Dhananjaya Kekuda

Chromium oxide thin films were deposited by DC magnetron sputtering under varying oxygen flow rates (14%–24%). This study evaluates the properties of both the as‐deposited and the post‐annealed samples. X‐ray diffraction (XRD) confirms the evolution from amorphous to crystalline Cr ₂ O ₃ and reduced structural disorder after thermal annealing. Optical measurements show bandgap values of ~2.70 eV for the as‐deposited films, increasing to ~3.07 eV after annealing due to decreased localized states and improved long range order. A significant decrease in Urbach energy was observed, from ~680 to ~390 meV, which indicate the reduced defects and localized states. Dielectric loss, optical conductivity, surface energy loss function (SELF), and volume energy loss function (VELF) progressively decrease with increasing oxygen flow and exhibit additional reduction upon annealing, reflecting improved film densification and enhanced optical stability. Photoluminescence (PL) spectra exhibit intrinsic Cr ³⁺ transitions in the ~399–550 nm range, while Hall measurements demonstrate a stable p‐type conduction with annealing effectively lowering the resistivity to 3–9 Ω·cm and increasing carrier density up to 10 ¹⁸ cm ⁻³ .

This study explores defect evolution in ceria thin films through combined experimental and theoretical approaches. Structural analyses confirm the retention of the cubic fluorite phase, with Raman spectra revealing additional features associated with oxygen vacancies and lattice disorder. Phonon lifetime evaluation indicates that vibrational stability is highly dependent on defect density and precursor concentration. Optical measurements show a progressive reduction in band gap energy, attributed to defect-induced states and variations in Urbach energy. Complementary DFT simulations demonstrate that oxygen vacancies create localized 4f levels, modify charge distribution, and stabilize mixed valence states of Ce ³⁺ /Ce ⁴⁺ . These findings highlight the strong interplay between structural defects, phonon dynamics, and electronic behavior in CeO ₂ thin films.

Cr ₂ O ₃ thin films were deposited by DC magnetron sputtering under varying oxygen flow rates to investigate the influence of oxygen content and annealing effect on their structural and electronic properties. XRD and Raman confirmed pure phase Cr ₂ O ₃ with improved crystallinity and reduced lattice strain after annealing. XPS analysis indicated predominant Cr³⁺ states with oxygen defects that decreased upon annealing, showing chemical stability. The Schottky diode current-voltage analysis demonstrated rectification, with thermionic emission and Norde models confirming reduced ideality factor, series resistance, and a stabilized barrier height (~ 0.78 eV). The Mott-Gurney space charge limited conduction model was used to determine mobility and trap density in the deposited films. Dielectric studies revealed that the thermal annealing suppressed polarization, lowered the dielectric loss, enhanced the AC conductivity and reduced Nyquist arc diameters.

A self-powered visible-light photodetector was fabricated using a coumarin-derived Schiff base, 4-FMCSB, as the active layer. The compound was synthesized via a two-step process and characterized using FT-IR, NMR, MALDI-TOF-MS, and UV-vis spectroscopy. The optical band gap of 4-FMCSB was determined to be 2.33 eV, with DFT calculations confirming a HOMO–LUMO gap of 2.79 eV. Thin films of 4-FMCSB were deposited on ITO substrates via spin coating, and aluminium contacts were thermally evaporated to form Al/4-FMCSB/ITO photodetectors. The device exhibited a strong rectification ratio, rapid photo response (rise time: 510 ms; fall time: 210 ms), and efficient operation under zero bias. Key performance metrics included a responsivity of 12.6 mA W⁻¹, detectivity of 9.31 × 10¹⁰ jones, and a linear dynamic range of 35.94 dB. These findings underscore the potential of coumarin-based Schiff bases in advancing the design of next-generation, energy-efficient optoelectronic devices.

This study investigates copper oxide thin films, deposited by reactive DC magnetron sputtering at room temperature, for use as absorber layers in thin‐film solar cells. Films are synthesized under varying oxygen flow rates (16–33%). Structural analysis (X‐ray diffraction, Raman) reveals a phase transition from mixed Cu ₄ O ₃ CuO to phase‐pure monoclinic CuO at 23% oxygen, correlating with enhanced crystallinity. Atomic force microscope shows oxygen flow‐influenced film morphology, correlating with crystallite growth. Optical properties vary with oxygen flow: lower flows improve absorption, while higher flows increase transmittance, indicating reduced defect density. The optical bandgap ranges from 1.73 to 1.98 eV in line with phase changes. X‐ray photoelectron spectroscopy further confirms the presence of Cu ₄ O ₃ at low oxygen flows and CuO at high oxygen flows, validating the observed phase evolution. Hall measurements demonstrate that oxygen flow significantly tunes the electrical properties, with optimal values observed at 23–28% oxygen. Using these parameters, SCAPS‐1D simulations of TiO ₂ /CuO solar cells predict a 22.8% power conversion efficiency and 89.3% fill factor for a 5 μm CuO layer with a 1.73 eV bandgap. Overall, the findings demonstrate the precise control over CuO thin film properties through oxygen flow tuning, underscoring their considerable potential for high‐efficiency solar energy applications.

This study investigates the AC electrical properties of Cu₂O/TiO₂ heterojunctions deposited via reactive DC magnetron sputtering, with a focus on the role of interfacial dynamics and post-deposition annealing. Mott–Schottky analysis revealed built-in potentials ranging from 0.45 V to 1.92 V, with carrier concentrations between 1.43 × 10¹⁶ and 9.93 × 10¹⁶ cm⁻³, influenced by the annealing temperature. The depletion width was estimated to be roughly 395 nm in the 150 °C annealed samples, and the TiO₂ layer was more depleted across all samples. Dielectric constant (ε′) values decreased from approximately 85 to about 10 as frequency increased from 1 kHz to 1 MHz, while tangent loss also diminished significantly, indicating reduced dipolar and space-charge polarization. The imaginary part of the dielectric constant (ε″) confirmed strong interfacial polarization at low frequencies. AC conductivity rose with frequency, supporting a thermally activated hopping conduction mechanism. Impedance spectroscopy, modelled with an R(CR)(QR)(CR) circuit, exhibited multiple relaxation behaviors, and incorporating a constant phase element (CPE) accounted for non-ideal dielectric effects caused by surface inhomogeneity. Rapid thermal annealing resulted in a decrease in series resistance, from 844 Ω at room temperature to 802 Ω at 150 °C. Annealing at 150 °C produced optimal outcomes, reducing interface losses and enhancing charge transport. These findings underscore the tunability and potential of Cu₂O/TiO₂ heterostructures for optoelectronic applications such as photodetectors and solar cells.

Increasing health concerns due to pollution has led to the development of various materials to control exposure to pollutants such as toxic gases and contaminated water. In this study, novel manganese stannate (MTO) composite thin films were synthesized via sol–gel spin coating and their structural, morphological, and chemical properties were extensively characterized. In addition, their photocatalytic and gas-sensing abilities were evaluated. In photocatalysis, degradation efficiency measures of how well a photocatalyst can degrade pollutants or dyes under light exposure. Remarkably, the MTO film exhibited a high degradation efficiency of 67% for methyl orange (MO) dye when exposed to UV light for 150 minutes. We also examined the gas-sensing properties of the MTO thin films, particularly their response to acetone. In gas sensors, sensitivity is often reported as a percentage, indicating the relative change in the sensor's response per unit change in analyte concentration. Herein, the sensors displayed a linear response within the 1–9 ppm range of acetone concentration at an operating temperature of 200 °C. They also exhibited excellent selectivity, sensitivity, and repeatability, thus emerging as promising candidates for acetone gas-sensing applications. A sensitivity of 22% was achieved by the sensors, allowing for a low detection limit of 1 ppm, which indicated their high sensitivity towards acetone gas. Moreover, the MTO sensor exhibited response and recovery times of 15 and 16 seconds, respectively. Based on these results, the MTO thin film is a potential material for photocatalytic MO degradation and a gas sensor for acetone detection.