Elevation from Binary to Ternary Resistive Switching Behaviors by Graphitizing Transformation from Nanodiamond to Onion-like Carbon in Their Chitosan Composites

The development of green high-density memristors is urgent for the coming big-data era. In this work, the graphitization degree of the nanodiamond (ND) was modulated by thermal annealing at different temperatures. Consequently, the graphitizing transformation from the ND structure to partial onion-like carbon (OLC-1) and complete OLC-2 was achieved, which has been validated by increased sp²/sp³ ratios and carbonyl contents. Furthermore, these carbon materials were encapsulated into chitosan (CS) to prepare ND or OLCs@CS biocomposites, which were further fabricated as memory devices. For ND-based memristors, only binary resistive switching (RS) behavior was detected, and the doping amount of 16% OLC-1 into CS resulted in ternary RS performance (ON1/OFF ratio of 3.12 × 10⁴, ON2/OFF ratio of 1.38 × 10⁶, and V_Set1 and V_Set2 of 0.89 and 1.58 V, respectively). Comparably, for OLC-2, only a 4% doping concentration presented excellent ternary RS performance, and the optimal RS parameters were achieved at a doping concentration of 12% (ON1/OFF ratio of 4.20 × 10⁴, ON2/OFF ratio of 2.46 × 10⁶, V_Set1 and V_Set2 of 0.70 and 1.97 V, respectively, and ternary yield of 62%). RS mechanisms have been explained as follows. In OLC-2, the disappearance of hydroxyl/carboxyl and the higher carbonyl content rendered weaker O–H···O═C hydrogen bonds, which facilitated the trap filling limiting (TFL) process. The larger conjugated degree of quasi-spherical graphitic layers enhanced the charge trapping capacity in the space charge limiting conduction (SCLC) process. The modulation rules of carbon materials will provide a theoretical guide for the construction of new green high-density memristors.