Roadmap on printable electronic materials for next-generation sensors

The dissemination of sensors is key to realizing a sustainable, ‘intelligent’ world, where everyday objects and environments are equipped with sensing capabilities to advance the sustainability and quality of our lives—e.g., via smart homes, smart cities, smart healthcare, smart logistics, Industry 4.0, and precision agriculture. The realization of the full potential of these applications critically depends on the availability of easy-to-make, low-cost sensor technologies. Sensors based on printable electronic materials offer the ideal platform: they can be fabricated through simple methods (e.g., printing and coating) and are compatible with high-throughput roll-to-roll processing. Moreover, printable electronic materials often allow the fabrication of sensors on flexible/stretchable/biodegradable substrates, thereby enabling the deployment of sensors in unconventional settings. Fulfilling the promise of printable electronic materials for sensing will require materials and device innovations to enhance their ability to transduce external stimuli—light, ionizing radiation, pressure, strain, force, temperature, gas, vapours, humidity, and other chemical and biological analytes. This Roadmap brings together the viewpoints of experts in various printable sensing materials—and devices thereof—to provide insights into the status and outlook of the field. Alongside recent materials and device innovations, the roadmap discusses the key outstanding challenges pertaining to each printable sensing technology. Finally, the Roadmap points to promising directions to overcome these challenges and thus enable ubiquitous sensing for a sustainable, ‘intelligent’ world

Low-operating temperature chemiresistive gas sensors: Fabrication and DFT calculations

Despite advantages highlighted by Metal OXides (MOX) based gas sensors, these devices still present drawbacks in their performances (e.g. selectivity, stability and high operating temperature), so further investigations are necessary. Researchers tried to address these problems in several ways, which includes new synthesis methods for innovative materials based on MOX, such as solid solutions, addition of catalysts and doping of MOX by using external atoms or oxygen vacancies. Concerning this last issue, literature presents a lack of studies on how the arrangement and number of oxygen vacancies affect the sensing performance and only a few preliminary works highlighted interesting results. Another way to overcome MOX sensor drawbacks is to investigate novel class of materials, such as metal organic framework or 2D materials. Among these, phosphorene is one of the best candidates for such technological application, since it shows a chemoresistive activity at room temperature. The goal of this work is to decrease the operating temperature of SnO2 based gas sensors by exploiting the oxygen vacancies. First, a theoretical investigation was done in the framework of Density Functional Theory (DFT) to investigate, on the atomic scale, how oxygen vacancies influence the physical and chemical properties of the material. The effect of oxygen vacancies on the structural, electronic and electrical properties of bulk SnO2 at two different concentrations was studied, then the formation of surface oxygen vacancies was investigated in order to study the adsorption of oxygen molecules from the surrounding atmosphere on the stoichiometric and reduced SnO2 surface. Then, reduced SnO2-x was synthesized and devices based on the produced material were fabricated and tested. The results showed a high response of the sensors towards low concentrations of nitrogen dioxide NO2 (500 ppb) at 130°C instead of the typical operating temperature of 450°C for SnO2-based gas sensors. This decrease in the operating temperature results in a decrease of the power consumption of the device, opening up to its possible employment on portable devices like mobile phones. The results were interpreted characterizing the material by mean of X-ray Powder Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscope (SEM) and Ultraviolet–visible spectroscopy (UV-visible) analysis. In the end, the experimental results were compared to the DFT outputs obtained. As mentioned before, phosphorene is one of the promising 2D materials for gas sensing applications, but it still presents some drawbacks, mainly due to the material degradation over the time when exposed to ambient conditions. Many investigations were done on decorating phosphorene with metal atoms in order to enhance its performance for different technological applications. Nickel is one of metals proposed for such purpose, but few studies were done on nickel decorated phosphorene for gas sensing applications, especially for gas sensing application. In the innovative work here proposed, DFT calculations were carried out to explain how nickel influences the electronic properties of phosphorene since the decoration with nickel showed better stability of the sensor and high response towards NO2 at room temperature. The theoretical results explained this behavior by studying the adsorption of oxygen molecules on pristine and nickel loaded phosphorene. The DFT calculations showed that oxygen molecules dissociate on the layer of pristine phosphorene and react with phosphorus atoms (oxidation of the material), while in the presence of the nickel atoms the later play the role of acceptors and interact with the oxygen molecules. Finally, the sensing mechanism towards NO2 was investigated theoretically by studying the charge transfer occurring at the surface of the material during the adsorption process.I sensori di gas basati sugli ossidi metallici semiconduttori (MOX) si sono rivelati negli ultimi anni una tecnologia estremamente vantaggiosa. Nonostante i progressi fatti in questo campo, questi dispositivi presentano ancora alcuni punti deboliche spingono la ricerca ad effettuare ulteriori indagini per perfezionare il loro funzionamento. I ricercatori hanno cercato di risolvere questi svantaggi in diversi modi, focalizzandosi sullo sviluppo di MOX innovativi, tra cui il drogaggio tramite l’utilizzo di additivi o l’introduzione nel materiale di vacanze di ossigeno a concentrazione controllata. Questa’alternativa sta attirando l’attenzione di molti gruppi di ricerca, anche se, ad oggi, la letteratura scientifica presenta una mancanza di studi su come la disposizione e concentrazione di vacanze di ossigeno influenzano le performance di sensing e solo alcuni lavori preliminari hanno portato a risultati interessanti. Per cercare di ovviare ai limiti dei sensori MOX, una seconda via è stata lo sviluppo e di materiali 2D basati su solfuri metallici, grafene o similari. Il fosforene è uno dei migliori candidati per tale applicazione tecnologica, poiché mostra un'attività elettrica anche a temperatura ambiente, anche se studi preliminari hanno evidenziato un alto tasso di degradazione nel tempo del materiale durante il suo utilizzo. L'obiettivo di questo lavoro è quello di diminuire la temperatura di funzionamento di sensori di gas basati su SnO2 sfruttando il controllo delle vacanze di ossigeno. A tale scopo, è stato fatto inizialmente uno studio della letteratura e un’analisi analitica nell’ambito della DFT per indagare come le vacanze di ossigeno influenzano le proprietà fisico-chimiche del materiale. È stato studiato l'effetto di due diverse concentrazioni di vacanze di ossigeno sulle proprietà chimico-fisiche dello SnO2 bulk. Successivamente è stata studiata la formazione della vacanze in superficie per investigare l'adsorbimento di molecole di ossigeno dall'atmosfera circostante sulla superficie dello SnO2 è stato sintetizzato tramite sintesi sol-gel e la riduzione è stata ottenuta tramite trattamento termico in presenza di H2 a diverse temperature. I risultati hanno mostrato un'alta risposta dei sensori basati su SnO2-x in presenza di basse concentrazioni di NO2 spostando a 130 °C la temperatura ottimale di funzionamento del dispositivo. Questa diminuzione della temperatura operativa implica una diminuzione del consumo energetico del dispositivo Come menzionato precedentemente, il fosforene è uno dei materiali 2D più promettenti per lo sviluppo di sensori di gas chemoresistivi, ma presenta ancora alcuni svantaggi. Molti studi sono stati sviluppati sulla decorazione del fosforene con atomi metallici al fine di migliorare le sue prestazioni per diverse applicazioni tecnologiche, ma non sono stati ancora condotti studi specifici su questa particolare forma di fosforene decorato per applicazioni di sensoristica gassosa. Nello studio qui proposto, sono stati eseguiti calcoli DFT per spiegare come il nichel influenzi le proprietà elettroniche del fosforene, poiché la decorazione con nichel ha mostrato una migliore stabilità del sensore e un’alta sensibilità all’NO2. Tramite simulazione DFT è stato possibile investigare l'adsorbimento delle molecole di ossigeno sul Fosforene tal quale e decorato con nichel. I risultati hanno evidenziato che le molecole di ossigeno si dissociano sullo strato di fosforene tal quale e reagiscono con gli atomi di fosforo, ossidandolo, mentre in presenza dei cluster di nichel è quest’ultimo a svolgere il ruolo di catalizzatore, interagendo con le molecole di ossigeno. Infine, il meccanismo di interazione tra NO2 e la superficie del fosforene tal quale e funzionalizzato è stato caratterizzato teoricamente studiando il trasferimento di carica che avviene sulla superficie del materiale in esame

A Toolkit for Human-Centred Engineering: An Experience with Pre-teens

IoTgo is an adaptable toolkit for human-centred engineering with micro-electronics. This paper reports on IoTgo for pre-teens. This guided them from exploring the workings of sensors, actuators, and wireless communication to the development of prototypes with them that interact with people. The paper explains the rationale of the toolkit for pre-teens, and what they accomplished with it

Teaching and Investigating on Modelling through Analogy in Primary School

Physics deals with complex systems by reducing them to relationships between a limited number of relevant quantities and general principles. Since we live in a reality characterised by an increasing complexity in all fields, an indispensable challenge arises for education to turn basic science instruction into a key stage of education per se. Is it possible to introduce some aspects of the physics approach as early as the first school years? Which ones, how, and with what results? Here, results of the initial phase of a three-year project on complexity are presented. This educational innovation path has been developed for elementary and middle schools and is designed as a gentle introduction to complex and systemic thinking. It aims to foster in children reasoning by analogies and the development of simple but effective and versatile basic concepts. The project exploits the use of the small set of primary metaphors already available in children’s cognitive toolkit to apply them to describing the characteristics of various circuits, from marbles to water and air to electricity. Pupils’ feedback was analysed through a single case study with a qualitative and quantitative methodology. Results were encouragingly positive and showed a wide range of abilities to capture and develop analogies on the topic of the circuit

Gas Sensing Capabilities of CuInS2/ZnO Core–Shell Quantum Dot

Chemoresistive gas sensors are surely one of the easiest and most commonly used methods to monitor the presence of different polluting gases. Nevertheless, there are still several challenges to overcome in order for these sensors to be widely used. In particular, the selectivity and sensitivity of chemoresistive gas sensors towards a wide range of analytes need to be improved. This is why new sensing materials capable of detecting different analytes in a sensitive and selective manner are being investigated. In this regard, this work is focused on the development and characterization of a new sensing material based on the quantum dot (QD) core–shell of CuInS2/ZnO (CIS-ZO). Optimized films of the QD core–shell of CIS-ZO were integrated into a micro-electromechanical system (MEMS)-based gas sensor platform, showing excellent sensing performance versus different gases and especially towards ethanol (C2H5OH)

Influence of Oxygen Vacancies in Gas Sensors Based on Tin Dioxide Nanostructure: A First Principles Study

So far, literature presents lacks of studies on how number and arrangement of oxygen vacancies affects the sensing performance of chemoresistive gas sensors, which usually needs a high operating temperature. Therefore, in order to enhance the behavior of SnO2 as active element in gas sensors devices, we propose a study concerning the impact of oxygen vacancies on its physical-chemical properties. Structural, electronic and electrical properties of the stochiometric SnO2 and the reduced one were studied

Influence of Oxygen Vacancies in Gas Sensors Based on Tin Dioxide Nanostructure: A First Principles Study

No abstract availabl

Adsorption of oxygen species on the SnO2 (110) surface: a Density Functional Theory investigation

none7Understanding the interaction between oxygen molecules and metal oxide semiconductors surface is important for the development of gas sensors based on this kind of materials. The adsorption of oxygen molecules on these material's surface is (at) the basis of reactions between the surface oxygen species and the target gases molecules. The SnO2 (110) surface is the most stable and most dominant surfaces of the cassiterite SnO2 and they are experimentally very well characterised. In this work, we are investigating the adsorption of O2 molecules on the clean and defective SnO2 (110) surfaces by mean of Density Functional Theory (DFT). For the defective surface, three kinds of oxygen vacancies are considered: formations of bridging oxygen (Obridge) vacancy, in-plane oxygen (Oin-plane) and the formation of an oxygen vacancy in the subsurface (Osub-surf). We are investigating also the impact of the thickness of the material on the relaxation of the structure, we are using 3-5- and 7-layers structures. Our preliminary results showed that the formation of an in-plane and in the subsurface oxygen vacancy needs more energy than the bridging one and consequently only the bridging oxygen vacancies are considered in this work. The corresponding formation energies of the different kinds of oxygen vacancies are reported in table1. The adsorption of O2 molecule on the different SnO2 (110) surfaces was studied by calculating the adsorption energy Eads of the molecule, this later was relaxed in the same cell with the different considered surfaces and different modes are considered.noneSoufiane Krik, Andrea Gaiardo, Matteo Valt, Barbara Fabbri, Cesare Malagù, Pierluigi Bellutti, Vincenzo GuidiKrik, Soufiane; Gaiardo, Andrea; Valt, Matteo; Fabbri, Barbara; Malagu', Cesare; Bellutti, Pierluigi; Guidi, Vincenz

Development of a Pt, Pd, Ag and Au Nanocluster Decorated SnO2 Sensor Array for Precision Agriculture

Nowadays, precision farming is a key topic. Because of the steady increase in the world's population, which is expected to reach 9.6 billion by 2050, it is vital to increase the productivity of agricultural land while reducing waste of water, fertilizers, pesticides and pesticide. To achieve these goals, precision agriculture aims to provide farmers with a wealth of information to optimize field management, by matching farming practices more closely to crop needs. This information is obtained exploiting satellite and weather data, and wireless sensor arrays, which combined with the use of GPS, Internet of Things (IoT) and machine learning allow the farmer to operate with both a control and predictive approach [1]. For the best use of precision agriculture, it is therefore essential to collect as much data as possible on the crop status. On the one hand, various technologies have been developed or improved to collect information directly in the field, in particular to measure the pH, the nitrogen compound concentrations and the humidity amount in the soil [2,3]. On the other hand, there is not yet a well-structured system for monitoring crop gas emissions, which together with the control of soil parameters, can lead to a comprehensive evaluation of the effective health status and growth of the crop [4]. In this work, a sensor array composed of four different sensing materials, i.e. SnO2 decorated with Ag, Pd, Pt and Au nanoclusters, were developed and investigated to selective detect five different gases commonly present or emitted by crops

Synthesis, Material and Electrical Characterization Combined with DFT Calculations of Reduced SnO2-x

none8The use of Density Functional Theory (DFT) simulations to predict the chemical-physical properties of nanostructured compounds and heterogeneous interactions (solid-gas) has become almost essential today, both to predict the properties of technologically advanced nanomaterials and to overcome the limits of experimental characterizations. Specifically, the use of DFT calculations can likewise be used in chemoresistive gas sensor applications, to investigate the physical-chemical properties of nanostructured semiconductors and their possible catalytic activity. Among the various gas sensing materials used, the Metal Oxide Semiconductors (MOXS) are the most investigated since the excellent sensitivity, good stability and low cost of production [1,2]. Nevertheless, besides all of these advantages they present also some drawbacks such as signal drift over the time, lack of selectivity and high operating temperature. Investigators have tried to address these problems in several manners, including the synthesis of solid solutions composed of different metal oxides, doping these materials with deferent kinds of elements and also with controlled concentrations of oxygen vacancies. The latter is a field still little explored, but preliminary experimental and theoretical works highlighted interesting results [3,4]. When the sensor is exposed to a reducing (oxidizing) gas, the gas molecules interact with the chemisorbed oxygen species from the surrounding atmosphere and then decrease (increase) the resistance of a n-type based gas sensor, and vice versa for a p-type semiconductor. This change in resistance is due to the exchange of electrons between the surface and the conduction band. For a stoichiometric semiconductor, the electrons involved in this reaction that are in the conduction band are coming from the valence band after heating the material, in this case they need a high energy to blow up from the valence band to the conduction band. But when one introduces some defects, new energy level will be created and then they will be a new electrons source, thus the energy that the sensor needs to be thermoactivated decrease; that is energy that electrons need to jump to the conduction band.noneSoufiane Krik; Andrea Gaiardo; Matteo Valt; Barbara Fabbri; Cesare Malagù; Giancarlo Pepponi; Pierluigi Bellutti; Vincenzo GuidiKrik, Soufiane; Gaiardo, Andrea; Valt, Matteo; Fabbri, Barbara; Malagù, Cesare; Pepponi, Giancarlo; Bellutti, Pierluigi; Guidi, Vincenz