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Projeto de investigação
Emerging Printed Electronics Research Infrastructure (EMERGE)
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Flexible nanostructured TiO2-based gas and UV sensors
Publication . Nunes, Daniela; Fortunato, Elvira; Martins, Rodrigo; CENIMAT-i3N - Centro de Investigação de Materiais (Lab. Associado I3N); DCM - Departamento de Ciência dos Materiais; UNINOVA-Instituto de Desenvolvimento de Novas Tecnologias; Discover
Flexible sensors have been attracting an ever-growing attention over the last years due to their outstanding characteristics, that include their lightweight and cost-effective characteristics, high stretchability, biocompatibility, and conformability. Moreover, the pursue of such devices has exponentially raised, with the IoT (Internet of Things) technology and the integration of several kinds of sensor devices that allow exchanging information on the internet, as well as remotely operating devices and collecting data. In fact, IoT is bringing sensor usage to a new level, where gas and ultraviolet (UV) sensors are largely integrated, guaranteeing the well-being and safety of people, with the immediate detection and response to changes in an environment. Gas and UV sensors based on titanium dioxide (TiO2) have been largely reported, where numerous efforts have been devoted to improving its sensing performance, especially when employing TiO2 at the nanoscale. TiO2 has the advantage of being chemical stable, non-toxic, inexpensive, and compatible with low-cost wet-chemical synthesis routes. This review outlines the current state of flexible gas and UV sensor technologies having TiO2 as the sensing layer and the impact of this nanostructured material on the field.
Screen-printed, flexible, and eco-friendly thermoelectric touch sensors based on ethyl cellulose and graphite flakes inks
Publication . Figueira, J.; Bonito, R. M.; Carvalho, J. T.; Vieira, E. M. F.; Gaspar, C.; Loureiro, Joana; Correia, J. H.; Fortunato, E.; Martins, R.; Pereira, L.; DCM - Departamento de Ciência dos Materiais; CENIMAT-i3N - Centro de Investigação de Materiais (Lab. Associado I3N); UNINOVA-Instituto de Desenvolvimento de Novas Tecnologias; IOP Publishing
Despite the undoubtable interest in energy conversion, thermoelectric (TE) materials can be approached from a temperature-sensitive perspective, as they can detect small thermal stimuli, such as a human touch or contact with cold/hot objects. This feature offers possibilities for different applications one of them being the integration with scalable and cost-effective, biocompatible, flexible, and lightweight thermal sensing solutions, exploring the combination of sustainable Seebeck coefficient-holding materials with printing techniques and flexible substrates. In this work, ethyl cellulose and graphite flakes inks were optimized to be used as functional material for flexible thermal touch sensors produced by screen-printing. Graphite concentrations of 10, 20 and 30 wt% were tested, with 1, 2 and 3 printed layers on four different substrates—office paper, sticker label paper, standard cotton, and organic cotton. The conjugation of these variables was assessed in terms of printability, sheet resistance and TE response. The best electrical-TE output combination is achieved by printing two layers of the ink with 20 wt% of graphite on an office paper substrate. Subsequently, thermal touch sensors with up to 48 TE elements were produced to increase the output voltage response (>4.5 mV) promoted by a gloved finger touch. Fast and repeatable touch recognition were obtained in optimized devices with a signal-to-noise ratio up to 340 and rise times bellow 0.5 s. The results evidence that the screen-printed graphite-based inks are highly suitable for flexible TE sensing applications.
Tailoring the synaptic properties of a-IGZO memristors for artificial deep neural networks
Publication . Pereira, Maria Elias; Deuermeier, Jonas; Freitas, Pedro; Barquinha, Pedro; Zhang, Weidong; Martins, Rodrigo; Fortunato, Elvira; Kiazadeh, Asal; DCM - Departamento de Ciência dos Materiais; CENIMAT-i3N - Centro de Investigação de Materiais (Lab. Associado I3N); UNINOVA-Instituto de Desenvolvimento de Novas Tecnologias
Neuromorphic computation based on resistive switching devices represents a relevant hardware alternative for artificial deep neural networks. For the highest accuracies on pattern recognition tasks, an analog, linear, and symmetric synaptic weight is essential. Moreover, the resistive switching devices should be integrated with the supporting electronics, such as thin-film transistors (TFTs), to solve crosstalk issues on the crossbar arrays. Here, an a-Indium-gallium-zinc-oxide (IGZO) memristor is proposed, with Mo and Ti/Mo as bottom and top contacts, with forming-free analog switching ability for an upcoming integration on crossbar arrays with a-IGZO TFTs for neuromorphic hardware systems. The development of a TFT compatible fabrication process is accomplished, which results in an a-IGZO memristor with a high stability and low cycle-to-cycle variability. The synaptic behavior through potentiation and depression tests using an identical spiking scheme is presented, and the modulation of the plasticity characteristics by applying non-identical spiking schemes is also demonstrated. The pattern recognition accuracy, using MNIST handwritten digits dataset, reveals a maximum of 91.82% accuracy, which is a promising result for crossbar implementation. The results displayed here reveal the potential of Mo/a-IGZO/Ti/Mo memristors for neuromorphic hardware.
Ecofriendly Printed Wood-Based Honey-Gated Transistors for Artificial Synapse Emulation
Publication . Vieira, Douglas Henrique; Carlos, Emanuel; Ozório, Maíza Silva; Morais, Maria; Fortunato, Elvira; Alves, Neri; Martins, Rodrigo; CENIMAT-i3N - Centro de Investigação de Materiais (Lab. Associado I3N); DCM - Departamento de Ciência dos Materiais; John Wiley and Sons Inc.
Printed electronics have traditionally used substrates and materials derived from fuel-based or less abundant and toxic resources, raising environmental concerns. Wood as a substrate reduces processing steps and enables the integration of intelligent functionalities in wooden furniture, offering biodegradability, nontoxicity, and derivation from renewable sources. In this work, sustainably printed transistors using zinc oxide nanoparticles as the active layer and honey electrolyte on wood substrates are demonstrated as a promising approach to reduce the environmental footprint of electronics. Despite the substrate's high roughness, the transistor exhibits excellent performance for screen-printed devices, with low on-voltage of 0.32 ± 0.12 V and high Ion/Ioff of (2.4 ± 0.9) × 104. Further analysis of hysteresis in transfer curves under varying scan rates and sweep ranges reveals the device's ability to adjust memory windows and on-current. Notably, these devices successfully emulate synapses, exhibiting neural facilitation and plasticity, indicating a shift toward sustainable computing. The device's dynamic response to single and successive presynaptic pulses demonstrates its ability to adjust synaptic weight, transition from transient to persistent memory, and pulse width-, frequency-, voltage-, and number-dependent excitatory postsynaptic currents. The successful emulation of the learning–forgetting–relearning–forgetting process underscores the device's potential for use in sustainable high-performance neuromorphic systems.
Floating TiO2-Cork Nano-Photocatalysts for Water Purification Using Sunlight
Publication . Matias, Maria Leonor; Morais, Maria; Pimentel, Ana; Vasconcelos, Francisco X.; Reis Machado, Ana S.; Rodrigues, Joana; Fortunato, Elvira; Martins, Rodrigo; Nunes, Daniela; UNINOVA-Instituto de Desenvolvimento de Novas Tecnologias; CENIMAT-i3N - Centro de Investigação de Materiais (Lab. Associado I3N); DCM - Departamento de Ciência dos Materiais; LAQV@REQUIMTE; DQ - Departamento de Química; Molecular Diversity Preservation International (MDPI)
In the present study, titanium dioxide (TiO2) nano-photocatalysts were synthesized through microwave irradiation. In a typical microwave synthesis, TiO2 nanomaterials were simultaneously produced in powder form and also directly covering cork substrates. The TiO2 nanopowder was analyzed by X-ray diffraction (XRD), Raman spectroscopy and transmission electron microscopy (TEM), revealing that the solvothermal microwave synthesis resulted only in the TiO2 anatase phase. From Fourier-transform infrared spectroscopy (FTIR), cork’s organic species, along with bands of TiO2, were detected. UV–VIS absorption spectrum revealed an absorption extension to the visible region, since a brown powdered TiO2 product was obtained. Very fine nanoparticles were observed displaying a nearly spherical shape that agglomerates in larger particles. These larger particles fully covered the surface of the honeycomb cork cells, originating TiO2 functionalized cork platforms. The TiO2 functionalized substrates were further tested as floating photocatalysts and their photocatalytic activity was assessed from rhodamine B degradation under solar simulating light and natural sunlight. Reusability tests were also performed under natural sunlight. The strategy applied in this research work allowed the production of green and low-cost cork platforms based on TiO2 photoactive materials with the ability to purify polluted water under natural sunlight.
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Entidade financiadora
European Commission
Programa de financiamento
H2020
Número da atribuição
101008701