Laboratorio Nacional Of Nanotecnologia Lnnano

Campinas, Brazil

Laboratorio Nacional Of Nanotecnologia Lnnano

Campinas, Brazil
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Soares M.R.S.,Federal University of São Carlos | Goncalves R.H.,Federal University of São Carlos | Nogueira I.C.,Federal University of Maranhão | Bettini J.,Laboratorio Nacional Of Nanotecnologia Lnnano | And 2 more authors.
Physical Chemistry Chemical Physics | Year: 2016

Hematite is considered to be the most promising material used as a photoanode for water splitting and here we utilized a sintered hematite photoanode to address the fundamental electrical, electrochemical and photoelectrochemical behavior of this semiconductor oxide. The results presented here allowed us to conclude that the addition of Sn4+ decreases the grain boundary resistance of the hematite polycrystalline electrode. Heat treatment in a nitrogen (N2) atmosphere also contributes to a decrease of the grain boundary resistance, supporting the evidence that the presence of oxygen is fundamental for the formation of a voltage barrier at the hematite grain boundary. The N2 atmosphere affected both doped and undoped sintered electrodes. We also observed that the heat treatment atmosphere modifies the surface states of the solid-liquid interface, changing the charge-transfer resistance. A two-step treatment, with the second being performed at a low temperature in an oxygen (O2) atmosphere, resulted in a better solid-liquid interface. © 2016 the Owner Societies.


Padilla-Ortega E.,CSIC - Institute of Materials Science | Padilla-Ortega E.,Autonomous University of San Luis Potosi | Darder M.,CSIC - Institute of Materials Science | Aranda P.,CSIC - Institute of Materials Science | And 4 more authors.
Applied Clay Science | Year: 2015

The objective of this work was the development of functional bionanocomposites based on the intercalation of the cationic biopolymer chitosan in natural or in organically modified vermiculite samples under experimental conditions involving ultrasound irradiation. The resulting materials were processed as macroporous foams with the aim to apply them in the removal of Cd(II) ions from aqueous solution. Physicochemical characterization confirmed the intercalation of chitosan into the interlayer space of vermiculite, causing the exfoliation of VU layers in those bionanocomposites. They were processed as foams by means of freeze-drying resulting in materials that show interconnected elongated macropores with average diameter around 150-200. μm, and the material in the cell walls exhibited a tendency to organize in parallel planes. The adsorption equilibrium data of Cd(II) on the bionanocomposite foams, carried out in batch mode, was interpreted with the Langmuir, Freundlich and Prausnitz-Radke (P-R) isotherm models, and the P-R isotherm showed the best fit to the experimental data. The adsorption capacity was increased by raising the solution pH, which most likely favors a chelation mechanism between the chitosan chains and the Cd(II) cations. The chitosan-vermiculite bionanocomposites with the highest chitosan content showed exceptionally high adsorption capacity values, at least three times higher than those of the individual components. © 2015 Elsevier B.V.


De Oliveira L.F.,Brazilian Synchrotron Light Laboratory (LNLS) | Bouchmella K.,Brazilian Synchrotron Light Laboratory (LNLS) | Goncalves K.D.A.,Laboratorio Nacional Of Biocieincias Lnbio | Bettini J.,Laboratorio Nacional Of Nanotecnologia Lnnano | And 2 more authors.
Langmuir | Year: 2016

The selective action of drugs in tumor cells is a major problem in cancer therapy. Most chemotherapy drugs act nonspecifically and damage both cancer and healthy cells causing various side effects. In this study, the preparation of a selective drug delivery system, which is able to act as a carrier for hydrophobic and anticancer drugs is reported. Amino-functionalized silica nanoparticles loaded with curcumin were successfully synthesized via sol-gel approach and duly characterized. Thereafter, the targeting ligand, folate, was covalently attached to amino groups of nanoparticle surface through amide bond formation. The cytotoxic effect of nanoparticles on prostate cancer cells line was evaluated and compared to normal cells line (prostate epithelial cell). Cytotoxicity experiments demonstrated that folate-functionalized nanoparticles were significantly cytotoxic to tumor cells, whereas normal cells were much less affected by the presence of these structures. © 2016 American Chemical Society.


Lagos M.J.,University of Campinas | Lagos M.J.,Laboratorio Nacional Of Nanotecnologia Lnnano | Lagos M.J.,Rutgers University | Autreto P.A.S.,University of Campinas | And 5 more authors.
Journal of Applied Physics | Year: 2015

We report here an atomistic study of the mechanical deformation of AuxCu(1- x ) atomic-size wires (nanowires (NWs)) by means of high resolution transmission electron microscopy experiments. Molecular dynamics simulations were also carried out in order to obtain deeper insights on the dynamical properties of stretched NWs. The mechanical properties are significantly dependent on the chemical composition that evolves in time at the junction; some structures exhibit a remarkable de-alloying behavior. Also, our results represent the first experimental realization of mixed linear atomic chains (LACs) among transition and noble metals; in particular, surface energies induce chemical gradients on NW surfaces that can be exploited to control the relative LAC compositions (different number of gold and copper atoms). The implications of these results for nanocatalysis and spin transport of one-atom-thick metal wires are addressed. © 2015 AIP Publishing LLC.


Deneke C.,Laboratorio Nacional Of Nanotecnologia Lnnano | Deneke C.,Leibniz Institute for Solid State and Materials Research | Malachias A.,Federal University of Minas Gerais | Rastelli A.,Leibniz Institute for Solid State and Materials Research | And 6 more authors.
ACS Nano | Year: 2012

Freestanding, edge-supported silicon nanomembranes are defined by selective underetching of patterned silicon-on-insulator substrates. The membranes are afterward introduced into a molecular beam epitaxy chamber and overgrown with InAs, resulting in the formation of InAs islands on flat areas and at the top of the Si nanomembranes. A detailed analysis of sample morphology, island structure, and strain is carried out. Scanning electron microscopy shows that the membrane stays intact during overgrowth. Atomic force microscopy reveals a lower island density on top of the freestanding membranes, denoting a modified wetting or diffusivity in these areas. An observed bending of the membrane indicates a strain transfer from the InAs islands to the compliant substrate. X-ray diffraction and finite-element modeling indicate a nonuniform strain state of the island ensemble grown on the freestanding membrane. A simulation of the bending of the nanomembranes indicates that the islands at the center of the freestanding area are highly strained, whereas islands on the border tend to be fully relaxed. Finally, continuum elasticity calculations suggest that for a sufficiently thin membrane InAs could transfer enough strain to the membrane to allow coherent epitaxial growth, something not possible on bulk substrates. © 2012 American Chemical Society.


Angelova T.,University of Valencia | Shtinkov N.,University of Ottawa | Ivanov T.,Sofia University | Donchev V.,Sofia University | And 5 more authors.
Applied Physics Letters | Year: 2012

Rolled-up semiconductor tubes of various diameters made of alternating In 0.215Ga 0.785As/GaAs layers have been investigated by means of Raman scattering. The optical and acoustic phonon modes of individual tubes have been studied and compared with the characteristics of the surrounding material. After tube formation, the frequency of the phonon modes shifts with respect to the as-grown material and disorder activated modes are observed. The frequency shifts are related to the residual strain in the tubes through the deformation potential approximation. Good agreement with atomistic valence force field simulations and x-ray micro-diffraction measurements is found. By comparison with x-ray data, a Raman strain constant K 0.65 is proposed for In 0.215Ga 0.785As. In the low frequency range, acoustic mode doublets are observed on the tubes that are absent in the surrounding material. They show clear evidence of the formation of periodic superlattices after the rolling-up process, and give insight into the quality of their interfaces. © 2012 American Institute of Physics.


Zhen H.L.,CAS Shanghai Institute of Technical Physics | Zhen H.L.,Leibniz Institute for Solid State and Materials Research | Huang G.S.,Fudan University | Kiravittaya S.,Leibniz Institute for Solid State and Materials Research | And 9 more authors.
Applied Physics Letters | Year: 2013

Pre-stressed multi-layer nanomembranes are rolled-up into a microtube in order to tune the strain applied to the contained coupled GaAs quantum wells. Additional GaAs/AlAs adjusting layers were deposited on the top of the nanomembrane to alter the thickness/stiffness of the to-be-rolled nanomembrane. In this way, microtubes with an adjustable diameter and strain are possible from a single initial grown sample. The internal strain state in the microtube affects the energy levels of the quantum wells and their coupling, which can be probed sensitively by photoluminescence. We measure different strain relaxation in rolled-up nanomembranes which we explain using a gradual change of the longitudinal relaxation as the distance of the nanomembrane from the etching front varies. © 2013 American Institute of Physics.


The successful results presented in the literature about the FSW aluminum-steel joints, ignore the appearance and formation of defects at the joint as reference points for evaluation. It also increases the controversy about the presence of intermetallic compounds of the type FexAly, and the lack of information about its origin. The objective of this study is to determine appropriate parameters for obtaining free defects aluminum-steel joints and their relation to the formation of deleterious phases during the FSW. Consolidated welded joints were obtained and determined the microstructure in aluminum alloy 6063-T5 and AISI SAE 1020 welds joints. It was used a tungsten carbide tool (WC-14Co) at rotation and weld speeds of 300 rpm and 150 mm. min-1, with tool offset of+0.5, +1.0and +1.5 mm. The results highlight the importance of heat input in the Al-steel welding surface appearance and penetration depth. The microstructural analysis reveals the formation of seven regions in the weld, highlighting the thermo-mechanically affected zone on the steel, a band of ultra fine grains offerrite and the absence of intermetallic compounds in the Al-steel interface.


PubMed | CSIC - Institute of Materials Science and Laboratorio Nacional Of Nanotecnologia Lnnano
Type: | Journal: Carbohydrate polymers | Year: 2016

Bionanocomposite foams based on alginate, potato starch and the microfibrous clay mineral sepiolite as reinforcing filler were prepared by lyophilization. Spectroscopic techniques were applied in order to assess the interaction mechanism established between the inorganic fibers and the polysaccharide chains, which is established between the hydroxyl groups in the polysaccharide chains and the silanol groups at the external surface of the sepiolite fibers. The textural properties studied by means of mercury intrusion porosimetry, FE-SEM and X-ray microtomography, revealed a decrease in porosity as the sepiolite content increased. Mechanical properties were also determined for the studied foams, showing an increase in compression moduli from 7.3MPa in the foam without sepiolite to 29MPa in foams containing 10% starch, 40% sepiolite and 50% alginate. Horizontal burning tests were carried out for a preliminary evaluation of the role of the inorganic fibers on the fire resistance properties of the bionanocomposite foams, revealing that bionanocomposite foams with sepiolite content >25% behave as auto-extinguishable materials. Post-synthesis cross-linking with CaCl


PubMed | Laboratorio Nacional Of Nanotecnologia Lnnano
Type: Journal Article | Journal: ACS nano | Year: 2012

Freestanding, edge-supported silicon nanomembranes are defined by selective underetching of patterned silicon-on-insulator substrates. The membranes are afterward introduced into a molecular beam epitaxy chamber and overgrown with InAs, resulting in the formation of InAs islands on flat areas and at the top of the Si nanomembranes. A detailed analysis of sample morphology, island structure, and strain is carried out. Scanning electron microscopy shows that the membrane stays intact during overgrowth. Atomic force microscopy reveals a lower island density on top of the freestanding membranes, denoting a modified wetting or diffusivity in these areas. An observed bending of the membrane indicates a strain transfer from the InAs islands to the compliant substrate. X-ray diffraction and finite-element modeling indicate a nonuniform strain state of the island ensemble grown on the freestanding membrane. A simulation of the bending of the nanomembranes indicates that the islands at the center of the freestanding area are highly strained, whereas islands on the border tend to be fully relaxed. Finally, continuum elasticity calculations suggest that for a sufficiently thin membrane InAs could transfer enough strain to the membrane to allow coherent epitaxial growth, something not possible on bulk substrates.

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