Grain size effect on the electrical response of SnO2 thin and thick film gas sensors

Porous nano and micro crystalline tin oxide films were deposited by RF Magnetron Sputtering and doctor blade techniques, respectively. Electrical resistance and impedance spectroscopy measurements, as a function of temperature and atmosphere, were performed in order to determine the influence of the microstructure and working conditions over the electrical response of the sensors. The conductivity of all samples increases with the temperature and decreases in oxygen, as expected for an n-type semiconducting material. The impedance plots indicated the existence of two time constants related to the grains and the grain boundaries. The Nyquist diagrams at low frequencies revealed the changes that took place in the grain boundary region, with the contribution of the grains being indicated by the formation of a second semicircle at high frequencies. The better sensing performance of the doctor bladed samples can be explained by their lower initial resistance values, bigger grain sizes and higher porosity.Fil: Savu, Raluca. Universidade Estadual Paulista Julio de Mesquita Filho; BrasilFil: Ponce, Miguel Adolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Joanni, Ednan. Universidade Estadual Paulista Julio de Mesquita Filho; BrasilFil: Bueno, Paulo Roberto. Universidade Estadual Paulista Julio de Mesquita Filho; BrasilFil: Castro, Miriam Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Cilense, Mario. Universidade Estadual Paulista Julio de Mesquita Filho; BrasilFil: Varela, Jose Arana. Universidade Estadual Paulista Julio de Mesquita Filho; BrasilFil: Longo, Elson. Universidade Estadual Paulista Julio de Mesquita Filho; Brasi

Clinical improvement after treatment with VEGF165 in patients with severe chronic lower limb ischaemia

The present study focuses on the application of a therapeutic strategy in patients with chronic severe lower limb ischaemia using a plasmid vector encoding the vascular endothelial growth factor (phVEGF165). It has been shown that VEGF promotes neo-vascularization and blood vessel network formation and thus might have the ability to improve blood-flow at the level of the affected limbs. However, little information is available regarding the necessary level of expression of VEGF and its possible related adverse effects. We have subcloned VEGF165isoform into pCMV-Script expression vector (Stratagene) under the control of the CMV promoter. Three patients with chronic ischaemia of the lower limb, considered as not suitable for surgical re-vascularization, received intramuscular injection with 0.5 ml saline solution containing 1011 copies of VEGF165 plasmid. The clinical evolution has been monitored by angiography and estimated by walking time on the rolling carpet (Gardner protocol). Two months after therapy, all three patients showed complete relief of rest pain, improvement of ischaemic ulcer lesions and increased walking distance on the rolling carpet most probably due to appearance of newly formed collateral vessels

Síntese de nanofios de óxidos semicondutores para aplicações em dispositivos ópticos e eletrônicos

A presente pesquisa teve como principal objetivo a obtenção de estruturas nanométricas de óxido de índio, óxido de estanho e óxido de zinco por evaporação térmica e síntese hidrotérmica e a construção e teste de sensores de gases e de fotodetectores de ultravioleta baseados nessas nanoestruturas. Foram realizados estudos da influência dos parâmetros experimentais das duas rotas de síntese usadas sobre as morfologias e as propriedades das estruturas. Para a obtenção das camadas nanoestruturadas por evaporação térmica foi especialmente construído um forno tubular que permitiu o controle da temperatura de deposição independente da temperatura de evaporação e da distância entre a fonte de evaporação e o substrato. Esses parâmetros, pouco explorados nas pesquisas reportadas na literatura, exerceram uma grande influência sobre a morfologia e as propriedades dos nanofios obtidos. O equipamento permitiu ainda um controle preciso da composição da atmosfera e da pressão de síntese. Na síntese química em solução, a construção de um reator hidrotérmico permitiu o estudo da influência da taxa de resfriamento sobre as dimensões, cristalinidade, morfologia e propriedades das nanoestruturas. Esse estudo, o primeiro do gênero na literatura, ressaltou a importância no controle deste parâmetro para sintetizar estruturas com propriedades melhoradas. As demais variáveis estudadas foram: a concentração das soluções, as camadas catalisadoras, a temperatura e o tempo de síntese. Foram testadas duas estratégias para a obtenção dos filmes nanoestruturados: spin-coating de suspensões de nanoestruturas sobre substratos de silício oxidado ou o crescimento das mesmas, durante a síntese, sobre substratos com camadas catalisadoras de zinco. Os nanofios e as camadas funcionais foram caracterizados por Difração de Raios-X (DRX), Microscopia Eletrônica de Varredura...The subject of this thesis covers the synthesis and growth of indium, tin and zinc oxide nanostructures by thermal evaporation and hydrothermal synthesis and the fabrication and testing of gas sensors and ultraviolet photodetectors based on these nanosized structures. For both chemical and physical routes, the influence of processing conditions over the morphology, dimensions and electrical properties of the nanowires was investigated. In order to obtain nanostructured layers by thermal evaporation a tubular furnace was specifically builti, allowed the control of the source-substrate distance and the deposition temperature independently of the evaporation one. These parameters, slightly explored in the literature, granted a big influence over the nanowires morphology and properties. Moreover, the equipment permitted the control of deposition atmosphere and pressure. The design and assembly of a hydrothermal reactor allowed studying the influence of the cooling rate over the dimension, morphology, cristallinity and, consequently, the properties of the nanostructures. This study highlighted the importance of controlling this particular parameter in the hydrothermal process, yielding nanostructured materials with enhanced properties. Variables such as solution concentration, synthesis temperature and time, surfanctants and precursors were also explored in the hydrothermal process. In order to obtain nanostructured thin films using the chemical bath deposition, two processing techniques were employed: spin-coating of powder suspensions over oxidized silicon substrates and nanostructured anisotropic growth directly from solution using zinc coated substrates. The nanowires and the functional nanostructured layers were characterized by X-Ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FE - SEM), Transmission Electron Microscopy (TEM) and X-ray Photoelectron Spectroscopy (XPS)... (Complete abstract click electronic access below)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Effect of processing conditions on the nucleation and growth of indium-tin-oxide nanowires made by pulsed laser ablation

Indium-tin oxide nanowires were deposited by excimer laser ablation onto catalyst-free oxidized silicon substrates at a low temperature of 500 degrees C in a nitrogen atmosphere. The nanowires have branches with spheres at the tips, indicating a vapor-liquid-solid (VLS) growth. The deposition time and pressure have a strong influence on the areal density and length of the nanowires. At the earlier stages of growth, lower pressures promote a larger number of nucleation centers. With the increase in deposition time, both the number and length of the wires increase up to an areal density of about 70 wires/mu m(2). After this point all the material arriving at the substrate is used for lengthening the existing wires and their branches. The nanowires present the single-crystalline cubic bixbyite structure of indium oxide, oriented in the [100] direction. These structures have potential applications in electrical and optical nanoscale devices

Low-temperature, self-nucleated growth of indium-tin oxide nanostructures by pulsed laser deposition on amorphous substrates

Indium-tin oxide nanostructures were deposited by excimer laser ablation in a nitrogen atmosphere using catalyst-free oxidized silicon substrates at 500 degrees C. Up to 1 mbar, nanowires grew by the vapor-liquid-solid (VLS) mechanism, with the amount of liquid material decreasing as the deposition pressure increased. The nanowires present the single-crystalline cubic bixbyite structure, oriented . For the highest pressure used, pyramids were formed and no sign of liquid material could be observed, indicating that these structures grew by a vapor-solid mechanism. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved

Influence of hydrothermal synthesis conditions and device configuration on the photoresponse of UV sensors based on ZnO nanorods

Zinc oxide nanorods in the form of powder or nanostructured films were synthesized by the hydrothermal method using aqueous solutions. Once the synthesis time was completed, the reaction vessel was naturally cooled or submitted to a quenching process. X-ray diffraction, Scanning Electron Microscopy and Transmission Electron Microscopy techniques were employed to characterize the crystallinity, morphology and dimensions of the nanorods as well as their growth direction. Suspensions of powder material were spin-coated over oxidized silicon substrates in order to obtain nanostructured layers. Photodetectors based on in-situ grown and spin-coated films were prepared in order to evaluate the influences of cooling rate and device configuration on the UV sensing characteristics. Spincoated layers showed an excellent performance (current change by more than four orders of magnitude), better than nanorods grown directly on the substrate during the hydrothermal process. For both configurations, the sensitive layers built from quenched samples exhibited enhanced UV photoresponses when compared to the naturally cooled ones.Fil: Savu, Raluca. Universidade Estadual Paulista Julio de Mesquita Filho; BrasilFil: Parra, Rodrigo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación en Ciencia y Tecnología de Materiales (i); Argentina. Universidad Nacional de Mar del Plata. Facultad de Ingeniería; ArgentinaFil: Jancar, Bostjan. Jozef Stefan Institute; EsloveniaFil: Zaghete, María Aparecida. Universidade Estadual Paulista Julio de Mesquita Filho; BrasilFil: Joanni, Ednan. Centro de Tecnologia da Informação Renato Archer; Brasi

Microwave heating time dependent synthesis of various dimensional graphene oxide supported hierarchical ZNO nanostructures and its photoluminescence studies

Microwave heating reaction time dependent various graphene oxide based zinc oxide (G-ZnO) heterostructures such as graphene oxide-ZnO microcubes (GZMC), graphene oxide-ZnO nanoflakes (GZNF) and graphene oxide ZnO nanoneedles (GZNN) are synthesized by simple and cost effective microwave assisted exfoliation method. These heterostructures supported on graphene oxide nanosheets (GNSs) represent three dimensional (3D) ZnO microcubes and various confined two dimensional (2D) nanoflakes and one dimensional (1D) ZnO nanoneedles like structures. The recorded PL intensity variations show the strong evidence of the interfaces interaction between graphene oxide and ZnO heterostructures. However the differences in the PL intensities are also caused by the 3D and various confined G-ZnO heterostructures. The photoluminescence characterization of GZMC, GZNF and GZNN nanostructures exhibit a decrement in the PL intensity. The PL intensity of the GZNN is lowered by 67.50% and 39.7% to the GZMC and GZNF nanostructures respectively. The results show that ZnO heterostructures grown on GNSs with different morphologies and dimensionalities exhibit the variation in PL intensity due to preventing a direct recombination of the electrons and holes in ZnO. A tentative growth mechanism has been given for the growth of various graphene based zinc oxide heterostructures111291300CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPComision Nacional de Investigacion Cientifica y Tecnologica (CONICYT

Microwave-assisted synthesis of void-induced graphene-wrapped nickel oxide hybrids for supercapacitor applications

Here we demonstrate a simple strategy for the large-scale synthesis of void-induced and graphene-wrapped nickel oxide (VGWN) hybrids using domestic microwave irradiation. When a homogeneously mixed aqueous suspension of partially microwave exfoliated graphene oxide (MEGO) sheets and nickel nitrate nanoparticles is irradiates with a microwave, the in situ formation of voids with wrapping of NiO nanoparticles with graphene sheets is easily realized. The novel VGWN hybrid materials were used for investigation of electrochemical capacitive behaviours. Remarkably, such hybrid structure provides the right combination of electrode properties for high-performance supercapacitors and cyclic stability. The wrapping of graphene sheets on the NiO nanoparticles can offer highly conductive pathways by bridging individual NiO nanoparticles together, thus facilitating the charge/discharge rate and cycling performance of supercapacitors. The hybrid materials displayed enhanced capacitive performance (549 F g−1 at 10 mV s−1). Additionally, over 88% of the initial capacitance was retained after repeating the cyclic voltammetry test for 2500 cycles. The enhanced electrochemical performance can be ascribed to the synergic effects of the two components' voids and wrapping, suggesting VGWN hybrids as novel electrode materials promising potential applications as high-performance energy storage devices.6322661226620CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPSem informaçãoSem informaçã