Sensor Substrate Research Articles

Novel Zn-based Metal Coordination Polymer for Ultrafast Capture and Electrochemical Sensing of Hg(Ⅱ)

The electrochemical sensor shows great promise in the detection of trace Hg(Ⅱ), of which the performance could be significantly enhanced by the functionalized material with the merits of effective and ultrafast capture for Hg(Ⅱ). In this study, the novel metal coordination polymers (MCPs) was synthesized by the 2-thio-barbituric acid as the organic ligand to modify the electrochemical sensor to address this issue. The as-prepared material was composed of regular flakes with a polyhedral and well-defined crystal structure, the successful loading of the abundant sulfurous group (7.49% of the total mass) endowed the Zn-TBA with the capability to efficiently uptake (97.4-99.9%) Hg(Ⅱ) at 500mg/L under a wider pHs as well as the high content of coexisting cations and anions, highlighted the excellent capacity, strong environmental adaptability, and selectivity. Notably, the superfast mass transfer was revealed in the adsorption kinetics test, in which the Hg(Ⅱ) content was effectively reduced from 50mg/L to 14 μg/L within 20s to meet the national emission standards. Based on this, Zn-TBA modified the carbon cloth (Zn-TBA/CC) and the glass carbon electrode (Zn-TBA/GCE) was prepared, thereinto, the current response of Zn-TBA/CC was approximately 60 times that of the pristine electrode. A strong positive correlation (R2=0.998) relationship could be attained across the content of 0.25-3μM, achieving the detection limit to be 0.29μM. The impressive performance was maintained in the complex matrices and regeneration test. In addition, Zn-TBA/CC exhibited better physical properties, charge transfer ability, and sensing properties than Zn-TBA/GCE, highlighting the advantages of CC as a flexible sensor substrate. Finally, the stable recovery (90-98.5%) in the spiked actual surface water confirmed that the two established methods possessed a promising application potential in capturing and detecting the trace Hg(Ⅱ) with high accuracy and precision. This study extended the application of MCPs in the electrochemical sensor and provided an available analysis method to trap and determine the metal content.

AIEgens-based luminescent metal-organic frameworks as novel electrochemiluminescence emitters Integrated with co-reaction amplification strategy for CA15-3 detection

A current research focus in the field of electrochemiluminescence (ECL) is the development of novel high-performance emitters. Herein, we reported the synthesis of a zirconium-based metal–organic framework (Zr-TBAPy-MOF) using the aggregation-induced emission luminogens (AIEgens) 1,3,6,8-tetra(4-carboxyphenyl)pyrene (H4TBAPy) as ligands and Zr6-clusters as nodes. The resulting AIE-active luminescent MOF (AIE-LMOF) exhibited superior ECL properties and was used as an ECL emitter to construct a high-sensitivity ECL immunosensor. Conceptual experiments demonstrated that Zr-TBAPy-MOF showed significantly stronger ECL emission compared to both the monomers and aggregates of H4TBAPy, attributed to the effective restriction of intramolecular motion (RIM). On the sensor substrate, we designed an Au@ZnO/Cu2O nanocomposite as a co-reactant accelerator. This significantly promoted the generation of sulfate radicals (SO4•−) from persulfate (S2O82−) through the sustainable switching of Cu+/Cu2+ oxidation states in copper oxide (Cu2O). Additionally, zinc oxide (ZnO), which had excellent electrochemical properties, further enhanced the catalytic activity of the materials. Leveraging these advantages, we developed a sandwich-type ECL immunosensor for the ultrasensitive detection of carbohydrate antigen 15–3 (CA15-3), demonstrating a wide sensitive range (0.001 − 100 U/mL) and a low detection limit (0.0007 U/mL). Overall, this work paves the way for the development of efficient ECL luminophores with significant potential in the field of immunoassays for the early diagnosis of disease.

Modeling, Calculation and Realization of Au/Nb2O5 Substrates for Surface Plasmon Resonance Sensors

Introduction. Sensor devices based on the surface plasmon resonance (SRP) phenomenon are widely used among the tools of information and diagnostic technologies. The main part of a device based on the surface plasmon resonance phenomenon is a sensor substrate, which consists of a glass plate, a film of plasma-supporting metal, usually gold, and additional layers to increase the sensitivity of the research. Depending on the thickness of the additional dielectric layers, the following types of sensors can be implemented: a conventional SPR sensor with a gold film without a dielectric; an Au/dielectric SPR sensor with a dielectric thickness less than the critical one, in which the system can maintain the plasmonic mode; a waveguide sensor on a metal sublayer, with a dielectric thickness sufficient for the emergence of waveguide modes. The Au/Nb2O5 thin-film system is promising for creating sensor substrates due to the high refractive index of Nb2O5 and its exceptional chemical and mechanical resistance. The purpose of the work. This work is devoted to computer modelling, calculation of performance characteristics and implementation of Au/Nb2O5 sensor substrates for SPR devices, including the Plasmontest series devices developed at the Institute of Cybernetics of the National Academy of Sciences of Ukraine. The behaviour of the characteristics of the SPR substrates with a plasma-supporting gold film, SPR substrates with sensitivity enhancement by an additional layer of Nb2O5 of nanometre thickness and with a waveguide layer of Nb2O5 thickness more than 150 nm are analysed. Calculations were performed for both refractive sensors on SPR and biosensors. Results. The theoretical analysis was carried out by computer modelling in Winspall and calculations in MATLAB using the Fresnel equations and the matrix method, which allowed a comprehensive analysis of the shape of the reflection curves, angular sensitivity, resolution and angular ranges for sensors with different dielectric coatings. It is shown that at a thickness of 0-10 nm, the Au/Nb2O5 structure will work as a SPR sensor with increased sensitivity, and at a thickness of 150-210 nm as a waveguide sensor on a metal sublayer. But, as calculations have shown, only the Au/Nb2O5 SPR sensor is promising for practical implementation to increase the sensitivity of biosensor measurements. The work carried out on the development of thin-film technology, which includes vacuum deposition of a thin-film structure of adhesive Nb (1–2 nm), plasma-supported Au (50 nm), Nb (3–5 nm) and thermal annealing (to oxidise the top layer of niobium), made it possible to implement Au/Nb2O5 substrates for SPR studies. Experimental studies have shown that the angular sensitivity of the Au/Nb2O5 refractometric SPR sensor is 1.5 times higher than that of a SPR sensor with a single Au film at niobium oxide layer thickness of about 6 nm. Thus, the experimentally determined increase in the angular sensitivity of the Au-Nb2O5 SPR sensor is consistent with the theoretical data. Conclusions. Calculations have shown an increase in the angular sensitivity of SPR sensors for Au/Nb2O5 sensor substrates compared to conventional Au film substrates for both refractometric (1.6 times) and biosensor (1.8 times) studies. The sensors on Au/Nb2O5 substrates for SPR studies, which we have designed and practically implemented, are cheap to manufacture, have higher sensitivity, and due to the exceptional chemical and mechanical stability of Nb2O5, can be used repeatedly in rather aggressive environments. Keywords: computer modelling, surface plasmon resonance, sensor, refractometer, biosensor.

Elastomeric Sensor-Triboelectric Nanogenerator Coupled System for Multimodal Strain Sensing and Organic Vapor Detection.

Stretchable, flexible sensors are one of the most critical components of smart wearable electronics and Internet of Things (IoT), thereby attracting multipronged research interest in the last decades. Following miniaturization and multicomponent development of several sensors in one could further propel the demand for wireless, multimodal platforms. Greener substitutes to conventional sensors that can operate in a self-powered configuration are highly desirable in terms of all-in-one sensor utilities. However, fabrication of composite-based ultrastretchable, self-powered sensors with multifunctionality, robustness, and conformability is still only partially achieved and, therefore, demands further investigation. In this work, we report a triboelectric nanogenerator (TENG)-based multifunctional strain and organic vapor sensor using cross-linked ethylene propylene diene monomer (EPDM) elastomer and conducting carbon black as active fillers in the presence of an ionic liquid. The resulting piezoresistive sensor demonstrates ultrahigh gauge factor (GF > 220k) and wide range strain sensitivity and is, therefore, suitable for subtle-to-high frequency motion detection devices. Supported by excellent triboelectric outputs (force sensitivity 0.5 V/N in the range of 50-300 N, maximum output voltage VOC ∼ 178 V, short circuit current ISC ∼ 18 μA, maximum power density 0.11 mW/cm2), the hybrid sensors offer remarkable mechanical toughness and seamless voltage generation under contact-separation, even after several thousand cycles of operations. Furthermore, the sensor substrates exhibited reproducible organic vapor-sensing behavior, with high responsivity of 1.92 and 1 for ethanol and acetone, respectively, under flowing vapor conditions. This work lays a strong foundation for developing a truly multimodal, TENG-based, self-powered organic vapor and strain sensors.

Novel screen-printed ceramic MEMS microhotplate for MOS sensors

We developed a new approach to the fabrication of MEMS substrates for MOS gas sensors. This full screen-printing process is based on the application of sacrificial material, which is solid at the near-room temperature of printing and turns to powder after the firing of the elements of the sensor. Therefore, this sacrificial material can be removed from under the suspended elements of the MEMS structure in ultrasonic bath. The glass-ceramic MEMS is a cantilever structure equipped with a Pt-based microheater made of Pt resistive material with sheet resistance of about 4 Ohm/square fabricated using core-shell technology. It is located at the end edge of the cantilever and is isolated from the contacts to the sensing layer by glass-ceramic insulation. Screen-printing provides cheap fabrication, robustness and low power (∼120 mW@450°C) of the sensing element. The functionality of the microhotplate was checked using ZnO nanomaterial deposited by microextruder, it demonstrated high response and selectivity of ZnO material to NO2 (response 41.6 at 200°C for 10 ppm).

Modelling and fabrication of flexible strain sensor using the 3D printing technology

The use of additive manufacturing (AM) or 3D printing in sensor technology is increasing daily because it can fabricate complex structures quickly and accurately. This study presents the modeling, fabrication, and characterization processes for the development of a resistance type flexible strain sensor. The finite element model of the sensor was developed using COMSOL software and was verified experimentally. The experimental results agreed well with the simulation results. The fabrication process was performed using the molding technique. The flexible substrate of the strain sensor was fabricated by fused deposition modeling (FDM), an AM method, with dimensions of 20 mm × 60 mm and a thickness of 2 mm. In this process, a flexible and durable elastomer material called thermoplastic polyurethane (TPU) was used. The liquid conductive silver was then injected into the mold channels. The characterization process was performed by establishing experimental and numerical setups. Studies were conducted to maximize sensitivity by changing the geometric properties of the sensor. At the 30% strain level, sensitivity increased by 9% when the sensor thickness decreased from 2 to 1.2 mm. As a result of the gradually applied force, the strain sensor showed a maximum displacement of 34.95 mm. Tensile tests were also conducted to examine the effects of stress accumulation on the flexible base. The results of this study show that the strain sensor exhibits high linearity-sensitivity and low hysteresis performance.

Comparative study of the sensitivity of H2S and NO2 in CuInSe2 gas sensors that are fabricated using screen printing and MEMS Integration

This study compares the gas response efficiency of a gas sensor substrate that is produced using screen-printing (SP) and micro-electro-mechanical systems (MEMS) technology, followed by deposition of CuInSe2 (CIS) film layers by radio-frequency (RF) sputtering and hyperthermal annealing for gas sensing applications. The SP substrates are used for CIS film deposition for RF sputtering, followed by various hyperthermal annealing treatments. SEM observations of the CIS film surfaces after annealing show surface particles with a size distribution of 155 to 30 nm, which demonstrate a phenomenon that is similar to Ostwald ripening and which creates structural variation and unevenness after annealing. The CIS film/MEMS substrates (MEMSs) gas sensor substrates are evaluated using a NIR thermal camera to determine the optimal operating temperature for direct annealing, which is 203.2 °C. Gas sensing response tests show that only H2S or NO2 gas rapidly and significantly elicit a response but a CIS film/SPs gas sensor exhibits significant resistance signal noise. The CIS film/MEMSs gas sensor is more stable than CIS film/SPs (after annealing) so it is more suitable for gas sensing. SEM images confirm that the film remains intact, so it is suitable for gas sensing applications.

Evaluation of Transducer Elements Based on Different Material Configurations for Aptamer-Based Electrochemical Biosensors.

The selection of an appropriate transducer is a key element in biosensor development. Currently, a wide variety of substrates and working electrode materials utilizing different fabrication techniques are used in the field of biosensors. In the frame of this study, the following three specific material configurations with gold-finish layers were investigated regarding their efficacy to be used as electrochemical (EC) biosensors: (I) a silicone-based sensor substrate with a layer configuration of 50 nm SiO/50 nm SiN/100 nm Au/30-50 nm WTi/140 nm SiO/bulk Si); (II) polyethylene naphthalate (PEN) with a gold inkjet-printed layer; and (III) polyethylene terephthalate (PET) with a screen-printed gold layer. Electrodes were characterized using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) to evaluate their performance as electrochemical transducers in an aptamer-based biosensor for the detection of cardiac troponin I using the redox molecule hexacyanoferrade/hexacyaniferrade (K3[Fe (CN)6]/K4[Fe (CN)6]. Baseline signals were obtained from clean electrodes after a specific cleaning procedure and after functionalization with the thiolate cardiac troponin I aptamers "Tro4" and "Tro6". With the goal of improving the PEN-based and PET-based performance, sintered PEN-based samples and PET-based samples with a carbon or silver layer under the gold were studied. The effect of a high number of immobilized aptamers will be tested in further work using the PEN-based sample. In this study, the charge-transfer resistance (Rct), anodic peak height (Ipa), cathodic peak height (Ipc) and peak separation (∆E) were determined. The PEN-based electrodes demonstrated better biosensor properties such as lower initial Rct values, a greater change in Rct after the immobilization of the Tro4 aptamer on its surface, higher Ipc and Ipa values and lower ∆E, which correlated with a higher number of immobilized aptamers compared with the other two types of samples functionalized using the same procedure.

Development of a condition monitoring of heat exchangers for corrosion progress and coolant condition

The transport sector, and thus also rail transport, needs to be completely decarbonised by 2050 at the latest. Considering the long service life of rail vehicles, this goal means enormous innovation and growth potential for the vehicle and supplier industry of railway technology in the coming years. This contribution presents the first results of an R&D project to reduce the total cost of ownership of passenger and freight rail vehicles. The reduced life cycle costs can be achieved over the operating life, among other things, with condition monitoring approaches for critical components of cooling systems to enable diagnosis-based maintenance. Based on guided elastic waves, an integrated system is being developed to analyse the depth and position of corrosion damage to heat exchangers in rail vehicles. This method is to be supplemented by a refractive index sensor integrated in the coolant circuit which can be used to derive influences of the coolant condition on corrosion. First, an acoustic measuring technique was put into operation. Suitable piezoelectric transducers were selected and test measurements, including the introduction of artificial damages, along different paths on a representative heat exchanger were carried out and evaluated. Measurement signals can be received over different distances, and a monitoring of larger areas of the heat exchanger seems possible. For the development of the monitoring of the coolant, plasmonically active sensor substrates with a gold nanostructure were produced and installed in a measuring flow cell. In laboratory tests, concentrations of water-coolant mixtures could be distinguished with the refractive index sensor. In the future, the refractive index sensing will be carried out by means of bypass flow measurement. Since the coolant is pumped in a circuit, the sensor system can be attached to one of the inlet/outlet lines.

Iron nanowire/carbon microsphere composite flexible fabric strain sensor for human motion monitoring

People pay more and more attention to sports and health, especially the goal of sports recovery and scientific sports is more and more clear. In order to avoid human injury caused by unreasonable sports, it is necessary to carry out real-time detection of human motion state. In this paper, the motion state of human body was taken as the test object, a flexible strain sensitive material combining iron nanowires and carbon microspheres was proposed, and polyester fabric was introduced as the sensor substrate to construct a sandwich structure flexible fabric strain sensor. Then a mechanical test platform was built to carry out mechanical property testing and practical application verification research. The mechanical test results show that the iron nanowires/carbon microspheres flexible fabric strain sensor has good linearity, the response time is 42 ms, and the hysteresis error is approximately 8.7 %. Finally, the flexible fabric strain sensor is fixed on the part of the human body that needs to be detected, and the electrical signal curve of the response is output by the electrochemical workstation. Through the analysis of the response curve, it can be seen that the iron nanowires/carbon microspheres flexible fabric strain sensor prepared in this paper has great potential in human movement health monitoring.

Integration of 3D printing with acoustic-assisted assembly of nanomaterials for tunable strain sensors

This study reports a novel methodology for the development of tunable strain sensors by leveraging 3D printing for structural designs and nanomaterial assembly for functional layer coating. We utilized material extrusion (MEX) to print sensor substrates using composite ink of polydimethylsiloxane (PDMS) and silica nanoparticles. MEX allows us to create a non-uniform strain distribution of the sensor substrate by designing alternating wide and thin strips with different mechanical properties along the stretching direction. Then, we assembled nanometer-thick graphene flakes on the surface of the substrate using an acoustic-assisted dip-coating method to construct strain sensors. The graphene network on the narrow strips will experience large deformation leading to significantly increased resistance. By fixing the width of wide strips and tailoring the width ratio of the wide strip over narrow strips (r), the gauge factor can be controlled from 8.53 (r = 1:1) to 33.15 (r = 16:1). Also, by printing the narrow strips with softer PDMS, the sensitivity of the sensor can be further increased. The research pioneers the integration of 3D printing and nanomaterial assembly for strain sensors. More importantly, it paves the way for the generic design of flexible electronics and other hybrid systems of polymer and nanomaterials.

Flexible NH3 gas sensors based on ZnO nanostructures deposited on kevlar substrates via hydrothermal method

Owing to their flexibility and high thermal resistance, para-aramid based Kevlar™ fabric substrates are an ideal candidate for obtaining flexible gas sensors for new-generation wearable technologies. The morphology of the surface of the substrate where the target gas comes into contact directly affects the important features of the sensor such as detection limit, selectivity, and response. In this context, a feasible technique is introduced to enhance the efficiency of flexible gas sensors utilizing ZnO/Kevlar™, entailing the modification of ZnO morphology. ZnO based gas sensing layers were deposited on Kevlar™ fabric substrates by a two-stage method. Initially, seed layer was produced on Kevlar™ fabric using the ultrasonic bath method, with five different seed layer processing times ranging from 1 min to 20 min. In the nucleation, all nanostructured layers were deposited by hydrothermal method with constant parameters and under the same conditions. As the seeding time was increased, nanorods (1D) formed on the surface became flakes (2D), leading to considerable improvement in NH3 gas sensing properties. The sensor with a 5-min seeding time showed a sensitivity of 49 % at an optimal operating temperature of 190 °C, while the sensor produced in 20 min showed the best response performance with 169 % at 130 °C for 50 ppm NH3 gas. The increase in seeding time not only reduced the operating temperature of the gas sensor through the conversion from 1D nanostructure to 2D, but also significantly increased the sensor response. Under constant hydrothermal conditions and solution concentration, the density per unit area increases. However, after 10 min of seeding, the length of nanorods shortens and turn into a rod-flake hybrid morphology. A superior sensor performance was demonstrated for the samples examined. The obtained results also showed that flexible Kevlar™ fabric could be a feasible and interesting substrate for nanostructured ZnO-based NH3 gas sensors.

Disposable electrochemical biosensors for the detection of bacteria in the light of antimicrobial resistance.

Persistent and inappropriate use of antibiotics is causing rife antimicrobial resistance (AMR) worldwide. Common bacterial infections are thus becoming increasingly difficult to treat without the use of last resort antibiotics. This has necessitated a situation where it is imperative to confirm the infection to be bacterial, before treating it with antimicrobial speculatively. Conventional methods of bacteria detection are either culture based which take anywhere between 24 and 96 hor require sophisticated molecular analysis equipment with libraries and trained operators. These are difficult propositions for resource limited community healthcare setups of developing or less developed countries. Customized, inexpensive, point-of-care (PoC) biosensors are thus being researched and developed for rapid detection of bacterial pathogens. The development and optimization of disposable sensor substrates is the first and crucial step in development of such PoC systems. The substrates should facilitate easy charge transfer, a high surface to volume ratio, be tailorable by the various bio-conjugation chemistries, preserve the integrity of the biorecognition element, yet be inexpensive. Such sensor substrates thus need to be thoroughly investigated. Further, if such systems were made disposable, they would attain immunity to biofouling. This article discusses a few potential disposable electrochemical sensor substrates deployed for detection of bacteria for environmental and healthcare applications. The technologies have significant potential in helping reduce bacterial infections and checking AMR. This could help save lives of people succumbing to bacterial infections, as well as improve the overall quality of lives of people in low- and middle-income countries.

Stretchable Sensor Materials Applicable to Radiofrequency Coil Design in Magnetic Resonance Imaging: A Review.

Wearable sensors are rapidly gaining influence in the diagnostics, monitoring, and treatment of disease, thereby improving patient outcomes. In this review, we aim to explore how these advances can be applied to magnetic resonance imaging (MRI). We begin by (i) introducing limitations in current flexible/stretchable RF coils and then move to the broader field of flexible sensor technology to identify translatable technologies. To this goal, we discuss (ii) emerging materials currently used for sensor substrates, (iii) stretchable conductive materials, (iv) pairing and matching of conductors with substrates, and (v) implementation of lumped elements such as capacitors. Applicable (vi) fabrication methods are presented, and the review concludes with a brief commentary on (vii) the implementation of the discussed sensor technologies in MRI coil applications. The main takeaway of our research is that a large body of work has led to exciting new sensor innovations allowing for stretchable wearables, but further exploration of materials and manufacturing techniques remains necessary, especially when applied to MRI diagnostics.

Fabricating process of thin‐strain sensor by utilizing wafer‐level‐packaging techniques

AbstractThis research has developed a fabricating process of thin‐strain sensor by utilizing wafer‐level‐packaging (WLP) techniques. The thickness of sensor makes thinner, its performance is able to highly increase. However, the thinner sensor was fragile, and so it was difficult to handle in post processes. Thus, a thin sensor with lid by utilizing WLP techniques, which is tough to break even when handled, is proposed in this research. More than 250‐µm‐deep grooves were fabricated around the lid by deep reactive ion etching. After the lid substrate was bonded on the sensor substrate with a resin, the sensor and lid substrates were respectively polished to 50 and 200 µm thickness. The lids were released along the grooves, and the 50‐µm‐thick strain sensors were able to be fabricated by utilizing WLP techniques. This sensor was used as a diaphragm to measure pressure. The sensors were assembled on a stainless steel housing without breakage. The performance of the developed sensor was almost showed with a conventional pressure sensor.

A non-invasive capacitive sensor to investigate the Leidenfrost phenomenon: a proof of concept study

A volatile sessile liquid droplet or a sublimating solid manifests levitation on its own vapor when placed on a sufficiently heated surface, illustrating the Leidenfrost phenomenon. In this study, we introduce a non-invasive capacitance method for investigating this phenomenon, offering a potentially simpler alternative to existing optical techniques. The designed sensor features in-plane miniaturized electrodes forming a double-comb structure, also known as an interdigitated capacitor. Initially, the sensor’s capacitance is characterized for various distances between the sensor and a dielectric material. The influence of the sensor substrate material and the spacing between the electrodes on the sensor’s capacitance is also investigated. To demonstrate the feasibility of the method, a sublimating dry ice pellet is placed on the capacitive sensor, and its performance is evaluated. We present results for the dimensionless vapor layer thickness and the pellet’s lifetime at different substrate temperatures, derived from the capacitance output. The results are compared with Optical Coherence Tomography (OCT) data, serving as a benchmark. While the temporal evolution of the sensor’s output, variation in the dimensionless vapor layer thickness, and the lifetime of the dry ice pellet align with expected results from OCT, notable quantitative deviations are observed. These deviations are attributed to practical experimental limitations rather than shortcoming in the sensor’s working principle. Although this necessitates further investigation, the methodology presented in this paper can potentially serve as an alternative for the detection and measurement of Leidenfrost vapor layers.

Research of flexible sensor based on nanomaterial

Research of flexible sensor based on nanomaterial

Dielectric Properties of Materials Used for Microwave-Based NOx Gas Dosimeters.

Nitrogen oxides (NOx), primarily generated from combustion processes, pose significant health and environmental risks. To improve the coordination of measures against excessive NOx emissions, it is necessary to effectively monitor ambient NOx concentrations, which requires the development of precise and cost-efficient detection methods. This study focuses on developing a microwave- or radio frequency (RF)-based gas dosimeter for NOx detection and addresses the optimization of the dosimeter design by examining the dielectric properties of LTCC-based (Low-Temperature Co-fired Ceramics) sensor substrates and barium-based NOx storage materials. The measurements taken utilizing the Microwave Cavity Perturbation (MCP) method revealed that these materials exhibit more pronounced changes in dielectric losses when storing NOx at elevated temperatures. Consequently, operating such a dosimeter at high temperatures (above 300 °C) is recommended to maximize the sensor signal. To evaluate their high-temperature applicability, LTCC substrates were analyzed by measuring their dielectric losses at temperatures up to 600 °C. In terms of NOx storage materials, coating barium on high-surface-area alumina resolved issues related to limited NOx adsorption in pure barium carbonate powders. Additionally, the adsorption of both NO and NO2 was enabled by the application of a platinum catalyst. The change in dielectric losses, which provides the main signal for an RF-based gas dosimeter, only depends on the stored amount of NOx and not on the specific type of nitrogen oxide. Although the change in dielectric losses increases with the temperature, the maximum storage capacity of the material decreases significantly. In addition, at temperatures above 350 °C, NOx is mostly weakly bound, so it will desorb in the absence of NOx. Therefore, in the future development of a reliable RF-based NOx dosimeter, the trade-off between the sensor signal strength and adsorption behavior must be addressed.

Breakdown performance of guard ring designs for pixel detectors in 150 nm CMOS technology

Silicon pixel sensors manufactured using commercial CMOS processes are promising instruments for high-energy particle physics experiments due to their high yield and proven radiation hardness. As one of the essential factors for the operation of detectors, the breakdown performance of pixel sensors constitutes the upper limit of the operating voltage. Six types of passive CMOS test structures were fabricated on high-resistivity wafers. Each of them features a combination of different inter-pixel designs and sets of floating guard rings, which differ from each other in the geometrical layout, implantation type, and overhang structure. A comparative study based on leakage current measurements in the sensor substrate of unirradiated samples was carried out to identify correlations between guard ring designs and breakdown voltages. TCAD simulations using the design parameters of the test structures were performed to discuss the observations and, together with the measurements, ultimately provide design features targeting higher breakdown voltages.

Structure-Property Relationships of Granular Hybrid Hydrogels Formed through Polyelectrolyte Complexation.

Hybrid hydrogels are hydrogels that exhibit heterogeneity in the network architecture by means of chemical composition and/or microstructure. The different types of interactions, together with structural heterogeneity, which can be created on different length scales, determine the mechanical properties of the final material to a large extent. In this work, the microstructure-mechanical property relationships for a hybrid hydrogel that contains both electrostatic and covalent interactions are investigated. The hybrid hydrogel is composed of a microphase-separated polyelectrolyte complex network (PEC) made of poly(4-styrenesulfonate) and poly(diallyldimethylammonium chloride) within a soft and elastic polyacrylamide hydrogel network. The system exhibits a granular structure, which is attributed to the liquid-liquid phase separation into complex coacervate droplets induced by the polymerization and the subsequent crowding effect of the polyacrylamide chains. The coacervate droplets are further hardened into PEC granules upon desalting the hydrogel. The structure formation is confirmed by a combination of electron microscopic imaging and molecular dynamics simulations. The interpenetration of both networks is shown to enhance the toughness of the resulting hydrogels due to the dissipative behavior of the PEC through the rupture of electrostatic interactions. Upon cyclic loading-unloading, the hydrogels show recovery of up to 80% of their original dissipative behavior in less than 300 s of rest with limited plasticity. The granular architecture and the tough and self-recoverable properties of the designed hybrid networks make them good candidates for applications, such as shape-memory materials, actuators, biological tissue mimics, and elastic substrates for soft sensors.