Dixit, Ambesh

Using a low-cost hydrothermal method, we demonstrated the fabrication of phase pure rutile phase high-density vertically aligned TiO2 nanorods-based catalyst-free hydrogen (H2) gas sensor. The synthesized TiO2 nanorods on FTO are decorated with the aluminum interdigitated electrode pattern for electrical measurements. TiO2 nanorods-based hydrogen sensor showed the optimum response of ∼53.18% at 150 ppm H2 concentration relative to air at 100 °C. The measured response and recovery time of TiO2 nanorods are 85 and 620 s, respectively. The TiO2 nanorods-based H2 gas sensor showed a relatively better response, good reproducibility, and stability at moderate temperatures, i.e., 50 and 100 °C. The electrochemical impedance measurements showed a small variation in the surface characteristics of TiO2 nanorods before and after exposing H2 gas. The carrier lifetime at 50 °C and 100 °C at 150 ppm are 5 μs and 3 μs, respectively. Interestingly, H2 selectivity is also observed against H2S, CO, and NH3 gases, suggesting that high-density vertically aligned TiO2 nanorods can be a good candidate for efficient hydrogen sensing at relatively low temperatures.

Cu2ZnSnS4 (CZTS) active material-based resistive random-access memory (RRAM) devices are investigated to understand the impact of three different Cu, Ag, and Al top electrodes. The dual resistance switching (RS) behaviour of spin coated CZTS on ITO/Glass is investigated up to 102 cycles. The stability of all the devices (Cu/CZTS/ITO, Ag/CZTS/ITO, and Al/CZTS/ITO) is investigated up to 103 sec in low- (LRS) and high- (HRS) resistance states at 0.2 V read voltage. The endurance up to 102 cycles with 30 msec switching width shows stable write and erase current. Weibull cumulative distribution plots suggest that Ag top electrode is relatively more stable for set and reset state with 33.61 and 25.02 shape factors, respectively. The charge carrier transportation is explained by double logarithmic plots, Schottky emission plots, and band diagrams, substantiating that at lower applied electric field intrinsic copper ions dominate in Cu/CZTS/ITO, whereas, at higher electric filed, top electrodes (Cu and Ag) dominate over intrinsic copper ions. Intrinsic Cu+ in CZTS plays a decisive role in resistive switching with Al electrode. Further, the impedance spectroscopy measurements suggest that Cu+ and Ag+ diffusion is the main source for the resistive switching with Cu and Ag electrodes.

In this paper, we present a surface decontamination system that substitutes traditional chemicals and scrubbing agents, which will be useful for the general public during a pandemic. The technique is based on a hybrid process in which UV-C light and its photons interact with metal oxide nano-catalysts to generate hydroxyl radicals, which can enhance the deactivation process, and the system can work even in the shadow regions via a dry process. The optimum number of UV light sources in combination with TiO2 nanoparticles catalysts on aluminum plates have been used synergistically in the system. The UV dose in the disinfection chamber has been optimized, which is between 60 and 500 mJ/cm2 throughout the disinfection chamber. The concentration of hydroxyl radicals is reported more than 25 000 ions/cm3 within the disinfection chamber. These ions are circulated throughout the disinfection volume. The disinfection efficiency has been tested on bacteria and spores, and the obtained results are correlated. Around 8 log reductions in the counts of the test bacteria of Escherichia coli and Klebsiella pneumoniae have been achieved in just 2 min of exposure in the continuous operation of the system. Tests have also been performed on Geobacillus stearothermophilus spores, and the method described here is the result of multiple tests, a review of the scientific literature, and the incorporation of current laboratory practice. The deactivation tested in the system is larger than that of known bacteria and viruses in terms of UV-doses, signifying its utility during the pandemic.

Enhancements in absorbance and thermal stability are essential for solar selective absorber coatings (SSACs) to convert solar energy efficiently into thermal energy. Considering the same, we investigated thin films of BiFeO3 (BFO) ternary perovskite on different metal substrates (copper, aluminum and stainless steel) for solar selective coatings using a simple and cost-effective solution-based method assisted by the spin coating process. BiFeO3 thin films coated on Cu (i.e., BFO/Cu) exhibit a high absorptance of 0.91 ± 0.03 in the UV-vis (0.2-0.8 μm) region and a low emittance of 0.12 ± 0.01 in the infrared region (2.5-25 μm). Furthermore, the detailed structural, microstructural, and optical properties are investigated and electrical impedance spectroscopy measurements are carried out on different thickness BFO-based SSACs to understand the overall impact on the spectral response. The BFO/Cu SSAC structure shows high thermal stability at 300 °C for 60 hours under ambient conditions no significant change in absorptance, but slight increase in emittance to 0.21 ± 0.01. Moreover, the corrosion characteristics of these SSACs suggest that BFO/Cu has a lower corrosion rate (0.001 mm peryear.) than that of a pristine Cu substrate, which is much larger, i.e., ∼0.058 mm per year. More interestingly, the absorptance has increased significantly to 0.94 ± 0.01, whereas the emittance has risen to 0.18 ± 0.01 after corrosion tests. These changes are attributed to the respective microstructural surface changes. Thus, the present work may lead to the development of all oxide-based highly stable SSACs for solar thermal applications.

Beyond von Neumann’s architecture, artificial neural network-based neuromorphic computing in a simple two-terminal resistive switching device is considered the future potential technology for simultaneous data processing and storage. These are also compatible with low-power consumption nanoelectronic devices and, thus, suitable for applications such as image recognition toward solving complex pattern recognition problems. Herein, motivated by the human biological brain, we successfully synthesized low-cost RRAM devices using the thermal oxidation of Cu, i.e., CuO as the active material together with Cu as the top electrode and FTO as the bottom contact for a two-terminal resistive switching device, and investigated characteristics for neuromorphic computing. Cu/CuO/FTO-based devices showed excellent bipolar analog RRAM characteristics with 150 repeatable cycles, retention for 11 000 s, and DC pulse endurance for 5000 cycles. Moreover, devices exhibit a remarkable mimicking ability, demonstrating spike time-dependent plasticity (STDP), pulse-paired facilitation (PPF), synaptic weight, and learning and forgetting characteristics, substantiating the recognition ability. Furthermore, the artificial neural network synaptic membrane exhibits excellent long-term (LTP) and short-term (STP) potentiation for six consecutive cycles. Thus, the present work on Cu/CuO/FTO-based devices provides a detailed understanding of CuO active material-based resistive switching with a potential for neuromorphic computing beyond the von Neumann architecture.

Ruddlesden–Popper (RP) phase metal halide organo perovskites are being extensively studied due to their quasi-two dimensional (2D) nature which makes them an excellent material for several optoelectronic device applications such as solar cells, photo-detectors, light emitting diodes (LEDs), lasers etc. While most of reports show use of linear carbon chain based organic moiety, such as n-Butylamine, as organic spacer in RP perovskite crystal structure, here we report a new series of quasi 2D perovskites with a ring type cyclic carbon group as organic spacer forming RP perovskite of type (CH)2(MA)n−1PbnI3n+1; CH = 2-(1-Cyclohexenyl)ethylamine; MA = Methylamine). This work highlights the synthesis, structural, thermal, optical and optoelectronic characterizations for the new RP perovskite series n = 1–4. The demonstrated RP perovskite of type for n = 1–4 have shown formation of highly crystalline thin films with alternate stacking of organic and inorganic layers, where the order of PbI6 octahedron layering are controlled by n-value, and shown uniform direct bandgap tunable from 2.51 eV (n = 1) to 1.92 eV (n = 4). The PL lifetime measurements supported the fact that lifetime of charge carriers increase with n-value of RP perovskites [154 ps (n = 1) to 336 ps (n = 4)]. Thermogravimetric analysis (TGA) showed highly stable nature of reported RP perovskites with linear increase in phase transition temperatures from 257 °C (n = 1) to 270 °C (n = 4). Scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX) are used to investigate the surface morphology and elemental compositions of thin films. In addition, the photodetectors fabricated for the series using (CH)2(MA)n−1PbnI3n+1 RP perovskite as active absorbing layer and without any charge transport layers, shown sharp photocurrent response from 17 nA/cm2 for n = 1 to 70 nA/cm2 for n = 4, under zero bias and low power illumination conditions (470 nm LED, 1.5 mW/cm2). Furthermore, for lowest bandgap RP perovskite n = 4, (CH)2MA3Pb4I13 the photodetector showed maximum photocurrent density of ~ 508 nA/cm2 at 3 V under similar illumination condition, thus giving fairly large responsivity (46.65 mA/W). Our investigations show that 2-(1-Cyclohexenyl)ethylamine based RP perovskites can be potential solution processed semiconducting materials for optoelectronic applications such as photo-detectors, solar cells, LEDs, photobatteries etc.

The relevant fundamental properties of Janus WSSe monolayers to photocatalytic water-splitting performance are presented here and investigated using density functional theory. The Janus WSSe monolayer with a direct band gap of 1.75 eV is subjected to biaxial strain, and related optoelectronic properties are investigated. The effect of strain is reflected in band gap change from direct to indirect. Hydrogen evolution reaction (HER) is active all over, whereas oxygen evolution reaction (OER) is active only at 4% and 6% compressive strains. The red- and blue-shifts under tensile and compressive strains, respectively, substantiate possible control over exciton-phonon interaction making it suitable for the water-splitting application. Graphic Abstract: Upon being irradiated by sunlight with sufficient energy, the biaxially strained Janus WSSe monolayer complying with HER/OER requirement produces hydrogen gas along with oxygen as a secondary product.[Figure not available: see fulltext.]

We report the hydrogen-sensing response on low-cost-solution-derived ZnO nanorods (NRs) on a glass substrate, integrated with aluminum as interdigitated electrodes (IDEs). The hydrothermally grown ZnO NRs on ZnO seed-layer-glass substrates are vertically aligned and highly textured along the c-axis (002 plane) with texture coefficient ∼2.3. An optimal hydrogen-sensing response of about 21.46% is observed for 150 ppm at 150 °C, which is higher than the responses at 100 and 50 °C, which are ∼12.98 and ∼10.36%, respectively. This can be attributed to the large surface area of ∼14.51 m2/g and pore volume of ∼0.013 cm3/g, associated with NRs and related defects, especially oxygen vacancies in pristine ZnO nanorods. The selective nature is investigated with different oxidizing and reducing gases like NO2, CO, H2S, and NH3, showing relatively much lower ∼4.28, 3.42, 6.43, and 3.51% responses, respectively, at 50 °C for 50 ppm gas concentration. The impedance measurements also substantiate the same as the observed surface resistance is initially more than bulk, which reduces after introducing the hydrogen gas during sensing measurements. The humidity does not show any significant change in the hydrogen response, which is ∼20.5 ± 1.5% for a large humidity range (from 10 to 65%). More interestingly, the devices are robust against sensing response, showing no significant change after 10 months or even more.

The present work investigates analytically and experimentally the multimodal performance analysis of piezoelectric (PZT-5A) based generic nanogenerators. The present nanogenerators consider both uni-morph and bimorph with offset-proof mass subjected to sinusoidal base excitation. The finite element-based multi-mode electromechanical coupled dynamics governing equations are derived to formulate the analytical expressions of uni-morph, and bimorph nano-harvesters for frequency responses function of output voltage, current, and power, respectively. The impact of base excitation, load resistance, thickness, length, and mass of offset-proof mass on the output voltage and harvested energy is investigated by considering multi-mode vibration bodies. PZT-5A is evenly distributed over the substructure for the single voltage output. Interestingly, we noticed that a uni-morph cantilever with offset-proof mass is the best among all the investigated configurations, showing the maximum power at different load conditions. Analytical solutions are in good agreement with nearly no error for the first few vibration modes as compared to what was obtained using numerical simulation. The experimental realization for a single mode of vibration has been explored, and results showed that the fundamental mode swings very similar behaviors in voltage and power output, mostly in pre-and post-resonance conditions as compared to analytical results, and the difference between these two results is about nearly 5%. Thus, the present work depicts an effectual correlation between analytical development, numerical results using COMSOL 2D, and experimental realization for analyzing energy harvesting devices. These results may be helpful for the experimentalists to design efficient nanogenerators.

The materials exhibiting the negative differential resistance (NDR) and write once read many (WORM), simultaneously are potential candidates for electronic devices such as oscillators and permanent storage devices. Here in, we investigated the impact of crystallinity on coexistence of NDR and WORM resistive switching on Cu(top contact)/BiFeO3 (amorphous/crystalline) (BFO as active material)/FTO (bottom electrode) memory device. The multiferroic BiFeO3 (BFO) active material is synthesized using a low-cost solution process on FTO substrates and thermal evaporation was used for deposing metal copper as the top contacts. The present device Cu/am-BFO/FTO showed the coexistence of WORM with high Ion/Ioff ratio of ~ 103 and NDR with peak (Vp) and valley (Vv) voltages ~ − 0.26 V and − 1.23 V, respectively. The power consumption is significantly low, ~ 66.94 µW in NDR region for am-BFO. The device with active crystalline material, i.e., Cu/c-BFO/FTO exhibits peak (Vp) and valley (Vv) voltages ~ − 1.22 V and − 1.40 V, respectively, and the power consumption is ~ 1.08 mW for devices based on crystalline BFO as an active material. The retention and endurance values are ~ 103 s and 103 cycles. The repeatability of the bipolar resistive switching of c-BFO is measured for 100 cycles, and relative cumulative Weibull distribution plots show the filament’s stability for both set and reset states. Thus, these results demonstrate the interplay between different switching characteristics in BFO, which can be tailored by manipulating the crystallinity of the active material.