Signatures of oxygen on Cu(3)Au(100): From isolated impurity to oxide regimes

We analyze the scanning tunneling microscopy (STM) signatures for the O/Cu(3)Au(100) surface from the low-coverage (isolated impurity) to high-coverage (oxide) regimes. First-principles calculations show that oxygen signatures switch from dark to bright spots as the oxygen coverage increases. This behavior is nicely traced back to a change in the oxygen orbital character of the Fermi-level electronic states. Our results allow for the chemical identification by STM of oxygen and copper atoms in the fully ordered O/Cu(3)Au(100)-c(2x2) surface.

Shear Stress Induces Nitric Oxide-Mediated Vascular Endothelial Growth Factor Production in Human Adipose Tissue Mesenchymal Stem Cells

It has been demonstrated that human adipose tissue-derived mesenchymal stem cells (hASCs) enhance vascular density in ischemic tissues, suggesting that they can differentiate into vascular cells or release angiogenic factors that may stimulate neoangiogenesis. Moreover, there is evidence that shear stress (SS) may activate proliferation and differentiation of embryonic and endothelial precursor stem cells into endothelial cells (ECs). In this work, we investigated the effect of laminar SS in promoting differentiation of hASCs into ECs. SS (10 dyn/cm(2) up to 96 h), produced by a cone plate system, failed to induce EC markers (CD31, vWF, Flk-1) on hASC assayed by RT-PCR and flow cytometry. In contrast, there was a cumulative production of nitric oxide (determined by Griess Reaction) and vascular endothelial growth factor (VEGF; by ELISA) up to 96 h of SS stimulation ( NO(2)(-) in nmol/10(4) cells: static: 0.20 +/- 0.03; SS: 1.78 +/- 0.38, n = 6; VEGF in pg/10(4) cells: static: 191.31 +/- v35.29; SS: 372.80 +/- 46.74, n = 6, P < 0.05). Interestingly, the VEGF production was abrogated by 5 mM N(G)-L-nitro-arginine methyl ester (L-NAME) treatment (VEGF in pg/10(4) cells: SS: 378.80 +/- 46.74, n = 6; SS + L-NAME: 205.84 +/- 91.66, n = 4, P < 0.05). The results indicate that even though SS failed to induce EC surface markers in hASC under the tested conditions, it stimulated NO-dependent VEGF production.

Influence of Aluminum Oxide Sandblasting Associated with Nd:YAG or Er:YAG Lasers on Shear Bond Strength of a Feldspathic Ceramic to Resin Cements

Objective: This in vitro study evaluated the influence of the surface pretreatment of a feldspathic ceramic on the shear bond strength of two different resin cements. Background Data: Although several conventional surface treatments have been used on feldspathic ceramic, few studies have investigated the effects of an alternative surface treatment, the association of aluminum oxide sandblasting with Nd:YAG and Er:YAG lasers. Methods: Sixty samples made of a feldspathic ceramic were divided into three groups (n = 20) and treated with (1) controlled-air abrasion with Al(2)O(3) + 10% hydrofluoric acid (HF), (2) Al(2)O(3) + Er:YAG laser, and (3) Al(2)O(3) + Nd:YAG laser. Afterward, silane (Dentsply) was applied on each treated surface. Each of the three main groups was divided into two subgroups (n = 10), where a different resin cement was employed for each subgroup. It was built a cylinder with resin cement (RelyX Arc) in subgroup (A) and with self-adhesive cement (RelyX U100) in subgroup (B). After 24 h at 37 degrees C, the prepared specimens were submitted to shear bond strength test and stereoscopic evaluation to determine the type of failure. Results: Bond strength mean values were not statistically significant for the surface treatment methods or resin cements. Conclusion: The null surface treatment proposed with aluminum oxide sandblasting associated with the Er:YAG or Nd:YAG laser and using cementation with self-adhesive cement can be an alternative bonding technique for feldspathic ceramic, since it was as effective as the conventional treatment with aluminum oxide sandblasting and hydrofluoric acid using the conventional resin cement.

Theory of nitride oxide adsorption on transition metal (111) surfaces: a first-principles investigation

In this work, we report a density functional theory study of nitric oxide (NO) adsorption on close-packed transition metal (TM) Rh(111), Ir(111), Pd(111) and Pt(111) surfaces in terms of adsorption sites, binding mechanism and charge transfer at a coverage of Theta(NO) = 0.25, 0.50, 0.75 monolayer (ML). Based on our study, an unified picture for the interaction between NO and TM(111) and site preference is established, and valuable insights are obtained. At low coverage (0.25 ML), we find that the interaction of NO/TM(111) is determined by an electron donation and back-donation process via the interplay between NO 5 sigma/2 pi* and TM d-bands. The extent of the donation and back-donation depends critically on the coordination number (adsorption sites) and TM d-band filling, and plays an essential role for NO adsorption on TM surfaces. DFT calculations shows that for TMs with high d-band filling such as Pd and Pt, hollow-site NO is energetically the most favorable, and top-site NO prefers to tilt away from the normal direction. While for TMs with low d-band filling (Rh and Ir), top-site NO perpendicular to the surfaces is energetically most favorable. Electronic structure analysis show that irrespective of the TM and adsorption site, there is a net charge transfer from the substrate to the adsorbate due to overwhelming back-donation from the TM substrate to the adsorbed NO molecules. The adsorption-induced change of the work function with respect to bare surfaces and dipole moment is however site dependent, and the work function increases for hollow-site NO, but decreases for top-site NO, because of differences in the charge redistribution. The interplay between the energetics, lateral interaction and charge transfer, which is element dependent, rationalizes the structural evolution of NO adsorption on TM(111) surfaces in the submonolayer regime.

Surface effects in the magnetic properties of crystalline 3 nm ferrite nanoparticles chemically synthesized

We have systematically studied the magnetic properties of ferrite nanoparticles with 3, 7, and 11 nm of diameter with very narrow grain size distributions. Samples were prepared by the thermal decomposition of Fe (acac)(3) in the presence of surfactants giving nanoparticles covered by oleic acid. High resolution transmission electron microscopy (HRTEM) images and XRD diffraction patterns confirms that all samples are composed by crystalline nanoparticles with the spinel structure expected for the iron ferrite. ac and dc magnetization measurements, as well in-field Mossbauer spectroscopy, indicate that the magnetic properties of nanoparticles with 11 and 7 nm are close to those expected for a monodomain, presenting large M(S) (close to the magnetite bulk). Despite the crystalline structure observed in HRTEM images, the nanoparticles with 3 nm are composed by a magnetically ordered region (core) and a surface region that presents a different magnetic order and it contains about 66% of Fe atoms. The high saturation and irreversibility fields in the M(H) loops of the particles with 3 nm together with the misalignment at 120 kOe in the in-field Mossbauer spectrum of surface component indicate a high surface anisotropy for the surface atoms, which is not observed for the core. For T < 10 K, we observe an increase in the susceptibility and of the magnetization for former sample, indicating that surface moments tend to align with applied field increasing the magnetic core size. (C) 2010 American Institute of Physics. [doi:10.1063/1.3514585]

An investigation of phosphate adsorption from aqueous solution onto hydrous niobium oxide prepared by co-precipitation method

The synthetic hydrous niobium oxide has been used for phosphate removal from the aqueous solutions. The kinetic data correspond very well to the pseudo second-order equation The phosphate removal tended. to increase with a decrease of pH. The equilibrium data describe very well the Langmuir isotherm. The peak appearing at 1050 cm(-1) in IR spectra after adsorption was attributed to the bending vibration of adsorbed phosphate. The adsorption capacities are high, and increased with increasing temperature. The evaluated Delta G degrees and Delta H degrees indicate the spontaneous and endothermic nature of the reactions. The adsorptions occur with increase in entropy (Delta S positive) value suggest increase in randomness at the solid-liquid interface during the adsorption. A phosphate desorbability of approximately 60% was observed with water at pH 12, which indicated a relatively strong bonding between the adsorbed phosphate and the sorptive sites on the surface of the adsorbent. (C) 2008 Elsevier B.V. All rights reserved.

Adsorption kinetic, thermodynamic and desorption studies of phosphate onto hydrous niobium oxide prepared by reverse microemulsion method

A type of Nb(2)O(5)center dot 3H(2)O was synthesized and its phosphate removal potential was investigated in this study. The kinetic study, adsorption isotherm, pH effect, thermodynamic study and desorption were examined in batch experiments. The kinetic process was described by a pseudo-second-order rate model very well. The phosphate adsorption tended to increase with a decrease of pH. The adsorption data fitted well to the Langmuir model with which the maximum P adsorption capacity was estimated to be 18.36 mg-Pg(-1). The peak appearing at 1050 cm(-1) in IR spectra after adsorption was attributed to the bending vibration of adsorbed phosphate. The positive values of both Delta H degrees and Delta S degrees suggest an endothermic reaction and increase in randomness at the solid-liquid interface during the adsorption. Delta G degrees values obtained were negative indicating a spontaneous adsorption process. A phosphate desorbability of approximately 68% was observed with water at pH 12, which indicated a relatively strong bonding between the adsorbed phosphate and the sorptive sites on the surface of the adsorbent. The immobilization of phosphate probably occurs by the mechanisms of ion exchange and physicochemical attraction. Due to its high adsorption capacity, this type of hydrous niobium oxide has the potential for application to control phosphorus pollution.

Evidences of the evolution from solid solution to surface segregation in Ni-doped SnO(2) nanoparticles using Raman spectroscopy

Ni-doped SnO(2) nanoparticles, promising for gas-sensing applications, have been synthesized by a polymer precursor method. X-ray diffraction (XRD) and transmission electron microscopy (TEM) data analyses indicate the exclusive formation of nanosized particles with rutile-type phase (tetragonal SnO(2)) for Ni contents below 10 mol%. The mean crystallite size shows a progressive reduction with the Ni content. Room-temperature Raman spectra of Ni-doped SnO(2) nanoparticles show the presence of Raman active modes and modes activated by size effects. From the evolution of the A(1g) mode with the Ni content, a solubility limit at similar to 2 mol% was estimated. Below that content, Raman results are consistent with the occurrence of solid solution (ss) and surface segregation (seg.) of Ni ions. Above similar to 2 mol% Ni, the redshift of A(1g) mode suggests that the surface segregation of Ni ions takes place. Disorder-activated bands were determined and their integrated intensity evolution with the Ni content suggest that the solid-solution regime favors the increase of disorder; meanwhile, that disorder becomes weaker as the Ni content is increased. Copyright (C) 2010 John Wiley & Sons, Ltd.

Quantification of MgO surface excess on the SnO(2) nanoparticles and relationship with nanostability and growth

In this work, we experimentally showed that the spontaneous segregation of MgO as surface excess in MgO doped SnO(2) nanoparticles plays an important role in the system`s energetics and stability. Using Xray fluorescence in specially treated samples, we quantitatively determined the fraction of MgO forming surface excess when doping SnO(2) with several different concentrations and established a relationship between this amount and the surface energy of the nanoparticles using the Gibbs approach. We concluded that the amount of Mg ions on the surface was directly related to the nanoparticles total free energy, in a sense that the dopant will always spontaneously distribute itself to minimize it if enough diffusion is provided. Because we were dealing with nanosized particles, the effect of MgO on the surface was particularly important and has a direct effect on the equilibrium particle size (nanoparticle stability), such that the lower the surface energy is, the smaller the particle sizes are, evidencing and quantifying the thermodynamic basis of using additives to control SnO(2) nanoparticles stability. (C) 2010 Elsevier B.V. All rights reserved.

Relationship between surface segregation and rapid propane electrical response in Cd-doped SnO2 nanornaterials

Controlling the surface properties of nanoparticles using ionic dopants prone to be surface segregated has emerged as an interesting tool for obtaining highly selective and sensitive sensors. In this work, the surface segregation of Cd cations on SnO2 nanopowders prepared by the Pechini`s method was studied by infrared spectroscopy, X-ray diffraction, and specific surface area analysis. We observed that the surface chemistry modifications caused by the surface segregation of Cd and the large specific surface area were closely responsible for a rapid and regular electrical response of 5 mol% Cd-doped SnO2 films to 100 ppm propane and NO, diluted in dry air at relatively low temperature (100 degrees C). (c) 2008 Elsevier B.V. All rights reserved.

Thin titanium oxide films deposited by e-beam evaporation with additional rapid thermal oxidation and annealing for ISFET applications

Titanium oxide (TiO(2)) has been extensively applied in the medical area due to its proved biocompatibility with human cells [1]. This work presents the characterization of titanium oxide thin films as a potential dielectric to be applied in ion sensitive field-effect transistors. The films were obtained by rapid thermal oxidation and annealing (at 300, 600, 960 and 1200 degrees C) of thin titanium films of different thicknesses (5 nm, 10 nm and 20 nm) deposited by e-beam evaporation on silicon wafers. These films were analyzed as-deposited and after annealing in forming gas for 25 min by Ellipsometry, Fourier Transform Infrared Spectroscopy (FTIR), Raman Spectroscopy (RAMAN), Atomic Force Microscopy (AFM), Rutherford Backscattering Spectroscopy (RBS) and Ti-K edge X-ray Absorption Near Edge Structure (XANES). Thin film thickness, roughness, surface grain sizes, refractive indexes and oxygen concentration depend on the oxidation and annealing temperature. Structural characterization showed mainly presence of the crystalline rutile phase, however, other oxides such Ti(2)O(3), an interfacial SiO(2) layer between the dielectric and the substrate and the anatase crystalline phase of TiO(2) films were also identified. Electrical characteristics were obtained by means of I-V and C-V measured curves of Al/Si/TiO(x)/Al capacitors. These curves showed that the films had high dielectric constants between 12 and 33, interface charge density of about 10(10)/cm(2) and leakage current density between 1 and 10(-4) A/cm(2). Field-effect transistors were fabricated in order to analyze I(D) x V(DS) and log I(D) x Bias curves. Early voltage value of -1629 V, R(OUT) value of 215 M Omega and slope of 100 mV/dec were determined for the 20 nm TiO(x) film thermally treated at 960 degrees C. (C) 2009 Elsevier B.V. All rights reserved.

Cell surface expression of adhesins for fibronectin correlates with virulence in Sporothrix schenckii

The virulence of four Sporothrix schenckii isolates was compared in a murine model of sporotrichosis, together with the protein pattern of the yeast cell surface and the capacity to bind the extracellular matrix protein fibronectin. Virulence was determined by the mortality rate, fungal burden and histopathology. Two clinical isolates were more virulent for C57BL/6 mice, but no direct correlation was seen between virulence and the clinical or environmental origin of the isolates. The lowest virulence was observed for an isolate recovered from a patient with meningeal sporotrichosis. Although all isolates could effectively disseminate, the dissemination patterns were not similar. Using flow cytometry analysis, we investigated the interaction of all the strains with fibronectin, and showed that the binding capacity correlated with virulence. Western blot analysis of S. schenckii cell wall extracts revealed positive bands for fibronectin in the range of 3792 kDa. The 70 kDa adhesin was also recognized by a protective monoclonal antibody raised against a gp70 antigen of S. schenckii (mAb P6E7). Confocal microscopy confirmed the co-localization of fibronectin and mAb P6E7 on the yeast cell surface. To our knowledge, this is the first report identifying adhesins for fibronectin on the surface of this human pathogen.

Effects of acidic treatments on the pore and surface properties of Ni catalyst supported on activated carbon

Activated carbon as catalyst support was treated with HCl, HNO3, and HF and the effects of acid treatments on the properties of the activated carbon support were studied by N-2 adsorption, mass titration, temperature-programmed desorption (TPD), and X-ray photoelectron spectrometry (XPS). Ni catalysts supported on untreated and treated activated carbons were prepared, characterized and tested for the reforming reaction of methane with carbon dioxide. It is found that acid treatment significantly changed the surface chemical properties and pore structure of the activated carbon. The surface area and pore volume of the carbon supports are generally enhanced upon acid treatment due to the removal of impurities present in the carbon. The adsorption capacity of Ni2+ on the carbon supports is also increased, and the increase can be closely correlated with the surface acidity. The impregnation of nickel salts decreases the surface area and pore volume of carbon supports both in micropores and mesopores. Acid treatment results in a more homogeneous distribution of the nickel salt in carbon. When the impregnated carbons are heated in inert atmosphere, there exists a redox reaction between nickel oxide and the carbon. Catalytic activity tests for methane reforming with carbon dioxide show that the activity of nickel catalysts based on the acid-treated carbon supports is closely related with the surface characteristics of catalysts. (C) 1998 Elsevier Science Ltd. All rights reserved.

The role of carbon surface chemistry in N2O conversion to N2 over Ni catalyst supported on activated carbon

The effect of acidic treatments on N2O reduction over Ni catalysts supported on activated carbon was systematically studied. The catalysts were characterized by N-2 adsorption, mass titration, temperature-programmed desorption (TPD), and X-ray photoelectron spectrometry (XPS). It is found that surface chemistry plays an important role in N2O-carbon reaction catalyzed by Ni catalyst. HNO3 treatment produces more active acidic surface groups such as carboxyl and lactone, resulting in a more uniform catalyst dispersion and higher catalytic activity. However, HCl treatment decreases active acidic groups and increases the inactive groups, playing an opposite role in the catalyst dispersion and catalytic activity. A thorough discussion of the mechanism of the N2O catalytic reduction is made based upon results from isothermal reactions, temperature-programmed reactions (TPR) and characterization of catalysts. The effect of acidic treatment on pore structure is also discussed. (C) 1999 Elsevier Science B.V. All rights reserved.

Effect of mesoporosity of vanadium oxide prepared by sol-gel process as cathodic material evaluated by cyclability during Li(+) insertion/deinsertion

The effect of pore structure on the behavior of lithium intercalation into an electrode containing porous V(2)O(5) film has been investigated and compared with the electrode containing a non-porous V(2)O(5) film. X-ray diffraction patterns indicate a lamellar structure for both materials. Nitrogen adsorption isotherms, t-plot method, and Scanning Electronic Microscopy show that the route employed for the preparation of mesoporous V(2)O(5) was successful. The electrochemical performance of these matrices as lithium intercalation cathode materials was evaluated. The porous material reaches stability after several cycles more easily compared with the V(2)O(5) xerogel. Lithium intercalation into the porous V(2)O(5) film electrode is crucially influenced by pore surface and film surface irregularity, in contrast with the non-porous surface of the V(2)O(5) xerogel.