Filmes de óxido de zinco e nitreto de zinco depositados por magnetron sputtering com diferentes pressões de argônio, oxigênio e nitrogênio.

O óxido de zinco é um material semicondutor que apresenta alta transparência óptica no espectro visível, alta energia de ligação de éxcitons e piezoeletricidade. Por suas propriedades, ele é utilizado na área de sensores, eletrodos transparentes e dispositivos optoeletrônicos. No entanto, sua utilização ainda é limitada pela dificuldade de obtenção de condutividade tipo p, cujo principal dopante é o nitrogênio, devido à assimetria de dopagem ocasionada por defeitos intrínsecos do material, dopagem em valências diferentes das esperadas e formação de níveis de aceitadores profundos na banda proibida. A aplicação em dispositivos piezoelétricos também exige alta resistividade e ótimas propriedades cristalinas. Muitos processos de deposição estabelecidos hoje ainda utilizam altas temperaturas, o que impede sua deposição sobre superfícies ou substratos sensíveis a altas temperaturas. O objetivo deste trabalho é desenvolver técnicas de deposição de filmes de ZnO, principalmente em baixas temperaturas ( 100°C), pelo método de magnetron sputtering de rádio frequência, para avaliar a influência dos gases de processo nas características estruturais, estequiométricas, elétricas e ópticas dos filmes. Para isso, foram obtidos filmes utilizando pressão total de argônio, e pressões parciais de argônio e oxigênio e argônio e nitrogênio, utilizando alvo cerâmico de óxido de zinco ou alvo metálico de zinco. Para alvo de ZnO, filmes com condutividade tipo n foram obtidos em ambiente de argônio, em condições que geraram deficiências de oxigênio. Filmes altamente resistivos foram obtidos com a utilização de pressão parcial de oxigênio no gás de processo, em condições que resultaram em filmes estequiométricos, inclusive com condutividade tipo p. Condutividade tipo p mais alta foi observada, apenas por ponta quente, para uma amostra obtida em argônio logo após a utilização de nitrogênio na câmara de processo, que provavelmente sofreu influência da dopagem não intencional do cobre, que foi identificado como um contaminante do processo devido à estrutura da câmara. Para alvo de Zn, observou-se a formação de nitreto de zinco, que demonstrou alta capacidade de oxidação em ambiente atmosférico, e portanto, transforma-se naturalmente ao longo do tempo ou por processos de oxidação térmica em ZnO dopado com nitrogênio. Filmes de ZnO produzidos a partir de nitreto de zinco foram os únicos dos testados que apresentaram fotoluminescência característica do ZnO, mesmo para processos onde não houve aquecimento intencional.

Earth-Abundant Zinc-IV-Nitride Semiconductors

This investigation is motivated by the need for new visible frequency direct bandgap semiconductor materials that are abundant and low-cost to meet the increasing demand for optoelectronic devices in applications such as solid state lighting and solar energy conversion. Proposed here is the utilization of zinc-IV-nitride materials, where group IV elements include silicon, germanium, and tin, as earth-abundant alternatives to the more common III-nitrides in optoelectronic devices. These compound semiconductors were synthesized under optimized conditions using reactive radio frequency magnetron sputter deposition. Single phase ZnSnN₂, having limited experimental accounts in literature, is validated by identification of the wurtzite-derived crystalline structure predicted by theory through X-ray and electron diffraction studies. With the addition of germanium, bandgap tunability of ZnSn_xGe_1-xN₂ alloys is demonstrated without observation of phase separation, giving these materials a distinct advantage over In_xGa_1-xN alloys. The accessible bandgaps range from 1.8 to 3.1 eV, which spans the majority of the visible spectrum. Electron densities, measured using the Hall effect, were found to be as high as 10²² cm⁻³ and indicate that the compounds are unintentionally degenerately doped. Given these high carrier concentrations, a Burstein-Moss shift is likely affecting the optical bandgap measurements. The discoveries made in this thesis suggest that with some improvements in material quality, zinc-IV-nitrides have the potential to enable cost-effective and scalable optoelectronic devices.

Antibacterial activity of root canal filling materials for primary teeth: zinc oxide and eugenol cement, Calen paste thickened with zinc oxide, Sealapex and EndoREZ

This study evaluated in vitro the antibacterial activity of 4 root canal filling materials for primary teeth - zinc oxide and eugenol cement (ZOE), Calen paste thickened with zinc oxide (Calen/ZO), Sealapex sealer and EndoREZ sealer - against 5 bacterial strains commonly found in endodontic infections (Kocuria rhizophila, Enterococcus faecalis, Streptococcus mutans, Escherichia coli and Staphylococcus aureus) using the agar diffusion test (agar-well technique). Calen paste, 1% chlorhexidine digluconate (CHX) and distilled water served as controls. Seven wells per dish were made at equidistant points and immediately filled with the test and control materials. After incubation of the plates at 37oC for 24 h, the diameter of the zones of bacterial growth inhibition produced around the wells was measured (in mm) with a digital caliper under reflected light. Data were analyzed statistically by analysis of variance and Tukey's post-hoc test (?=0.05). There were statistically significant differences (p<0.0001) among the zones of bacterial growth inhibition produced by the different materials against all target microorganisms. K. rhizophila was inhibited more effectively (p<0.05) by ZOE, while Calen/ZO had its highest antibacterial activity against E. faecalis (p<0.05). S. mutans was inhibited by Calen/ZO, Sealapex and ZOE in the same intensity (p>0.05). E. coli was inhibited more effectively (p<0.05) by ZOE, followed by Calen/ZO and Sealapex. Calen/ZO and ZOE were equally effective (p>0.05) against S. aureus, while Sealapex had the lowest antibacterial efficacy (p<0.05) against this microorganism. EndoREZ presented antibacterial activity only against K. rhizophila and S. aureus. The Calen paste and Calen/ZO produced larger zones of inhibition than 1% CHX when the marker microorganism was E faecalis. In conclusion, the in vitro antibacterial activity of the 4 root canal filling materials for primary teeth against bacterial strains commonly found in endodontic infections can be presented in a decreasing order of efficacy as follows: ZOE>Calen/ZO>Sealapex>EndoREZ.

Effect of ultrasonic instrumentation on the bond strength of crowns cemented with zinc phosphate cement to natural teeth. An in vitro study

Several studies have reported the benefits of sonic and/or ultrasonic instrumentation for root debridement, with most of them focusing on changes in periodontal clinical parameters. The present study investigated possible alterations in the tensile bond strength of crowns cemented with zinc phosphate cement to natural teeth after ultrasonic instrumentation. Forty recently extracted intact human third molars were selected, cleaned and stored in physiologic serum at 4°C. They received standard preparations, at a 16º convergence angle, and AgPd alloy crowns. The crowns were cemented with zinc phosphate cement and then divided into four groups of 10 teeth each. Each group was then subdivided into two subgroups, with one of the subgroups being submitted to 5,000 thermal cycles ranging from 55 ± 2 to 5 ± 2°C, while the other was not. Each group was submitted to ultrasonic instrumentation for different periods of time: group 1 - 0 min (control), group 2 - 5 min, group 3 - 10 min, and group 4 - 15 min. Tensile bond strength tests were performed with an Instron testing machine (model 4310). Statistical analysis was performed using ANOVA and Tukey's test at the 5% level of significance. A significant reduction in the tensile bond strength of crowns cemented with zinc phosphate and submitted to thermal cycles was observed at 15 min (196.75 N versus 0 min = 452.01 N, 5 min = 444.23 N and 10 min = 470.85 N). Thermal cycling and ultrasonic instrumentation for 15 min caused a significant reduction in tensile bond strength (p < .05).

Catalytic enantioselective arylations: boron to zinc exchange as a powerful tool for the generation of transferable aryl groups

The transmetalation between boron and zinc is of great importance for application in organic synthesis, since it allows the formation of new carbon-carbon bonds between organometallic units and electrophiles. The direct arylation of aldehydes or more scarcely ketones, in a catalytic, enantioselective manner using chiral catalysts has been described recently. The enantiomerically enriched diarylmethanols obtained in these reactions are valuable precursors for important bioactive molecules. This review provides a synopsis of this ever-growing field and highlights some of the challenges that still remain.

Metallochlorophylls of magnesium, copper and zinc: evaluation of the influence of the first coordination sphere on their solvatochromism and aggregation properties

In this study the role of different metal centers (magnesium, zinc and copper) on the enhancement of the hydrophilic character of metallochlorophylls, was evaluated. The solvatochromism as well as the aggregation process for these compounds in water/ethanol mixtures at different volume ratios were evaluated using Fluorescence, and Resonant Light Scattering (RLS) measurements, aiming to characterize the behavior of these compounds. Independently on the studied metallochlorophyll, the presence of at least 60% of water results in a considerable increase in the fluorescence emission, probably a direct consequence of a lower aggregation of these compounds, which is confirmed by the results from RLS measurements. Additionally, the results suggest that magnesium and zinc chlorophyll should be promising phototherapeutic agents for Photodynamic Therapy.

Digestible lysine and organic zinc for male broiler from 1 to 11 days of age: performance and body composition

This study evaluated levels of digestible lysine and organic zinc for male Ross strain broilers from 1 to 11 days of age. It was used 1,050 chicks distributed in randomized block design, in 5 × 2 factorial scheme, with seven repetitions of 15 birds per experimental unit. The dietary concentrations of digestible lysine were 0.90; 1.00; 1.10; 1.20; and 1.40% combined with 43 and 253 ppm zinc chelate. The diets contained 2,965 ± 18 kcal/kg of apparent metabolizable energy (AME) and 21.48 ± 0.18% of CP. It was determined chemical composition, protein, lipid, mineral and water depositions on carcass and empty body. There was no interaction among the factors digestible lysine and organic zinc. Effect of zinc concentration increase was observed on greatest deposition of body fat, indicating that there is interference in lipid metabolism of the birds in the studied phase. The most pronounced effects resulted from the dietary inclusion of lysine. There was a linear effect on reconstituted body weight as a response to the increase of dietary lysine, which suggests equal or superior requirement to the greatest studied level. However, the deposition of water and protein on the carcass had a quadratic increase, characterizing higher muscle mass accumulation up to the levels 1.25 and 1.27 of this amino acid in the diet. Considering the studied strain, broiler chickens from the first to the 11th days of age require 1.28 ± 0.01% of digestible lysine, according to the deposition of muscle mass.

Lysine and zinc chelate in diets for brown laying hens: effects on egg production and composition

It was evaluated the effects of levels of digestible lysine and chelate zinc combined in the diet for laying on the egg quality. It was used 720 birds, from 48 to 60 weeks of age, distributed in a completely randomized design in a 3 × 5 factorial scheme with three levels of zinc and five levels of lysine, applied into six replicates in the experimental units of eight birds per plot. The levels were: 137, 309 and 655 ppm zinc and 0.482, 0.527, 0.582, 0.644 and 0.732% digestible lysine. It was not observed any interaction among digestible lysine and zinc for the primary variables of fractions and egg composition. Levels of zinc reduced egg weight, suggesting the lowest efficiency in nutrient intake. At the highest dietary concentration of zinc, the addition of digestible lysine coincided with a linear increase in shell weight. However, zinc addition, regardless of lysine level in the diet, resulted in the reduction of egg weight and of the percentage of mineral matter in the yolk, limiting the efficiency of mineral deposition in this fraction of the egg. Concentration of zinc that produced the best results was 137 ppm inasmuch as higher quantities limit the use of digestible lysine, with effects harming composition and egg quality. The study indicates the following requirement for digestible lysine: 0.639% from the 48th to the 52nd week, 0.679% from the 52nd to 56th week, and 0.635% from the 56th to the 60th week. Considering the total period from 48th to the 60th week, the level 0.638% of lysine or the daily intake of 707 mg of the amino acid met the requirement for egg quality of semi-heavy layers used in this study.

Effect of zinc insertion and hydrophobicity on the membrane interactions and PDT activity of porphyrin photosensitizers

A series of photosensitizers (PS), which are meso-substituted tetra-cationic porphyrins, was synthesized in order to study the role of amphiphilicity and zinc insertion in photodynamic therapy (PDT) efficacy. Several properties of the PS were evaluated and compared within the series including photophysical properties (absorption spectra, fluorescence quantum yield Phi(f), and singlet oxygen quantum yield Phi(Delta)), uptake by vesicles, mitochondria and HeLa cells, dark and phototoxicity in HeLa cells. The photophysical properties of all compounds are quite similar (Phi(f) <= 0.02; Phi(Delta) similar to 0.8). An increase in lipophilicity and the presence of zinc in the porphyrin ring result in higher vesicle and cell uptake. Binding in mitochondria is dependent on the PS lipophilicity and on the electrochemical membrane potential, i.e., in uncoupled mitochondria PS binding decreases by up to 53%. The porphyrin substituted with octyl groups (TC8PyP) is the compound that is most enriched in mitochondria, and its zinc derivative (ZnTC8PyP) has the highest global uptake. The stronger membrane interaction of the zinc-substituted porphyrins is attributed to a complexing effect with phosphate groups of the phospholipids. Zinc insertion was also shown to decrease the interaction with isolated mitochondria and with the mitochondria of HeLa cells, an effect that has been explained by the particular characteristics of the mitochondrial internal membrane. Phototoxicity was shown to increase proportionally with membrane binding efficiency, which is attributed to favorable membrane interactions which allow more efficient membrane photooxidation. For this series of compounds, photodynamic efficiency is directly proportional to the membrane binding and cell uptake, but it is not totally related to mitochondrial targeting.

Analgesic and Anti-Inflammatory Activities of Salicylaldehyde 2-Chlorobenzoyl Hydrazone (H(2)LASSBio-466), Salicylaldehyde 4-Chlorobenzoyl Hydrazone (H(2)LASSBio-1064) and Their Zinc(II) Complexes

Salicylaldehyde 2-chlorobenzoyl hydrazone (H(2)LASSBio-466), salicylaldehyde 4-chlorobenzoyl hydrazone (H(2)LASSBio-1064) and their complexes [Zn(LASSBio-466) H(2)O](2) (1) and [Zn(HLASSBio-1064) Cl](2) (2) were evaluated in animal models of peripheral and central nociception, and acute inflammation. All studied compounds significantly inhibited acetic acid-induced writhing response. Upon coordination the anti-nociceptive activity was favored in the complex 1. H(2)LASSBio-466 inhibited only the first phase of the formalin test, while 1 was active in the second phase, like indomethacin, indicating its ability to inhibit nociception associated with the inflammatory response. Hence coordination to zinc(II) altered the pharmacological profile of H(2)LASSBio-466. H(2)LASSBio-1064 inhibited both phases but this effect was not improved by coordination. The studied compounds did not increase the latency of response in the hot plate model, indicating their lack of central anti-nociceptive activity. All compounds showed levels of inhibition of zymosan-induced peritonitis comparable or superior to indomethacin, indicating an expressive anti-inflammatory profile.

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.

Simultaneous preconcentration of copper, zinc, cadmium, and nickel in water samples by cloud point extraction using 4-(2-pyridylazo)-resorcinol and their determination by inductively coupled plasma optic emission spectrometry

A procedure for simultaneous separation/preconcentration of copper. zinc, cadmium, and nickel in water samples, based on cloud point extraction (CPE) as a prior step to their determination by inductively coupled plasma optic emission spectrometry (ICP-OES), has been developed. The analytes reacted with 4-(2-pyridylazo)-resorcinol (PAR) at pH 5 to form hydrophobic chelates, which were separated and preconcentrated in a surfactant-rich phase of octylphenoxypolyethoxyethanol (Triton X-I 14). The parameters affecting the extraction efficiency of the proposed method, such as sample pH, complexing agent concentration, buffer amount, surfactant concentration, temperature, kinetics of complexation reaction, and incubation time were optimized and their respective values were 5, 0.6 mmol L(-1). 0.3 mL, 0.15% (w/v), 50 degrees C, 40 min, and 10 min for 15 mL of preconcentrated solution. The method presented precision (R.S.D.) between 1.3% and 2.6% (n = 9). The concentration factors with and without dilution of the surfactant-rich phase for the analytes ranged from 9.4 to 10.1 and from 94.0 to 100.1, respectively. The limits of detection (L.O.D.) obtained for copper, zinc, cadmium, and nickel were 1.2, 1.1, 1.0. and 6.3 mu g L(-1), respectively. The accuracy of the procedure was evaluated through recovery experiments on aqueous samples. (C) 2009 Published by Elsevier B.V.

Characterization of copper-silicon nitride composite electrocoatings

Silicon nitride particles were incorporated to electrolytic copper by co-electrodeposition in acidic sulfate bath, aiming the improvement of its mechanical resistance. Smooth deposits containing well-distributed silicon nitride particles were obtained. The current density did not show significant influence on incorporated particle volume fraction, whereas the variation of particle concentration in the bath had a more pronounced effect. The microhardness of the composite layers was higher than that of pure copper deposits obtained under the same conditions and increased with the increase of incorporated particle volume fraction. The microhardness of composites also increased with the increase of current density due to copper matrix grain refining. The composite coatings were slightly more corrosion resistant than pure copper deposits in 3.5% NaCl solutions.

Crystallographic characterization of silicon nitride ceramics sintered with Y(2)O(3)-Al(2)O(3) or E(2)O(3)-Al(2)O(3) additions

Silicon nitride ceramics were sintered using Y(2)O(3)-Al(2)O(3) or E(2)O(3)-Al(2)O(3) (E(2)O(3) denotes a mixed oxide Of Y(2)O(3) and rare-earth oxides) as sintering additives. The intergranular phases formed after sintering was investigated using high-resolution X-ray diffraction (HRXRD). The use of synchrotron radiation enabled high angular resolution and a high signal to background ratio. Besides the appearance Of beta-Si(3)N(4) phase the intergranular phases Y(3)Al(5)O(12) (YAG) and Y(2)SiO(5) were identified in both samples. The refinement of the structural parameters by the Rietveld method indicated similar crystalline structure Of beta-Si(3)N(4) for both systems used as sintering additive. On the other hand, the intergranular phases Y(3)Al(5)O(12) and Y(2)SiO(5) shown a decrease of the lattice parameters, when E(2)O(3) was used as additive, indicating the formation of solid solutions of E(3)Al(5)O(12) and E(2)SiO(5), respectively. (C) 2007 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Wetting behaviour of silicon nitride ceramics by Ti-Cu alloys

The wetting of Ti-Cu alloys on Si3N4 was analyzed by the sessile drop method, using an imaging system with a CCD camera during the heating under argon flow. The contact angle was measured as a function of temperature and time. The samples were cut transversally and characterized by scanning electron microscopy and energy dispersive spectrometry (SEM/EDS). Wettability of the Ti-Cu alloy on Si3N4 is influenced by the reaction between the Ti and the ceramic. The TC1 and TC2 alloys presented low final contact angle values around 2 degrees and 26 degrees, respectively, indicating good wetting on Si3N4. (c) 2006 Elsevier Ltd and Techna Group S.r.l. All rights reserved.