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In this article, we report the synthesis techniques of ZnO nanoparticles (NPs) in open air atmosphere by pulse laser ablation (PLA) method using solid ZnO polycrystalline palette followed by fabrication of formaldehyde (HCHO) sensor. The crystalline phase and morphology of the obtained ZnO NPs were studied by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM), respectively. The XRD patterns showed that the NPs were polycrystalline structure with good crystallinity. The FESEM images revealed that the NPs were spherical in shape and loosely agglomerated. The average diameter of the NPs was in the range of 30–43 nm. Moreover, the ZnO NPs-based sensor exhibited excellent formaldehyde sensing performance at a temperature of 350 °C. The sensor exhibited a gas response of about 5.2 toward 300 ppm formaldehyde with 25 s response and 12 s recovery time. Furthermore, the ZnO NPs-based sensor exhibited excellent reliability and reproducibility to formaldehyde. On the other hand, the sensor showed high sensitivity of about 0.2% ppm −1 to formaldehyde with a 50 ppm lower detection limit. In addition, the sensor showed an excellent linear relationship (R2 = 0.7948) between the response and the concentration of formaldehyde in the range of 50–400 ppm. This work demonstrates that PLA in open air is a rapid and cost-effective method for synthesizing metal oxide NPs for gas-sensing applications without the need for wet chemical routes. [ABSTRACT FROM AUTHOR]

We have developed a highly tunable film bulk acoustic wave resonator (TFBAR) using magnetostrictive (MS) Fe65Co35 thin films in acoustic layer stack. The resonator acoustic layer stack consists of Pt/ZnO/Fe65Co35 layers to tune the devices. Due to $\Delta {E}$ effect, TFBAR resonance frequency was up-shifted ~106.9 MHz (4.91%) in the presence of 2-kOe magnetic field. From experimental measurement, $\Delta {E}$ enhancement was estimated to be ~35 GPa. Further, it is observed that return loss (${S}_{{11}}$), phase response, and quality factor were improved in the presence of magnetic field. This improvement is due to the field-induced stiffness in the magnetic layer. Equivalent-modified Butterworth–Van Dyke (mBVD) circuit model was developed and fit with the experimental data, and circuit parameters were extracted. The proposed resonator is compact, low loss, power efficient, and highly tunable. This method also facilitates a new method of tuning FBAR devices using MS thin films. [ABSTRACT FROM AUTHOR]

This article reported about the ultraviolet (UV) radiation effect on the resonance frequency response of a AT-cut piezoelectric quartz crystal. A large resonance frequency upshift was observed when the quartz crystal was irradiated by UV light of 355-nm wavelength using a Q-switched pulsed Nd:YVO4 UV laser. The dynamic frequency response behavior was systematically investigated by illuminating the quartz crystal with UV light in which the UV intensity was varied with time in staircase- and linear pulse-shaped patterns. From the experimental analysis, we measured the limit of detection and the sensitivity of the quartz crystal, which are about 0.5 mW/cm2 and 0.706 Hz/(mW/cm2), respectively. For a constant UV irradiation, a moderate response (<10 s) and recovery (<10 s) times were achieved during the on and off cycles of the UV light. The short-term repeatability and maximum operating limit of AT-cut quartz crystal were also further studied upon exposure to UV light with different intensities. In this work, we not only demonstrate the impact of UV irradiation on quartz crystal but also discuss the mechanism of upshift in resonance frequency upon exposure to UV light. This study shows the applicability of quartz crystal for the detection of UV light. [ABSTRACT FROM AUTHOR]

Here, an ultrafast direct laser patterning technique to fabricate a low-cost microsensor and its application for formaldehyde detection are reported. The patterns of microheater and interdigitated electrodes (IDEs) were realized using laser micromachining techniques by ablation of gold thin film on alumina substrate. The thin film of gold microheater showed good stability up to 300 °C with a fast response time of 80 s and temperature coefficient of resistance (TCR) was calculated as 1.37 × 10−3/°C. Moreover, gold microheater exhibited long-term reliability under self-heating mode with a negligible resistance drift < 0.5% over a period of 330 h at 250 °C through consuming low power with a heating efficiency of 0.23 °C/mW. Thermal imaging camera revealed the uniform temperature distribution with negligible heat gradient profile over the whole microsensor platform. To state-of-the-art gas sensing application of this coplanar sensing platform, a nanostructured SnO2 was deposited on IDE, which exhibited high sensitivity (13.96% ppm−1) to formaldehyde even to detect sub-ppm concentrations with fast response (32 s) and recovery kinetics (72 s). Moreover, the microsensor was also used on-site rapid screening for the detection and quantification of formaldehyde concentration in formalin-treated fish sample. [ABSTRACT FROM AUTHOR]

In this work, the MoS2 functionalized AlGaN/GaN high-electron mobility transistor (HEMT) was utilized for the first time to detect toxic mercury (Hg2+) ions under ultraviolet (UV) illumination. The AlGaN/GaN HEMT was fabricated on the sapphire substrate, and corresponding structural and electrical properties were investigated. Subsequently, the optimization of MoS2 concentration for device functionalization was carried out by performing sensing analysis of Hg2+ ions on three devices, and it was observed that the 20 mg/mL concentration of MoS2 is optimum for the detection of Hg2+ ions. Furthermore, the detection of Hg2+ ions was performed under UV exposure, where the developed sensor showed much-improved sensitivity of 548.07~μ A/ppb compared with normal light. The comparative analysis indicates the increase of three orders of magnitude in sensitivity under UV irradiation, and it is the highest sensitivity ever observed by the AlGaN/GaN HEMT sensor for Hg2+ ion detection. Moreover, the sensor also exhibits the limit of detection (LoD) of 6.14 parts per trillion (ppt) that is much lower than the World Health Organization (WHO) standard limit for Hg2+ ions in drinking water. Due to the photoexcitation process, the generation of electron–hole pairs provides more binding sites on the MoS2 surface, which results in the ultrasensitive detection of the Hg2+ ions at trace and ultratrace levels. [ABSTRACT FROM AUTHOR]

When exploring the charge transport in the MoS2/Si heterojunction, it is imperative to understand the contribution of different carrier interactions and scattering mechanisms in the conduction process. Here, we have demonstrated an ultrasensitive photodetector based on MoS2/Si (for both p-type and n-type Si) van der Walls (vdW) heterojunction, which provides a high photoresponsivity of greater than 103 A/W along with a large detectivity of ≈ 1012 Jones (Jones = $\text{cm} \cdot \text{Hz}^{ {1/2}} \cdot \text{W}^{-1}$). This high photoresponsivity is attributed to the high absorption rate of incident photons and large current carrying capacity of a few layer MoS2. The tuning of barrier height at the MoS2/n-Si interface with photoexcitation of different wavelengths was interpreted by using Bardeen’s model. The increase in carrier density due to the photon energy results in a reduction of barrier height at the heterojunction. Because of increase in carrier density with wavelength, it was observed that the inverse Auger process prevails at higher wavelength for the relaxation of photoinduced charge carriers at the MoS2/Si interface over other scattering mechanisms. Our obtained results unveil the great potential of the MoS2/Si vdW heterojunction that may pave the way for new generation photodetectors. [ABSTRACT FROM AUTHOR]

We report neutron irradiation resistance of the barium strontium titanate (BST) thin-film-based varactor under different neutron fluences. BST thin films were deposited on sapphire substrate by RF magnetron sputtering and gold interdigital capacitor (IDC) electrodes were patterned with the photolithography technique. Capacitance-voltage ( $C$ – $V$ ) and leakage current characteristics were measured at several neutron fluences. A small change in capacitance is observed at different fluences. The changes are attributed to the radiation-induced defect dipoles and other charged defects, which serve as effective domain wall pinning sites. We supplemented this macroscopic $C$ – $V$ behavior of BST varactor with investigation through X-ray diffraction and atomic force microscopy for their structural and morphological changes, respectively. This paper shows that BST varactor can be used in neutron environment due to its high tolerance. [ABSTRACT FROM AUTHOR]

Ba0.5Sr0.5TiO_3 (BST) thin films were deposited on sapphire substrate by RF magnetron sputtering techniques and interdigital capacitor (IDC) structures were fabricated using photolithography. Gamma irradiation induced changes of the BST based tunable capacitor have been investigated under various doses from 0 kGy to 600 kGy. Structural and surface morphological studies have been carried out for un-irradiated and irradiated film and revealed that the grain sizes and crystallinity are strongly depended on gamma irradiation doses. The leakage current is increased with increasing gamma irradiation doses due to creation of charge carriers and large numbers of defect in close proximity, provided path for charge carriers. The capacitance of the IDC devices decreased with increasing gamma dose up to 50 kGy and thereafter capacitance gradually increased with radiation doses and reached higher than the un-irradiated device at 600 kGy for 1 MHz frequency. The observed tunability (\sim 25\% ) of the un-irradiated device was found nearly constant with gamma irradiation doses. This study shows that gamma ray induced defects play important role to the electrical properties of the devices and the BST based devices are highly resistant to gamma radiation, which reflects possible use in space and nuclear applications. [ABSTRACT FROM AUTHOR]

In this paper, a xenon-filled coaxial dielectric barrier discharge (DBD) has been studied to understand the high-pressure nonequilibrium nonthermal plasma discharge. A quartz coaxial DBD tube (ID: 6 mm, OD: 12 mm) at 400-mbar xenon-filled pressure has been used in the experiment. A unipolar pulselike voltage up to a -6-kV peak working at 30 kHz has been applied to the discharge electrodes for the generation of microdischarges. A single discharge is observed per applied voltage pulse. Visual images of the discharge and electrical waveform confirm the diffused-type discharges. The knowledge obtained by dynamic processes of DBDs in the discharge gap explains quantitatively the mechanism that is obtained in the ignition, development, and extinction of DBDs. The behavior of different discharge parameters has also been analyzed. From the experimental results and equivalent electrical circuit, the dynamic nature of equivalent capacitance has been reported. The relative intensity analysis of the Xe peak in the optical emission spectra (172 nm) has also been carried out for different supplied powers, and it is found that the radiation power has increased with supplied power. [ABSTRACT FROM AUTHOR]