Papers by Pedro Pablo González Borrero
DOAJ (DOAJ: Directory of Open Access Journals), Dec 1, 2010
ABSTRACT
International Journal of Food Science & Technology, 2015
Brazilian Journal of Development, Apr 19, 2021
Este trabalho relata uma atividade realizada pelo Programa Educacional Tutorial do curso de Licen... more Este trabalho relata uma atividade realizada pelo Programa Educacional Tutorial do curso de Licenciatura em Física da Universidade Estadual do Centro Oeste, Unicentro, do Paraná. A atividade consistiu no desenvolvimento e construção de experimentos de baixo custo com o intuito de reduzir custos e aumentar a acessibilidade de ferramentas de ensino prático, sem a necessidade de um laboratório tradicional. Foram desenvolvidos 32 experimentos de diferentes áreas de Física Geral e Moderna. Cada experimento está acompanhado de um roteiro experimental para facilitação da construção e aplicação da prática de ensino, assim como de um plano de aulas dirigido a assuntos relacionados com as diretrizes da disciplina de Física. Os resultados obtidos têm como base os relat os dos próprios desenvolvedores da instrumentação que utilizaram desses materiais para o ensino, e mostram que a experimentação em Física pode ser feita utilizando ferramentas mais acessíveis.
Physical review, Nov 13, 2017
The effect of dynamical properties of the periodic Lorentz gas on the autocorrelation function an... more The effect of dynamical properties of the periodic Lorentz gas on the autocorrelation function and diffusion coefficient are investigated in various geometric transitions between billiards without horizon and infinite horizon. Numerical simulations are performed using a double square lattice which permits us to isolate different types of corridors and to describe the individual effects of each corridor. The results are compared with a stochastic model based on a escape-rate formalism which reveals the sensibility of the diffusion coefficient and clarifies the role of the open corridors mechanism on the dynamical transitions
Revista brasileira de aplicações de vácuo, Feb 7, 2008
Optical characterization of (GaAs) 5 /(AlAs) 5 superlattices grown on (111)A, (311)A and (001) or... more Optical characterization of (GaAs) 5 /(AlAs) 5 superlattices grown on (111)A, (311)A and (001) oriented semiinsulating substrate of GaAs is reported in this work. The samples were grown by the MBE technique. An investigation of the photoluminescence spectra as a function of the temperature reveals an increase of thermal activation energy in sample grown on (311)A plane when compared with the others, evidencing an additional lateral confinement. The results suggest that the superlattice grown on (111)A has a better interface. The energy peak dependence on temperature shows a bimodal behavior, having a certain behavior up to a critical temperature and, starting from this temperature, seems to follow the dependence of the AlAs energy gap. Pseudodirect transitions were observed for all directions.
Brazilian Journal of Physics, Mar 1, 1997
The photoluminescence of electron excitations in the InxGa1 xAs selfassembled quantum dot system ... more The photoluminescence of electron excitations in the InxGa1 xAs selfassembled quantum dot system was measured at di erent temperatures. The temperature dependence of both the photoluminescence intensity and the electron recombination energy give an evidence of formation of quantum dots. The strong proof of the lower dimensionality of the quantum dots comparative to the reference quantum well was obtained from the temperature shift of the photoluminescence peaks.
Physica E-low-dimensional Systems & Nanostructures, Jun 1, 2001
The Raman spectra of the optical conÿned phonons in the GaAs=AlAs ultra-thin layer superlattices ... more The Raman spectra of the optical conÿned phonons in the GaAs=AlAs ultra-thin layer superlattices grown with di erent growth conditions were used to determine the compositional proÿles and to study the process of segregation at the heterointerfaces. A modiÿed kinetic model was developed in order to calculate the compositional proÿles in the samples under investigation. The comparison between the experimentally obtained compositional proÿles and those calculated by the kinetic model allowed us to determine the parameters characterizing the segregation. It was shown that the increase of pressure of As acts equivalently to the decrease of the growth temperature, resulting in a more abrupt compositional proÿle.
Physica B-condensed Matter, Jun 1, 2012
ABSTRACT The competition between confinement potential fluctuations and band-gap renormalization ... more ABSTRACT The competition between confinement potential fluctuations and band-gap renormalization (BGR) in GaAs/AlxGa1−xAsGaAs/AlxGa1−xAs quantum wells grown on [1 0 0] and [3 1 1]A GaAs substrates is evaluated. The results clearly demonstrate the coexistence of the band-tail states filling related to potential fluctuations and the band-gap renormalization caused by an increase in the density of photogenerated carriers during the photoluminescence (PL) experiments. Both phenomena have strong influence on temperature dependence of the PL-peak energy (EPL(T))(EPL(T)). As the photon density increases, the EPL can shift to either higher or lower energies, depending on the sample temperature. The temperature at which the displacement changes from a blueshift to a redshift is governed by the magnitude of the potential fluctuations and by the variation of BGR with excitation density. A simple band-tail model with a Gaussian-like distribution of the density of state was used to describe the competition between the band-tail filling and the BGR effects on EPL(T).
Superlattices and Microstructures, Jul 1, 1997
In this work we have studied the optical properties of InAs quantum dots (QDs) grown by molecular... more In this work we have studied the optical properties of InAs quantum dots (QDs) grown by molecular-beam epitaxy on GaAs (211)A, on (n11)A/B (where n is 1, 5 and 7), and on reference (100) substrates. Investigation of orientation and polarity effects by means of photoluminescence (PL) are also presented. The PL spectra reveal interesting differences in amplitude, integral luminescence, peak
Journal of Crystal Growth, May 1, 2002
The evolution of self-assembled InAs quantum dots grown by molecular beam epitaxy on GaAs(0 0 1) ... more The evolution of self-assembled InAs quantum dots grown by molecular beam epitaxy on GaAs(0 0 1) substrates was investigated as a function of the amount of InAs deposited on the surface. A single highly inhomogeneous sample was intentionally grown, where the thickness of the InAs layer varied in such a way that the InAs islands could be continuously analyzed from nucleation to coalescence, avoiding problems of reproducibility and thickness control that are common when a discrete set of samples is used. Extremely careful atomic-force microscopy measurements were carried out at many different locations of the sample and showed for the first time, unambiguously, that the size (height and diameter) histograms of the quantum dots become narrower and tend to an equilibrium value when the amount of InAs increases.
Program and Abstracts, 1997
Microelectronic Engineering, Aug 1, 1998
In this work we have investigated the temperature dependence of photoluminescence (PL) properties... more In this work we have investigated the temperature dependence of photoluminescence (PL) properties of GaAs /AlAs ultrathin-layer superlattices (UTLS) grown by molecular beam epitaxy on high index surfaces. The temperature dependence reveals an anomalous decrease of the PL linewidth with the increase of the temperature, which is explained in terms of the exciton thermal activation energy transfer between nanometre-steps formed in the corrugated interfaces.
Journal of Raman Spectroscopy, Oct 1, 2001
A Raman scattering study of cation segregation in GaAs/AlAs ultrathin‐layer superlattices grown w... more A Raman scattering study of cation segregation in GaAs/AlAs ultrathin‐layer superlattices grown with different temperatures and As pressures is reported. The optical confined modes of the samples were measured. The kinetic segregation model was modified in order to allow the calculation of the compositional profiles of the samples. After utilizing the Raman wavenumbers as references to adjust the calculated values by the next‐nearest‐neighbor linear chain model, it was possible to determine the parameters characterizing the segregation. It is shown that an increase in the pressure of As results in a more abrupt compositional profile, equivalent to the decrease in the growth temperature. Copyright © 2001 John Wiley & Sons, Ltd.
Thin Solid Films, May 1, 2002
The evolution of InAs quantum dots (QDs) deposited on GaAs (001) was investigated in a continuous... more The evolution of InAs quantum dots (QDs) deposited on GaAs (001) was investigated in a continuous and unambiguous way as a function of the InAs coverage. Taking advantage of the intrinsic non-uniformity of the In flux in the molecular beam epitaxy system, a single sample was grown where the amount of InAs material varied in a monotonic way along the sample area. Highquality atomic force microscopy (AFM) images showed a saturation of the number of QDs nucleated out of the surface steps as the system evolved and confirmed that QDs can be effectively aligned along the surface steps up to the highest densities, which is an important subject for device application.
Physical review, Mar 1, 2001
The collective plasmon-LO phonon excitations were studied by Raman scattering in intentionally di... more The collective plasmon-LO phonon excitations were studied by Raman scattering in intentionally disordered GaAs/AlGaAs superlattices with various strengths of disorder. The results were compared with the data obtained in the differently doped superlattices where the fixed disorder was mainly provided by the monolayer fluctuations of the layer thicknesses. Thus, the influences of both disorder and electron-electron interaction on the behavior of localized electrons were explored. We found that in the presence of disorder, the collective excitations tend to form coherently oscillating clusters with a finite extent. It was shown that while interaction causes the formation of coherent clusters, the effect of both the temperature and disorder is to destroy them; these evolutions of the clusters revealed a critical behavior.
Journal of Crystal Growth, May 1, 1997
ABSTRACT In this paper we report optical properties of InAs quantum dots (QD) grown by molecular-... more ABSTRACT In this paper we report optical properties of InAs quantum dots (QD) grown by molecular-beam epitaxy on GaAs (2 1 1)A, , where n is 1, 5 and 7, and on reference (0 0 1) substrates. The photoluminescence (PL) spectra reveal differences in amplitude, integral luminescence, peak position and shape. Temperature dependence indicates an additional lateral confinement on (0 0 1), (n 1 1)B, (2 1 1)A and (1 1 1)A substrates. Our results also show an enhancement of QD onset thermal quenching energy by a factor of ∼ 3 for these orientations, when compared with the reference quantum well. PL polarization measurements show strong in-plane dependence caused by the quantum dot's structural anisotropy. However, the structure grown on (5 1 1)A and (7 1 1)A surface does not exhibit QD formation.
International Journal of Food Science and Technology, May 30, 2015
ABSTRACT Agaricus brasiliensis is a medicinal mushroom traditionally employed in prevention and t... more ABSTRACT Agaricus brasiliensis is a medicinal mushroom traditionally employed in prevention and treatment of cancer, used as immunostimulant and as a source of antioxidants. We investigated the chemical composition of the mycelium produced by submerged (SF) and solid-state fermentation (SSF), using residues from food industry as substrates. After fermentation, antiradical activity and levels of antioxidants were enhanced, indicating that the micro-organism produces these metabolites. For myceliated substrate (mushroom mycelia grown around and into the substrate particles) obtained by SSF, phenolics ranged from 18.57 to 70.46 mg g−1 and flavonoids from 0.83 to 4.51 mg g−1. For myceliated substrate obtained by SF, the variation was 27.19 to 66.99 mg g−1 and 0.75 to 5.34 mg g−1 for phenolics and flavonoids, respectively. The fatty acid profile determined by FT-ICR MS and UPLC-MS showed predominance of palmitic, linoleic, linolenic and oleic acids. Our findings indicated that mycelium has nutraceutical potential and can be incorporated in food supplements.
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Papers by Pedro Pablo González Borrero