Highly Responsive Near-Infrared Si/Sb2Se3 Photodetector via Surface Engineering of Silicon.

The development of imaging technology and optical communication demands a photodetector with high responsiveness. As demonstrated by microfabrication and nanofabrication technology advancements, recent progress in plasmonic sensor technologies can address this need. However, these photodetectors have low optical absorption and ineffective charge carrier transport efficiency. Sb2Se3 is light-sensitive material with a high absorption coefficient, making it suitable for photodetector applications. We developed an efficient, scalable, low-cost near-infrared (NIR) photodetector based on a nanostructured Sb2Se3 film deposited on p-type micropyramidal Si (made via the wet chemical etching process), working on photoconductive phenomena. Our results proved that, at the optimized thickness of the Sb2Se3 layer, the proposed Si micropyramidal substrate enhanced the responsivity nearly two times, compared with that of the Sb2Se3 deposited on a flat Si reference sample and a glass/Sb2Se3 sample at 1064 nm (power density = 15 mW/cm2). More interestingly, the micropyramidal silicon-based device worked at 0 V bias, paving a path for self-bias devices. The highest specific detectivity of 2.25 × 1015 Jones was achieved at 15 mW/cm2 power density at a bias voltage of 0.5 V. It is demonstrated that the enhanced responsivity was closely linked with field enhancement due to the Kretschmann configuration of Si pyramids, which acts as hot spots for Si/Sb2Se3 junction. A high responsivity of 47.8 A W-1 proved it suitable for scalable and cost-effective plasmonic-based NIR photodetectors.

Na ion batteries: An India centric review.

Developing low-cost and safe energy storage devices is the primary goal of every country to make a carbon-neutral atmosphere by ∼2050. Batteries and supercapacitors are the backbones of future sustainable energy sources for electrical vehicles (EVs), smart electronic devices, electricity supply to off-grid regions, etc. Hence, these battery-dependent devices are substantially gaining the market. Although lithium-ion batteries account for powering most of these devices, lithium availability and price pose a severe problem since lithium resources are not abundant in nature. Thus, alternative research on sodium-ion or other multi-charged cations (Al3+/Mg2+/Ca2+/K+) based energy storage devices is needed to substitute lithium-ion batteries. India and many other countries have sodium in abundance. Sodium also has potential in designing and developing efficient charge storage devices. This review article discusses the status of sodium-ion battery research activities, cost, market analysis, and future strategies of the Indian government or private bodies, industries, and research institutes of India.

Photocatalytic Carbon Dioxide Conversion by Structurally and Materially Modified Titanium Dioxide Nanostructures.

TiO2 has aroused considerable attentions as a promising photocatalytic material for decades due to its superior material properties in several fields such as energy and environment. However, the main dilemmas are its wide bandgap (3-3.2 eV), that restricts the light absorption in limited light wavelength region, and the comparatively high charge carrier recombination rate of TiO2, is a hurdle for efficient photocatalytic CO2 conversion. To tackle these problems, lots of researches have been implemented relating to structural and material modification to improve their material, optical, and electrical properties for more efficient photocatalytic CO2 conversion. Recent studies illustrate that crystal facet engineering could broaden the performance of the photocatalysts. As same as for nanostructures which have advantages such as improved light absorption, high surface area, directional charge transport, and efficient charge separation. Moreover, strategies such as doping, junction formation, and hydrogenation have resulted in a promoted photocatalytic performance. Such strategies can markedly change the electronic structure that lies behind the enhancement of the solar spectrum harnessing. In this review, we summarize the works that have been carried out for the enhancement of photocatalytic CO2 conversion by material and structural modification of TiO2 and TiO2-based photocatalytic system. Moreover, we discuss several strategies for synthesis and design of TiO2 photocatalysts for efficient CO2 conversion by nanostructure, structure design of photocatalysts, and material modification.

Temperature-Dependent n-p-n Switching and Highly Selective Room-Temperature n-SnSe2/p-SnO/n-SnSe Heterojunction-Based NO2 Gas Sensor.

Many toxic gases are mixed into the atmosphere because of increased air pollution. An efficient gas sensor is required to detect these poisonous gases with its ultrasensitive ability. We employed the thermal evaporation method to deposit an n-SnSe2/p-SnO/n-SnSe heterojunction and observed a temperature-dependent n-p-n switching NO2 gas sensor with high selectivity working at room temperature (RT). The structural and morphological properties of the material were studied using the characterization techniques such as XRD, SEM, Raman spectroscopy, XPS, and HRTEM, respectively. At RT, the device response was 256% for 5 ppm NO2. The response/recovery times were 34 s/272 s, respectively. The calculated limit of detection (LOD) was ∼115 ppb with a 38% response. The device response was better with NO2 gas than with SO2, NO, H2S, CO, H2, and NH3. The mechanism of temperature-dependent n-p-n switching, fast response, recovery, and selective detection of NO2 at RT has been discussed on the basis of physisorption and charge transfer. Thus, this work will add a new dimension to 2D materials as selective gas detectors at room temperature.

NO2 Gas Sensor Based on SnSe/SnSe2p-n Hetrojunction.

Air pollution is a big concern as it causes harm to human health as well as environment. NO2 can cause several respiratory diseases even in low concentration and therefore an efficient sensor for detecting NO2 at room temperature has become one of the priorities of the scientific community. Although two dimensional (2D) materials (MoS2 etc.) have shown potential for NO2 sensing at lower temperatures, but these have poor desorption kinetics. However, these limitations posed by slow desorption can be overcome, if a material in the form of a p-n junction can be suitably employed. In this work, ~150 nm thick SnSe2 thin film has been deposited by thermally evaporating in-house made SnSe2 powder. The film has been studied for its morphological, structural and gas sensing applications. The morphology of the film showed that the film consists of interconnected nanostructures. Detailed Raman studies further revealed that SnSe2 film had 31% SnSe. The SnSe-SnSe2 nanostructured sensor showed a response of ~112% towards 5 ppm NO2 at room temperature (30 °C). The response and recovery times were ~15 seconds and 10 seconds, respectively. Limit of detection for NO2 was in sub-parts per million (sub-ppm) range. The device demonstrated a better response towards NO2 compared to NH3, CH4, and H2. The mechanism of room temperature fast response, recovery and selective detection of NO2 independent of humidity conditions has been discussed based on physisorption, charge transfer, and formation of SnSe-SnSe2 (p-n) nano-junctions. Depositing a nanostructured film consisting of nano-junctions using an industrially viable thermal evaporation technique for sensing a very low concentration of NO2 is the novelty of this work.

Au/Pd Bimetallic Nanoparticles Decorated SnSe2 Thin Films for NO2 Detection.

In order to have a check and balance of the toxic gases in the environment, various kinds of sensors are currently being researched upon. As many of the toxic gases are also inflammable, therefore, there is a constant search for materials which can detect the gases at lower temperatures. Also, it is important that the sensor is selective for a particular gas. To meet such requirements, nanos-tructured materials are extensively being explored for such gas sensing applications, due to their large effective surface area. And, in order to further improve the gas sensing properties, metal catalysts are deposited over such nanomaterials. The smaller sized nanoparticles show better catalytic activity due to its effective larger surface area per unit volume. Depositing bimetallic materials is thus advantageous, since it can reduce the size of nanoparticles produced. In this work, ~7 nm thick Au/Pd thin film was sputter-coated over SnSe2 nanostructured thin films. SnSe2 thin film were deposited by thermally evaporating SnSe2 powder. The materials were characterized for their structural, morphological and gas sensing properties. The ambient temperature response for 5 parts per million (ppm) NO2 gas was measured to be 117%, with the response and recovery times being 10 and 19 seconds, respectively. The performance of the sensor improved with increase in the gas concentration and for 10 ppm gas, the recorded response was 137%, with the corresponding response and recovery times being 9 and 8 seconds, respectively. The limit of detection was 655 parts per billion (ppb). The mechanism of ambient temperature high response and low response/recovery times have been discussed based on physisorption, charge transfer, Au/Pd decoration and SnSe-SnSe2 based p-n junction. In addition, an important aspect of this work worth pointing out is the deposition of a thin film consisting of nanostructured network using an industrially viable thermal evaporation method. Thus, this work opens a new dimension for 2D materials that can be used for selective gas detection at ambient temperature.

Tin-selenide as a futuristic material: properties and applications.

SnSe/SnSe2 is a promising versatile material with applications in various fields like solar cells, photodetectors, memory devices, lithium and sodium-ion batteries, gas sensing, photocatalysis, supercapacitors, topological insulators, resistive switching devices due to its optimal band gap. In this review, all possible applications of SnSe/SnSe2 have been summarized. Some of the basic properties, as well as synthesis techniques have also been outlined. This review will help the researcher to understand the properties and possible applications of tin selenide-based materials. Thus, this will help in advancing the field of tin selenide-based materials for next generation technology.

Tuning the Thermoelectric Material's Parameter: A Comprehensive Review.

Thermoelectric is a device that converts heat into electricity. As thermodynamically it is not possible to make device which is 100 percent efficient, some amount of energy is wasted in the form of heat. Thermoelectric materials can play a major role in harnessing such waste energy. Although thermoelectric is a useful device still its efficiency is not good enough for commercialization. Therefore, lots of research have been carried out in finding out the best possible material, device geometry etc. There are thousands of papers describing various optimization processes. The present work reviews the basics of thermoelectric device parameters which determine the performance of the device and how to control these parameters for better thermoelectric efficiency. The efforts made to optimize parameters like power factor, thermal conductivity etc. have been summarized. Experimental results have been described with examples. Highest reported ZT values of various materials have been presented in this review.

Photo-Current Enhancement in Carbon Quantum Dots Functionalized Titania Nanotube Arrays.

Highly aligned, vertically oriented, TiO2 nanotube arrays fabricated by electrochemical anodization were functionalised by carbon quantum dots (CQD) synthesized by an electrochemical reduction technique. Here, we report the photo-electrochemical properties of such TiO2 nanotubes array-CQD composite material and it has been found that the properties are significantly enhanced compared to that in pristine (bare) nanotubes. The TiO2 nanotubes were characterized by X-ray diffraction and scanning electron microscopy, whereas the CQD samples were characterized by transmission electron microscopy, optical absorption spectroscopy. CQDs synthesized under two different conditions showed a distinct size difference and corresponding absorption spectra revealed concominant shift in the absorption edges. Furthermore, the photo-electrochemical measurements were carried out with the help of photo-current, incident photon to current conversion efficiency (IPCE), Mott-Schottky plots and the impedance analysis. The photo-current data revealed 30% improvement in TiO2-CQD samples compared to bare TiO2 nanotubes samples. A higher photo-conversion efficiency was observed along with the shifting of the peak value towards visible wavelengths. The Mott-Schottky plots revealed shift in the flat-band potential in the CQD-TiO2 samples and corresponding lowering of the charge transfer resistance was observed through the impedance spectroscopy.

Generation of fuel from CO2 saturated liquids using a p-Si nanowire ‖ n-TiO2 nanotube array photoelectrochemical cell.

Light-driven, electrically biased pn junction photoelectrochemical (PEC) cells immersed in an electrolyte of CO(2) saturated 1.0 M NaHCO(3) are investigated for use in generating hydrocarbon fuels. The PEC photocathode is comprised of p-type Si nanowire arrays, with and without copper sensitization, while the photoanode is comprised of n-type TiO(2) nanotube array films. Under band gap illumination, the PEC cells convert CO(2) into hydrocarbon fuels, such as methane, along with carbon monoxide and substantial rates of hydrogen generation due to water photoelectrolysis. In addition to traces of C3-C4 hydrocarbons, methane and ethylene were formed at the combined rate of 201.5 nM/cm(2)-hr at an applied potential of -1.5 V vs. Ag/AgCl. The described technique provides a unique approach, utilizing earth abundant materials, for the photocatalytic reduction of CO(2) with subsequent generation of higher order hydrocarbons and syngas constituents of carbon monoxide and hydrogen.

Theory, instrumentation and applications of magnetoelastic resonance sensors: a review.

Thick-film magnetoelastic sensors vibrate mechanically in response to a time varying magnetic excitation field. The mechanical vibrations of the magnetostrictive magnetoelastic material launch, in turn, a magnetic field by which the sensor can be monitored. Magnetic field telemetry enables contact-less, remote-query operation that has enabled many practical uses of the sensor platform. This paper builds upon a review paper we published in Sensors in 2002 (Grimes, C.A.; et al. Sensors 2002, 2, 294-313), presenting a comprehensive review on the theory, operating principles, instrumentation and key applications of magnetoelastic sensing technology.

Synthesis and applications of electrochemically self-assembled titania nanotube arrays.

Highly ordered vertically oriented TiO(2) nanotube arrays fabricated by electrochemical anodization offer a large surface area architecture with precisely controllable nanoscale features. These nanotubes have shown remarkable properties in a variety of applications including, for example, their use as hydrogen sensors, in the photoelectrochemical generation of hydrogen, dye-sensitized and solid-state heterojunction solar cells, photocatalytic reduction of carbon dioxide into hydrocarbons, and as a novel drug delivery platform. Herein we consider the development of the various nanotube array synthesis techniques, different applications of the TiO(2) nanotube arrays, unresolved issues, and possible future research directions.