Black Phosphorus Quantum Dots Functionalized with Photochromic Poly(vinylspiropyran)-Grafted Polydopamine for Transient Digital-Type Memristors

The covalent functionalization of black phosphorus quantum dots (BPQDs) with organic species or polymers will inevitably change or damage their electronic structure and intrinsic structure. To address this problem and explore application of BPQDs in transient digital-type memristors, a polydopamine (PDA) thin film is first synthesized in situ on the surface of BPQDs to produce a donor–acceptor type BPQDs@PDA composite which is directly used to react with 2-bromoisobutyryl bromide to give BPQDs@PDA-Br. By using BPQDs@PDA-Br as atom transfer radical polymerization agent, a large number of polyvinylspiropyran chains (PSP) are in situ grown from the PDA surface to yield BPQDs@PDA-PSP. Upon UV/visible light illumination, the spiropyran’s two isomers (ring-closed spiropyran form and ring-opened merocyanine) in the PSP moieties will interconvert into each other rapidly. As expected, the as-fabricated ITO/BPQDs@PDA-PSP/ITO device exhibits typical nonvolatile digital-type memristive performance under visible irradiation, with a small turn-on voltage of -1.52 V, a turn-off voltage of +1.16 V, and an ON/OFF ratio of with an ON/OFF current ratio of 1.02 ×104. Upon UV illumination, the information stored in the device is quickly and completely erased within six seconds. By utilizing a simple memristor-based convolutional neural network, one can easily realize handwritten digit recognition. After 10 epochs of training, numeral recognition accuracy can reach up to 96.21%.