Prashant Bisht

Highly sensitive and energy-efficient gas sensors are essential for real-time environmental monitoring and air quality assessment. In this work, we present an optically programmable gas sensor based on WSe₂/hBN heterostructure transistors for NO_x detection. The hBN interfacial layer enhances device performance by reducing charge trapping and improving transport, enabling the WSe₂/hBN configuration to achieve a higher sensing response and faster recovery than WSe₂/SiO₂ devices. To understand the sensing mechanism, in situ Kelvin probe force microscopy (KPFM) was used, revealing that NO_x adsorption at the metal/semiconductor interface modulates the Schottky barrier height (SBH), which governs charge transport and gas sensitivity. Furthermore, we demonstrate that UV-induced charge modulation allows dynamic control of the sensor response, offering a tunable and reversible method for optimizing gas detection. This study highlights the potential of heterostructure engineering and optoelectronic modulation in developing next-generation, low-power, smart gas sensors for environmental monitoring applications.

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.

In this work, effect of gamma irradiation on chemical vapor deposition grown ReS₂ thin films vis‐a‐vis change in its structure, morphology, chemical composition, and memristive behaviour is reported to assess its radiation hardness for space applications. High‐resolution transmission electron micrographs and selected area electron diffraction pattern infer polycrystalline to amorphous phase transition and increase in the number of grain boundaries (GBs) after exposure to 25 kGy of gamma radiation. X‐ray photoelectron spectroscopy and low‐temperature photoluminescence measurements reveal the formation of sulfur vacancies (S_V) accompanied with partial oxidation of film. Memristors are then fabricated on the as‐grown film using different metal electrodes, which are Ag, Pt, and Ti in lateral geometry, and their resistive switching (RS) mechanism is studied along with the impact of gamma irradiation. RS is attributed to the formation of conducting filaments due to GB‐mediated migration of metal ions, S_V, and oxygen ions from the partially oxidized film. Furthermore, irradiation is found to increase current in the high resistance state of the device, which subsequently reduces the memory window. This impact is observed to be consistent across all the devices which validates the effect of irradiation irrespective of the nature of the metal electrode used.

This study employs novel growth methodologies and surface sensitization with metal nanoparticles to enhance and manipulate gas sensing behavior of two‐dimensional (2D)SnS film. Growth of SnS films is optimized by varying substrate temperature and laser pulses during pulsed laser deposition (PLD). Thereafter, palladium (Pd), gold (Au), and silver (Ag) nanoparticles are decorated on as‐grown film using gas‐phase synthesis techniques. X‐ray diffraction (XRD), Raman spectroscopy, and Field‐emission scanning electron microscopy (FESEM) elucidate the growth evolution of SnS and the effect of nanoparticle decoration. X‐ray photoelectron spectroscopy (XPS) analyses the chemical state and composition. Pristine SnS, Ag, and Au decorated SnS films are sensitive and selective toward NO₂ at room temperature (RT). Ag nanoparticle increases the response of pristine SnS from 48 to 138% toward 2 ppm NO_2, which indicates electronic and chemical sensitization effect of Ag. Pd decoration on SnS tunes its selectivity toward H₂ gas with a response of 55% toward 70 ppm H₂ and limit of detection (LOD) < 1 ppm. In situ Kelvin probe force microscopy (KPFM) maps the work function changes, revealing catalytic effect of Ag toward NO₂ in Ag‐decorated SnS and direct charge transfer between Pd and SnS during H₂ exposure in Pd‐decorated SnS.