Characterization of Metal Oxide-Based Gas Nanosensors and Microsensors Fabricated via Local Anodic Oxidation Using Atomic Force Microscopy

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)This work reports on nanoscale and microscale metal oxide gas sensors, consisting of metal-semiconductor-metal barriers designed via scanning probe microscopy. Two distinct metal oxides, molybdenum and titanium oxides, were tested at different temperatures using CO2 and H-2 as test gases. Sensitivities down to ppm levels are demonstrated, and the influence of dry and humid working atmospheres on these metal oxide conductivities was studied. Furthermore, the activation energy was evaluated and analyzed within working sensor temperature range. Finally, full morphological, chemical, and structural analyses of the oxides composites are provided allowing their identification as MoO3 and TiO2-x.Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG)Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ)FinepInstituto do Milenio de Nanociencias e Nanotecnologia/MCTCT-Petro/MCTConselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Activation of Tungsten Oxide for Propane Dehydrogenation and Its High Catalytic Activity and Selectivity

Abstract: Dehydrogenation of propane to propene is one of the important reactions for the production of higher-value chemical intermediates. In the commercial processes, platinum- or chromium oxide-based catalysts have been used for catalytic propane dehydrogenation. Herein, we first report that bulk tungsten oxide can serve as the catalyst for propane dehydrogenation. Tungsten oxide is activated by hydrogen pretreatment and/or co-feeding of hydrogen. Its catalytic activity strongly depends on hydrogen pretreatment time and partial pressure of hydrogen in the feed gas. The activation of tungsten oxide by hydrogen is attributed to reduction of the metal oxide and presence of multivalent oxidation states. Comparison of the catalytic performance of partially reduced WO3−xto other highly active metal oxides shows that WO3−xexhibits superior catalytic activity and selectivity than Cr2O3and Ga2O3. The findings of this work provide the possibility for activation of metal oxides for catalytic reactions and the opportunity for the development of new type of catalytic systems utilizing partially reduced metal oxides. Graphical Abstract: [Figure not available: see fulltext.

Nanoscale lateral switchable rectifiers fabricated by local anodic oxidation

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Scanning probe lithography as a mean to pattern, implement, and discover new devices in different materials systems provides an elevated degree of flexibility, permitting one to tailor device geometries and structures at will, in particular by virtue of modification of the local chemistry. Here we define metal-insulator-metal junctions exhibiting a switchable rectifier behavior by patterning titanium channels through local anodic oxidation techniques. The nanoscale TiO(2) junctions thus formed exhibit IV characteristics with non-volatile switchable rectification and memristive behavior due to ionic motion through the metal-semiconductor interfaces. VC 2011 American Institute of Physics. [doi:10.1063/1.3609065]1102Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)HP BrazilFundação de Amparo à Pesquisa do Estado de Minas Gerais (FAPEMIG)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)FAPESP [05/04643-7

Plasmon-Tunable Tip Pyramids: Monopole Nanoantennas for Near-Field Scanning Optical Microscopy

Squeezing optical fields into nanometer scale is the key step to perform spatially resolved near-field optics. In scattering-type near-field optical microscopy, this task is accomplished by nanoantennas that convert propagating radiation to local near-fields and vice versa. The usual nanoantenna is composed by an elongated metal structure whose longitudinal dimension is scaled to support dipole modes of localized surface plasmon resonances. However, monopole modes can also be explored if the elongated metal nanoparticle is electrically grounded on a flat metallic plateau that acts like a mirror providing the monopole's image that closes the dipole system. Here, a method for batch production of monopole nanoantennas for scattering-type near-field scanning optical microscopy is presented. The nanoantennas are composed of a micropyramidal body with a nanopyramidal end whose lateral dimension can be scaled to fine-tune localized surface plasmon resonance modes. The monopole character of the nanoantennas is revealed by electron energy loss spectroscopy, and their efficiency and reproducibility are tested in tip-enhanced Raman spectroscopy experiments performed on single-layer graphene and single-walled carbon nanotubes

Crystallinity, oxidation states and morphology of polyaniline coated curaua fibers in polyamide-6 composites

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Polyaniline (PAni) is one of the most studied conductive polymers due to its ability to exist in various redox states. The possibility of depositing PAni on vegetable fibers and incorporating this in polymeric matrices, such as polyamide-6, enables production of antistatic reinforced materials. In this work, polyaniline was deposited on fiber surfaces on a pilot plant scale and the composites were prepared by extrusion. The microstructures of the polyaniline coated curaua fibers and polyamide-6 were characterized by X-ray diffraction (XRD) measurements and the crystallinity degree of the polyamide-6 was evaluated by differential scanning calorimetry and XRD. Atomic force and electron scanning microscopies were employed to observe the distribution and morphology of the PAni nanoparticles. The oxidation states of PAni were determined by X-ray photoelectron spectroscopy. The results showed that polyaniline supported on the fibers presents amorphous domains and nanometer scale sizes. (C) 2013 Elsevier Ltd. All rights reserved.88106112Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)FAPESP [Proc. 2010/17804-7]FAPESP [FAPESP 2010/17871-6

Multi-Scale Evaluation ofWear in UHMWPE-Metal Hip Implants Tested in a hip Joint Simulator

Wear is a critical issue related to the performance of hip joint implants, namely for ultra-high molecular weight (UHMWPE) fabricated components. A greater knowledge and understanding of the attributes and capabilities of UHMWPE related to wear, at macro to nano scale levels, is crucial in the context of engineering design aiming the improvement of the implants’ behaviour. Various multi-scale characterization techniques (gravimetry, geometrical analysis using coordinate measuring machine, profilometry, optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, atomic force microscopy and Raman spectroscopy) were combined for the wear assessment of UHMWPE/metal (stainless steel and cobalt–chromium) implants tested in a hip joint simulator. The wear rate of the UHMWPE was about 48 mg/106 cycles, equivalent to a linear wear rate of 0.16 mm/year, independently of the femoral head material. Two main mechanisms determined polymer wear: a) abrasion, by second-body action of counterface metal asperities and by third-body debris; b) adhesion/fatigue, disclosed by micro-scale ripples, resulting from cyclic plastic strain accumulation. Going deeply into the analysis by AFM and Raman spectroscopy it was also observed that the structure of the material changes after wear but in distinct modes: the scratched areas became more crystalline while the smooth areas remained without structural modifications