Showing papers by "Mahesh Kumar published in 2020"

Room-Temperature Gas Sensors Under Photoactivation: From Metal Oxides to 2D Materials

Abstract: Room-temperature gas sensors have aroused great attention in current gas sensor technology because of deemed demand of cheap, low power consumption and portable sensors for rapidly growing Internet of things applications. As an important approach, light illumination has been exploited for room-temperature operation with improving gas sensor’s attributes including sensitivity, speed and selectivity. This review provides an overview of the utilization of photoactivated nanomaterials in gas sensing field. First, recent advances in gas sensing of some exciting different nanostructures and hybrids of metal oxide semiconductors under light illumination are highlighted. Later, excellent gas sensing performance of emerging two-dimensional materials-based sensors under light illumination is discussed in details with proposed gas sensing mechanism. Originated impressive features from the interaction of photons with sensing materials are elucidated in the context of modulating sensing characteristics. Finally, the review concludes with key and constructive insights into current and future perspectives in the light-activated nanomaterials for optoelectronic gas sensor applications. Highlights: 1 Operations of metal oxide semiconductors gas sensors at room temperature under photoactivation are discussed.2 Emerging two-dimensional (2D) materials-based gas sensors under light illumination are summarized.3 The advantages and limitations of metal oxides and 2D-materials-based sensors in gas sensing at room temperature under photoactivation are highlighted.

Transition metal dichalcogenides-based flexible gas sensors

Abstract: In recent years, two-dimensional (2D) layered materials, such as MoS2, MoSe2, WS2, WSe2, SnS2, etc., have gained enormous interest in sensing applications with low-power consumption owing to their unique electrical, chemical, and mechanical properties. Among a broad range of sensors, rapid advances in flexible and wearable sensors have paved the way for smart sensing applications, including electronic skin (e-skin), home security, air- and health-monitoring, etc. This review aims at summarizing recent progress in energy-efficient flexible gas sensors by utilizing 2D transition metal dichalcogenides (TMDCs) materials. Main concepts and different approaches are overviewed for optimizing the gas sensing characteristics on flexible sensing platforms. The different strategies and challenges for incorporating 2D TMDCs materials into e-skin-oriented and e-textiles gas sensors are also highlighted. In addition, this review also includes the challenges and future perspectives for TMDCs materials in emerging flexible and wearable gas sensing field.

Highly sensitive and selective detection of acetone based on platinum sensitized porous tungsten oxide nanospheres

Abstract: Metal oxide semiconductors (MOS) are important candidates as the sensing layer for chemical gas sensors to detect volatile organic compounds (VOCs). However, the low surface activity limits the use of MOS in future high performance gas sensors. The design of susceptive nanostructures with prominent surface modification can be an effective strategy to achieve high sensitivity and high selectivity. Herein, Pt nanoparticles with a fine size of below 1 nm serving as the sensitizers are functionalized on porous W18O49 nanospheres via atomic layer deposition and investigated for acetone detection. The W18O49/Pt spheres combine the advantages of fast gas diffusion enabled by the porous shells and catalytic properties of Pt nanocatalysts. Gas sensing tests reveal that W18O49/Pt has a very high response to 20 ppm acetone (Ra/Rg = 85), which is ∼40 times higher than that of pure W18O49 (Ra/Rg = 2.1) at a low operating temperature of 180 °C. Meanwhile, W18O49/Pt shows fast response-recovery speed and good stability as well as excellent selectivity to acetone against other interfering gases. In addition, an ultrahigh sensitivity of 1.01 ppm−1 and a very low limit of detection of 52 ppb is obtained. The superior gas sensing performances of the W18O49/Pt materials indicates a strong potential for detection of biomarkers for exhaled breath diagnosis, and also paves the way to manipulate other metal oxide semiconductor-based sensors with high performances.

Real time detection of Hg2+ ions using MoS2 functionalized AlGaN/GaN high electron mobility transistor for water quality monitoring

Abstract: A sensor for highly sensitive, selective, and rapid determination of the trace amount of toxic Hg2+ ions is developed for the first-time using molybdenum disulfide (MoS2) functionalized AlGaN/GaN high electron mobility transistor (HEMT). The vertically aligned, flower-like MoS2 structures are synthesized through a simple hydrothermal route and applied on the gate region of AlGaN/GaN HEMT. The scanning electron microscopy, Raman spectroscopy, and X-ray diffraction are performed for structural characterization of MoS2. Further, the sensing of Hg2+ ions is performed by electrical characterizations of MoS2 functionalized AlGaN/GaN HEMT. The sensor showed an excellent sensitivity of 0.64 μA/ppb and detection limit of 0.01152 ppb with the rapid response time of 1.8 s. The sensor exhibits the linear range of detection from 0.1 ppb to 100 ppb and highly selective behavior towards Hg2+ ions. The results demonstrated that the MoS2 possess excellent Hg2+ ions capture property, that could be attributed to the complexation of Hg2+ ions with sulfur and the electrostatic interaction between MoS2 and Hg2+ ions alters the drain to source current (IDS) of the HEMT at a constant drain to source voltage (VDS). Therefore, the MoS2 based AlGaN/ GaN HEMT devices have a huge potential for next-generation ion sensing applications.

Development of ZnO nanostructure film for pH sensing application

Abstract: Nanostructured zinc oxide sensing film was deposited on the Si/SiO2/Pt substrate by the RF magnetron sputtering process. The film was characterized by FESEM (field-emission scanning electron microscope) and XRD (X-ray diffraction) for their morphology and structural analysis. The FESEM results show that the film morphology is in nanophase with an average nanostructure size of ~ 50 nm. XRD results show that the film is polycrystalline. The AFM (atomic force microscopy) and Raman spectroscopy were done to analyze the surface roughness and the structural properties of the film, respectively. FTIR (Fourier-transform infrared spectroscopy) was used to analyze the presence of ZnO. Further, the ZnO nanostructure film has been explored for pH sensing for pH (4–12). The sensitivity of the film was found to be 31.81 mV/pH. The drift characteristics of the film were also done to find out the stability of the film.

Davydov Splitting, Resonance Effect and Phonon Dynamics in CVD grown Layered MoS2.

Abstract: We present a comprehensive temperature dependent Raman measurements for horizontally aligned CVD grown layered MoS2 in a temperature range of 4 to 330 K under resonance condition. Our analysis of temperature dependent phonon frequency shift and linewidth suggest a finite role of three and four phonon anharmonic effect. We observed Davydov splitting of the out-of-plane (A1g ) and in-plane (E12g ) modes, attributed to the weak interlayer interaction, and reflected in the appearance of additional modes with decreasing temperature for both 3 layers and few layers system. We also observed that the number of Davydov splitting components are more in few layers as compared to 3L MoS2, suggesting it increases with increasing number of layers. Temperature evaluation of the Raman spectra shows that the Davydov splitting, especially for A1g mode, is very strong and well resolved at low temperature. We note that A1g mode shows splitting at low temperature, while E12g mode is splitted even at room temperature, and that suggests to prominent role of A1g mode to the interlayer interaction. Further, the temperature dependence tuning of resonance effect is observed, via almost sixty fold increase in the intensity of the phonon modes at low temperature.

Fabrication of Microsensor for Detection of Low-Concentration Formaldehyde Gas in Formalin-Treated Fish

Abstract: 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 $1.37\times 10^{-{3}}/^{\circ }\text{C}$ . Moreover, gold microheater exhibited long-term reliability under self-heating mode with a negligible resistance drift $^{-{1}}$ ) 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.

Anisotropic electron-photon-phonon coupling in layered MoS 2

Abstract: Transition metal dichalcogenide, MoS2 has attracted a lot of attention recently owing to its tunable visible range band gap, and anisotropic electronic and transport properties. Here, we report comprehensive inelastic light scattering measurements on both chemical vapor deposition grown (horizontally and vertically aligned) flakes, and mechanically exfoliated flakes of single crystal MoS2. We probe the anisotropic optical response by studying the polarization dependence intensity of the Raman active phonon modes as a function of different incident photon energy and flake thickness. Our polarization dependent Raman studies reveal strong anisotropic behavior reflected in the anomalous renormalization of the modes intensity as a function of flake thickness, phonons and photon energy. Our observations reflect the strong anisotropic light-matter interaction in this high crystalline symmetric layered MoS2 system, especially for the in-plane vibrations, crucial for understanding as well as future applications of these materials.

Ultrasensitive Detection of Mercury Ions Under UV Illumination of MoS 2 Functionalized AlGaN/GaN Transistor

Abstract: 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 $548.07~\mu \text{A}$ /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.

Highly Tunable Film Bulk Acoustic Wave Resonator Based on Pt/ZnO/Fe 65 Co 35 Thin Films

Abstract: 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.

Modulation of GmFAD3 expression alters responses to abiotic stress in soybean

Abstract: FAD3 play important roles in modulating membrane fluidity in response to various abiotic stresses. However, a comprehensive analysis of FAD3 in drought, salinity and heat stress tolerance is lacking in soybean. The present study assessed the functional role of fatty acid desaturase 3 to abiotic stress responses in soybean. We used Bean Pod Mottle Virus -based vector to alter expression of Glycine max omega-3 fatty acid desaturase . Higher levels of recombinant BPMV-GmFAD3 transcripts were detected in overexpressing soybean plants. Overexpression of GmFAD3 in soybean resulted in increased levels of jasmonic acid and higher expression of GmWRKY54 as compared to mock-inoculated, vector-infected and FAD3-silenced soybean plants under drought and salinity stress conditions. FAD3 overexpressing plants showed higher levels of chlorophyll content, leaf SPAD value, relative water content, chlorophyll fluorescence, transpiration rate, carbon assimilation rate, proline content and also cooler canopy under drought and salinity stress conditions as compared to mock-inoculated, vector-infected and FAD3-silenced soybean plants. Results from current study revealed that GmFAD3 overexpressing soybean plants exhibited drought and salinity stress tolerance although tolerance to heat stress was reduced. On the other hand, soybean plants silenced for GmFAD3 exhibited tolerance to heat stress, but were vulnerable to drought and salinity stress

Detection of cadmium ions Byg-C3N4 functionalization on AlGaN/GaN high electron mobility transistor

Abstract: In this study, a novel, highly sensitive AlGaN/ GaN high electron mobility transistor (HEMT) sensor is demonstrated for the detection of cadmium ions by the functionalization of graphitic carbon nitride (g-C3N4). The preparation of g-C3N4 was done using the pyrolysis process of urea. The prepared g-C3N4 was functionalized on Au gated AlGaN/ GaN HEMT and the sensing performance was observed by the measurement of electrical characteristics of the device. The sensitivity and limit of detection of the modified g-C3N4 based AlGaN/ GaN HEMT sensor was observed as 0.2606 µA/ppb and 0.533 ppb respectively. The observed limit of detection is very low than the standard guideline values of World Health Organization (WHO) for drinking water. Furthermore, using AlGaN/GaN HEMT theory, we show that the sensing response is very fast due to the availability of 2-D electron gas (2DEG) and very sensitive due to the change in gate potential. The mechanism suggests that the decrement in the drain current was due to the reduction of Cd2+ ions on the g-C3N4 surface which generates negative redox potential at the gate terminal while exposing the functionalized HEMT to Cd2+ ions. Hence, a simple, miniaturized, sensitive and real-time sensor has been developed using AlGaN/GaN HEMT functionalized by g-C3N4 to detect Cd2+ ions in an aqueous environment.

Ultrafast spectroscopy of Bi2Se3 topological insulator

Abstract: We investigate the ultrafast transient absorption spectrum of Bi2Se3 topological insulator. Bi2Se3 single crystal is grown through conventional solid-state reaction routevia self-flux method. The structural properties have been studied in terms of high-resolution Powder X-ray Diffraction (PXRD). Detailed Rietveld analysis of PXRD of the crystal showed that sample is crystallized in the rhombohedral crystal structure with a space group of R-3m, and the lattice parameters are a=b=4.14(2)A and c=28.7010(7)A. Scanning Electron Microscopy (SEM) result shows perfectly crystalline structure with layered type morphology which evidenced from surface XRD. Energy Dispersive Spectroscopy (EDS) analysis determined quantitative amounts of the constituent atoms, found to be very close to their stoichiometric ratio. Further the fluence dependent nonlinear behaviour is studied by means of ultrafast transient absorption spectroscopy. The ultrafast spectroscopy also predicts the capability of this single crystal to generate Terahertz (THz) radiations (T-rays).

Gamma Radiation Detection Response of Pt/PZT/SRO Based Capacitor for Dosimetry Application

Abstract: Radiation induced changes in the electrical properties of PbZrTiO3 (PZT) thin films have been studied for dosimetry application. The radiation detection was based on radiation induced changes in the electrical properties under the influence of gamma radiation. Epitaxial heterostructure of ferroelectric PbZr0.52 Ti0.48O3 (001)/SrRuO3 (SRO) were grown on single crystal SrTiO3 (001) substrates by pulsed laser deposition and platinum (Pt) electrode was deposited on top of the PZT film. The maximum capacitance of the heteroepitaxial capacitor devices was $\approx ~25$ pF with a corresponding small leakage current. The effect of gamma ( $\gamma $ -ray) irradiation on the intrinsic electrical behavior of the Lead Zirconate Titanate (PZT) capacitor devices were explored in form of the current–voltage (I–V) and capacitance–voltage (C–V) properties. The PZT devices were exposed to a 60Co Gamma source with 2.8 kGy/h dose rate from 0 kGy to 400 kGy doses. Gamma radiation induced broadening was observed in full width half maxima (FWHM) of the x-ray diffraction (00l) peak with the increasing gamma doses. All devices showed a consistence changes in conductance and capacitance with increasing gamma doses. The results demonstrated linear relationship in electrical response of PZT thin-film capacitors as a function of gamma doses. The device showed significant changes in the values of current and capacitance with the increase in dose up to 400 kGy and are therefore suitable for high-dose dosimetry applications.

Gallium nitride nanocrystal formation in Si 3 N 4 matrix by ion synthesis

Abstract: Synthesis of nanoparticles in insulators attracts tremendous attention due to their unique electrical and optical properties. Here, the gallium (Ga) and gallium nitride (GaN) nanoclusters have been synthesized in the silicon nitride matrix by sequential ion implantation (gallium and nitrogen ions) followed by either furnace annealing (FA) or rapid thermal annealing (RTA). The presence of Ga and GaN nanoclusters has been confirmed by Fourier-transform infrared, Raman and X-ray photoelectron spectroscopy. Thereafter, the effect of RTA and FA on the conduction of charge carriers has been studied for the fabricated devices. It is found from the current–voltage measurements that the carrier transport is controlled by the space charge limited current conduction mechanism, and the observed values of parameter m (trap density and the distribution of localized state) for the FA and RTA devices are ~2 and ~4.1, respectively. This reveals that more defects are formed in the RTA device and that FA provides better performance than RTA from the viewpoint of opto- and nano-electronic applications.

Anisotropic Electron-Photon-Phonon Coupling in Layered MoS2

Abstract: Transition metal dichalcogenide, especially MoS2 has attracted lot of attention recently owing to its tunable visible range band gap and anisotropic electronic and transport properties. Here, we report a comprehensive inelastic light scattering measurements on CVD grown (horizontally and vertically aligned flakes) as well as single crystal flakes of MoS2, probing the anisotropic optical response via studying the polarization dependence intensity of the Raman active phonon modes as a function of different incident photon energy and flake thickness. Our polarization dependent Raman studies intriguingly revealed strong anisotropic behavior reflected in the anomalous renormalization of the modes intensity as a function of flake thickness, phonons and photon energy. Our observations reflects the strong anisotropic light-matter interaction in this high crystalline symmetric layered MoS2 system especially for the in-plane vibrations, which is crucial for understanding as well application of these materials for future application such as optoelectronic applications.