Pankaj Misra

Hydroxyl functionalisation on ONS thiosemicarbazone resulted in stable Cd( ii ) complexes and are found effective for photocatalytic, biological and ammonia sensing applications, making otherwise toxic cadmium ions environmentally friendly materials.

Synergistic integration of Al-doped ZnO, a SiO ₂ electron-blocking interlayer, and a MoS ₂ –PDMS nanocomposite results in a flexible high-output triboelectric nanogenerator capable of lighting 400 LEDs and maintaining long-term operational stability.

In recent years, ZnO based piezoelectric nanogenerators (PENGs) have gained considerable attention for vibration energy harvesting and self-powered applications. This study reports the development and optimization of flexible ZnO based PENGs (ITO/ZnO/Al) through vanadium (V) doping and the insertion of a SiO ₂ interlayer. When V concentration was increased to 3% the open-circuit voltage and short-circuit current of the PENG increased from ~0.9 V/0.1 μA to 2.2 V/0.3 μA. However, further increasing the V doping to 5% reduced the output to ~1.9 V/0.2 μA. X-ray photoelectron spectroscopy (XPS) analysis showed that at low to moderate V doping levels (1%-3%), the V ⁵⁺ /V ³⁺ ratio increases, leading to enhanced internal polarization and, consequently, an improved piezoelectric output performance. At higher V doping levels (5%), excess vanadium introduces structural defects in ZnO, increasing oxygen vacancies and thereby deteriorating the output performance of the PENG. A 100 nm SiO ₂ interlayer was inserted between the 3% V-doped ZnO (VZO) and the Al electrode which introduces a conduction band offset of ~6.4 eV as evaluated from band offset studies. This band offset effectively reduces the leakage current in VZO piezoelectric layer and enhanced the output to ~4.4 V/0.6 μA. The optimized PENG generated an instantaneous power density of ~0.1 μW/cm ² with normalized power density per unit force and frequency ~8.3 × 10 ^-4 μW·cm ² /(N·Hz) which was successfully powered commercial capacitors (1 μF to 10 μF), stopwatch LCD screen and LEDs. This work highlights the role of vanadium states, oxygen vacancies and SiO ₂ interlayer in tuning ZnO based PENG performance and demonstrates its potential for powering micro/nanoelectronic devices in self-powered applications.

Yttrium doped hafnia (Y-doped HfO2) thin film based devices have recently shown their potential for advanced nanoelectronics applications. Here, we report the fabrication of device-grade Hf(1−x)YxO2 (x = 0, 0.10, and 0.20) thin films on both Si(100) and platinized silicon substrates using an optimized Nd:YAG pulsed laser deposition system, wherein detailed structural and compositional characterizations were carried out to establish a structural-dielectric property correlation. The capacitance-frequency (C–F), capacitance-voltage (C–V), and current-voltage (I–V) measurements of these as-grown films were carried out in Pt top-bottom electrode-based metal-insulator-metal capacitor configuration. The increase in high frequency (1 MHz) dielectric constant values from ∼24 to 38, with an increase in Y doping from x = 0 to 0.20, is assigned to the phase transition from pure monoclinic to pure cubic configuration, as confirmed from grazing incidence x-ray diffraction and high resolution transmission electron microscopy measurements. However, the increment in low-frequency dielectric loss (at 100 Hz) and leakage current density values (at 1 V applied bias) from ∼0.6 to 35 and from ∼2.5 × 10−5 to 5.3 × 10−3 A/cm2, respectively, with increasing Y doping is attributed to the enhancement in yttrium-induced oxygen vacancy concentration in the hafnia matrix, as confirmed by x-ray photoelectron spectroscopy measurements. These tailorable device parameters make Y-doped hafnia a promising candidate for next-generation nanoelectronics applications.

Enhanced interface confined carrier relaxation and transport in an Al ₂ O ₃ /TiO ₂ nanolaminate, from a suitable combination of sublayer and cap layer thicknesses, is promising for high density energy storage applications.

Maxwell–Wagner relaxation dominated Al2O3/TiO2 nanolaminates (ATA NLs) have recently demonstrated their potential for high-density energy storage applications. In this report, we have unraveled the defect-mediated transport mechanisms prevailing in Al2O3/TiO2 sub-nanometric laminates. Temperature-dependent ac conductivity measurements revealed the signature of small polaron hopping in TiO2 active layers and trap-assisted tunneling transport through Al2O3 barrier layers, which was corroborated by resonant photoelectron spectroscopy and temperature-dependent current–voltage measurement. The polaronic defect states, found ∼1 eV below the Fermi level, served as the hopping centers and leakage paths for current. The signature of quantum tunneling transport and the negative differential conductance observed toward higher electric field was attributed to the splitting of delocalized minibands. These transport properties of Al2O3/TiO2 nanolaminates will help in tailoring these materials for next-generation storage capacitors.

ZnO based piezoelectric nanogenerators (PENG) hold immense potential for harvesting ambient vibrational mechanical energy into electrical energy, offering sustainable solutions in the field of self-powered sensors, wearable electronics, human–machine interactions etc. In this study, we have developed flexible ZnO-based PENGs by incorporating ZnO microparticles into PDMS matrix, with ZnO concentration ranging from 5 to 25 wt%. Among these, the PENG containing 15 wt% ZnO exhibited the best performance with an open-circuit output voltage/short-circuit current of ~ 42.4 V/2.4 µA. To further enhance the output performance of PENG, p-type NiO was interfaced with ZnO in a bulk hetero-junction geometry. The concentration of NiO was varied from 5 to 20 wt% with respect to ZnO and incorporated into the PDMS matrix to fabricate the PENGs. The PENG containing 10 wt% NiO exhibits the best performance with an open-circuit output voltage/short-circuit current of ~ 65 V/4.1 µA under loading conditions of 30 N and 4 Hz. The PENG exhibiting the best performance demonstrates a maximum instantaneous output power density ~ 37.9 µW/cm² across a load resistance of 20 MΩ under loading conditions of 30 N and 4 Hz, with a power density per unit force and Hertz of about ~ 0.32 µW/cm²·N·Hz. The enhanced output performance of the PENG is attributed to the reduction in free electron concentration, which suppresses the internal screening effect of the piezopotential. To assess the practical utility of the optimized PENG, we tested the powering capability by charging various commercial capacitors and used the stored energy to illuminate 10 LEDs and to power a stopwatch displays. This work not only presents a straightforward, cost-effective, and scalable technique for enhancing the output performance of ZnO-based PENGs but also sheds light on its underlying mechanism.

The tunability and controllability of conductance quantization mediated multilevel resistive switching (RS) memory devices, fabricated in crossbar geometry can be a promising alternative for boosting storage density. Here, we report fabrication of Cu/TiO₂/Pt based RS devices in 8 × 8 crossbar geometry, which showed reliable bipolar RS operations. The crossbar devices showed excellent spatial and temporal variability, time retention and low switching voltage (μA). Furthermore, during the reset switching, highly repeatable and reliable integral and half-integral quantized conductance (QC) was observed. The observed QC phenomenon was attributed to the two dimensional confinement of electrons as lateral width of the conducting filament (CF) matches the fermi wavelength. The magnitude and number of the QC steps were found to increase from ∼2.5 to 12.5 and from 5 to 18, respectively by increasing the compliance current (I _C) from 50 to 800 μA which also increased the diameter of the CF from ∼1.2 to 3.3 nm. The enhancement in both number and magnitude of QC states was explained using electrochemical dissolution mechanism of CF of varying diameter. A thicker CF, formed at higher I _C, undergoes a gradual rupture during reset process yielding a greater number of QC steps compared to a thinner CF. The realisation of QC states in the crossbar Cu/TiO₂/Pt device as well as I _C mediated tunability of their magnitude and number may find applications in high-density resistive memory storage devices and neuromorphic computing.

A self-powered UV sensor with high responsivity was developed by coupling ZnO based piezoelectric nanogenerator and photodetector for uninterrupted real-time monitoring of UV radiation. Unlike conventional UV photodetectors, our approach couples a ZnO based metal-semiconductor-metal photodetector as a variable load resistor with a flexible ZnO:PVDF piezoelectric nanogenerator through impedance matching to realize self-powering of photodetector. The as fabricated UV photodetector exhibits a dark resistance of approximately 55 MΩ and change of resistance from 12 to 2 MΩ in response to UV illumination ranging from 1.5 to 14.5 mW/cm2. Under UV exposure of 1.5 mW/cm2, the output voltage of self-powered UV sensor drops from ∼14.6 V (dark) to ∼3.88 V. With increasing UV intensity from 1.5 to 14.5 mW/cm2, the output voltage gradually decreases from ∼3.88 to ∼1.04 V due to reduced ZnO photodetector resistance. This self-powered UV sensor exhibits excellent performance with a sensitivity of ∼93%, a voltage responsivity of 7.14 V (mW−1 cm−2), a response time of 0.67 s, and a recovery time of 4 s, which are better than the previous reports. The environmentally stable and biocompatible nature of ZnO based system makes it a promising candidate for self-powered real time ultraviolet remote sensing applications.