Photoluminescence Stokes shift and exciton fine structure in CdTe nanocrystals

The photoluminescence spectra of spherical CdTe nanocrystals with zincblende structure are studied by size-selective spectroscopic techniques. We observe a resonant Stokes shift of 15 meV when the excitation laser energy is tuned to the red side of the absorption band at 2.236 eV. The experimental data are analyzed within a symmetry-based tight-binding theory of the exciton spectrum, which is first shown to account for the size dependence of the fundamental gap reported previously in the literature. The theoretical Stokes shift presented as a function of the gap shows a good agreement with the experimental data, indicating that the measured Stokes shift indeed arises from the electron-hole exchange interaction.Comment: 8 pages, 4 figures, LaTe

Módulos de pré-concentração miniaturizados mediante o uso da tecnologia LTCC e zeólitas.

A conjugação do binômio miniaturizaçãointegração tem permitido estabelecer a base conceitual para o desenvolvimento de uma nova geração de dispositivos miniaturizados, capazes de integrar todas as etapas necessárias para a realização de uma análise química. As cerâmicas verdes apresentam-se muito mais versáteis que qualquer dos materiais com os quais já se trabalhou até o momento no campo da miniaturização, dado que permitem a construção de dispositivos tridimensionais, de uma maneira rápida e simples. O objetivo desse trabalho é avaliar a zeólita natural como material para a construção de filtros empregados na préconcentração de fosfatos presentes na água, mediante sua integração em um dispositivo reutilizável baseado em cerâmicas verdes

Sistema para Sensoriamento de Potássio no Solo.

bitstream/CNPDIA/10447/1/BPD09_2004.pd

Determinação de selenometionina por quimiolumiescência em castanha do Brasil.

Selênio é reconhecido como um micronutriente essencial. Porém, a bioutilidade deste elemento está intrísecamente dependente da sua forma química. Espécies orgânicas de selênio são mais facilmente absorvidas por organismos humanos quando comparado a suas espécies inorgânicas. Castanhas do Brasil podem ser consideradas uma boa fonte de selênio, pois apresenta concentrações significativas deste elemento, principalmente na forma de selenometionina.1 Neste trabalho, sistema para análise em fluxo para a determinação de selenometionina em amostras de castanha do Brasil empregando quimioluminescência foi desenvolvido, utilizando uma célula de reação com estrutura em vórtex construída com tecnologia LTCC2

Western U.S. lake expansions during Heinrich stadials linked to Pacific Hadley circulation

Unidad de excelencia María de Maeztu MdM-2015-0552Lake and cave records show that winter precipitation in the southwestern United States increased substantially during millennial-scale periods of Northern Hemisphere winter cooling known as Heinrich stadials. However, previous work has not produced a clear picture of the atmospheric circulation changes driving these precipitation increases. Here, we combine data with model simulations to show that maximum winter precipitation anomalies were related to an intensified subtropical jet and a deepened, southeastward-shifted Aleutian Low, which together increased atmospheric river-like transport of subtropical moisture into the western United States. The jet and Aleutian Low changes are tied to the southward displacement of the intertropical convergence zone and the accompanying intensification of the Hadley circulation in the central Pacific. These results refine our understanding of atmospheric changes accompanying Heinrich stadials and highlight the need for accurate representations of tropical-extratropical teleconnections in simulations of past and future precipitation changes in the region

Cinética da adsorção de Cd, Co, Cr, Cu, K, Ni e Zn em soluções aquosas usando zeólita natural integrada à tecnologia LTCC.

Materiais naturais, disponíveis em grandes quantidades e que possam ser empregados como adsorventes de baixo custo para o tratamento de efluentes, vem sendo o alvo de inúmeras pesquisas. Quitosana, zeólitas, esponjas naturais e carvão ativado são empregados com sucesso para este propósito1. Dentro deste contexto, o objetivo do trabalho foi investigar a capacidade de remoção de Cd, Co, Cr, Cu, K, Ni e Zn através de uma amostra de zeólita natural integrada a dispositivos cerâmicos mediante a tecnologia LTCC

Bidimensional planar micro-optics for optochemical absorbance sensing

A new approach for developing optochemical absorbance sensors is presented. The method is based on a planar micro-optic circuit in which an optochemically active membrane that responds to selective compounds is deposited in the device, yielding a part of the guiding planar structure. In this way the optical field is confined in the direction transverse to the substrate and controlled in the lateral direction by means of planar micro-optics components. High sensitivity of the device can be easily obtained because of the relatively long light paths through the membrane, and the response time is low because the analyte has to diffuse through a several-micrometer-thin membrane. Experimental results of measurements of the concentration of potassium are also presented to verify the possibilities of these devices as specific absorbance sensors

Novel LTCC-potentiometric microfluidic device for biparametric analysis of organic compounds carrying plastic antibodies as ionophores: Application to sulfamethoxazole and trimethoprim

Monitoring organic environmental contaminants is of crucial importance to ensure public health. This requires simple, portable and robust devices to carry out on-site analysis. For this purpose, a low-temperature co-fired ceramics (LTCC) microfluidic potentiometric device (LTCC/μPOT) was developed for the first time for an organic compound: sulfamethoxazole (SMX). Sensory materials relied on newly designed plastic antibodies. Sol–gel, self-assembling monolayer and molecular-imprinting techniques were merged for this purpose. Silica beads were amine-modified and linked to SMX via glutaraldehyde modification. Condensation polymerization was conducted around SMX to fill the vacant spaces. SMX was removed after, leaving behind imprinted sites of complementary shape. The obtained particles were used as ionophores in plasticized PVC membranes. The most suitable membrane composition was selected in steady-state assays. Its suitability to flow analysis was verified in flow-injection studies with regular tubular electrodes. The LTCC/μPOT device integrated a bidimensional mixer, an embedded reference electrode based on Ag/AgCl and an Ag-based contact screen-printed under a micromachined cavity of 600 μm depth. The sensing membranes were deposited over this contact and acted as indicating electrodes. Under optimum conditions, the SMX sensor displayed slopes of about −58.7 mV/decade in a range from 12.7 to 250 μg/mL, providing a detection limit of 3.85 μg/mL and a sampling throughput of 36 samples/h with a reagent consumption of 3.3 mL per sample. The system was adjusted later to multiple analyte detection by including a second potentiometric cell on the LTCC/μPOT device. No additional reference electrode was required. This concept was applied to Trimethoprim (TMP), always administered concomitantly with sulphonamide drugs, and tested in fish-farming waters. The biparametric microanalyzer displayed Nernstian behaviour, with average slopes −54.7 (SMX) and +57.8 (TMP) mV/decade. To demonstrate the microanalyzer capabilities for real applications, it was successfully applied to single and simultaneous determination of SMX and TMP in aquaculture waters

Enhancement of the electron spin memory by localization on donors in a quantum well

We present easily reproducible experimental conditions giving long electron spin relaxation and dephasing times at low temperature in a quantum well. The proposed system consists in an electron localized by a donor potential, and immerged in a quantum well in order to improve its localization with respect to donor in bulk. We have measured, by using photoinduced Faraday rotation technique, the spin relaxation and dephasing times of electrons localized on donors placed in the middle of a 80A CdTe quantum well, and we have obtained 15ns and 18ns, respectively, which are almost two orders of magnitude longer than the free electron spin relaxation and dephasing times obtained previously in a similar CdTe quantum well (J. Tribollet et al. PRB 68, 235316 (2003)).Comment: 15 pages, 4 figure