Employing high-yield production of layered materials by liquid-phase exfoliation, molybdenum disulfide (MoS2) dispersions with large populations of single and few layers were prepared. Electron microscopy verified the high quality of the two-dimensional MoS2 nanostructures. Atomic force microscopy analysis revealed that ~39% of the MoS2 flakes had thicknesses of less than 5 nm. Linewidth and frequency difference of the E(1)2g and A1g Raman modes confirmed the effective reduction of flake thicknesses from the bulk MoS2 to the dispersions. Ultrafast nonlinear optical (NLO) properties were investigated using an open-aperture Z-scan technique. All experiments were performed using 100 fs pulses at 800 nm from a mode-locked Ti:sapphire laser. The MoS2 nanosheets exhibited significant saturable absorption (SA) for the femtosecond pulses, resulting in the third-order NLO susceptibility Imχ((3)) ~ 10(-15) esu, figure of merit ~10(-15) esu cm, and free-carrier absorption cross section ~10(-17) cm(2). Induced free carrier density and the relaxation time were estimated to be ~10(16) cm(-3) and ~30 fs, respectively. At the same excitation condition, the MoS2 dispersions show better SA response than the graphene dispersions.
Optoelectronic synaptic devices, which combine the functions of photosensitivity and information processing, are essential for the development of artificial visual perception systems. Nevertheless, improving the paired pulse facilitation (PPF) index of optoelectronic synaptic devices, which is an urgent problem in the construction of high‐precision artificial visual perception systems, has received less attention so far. Herein, a light‐stimulated synaptic transistor (LSST) device with an ultra‐high PPF index (≈196%) is presented by introducing an ultra‐thin carrier regulator layer hexagonal boron nitride (h‐BN) into a classic graphene‐based hybrid transistor frame (graphene/CsPbBr3 quantum dots). Crucially, analysis of the rate‐limiting effect of h‐BN on photogenerated carriers reveals the mechanism behind the LSST ultra‐high PPF index. Furthermore, a two‐layer artificial neural network connected by LSST devices demonstrate ≈91.5% recognition accuracy of handwritten digits. This work provides an effective method for constructing artificial visual perception systems using a hybrid transistor frame in the future.
A new method, Fe/Mg co-doping, is proposed for the first time to optimize thermochromic VO2 and the promising performance of VO2-based smart windows for practical applications is successfully achieved.
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