Two dimensional (2D) Molybdenum disulfide (MoS2) has evolved as a promising material for next generation optoelectronic devices owing to its unique electrical and optical properties, such as band gap modulation, high optical absorption, and increased luminescence quantum yield. The 2D MoS2 photodetectors reported in the literature have presented low responsivity compared to silicon based photodetectors. In this study, we assembled atomically thin p-type MoS2 with graphene to form a MoS2/graphene Schottky photodetector where photo generated holes travel from graphene to MoS2 over the Schottky barrier under illumination. We found that the p-type MoS2 forms a Schottky junction with graphene with a barrier height of 139 meV, which results in high photocurrent and wide spectral range of detection with wavelength selectivity. The fabricated photodetector showed excellent photosensitivity with a maximum photo responsivity of 1.26 AW(-1) and a noise equivalent power of 7.8 × 10(-12) W/√Hz at 1440 nm.

www.particle-journal.com www.MaterialsViews.com COMMUNICATIONsubstrates for 2D morphology-controlled ZnO nanostructure growth. Graphene is a 2D carbon nanostructure, which has been studied extensively in recent years due its remarkable mechanical, optical, and electronic properties. [ 13 ] These properties makes graphene a promising candidate for many potential applications including electronic and optical devices. Graphene electrodes with nanostructures can also be applied as synergistic electrodes for different fl exible and transparent conducting devices. The growth mechanism of the synthesized 2D ZnO nanostructures is studied in detail with the help of scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and selected area electron diffraction (SAED). Based on the data, we believe that ZnO nanofl akes are oriented along (0001) plane and grow laterally along (0110) plane. Furthermore, the electrical and optical data show excellent conduction and transmission properties, respectively. Our synthesis method is a low-cost, low-temperature, scalable, and potentially high-throughput process, which can be further extended for the synthesis of wide range of other 2D materials for different applications in electronics and optoelectronics devices.We used zinc nitrate hexahydrate [ZNH; Zn(NO 3 )·6H 2 O] and hexamethylenetetramine [HMT; (CH 2 ) 6 ·N 4 ] (both from SigmaAldrich) for the sonochemical synthesis of ZnO nanofl akes. [ 12 ] ZNH provides Zn 2+ ions and H 2 O molecules in the solution provide O 2− ions. HMT has been used as a shape-inducing polymer in ZnO nanowire growth as polymer as it attaches to the nonpolar facets of ZnO cutting the supply of Zn 2+ ions, thus allowing the growth of ZnO in only <0001> direction. [ 14 ] However, the shape of the nanostructures strongly depends on the concentration of ZNH/HMT solutions, which affects the precipitation mechanism of the oxide. [ 15,16 ] It was observed that as the concentration of ZNH/HMT aqueous solution increased, the length of the ZnO nanorods decreased. [ 15 ] In the present case, the concentration of the precursors is increased by 10-20 times and the sonication amplitude is increased by 20% compared with the earlier process. [ 12 ] The process temperature does not exceed 70 ° C, as amplitude of the sonication is increased. At the higher concentrations used in this process and fast reaction rates achieved under sonication, HMT releases large amounts of OH − and NH 4 + ions in a short period of time. At this higher concentrations, precipitation of Zn 2+ ions occurs at faster rate than required for HMT-assisted oriented growth of ZnO nanostructures, [ 14,15 ] resulting in growth of nonpolar planes of ZnO along with polar (0001) plane forming parallelogram-shaped 2D ZnO nanofl akes.Figure 1 a,b shows the SEM pictures of the ZnO nanofl ake growth on Si substrate at 30 s and 1 min. 2D ZnO nanofl akes grow from sheet structures to hexagonal crystal structure, Semiconductor nanostructures have attracted considerable research i...

We propose and systematically investigate a novel tunable, compact room temperature terahertz (THz) source based on difference frequency generation in a hybrid optical and THz micro-ring resonator. We describe detailed design steps of the source capable of generating THz wave in 0.5–10 THz with a tunability resolution of 0.05 THz by using high second order optical susceptibility (χ(2)) in crystals and polymers. In order to enhance THz generation compared to bulk nonlinear material, we employ a nonlinear optical micro-ring resonator with high-Q resonant modes for infrared input waves. Another ring oscillator with the same outer radius underneath the nonlinear ring with an insulation of SiO2 layer supports the generated THz with resonant modes and out-couples them into a THz waveguide. The phase matching condition is satisfied by engineering both the optical and THz resonators with appropriate effective indices. We analytically estimate THz output power of the device by using practical values of susceptibility in available crystals and polymers. The proposed source can enable tunable, compact THz emitters, on-chip integrated spectrometers, inspire a broader use of THz sources and motivate many important potential THz applications in different fields.

We report on numerical study of dispersion properties and frequency dependent absorption characteristics of asymmetric dual grating gate terahertz (THz) plasmonic crystals. The study shows that the dispersion relations of plasmons in a two‐dimensional electron gas (2DEG) capped with asymmetric dual grating gates have energy band gaps in the Brillion zones. Depending on the wave vector, the plasmons can have symmetrical, anti‐symmetrical, and asymmetrical charge distributions that are different from the ones for uniform gratings case. Plasmons in the studied plasmonic crystal exhibit both tightly confined/weakly coupled behavior and propagating/strongly coupled behavior depending on the plasmonic modes. The responsivity of the plasmonic detector based on asymmetric dual grating gate does not monotonically decrease with the frequency, which is in contrast to the responsivity of uniform grating THz detectors. The cross‐section of an asymmetric dual grating gate terahertz plasmonic device under THz illumination is represented, where excited plasmons are shown in red.

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