The outbreak of the recent Covid-19 pandemic changed many aspects of our daily life, such as the constant wearing of face masks as protection from virus transmission risks. Furthermore, it exposed the healthcare system’s fragilities, showing the urgent need to design a more inclusive model that takes into account possible future emergencies, together with population’s aging and new severe pathologies. In this framework, face masks can be both a physical barrier against viruses and, at the same time, a telemedical diagnostic tool. In this paper, we propose a low-cost, 3D-printed face mask able to protect the wearer from virus transmission, thanks to internal FFP2 filters, and to monitor the air quality (temperature, humidity, CO2) inside the mask. Acquired data are automatically transmitted to a web terminal, thanks to sensors and electronics embedded in the mask. Our preliminary results encourage more efforts in these regards, towards rapid, inexpensive and smart ways to integrate more sensors into the mask’s breathing zone in order to use the patient’s breath as a fingerprint for various diseases.

The COVID-19 pandemic outbreak, declared in March 2020, has led to several behavioral changes in the general population, such as social distancing and mask usage among others. Furthermore, the sanitary emergency has stressed health system weaknesses in terms of disease prevention, diagnosis, and cure. Thus, smart technologies allowing for early and quick detection of diseases are called for. In this framework, the development of point-of-care devices can provide new solutions for sanitary emergencies management. This work focuses on the development of useful tools for early disease diagnosis based on nanomaterials on cotton substrates, to obtain a low-cost and easy-to-use detector of breath volatiles as disease markers. Specifically, we report encouraging experimental results concerning acetone detection through impedance measurements. Such findings can pave the way to the implementation of VOCs (Volatile Organic Compounds) sensors into smart and user friendly diagnostic devices.

Questo lavoro si concentra sulla possibile applicazione di nanoparticelle d'oro su tessuti di cotone flessibili come substrati sensibili all'acetone e all'etanolo mediante misurazioni di impedenza. Nello specifico, nanoparticelle d'oro (NP Au) funzionalizzate con citrato e polivinilpirrolidone (PVP) sono state sintetizzate utilizzando procedure verdi e consolidate e depositate su tessuto di cotone. Una caratterizzazione strutturale e morfologica completa è stata condotta utilizzando la spettroscopia UV-VIS e infrarossa a trasformata di Fourier (FT-IR), la microscopia a forza atomica (AFM) e la microscopia elettronica a scansione (SEM). Una caratterizzazione dielettrica dettagliata del substrato vuoto ha rivelato effetti di polarizzazione interfacciale legati sia alle NP Au che alla loro specifica funzionalizzazione superficiale. Ad esempio, rivestendo interamente il tessuto di cotone (ovvero creando una matrice più isolante), è stato riscontrato che il PVP aumenta la resistenza del campione, ovvero diminuisce l'interconnessione elettrica delle NP Au rispetto al campione funzionalizzato con citrato. Tuttavia, è stato osservato che la funzionalizzazione del citrato ha fornito una distribuzione uniforme delle NP Au, che ha ridotto la loro spaziatura e, quindi, facilitato il trasporto degli elettroni. Per quanto riguarda il rilevamento dei composti organici volatili (COV), le misurazioni della spettroscopia di impedenza elettrochimica (EIS) hanno mostrato che il legame idrogeno e la risultante impedenza di migrazione protonica sono fondamentali per distinguere l'etanolo dall'acetone. 

This study aims to identify effective engagement tools and strategies that may strengthen student learning processes with a long-term impact. The context of learning plays an active role in student performance and needs to be carefully considered when designing collaborative learning environments. In the framework of a CDIO course entitled Project Course in Applied Physics (12 ECTS), master’s students in applied physics, electrical engineering, biomedical engineering, material science and nanotechnology work in groups of four to seven people for realizing their own project idea given three broad requirements: (i) use gas sensors, (ii) manage a certain maximum budget to purchase components, and (iii) build a working prototypefor any indoor air quality monitoring application of interest for them and their customer. Groupsare generally multicultural and multidisciplinary. Qualified supervision and skills training activities are adapted to facilitate the students’ progress and guarantee the success of their project work. Based on observations, feedback, and results over a five-year period, this approach appears more engaging and inspiring for both students and teachers compared to more defined projects. Encouraging the students to conceive their own original ideas, involving them in the co-creation of the learning process, and building knowledge, understanding, and skills through a variety of engaging experiences, helps their motivation, interest, active participation, and creativity with a direct impact on the quality of their learning. As an example of successful project work, here we report on two groups of students at Linköping University, Sweden, who have recently designed, developed, and tested an innovative sensor system prototype for smart monitoring of gas and particle emissions from cooking activities. The project course has received 5.0/5.0 as an overall students’ evaluation.

Human health has always been a major concern for science. Over the years, health research has included different areas, ranging from specific therapies to patients lifestyle and social information: "patient-oriented" approaches have increasingly emerged as a crucial tool for health care systems, as clearly shown during the recent SARS-CoV-2 pandemic. In this context, the synergy between different scientific and technological fields, such as biology, chemistry, physics, and engineering, is increasingly considered an essential requirement. This work presents a low cost and easy-to-use sensor of volatile organic compounds (VOCs) in exhaled breath, with the purpose of serving as a rapid, non-invasive and versatile diagnostic tool in smart medicine applications. A "lockand-key" system relying on gold nanoparticles deposited on cotton fabric enables the detection of target molecules, whose adsorption produces variations in terms of electrical impedance. The system has been exposed to ethanol-based solutions in an experimental campaign to investigate the sensing capabilities at 1 Hz - 1 MHz frequency range. The results achieved demonstrate the feasibility in obtaining health-relevant VOCs detection based on impedance analysis.

This work focuses on the possible application of gold nanoparticles on flexible cotton fabric as acetone- and ethanol-sensitive substrates by means of impedance measurements. Specifically, citrate- and polyvinylpyrrolidone (PVP)-functionalized gold nanoparticles (Au NPs) were synthesized using green and well-established procedures and deposited on cotton fabric. A complete structural and morphological characterization was conducted using UV–VIS and Fourier transform infrared (FT–IR) spectroscopy, atomic force microscopy (AFM), and scanning electron microscopy (SEM). A detailed dielectric characterization of the blank substrate revealed interfacial polarization effects related to both Au NPs and their specific surface functionalization. For instance, by entirely coating the cotton fabric (i.e., by creating a more insulating matrix), PVP was found to increase the sample resistance, i.e., to decrease the electrical interconnection of Au NPs with respect to citrate functionalized sample. However, it was observed that citrate functionalization provided a uniform distribution of Au NPs, which reduced their spacing and, therefore, facilitated electron transport. Regarding the detection of volatile organic compounds (VOCs), electrochemical impedance spectroscopy (EIS) measurements showed that hydrogen bonding and the resulting proton migration impedance are instrumental in distinguishing ethanol and acetone. Such findings can pave the way for the development of VOC sensors integrated into personal protective equipment and wearable telemedicine devices. This approach may be crucial for early disease diagnosis based on nanomaterials to attain low-cost/low-end and easy-to-use detectors of breath volatiles as disease markers.

Although many chemical gas sensors report high sensitivity towards volatile organic compounds (VOCs), finding selective gas sensing technologies that can classify different VOCs is an ongoing and highly important challenge. By exploiting the synergy between virtual electronic noses and machine learning techniques, we demonstrate the possibility of efficiently discriminating, classifying, and quantifying short-chain oxygenated VOCs in the parts-per-billion concentration range. Several experimental results show a reproducible correlation between the predicted and measured values. A 10-fold cross-validated quadratic support vector machine classifier reports a validation accuracy of 91% for the different gases and concentrations studied. Additionally, a 10-fold cross-validated partial least square regression quantifier can predict their concentrations with coefficients of determination, R-2, up to 0.99. Our methodology and analysis provide an alternative approach to overcoming the issue of gas sensors selectivity, and have the potential to be applied across various areas of science and engineering where it is important to measure gases with high accuracy.

Due to the SARS-CoV-2 outbreak, wearing a disposable face mask has become a worldwide daily routine, not only for medical operators or specialized personnel, but also for common people. Notwithstanding the undeniable positive effect in reducing the risk of virus transmission, it is important to understand if a prolonged usage of the same face mask can have effectiveness on filtering capability and potential health consequences. To this aim, we present three investigations. A survey, carried out in central Italy, offers an overview of the distorted public awareness of face mask usage. A functional study shows how prolonged wearing leads to substantial drops in humid air filtration efficiency. Finally, a morphological analysis reports the proliferation of fungal or bacteria colonies inside an improperly used mask. Our study highlights therefore that wearing a face mask is really beneficial only if it is used correctly.

Many aspects of the world population's daily life have been recently changed by the events following the SARS-COV-2 pandemic outbreak. Among all the consequences, wearing face masks has become a common routine to protect from virus transmission risks. This work presents a simple colorimetric system able to detect the carbon dioxide (CO2) saturation inside a disposable face mask, which is useful to determine the level of wear and degradation and to visually provide indications on its disposal time. The experiments were carried out by wearing a FFP2 face mask externally treated with a phenolphthalein solution and including in its breathing zone a CO2 sensor. Changes in face mask color were recorded by a camera and analyzed with ImageJ. A strong correspondence was found between the high values of CO2 detected by the sensor and the analyzed data. The results are promising and suggest further efforts in developing easy-to-use colorimetric methods as a visual indicator of the life cycle of a disposable face mask.

The gas sensing mechanisms, response, and behaviour of a real and a virtual solid-state chemical gas sensor operating either in static or in dynamic mode have been compared. The analysis was done by exposing simultaneously both sensors to different concentrations of various volatile organic compounds diluted in dry, as well as humid, synthetic air. The results revealed similar responses and behaviours for both types of measurement modes when the sensors were exposed towards single gas compounds, but a sensitivity enhancement in measurements comprising mixtures of gases when the sensors were operated in dynamic mode. The method used is able to overcome surface saturation problems and is beneficial for applications where mixtures of gases diluted in relative humidity are present.

The introduction of silicon carbide as the semiconductor in gas-sensitive field effect devices has disruptively improved this sensor platform extending the operation temperature to more than 600 °C with an increased number of detectable gases. Here, we review recent progress in research and applications, starting with transducer and detection mechanisms, presenting new material combinations as sensing layers for improved selectivity and detection limits down to subparts per billion. We describe how temperature cycled operation combined with advanced data evaluation enables one sensor to act as a sensor array thereby vastly improving selectivity. Field tests require advanced packaging, which is described, and examples of possible applications like selective detection of ammonia for urea injection control in diesel exhausts and toxic volatile organic compounds for indoor air quality monitoring and control are given.

In this work, we investigated the sensing performance of epitaxial graphene on Si-face 4H-SiC (EG/SiC) for liquid-phase detection of heavy metals (e.g., Pb and Cd), showing fast and stable response and low detection limit. The sensing platform proposed includes 3D-printed microfluidic devices, which incorporate all features required to connect and execute lab-on-chip (LOC) functions. The obtained results indicate that EG exhibits excellent sensing activity towards Pb and Cd ions. Several concentrations of Pb2+ solutions, ranging from 125 nM to 500 mu M, were analyzed showing Langmuir correlation between signal and Pb2+ concentrations, good stability, and reproducibility over time. Upon the simultaneous presence of both metals, sensor response is dominated by Pb2+ rather than Cd2+ ions. To explain the sensing mechanisms and difference in adsorption behavior of Pb2+ and Cd2+ ions on EG in water-based solutions, we performed van-der-Waals (vdW)-corrected density functional theory (DFT) calculations and non-covalent interaction (NCI) analysis, extended charge decomposition analysis (ECDA), and topological analysis. We demonstrated that Pb2+ and Cd2+ ions act as electron-acceptors, enhancing hole conductivity of EG, due to charge transfer from graphene to metal ions, and Pb2+ ions have preferential ability to binding with graphene over cadmium. Electrochemical measurements confirmed the conductometric results, which additionally indicate that EG is more sensitive to lead than to cadmium.

Gases, such as nitrogen dioxide, formaldehyde and benzene, are toxic even at very low concentrations. However, so far there are no low-cost sensors available with sufficiently low detection limits and desired response times, which are able to detect them in the ranges relevant for air quality control. In this work, we address both, detection of small gas amounts and fast response times, using epitaxially grown graphene decorated with iron oxide nanoparticles. This hybrid surface is used as a sensing layer to detect formaldehyde and benzene at concentrations of relevance (low parts per billion). The performance enhancement was additionally validated using density functional theory calculations to see the effect of decoration on binding energies between the gas molecules and the sensor surface. Moreover, the time constants can be drastically reduced using a derivative sensor signal readout, allowing the sensor to work at detection limits and sampling rates desired for air quality monitoring applications.

Compared with the most commonly used silicon and germanium, which need to work at cryogenic or low temperatures to decrease their noise levels, wide-bandgap compound semiconductors such as silicon carbide allow the operation of radiation detectors at room temperature, with high performance, and without the use of any bulky and expensive cooling equipment. In this work, we investigated the electrical and spectroscopic performance of an innovative position-sensitive semiconductor radiation detector in epitaxial 4H-SiC. The full depletion of the epitaxial layer (124 µm, 5.2 × 10¹³ cm⁻³) was reached by biasing the detector up to 600 V. For comparison, two different microstrip detectors were fully characterized from −20 °C to +107 °C. The obtained results show that our prototype detector is suitable for high resolution X-ray spectroscopy with imaging capability in a wide range of operating temperatures.

2D materials offer a unique platform for sensing with extreme sensitivity, since minimal chemical interactions cause noticeable changes in the electronic state. An area where this is particularly interesting is environmental monitoring of gases that are hazardous at trace levels. In this study, SiC is used as a base for epitaxial growth of high quality, uniform graphene, and for templated growth of atomically thin layers of platinum, with potential benefits in terms of the ability to operate at higher temperature and to serve as a more robust template for fiinctionalization compared to graphene. Fiinctionalization with nanoparticles allows tuning the sensitivity to specific molecules without damaging the 2D sensor transducer. With this platform we demonstrate detection of nitrogen dioxide, formaldehyde, and benzene at trace concentrations. This, combined with smart sensor signal evaluation allowing fast response times, could allow real-time monitoring of these toxic pollutants at concentrations of relevance to air quality monitoring.

Two-dimensional materials may constitute key elements in the development of a sensing platform where extremely high sensitivity is required, since even minimal chemical interaction can generate appreciable changes in the electronic state of the material. In this work, we investigate the sensing performance of epitaxial graphene on Si-face 4H-SiC (EG/SiC) for liquid-phase detection of heavy metals (e.g., Pb). The integration of preparatory steps needed for sample conditioning is included in the sensing platform, exploiting fast prototyping using a 3D printer, which allows direct fabrication of a microfluidic chip incorporating all the features required to connect and execute the Lab-on-chip (LOC) functions. It is demonstrated that interaction of Pb²⁺ ions in water-based solutions with the EG enhances its conductivity exhibiting a Langmuir correlation between signal and Pb²⁺ concentration. Several concentrations of Pb²⁺ solutions ranging from 125 nM to 500 µM were analyzed showing good stability and reproducibility over time.

It has been found that two-dimensional materials, such as graphene, can be used as remarkable gas detection platforms as even minimal chemical interactions can lead to distinct changes in electrical conductivity. In this work, epitaxially grown graphene was decorated with iron oxide nanoparticles for sensor performance tuning. This hybrid surface was used as a sensing layer to detect formaldehyde and benzene at concentrations of relevance in air quality monitoring (low parts per billion). Moreover, the time constants could be drastically reduced using a derivative sensor signal readout, allowing detection at the sampling rates desired for air quality monitoring applications.

Static and dynamic responses of a silicon carbide field-effect transistor gas sensor have been investigated at two different gate biases in several test gases. Especially the dynamic effects are gas dependent and can be used for gas identification. The addition of ultraviolet light reduces internal electrical relaxation effects, but also introduces new, temperature-dependent effects.

In this study,we focus on the plant bioelectric potential response as a low-cost and a high sensitivity evaluation technique of plant physiological activities for an agriculture support system. We developed a cultivation light intensity control system using bioelectric potential response. This system contributes to improvement of the cultivation environment and provides energy saving effect.In addition, we introduced a field effect transistor based on silicon carbide (SiC-FET)gas sensor and evaluated the characteristics of the sensor by changing several parameters. The results showed that iridium gated SiC-FET sensor has high sensitivity to ethylene,and the highest response is achieved at 200 ◦C. We aim at the development of an agriculture support system, which combines the plant bioelectrical potential and the SiC-FET gas sensor response.

It is widely known that ethylene treatment is an effective method for postharvest handling of fruit. In this study, we employed a field effect transistor based on silicon carbide (SiC-FET) gas sensor for detecting ethylene produced from fruits. The characteristics of the sensor was evaluated regarding several parameters. The selectivity and sensitivity of SiC-FET sensors can be controlled toward a few target gases by changing the operating temperature, gate material and material structure. We studied an iridium and a platinum gated SiC-FET sensors and characterized the sensing of these for different ethylene concentrations as the target gas at different operating temperatures. The results showed that the iridium gated SiC-FET sensor has high sensitivity to ethylene, and the highest response is achieved at 200 degrees C.

Data from a silicon carbide based field-effect transistor were recorded over a period of nine days in a ventilated school room. For enhanced sensitivity and selectivity especially to formaldehyde, porous iridium on pulsed laser deposited tungsten trioxide was used as sensitive layer, in combination with temperature cycled operation and subsequent multivariate data processing techniques. The sensor signal was compared to reference measurements for formaldehyde concentration, CO2 concentration, temperature, and relative humidity. The results show a distinct pattern for the reference formaldehyde concentration, arising from the day/night cycle. Taking this into account, the projections of both principal component analysis and partial least squares regression lead to almost the same result concerning correlation to the reference. The sensor shows cross-sensitivity to an unidentified component of human activity, presumably breath, and, possibly, to other compounds appearing together with formaldehyde in indoor air. Nevertheless, the sensor is able to detect and partially quantify formaldehyde below 40 ppb with a correlation to the reference of 0.48 and negligible interference from ambient temperature or relative humidity.

In this work, we exposed an MIS capacitor with porous platinum as gate material to different concentrations of CO and NH3. Its capacitance and typical reaction products (water, CO2 and NO) were monitored at high and low oxygen concentration and different gate bias voltages. We found that the gate bias influences the switch-point of the binary CO response usually seen when either changing the temperature at constant gas concentrations or the CO/O-2 ratio at constant temperature. For NH3, the sensor response as well as product reaction rates increase with bias voltages up to 6 V. A capacitance overshoot is observed when switching on or off either gas at low gate bias, suggesting increasing oxygen surface coverage with decreasing gate bias.

Gas sensitive metal/metal-oxide field effect transistors based on silicon carbide were used to study the sensor response to benzene (C₆H₆) at the low parts per billion (ppb) concentration range. A combination of iridium and tungsten trioxide was used to develop the sensing layer. Highsensitivity to 10 ppb C₆H₆ was demonstrated during several repeated measurements at a constant temperature from 180 to 300 °C. The sensor performance was studied also as a function of the electrical operating point of the device, i.e., linear, onset of saturation, and saturation mode. Measurements performed in saturation mode gave a sensor response up to 52 % higher than those performed in linear mode.

Temperature cycled operation and multivariate statistics have been used to compare the selectivity of two gate (i.e. sensitive) materials for gas-sensitive, silicon carbide based field effect transistors towards naphthalene and ethanol in different mixtures of the two substances. Both gates have a silicon dioxide (SiO2) insulation layer and a porous iridium (Ir) electrode. One of it has also a dense tungsten trioxide (WO3) interlayer between Ir and SiO2. Both static and transient characteristics play an important role and can contribute to improve the sensitivity and selectivity of the gas sensor. The Ir/SiO2 is strongly influenced by changes in ethanol concentration, and is, thus, able to quantify ethanol in a range between 0 and 5 ppm with a precision of 500 ppb, independently of the naphthalene concentrations applied in this investigation. On the other hand, this sensitivity to ethanol reduces its selectivity towards naphthalene, whereas Ir/WO3/SiO2 shows an almost binary response to ethanol. Hence, the latter has a better selectivity towards naphthalene and can quantify legally relevant concentrations down to 5 ppb with a precision of 2.5 ppb, independently of a changing ethanol background between 0 and 5 ppm. (C) 2016 Elsevier B.V. All rights reserved.

This contribution treats the latest developments in the understanding of basic principles regarding device design, transduction mechanisms, gas-materials-interactions, and materials processing for the tailored design and fabrication of SiC FET gas sensor devices, mainly intended as products for the automotive sector.

Two-dimensional materials offer a unique platform for sensing where extremely high sensitivity is a priority, since even minimal chemical interaction causes noticeable changes inelectrical conductivity, which can be used for the sensor readout. However, the sensitivity has to becomplemented with selectivity, and, for many applications, improved response- and recovery times are needed. This has been addressed, for example, by combining graphene (for sensitivity) with metal/oxides (for selectivity) nanoparticles (NP). On the other hand, functionalization or modification of the graphene often results in poor reproducibility. In this study, we investigate thegas sensing performance of epitaxial graphene on SiC (EG/SiC) decorated with nanostructured metallic layers as well as metal-oxide nanoparticles deposited using scalable thin-film depositiontechniques, like hollow-cathode pulsed plasma sputtering. Under the right modification conditions the electronic properties of the surface remain those of graphene, while the surface chemistry can betuned to improve sensitivity, selectivity and speed of response to several gases relevant for airquality monitoring and control, such as nitrogen dioxide, benzene, and formaldehyde.

With the increased interest in development of cheap, simple means for indoor air quality monitoring, and specifically in relation to certain well-known pollutant substances with adverse health effects even at very low concentrations, such as different Volatile Organic Compounds (VOCs), this contribution aims at providing an overview of the development status of the silicon carbide field effect transistor (SiC FET) based sensor platform for ppb level detection of VOCs. Optimizing the transducer design, the gas-sensitive material(s) composition, structure and processing, its mode of operation - applying temperature cycled operation in conjunction with multivariate data evaluation - and long-term performance it has been possible to demonstrate promising resultsregarding the sensor technology’s ability to achieve both single-digit ppb sensitivity towards e.g. naphthalene as well as selective detection of individual substances in a mixture of different VOCs.

High-temperature iridium-gated field effect transistors based on silicon carbide have been used for sensitive detection of specific volatile organic compounds (VOCs) in concentrations of health concern, for indoorair quality monitoring and control. Formaldehyde, naphthalene, and benzene were studied as hazardous VOCs at parts per billion (ppb) down to sub-ppb levels. The sensor performance and characteristics were investigated at a constant temperature of 330° C and at different levels of relative humidity up to 60 %, showing good stability and repeatability of the sensor response, and excellent detection limits in the sub-ppb range.

Gas sensitive field effect transistors based on silicon carbide, SiC-FETs, have been studied for indoor air quality applications. The selectivity of the sensors was increased by temperature cycled operation, TCO, and data evaluation based on multivariate statistics. Discrimination of benzene, naphthalene, and formaldehyde independent of the level of background humidity is possible by using shape describing features as input for Linear Discriminant Analysis, LDA, or Partial Least Squares – Discriminant Analysis, PLS-DA. Leave-one-out cross-validation leads to a correct classification rate of 90 % for LDA, and for PLS-DA a classification rate of 83 % is achieved. Quantification of naphthalene in the relevant concentration range, i.e. 0 ppb to 40 ppb, was performed by Partial Least Squares Regression and a combination of LDA with a second order polynomial fit function. The resolution of the model based on a calibration with three concentrations was approximately 8 ppb at 40 ppb naphthalene for both algorithms.

Hence, the suggested strategy is suitable for on demand ventilation control in indoor air quality application systems.

Packaging of chemical sensors is still an area, which is not much explored. Low temperature co-fired ceramic, LTCC, packaging offers large advantages in terms of 3D design, integration of advanced functionality and fast processing. SiC based FET gas sensors are possible to integrate directly in the LTCC co-firing process at 850 °C, whereby both high temperature and other advanced applications like ultra-low detection of toxic gases are greatly improved. The LTCC packaging is also used for development of particle detectors as well as packaging for an electrical method to detect toxic effect on cells by particles.

Graphene-based chemical gas sensors normally show ultra-high sensitivity to certain gas molecules but at the same time suffer from poor selectivity and slow response and recovery Limes. Several approaches based on functionalization or modification of the graphene surface have been demonstrated as means to improve these issues, but most such measures result in poor reproducibility. In this study we investigate reproducible graphene surface modifications by sputter deposition of thin nanostructured Au or Pt layers. It is demonstrated that under the right metallization conditions the electronic properties of the surface remain those of graphene, while the surface chemistry is modified to improve sensitivity, selectivity and speed of response to nitrogen dioxide.

Gas sensitive FETs based on SiC have been studied for the discrimination and quantification of hazardous volatile organiccompounds (VOCs) in the low ppb range. The sensor performance was increased by temperature cycled operation (TCO) anddata evaluation based on multivariate statistics, here Linear Discriminant Analysis (LDA). Discrimination of formaldehyde,naphthalene and benzene with varying concentrations in the ppb range is demonstrated. In addition, it is shown that naphthalenecan be quantified in the relevant concentration range independent of the relative humidity and against a high ethanol background.Hence, gas sensitive SiC-FETs are suitable sensors for determining indoor air quality.

In this study, we use two different sensor technologies based on gas sensitive silicon carbide field effect transistors (SiC-FETs) and epitaxial graphene on SiC (EG/SiC) for highly sensitive and selective detection of trace amounts of three hazardous volatile organic compounds (VOCs), i.e. formaldehyde (CH₂O), benzene (C₆H₆), and naphthalene (C₁₀H₈), present in indoor environments in concentrations of health concern.

Iridium and platinum are used as sensing layers for the gate contacts. The FET sensors are operated at high temperature, under static and dynamic conditions. Excellent detection limits of 10 ppb for CH₂O, about 1 ppb for C₆H₆, and below 0.5 ppb for C₁₀H₈ are measured at 60 % relative humidity (r.h.) [1]. The selectivity of the sensors is increased by temperature cycled operation and data evaluation based on multivariate statistics. Discrimination of CH₂O, C₆H₆, and C₁₀H₈ independent of the level of background humidity is possible with a very high cross-validation rate up to 90 % [2]. These results are very encouraging for indoor air quality control, being below the threshold limits recommended by the WHO guidelines.

Graphene-based chemical sensors offer the advantage of extreme sensitivity due to graphene’s unique electronic properties and the fact that every single atom is at the surface and available to interact with gas molecules. For this reason, uniform monolayer graphene is crucial [3], which is guaranteed by our optimized epitaxial growth process. Graphene-based chemical gas sensors normally show ultra-high sensitivity to certain gas molecules but suffer from poor selectivity. Functionalization or modification of the graphene surface can improve selectivity, but most such measures result in poor reproducibility. We demonstrate reproducible, non-destructive means of graphene surface decoration with nanostructured metals and metal oxides, and study their effect on the gas interactions at the graphene surface.

Semiconductor detectors for in vivo dosimetry haveserved in recent years as an important part of quality assurancefor radiotherapy. Silicon carbide (SiC) can represent a bettersemiconductor with respect to the more popular silicon (Si) thanksto its physical characteristics such as wide bandgap, high electronsaturation velocity, lower effective atomic number, and high radiationresistance to X and gamma rays. In this article we present aninvestigation aimed at characterizing 4H-SiC epitaxial Schottkydiodes as in vivo dosimeters. The electrical characterization atroom temperature showed ultra low leakage current densities aslow as 0.1 pA/cm at 100 V bias with negligible dependence ontemperature. The SiC diode was tested as radiotherapy dosimeterusing 6 MV photon beams from a linear accelerator in a typicalclinical setting. Collected charge as a function of exposed radiationdose were measured and compared to three standard commerciallyavailable silicon dosimeters. A sensitivity of 23 nC/Gy withlinearity errors within 0.5% and time stability of 0.6% wereachieved. No negligible effects on the diode I-V characteristicsafter irradiation were observed.

Gas sensitive silicon carbide field effect transistors with nanostructured Ir gate layershave been used for the first time for sensitive detection of volatile organic compounds (VOCs) atpart per billion level, for indoor air quality applications. Formaldehyde, naphthalene, and benzenehave been used as typical VOCs in dry air and under 10% and 20% relative humidity. A singleVOC was used at a time to study long-term stability, repeatability, temperature dependence, effectof relative humidity, sensitivity, response and recovery times of the sensors.

Silicon Carbide (SiC) is a wide bandgap semiconductor with attractive physical properties for manufacturing X-ray detectors [1]. The density of SiC crystal allow an X‑ray absorption similar to Silicon. The wide bandgap of SiC (3.2 eV) allows to make high Schottky barriers and minimises the reverse current from thermal generation of charge carriers. The SiC breakdown field (2 MV/cm) and the high saturation velocities of the charge carriers (200 mm/ns) make the detector response very fast and not affected by charge trapping degradation.

In this talk, we present the SiC X-ray detectors we have developed. The detectors show leakage current densities as low as J=0.1 pA/cm² at +25°C, three orders of magnitude lower than those of the best silicon detectors and make SiC detectors practically noiseless at room temperature. The detectors have been tested also at high temperatures: at T=+100°C the J= 1 nA/cm², allowing excellent X-ray spectrometry even at such high temperatures, forbidden to conventional semiconductor detectors. In addition we will show that our SiC detectors can also operate while the temperature is freely changing of tens of °C, without affecting spectra quality.

The possibility to make the detector operating without any cooling system even at high temperature with adequate energy resolution can open new perspectives in X‑ray spectrometry applications, even ever considered before.

An SPX4 4H-silicon carbide detector consisting of 4 x 4 pixels was developed and studied experimentally. Its pixel size is 400 μm x 400 μm . A timing resolution of 117 11 ps fullwidth at half-maximum (FWHM) has been measured for thedetection of alphas. With such good timing performance andhigh granularity, the SiC pixel detector holds great promise as anassociated alpha-particle detector for fast neutron imaging.

The Asterix iodine laser of the PALS laboratory in Prague, operating at 1315 nm fundamental frequency, 300 ps pulse duration, 600 J maximum pulse energy and 10¹⁶ W/cm² intensity, is employed to irradiatethin hydrogenated targets placed in high vacuum. Different metallic and polymeric targets allow togenerate multi-energetic and multi-specie ion beams showing peculiar properties. The plasma obtainedby the laser irradiation is monitored, in terms of properties of the emitted charge particles, by using time-of-flight techniques and Thomson parabola spectrometer (TPS). A particular attention is given tothe proton beam production in terms of the maximum energy, emission yield and angular distributionas a function of the laser energy, focal position (FP), target thickness and composition.

We present the performance of a Silicon Carbide (SiC) detector in the acquisition of the radiation emittedby laser generated plasmas. The detector has been employed in time of flight (TOF) configuration withinan experiment performed at the Prague Asterix Laser System (PALS). The detector is a 5 mm2 area 100 nmthick circular Ni SiC Schottky junction on a high purity 4H-SiC epitaxial layer 115 μm thick. Currentsignals from the detector with amplitudes up to 1.6 A have been measured, achieving voltage signals over 80 V on a 50 Ω load resistance with excellent signal to noise ratios. Resolution of few nanoseconds hasbeen experimentally demonstrated in TOF measurements. The detector has operated at 250 V DC biasunder extreme operating conditions with no observable performance degradation.

Large variations have been observed in the thickness uniformity and carrier concentration of epitaxial graphene grown on SiC by sublimation for samples grown under identical conditions and on nominally on-axis hexagonal SiC (0001) substrates. We have previously shown that these issues are both related to the morphology of the graphene-SiC surface after sublimation growth. Here we present a study on how the substrate polytype, substrate surface morphology and surface restructuring during sublimation growth affect the uniformity and carrier concentration in epitaxial graphene on SiC. These issues were investigated employing surface morphology mapping by atomic force microscopy coupled with local surface potential mapping using scanning Kelvin probe microscopy.

Radiation detectors on a semi-insulating (SI) 4H siliconcarbide (SiC) wafer have been manufactured and characterizedwith X and photons in the range 8–59 keV. The detectors were 400 μm diameter circular Ni-SiC junctions on an SI 4H-SiC wafer thinned to 70 μm. Dark current densities of 3.5 nA/cm² at 20 °C and 0.3 μA/cm² at 104 °C with an internal electric field of 7 kV/cm have been measured. X-γ ray spectra from ²⁴¹Am have been acquired at room temperature with pulser line width of 756 eV FWHM. The charge collection efficiency (CCE) has been measured under different experimental conditions with a maximum CCE = 75 % at room temperature. Polarization effects have been observed, and the dependence of CCE on time and temperature has been measured and analyzed. The charge trapping has been described by the Hecht model with a maximum totalmean drift length of 107 μm at room temperature.