Gamma-induced stress, strain and p-type doping in MBE-grown thin film MoTe2.

A thorough examination of the stability of a 2D MoTe2 thin film exposed to high-dose gamma radiation (γ) is addressed in this study. This study compares the film before and after irradiation (10-600 kGy dosage) to report the impact of γ radiation on the surface morphology, work function, tensile strain and charge redistribution in the MoTe2 thin film. The radiation damage to the film is monitored by optical micrographs (OM) and with atomic force microscopy (AFM) and conceptualized by thermal strain in the film. Raman spectroscopy has been used to analyze the shifting and to address the strain that arises due to irradiation in its vibrational mode. Kelvin probe force microscopy (KPFM) has been performed to evaluate the work function of the film, which increases by 0.14 eV for the 600 kGy γ-irradiated sample, implying shifting of the Fermi-level to the valence band of the spectrum and thus it results in p-type doping in the film. Owing to the reduced atomic mass and high energy of tellurium atoms, γ-irradiation causes tellurium vacancies, which lead to the formation of dangling bonds at unoccupied sites. When oxygen is adsorbed at these reactive spots, a charge-transfer mechanism takes place. This mechanism involves the transfer of electrons from the thin MoTe2 film to the adsorbed oxygen, forming oxides and causing p-type doping. Furthermore, p-doping is verified by the valence band shifting by 1.27 eV in 600 kGy in γ-irradiated samples in X-ray photoelectron spectroscopy. This comprehensive study shows how γ irradiation affects the chemical and physical characteristics of the MoTe2 thin film. Consequently, it shows that if devices integrating MoTe2 thin films are meant to be used in high-dose radiation conditions, the adsorbate concentrations, radiation shielding and required lifetimes must be carefully evaluated.

High-Performance Visible-to-SWIR Photodetector Based on the Layered WS2 Heterojunction with Light-Trapping Pyramidal Black Germanium.

This study presents a layered transition metal dichalcogenide/black germanium (b-Ge) heterojunction photodetector that exhibits superior performance across a broad spectrum of wavelengths spanning from visible (vis) to shortwave infrared (SWIR). The photodetector includes a thin layer of b-Ge, which is created by wet etching of germanium (Ge) wafer to form submicrometer pyramidal structures. On top of this b-Ge layer, the WS2 thin film is deposited using pulsed laser deposition. In comparison to conventional germanium, b-Ge absorbs about 25% more light between 850 and 1750 nm wavelengths. The WS2/b-Ge photodetector has a peak photoresponsivity of 0.65 A/W, which is more than twice the photoresponsivity of the WS2/Ge photodetector at 1540 nm. Additionally, it shows better responsivity and response speed compared with other similar state-of-the-art photodetectors. Such an improvement in the performance of the device is credited to the light-trapping effect enabled by the germanium pyramids. Theoretical simulations employing the finite-difference time-domain technique help validate the concept. This novel photodetector holds promise for efficient detection of light across the vis to SWIR spectrum.

Detection of chikungunya virus DNA using two-dimensional MoS2 nanosheets based disposable biosensor.

Development of platforms for a reliable, rapid, sensitive and selective detection of chikungunya virus (CHIGV) is the need of the hour in developing countries. To the best of our knowledge, there are no reports available for the electrochemical detection of CHIGVDNA. Therefore, we aim at developing a biosensor based on molybdenum disulphide nanosheets (MoS2 NSs) for the point-of-care diagnosis of CHIGV. Briefly, MoS2 NSs were synthesized by chemical route and characterized using scanning electron microscopy, transmission electron microscopy, UV-Vis spectroscopy, Raman spectroscopy and X-Ray Diffraction. MoS2 NSs were then subjected to physical adsorption onto the screen printed gold electrodes (SPGEs) and then employed for the detection of CHIGV DNA using electrochemical voltammetric techniques. Herein, the role of MoS2 NSs is to provide biocompatibility to the biological recognition element on the surface of the screen printed electrodes. The detection strategy employed herein is the ability of methylene blue to interact differentially with the guanine bases of the single and double-stranded DNA which leads to change in the magnitude of the voltammetric signal. The proposed genosensor exhibited a wide linear range of 0.1 nM to 100 µM towards the chikungunya virus DNA.