Synthesis of Wafer-Scale Monolayer Pyrenyl Graphdiyne on Ultrathin Hexagonal Boron Nitride for Multibit Optoelectronic Memory.

Graphdiyne is a new two-dimensional carbon allotrope with many attractive properties and has been widely used in various applications. However, the synthesis of large-area, high-quality, and ultrathin (especially monolayer) graphdiyne and its analogues remains a challenge, hindering its application in optoelectronic devices. Here, a wafer-scale monolayer pyrenyl graphdiyne (Pyr-GDY) film is obtained on hexagonal boron nitride (hBN) via a van der Waals epitaxial strategy, and top-floating-gated multibit nonvolatile optoelectronic memory based on Pyr-GDY/hBN/graphene is constructed, using Pyr-GDY as a photoresponsive top-floating gate. Benefiting from the excellent charge trapping capability and strong absorption of the graphdiyne film, as well as the top-floating-gated structure and the ultrathin hBN film used in the device, the optoelectronic memory exhibits high storage performance and robust reliability. A huge difference in the current between the programmed and erased states (>26 µA µm-1 at Vds = 0.1 V) and a prolonged retention time (>105 s) enable the device to achieve multibit storage, for which eight and nine distinct storage levels (3-bit) are obtained by applying periodic gate voltages and optical pulses in the programming and erasing processes, respectively. This work provides an important step toward realizing versatile graphdiyne-based optoelectronic devices in the future.

Multilevel MoS2 Optical Memory with Photoresponsive Top Floating Gates.

Optoelectronic memory devices, whose states can be controlled using electrical optical signals, are receiving much attention for their potential applications in image sensing and parallel data transmission and processes. Here, we report MoS2-based devices with top floating gates of Au, graphene, and MoS2. Unlike conventional floating gate memory devices, our devices have the photoresponsive floating gate at the top, acting as a charge trapping layer. Stable and reliable switching with an on/off ratio of ∼106 and a retention time of >104 s is achieved by illumination with 405 nm light pulses as well as application of gate voltage pulses. However, upon illumination with 532 or 635 nm light pulses, multilevel optical memory effects are observed, which are dependent on the wavelength and the optical exposure dosage. In addition, compared to the device employing a graphene floating gate, the device with an MoS2 floating gate is more sensitive to light, suggesting that the multilevel optical memory properties originate from photoexcited carriers in the top floating gate and can be modulated by adjusting the top floating gate materials. The structure of the top floating gate may open up a new way to novel optoelectronic memory devices.