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448 results on '"Abramof, E."'

102. MBE growth and characterization of Sn1-xEu xTe

Author

Ueta, A. Y., Rappl, P. H. O., Closs, H., Motisuke, P., Abramof, E., Anjos, V. R. dos, Chitta, V. A., Coaquira, J. A., Oliveira Jr., N. F., and Bauer, G.

Abstract

Epilayers of Sn1-xEu xTe (0 < x < 0:03) were grown by molecular beam epitaxy on freshly cleaved BaF2(111) substrates and their structural, electrical and optical properties were investigated. The thicknesses of epilayers were about 1.5 mum and deposition was carried out at growth temperatures of 300 ºC. The structural properties were investigated by high resolution X-ray diffraction and a sharp film degradation could be observed with increasing europium content. Electrical measurements with temperature varying from 300 to 10K indicated that the epilayers present carrier concentration ranging between 3 x 10(20) and 6 x 10(20)cm-3 and a low resistivity from 6.3 x 10-5 to 1.2 x 10-4 omega.cm. From optical measurements it could be seen that spectra present a low energy edge corresponding to the beginning of intra band excitations and the high energy edge due to inter band excitations.

Published
2004

103. Luminescence from miniband states in heavily doped superlattices

Author

Oliveira, R.F., Henriques, A.B., Lamas, T.E., Quivy, A.A., Pires, M.P., Souza, P.L., Yavich, B., and Abramof, E.

Subjects
Condensed Matter::Quantum Gases, Condensed Matter::Materials Science, Condensed Matter::Other, Condensed Matter::Strongly Correlated Electrons, Condensed Matter::Mesoscopic Systems and Quantum Hall Effect
Abstract

We have studied doped superlattices of GaAs/AlGaAs composition. When the doping atoms are introduced into the barriers surrounding the superlattice, as well as to the inner ones, but with half of the concentration, the photoluminescence due to interband transitions from extended superlattice states is detected. This is demonstrated by a study of the sample´s photoluminescence in a magnetic field, whose intensity oscillates in concomitance with the SdH spectrum of electrons confined in the miniband.

Published
2004

104. Magnetic field induced absorption in Pb xEu1-xTe magnetic semiconductors

Author

Hanamoto,L. K., Henriques,A. B., Rappl,P. H. de Oliveira, Oliveira,N. F., Ueta,A. Y., and Abramof,E.

Subjects
Condensed Matter::Materials Science
Abstract

We report an investigation of the optical absorption spectrum, using non-polarized light, in Pb xEu1-xTe, x=0 and x=0.095, epitaxial thick layers grown by molecular beam epitaxy (MBE). The absorption edge is described by a broad band, due to the electronic transitions from the 4f7 of Eu2+ to the states in 4f6 5d configuration, as seen previously in bulk Eu chalcogenides. When a magnetic field is applied, a narrow absorption band (full width ~50 meV) emerges from the broad one. The energy of this absorption peak red shifts when the magnetic field increases, and reaches saturation when the Eu2+ attain ferromagnetic arrangement. This behaviour can be described by a localized excitation model with d - f exchange interaction.

Published
2004

107. Systematic study of doping dependence on linear magnetoresistance in p-pbte

Author

Schneider, J.M., Peres, M.L., Wiedmann, S., Zeitler, U., Chitta, V.A., Abramof, E., Rappl, P.H.O., Castro, S. de, Soares, D.A.W., Mengui, U.A., Oliveira, N.F., Schneider, J.M., Peres, M.L., Wiedmann, S., Zeitler, U., Chitta, V.A., Abramof, E., Rappl, P.H.O., Castro, S. de, Soares, D.A.W., Mengui, U.A., and Oliveira, N.F.

Abstract

Contains fulltext : 133237.pdf (publisher's version ) (Open Access)

Published
2014

113. Interfacial layers and impurity segregation in InP/In0.53Ga0.47As superlattices

Author

Hanamoto, L. K., Henriques, A. B., Tribuzy, C. V.-B., Souza, P. L., Yavich, B., and Abramof, E.

Abstract

The interfaces in InP=In0.53 Ga0.47As superlattices modulation doped with Si were investigated using magneto-transport, capacitance-voltage, and high resolution X-ray diffraction measurements. Results indicate that a thick interfacial layer is formed when InP is grown on top of In xGa1-xAs, and that Si atoms that fall in the interfacial layer have a high probability of not forming a shallow donor center. Using a simple theoretical model the width of the interfacial layer which was estimated to be 7±1 monolayers.

Published
2002

114. Reciprocal Space Mapping of Silicon Implanted with Nitrogen and Carbon by PIII

Author

Abramof, E., Beloto, A. F., Ueda, M., Guenzel, R., and Reuther, H.

Subjects
inorganic chemicals, stomatognathic diseases, technology, industry, and agriculture, equipment and supplies, complex mixtures
Abstract

Reciprocal Space Mapping was performed on Silicon Implanted with Nitrogen and Carbon by PIII

Published
2000

115. High Dose Nitrogen and Carbon Shallow Implantations in Silicon by PIII

Author

Ueda, M., Reuther, H., Guenzel, R., Beloto, A. F., Abramof, E., and Berni, L. A.

Subjects
inorganic chemicals, stomatognathic diseases, technology, industry, and agriculture, equipment and supplies, complex mixtures
Abstract

Silicon was implanted with high doses of nitrogen and carbon Shallow by PIII.

Published
2000

116. Porous Silicon Implanted with N by PIII

Author

Beloto, A. F., Ueda, M., Abramof, E., Senna, J. R., Leite, N. F., Silva, M. D., and Reuther, H.

Subjects
inorganic chemicals, stomatognathic diseases, technology, industry, and agriculture, equipment and supplies, complex mixtures
Abstract

Porous silicon was implanted with N by PIII.

Published
2000

120. Investigation of negative photoconductivity in p-type Pb1-xSnxTe film.

Author

Tavares, M. A. B., da Silva, M. J., Peres, M. L., de Castro, S., Soares, D. A. W., Okazaki, A. K., Fornari, C. I., Rappl, P. H. O., and Abramof, E.

Subjects
PHOTOCONDUCTIVITY, BAND gaps, PHOTODETECTORS, SEMICONDUCTOR lasers, VALENCE bands
Abstract

We investigated the negative photoconductivity (NPC) effect that was observed in a p-type Pb1-xSnxTe film for temperatures varying from 300K down to 85 K. We found that this effect is a consequence of defect states located in the bandgap which act as trapping levels, changing the relation between generation and recombination rates. Theoretical calculations predict contributions to the NPC from both conduction and valence bands, which are in accordance with the experimental observations. [ABSTRACT FROM AUTHOR]

Published
2017
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121. Preservation of pristine Bi2Te3 thin film topological insulator surface after ex situ mechanical removal of Te capping layer.

Author

Fornari, C. I., Rappl, P. H. O., Morelhão, S. L., Peixoto, T. R. F., Bentmann, H., Reinert, F., and Abramof, E.

Subjects
ELECTRIC insulators & insulation, THIN films
Abstract

Ex situ analyses on topological insulator films require protection against surface contamination during air exposure. This work reports on a technique that combines deposition of protective capping just after epitaxial growth and its mechanical removal inside ultra-high vacuum systems. This method was applied to Bi2Te3 films with thickness varying from 8 to 170 nm. Contrarily to other methods, this technique does not require any sputtering or thermal annealing setups installed inside the analyzing system and preserves both film thickness and surface characteristics. These results suggest that the technique presented here can be expanded to other topological insulator materials. [ABSTRACT FROM AUTHOR]

Published
2016
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122. Plasma sputtering of PbEuTe films with varied composition and structure.

Author

Zimin, S., Amirov, I., Gorlachev, E., Naumov, V., Abramof, E., and Rappl, P.

Abstract

We investigate the sputtering of single-crystal and polycrystalline films of PbEuTe ( x = 0.02-0.10) in high-frequency inductively coupled argon plasma. Layers of PbEuTe are grown via molecular beam epitaxy on barium-fluoride substrates of the (111) orientation at 340 and 200°C. For single-crystal films, the dependence of the sputtering rate on the europium concentration is found. For polycrystalline layers, a decrease in the sputtering rate is observed. This is caused by the effect of europium oxidation at the surface of the polycrystallites. [ABSTRACT FROM AUTHOR]

Published
2016
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125. Band-edge polarized optical absorption in europium chalcogenides

Author

Henriques, A.B., Wierts, A., Manfrini, M.A., Springholz, G., Rappl, P.H.O., Abramof, E., Ueta, A.Y., Henriques, A.B., Wierts, A., Manfrini, M.A., Springholz, G., Rappl, P.H.O., Abramof, E., and Ueta, A.Y.

Abstract

The band-edge optical absorption of EuTe and EuSe, grown by molecular beam epitaxy, was measured, using circularly polarized light, in the Faraday configuration, at T=1.8 K. In thin layers (less than 0.4 µm ), a doublet of absorption lines could be observed, with a full width at half maximum of about 50 meV in EuTe and 80 meV in EuSe. The lines are separated by about 200 meV in EuTe and 300 meV in EuSe, and they show a strong magnetic circular dichroism. The oscillator strength for these lines increases by a factor of almost 20 when the antiferromagnetic order is changed to ferromagnetic by the application of an external magnetic field. Faraday rotation in the transparency gap shows a strongly nonlinear dependence on the intensity of the magnetic field. These results are interpreted in the framework of the model of electronic transitions between the localized ground |4f7(8S7/2)M=-7/2} and excited states comprised in |4f6(7F)JMJ;X} [where X represents the 5d(t2g) states], yielding good agreement with experiment. The strong enhancement of the oscillator strength with increasing magnetic field may be an indication of exciton formation due to the compression of the zero-field Bloch-like extended electronic wave function.

Published
2005

127. Grazing incidence X-ray diffraction of SS304 steel surfaces modified by high- and low- pressure ion nitriding processes

Author

Ueda, M., Gomes, G., Abramof, E., Reuther, H., Ueda, M., Gomes, G., Abramof, E., and Reuther, H.

Abstract

Ion nitriding is an important surface modification technique used routinely in the advanced technology industries aiming at producing high added value components with increased hardness and wear resistance. To further improve the performance of critical-part components, new methods for surface strengthening are being developed with success, like plasma immersion ion implantation (PIII) and hybrid surface treatments combining PIII and ion nitriding. In particular, a combination of high-pressure (40 Pa), high-temperature (up to 450 degreesC) glow discharge nitriding with low-pressure (8 x 10(-2) Pa) ion nitriding was implemented. Analysis of the SS304 samples treated by this hybrid method was carried out using the technique of grazing incidence X-ray diffraction (GIXRD) and the results were supported by both normal XRD and AES (Auger electron spectroscopy) measurements. Depending on the particular conditions of the treatment and the depth probed, mixed phases Of gamma(N), and gamma were measured. The improvement in hardness of the obtained surfaces (up to a factor of 2.7) was also in accordance with the results of other analysis.

Published
2004

135. Optical third-harmonic spectroscopy of the magnetic semiconductor EuTe

Author

Lafrentz, M., primary, Brunne, D., additional, Kaminski, B., additional, Pavlov, V. V., additional, Henriques, A. B., additional, Pisarev, R. V., additional, Yakovlev, D. R., additional, Springholz, G., additional, Bauer, G., additional, Abramof, E., additional, Rappl, P. H. O., additional, and Bayer, M., additional

Published
2010
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139. Study of PbTe p-Type Doping With BaF[sub 2]

Author

Mengui, U. A., primary, Rappl, P. H. O., additional, Díaz, B., additional, Closs, H., additional, Ueta, A. Y., additional, Abramof, E., additional, Caldas, Marília, additional, and Studart, Nelson, additional

Published
2010
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142. Sponge-like and columnar porous silicon implanted with nitrogen by plasma immersion ion implantation (PIII)

Author

Beloto, A. F., Ueda, M., Abramof, E., Senna, J. R., Da Silva, M. D., Kuranaga, C., Reuther, H., Ferreira Da Silva, A., Pepe, I., Beloto, A. F., Ueda, M., Abramof, E., Senna, J. R., Da Silva, M. D., Kuranaga, C., Reuther, H., Ferreira Da Silva, A., and Pepe, I.

Abstract

Sponge-like and columnar porous silicon implanted with nitrogen by plasma immersion ion implantation (PIII)

Published
2002

149. Electrical resistivity and band-gap shift of Si-doped GaN and metal-nonmetal transition in cubic GaN, InN and AlN systems

Author

Fernandez, J. R. L., Araujo, C. M., da Silva, A. F., Leite, J. R., Sernelius, B. E., Tabata, A., Abramof, E., Chitta, V. A., Persson, Clas, Ahuja, R., Pepe, I., As, D. J., Frey, T., Schikora, D., Lischka, K., Fernandez, J. R. L., Araujo, C. M., da Silva, A. F., Leite, J. R., Sernelius, B. E., Tabata, A., Abramof, E., Chitta, V. A., Persson, Clas, Ahuja, R., Pepe, I., As, D. J., Frey, T., Schikora, D., and Lischka, K.

Abstract

The critical impurity concentration N-c of the metal-nonmetal (MNM) transition for the cubic GaN, InN and AIN systems. is calculated using the following two different criteria: vanishing of the donor binding energy and the crossing point between the energies in the metallic and insulating phases. A dielectric function model with a Lorentz-Lorenz correction is used for the insulating phase. The InN presents an order of magnitude increase in N-c as compared to the other two systems. The electrical resistivity of the Si-donor system GaN is investigated theoretically and experimentally from room temperature down to 10K. It presents a metallic character above a certain high impurity concentration identified as N-c. The samples were grown by plasma assisted molecular beam epitaxy (MBE) on GaAs (0 0 1) substrate. The model calculation is carried out from a recently proposed generalized Drude approach (GDA) presenting a very good estimation for the metallic region. The band-gap shift (BGS) of Si-doped GaN has also been investigated above the MNM transition where this shift is observed. Theoretical and experimental results have a rough agreement in a range of impurity concentration of interest., QC 20100525

Published
2001
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150. Electrical resistivity and band-gap shift of Si-doped GaN and metal-nonmetal transition in cubic GaN, InN and AlN systems

Author

Fernandez, JRL, Araujo, CM, da, Silva AF, Leite, JR, Sernelius, BE, Tabata, A, Abramof, E, Chitta, VA, Persson, C, Ahuja, R, Pepe, I, As, DJ, Frey, T, Schikora, D, Lischka, K, Fernandez, JRL, Araujo, CM, da, Silva AF, Leite, JR, Sernelius, BE, Tabata, A, Abramof, E, Chitta, VA, Persson, C, Ahuja, R, Pepe, I, As, DJ, Frey, T, Schikora, D, and Lischka, K

Abstract

The critical impurity concentration N-c of the metal-nonmetal (MNM) transition for the cubic GaN, InN and AIN systems. is calculated using the following two different criteria: vanishing of the donor binding energy and the crossing point between the energ, Addresses: da Silva AF, Univ Fed Bahia, Inst Fis, Campus Univ Ondina, BR-40210340 Salvador, BA, Brazil. Univ Fed Bahia, Inst Fis, BR-40210340 Salvador, BA, Brazil. Univ Sao Paulo, Inst Fis, BR-05315970 Sao Paulo, SP, Brazil. Linkoping Univ, Dept Phys & Me

Published
2001

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