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Made available in DSpace on 2020-12-10T17:35:40Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-06-17 China Scholarship Council NSERC (DG) Poly-3-hexylthiophene (P3HT) is a benchmark semiconducting polymer in organic electronics. Ion-gated transistors (IGTs), making use of ionic gating media, are particularly interesting for flexible and printable& x2423;organic electronic applications. The molecular weight of P3HT is known to affect the morphology and structure of the corresponding films and, ultimately, the performance of devices based thereon. Here we report on IGTs based on films of P3HT with different molecular weights (similar to 20 kDa, 30-50 kDa and 80-90 kDa) and, as the gating medium, the well-investigated ionic liquid [EMIM][TFSI], to investigate the effects of the film morphological and structural properties on charge carrier transport and, eventually, IGT performance. P3HT films were deposited over rigid (SiO2/Si) and flexible (polyimide) substrates. All the P3HT IGTs could be operated at low voltage (about 1 V) and achieved a hole mobility larger than 0.1 cm(2) V-1 s(-1), pointing to the extremely favorable [EMIM][TFSI]/P3HT interface for IGT applications, for all the molecular weights investigated. We finally investigated the stability of flexible devices considering two different bending radii (R = 10 mm andR = 5 mm). Polytech Montreal, Engn Phys Dept, Montreal, PQ H3C 3A7, Canada Sao Paulo State Univ, Dept Fis Quim, BR-14800060 Sao Paulo, Brazil Sao Paulo State Univ, Dept Fis Quim, BR-14800060 Sao Paulo, Brazil

Made available in DSpace on 2020-12-10T19:59:50Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-05-07 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Fluid Interface Reactions, Structures and Transport (FIRST) Center, an Energy Frontier Research Center (EFRC) - DOE Office of Science, Office of Basic Energy Sciences NSERC The structure of electrical double layers at electrified interfaces is of utmost importance for electrochemical energy storage as well as printable, flexible, and bioelectronic devices, such as ion-gated transistors (IGTs). Here we report a study based on atomic force microscopy force-distance profiling on electrical double layers forming at the interface between the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide and sol-gel films of mesoporous tungsten oxide. We successfully followed, under in operando conditions, the evolution of the arrangement of the ions at the interface with the tungsten oxide films used as channel materials in IGTs. Our work sheds light on the mechanism of operation of IGTs, thus offering the possibility of optimizing their performance. Univ Estadual Paulista, Dept Fis Quim, BR-14800060 Araraquara, SP, Brazil Polytech Montreal, Dept Genie Phys, Montreal, PQ H3C 3A7, Canada Oak Ridge Natl Lab, Ctr Nanophase Mat Sci, Oak Ridge, TN 37831 USA Univ Estadual Paulista, Dept Fis Quim, BR-14800060 Araraquara, SP, Brazil CAPES: FAPESP/CAPES 2014/27079-9 CAPES: 2015/50526-4 CAPES: 2016/09033-7

Made available in DSpace on 2021-06-25T10:18:29Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-12-01 Combined in situ cyclic electrochemical and UV-vis spectroscopic methods were employed to monitor the memory loss of electrochromic properties of layered α-MoO3 nanoplates. The time-resolved characteristics of this in situ study allowed for the quantification of changes in charge and optical densities as a function of electrochemical potential over time. Lithium ions trapped in the crystalline lattice of α-MoO3 during the bleaching process, along with the irreversible reduction of Mo6+ to Mo5+, govern the memory loss responsible for the degradation of the electrochromic properties. These experiments demonstrated the existence of a saturation limit of the structural charge insertion that effectively contributes to the electrochromic performance of α-MoO3 nanoplates. The study improves the understanding of electrochromic memory loss and the degradation mechanism and suggests a two-step electrochemical reaction that controls the electrochromic activity of the α-MoO3 phase. Department of Engineering Physics and Mathematics Chemistry Institute São Paulo State University (UNESP) Department of Engineering Physics and Mathematics Chemistry Institute São Paulo State University (UNESP)

Made available in DSpace on 2022-04-28T19:47:56Z (GMT). No. of bitstreams: 0 Previous issue date: 2022-01-01 Molecular hydrogen (H2) shows promise as a future renewable energy carrier. However, due to safety concerns, its reliable detection in different atmospheres is an important issue. Here, we propose a hydrogen sensor based on ion-gated transistors exploiting the interface between tungsten oxide and ionic liquids. Two different approaches to gas sensors (metal oxide gas sensor and ionic liquid-based electrochemical sensor) are integrated in a single device. We demonstrate that ionic liquid gating enhances the effect of H2 on the tungsten oxide transistor channel. The transistor current response permits the detection of H2 in an O2-free environment with the device operating in room temperature. After H2 sensing, the initial properties of the tungsten oxide channel can be recovered by exposure to O2. Instituto de Química Universidade Federal de Goiás (UFG), Av. Esperança, s/n - Chácaras de Recreio Samambaia, Goiânia Departamento de Física Engenharia e Matemática São Paulo State University (UNESP), Rua Professor Degni, 55 Département de Génie Physique Polytechnique Montréal, C.P. 6079, Succ. Centre-Ville Departamento de Física Engenharia e Matemática São Paulo State University (UNESP), Rua Professor Degni, 55

Made available in DSpace on 2020-12-10T19:38:03Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-12-12 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) MRSEC Program of the National Science Foundation This work reports on the gas sensor response of undecorated 1D stannous oxide nanobelts and those decorated with Pt and Pd nanoparticles. The sensor device responses to H-2, CO and NO2 were measured in dry air baseline atmosphere as functions of the analyte concentration (1-1000 ppm) and temperature (100-350 degrees C). Noble metal decorated SnO devices exhibited enhanced chemical sensitization, resulting in increased sensitivity upon exposure to reducing gases at different working temperatures. Differences in enhancement levels are attributed to strong electronic sensitization effects that are dependent on the respective Pt and Pd work functions and the unique SnO band structure, characterized by a small band gap. Gas sensing results also showed superior selectivity to H-2 for metal-decorated nanobelts. Based on the findings in this work, we propose an array based on SnO structures capable of detecting and distinguishing reducing and oxidizing gases. Sao Paulo State Univ, Dept Phys Chem, BR-14800900 Araraquara, SP, Brazil MIT, Dept Mat Sci & Engn, Cambridge, MA 02139 USA Sao Paulo State Univ, Dept Phys Chem, BR-14800900 Araraquara, SP, Brazil FAPESP: 2012/51195-3 FAPESP: 2013/08734-3 FAPESP: 2013/18511-1 FAPESP: 2014/50725-4 CNPq: 447760/2014-9 CNPq: 443138/2016-8 MRSEC Program of the National Science Foundation: DMR - 141,980

Made available in DSpace on 2019-10-04T12:38:12Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-07-24 NSERC DG MESI PSIIRI 936 China Scholarship Council Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Trottier Energy Institute FRQNT-RQMP Ion-gated transistors employ ionic gating media (e.g. ionic liquids, polymer electrolytes, aqueous saline solutions) to modulate the density of the charge carriers in the transistor channel. Not only they operate at low voltages (ca 0.5-1 V) but they can also feature printability, flexibility and easy integration with chemo- and bio-sensing platforms. Metal oxides are transistor channel materials interesting for their processability in air, at low temperature. Among metal oxides, tungsten oxide (band gap ca 2.5-2.7 eV) stands out for its electrochromic, gas sensing and photocatalytic properties. Here we demonstrate ion-gated tungsten oxide transistors and phototransistors working in different ion gating media, such as one hydrophobic ionic liquid and an aqueous electrolyte, fabricated both on rigid and flexible substrates. Ion-gated tungsten oxide phototransistors operating in aqueous media could be used as photocatalytic sensors in portable applications. Polytech Montreal, Dept Genie Phys, CP 6079,Succ Ctr Ville, Montreal, PQ H3C 3A7, Canada Univ Fed Minas Gerais, Dept Fis, BR-30123970 Belo Horizonte, MG, Brazil Polytech Montreal, Dept Genie Chim, CP 6079,Succ Ctr Ville, Montreal, PQ H3C 3A7, Canada Univ Estadual Paulista, Dept Fis Quim, Rua Prof Degni 55, BR-14800060 Araraquara, Brazil Univ Montreal, Dept Chim, CP 6128,Succ Ctr Ville, Montreal, PQ H3C 3J7, Canada Univ Bologna, Dipartimento Chim Giacomo Ciamician, Via Selmi 2, I-40126 Bologna, Italy Univ Estadual Paulista, Dept Fis Quim, Rua Prof Degni 55, BR-14800060 Araraquara, Brazil FAPESP: 2014/27079-9 FAPESP: 2015/50526-4 FAPESP: 2016/09033-7

Introduction Semiconducting metal oxides (SMOx) are the most studied materials for gas sensing applications due to their outstanding capacity to detect flammable and toxic gases, and their low-cost processing and ease of handling. [1,2] Many strategies have been developed attempting to achieve materials with improved sensor performance, including surface functionalization. The most common SMOx surface functionalization species are noble metal nanoparticles (NPs) given the possibilities to present both chemical and electronic sensitization effects.[3] This work reports on the gas sensing response of pristine and Pt and Pd decorated stannous oxide nanobelts. The responses of devices to different analytes (H2, CO and NO2) were measured in dry air baseline atmosphere as function of the analyte concentration (1–1000 ppm) and temperature (150-350 °C). Method Stannous oxide nanobelts were synthesized by a carbothermal reduction method using a mixture of SnO2 powder (Sigma-Aldrich, 99.9% purity) and carbon black (Union Carbide, > 99% purity) in the molar ratio of 1.5:1 (SnO2:C) as starting material.[4] The nanoparticles (Pt and Pd) used to functionalize the surface of nanobelts were prepared by the polyol method. Samples were characterized by field-emission scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to study their morphology and crystalline structure. Suspensions of pristine and functionalized materials were deposited onto interdigitated platinum electrode arrays to perform the gas sensor measurements. The devices were placed in a temperature-controlled tubular furnace chamber, where the electric current was monitored under a constant applied voltage. Synthetic dry air was used as baseline and the analytes (NO2, H2 and CO) were introduced into the chamber using mass flow controllers. Gas sensor measurements were performed ranging from 150 °C to 350 °C. Results and Conclusions SEM and TEM results showed that obtained materials were nanobelts in the SnO phase. Moreover, functionalization with noble metal nanoparticles was successful, presenting disperse nanoparticles (< 15 nm) over nanobelts surface. About the gas sensing measurements, pristine devices are both sensitive and selective for nitrogen dioxide (NO2) molecules between 100 and 250 °C. In addition, both Pd- and Pt- functionalized devices present excellent selectivity to H2 at 300 and 350 °C. Moreover, Pt- functionalized device presented good selectivity for high concentrations of CO (>200 ppm) at low temperatures (100 and 150 °C). Then, results showed that noble metal decorated devices exhibited enhanced chemical sensitization, resulting in increased sensitivity upon exposure to reducing gases at different working temperatures. Differences in enhancement levels are attributed to strong electronic sensitization effects that are dependent on the respective Pt and Pd work functions and the unique SnO band structure, characterized by a small band gap (0.6 eV). Values showed that while Pt0 and Pt2+ promotes a high potential barrier with SnO nanobelts, Pd0 does not have this effect. Based on these findings, we propose an array based on pristine and NPs-functionalized SnO structures capable of detecting and distinguishing reducing and oxidizing gases. Furthermore, electronic sensitization mechanism is elucidated based on the band diagram of materials. Results presented here are important to engineer high performance sensor devices by selecting the better work function of nanoparticles, depending on the Fermi level of semiconductor. References [1] A. Goldoni, V. Alijani, L. Sangaletti and L. D’Arsiè, Electrochim. Acta, 2018, 266, 139–150. [2] A. Dey, Mater. Sci. Eng. B Solid-State Mater. Adv. Technol., 2018, 229, 206–217. [3] M. E. Franke, T. J. Koplin and U. Simon, Small, 2006, 2, 36–50. [4] P. H. Suman and M. O. Orlandi, J. Nanoparticle Res., 2011, 13, 2081–2088.

Electrolyte-gated transistors hold promise for applications in printable and flexible electronics. Metal oxide semiconductors are particularly interesting as electrolyte-gated channel materials for their abundance, thermodynamic stability and ease of processing under ambient conditions. In this work, we synthesized by sol–gel and hydrothermal methods different types of tungsten oxide to be used as channel materials in ion gel-gated transistors. X-ray diffraction and scanning and transmission electron microscopy revealed that the differently processed oxides show a different structure (hexagonal and monoclinic) and morphology (granular, nanofiber and nanoplate). We studied the electrochemical and transistor properties of the oxides using, as the gating media, two different ion gels prepared from the same ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM]TFSI), and two different block copolymers. We tentatively propose that for sufficiently high values of the gate–source bias, the doping results from chemical and electrochemical contributions.

Made available in DSpace on 2022-04-28T19:01:35Z (GMT). No. of bitstreams: 0 Previous issue date: 2015-09-17 Electrolyte-gated (EG) transistors, based on electrolyte gating media, are powerful device structures to modulate the charge carrier density of materials by orders of magnitude, at relatively low operating voltages (sub-2 V). Tungsten trioxide (WO3) is a metal oxide semiconductor well investigated for applications in electrochromism, sensing, photocatalysis, and photoelectrochemistry. In this work, we report on EG transistors making use of mesoporous nanostructured WO3 thin films easily permeated by the electrolyte as the transistor channel and bis(trifluoromethylsulfonyl)imide ([TFSI])-based ionic liquids as the gating media. The WO3 EG transistors operate at ca. 1 V. Using a combination of cyclic voltammetry, X-ray diffraction, and transistor performance characterizations, complemented by spectroscopic (Raman and infrared) investigations, we correlate the metal oxidation state and the charge transport properties of the metal oxide, shedding light on the doping process in electrically biased WO3 nanostructured thin films exposed to electrolytes. Département de Génie Physique Polytechnique Montréal, C.P. 6079, Succ. Centre Ville Departamento de Físico-Química Universidade Estadual Paulista, Rua Professor Degni, 55 CNR-IENI Dipartimento di Scienze Chimiche Università di Padova, Via F. Marzolo 1 Département de Chimie Université de Montréal, C.P. 6128, Succ. Centre Ville Dipartimento di Chimica giacomo Ciamician Università di Bologna, Via Selmi, 2 Departamento de Físico-Química Universidade Estadual Paulista, Rua Professor Degni, 55

Made available in DSpace on 2018-11-28T00:05:43Z (GMT). No. of bitstreams: 0 Previous issue date: 2017-02-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) MRSEC Program of the National Science Foundation The gas sensor response of tin monoxide micro-disks, functionalized with noble metal nanoparticles (Pd and Ag), to NO2, H-2 and CO were studied by monitoring changes in their resistance upon exposure to the various gases. The tin monoxide, with unusually low Sn oxidation state, was synthetized by carbothermal reduction. Surface modification by Pd and Ag catalysts was achieved by coating the micro-disks by metallic nanoparticle dispersions, prepared by the polyol reduction process, followed by thermal treatment. SEM and TEM analysis showed nanoparticles to be well-dispersed over the SnO surfaces. The decorated SnO micro-disks exhibited high sensor response to reducing gases such as H-2 and CO. On the other hand, the catalytic particles tended to reduce the sensor response to oxidizing gases such as NO2. The catalytic activity of Pd nanoparticles was tied to chemical sensitization while that of Ag nanoparticles to electronic sensitization. Impedance spectroscopy enabled deconvolution of different contributions to the sensor response with only the Ag-decorated specimens exhibiting two RC time constants. Thus, in contrast to undecorated and Pd-decorated specimens, nearly 80% of Ag modified SnO's response to H-2 was controlled by changes in the interface between particles and disks. Sensor response to H-2 was optimal at higher temperatures (300 degrees C), NO2 at 200 degrees C while that for Pd-decorated materials; maximum sensor response to CO was observed at lower temperatures (under 150 degrees C), where CO absorption by metal nanoparticles is favored. (C) 2016 Elsevier B.V. All rights reserved. Sao Paulo State Univ, Dept Phys Chem, BR-14800900 Sao Paulo, Brazil MIT, Dept Mat Sci & Engn, Cambridge, MA 02139 USA Sao Paulo State Univ, Dept Phys Chem, BR-14800900 Sao Paulo, Brazil FAPESP: 2012/51195-3 FAPESP: 2013/08734-3 FAPESP: 2013/18511-1 FAPESP: 2014/50725-4 CNPq: 447760/2014-9 MRSEC Program of the National Science Foundation: DMR - 141980