structure of modified silk fibroin protein (MSFP) formed by hydrogen-bond interactions. c Analogue electrical resistive switching behaviour of the Au/MSFP/Au memory in which the MSFP function switching function film is synthesised by the SFP solution, Pg-3, and 5,6-DHI. The voltage scanning rate is 0.2 V/s. d The long-term potentiation and depression under the continuous positive pulse stimuli (0.7 V, 50 μs) and negative (−0.7 V, 50 μs) pulse stimuli. The conductance states are readout by a read voltage pulse (0.1 V, 50 μs). e Switching mechanisms of analogue electrical resistive switching behaviours induced by the iteration processes of electron filling in the traps. f Tuneable and light intensity-dependent NPM and PPM, indicating the fully optical set and reset processes. FTIR spectra peak fittings of the MSFP thin film secondary structures in the Amide first region under (g)  40 mW and (h)  80 mW UV light, respectively, suggesting the light illumination can alter the MSFP secondary structure. i Schematics of optically induced secondary structure changes leading to PPM and NPM effects. The PPM effect is mainly dominated by the net increasing amount of β-sheet secondary structures, while the NPM effect is dominated by the net increasing amount of β-turn secondary structures. j Measurement setup of current-sensor atomic force microscope (CS-AFM) for the Au/MSFP sample. k CS-AFM images of the Au/MSFP sample under a variety of light intensities. The sample exhibited obvious NPM and PPM effects when illuminated by the 10–65 mW and 80–100 mW 405 nm lasers, respectively. The light-related measurements of (f–h) and (k) are conducted in air ambient with relative humidity of 45% with the light exposure duration of 2.0 s.