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Dantas N.O.,Federal University of Minas Gerais | Silva A.D.S.,Federal University of Minas Gerais | Ayta W.E.F.,Federal University of Minas Gerais | Silva S.W.D.,University of Brasilia | And 4 more authors.
Chemical Physics Letters | Year: 2012

Zn 1-xMn xTe dilute magnetic nanocrystals (NCs) were synthesized by fusion method in a glass template and annealed post-growth. Magnetism and quantum confinement of incorporated Mn-ions were confirmed by magnetic force microscopy (MFM), Raman scattering (RS) and electron paramagnetic resonance (EPR). A blueshift in the RS spectra were clear signatures of Mn 2+ incorporation in the dot structure which were monitored as a function of increasing doping concentration, x. MFM images strongly indicated the formation of Zn 1-xMn xTe magnetic phases in the glass system. The EPR spectra showed six lines associated to the S = 5/2 spin half filled d-state, characteristic of Mn 2+ ions. © 2012 Elsevier B.V. All rights reserved.

Neto E.S.F.,Federal University of Uberlandia | Dantas N.O.,Federal University of Uberlandia | Da Silva S.W.,University of Brasilia | Morais P.C.,University of Brasilia | And 2 more authors.
Journal of Raman Spectroscopy | Year: 2010

This work gives the evidence of the lattice contraction in CdSe nanocrystals (NCs) grown in a glass matrix. The CdSe NCs were investigated by atomic force microscopy (AFM), optical absorption (OA), and Raman spectroscopy. The average size of CdSe NCs can be estimated by AFM images. Using the OA spectra and the effective-mass approximation, it was also possible to estimate the average sizes of CdSe NCs, which agree very well with the AFM data. These results showed that the CdSe NCs grow with increasing time of heat treatment. The blue shift of the longitudinal optical (LO) modes and surface optical (SO) phonon modes with an increase in the average radius of the NCs, shown in the Raman spectra, was explained by the lattice contraction in CdSe NCs caused by thermodynamic interactions at the interface with the host glass matrix. Copyright © 2010 John Wiley & Sons, Ltd.

Neto E.S.F.,Federal University of Uberlandia | Da Silva S.W.,University of Brasilia | Morais P.C.,University of Brasilia | Vasilevskiy M.I.,University of Minho | And 3 more authors.
Journal of Raman Spectroscopy | Year: 2011

Optical phonon modes, confined in CdS xSe 1-x nanocrystal (NC) quantum dots (≈2 nm in radius) grown in a glass matrix by the melting-nucleation method, were studied by resonant Raman scattering (RRS) spectroscopy and theoretical modeling. The formation of nanocrystalline quantum dots (QDs) is evidenced by the observation of absorption peaks and theoretically expected resonance bands in the RRS excitation spectra. This system, a ternary alloy, offers the possibility to investigate the interplay between the effects of phonon localization by disorder and phonon confinement by the NC/matrix interface. Based on the concept of propagating optical phonons, which is accepted for two-mode pseudo-binary alloys in their bulk form, we extended the continuous lattice dynamics model, which has successfully been used for nearly spherical NCs of binary materials, to the present case. After determining the alloy composition for NCs (that was evaluated with only 2-3% uncertainty using the bulk longitudinal optical phonon wavenumbers) and the NC size (using atomic force microscopy and optical absorption data), the experimental RRS spectra were described rather well by this theory, including the line shape and polarization dependence of the scattering intensity. Even though the presence of a compressive strain in the NCs (introduced by the matrix) masks the expected downward shift owing to the phonons' spatial quantization, the asymmetric broadening of both Raman peaks is similar to that characteristic of NCs of pure binary materials. Although with some caution, we suggest that both CdSe-like and CdS-like optical phonon modes indeed are propagating within the NC size unless the alloy is considerably heterogeneous. Copyright © 2011 John Wiley & Sons, Ltd.

Ferri F.A.,University of Sao Paulo | Pereira-Da-Silva M.A.,University of Sao Paulo | Pereira-Da-Silva M.A.,Centro Universitario Central Paulista | Zanatta A.R.,University of Sao Paulo
Materials Chemistry and Physics | Year: 2011

Thin films of Si with Mn concentrations up to 20 at.% were prepared by conventional radio frequency sputtering. After deposition, the films were submitted to thermal annealing treatments and their properties were investigated by composition analysis, Raman scattering, microscopic techniques, optical transmission, and electrical transport. The experimental results show that all as-deposited films are amorphous, with the Mn atoms being effective and controllably incorporated into the Si matrix. Moreover, thermal annealing at increasing temperatures induces the crystallization of the films as well as the growth of the MnSi 1.7 silicide phase in the Mn-containing samples. Along with sample crystallization, some films become covered by small structures that are randomly distributed all over their surfaces. These structures are essentially Mn-containing Si crystals with typical sizes in the (sub-) micrometer range and, as the thermal annealing advances, the density of structures increases at the expense of their individual average dimension. The development and characteristics of the observed superficial structures are discussed in view of the main structural and morphological properties of the samples. © 2011 Elsevier B.V.

Tonoli G.H.D.,Federal University of Lavras | Teixeira E.M.,Laboratorio Nacional Of Nanotecnologia Para O Agronegocio Lnna | Correa A.C.,Laboratorio Nacional Of Nanotecnologia Para O Agronegocio Lnna | Marconcini J.M.,Laboratorio Nacional Of Nanotecnologia Para O Agronegocio Lnna | And 4 more authors.
Carbohydrate Polymers | Year: 2012

There is growing interest in cellulose nanofibres from renewable sources for several industrial applications. However, there is a lack of information about one of the most abundant cellulose pulps: bleached Eucalyptus kraft pulp. The objective of the present work was to obtain Eucalyptus cellulose micro/nanofibres by three different processes, namely: refining, sonication and acid hydrolysis of the cellulose pulp. The refining was limited by the low efficiency of isolated nanofibrils, while sonication was more effective for this purpose. However, the latter process occurred at the expense of considerable damage to the cellulose structure. The whiskers obtained by acid hydrolysis resulted in nanostructures with lower diameter and length, and high crystallinity. Increasing hydrolysis reaction time led to narrower and shorter whiskers, but increased the crystallinity index. The present work contributes to the different widespread methods used for the production of micro/nanofibres for different applications. © 2012 Elsevier Ltd. All rights reserved.

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