Li-Ion Synaptic Transistor for Low Power Analog Computing.

Nonvolatile redox transistors (NVRTs) based upon Li-ion battery materials are demonstrated as memory elements for neuromorphic computer architectures with multi-level analog states, "write" linearity, low-voltage switching, and low power dissipation. Simulations of backpropagation using the device properties reach ideal classification accuracy. Physics-based simulations predict energy costs per "write" operation of <10 aJ when scaled to 200 nm × 200 nm.

Defect-induced photoluminescence in monolayer semiconducting transition metal dichalcogenides.

It is well established that defects strongly influence properties in two-dimensional materials. For graphene, atomic defects activate the Raman-active centrosymmetric A1g ring-breathing mode known as the D-peak. The relative intensity of this D-peak compared to the G-band peak is the most widely accepted measure of the quality of graphene films. However, no such metric exists for monolayer semiconducting transition metal dichalcogenides such as WS2 or MoS2. Here we intentionally create atomic-scale defects in the hexagonal lattice of pristine WS2 and MoS2 monolayers using plasma treatments and study the evolution of their Raman and photoluminescence spectra. High-resolution transmission electron microscopy confirms plasma-induced creation of atomic-scale point defects in the monolayer sheets. We find that while the Raman spectra of semiconducting transition metal dichalcogenides (at 532 nm excitation) are insensitive to defects, their photoluminescence reveals a distinct defect-related spectral feature located ∼0.1 eV below the neutral free A-exciton peak. This peak originates from defect-bound neutral excitons and intensifies as the two-dimensional (2D) sheet is made more defective. This spectral feature is observable in air under ambient conditions (room temperature and atmospheric pressure), which allows for a relatively simple way to determine the defectiveness of 2D semiconducting nanosheets. Controlled defect creation could also enable tailoring of the optical properties of these materials in optoelectronic device applications.

Extraordinary photoresponse in two-dimensional In(2)Se(3) nanosheets.

We demonstrate extraordinary photoconductive behavior in two-dimensional (2D) crystalline indium selenide (In2Se3) nanosheets. Photocurrent measurements reveal that semiconducting In2Se3 nanosheets have an extremely high response to visible light, exhibiting a photoresponsivity of 3.95 × 10(2) A·W(-1) at 300 nm with an external quantum efficiency greater than 1.63 × 10(5) % at 5 V bias. The key figures-of-merit exceed that of graphene and other 2D material-based photodetectors reported to date. In addition, the photodetector has a fast response time of 1.8 × 10(-2) s and a specific detectivity of 2.26 × 10(12) Jones. The photoconductive response of α-In2Se3 nanosheets extends into ultraviolet, visible, and near-infrared spectral regions. The high photocurrent response is attributed to the direct band gap (EG = 1.3 eV) of In2Se3 combined with a large surface-area-to-volume ratio and a self-terminated/native-oxide-free surface, which help to reduce carrier recombination while keeping fast response, allowing for real-time detection under very low-light conditions.