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Structural and Magnetic Properties of Monophasic Maghemite (γ-fe2O3) nanocrystalline Powder

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Advances in nanoparticles 2014年第3期3卷 114-121页

作者： Juan Adrián Ramos Guivar Arturo Isaías Martínez Ana Osorio Anaya Luis De Los Santos Valladares lizbet león félix Angel Bustamante Dominguez Cavendish Laboratory Department of Physics University of Cambridge Cambridge UK Centro de Investigación y Estudios Avanzados del Instituto Politécnico nacional Cinvestav Unidad Saltillo Ciudad de México México Ciudad de México México Laboratorio de Cerámicos y nanomateriales Facultad de Ciencias Físicas Universidad Nacional Mayor de San Marcos Lima Perú Laboratorio de nanotecnología e Innovación Tecnológica Departamento de Química e Ingeniería Química Universidad Nacional Mayor de San Marcos Lima Perú núcleo de física Aplicada Instituto de Física Universidade de Brasília Brasília Brasil

Structural and magnetic studies of monophasic maghemite (γ-fe2O3) magnetic nanocrystallites (MnCs) synthesized by the co-precipitation chemical route are reported in this paper. for the synthesis, a starting precursor of magnetite (fe3O4) in basic medium was oxidized at room temperature by adjusting the pH = 3.5 at 80°C in an acidic medium without surfactants. X-ray diffraction (XRD) pattern shows widened peaks indicating nanometric size and Rietveld Refinement confirms only one single-phase assigned to γ-fe2O3 MnCs. High Resolution Transmission Electron Microscopy (HR-TEM) demonstrates the formation of nanoparticles with diameter around D ≈ 6.8 ± 0.1 nm which is in good agreement with Rietveld Refinement (6.4 ± 1 nm). A selected area electron diffraction pattern was carried out to complement the study of the crystalline structure of the γ-fe2O3 MnCs. M(H) measurements taken at different temperatures show almost zero coercivity and remanence indicating superparamagnetic domain and high magnetic saturation.

关键词： Monophasic nanomaghemite Rietveld Refinement TEM SAED M-H Loops ZfC

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Crystallization and Morphology of Gold Thin films on Unpolished Si（100） Substrates after furnace and flame Annealing

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材料科学与工程（中英文版） 2010年第1期4卷 1-10页

作者： Luis De Los Santos V Angel Bustamante D. lizbet leon f. Thanos Mitrelias Adrian Ionescu JustinianoQuispe M. Crispin H. W. Barnes Cavendish Laboratory University of Cambridge J. J Thomson .Av. Cambridge CB3 0HE United Kingdom facultad de Ciencias fisicas Universidad Nacional Mayor de San Marcos Ap. Postal 14-0149 Peru

A crystallization and surface evolution study of Au thin film on unpolished Si(100) substrates after annealing at different temperatures above the eutectic point of the Au/Si system are reported. Samples were prepared by conventional evaporation of gold in high vacuum (10-7mbar) environment on substrates at room temperature. Thermal treatments were performed by both furnace and flame annealing techniques. After evaporation, some Au crystallizes were textured in the (111) direction. However, most of the thin film was amorphous and gold silicides such as Au7Si and Au3Si were also found. This crystallization can be achieved by furnace annealing or flame annealing in spite of the differences between their cell parameters. Annealing overcomes the mismatch between the cell parameters arranging the Au layers in the (111) direction and forming gold islands on the surface. Crystallization of gold strongly depends on both, the temperature and time of annealing. Epitaxial formation of Au can be easily reached after some minutes in the case of flame annealing. The epitaxial temperature for Au/Si(100) should be around the eutectic (363 oC). Above the eutectic point, the Au layer melt, the melting starts most likely from grain boundaries and from the interface allowing the islands separate even further and change shapes until hexagonal geometries. The mean crystallite diameters grow up to a maximum mean size of around 90 nm. The free activation energy for grain boundary migration above the eutectic temperature is 0.09 eV. Therefore the type of the silicon substrate changes the mechanism of diffusion and growth of crystallites during annealing of the Au/Si system.

关键词：退火工艺薄膜形貌热处理炉硅衬底黄金火焰结晶糙米

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