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28 results on '"Bortoleto, J. R. R."'

5. Structural and optical properties of InP quantum dots grown on GaAs(001).

Author

de Godoy, M. P. F., Nakaema, M. K. K., Iikawa, F., Brasil, M. J. S. P., Lopes, J. M. J., Bortoleto, J. R. R., Cotta, M. A., Magalhães-Paniago, R., Mörschbächer, M. J., and Fichtner, P. F. P.

Subjects
QUANTUM dots, SEMICONDUCTORS, OPTICAL properties, GALLIUM arsenide, INDIUM phosphide, X-ray diffraction, TRANSMISSION electron microscopy
Abstract

We investigated structural and optical properties of type-II InP/GaAs quantum dots using reflection high energy electron diffraction, transmission electron microscopy, atomic force microscopy, grazing incidence x-ray diffraction, and photoluminescence techniques. The InP dots present an efficient optical emission even when they are uncapped, which is attributed to the low surface recombination velocity in InP. We compare the difference in the optical properties between surface free dots, which are not covered by any material, with dots covered by a GaAs capping layer. We observed a bimodal dispersion of the dot size distribution, giving rise to two distinct emission bands. The results also revealed that the strain accumulated in the InP islands is slightly relieved for samples with large InP amounts. An unexpected result is the relatively large blue shift of the emission band from uncapped samples as compared to capped dots. [ABSTRACT FROM AUTHOR]

Published
2007
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6. Compositional modulation and surface stability in InGaP films: Understanding and controlling surface properties.

Author

Bortoleto, J. R. R., Gutiérrez, H. R., Cotta, M. A., and Bettini, J.

Subjects
*INDIUM phosphide, *GALLIUM compounds, *BIOLOGICAL interfaces, *THIN films, *QUANTUM dots, *ORDER-disorder in alloys
Abstract

We investigate the formation of compositional modulation and atomic ordering in InGaP films. Such bulk properties—as well as surface morphologies—present a strong dependence on growth parameters, mainly the V/III ratio. Our results indicate the importance of surface diffusion and, particularly, surface reconstruction for these processes. Most importantly from the application point of view, we show that the compositional modulation is not necessarily coupled to the surface instabilities, so that smooth InGaP films with periodic compositional variation could be obtained. This opens a new route for the generation of templates for quantum dot positioning and three-dimensional arrays of nanostructures. [ABSTRACT FROM AUTHOR]

Published
2007
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7. Role of group V exchange on the shape and size of InAs/InP self-assembled nanostructures.

Author

Gutiérrez, H. R., Cotta, M. A., Bortoleto, J. R. R., and de Carvalho, M. M. G.

Subjects
NANOSTRUCTURES, MOLECULAR self-assembly, INDIUM compounds
Abstract

We have studied the influence of Group V overpressure on the final shape and size of InAs nanostructures grown on (001) InP substrates. The mechanisms leading to postgrowth modifications in the InAs nanostructures are discussed. The simultaneous action of Group V overpressure and stress field—produced by the InAs nanostructures—can induce strong material transport. The direction of this material net current depends on the type of Group V element used for the overpressure flux. In situ reflection high-energy electron diffraction, atomic force microscopy, and transmission electron microscopy measurements were used to characterize the transitions in morphology. Our results show that morphological studies considering the grown surface that do not take into account postgrowth processes can be misleading to understand the growth mechanisms governing the self-assembling process. [ABSTRACT FROM AUTHOR]

Published
2002

12. Carrier dynamics in stacked InP∕GaAs quantum dots

Author

Veloso, A. B., primary, Nakaema, M. K. K., additional, de Godoy, M. P. F., additional, Lopes, J. M. J., additional, Iikawa, F., additional, Brasil, M. J. S. P., additional, Bortoleto, J. R. R., additional, Cotta, M. A., additional, Fichtner, P. F. P., additional, Morschbächer, M., additional, and Madureira, J. R., additional

Published
2007
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14. Exciton binding energy in type II quantum dots

Author

Gomes, P. F., primary, Godoy, M. P. F., additional, Veloso, A. B., additional, Nakaema, M. K. K., additional, Iikawa, F., additional, Brasil, M. J. S. P., additional, Bortoleto, J. R. R., additional, Cotta, M. A., additional, and Madureira, J. R., additional

Published
2007
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17. Excitongfactor of type-IIInP∕GaAssingle quantum dots

Author

de Godoy, M. P. F., primary, Gomes, P. F., additional, Nakaema, M. K. K., additional, Iikawa, F., additional, Brasil, M. J. S. P., additional, Caetano, R. A., additional, Madureira, J. R., additional, Bortoleto, J. R. R., additional, Cotta, M. A., additional, Ribeiro, E., additional, Marques, G. E., additional, and Bittencourt, A. C. R., additional

Published
2006
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22. Magneto‐optics from type‐II single quantum dots

Author

Godoy, M. P. F., primary, Nakaema, M. K. K., additional, Iikawa, F., additional, Brasil, M. J. S. P., additional, Bortoleto, J. R. R., additional, Cotta, M. A., additional, Ribeiro, E., additional, and Medeiros‐Ribeiro, G., additional

Published
2004
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26. Carbon nanotube probe resolution: a quantitative analysis using Fourier Transform

Author

Gutiérrez, H. R., Nakabayashi, D., Silva, P. C., Bortoleto, J. R. R., Rodrigues, V., Clerici, J. H., Cotta, M. A., and Ugarte, D.

Abstract

A method to quantify the resolution of atomic force microscopy (AFM) probes using Fourier analysis of the AFM images is proposed. The maximum detectable spatial frequency obtained from the power spectrum was used to estimate the lateral resolution. Carbon nanotube tips were successfully used to study very dense arrays of semiconductor nanostructures. In particular, accurate measurements of shallow facet angles were obtained, which are in perfect agreement with results obtained by two complementary techniques – High Resolution Transmission Electron Microscopy and Reflection High-Energy Electron Diffraction. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Published
2004
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28. Designing spatial correlation of quantum dots: towards self-assembled three-dimensional structures.

Author

Bortoleto JR, Zelcovit JG, Gutiérrez HR, Bettini J, and Cotta MA

Abstract

Buried two-dimensional arrays of InP dots were used as a template for the lateral ordering of self-assembled quantum dots. The template strain field can laterally organize compressive (InAs) as well as tensile (GaP) self-assembled nanostructures in a highly ordered square lattice. High-resolution transmission electron microscopy measurements show that the InAs dots are vertically correlated to the InP template, while the GaP dots are vertically anti-correlated, nucleating in the position between two buried InP dots. Finite InP dot size effects are observed to originate InAs clustering but do not affect GaP dot nucleation. The possibility of bilayer formation with different vertical correlations suggests a new path for obtaining three-dimensional pseudocrystals.

Published
2008
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