In this work, we propose a facile, low-cost, and cleanroom-free approach for fabricating flexible capacitive pressure sensors based on paintable Ag electrodes on stationery paper substrates (Ag-paper electrodes) and a random microstructured polydimethylsiloxane (PDMS) dielectric layer transferred from emery paper. COMSOL Multiphysics simulations and experimental investigations suggest that the pressure sensor with random microstructured PDMS dielectric layer performs better than the sensor with ordered micropyramidal dielectric layer. The developed Ag-paper electrode and random microstructured PDMS dielectric layer-based pressure sensors are workable in a wide pressure range (up to 630 kPa) and exhibit a high sensitivity of 0.132 kPa-1 up to 1 kPa, low hysteresis (6.6%) with loading-unloading of similar to 500 kPa pressure, high stability during a similar to 5250 cyclic test, and the ability to sense a low pressure of similar to 27 Pa. The developed sensor also successfully transduces arterial pulse wave forms when it is properly attached to the wrist. Using the proposed process, a flexible capacitive pressure sensor matrix of 4 x 4 array is also successfully developed for single- and multiple-point pressure mapping with minimal cross-talk. The proposed sensor process is simple and inexpensive to implement, and offers spatial pressure mapping for e-skin applications.

Rapid development of flexible pressure sensors is indispensable in electronic skin to have the sensing capability to static and dynamic pressures. Besides high sensitivity and low hysteresis, the high flexibility and stability of these sensors are of paramount importance owing to the application requirement of conformable pressure mapping and rugged structure. Here, we describe a novel approach for highly flexible capacitive pressure sensors with engineered stable interfaces employing PDMS-based substrates and a micropyramidal dielectric layer, Au electrodes, and molecular adhesive. The sensor/matrix stack consists of five interfaces with strong interfacial adhesion achieved using MPTMS molecular adhesive and a partially cured PDMS lamination layer. A highly flexible capacitive pressure sensor capable of a wide pressure sensing range (up to 550 kPa) is developed with a high sensitivity (46.6 MPa-1 in ≤1 kPa), capability to sense pressure as low as 27 Pa, low hysteresis (4.05%), and high stability for large pressures (11,400 cycles @ 250 kPa). The sensor is successfully demonstrated for arterial pulse signal acquisition and performing a press task when attached on the forefinger. A flexible pressure sensor matrix of 4 × 4 pixels is developed. It can be flexed or crumpled; hence, it is conformably attached on a planar surface and a non-planar 3D-printed surface for single-point and multipoint pressure sensing. The sensor exhibited a maximum shear strain of 2.27 N before breakage. These highly flexible pressure sensor and matrix are also compared with a semi-flexible IO-PET electrode-based pressure sensor and matrix to clearly bring out the flexibility and stability advantages. The proposed process is simple and scalable and offers a conformably stable pressure sensor matrix for electronic skin development.

In the modern world of small-scale electronics, touch sensors unfold many numerous novel interaction techniques and other possibilities. Self-powered and flexible sensors are the future and this is where triboelectric nanogenerator-based touch sensors come. Here, surface engineering provided sufficient output performance such as 25 V, 0.4 mA/m2, and 16 mW/m2, for a Polydimethylsiloxane (PDMS) and Cellulose Acetate based TENG with micrometer separation distance. Additionally, the effect of surface modification is also quantified for better understanding. Moreover, the fabricated TENG device with micropatterned contact surfaces shows excellent tactile sensing capability of detecting and distinguishing forces of ∼0.05 N and exhibited a sensitivity of ∼3.67 V/N for small forces (<1 N).

Clinical diagnostics for SARS-CoV-2 infection usually comprises the sampling of throat or nasopharyngeal swabs that are invasive and create patient discomfort. Hence, saliva is attempted as a sample of choice for the management of COVID-19 outbreaks that cripples the global healthcare system. Although limited by the risk of eliciting false-negative and positive results, tedious test procedures, requirement of specialized laboratories, and expensive reagents, nucleic acid-based tests remain the gold standard for COVID-19 diagnostics. However, genetic diversity of the virus due to rapid mutations limits the efficiency of nucleic acid-based tests. Herein, we have demonstrated the simplest screening modality based on label-free surface enhanced Raman scattering (LF-SERS) for scrutinizing the SARS-CoV-2-mediated molecular-level changes of the saliva samples among healthy, COVID-19 infected and COVID-19 recovered subjects. Moreover, our LF-SERS technique enabled to differentiate the three classes of corona virus spike protein derived from SARS-CoV-2, SARS-CoV and MERS-CoV. Raman spectral data was further decoded, segregated and effectively managed with the aid of machine learning algorithms. The classification models built upon biochemical signature-based discrimination method of the COVID-19 condition from the patient saliva ensured high accuracy, specificity, and sensitivity. The trained support vector machine (SVM) classifier achieved a prediction accuracy of 95% and F1-score of 94.73%, and 95.28% for healthy and COVID-19 infected patients respectively. The current approach not only differentiate SARS-CoV-2 infection with healthy controls but also predicted a distinct fingerprint for different stages of patient recovery. Employing portable hand-held Raman spectrophotometer as the instrument and saliva as the sample of choice will guarantee a rapid and non-invasive diagnostic strategy to warrant or assure patient comfort and large-scale population screening for SARS-CoV-2 infection and monitoring the recovery process.

Triboelectric nanogenerators are emerging mechanical energy harvesting devices in the era of the Internet of Things (IoT) for powering small-scale electronic devices or functioning as state-of-the-art self-powered sensors. Furthermore, observing vibration patterns from different electronic gadgets helps in assessing the health of the gadgets and also allows to detect the downtime as well as faults pre-emptively. Here, a triboelectric nano generator based on electrospun cellulose acetate nanofibers and surface modified PDMS is fabricated for powering commercial sensors. In addition, the effect of surface patterning on PDMS film such as arrays of micropyramid and microdome structures on the output characteristics of TENG has been systematically investigated. The PDMS with micropyramidal arrays in combination with electrospun cellulose acetate nanofibers showed a massive enhancement (~180 times) in the power density of TENG, as compared to the flat PDMS film based device. The fabricated facile and flexible TENG with micropyramidal surface modification on PDMS can generate an output voltage of 400 V, short circuit current of 3 mA/m(2) and peak power density of 0.9 W/m(2) respectively. In addition, with a little tweak in the structure, the same cellulose acetate nanofiber-PDMS based TENG is transformed into an active self-powered vibration sensor. Utilizing this, the vibration profile of an electric-sewing machine is mapped under various frequencies of operation. Additionally, anomalous vibrational behaviours from different electronic gadgets such as hard disks and computer fans, as a result of mechanical imbalances, are also detected using the self-powered triboelectric vibrational sensor.

The development of reproducible flexible capacitive pressure sensors with tunable sensitivity is vital for electronic-skin applications. Herein, we propose an improved fabrication process of flexible capacitive pressure sensors by completely eliminating the lamination layer step without compromising on sensor performance. For this, a facile isotropic etching process is also developed for silicon mold with inverted microdome like structures. Flexible capacitive pressure sensors having a similar to 81 mu m thick microdome like structured PDMS dielectric layer, and with and without a lamination layer are fabricated. Sensor having no lamination layer is outperformed the sensor with a lamination layer in a wide pressure range (< 500 kPa), exhibited stable relative capacitance (Delta C/Co) up to 1000 cycles, and able to sense low pressure (similar to 55 Pa). The developed sensors are also used for in-vivo arterial pulse waveform monitoring when properly attached on wrist. The single lap shear adhesion test of sensors indicates that the sensor having no lamination layer exhibited maximum shear stress of similar to 2.7 N (before breakage) compared to the sensor with lamination layer (similar to 1.9 N). The COMSOL simulations also support our experimental findings with large Delta C/C-o in the case of sensor having no lamination layer. This study presents a novel process for facile preparation of microdome like structures and improved adhesion between different layers of flexible capacitive pressure sensors, which is important for reproducible pressure sensors. (c) 2022 Elsevier B.V. All rights reserved.

On the 4H-SiC substrate, C-face and Si-face oxide layers have been grown by thermal oxidation process and sputtering. The thermal oxidation temperature dependence of 4H-silicon carbide (SiC) is systematically investigated using capacitance-voltage (C–V) measurements. The oxidation quality and thickness vary according to the temperature and time duration of the thermal oxidation. The layers’ thicknesses are determined by atomic force microscopy (AFM), and the temperature range is between 800°C and 1110 °C. The primary reason to fabricate the Metal-Oxide-Silicon (MOS) capacitor is to know the thermal oxidation process and a working principle. In this paper, we optimize a thermal oxidation process and fabricate the MOS structure. Then we determine the various parameters such as flat band voltage (V f b ), Inversion threshold voltage (V t ), Surface depletion capacitance (C dep ), Oxide capacitance (C ox ), the total capacitance of the device (C o ), doping concentration (N d ), Depletion width (X d ), Maximum depletion width (X dt ) and Interface trap density (D it ). Finally, we analyze and discuss the MOS capacitance.

Recently, microstructured PDMS based pressure sensors are explored as a potential candidate in bio-signal monitoring and electronic-skin applications. Here, we have fabricated capacitive pressure sensors with micro-pyramidal PDMS dielectric thin films, and studied the influence of surface coverage and arrangement of these structures on the sensitivity of pressure sensor devices. Pressure sensor with periodically arranged pyramids (surface coverage: 36.7%) exhibited sensitivity of 0.16 kPa(-1) in <1 kPa and 0.04 kPa(-1) in 0.75-2.5 kPa pressure range, whereas the pressure sensor with diagonally arranged pyramids (surface coverage: 45.2%) exhibited sensitivity of 0.1 kPa(-1) in <1 kPa and 0.05 kPa(-1) in 0.75-2.5 kPa pressure range respectively. Despite having large surface coverage, pressure sensor with the diagonally arranged pyramids exhibited high sensitivity (0.05 kPa(-1)) in 1-2.5 kPa pressure range than the periodically arranged pyramids owing to the large displacement and increase in effective permittivity of diagonally arranged pyramids. Simulation studies on the developed pressure sensor structures using Ansys and Opera also confirmed the relatively large displacement and Delta C/Co in diagonally arranged pyramids compared to periodically arranged pyramids having slightly low surface coverage. Experimental results and simulations demonstrate that the sensitivity of these kinds of pressure sensors can also be tuned by arrangement of pyramids. Also, the developed flexible capacitive pressure sensor is demonstrated for in-vivo, real-time pulse wave form recording. (C) 2020 Elsevier B.V. All rights reserved.

Here, we report on the experimental and theoretical understanding of seamless junction Au mesh network flexible transparent heaters. Three Au mesh transparent conductors (TCs) are fabricated using the photolithography-etching process to compare the influence of metal surface coverage on their electrical and thermal performance. The fabricated mesh networks are quite transparent (T similar to 80%) in the 400-900 nm spectral region and exhibit small variation in sheet resistance (Delta R-max similar to 0.12, 0.05, and 0.22 Omega square(-1)) under different bending radii (minimum radii of similar to 7.5 mm). The Au mesh with large surface coverage (i.e. similar to 4.8%) exhibited the highest figure of merit (1035), and the Au mesh with small surface coverage (i.e. similar to 2.5%), which eventually tested as a heater, exhibited the highest thermal efficiency (i.e. 249 degrees C/(W/cm(2))) and temperature of 150 degrees C at the lowest input power (0.5 W cm(-2)). A 1D analytical heat transfer model is developed for quick estimation of temperature of heater samples. The thermal simulation of heaters is carried out using an ANSYS tool. The experimental, simulation and 1D analytical results are compared and validated, revealing that the simulation results are more aligned with experimental results. The flexible TCs with short response time and high thermal resistance are very useful in various flexible heating applications.

Graphene, which is mechanically flexible, electrically conductive, and optically nearly transparent, is a promising contact material in flexible electronics and photovoltaic devices. In the present investigation, methods to obtain graphene film on silicon wafer and fabricate a graphene based Schottky solar cell have been presented. Scrutiny of atomic force microscopy (AFM) and Raman spectroscopy elucidates the formation of thin layer graphene on silicon. Further, I-V (current-voltage) characteristics of Schottky junction (graphene/silicon junction) have also been studied and presented.

Notrogen dioxide (NO2) gas sensors are important for the safety of environment and living beings. N02 gas is a filthy-smelling air pollutant from fossil fuel combustion, road traffic, etc and is one of the cancers causing pollutants [I]. Gas sensors based on Carbon Nanotubes (CNTs) are used for improving the gas sensitivity due to high surface area to interact with target gas molecules [2]. Basically, in CNTs based gas sensors, resistance changes when a particular gas molecules are adsorbed on the surface from the surroundings [3]. CNTs gas sensors are classified as chemi-resistive, chemi-capacitive and chemi- field effect transistor [4]. The simplest sensor architecture is the chemiresistor, which consists of two metal electrodes connected by a SWCNT film. Here, we report fabrication and characterization of SWCNT cherniresistive sensor for N02. Functionalization of SWCNTs is performed by oxidation in nitric acid (HN03) for 3 hours. To confirm the attachment of -COOH group on SWCNTs, FTIR spectroscopy (Bruker optic tensor 37) was carried out. A SWCNT-COOH dispersion of 3mg/mL was prepared in DI water by using horn type sonicator (model VCX 750). A thin film of functionalized SWCNTs dispersion was drop-cast over fabricated gold micro electrode structure on silicon substrate with the help of l .5µL micropipette. The SWCNT chemiresistor was kept at room temperature until the DI water evaporates, followed by drying at a temperature of I 00 °C. The fabricated gas sensor was exposed to N02 in an enclosed chamber and the response was measured at concentrations up to 50 ppm at room temperature. Sensitivity of fabricated chemiresistor was measured at different concentrations from IO ppm to 50 ppm. Initially sensor was purged with dry air for 15 minute and initial resistance was measured 4.24 kohm. Exposure time of dry air and N02 gas was 5 minute each. Resistance of chemiresistor decreases in presence ofN02 gas at IO ppm and recovers partially to its original value after removal N02. Variation of sensor resistance with NO2 concentration (10ppm-50ppm). SWCNTs chemiresistor shows resistance variations from 4.24 kohm to 2.89 kohm when exposed to N02 concentration from IO ppm to 50 ppm. Corresponding calculated sensitivities are 12.16% at IO ppm and 31.88% at 50 ppm. This study shows the potential of SWCNTs for room temperature N02 sensor applications in environmental monitoring.

The quasi-steady state photo conductance technique is employed to probe effective minority carrier lifetime (τeff) modifications after integrating silver nanoparticles (Ag NPs) on n-type and p-type silicon wafers with a native oxide surface. Our observations reveal that τeff modification is very sensitive to Ag NPs size, surface coverage and also wafer type. With an optimized Ag NPs, τeff is enhanced from 4.4 μs to 10 μs for a p-type silicon wafer, and from 8.1 μs to 14 μs for an n-type silicon wafer. We attributed the enhancement in τeff to the partial field effect passivation of the silicon surface by the surface plasmon resonance near-fields of Ag NPs after excitation. Our investigations demonstrate that an optimized Ag NPs on any silicon wafer with a native oxide layer can work as both a light trapping and a surface-passivating layer.

Silicon solar cells with different front texturization are used for understanding pyramidal size influence on plasmonic light trapping. Cells with different pyramidal heights and widths have shown strong light back scattering in the surface plasmon resonance (SPR) region and minimal light forward scattering in the off-resonance region of silver nanoparticles (NPs). On the other hand, cell surface with similar pyramidal heights and widths has shown reduced back scattering in the SPR region, as well as enhanced light forward scattering in the off-resonance region of NPs with good optical impedance matching. The reason for these types of light interaction with NPs (nanoscale) and textured silicon (micrometer-scale) is explained, and plasmonic textured silicon solar cell performance with different pyramidal sizes using quantum efficiency measurements is verified.

Quantum efficiency and impedance spectroscopy tools are employed for understanding the influence of parasitic absorption losses and partial field effect surface passivation by the silver nanoparticles (Ag NPs) on electrical properties of textured silicon solar cells without and with Si3N4 spacer layer. The parasitic absorption losses from Ag NPs reduced the internal quantum efficiency near the surface plasmon resonance region. The passive components like; series and parallel resistances, chemical capacitance of solar cells without and with Ag NPs are estimated after fitting impedance semicircles, which are further used for estimating effective carrier lifetime (tau(eff)) values. Under AM1.5G illumination, cells with Si3N4 spacer layer showed a large decrease in the tau(eff) due to the strong parasitic absorption losses from the Ag NPs. But, the cells without Si3N4 spacer layer showed a small decrease in the tau(eff) due to the reduced surface recombination after partial field effect passivation from near-fields of Ag NPs' surface plasmon resonances on the emitter surface. (C) 2016 Elsevier Ltd. All rights reserved.

We report the synthesis of graphene oxide colloid, and its transformation as a few-layer graphene oxide (GO) thin film on a glass and silicon substrates using a spin coating technique for plasmonic substrates. Annealed graphene oxide (AGO) thin films of variable thicknesses are used as substrates for silver nanoparticles (Ag NPs) formation. In surface morphological study, we observed modified Ag NPs growth by the presence of AGO thin film on glass and silicon substrates when compared to substrates without AGO film. Well-separated and worm-like Ag NPs formation was observed due to the high surface diffusion of Ag provided by the underlying AGO thin film; in contrast, dense and spheroid-like NPs formation was observed on uncoated substrates. Silver NPs prepared on AGO thin films are characterized by transmittance measurements on glass substrates and total reflectance measurements on silicon substrates from 200 to 1200 nm. We observed AGO film thickness dependent quadrupolar resonances of Ag NPs and total reflectance at longer wavelengths (> 800 nm) region, while dipolar resonances are insensitive to the variation of AGO film thickness. The modified absorption/scattering profiles and intensities are explained by surface plasmon dipolar and quadrupolar resonance mode confinement variation at the AGO thin film-nanoparticles interface.

Here, we report average reflectance reduction of ∼8% in wavelength range of 300–1100 nm after coupling surface plasmon resonances (SPRs) of silver nanoparticles (NPs) to textured silicon (T-Si) surface. The enhancement of photocurrent from T-Si solar cell in off-resonant SPR region observed due to better radiative efficiency of NPs leading to outflow of scattered far-field into silicon maximized power generating electrons. Improvement in series resistance, fill factor, and open-circuit voltage (insensitive NPs size and morphology) are also observed with NPs along with photocurrent enhancement (sensitive to NPs sizes), which resulted cell efficiency enhancement from 4.49% to 6.42% for large area of 12.24 cm2.

We report a simple method to mitigate ultra-violet (UV) degradation in TiO2 based perovskite solar cells (PSC) using a transparent luminescent down-shifting (DS) YVO4:Eu3+ nano-phosphor layer. The PSC coated with DS phosphor showed an improvement in stability under prolonged illumination retaining more than 50% of its initial efficiency, whereas PSC without the phosphor layer degraded to ∼35% of its initial value. The phosphor layer also provided ∼8.5% enhancement in photocurrent due to DS of incident UV photons into additional red photons. YVO4:Eu3+ layer thus served a bi-functional role in PSC by reducing photo-degradation as well as enhancing energy conversion efficiency.

Silver nanoparticles (Ag NPs) of various sizes and concentration were integrated on textured silicon solar cells for further confinement of incident light, generated photocurrent modifications were investigated using spectrally resolved short-circuit current measurements. Internal quantum efficiency (IQE) spectra were used for quantifying the effective minority carrier diffusion lengths (Leff) of plasmonic cells in the long wavelength region (850 < λ < 1020 nm). The Leff of an optimized plasmonic solar cell enhanced to 431 µm compared to 338 µm of the bare cell, which is due to interacting Ag NPs' scattered fields, leading to enhanced light absorption in the plasmonic cell. Despite the enhanced Leff values, the overall generated photocurrent reduced with Ag NPs which is due to the significant losses near the surface plasmon resonant region. Reduced IQE of plasmonic cells near and below the surface plasmon resonant region is due to size-dependent parasitic absorption and enhanced back scattering of Ag NPs, and a modified surface recombination process due to Ag NPs' strong near-fields.

Gold nanoparticles (GNPs) of various sizes (range of 5-85 nm) were synthesized and various concentrations (range of 0.1-0.7 wt%) were blended with TiO2 nanopowder for fabricating conformal Ti0(2) Au nanocomposite (NC) films. In optical and electrical studies, we have observed that GNPs of sizes in the range of 15-40 nm, and concentrations in the range of 0.1-0.25 wt% offer the maximum enhancement in dye-sensitized solar cell (DSSC) performance due to the enhanced near-field excitation of dye molecules along with incident light far-field. The best plasmonic DSSC performance was observed with 0.24 wt% of similar to 36 nm GNPs with an enhancement of 18.44% in photocurrent. Despite the strong absorptance with nm GNPs, only a modest improvement in photovoltaic behavior was observed due to plasmonic heating effects of strongly localized near-fields instead of dye molecules excitation. With similar to 85 nm GNPs, we have observed minimal enhancement in device performance due to large scattering cross-sections, which result in the incident energy to be sent back to the far-field after interacting with GNPs instead of localizing around them. The optimized size and concentration of GNPs were also used for fabricating high efficiency DSSCs using commercial TiO2 paste and two different dyes (N719 and N749) in order to study the effects of apparent extinction coefficients of the dyes as well as device thickness on photocurrent and energy conversion efficiency enhancements of' DSSCs. (C) 2014 Elsevier Ltd. All rights reserved.

Silver nanoparticles of various sizes, shapes and modified distances between them were prepared on silicon substrates using thermally evaporated metal thin films of varying thicknesses followed by annealing. The similar to 4 nm silver thin film annealed around similar to 300 degrees C showed considerable reflectance reduction from the silicon substrate in the entire polychromatic spectrum. The effects of dipolar and quadrupolar resonances of silver nanoparticles on the reflectance reduction from the silicon substrate are discussed. The quadrupolar resonances of silver nanoparticles lead to reduced reflectance from the silicon substrate in the near UV-visible region (similar to 350-600 nm) due to the enhanced forward scattering. The reflectance reduction in the Vis and NIR regions (similar to 600-1300 nm range) is explained by the interaction of the surface plasmons of the metal nanoparticles, which is very sensitive to the size and shape of the particles, and the distances between them. Some of the waveguide modes existing at the interface between the silicon and the metal nanoparticles also couple the excited surface plasmons, which helps in trapping the light near the NIR region. With proper tuning of the metal particle sizes, shapes and distances between the particles in the layers, one can reduce the total reflectance from the silicon substrate in the entire polychromatic solar spectrum.