Encontrados 12 documentos, a visualizar página 1 de 2
Variable range hopping conduction in low-temperature molecular beam epitaxy GaAs
Rubinger,R. M.; Albuquerque,H. A.; Silva,R. L. da; Oliveira,A. G. de; Ribeiro,G. M.; Rodrigues,W. N.; Rubinger,C. P. L; Moreira,M. V. B.Electric transport properties measured by Van der Pauw resistivity experiments of Low-Temperature Molecular Beam Epitaxy (LT-MBE) GaAs samples are used to identify a method to improve the resistivity of GaAs material. We present results on five samples grown at 265, 310, 315, 325, and 345 ºC. The electric measurements were carried out at temperatures ranging from 130 to 300 K. In this temperature range the domi...
Piezoelectric and optical response of uniaxially stretched (VDF/TrFE) (75/25) c...
Nunes, J. Serrado; Kouvatov, A.; Mueller, V.; Beige, H.; Brandão, P. M.; Belsley, M.; Moreira, M. V.; Lanceros-Méndez, S.The phase diagram of the poly(vinylidene fluoride-trifluorethylene) (P(VDF-TrFE)) copolymer system shows for VDF contents of 50...85 mol% a ferroelectric (FE)-paraelectric (PE) phase transition below melting temperature. Investigations on P(VDF-TrFE) 75/25 samples revealed a slight anisotropic behaviour, which leads to a strongly anisotropic stretching effect both on the phase transition and on the amount and n...
Controladores robustos H¥ não frágeis
Moreira,M. V.; Basilio,J. C.Em um artigo recente, Keel e Bhattacharyya sugerem, a partir de exemplos simples extraídos da literatura, que os controladores robustos H<FONT FACE=Symbol>¥</FONT> podem ser frágeis no sentido de que uma pequena perturbação nos seus parâmetros pode instabilizar o sistema realimentado. Trabalhos subseqüentes ligaram este problema à forma de implementação dos controladores e sugeriram a utilização de métodos mais...
Exciton polariton emission from a resonantly excited GaAs microcavity
Cotta,E. A.; Ribeiro Filho,H. P.; Matinaga,F. M.; Cury,L. A.; Moreira,M. V. B; Rodrigues,W. N.; Oliveira,A. G. deCoherent emission efficiency in a 100Å GaAs SQW microcavity was enhanced one order when pumped resonantly at 10 K, compared to the off-resonant excitation. The usual kink observed in the exciton emission linewidth as well as in the emission intensity in relation to the pump power, changes smoothly instead of the usual abrupt kink observed in the off-resonant microcavity laser. In addition, polarization measurem...
Hall effect in InAs/GaAs superlattices with quantum dots: identifying the prese...
Rubinger,R.M.; Ribeiro,G.M.; Oliveira,A.G. de; Albuquerque,H.A.; Silva,R.L. da; Rodrigues,W.N.; Moreira,M.V.B.We have carried out van der Pauw resistivity and Hall effect measurements on a series of Molecular Beam Epitaxy InAs/GaAs superlattice samples containing InAs quantum dots. Three growth parameters were varied, the InAs coverage, the number of repetitions of the InAs/GaAs layers, and the GaAs spacer thickness. The results can be grouped in two sets, those samples presenting low and high resistivity. The group pr...
X-ray scattering from self-assembled InAs islands
Malachias,A.; Neves,B. R. A.; Rodrigues,W. N.; Moreira,M. V. B.; Kycia,S.; Metzger,T. H.; Magalhães-Paniago,R.In this work several structural and chemical properties of self-assembled InAs islands grown on GaAs(001) are studied using surface x-ray scattering with synchrotron radiation. The technique of x-ray diffraction under grazing incidence condition was employed to differentiate coherent and incoherent islands. We used a model of a strained pyramidal island to interpret the x-ray results and correlate size and stra...
Comparison between bulk micromachined and CMOS detectors for X-ray measurements
Rocha, J. G.; Schabmueller, C. G. J.; Ramos, N. F.; Lanceros-Méndez, S.; Moreira, M. V.; Evans, A. G. R.; Wolffenbuttel, R. F.; Correia, J. H.This paper compares two x-ray detectors fabricated using two different technologies: one is based on a bulk micromachined silicon photodetector and the other is based on a standard CMOS photodetector. The working principle of the two detectors is similar: a scintillating layer of CsI:Tl is placed above the photodetector, so the x-rays are first converted into visible light (560 nm) which is then converted into ...
CMOS X-rays microdetector based on scintillating light guides
Rocha, J. G.; Ramos, N. F.; Moreira, M. V.; Lanceros-Méndez, S.; Wolffenbuttel, R. F.; Correia, J. H.This paper describes a pixel imaging array consisting in 400 um x 400 um photodiodes fabricated in CMOS technology. Above the photodiodes, an array of scintillating CsI:Tl crystals are placed. The scintillating crystals are encapsulated in aluminum walls forming a light path to guide the produced visible light into the photodiodes. So, the x-ray energy is first converted into visible light which is then detec...
X-rays microdetectors based on an array of scintillators : a maskless process u...
Rocha, J. G.; Moreira, M. V.; Wolffenbuttel, R. F.; Ramos, N. F.; Lanceros-Méndez, S.; Correia, J. H.This paper describes a X-rays microdetector based on an array of wells filled with scintillator crystals. A thick-film of aluminum (500 um) is etched by Laser Ablation Technique (LAT) in order to achieve a square well with side of 100 um and 490 um deep vertical sidewalls. The aluminum thick-film was chosen because it is a good reflector in the visible range and for improving the number of photons collected by...
Observation of low frequency oscillations in GaAs samples grown by molecular be...
Rubinger,R. M.; Oliveira,A. G. de; Ribeiro,G. M.; Soares,D. A. W.; Moreira,M. V. B.We have observed Low Frequency Oscillations (LFO) in a GaAs sample grown by molecular beam epitaxy (MBE) at 300 °C as a function of applied electric field, temperature and illumination intensity. Time series of the oscillations for different values of the applied electric field at room temperature were obtained. We have also obtained the jxE characteristics as a function of temperature and light intensity. We w...
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