Santanu Das

In this work, we investigate the effect of oxidation with nitric acid on the structural, electronic, and electrocatalytic properties of carbon nanostructures (CNs) in the hydrogen evolution reaction (HER) in acidic and alkaline medium. Commercially available single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs), and graphene were functionalized using a simple gram-scale protocol based on concentrated HNO3 under ambient conditions. Transmission electron microscopy indicates that the overall graphitic structure of the materials is largely preserved after treatment, while Raman spectroscopy confirms the introduction of a limited number of defects. Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy reveal the formation of oxygen-containing surface functional groups, such as -CO, -COOH, and -OH along with nitrogen containing species -C-N and -NO2. Electrochemical measurements show that functionalized carbon nanomaterials exhibit improved HER activity compared to their pristine counterparts in both acidic and alkaline electrolytes. XPS analysis of the valence band suggests a modification of the electronic structure and density of states near the Fermi level after functionalization, which is more pronounced in SWCNTs than in MWCNTs or graphene. Calculations based on density functional theory support these experimental observations by indicating similar trends in the modulation of the electronic structure following oxidation. These results highlight the role of controlled oxidative functionalization in improving the HER performance of carbon nanomaterials and provide insight into their potential use as metal-free electrocatalysts or catalytic supports.

We report quantized conductance and quantum point contact (QPC) formation in memristive devices comprising exfoliated hexagonal boron nitride (hBN) over HfO ₂ as the active layer. The scattered hBN flakes locally enhance oxygen vacancy concentration, forming the filamentary paths beneath Ag top electrodes (TEs). These topographical inhomogeneities create atomically narrow constrictions that act as QPCs. X-ray diffraction measurements indicate strain in the hBN stacks, whereas the Raman E 2g mode shows a small shift (1364–1366 cm ⁻¹ ) and broadening indicative of strain and substrate coupling. Electrical characterization exhibits conductance plateaus close to integer and half-integer multiples of G 0 = 2 e 2 / h , along with hysteretic current–voltage behavior consistent with filament evolution. We propose a unified morphological-ionic model where randomly distributed hBN flakes create nanoscale topography that steers oxygen-vacancy accumulation and produces QPCs at the TE/hBN interface. The results highlight van-der-Waals/oxide heterostructures as promising platforms for atomic-scale memristive devices and secure stochastic hardware primitives.

Changing the Ar/O ₂ flow ratio at the gas inlet leads to an increase in TCR at low-temperature deposition in a sputtering chamber.

In this study, we investigate the quality of junction formation and its impact on the electronic and optoelectronic properties of two-dimensional (2D) multilayered molybdenum disulfide (MoS₂) films directly grown on three-dimensional (3D) p-type silicon (p-Si) (110) substrates. Large-area (15 mm × 15 mm), few-layer (8–10 layers) MoS₂ films were synthesized using a facile vapor-phase transport method, achieving seamless integration with the underlying Si substrate. Comprehensive structural and morphological characterizations confirm the uniform growth of multilayer 2D-MoS₂ and the formation of a well-defined 2D/3D MoS₂/Si heterojunction interface. The vertical MoS₂/Si heterostructure exhibits a maximum photocurrent of ∼2.131 × 10⁻⁶ A and a responsivity of ∼13.31 A W⁻¹ under white light illumination of 20 µW cm⁻² at a bias voltage of −3 V. These results highlight the critical role of engineered heterointerfaces in enhancing device performance, including improved adhesion and charge transport across the active layers. This work demonstrates the feasibility of integrating a variety of 2D materials, including 2D-MoS₂, with silicon platforms for complementary metal oxide semiconductor (CMOS) compatible optoelectronic applications. The findings present promising opportunities for developing next-generation photosensors, photodetectors, p–n heterojunction diodes, and vertical junction transistors based on 2D/3D hybrid architectures.

Surface-enhanced Raman scattering (SERS) stands out as a powerful analytical technique, offering exceptional capabilities in molecular detection and characterization distinguished by its extraordinary sensitivity, high selectivity, and versatility. In this study, we present the synthesis of silver nanostructures, primarily triangular silver nanostructure (t-Ag NS) in morphology, which exhibits plasmonic properties. When dispersed on a seamless monolayer of 2D-MoS₂ (t-Ag NS/MoS₂), these nanostructures facilitate the formation of a Schottky barrier and induce a phase transition in MoS₂ from the 2H semiconducting phase to the 1T metallic phase. The Schottky barrier promotes the transfer of plasmonic hot electrons from the metallic Ag nanostructures to the MoS₂ layers while preventing recombination through its energy barrier. The transition to the metallic phase, coupled with the dispersion effect, synergistically boosts the overall performance and sensitivity of the sensing device. We further demonstrate the efficacy of t-Ag NS/Ag-MoS₂ substrates exhibiting remarkable performance in the detection of dyes such as methylene blue (MB) and brilliant yellow (BY) achieving an impressively high sensitivity at the nanomolar concentration level, reaching as high as 1.1*10⁷ and 8.8*10⁶, respectively., We believe that the newly developed t-Ag NS and their strategic distribution across MoS₂ substrates, giving a high enhancement factor (EF) in the nanomolar range, underscore the substrates’ ability to dramatically increase the detection signal, thereby improving the overall sensitivity leading to new possibilities for applications requiring extremely precise and sensitive molecular identification in minute analyte concentration.