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The next generation of photonics and nano-optical devices may be based on two-dimensional(2D) transition metal dichalcogenides (TMDs). In this research, molybdenum diselenide () nanosheets, as one important member of TMDs, have been synthesized by the solvothermal method and characterized through XRD patterns, SEM, and TEM images. Nanosheets were found to have a hexagonal phase based on XRD patterns and the crystallinity percentage is 24.8 %. The lattice constants of the hexagonal phase of are calculated as a= 3.08 ºA, c= 13.72 ºA. The calculated average value of the crystallite size, dislocation density, and micro strain are 21.935 nm, 2.138 nm-2 and 9.070, respectively. A few layers of nanosheets without wrinkles were observed on TEM and SEM. Next, the synthesized nanosheets were employed to prepare thin films with three different thicknesses using the spin coating method. By employing a continuous wave (CW) Nd : YAG laser at 532 nm via a Z-scan approach, this study investigates how thin film thickness affects the thermal nonlinear optical (NLO) responses of nanosheets. The magnitude of NLO coefficients of the prepared thin films decreased with increasing film thickness. It is observed that the prepared thin films possess saturable absorption (SA) as well as the self-focusing effect. Saturable absorbers and mode-locking devices can be developed with thin films because of their improved NLO properties. [ABSTRACT FROM AUTHOR]

We present the results of a numerical study on the characteristics of MoS2-based field-effect photodetectors (FEPhDs). These FEPhDs consist of 12-nm-long and 1.42-nm (1.45-nm)-wide MoS2 armchair (zigzag)-nanoribbons (MoS2-A(Z)NRs), acting as channels connected to two semi-infinite graphene electrodes, serving as source and drain terminals to minimize the terminals' series resistances. The simulation method used here is the nonequilibrium Green's function formalism plus an atomistic tight-binding (TB) model. We employed the TB model to obtain characteristics like the density of states versus electron energy, current–voltage curve, and photocurrent versus photon wavelength (λ). For the latter, we consider illuminating the A(Z)NR channels with a broadband optical signal covering the λ = 330–830 nm range. Our simulations show that passivation of ANR edges with H2 and OH molecules reduces the semiconducting bandgap by ~ 28% (for H-ANR) and ~ 28.6% (for OH-ANR). The numerical results show that, among the three ANR channels, the optimum photoresponsivity of Rph ≈ 43.88 mA μW−1 belongs to the FEPhD with the MoS2-OH-ANR channel biased at VDS = 200 mV and VGS = 0, at λ ≈ 451 nm, independent of the illumination intensity. Among the three ZNR channels, the best photoresponsivity of Rph ~ 27.02 mA μW−1 belongs to the unpassivated channel under the same biasing condition but at λ ≈ 477 nm. The results also show that the optimum biasing condition differs from one FEPhD to another. The results show that the proposed MoS2-A(Z)NR-based FEPhDs can be promising candidates for nanoscale optoelectronic devices in the UV–Vis range. [ABSTRACT FROM AUTHOR]

Employing the non-equilibrium Green's function with the third order tight binding Hamiltonian, we show that 12.7 nm long and 1.11 nm wide zigzag and armchair graphene nanoribbons (ZGNR and AGNR) in contact with asymmetric source and drain, consisting of graphene topped with Au and Ti, respectively, can operate as visible and solar blind photodetectors under zero externally applied biases. The carbon atoms at the channels' edges are considered to be hydrogen passivated. Numerical simulations show that the unbiased Au-ZGNR-Ti and Au-AGNR-Ti photodetectors can detect photons of energies 2.72 eV (456 nm, visible reign) and 5.02 eV (247 nm, solar blind reign), respectively, with the corresponding quantum efficiencies as high as 90% and 60% and responsivities of 93.8 and 13.4 A/mW. We also show that in Au-ZGNR-Ti the local photocurrents are distributed more around the ZGNR edges in regions near the source and drain sides of the channel, for the zero gate-source voltage (VGS=0), whereas in Au-AGNR-Ti for the same biasing condition, the local photocurrents are distributed far from the AGNR edges within regions near the source and drain sides of the channel. As the applied gate voltage moves away from the Dirac point, the peaks of the local photocurrents move away from the source and drain sides of the channel in opposite directions, in either asymmetric photodetector. Polarities of the local photocurrents are altered, as the gate-source voltage approaches the Dirac point, where the total photocurrent is maximized for both asymmetric photodetectors. [ABSTRACT FROM AUTHOR]