Abstract Mitigating the adverse effects of humidity on the sensing performance of one-dimensional (1D) metal oxide semiconductors has been a key challenge in gas sensor development. This study investigated the humidity-enhanced effect of gold (Au) nanoparticles on the ethanol response of 1D ZnO nanostructures. ZnO nanowires were grown using a thermal evaporation–condensation method with Au-catalyzed growth kinetics for the fabrication of conductometric chemical sensors. Au nanoparticles were then additionally decorated on ZnO nanostructures by sputtering with varying times from 2 to 10 s. Structural examinations demonstrated Au nanoparticles with diverse diameters (10–70 nm) widely distributed on ZnO nanowires exhibiting lengths of 0.1–1 μm and diameters of 10–30 nm. All fabricated sensors were systematically evaluated toward NO2, NH3, C3H6O, CO, and C2H5OH at 250–400 °C under dry and humid conditions. ZnO nanowires functionalized with Au for 5 s were found to exhibit the highest response of 93.75 to 70 ppm of C2H5OH, which was significantly greater than that of the pristine ZnO nanowire sensor (1.86) at 50% relative humidity (RH) and the optimum sensing temperature of 350 °C. Interestingly, the optimally Au-decorated ZnO nanowire sensor showed humidity-enhanced behaviors with significantly boosted ethanol responses at 50% RH. In addition, the optimal sensor displayed a low theoretical limit of detections (3.7 ppb) and high C2H5OH selectivity against interfering gases, including NO2, NH3, C3H6O, and CO. The observed ethanol response improvement and humidity-enhanced effect might be ascribed to the attributes of ohmic metal–semiconductor junctions formed at Au–ZnO interfaces and the capabilities of very fine sputtered Au nanoparticles to enhance oxygen chemisorption and suppress the formation of surface hydroxyl and hydronium species on ZnO nanowires. According to the results, Au-decorated ZnO nanowires fabricated by evaporation–condensation and sputtering could be potential candidates for use as practical C2H5OH sensors.

NO2 is a toxic gas mainly generated by combustion processes, such as vehicle emissions and industrial activities. It is a key contributor to smog, acid rain, ground-level ozone, and particulate matter, all of which pose serious risks to human health and the environment. Conventional resistive gas sensors, typically based on metal oxide semiconductors, detect NO2 by resistance modulation through surface interactions with the gas. However, they often suffer from low responsiveness and poor selectivity. This study investigates NO2 detection using nanoporous zinc oxide thin films integrated into a resistor structure and floating-gate field-effect transistor (FGFET). Both Silvaco-Atlas simulations and experimental fabrication were employed to evaluate sensor behavior under NO2 exposure. The results show that FGFET provides higher sensitivity, faster response times, and improved selectivity compared to resistor-based devices. In particular, FGFET achieves a detection limit as low as 89 ppb, with optimal performance around 400 °C, and maintains stability under varying humidity levels. The enhanced performance arises from quantum well effects at the floating-gate Schottky contact, combined with NO2 adsorption on the ZnO surface. These interactions extend the depletion region and confine charge carriers, amplifying conductivity modulation in the channel. Overall, the findings demonstrate that FGFET is a promising platform for NO2 sensors, with strong potential for environmental monitoring and industrial safety applications.

As high-efficiency electrochemical devices that directly convert chemical energy into electrical energy via electrochemical reactions, Solid Oxide Fuel Cells (SOFCs) offer the possibility of an environmentally friendly approach to energy conversion. They have gained great interest due to their potential for operating at intermediate temperatures (less than 800 °C), which is essential for expanding their practical use. SOFCs have attracted increased attention as sustainable energy sources, since when supplied with hydrogen (H 2 ) and oxygen (from air), they produce electricity through the following electrochemical reactions: (1) H 2 + 1/2 O 2- <--> H 2 O + 2 e - (2) O 2 + 4 e - <--> 2 O 2- with the only by-product resulting in water (H 2 O). The energy conversion efficiency of SOFCs can theoretically reach 60-80%, as they are not constrained by the Carnot cycle, given that combustion is not involved in the SOFC process. One crucial point which attracts interest research in the field is that the SOFC power output is closely related to the electrochemical reactions at the electrodes [1, 2]. Therefore, the nanostructuration of the anode, which increases the surface-to-volume ratio of the three-phase boundary (TPB) conditions where the reactions occur, should in principle improve the SOFC performance. In this work, the preparation by Vapor-Liquid-Solid (VLS) growth technique and systematic morphological and structural characterization of nanostructured anodes based on Nikel Oxide and Gadolinium doped Ceria (NiO-GDC) nanowires (NWs) are proposed. The NiO-GDC NWs were synthesized using the VLS growth method and thoroughly characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and Raman spectroscopy. Additionally, the performance of the fuel cell, including power output and Electrochemical Impedance Spectroscopy (EIS) analysis, was assessed at different temperatures and hydrogen/air flow rates. Starting from the results obtained in previous works where the synthesis of NiO-GDC NWs was investigated [3, 4], in the present study the performance of the NWs-based fuel cell was compared with a commercial SOFC (Next Cell 2.0, from fuelcellmaterials company) and a hybrid one prepared by depositing NiO-GDC NWs on top of a commercial NC. In Figure 1a-b, the scheme and multilayer structure of the commercial SOFC (Next Cell) and the nanostructured SOFC with NiO-GDC NWs. After a careful preparation of the NiO-GDC NWs via VLS growth technique (shown schematically in Figure 1c), the SOFC performance was tested with the following parameters: T = 600, 700, 800° C; H 2 /AIR flux = 100/200, 150/300, 200/400. NiO-GDC NWs successfully grown by VLS technique on top of the anode of NC (commercial SOFC) and on top of the HC electrolyte with Au catalyst. The following samples were obtained and then analyzed: NC: commercial SOFC (Next Cell 2.0) NC+NWs: commercial SOFC (Next Cell 2.0) with NiO-GDC NWs deposited on the anode HC+NWs: Half Cell (NC without anode) with NiO-GDC NWs deposited as nanostructured anode Advantages of SOFCs include low emissions, long-term stability, and relatively low cost, making them a promising sustainable energy source. By enhancing anode performance through nanostructuring, SOFC electrochemical performance can be improved. The electrochemical reactions at the anode occur at the TPB, where the electrolyte, electron-conducting metal, and gas phases meet. Extending the TPB length enhances the electrochemical reaction, thereby improving anode performance. Researchers are currently investigating the role of nanomaterials in SOFC technology to enhance performance. It has been shown that reducing electrode grain size increases TPB length, particularly when the grain size is below 2 μm. In NiO-GDC NWs, the reduction of NiO and GDC grain sizes to the nanoscale significantly increases the interfacial area between NiO and GDC, thereby extending the TPB and improving the electrical performance of the anode. After systematically investigating the growth parameters that optimize NiO-GDC NWs morphology and composition using SEM, XRD, and Raman spectroscopy, the NiO-GDC NWs were grown on a commercial single-electrode button cell (with a cathode only) to assess the electrochemical behavior of the cell. A thorough analysis of the results indicates that the NiO-GDC NWs show considerable promise as an anode material for SOFCs. This study presents the synthesis and performance of NiO-GDC NWs-based SOFCs, with an in-depth investigation of the morphology and composition of the nanowires using SEM, XRD, and Raman techniques. Ultimately, NiO-GDC NWs were grown directly on a commercial single-electrode button cell to evaluate electrochemical performance, with preliminary results suggesting significant potential for NiO-GDC NWs as an anode material in SOFCs. Structural characterization by Raman and X-ray Diffraction carried out before and after electrical tests. In Figure 2, the SEM images (a), Raman spectra (b) and electrical I-V characterization of the samples: NC, NC+NWs, HC+NWs. From SEM images (in Fig. 2a, associated with samples sketches), NWs grown on the commercial anode surface (Fig. 2a middle) and on top of the electrolyte (Fig. 2a right) is shown. Raman signal (in Fig. 2b) from the anode presents NiO peaks and Scandia stabilized Zirconia (ScSZ) from the underlying electrolyte. The I-V characteristics and EIS of the fuel cell were measured using a SOFC test setup from Fiaxell SOFC Technologies TM Fiaxell. During the tests, the single-cell was placed in a KITTEC® SquadroKitted Squadro muffle furnace, with the cell sandwiched between the anode and cathode collector discs. The setup was connected to gas-tight fittings for the delivery of air and hydrogen to the cell. The tests were conducted at temperatures of 600°C, 700°C, and 800°C. The I-V characteristics were obtained using slow-scan galvanostatic linear sweep voltammetry (LSV). After the electrical tests, cracks were observed on the anode surface of NC which probably make the performance decrease. NC+NWs sample shows less cracks and a more stable power output. Unfortunately, it was observed that after the electrical tests most of the NiO-GDC NWs are destroyed, probably for the high operating temperatures or for the mechanical stress (data not shown here). At 800 °C, with hydrogen and air flows of 100 sccm and 200 sccm respectively, an Open Circuit Voltage (OCV) of 1.06 V and a power density of 373 mW/cm² were achieved. In conclusion, NiO-GDC NWs were successfully grown on top of the electrolyte and on top of the anode of a commercial SOFC, by VLS technique; a systematic morphological (by SEM) and structural (by Raman and X-ray Diffraction) characterization carried out before and after V-I electrical test; NiO-GDC NWs do not really improve the SOFC performance, however they can preserve the anode layer to be damaged during the electrical testing; nanostructured SOFC with NiO-GDC NWs grown by VLS on the electrolyte showed comparable performance with respect to the commercial multi-layered anode SOFC. Finally, the electrical I-V characterization associated with the impedance spectroscopy analysis allows us to evaluate and compare the performances of the different anodes morphology, to model the electrical equivalent circuit and extract the best deposition parameters and the SOFC nanoarchitecture, in order to further enhance the final performance. References [1] Helal, H.; Ahrouch, M.; Rabehi, A.; Zappa, D.; Comini, E. Nanostructured Materials for Enhanced Performance of Solid Oxide Fuel Cells: A Comprehensive Review. Crystals 2024, 14, 306. [2] M. Singh, D. Zappa, E. Comini, Solid oxide fuel cell: Decade of progress, future perspectives and challenges, International Journal of Hydrogen Energy. International Journal of Hydrogen Energy 46, 2021, 27643. [3] M. Singh, D. Zappa, E. Comini, NiO-GDC nanowire anodes for SOFCs: novel growth, characterization and cell performance. Mater. Adv., 2022, 3, 5922. [4] Helal H, Botticini S, Rigoni F, Zappa D, Hakkoum H, Chua D, Lee P-S, Comini E (2024). Synthesis and Characterization of NiO-GDC Nanowires for High-Performance Solid Oxide Fuel Cell Anodes. In: EFCF 2024 Proceeding of the Conference (PoC) B-Sessions: Abstracts & Papers. Lucerna (CH), 2 - 5 July 2024. Acknowledgements Funded by the “Ministero Affari Esteri e Cooperazione Internazionale” under the Italy-Singapore joint project PGR01187 “Thin-film solid oxide fuel cell with hierarchical mixed oxides nanostructured electrodes”. FIGURE 1 caption: Scheme and multilayer structure of a) commercial SOFC (Next Cell 2.0, fuelcellmaterials) and b) nanostructured SOFC with NiO-GDC NWs. Synthesis scheme by VLS, after Au catalyst deposition by sputtering, of NiO-GDC NWs on top of the commercial Next Cell and the Half Cell (with no anode). FIGURE 2 caption: Sample sketches and SEM images (a), Raman spectra (b) and electrical I-V characterization of, from left to right: Next Cell anode, NiO-GDC NWs grown on Next Cell anode, NiO-GDC NWs grown on Half Cell anode. Figure 1 Figure 2

Herein, we present an innovative design utilizing two metal oxides, ZnO and Co3O4, which exhibit exceptional gas response and outstanding selectivity. The proposed p-Co3O4/n-ZnO composite nanowires are prepared by insitu thermal oxidation and evaporation at a temperature of 800 degrees C. The successful growth of these Co3O4/ZnO composite nanowires has been confirmed through detailed morphological, compositional, and structural analyses. These nanowires feature a unique architecture with Co3O4 at the root, ZnO forming the body, and Pt and Co3O4 at the tip. Preliminary gas sensing tests reveal promising acetone (C3H6O) detection capabilities, which are attributed to the presence Pt nanoparticles and the Co3O4 segment at the tip. Moreover, the formation of p-n heterojunctions, combined with the synergistic gas sensing effect, and the catalytic activity, significantly enhances the response of the sensor. The sensors demonstrate an impressive gas response (Delta G/G) of 5780 towards 50 ppm of C3H6O at 250 degrees C in 40 %RH air, with an estimated detection limit of 0.4 ppm. The underlying sensing mechanisms are thoroughly analyzed, providing insights into how the unique design leads to superior gas sensing performance.

An automated device is designed to measure the density of a liquid material using hydrostatic pressure method. A low cost pressure sensor is calibrated and used to get highly accurate readings. The calibration is done by measuring the pressure values vs. the generated voltage signal. The calibration has been challenging due to the low accuracy of the sensor but proved to be highly effective in applications. The interface is developed using a microcontroller, motor drives, analog to digital converters and sensors. The device is designed to get several readings automatically by changing the positions of the device/liquid column heights to increase the accuracy. Also the device can be programmed to measure the real time density of a liquid continuously. The readings were analyzed and averaged by a software developed in python language. The instruments accuracy was tested against 3 liquid types, water, coconut oil, kerosene oil, and showed a low error (0.007%, 0.001%, and 0.002% respectively) compared to the readings of a standard Pycnometer. The low error percentages confirm the accuracy of the device and the effectiveness of the sensor calibrations.

By uncovering novel aspects of second harmonic generation in aluminum we show that there are unusual and remarkable consequences of resonant absorption, namely an unexpectedly critical role that bound electrons play for light-matter interactions across the optical spectrum, suggesting that a different basic approach is required to fully explain the physics of surfaces. We tackle an issue that is never under consideration given the generic hostile conditions to the propagation of light under resonant absorption. Unlike most noble metals, aluminum displays Lorentz-like behavior and interband transitions centered near 810 nm, thus splitting the plasmonic range in an atypical manner and setting its linear and nonlinear optical properties apart. Studies of aluminum nanostructures having complex topologies abound, as do reported inconsistencies in the linear spectral response of surface plasmons and harmonic generation. Our experimental observations of second harmonic generation from aluminum nanolayers show that bound electrons are responsible for a unique signature neither predicted nor observed previously: a hole in the second harmonic spectrum. A hydrodynamic-Maxwell theory explains these findings exceptionally well and becomes the basis for renewed studies of surface physics.

Light and active mobility, as well as multimodal mobility, could significantly contribute to decarbonization. Air quality is a key parameter to monitor the environment in terms of health and leisure benefits. In a possible scenario, wearables and recharge stations could supply information about a distributed monitoring system of air quality. The availability of low-power, smart, low-cost, compact embedded systems, such as Arduino Nicla Sense ME, based on BME688 by Bosch, Reutlingen, Germany, and powered by suitable software tools, can provide the hardware to be easily integrated into wearables as well as in solar-powered EVSE (Electric Vehicle Supply Equipment) for scooters and e-bikes. In this way, each e-vehicle, bike, or EVSE can contribute to a distributed monitoring network providing real-time information about micro-climate and pollution. This work experimentally investigates the capability of the BME688 environmental sensor to provide useful and detailed information about air quality. Initial experimental results from measurements in non-controlled and controlled environments show that BME688 is suited to detect the human-perceived air quality. CO2 readout can also be significant for other gas (e.g., CO), while IAQ (Index for Air Quality, from 0 to 500) is heavily affected by relative humidity, and its significance below 250 is quite low for an outdoor uncontrolled environment.

In this work, the gas sensing properties of a single ZnO nanowire (NW) are investigated, simultaneously in terms of photoluminescence (PL) and photocurrent (PC) response to NO2 gas, with the purpose of giving new insights on the gas sensing mechanism of a single 1D ZnO nanostructure. A single ZnO NW sensing device was fabricated, characterized, and compared with a sample made of bundles of ZnO NWs. UV near-band-edge PL emission spectroscopy was carried out at room temperature and by lowering the temperature down to 77 K, which allows detection of resolved PL peaks related to different excitonic transition regions. Surface effects were observed in PL maps, considering different nano and microstructures. Electrical and optical measurements were acquired at the same time during the NO2 gas exposure, allowing for the comparison of PL and PC response times and signal recovery. During NO2 gas desorption, irreversible behavior in the surface-related and donor-acceptor pair (DAP) regions is interpreted as the effect of an initial transient when electronic transfer from the gas molecules to the bulk occurs through the ZnO NW surface which acts as a channel. To the best of our knowledge, this is the first work which investigates the simultaneous PL optical and PC electrical response signals of a single ZnO NW to gas exposure.

Solid oxide fuel cells (SOFCs) have emerged as promising candidates for efficient and environmentally friendly energy conversion technologies. Their high energy conversion efficiency and fuel flexibility make them particularly attractive for various applications, ranging from stationary power generation to portable electronic devices. Recently, research has focused on utilizing nanostructured materials to enhance the performance of SOFCs. This comprehensive review summarizes the latest advancements in the design, fabrication, and characterization of nanostructured materials integrated in SOFC. The review begins by elucidating the fundamental principles underlying SOFC operation, emphasizing the critical role of electrode materials, electrolytes, and interfacial interactions in overall cell performance, and the importance of nanostructured materials in addressing key challenges. It provides an in-depth analysis of various types of nanostructures, highlighting their roles in improving the electrochemical performance, stability, and durability of SOFCs. Furthermore, this review delves into the fabrication techniques that enable precise control over nanostructure morphology, composition, and architecture. The influence of nanoscale effects on ionic and electronic transport within the electrolyte and electrodes is thoroughly explored, shedding light on the mechanisms behind enhanced performance. By providing a comprehensive overview of the current state of research on nanostructured materials for SOFCs, this review aims to guide researchers, engineers, and policymakers toward the development of high-performance, cost-effective, and sustainable energy conversion systems.

An electronic nose, designed to replicate human olfaction, captures distinctive ‘fingerprint’ data from mixed gases or odors. Comprising a gas sensing system and an information processing unit, electronic noses have evolved significantly since their inception in the 1980s. They have transitioned from bulky, costly, and energy-intensive devices to today’s streamlined, economical models with minimal power requirements. This paper presents a comprehensive and systematic review of the electronic nose technology domain, with a special focus on advancements over the last five years. It highlights emerging applications, innovative methodologies, and potential future directions that have not been extensively covered in previous reviews. The review explores the application of electronic noses across diverse fields such as food analysis, environmental monitoring, and medical diagnostics, including new domains like veterinary pathology and pest detection. This work aims to underline the adaptability of electronic noses and contribute to their continued development and application in various industries, thereby addressing gaps in current literature and suggesting avenues for future research.

Layered transition metal dichalcogenides (TMDCs) are considered among the next-generation materials for gas sensing. Here, we report exfoliated 2H-WS2 nanosheets for the fabrication of highly performing NO2 sensors. Thermal annealing at several temperatures was performed to investigate the oxidation of WS2. The long-term stability of 2H-WS2 bulk was verified. Using droplet variation method, three batches of conductometric sensors from 2H-WS2 dispersions were fabricated on electrical transducers, namely two layers (2L), five layers (5L) and ten layers (10L) WS2 nanosheets. These sensors were tested towards low NO2 concentrations at different temperatures (Room Temperature (20 ℃), 50 ℃ and 100 ℃) and relative humidity (RH) levels (20%, 40%, 60%, 80% and 90% RH). 2L-WS2 based sensor showed the highest response at room temperature (RT). Excellent repeatability (4 cycles) towards 1 ppm NO2 and long-term stability (more than two months) were achieved. Full selectivity towards NO2 (1 ppm) at RT was observed over NH3 (15 ppm), H2S (15 ppm), ethanol (30 ppm) and acetone (30 ppm). Our results confirm that low-power consumption devices with high sensitivity (even at high RH), long-term stability and excellent selectivity towards NO2 were fabricated using 2H-WS2 nanosheets.

The dissemination of sensors is key to realizing a sustainable, ‘intelligent’ world, where everyday objects and environments are equipped with sensing capabilities to advance the sustainability and quality of our lives—e.g. via smart homes, smart cities, smart healthcare, smart logistics, Industry 4.0, and precision agriculture. The realization of the full potential of these applications critically depends on the availability of easy-to-make, low-cost sensor technologies. Sensors based on printable electronic materials offer the ideal platform: they can be fabricated through simple methods (e.g. printing and coating) and are compatible with high-throughput roll-to-roll processing. Moreover, printable electronic materials often allow the fabrication of sensors on flexible/stretchable/biodegradable substrates, thereby enabling the deployment of sensors in unconventional settings. Fulfilling the promise of printable electronic materials for sensing will require materials and device innovations to enhance their ability to transduce external stimuli—light, ionizing radiation, pressure, strain, force, temperature, gas, vapours, humidity, and other chemical and biological analytes. This Roadmap brings together the viewpoints of experts in various printable sensing materials—and devices thereof—to provide insights into the status and outlook of the field. Alongside recent materials and device innovations, the roadmap discusses the key outstanding challenges pertaining to each printable sensing technology. Finally, the Roadmap points to promising directions to overcome these challenges and thus enable ubiquitous sensing for a sustainable, ‘intelligent’ world.

Unlike the conventional one-dimensional (1D) core–shell nanowires (NWs) composed of p-type shells and n-type cores, in this work, an inverse design is proposed by depositing n-type ZnO (shell) layers on the surface of p-type CuO (core) NWs, to have a comprehensive understanding of their conductometric gas-sensing kinetics. The surface morphologies of bare and core–shell NWs were investigated by field emission scanning electron microscope (FE-SEM). The ZnO shell layer was presented by overlay images taken by electron dispersive X-ray spectroscopy (EDX) and high-resolution transmission electron microscopy (HRTEM). The pronounced crystalline plane peaks of ZnO were recorded in the compared glancing incident X-ray diffraction (GI-XRD) spectra of CuO and CuO–ZnO core–shell NWs. The ZnO shell layers broaden the absorption curve of CuO NWs in the UV-vis absorption spectra. As a result of the heterostructure formation, the intrinsic p-type sensing behavior of CuO NWs towards 250 and 500 ppm of hydrogen (H2) switched to n-type due to the deposition of ZnO shell layers, at 400 °C in dry airflow.

Titanium dioxide nanobelts were prepared via the alkali-hydrothermal method for application in chemical gas sensing. The formation process of TiO2-(B) nanobelts and their sensing properties were investigated in detail. FE-SEM was used to study the surface of the obtained structures. The TEM and XRD analyses show that the prepared TiO2 nanobelts are in the monoclinic phase. Furthermore, TEM shows the formation of porous-like morphology due to crystal defects in the TiO2-(B) nanobelts. The gas-sensing performance of the structure toward various concentrations of hydrogen, ethanol, acetone, nitrogen dioxide, and methane gases was studied at a temperature range between 100 and 500 °C. The fabricated sensor shows a high response toward acetone at a relatively low working temperature (150 °C), which is important for the development of low-power-consumption functional devices. Moreover, the obtained results indicate that monoclinic TiO2-B is a promising material for applications in chemo-resistive gas detectors.

Temperature sensors have been widely developed to control the course of diseases, improve haptic feelings, and in multisensing systems to compensate for the output of other temperature-sensitive sensors. The use of additive manufacturing to produce resistive temperature detectors (RTDs) with reduced dimensions and bulkiness is attracting great interest. Among the relevant process parameters and design choices, the curing process must be considered. In this work, two different commercial metallic-based materials are cured at various temperatures to evaluate the differences in their microscopic and macroscopic behavior. The sensors were designed, developed, and evaluated for their temperature coefficient of resistance (TCR) at different curing temperatures using a programmable climatic chamber. A scanning electron microscope (SEM) has been used to microscopically inspect the sensing structures with respect to the different curing temperatures. The results show insightful correlations between the macroscopic and microscopic behavior of the used inks as well as the performance of the sensors. In particular, increasing the curing temperature decreased the room temperature resistance in all the samples by up to 70% and increased the sensitivity by up to 95%. These findings will help propose better processes as well as design choices for the development of printed resistive temperature sensors.

This study presents conductometric sensors based on Co3O4 nanowires for hydrogen detection at ppb levels. The nanowires are synthesized through thermal oxidation of a 50 nm cobalt layer, exhibiting diameters between 6–50 nm and lengths of 1–5 μm, primarily growing along the (311) direction of spinal Co3O4. Raman investigation reveals five characteristic peaks at 195, 482, 521, 620, and 692 cm−1, corresponding to symmetric phonon modes of crystalline Co3O4. Electron paramagnetic resonance measurements confirm the presence of a ferromagnetic phase, attributed to incomplete cobalt oxidation, which disappears after 8 h of thermal aging at 400 °C. Conductometry measurements are performed in the temperature range of 300–500 °C. At temperatures above 300 °C, sensors exhibit abnormal n‐type semiconducting behavior due to lattice oxygen's involvement in the hydrogen sensing mechanism. Operating at 450 °C in dry air, the sensor shows a higher 232% response to 100 ppm H2 compared to ethanol, acetone, methane, carbon monoxide, and nitrogen dioxide. Remarkably, the sensor maintains a consistent conductance baseline even under high humidity (90%) for 25 d, with three‐cycle repeatability. This distinctive gas‐sensing capability is attributed to the catalytic activity and elevated operating temperature.

We study second harmonic generation in dielectric nanocylinders as a function of the wavelength of the incident field and geometrical dimensions. Uncommonly, we consider a spectral range in which the emitted nonlinear signal is partially absorbed by the dielectric. Surprisingly, we reveal that the second harmonic efficiency does not decrease as the imaginary part of the complex dielectric refractive index increases. Indeed, the presence of higher order multipoles supported by the resonators at the fundamental wavelength can significantly boost the generated second harmonic signal even in the dielectric absorption spectral region achieving nonlinear efficiency of the same order of magnitude with respect to the lossless case.

Hyperspectral imaging has been flourished thanks to the huge investigation of the infrared spectrum from NIR to LWIR bands. The ternary InGaAs has been investigated herein in the context of studying the structural de-pendences of localization phenomenon by X-ray diffraction (XRD), scanning electron microscopy-energy dispersive X-ray (SEM-EDX), Raman, ultraviolet-visible (UV-vis), and photoluminescence (PL) techniques. Using metal-organic vapor phase epitaxy (MOVPE), we succeed to grow the InGaAs directly on InP substrate at 560 degrees C as an active layer with indium concentration exceeding the "golden" value (53%) to enlarge its cutoff absorption wavelength. X-ray diffraction proved a good crystallinity of the heterostructure with a sharp peak related to the thick substrate and another peak attributed to the thin layer of InGaAs. Moreover, an interfacial layer appeared at the logarithmic scale of XRD patterns and was confirmed by Raman analysis. The SEM-EDX revealed an average indium concentration (62%), almost the growth concentration. However, a cross-section compositional profile over the heterostructure showed an inhomogeneous distribution of the indium. This is predictable from the composition fluctuation in the indium-containing alloys and the volatility (surface segre-gation) of As (In). On the other side, the optical investigation of InGaAs demonstrated an anomalous behavior of luminescence versus temperature, manifested by the S-shape feature. This trend stems from the potential fluc-tuation induced by the non-uniform distribution of indium. A numerical simulation was developed based on the localized state ensemble (LSE) model to well-reproduce this anomaly by giving the best fitting parameters and comparing them with those calculated using the semi-empirical models (Vin similar to a and Pa center dot ssler). The results reported here will help in optimizing the epitaxy design of future InGaAs/InP and further studying its surface morphology and device performance.

Two-dimensional (2D) semiconducting heterojunction chemical sensors are in high demand because of their enhanced response, stability, and selectivity. However, fine-tuning heterojunctions using vapor deposition growth still needs further research. Our present study focuses on the ambient pressure chemical vapor deposition (CVD) synthesis of hexagonal tungsten sulfide-tungsten selenide (WS2-WSe2) p-p heterojunctions (as a 2D-2D arrangement). We use the liquid-phase exfoliation method to disperse bulk WS2 and WSe2 and decorate large flakes of WS2 with smaller WSe2 nanosheets in CVD. Electron microscopy and related surface investigations reveal their homogeneity on drop-casting. Two drops from the exfoliated heterojunction dispersion were drop-cast on a transducer to study the NO2 response and related sensing properties. The sensor showed long-term stability (>2 months), even at high humidity levels (40- 90%). The gas-sensing properties of this layered p-p heterojunction-based nanocomposite strongly suggest an affinity toward NO2 gas, leading to improved response, high stability, independent of humidity effects, and high selectivity.

Metal oxides nanowires and novel heterostructures are synthesized using different techniques and finally integrated into gas sensing platform. In particular, nanowires were synthesized using thermal oxidation and VLS mechanism. While, heterostructures i.e. NiO/ZnO (p-n) and NiO/NiWO 4 /WO 3 (p-p-n) were synthesized using VLS and VS mechanisms. Detailed investigations reveal the dependence of sensors selectivity and sensitivity on nanowires synthesis techniques. While, the superior performance of heterostructures as compared to bare nanowires presents the novel pathway to further enhance the performance of nanostructured gas sensors.