Magnetic Properties of a-Si films doped with rare-earth elements

Amorphous silicon films doped with Y, La, Gd, Er, and Lu rare-earth elements (a-Si:RE) have been prepared by co-sputtering and studied by means of electron spin resonance (ESR), dc-magnetization, ion beam analysis, optical transmission, and Raman spectroscopy. For comparison the magnetic properties of laser-crystallized and hydrogenated a-Si:RE films were also studied. It was found that the rare-earth species are incorporated in the a-Si:RE films in the RE3+ form and that the RE-doping depletes the neutral dangling bonds (D0) density. The reduction of D0 density is significantly larger for the magnetic REs (Gd3+ and Er3+) than for the non-magnetic ones (Y3+, La3+, Lu3+). These results are interpreted in terms of a strong exchange-like interaction, J RE-DB SRE SDB, between the spin of the magnetic REs and that of the D0. All our Gd-doped Si films showed basically the same broad ESR Gd3+ resonance (DHpp ~ 850 Oe) at g ~ 2.01, suggesting the formation of a rather stable RE-Si complex in these films.Comment: 15 pages, 7 figure

The Nature of Carbon Dioxide in Bare Ionic Liquids

FCT- PTDC/QUI-QFI/31508/2017; Coordenação de Aperfeiçoamento de Pessoal de Nível Superior. Grant Numbers: 158804/2017-01, 001; Conselho Nacional de Desenvolvimento Científico e Tecnológico. Grant Numbers: 406260/2018-4, 406750/2016-5, 465454/2014-3; Fundação de Amparo à Pesquisa do Estado do Rio Grande do Sul. Grant Numbers: 16/2552-0000, 18/2551-0000561-4; Fundación Séneca. Grant Number: 20790/PI/18.Ionic liquids (ILs) are among the most studied and promising materials for selective CO2 capture and transformation. The high CO2 sorption capacity associated with the possibility to activate this rather stable molecule through stabilization of ionic/radical species or covalent interactions either with the cation or anion has opened new avenues for CO2 functionalization. However, recent reports have demonstrated that another simpler and plausible pathway is also involved in the sorption/activation of CO2 by ILs associated with basic anions. Bare ILs or IL solutions contain almost invariable significant amounts of water and through interaction with CO2 generate carbonates/bicarbonates rather than carbamic acids or amidates. In these cases, the IL acts as a base and not a nucleophile and yields buffer-like solutions that can be used to shift the equilibrium toward acid products in different CO2 reutilization reactions. In this Minireview, the emergence of IL buffer-like solutions as a new reactivity paradigm in CO2 capture and activation is described and analyzed critically, mainly through the evaluation of NMR data.authorsversionpublishe

Ergodicity breaking in strong and network-forming glassy system

The temperature dependence of the non-ergodicity factor of vitreous GeO$_2$, $f_{q}(T)$, as deduced from elastic and quasi-elastic neutron scattering experiments, is analyzed. The data are collected in a wide range of temperatures from the glassy phase, up to the glass transition temperature, and well above into the undercooled liquid state. Notwithstanding the investigated system is classified as prototype of strong glass, it is found that the temperature- and the $q$-behavior of $f_{q}(T)$ follow some of the predictions of Mode Coupling Theory. The experimental data support the hypothesis of the existence of an ergodic to non-ergodic transition occurring also in network forming glassy systems

Estoque de carbono na biomassa de Pinus taeda em sítios de diferentes potenciais produtivos.

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Estoques de carbono e fluxos de gases de efeito estufa em plantios de pinus.

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Estoque de carbono e fluxos de gases de efeito estufa no solo em floresta nativa.

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