Devices For Sensing Applications Research Articles

Effect of Cu2+ ions on structural, morphological, optical and magnetic behaviors of ZnAl2O4 spinel

Zn1−xCuxAl2O4 nanoparticles were prepared by microwave combustion technique with metal nitrates as precursor materials. Powder x-ray diffraction studies confirm the formation of single phase of spinel pure and copper doped zinc aluminates. HR-SEM images reveal the agglomerated coalescence morphology with pores. Elemental analysis (EDX) confirm the presence of Zn, Cu, Fe and O. UV-Visible Diffuse reflectance spectroscopy is used to find the optical bandgap and it is found to decreases from 5.45 eV to 3.57 eV. IR spectra show three major peaks which confirm the phase formation of Zn1−xCuxAl2O4 nano aluminates with spinel structure. Vibrating sample magnetometer (VSM) measurements reveal the super paramagnetic nature of pure and copper doped zinc alumintes. The obtain results are confirmed that present pure and copper doped ZnAl2O4 particles at nanoscale are to be potential candidate for catalytic, sensor and optoelectronic device applications.

Structure, optical and electrical properties of sol-gel derived Zn1.5+xSn1.5-xO4 nanostructured films for optoelectronic applications

This work reports the structure-property relationship of sol gel synthesized Zn1.5+xSn1.5-xO4 films using acetylacetone as precursor solvent and stabilizer. These samples were characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), Raman spectroscopy, optical spectroscopy and Hall measurements. XRD study reveals the preferentially grown along (311) with a change in its intensity for different compositions in Zn-Sn-O system. The surface morphology varies with composition has been observed in both SEM and AFM studies. The dominant Raman active modes were observed at 556 and 667 cm−1 corresponding to F2g and A1g modes respectively of Zn2SnO4 system. The optical gap varies between 3.85 eV to 3.96 eV and defect related emission spectra dominate the luminescence characteristics for the present system. The minimum electrical resistivity 8.4 × 10−3 Ω-cm and maximum figure of merit of 0.09 Ω−1 has been found for Zn2.25Sn0.75O4 films. These results show their suitability for fabrication of transparent conductors and other sensing device applications.

The investigation of the electromagnetic coupling effect in terahertz toroidal metasurfaces and metamaterials

We proposed and fabricated toroidal dipole (TD) metasurfaces(MSs) with a metamolecule of two coplanar U-shaped split ring resonators(USRRs) fabricated on polyimide substrate, and TD metamaterials (MMs) were the stacks of two TD MSs layers, whose frequencies, electromagnetic (EM) distributions and Q factor can be efficiently affected by the EM coupling effect in TD MSs/MMs. It was found that the resonances frequencies of TD MMs were shifted to lower frequencies due to the increase of inductance by the stacks of metallic layer. Meanwhile, the high-frequency TD resonance in TD MMs would be tailored by the periodicity. Considering the relation between TD resonances and the scattering power of TD (Ty), the Q factor depended highly on the value of Ty in the same metamolecule structure. The optimization in excitation of TD provide opportunity to further increase the Q-factor of metamaterial and pave a way for potential applications in terahertz sensor and other functional devices.

An Optimization Study of Estimating Blood Pressure Models Based on Pulse Arrival Time for Continuous Monitoring

Continuous blood pressure (BP) monitoring has a significant meaning for the prevention and early diagnosis of cardiovascular disease. However, under different calibration methods, it is difficult to determine which model is better for estimating BP. This study was firstly designed to reveal a better BP estimation model by evaluating and optimizing different BP models under a justified and uniform criterion, i.e., the advanced point-to-point pairing method (PTP). Here, the physical trial in this study caused the BP increase largely. In addition, the PPG and ECG signals were collected while the cuff bps were measured for each subject. The validation was conducted on four popular vascular elasticity (VE) models (MK-EE, L-MK, MK-BH, and dMK-BH) and one representative elastic tube (ET) model, i.e., M-M. The results revealed that the VE models except for L-MK outperformed the ET model. The linear L-MK as a VE model had the largest estimated error, and the nonlinear M-M model had a weaker correlation between the estimated BP and the cuff BP than MK-EE, MK-BH, and dMK-BH models. Further, in contrast to L-MK, the dMK-BH model had the strongest correlation and the smallest difference between the estimated BP and the cuff BP including systolic blood pressure (SBP) and diastolic blood pressure (DBP) than others. In this study, the simple MK-EE model showed the best similarity to the dMK-BH model. There were no significant changes between MK-EE and dMK-BH models. These findings indicated that the nonlinear MK-EE model with low estimated error and simple mathematical expression was a good choice for application in wearable sensor devices for cuff-less BP monitoring compared to others.

Adsorption of gas molecules on a C3N monolayer and the implications for NO2 sensors

Recent reports have raised exciting prospects for the use of C3N monolayers exhibiting excellent adsorptive properties in nanodevice applications. In this study, we carried out first-principle calculations to investigate the adsorption of NO2, NO, CO, HCN, NH3, CO2, H2, N2, CH4, H2O, O2, and N2O gas molecules on a C3N monolayer as well as its potential applications in gas sensor devices. Our results reveal that the chemisorption of NO2 can significantly influence the electronic properties of the C3N monolayer (e.g., changing semiconducting behavior to conducting behavior). In contrast, physisorption of the other gas molecules had little effect on the electronic properties of the C3N monolayer. These results suggest that the C3N monolayer is much more sensitive and selective to NO2 than to the other gases. The recovery time of NO2 at T = 300 K is only 0.62 s. Moreover, the optical properties of the C3N monolayer can be modified as a result of the adsorption of different molecules, especially the NO2 molecule. Thus, the C3N monolayer is a promising and desirable candidate for use as a suitable material in gas sensors for NO2 detection.

Tunable mid-infrared dual-band and broadband cross-polarization converters based on U-shaped graphene metamaterials.

We propose a tunable dual-band reflective cross-polarization converter composed of periodically arranged single layer U-shaped graphene nanostructures in mid-infrared region. The proposed dual-band reflective cross-polarization converter can convert the polarization state of an incident wave from the linear polarization state to its cross polarization state at the operating frequencies of 34.67 and 44.13 THz with the high-efficiency polarization conversion ratio (PCR) approaching 100%. Furthermore, as a complementary structure, a reflective cross-polarization converter with a hollow-carved U-shaped graphene sheet shows a broadband polarization conversion performance with a bandwidth of 1 THz and the PCR over 90%. The bandwidth of this broadband converter can be further extended to 2 THz after certain geometric parameter optimization. More importantly, both the dual-band and broadband cross-polarization converters not only can dynamically tune their PCR peak frequencies and magnitudes by adjusting the chemical potential and relaxation time of graphene without changing the geometric structure but also have good angular stability with high PCR in a wide range of incident angle up to 55°. These polarization converters may have great potential applications in mid-infrared spectroscopy, radiometer, sensor, and other photonic devices.

Generation and manipulation of the Fano resonance with high refractive index sensitivity based on the square split ring dimer

The Optical properties of the Square Split Ring dimer (SSRD) nanostructure is studied by the finite element method (FEM). Fano resonance can be excited in the visible and near-infrared bands by changing geometrical parameters of the SSRD or the arrangement of two square split rings (SSR). The production mechanism of Fano resonance is illustrated by using the plasmon hybridization theory (PHT). At the meantime, a pair of reverse current circulation is formed in the SSRD nanostructures and the maximum magnetic field enhancement reaches 45.69. In addition, calculation results show that the maximum refractive index sensitivities and the figure of merit (FOM) of SSRD systems reached 2043 nm/RIU and 57.9, respectively. Based on these features of the SSRD system, it may have potential application in sensor devices and surface-enhanced Raman scattering (SERS).

High‐performance flexible sensing devices based on polyaniline/MXene nanocomposites

AbstractHighly active two‐dimensional (2D) nanocomposites, integrating the unique merits of individual components and synergistic effects of composites, are greatly desired for flexible sensing device applications. Although 2D transition metal carbides and nitrides (MXenes) combined with their high metallic conductivity and versatile surface chemistry have shown its huge potential for sensing reactions, it still remains a major challenge to construct functional materials with intriguing sensing performance at room temperature (RT). Herein, we used an integration of density functional theory (DFT) simulations and bulk electrosensitive measurements to show high electrocatalytic sensitivity of polyaniline/MXene (PANI/Ti3C2T x) nanocomposites. Thanks to the synergistic properties of nanocomposites and high catalytic/absorption capacity of Ti3C2T x MXene, PANI nanoparticles are rationally decorated on Ti3C2T x nanosheet surface via in situ polymerization by low temperature approach to induce remarkable detection sensitivity, rapid response/recovery rate, and mechanical stability at RT. This study offers a versatile platform to use MXenes to fabricate 2D nanocomposites materials for high‐performance flexible gas sensors.

Opto-electro-mechanical percolative composites from 2D layered materials: Properties and applications in strain sensing

The fragmentation rate (FR) of two-dimensional layered materials (2DLMs) MoS2, WS2, and graphene in N-methyl-pyrrolidinone (NMP) was computed, where FR is a measure of the particle size reduction with ultrasonication time. For the 2DLMs, the highest FR generally occurred for sonication times tsonic = 30 min, with FRGraphite ∼ −1176.4 μm-hr−1, FRWS2 ∼ −32.4 μm-hr−1and FRMoS2 ∼ −3.8 μm-hr−1. This is in contrast to a non-layered material, Al nanoparticles, where FRAl ∼0 μm-hr−1 for tsonic = 30 min. Knowledge of the particle size as a function of tsonic has not been reported previously for 2DLMs, and is extremely important as these materials are integrated into additively manufactured platforms, such as ink-jet printing and three-dimensional (3D) printing. The treated materials were then infused with two types of polymers, flexible and stretchable polyisoprene, and an optically transparent acrylic, poly-methyl-methacrylate (PMMA) for opto-electro-mechanical strain-based sensing device applications. In particular, the hybrid composites of graphene with optically transparent and bendable PMMA revealed the potential of forming opto-mechanical filters, where optical filtering can be engineered through the graphene loading. The polyisoprene-graphene composites were piezoresistive with potential for wearable electronics, where mechanical strain, as induced at joint movements on a finger for example, modulates the current with joint displacement. Strain levels of up to 200% were observed and the gauge factor of these devices was measured to be ∼75 which is > 10X higher compared to conventional metal-foil based strain sensors. This work sheds fundamental insights into the role of sonication on the materials properties of 2DLMs in solution dispersions and shows their potential in hybrid composites for opto-electro-mechanical strain based sensing applications and in wearable electronics.

Self-doped SnO2:F synthesis by aerosol-spray deposition technique and their application in relative humidity sensor devices

Fluorine-doped tin-oxide (SnO2:F) thin films were prepared by aerosol-spray deposition technique on soda lime glass substrate by one-step deposition process. Tin (II) fluoride (SnF2) was used as source of tin (Sn) and doping element fluorine (F), to synthesis a self-doped transparent conducting electrode. The doping concentration of the thin films was controlled by varying deposition temperature and the molar concentration of the SnF2 solution. Electrical resistivity of the samples was measured by Van Der Pauw method and the mobility was calculated by Hall measurement technique. SnO2:F thin films grown under optimum condition showed 1.2 × 10−4 Ω-cm resistivity and 6.5 × 1020/cm3 carrier concentration. Surface-free energy of the deposited thin films was calculated from the measurement of contact angle for three different probe liquids using the Wendt theory. Sample grown at optimum condition showed the lowest surface-free energy of 63.55 mJ/m2 with dominating polar component. Reduced graphene oxide was used to produce a resistive humidity-sensing device to study the effectiveness of FTO thin film as back electrode. Maximum of 18.27% responsivity was observed for the relative humidity of 90% along with the sensitivity of 1.16 Ω/% RH.

A New Class of Low‐Temperature Plasma‐Activated, Inorganic Salt‐Based Particle‐Free Inks for Inkjet Printing Metals

AbstractInkjet printing is rapidly emerging as a means to fabricate low‐cost electronic devices; however, its widespread adoption is hindered by the complexity of the inks and the relatively high processing temperatures, limiting it to only a few metals and substrates. A new approach for inkjet printing is described, based on commercially available, particle‐free inks formulated from inorganic metal salts and their subsequent low‐temperature conversion to metallic structures by a non‐equilibrium, inert gas plasma. This single, general method is demonstrated for a library of metals including gold (Au), silver (Ag), copper (Cu), palladium (Pd), platinum (Pt), lead (Pb), bismuth (Bi), and tin (Sn). As one figure of merit, the resistivities of the printed metals are measured to be between 2× and 10× of the respective bulk metals. Uniquely, it is found that the printed metal films exhibit a very large surface area because of the plasma‐initiated nucleation and growth process, making this technique attractive for sensing device applications. A Bi‐based trace Pb sensor, an Au‐based amyloid‐β42 sensor, and an Au‐based strain gauge are fabricated as representative chemical, biological, and mechanical sensors, and are found to exhibit enhanced sensitivity compared to analogues made with conventional methods.

Na2Ti7O15 Nanowires with an Oriented Tunnel Structure and High Mechanical Stability: A Potential Anode of Sodium-Ion Batteries and Gas Sensing Materials

Na2Ti7O15 (NTO) can be selected as candidate anode for high-performance sodium-ion batteries (SIBs). However, there are few reports of research on the mechanical properties of low-dimensional NTO, which is important for the stability of SIBs. In this work, by using the one-step hydrothermal method, NTO nanowires (NWs) with good orientation were prepared successfully. The transmission electron microscopy (TEM) and selected area electron diffraction (SAED)showed that the NTO NWs had a good aspect ratio and dispersion, with lengths over 20 μm. Further microstructure analysis showed that the nanowires grew along the (020) direction, and there were some "stripe" structures along the growing direction, which provides a good tunnel structure for Na ion channels. Further, the in situ mechanical analysis showed that the NTO NWs had excellent elastic deformation characteristics and mechanical structural stability. In addition, the NTO NWs also showed a good gas sensitivity to NO and NH3. Our results showed that the prepared NTO nanowires with a stripe tunnel oriented-structure and excellent mechanical properties may have a potential application in SIBs or other wearable sensor devices.

Wearable Sensor Devices for Prevention and Rehabilitation in Healthcare: Swimming Exercise With Real-Time Therapist Feedback

Wearable sensor devices are playing an increasingly important role in providing pervasive and personalized healthcare. Important elements of modern healthcare services are physical rehabilitation and injury prevention. Wearable sensor devices attached to the patient can offer valuable supplemental information to healthcare professionals during treatment or therapy. In physical rehabilitation, wearable inertial sensor devices help therapists to monitor and evaluate parameters and key performance indicators of the rehabilitation activities. Therapy efficiency can be increased by using real-time feedback systems. Three different feedback system architectures are defined and studied: 1) therapist; 2) user; and 3) cloud system. A case study involving rehabilitation therapy based on swimming exercises was performed. Field test results show that the developed sensor device and real-time therapist feedback application provide sufficiently accurate and precise data for the efficient evaluation of swimming parameters, such as stroke time and stroke rotation angle symmetry. Rehabilitation therapists should be able to operate the system without the constant presence of trained and experienced technical personnel (engineers). The wide adoption of wearable sensor device-based applications will lead to cloud systems where big data analytics will offer additional benefits to healthcare, well-being, and quality of life.

Production and characterization of flexible semiconducting polymer-nanoparticle composites for x-ray sensors

Fabrication and characterization of flexible semiconducting polymer-nanoparticles composite membranes for x-ray sensor device applications are presented in this work. Poly(vinyl alcohol) (PVA) polymer was initially doped with glycerol ionic liquid (IL) that permitted the control of its electrical resistivity. Metal-oxide Bi2O3 nanoparticles were prepared by a modified sol-gel method. The average nanoparticle size was found to be 39 ± 10 nm. Thin films of flexible polymer membranes with different nanoparticle concentrations were prepared using a solution casting method. Compositional characterizations revealed the formation of homogeneous polymer-nanoparticle membranes. Electrical impedance measurements of the membranes were performed for the membranes in a form of capacitor structure as a function of temperature and nanoparticle concentration. The measurements demonstrated that the membranes could be modeled with a pair of parallel resistor and capacitor that were assigned to the contributions of grain boundaries as well as the region of electron depletion in the membrane. As nanoparticle concentration increases, the resistivity and activation energy decrease. Current-voltage measurements demonstrated that the produced membranes function as x-ray sensors, and their response increases as a function of nanoparticle concentration. The produced membranes exhibit semiconducting properties that qualify them as potential candidates for device applications in the field of x-ray dosimeter.

Thin Films Sensor Devices for Mycotoxins Detection in Foods: Applications and Challenges

Mycotoxins are a group of secondary metabolites produced by different species of filamentous fungi and pose serious threats to food safety due to their serious human and animal health impacts such as carcinogenic, teratogenic and hepatotoxic effects. Conventional methods for the detection of mycotoxins include gas chromatography and high-performance liquid chromatography coupled with mass spectrometry or other detectors (fluorescence or UV detection), thin layer chromatography and enzyme-linked immunosorbent assay. These techniques are generally straightforward and yield reliable results; however, they are time-consuming, require extensive preparation steps, use large-scale instruments, and consume large amounts of hazardous chemical reagents. Rapid detection of mycotoxins is becoming an increasingly important challenge for the food industry in order to effectively enforce regulations and ensure the safety of food and feed. In this sense, several studies have been done with the aim of developing strategies to detect mycotoxins using sensing devices that have high sensitivity and specificity, fast analysis, low cost and portability. The latter include the use of microarray chips, multiplex lateral flow, Surface Plasmon Resonance, Surface Enhanced Raman Scattering and biosensors using nanoparticles. In this perspective, thin film sensors have recently emerged as a good candidate technique to meet such requirements. This review summarizes the application and challenges of thin film sensor devices for detection of mycotoxins in food matrices.

Synthesis of Two-Dimensional Alloy Ga0.84In0.16Se Nanosheets for High-Performance Photodetector.

The electronic and optoelectronic properties of 2D alloy Ga0.84In0.16Se were investigated for the first time. 2D Ga0.84In0.16Se FETs show p-type conduction behaviors. 2D Ga0.84In0.16Se photodetectors show high photoresponse in the visible light range of 500 to 700 nm. The responsivity value is 258 A/W for alloy photodetector (500 nm illumination), and it is 92 times and 20 times higher than those of 2D GaSe and InSe photodetectors, respectively. Moreover, the alloy photodetector exhibits good photoresponse stability and rapid photoresponse time. Our results demonstrate that 2D alloy Ga0.84In0.16Se has great potential for application in photodetection and sensor devices.

Optical oxygen sensors based on microfibers formed from fluorinated copolymers

Polymeric microfibers, particularly the fluorinated copolymers’ fibers, are promising functional materials for photoelectric devices, sensing, and energy storage due to their various surface characteristics. However, to obtain the high fluorine content copolymer-based fibers with considerable uniformity is likely to be especially challenging, which seriously debilitates their applications in sensor devices. Herein, for the first time, we presented a high fluorine content platinum porphyrin-grafted poly(isobutyl methacrylate-co-dodecafluoroheptyl methacrylate) copolymers (PtTFPP-p(IBM-co-DFHMA)) microfibrous thin-films used as optical oxygen sensors. The porous thin-film frameworks were formed of uniform microfibers, which afforded an exceptional improvement in sensitivity and exhibited 584% higher sensitivity than the solid sensing film owing to the large specific surface area, porous structures and oxygen diffusion enhancement by fluorine elements. Additionally, the remarkable emission intensity-changing characteristic of the microfiber sensing film under various air pressures facilitates convenient visualization of pressure distributions on film surface. The characteristics are particularly important for the computational fluid dynamics simulations in various sensing fields such as unsteady flow visualization and unsteady pressure measurements, etc. Owing to its attractive advantages and versatile performance, fluorine-containing copolymers fibers are expected to provide a new strategy for the rational design of high performance gas sensor devices.

Temperature dependence of current-perpendicular-to-plane giant magnetoresistance in the junctions with interface tailored Heusler alloy electrodes

Abstract Current-perpendicular-to-plane, CPP, giant magnetoresistance, GMR junctions attract interests for application of sensor devices, such as read head element of hard disk drives. Temperature dependence of the CPP-GMR effects was investigated, in this study, for junctions consisting of the half-metallic Heusler alloy, Co2(Fe-Mn)Si, electrodes and an L12-type Ag3Mg spacer with the ultra-thin interface layers, Fe or Mg. For the Fe insert junctions, MR ratio exhibited local maximum at a temperature ranging from 50 K to 250 K which depends on the insertion thickness. The reason is unclear for the anomalous temperature dependence of the Fe junctions, however, a possibility is reduction of the Curie temperature for the Fe insert at the ultra-thin regime. On the other hand, MR ratios monotonically increased with decreasing the temperature for the Mg insert junctions, for which MR ratio of about 100% was observed at 10 K. Ratios of MR at 300 K to the low temperature are almost independent of the insertion thickness. Considering a fact that the shapes of MR curves nearly unchanged by the temperature change, it is suggested that the Mg insert works as a diffusion barrier at the Co2(Fe-Mn)Si/Ag3Mg interfaces.

Ambient Condition Production of High Quality Reduced Graphene Oxide

Reduced graphene oxide becomes one of the most popular materials for applications in various optical, electronic and sensor devices. Even though many methods have been already reported for reduced graphene oxide synthesis, they usually rise issues related to their efficiency, quality and environmental impact. This work demonstrates a simple, environmentally friendly and effective method for reducing graphene oxide under ambient conditions using nanosecond infrared laser irradiation. As a result, a Raman band intensity ratio of I(G)/I(D) of 4.59 was achieved with an average crystallite size of ~90 nm. This graphene is of higher quality than what can be achieved with most of the existing methods. Additionally, the demonstrated reduction technique allows the selective reduction of graphene oxide and control the amount of functional groups on the surface of the material. Gas sensors fabricated according to the proposed technique efficiently detect NO$_2$, NH$_3$, and H$_2$S with the sensitivity down to 10 ppm.

Monitoring Ultrafast Spin Crossover Intermediates in an Iron(II) Complex by Broad Band Stimulated X-ray Raman Spectroscopy.

The photoinduced spin crossover dynamics of transition metal complexes is of fundamental scientific importance and is used for sensor device applications and solar energy harvesting. Current X-ray and optical spectroscopy experiments for [FeII(bpy)3], an archetypal earth-abundant metal complex, show conflicting spin dynamics. We have simulated the broad band transient X-ray absorption and hybrid (broad + narrow band) X-ray stimulated Raman signals at the N and Fe K-edges of the key excited state intermediates involved in the spin crossover process of this complex. We find that these signals are much more sensitive to electron and spin populations than transition absorption and may be useful in the design of photovoltaic and artificial photosynthetic systems.