Growth of EuTe islands on SnTe by molecular beam epitaxy

Semiconductor magnetic quantum dots are very promising structures, with novel properties that find multiple applications in spintronic devices. EuTe is a wide gap semiconductor with NaCl structure, and strong magnetic moments S=7/2 at the half filled 4f(7) electronic levels. On the other hand, SnTe is a narrow gap semiconductor with the same crystal structure and 4% lattice mismatch with EuTe. In this work, we investigate the molecular beam epitaxial growth of EuTe on SnTe after the critical thickness for island formation is surpassed, as a previous step to the growth of organized magnetic quantum dots. The topology and strain state of EuTe islands were studied as a function of growth temperature and EuTe nominal layer thickness. Reflection high energy electron diffraction (RHEED) was used in-situ to monitor surface morphology and strain state. RHEED results were complemented and enriched with atomic force microscopy and grazing incidence X-ray diffraction measurements made at the XRD2 beamline of the Brazilian Synchrotron. EuTe islands of increasing height and diameter are obtained when the EuTe nominal thickness increases, with higher aspect ratio for the islands grown at lower temperatures. As the islands grow, a relaxation toward the EuTe bulk lattice parameter was observed. The relaxation process was partially reverted by the growth of the SnTe cap layer, vital to protect the EuTe islands from oxidation. A simple model is outlined to describe the distortions caused by the EuTe islands on the SnTe buffer and cap layers. The SnTe cap layers formed interesting plateau structures with easily controlled wall height, that could find applications as a template for future nanostructures growth. (C) 2010 Elsevier B.V. All rights reserved.

Low-energy nuclear reactions with double-solenoid based radioactive nuclear beam

The University of Notre Dame, USA (Becchetti et al, Nucl. Instrum. Metho ds Res. A505, 377 (2003)) and later the University of Sao Paulo, Brazil (Lichtenthaler et al, Eur. Phys. J. A25, S-01, 733 (2005)) adopted a system based on superconducting solenoids to produce low-energy radioactive nuclear beams. In these systems the solenoids act as thick lenses to collect, select, and focus the secondary beam into a scattering chamb er. Many experiments with radioactive light particle beams (RNB) such as (6)He, (7)Be, (8)Li, (8)B have been performed at these two facilities. These low-energy RNB have been used to investigate low-energy reactions such as elastic scattering, transfer and breakup, providing useful information on the structure of light nuclei near the drip line and on astrophysics. Total reaction cross-sections, derived from elastic scattering analysis, have also been investigated for light system as a function of energy and the role of breakup of weakly bound or exotic nuclei is discussed.

Ion beam assisted deposition of an organic light emitting diode electrode

This work presents the electro-optical characterization of metal-organic interfaces prepared by the Ion Beam Assisted Deposition (IBAD) method. IBAD applied in this work combines simultaneously metallic film deposition and bombardment with an independently controlled ion beam, allowing different penetration of the ions and the evaporated metallic elements into the polymer. The result is a hybrid, non-abrupt interface, where polymer, metal and ion coexists. We used an organic light emitting diode, which has a typical vertical-architecture, for the interface characterization: Glass/Indium Tin Oxide (ITO)/Poly[ethylene-dioxythiophene/poly{styrenesulfonicacid}]) (PEDOT:PSS) /Emitting Polymer/Metal. The emitting polymer layer comprised of the Poly[(9,9-dioctyl-2,7-divinylenefluorenylene)-alt-co-{2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene}] (PFO) and the metal layer of aluminum prepared with different Ar(+) ion energies varying in the range from 0 to 1000 eV. Photoluminescence, Current-Voltage and Electroluminescence measurements were used to study the emission and electron injection properties. Changes of these properties were related with the damage caused by the energetic ions and the metal penetration into the polymer. Computer simulations of hybrid interface damage and metal penetration were confronted with experimental data. (C) 2010 Elsevier B.V. All rights reserved.

Infrared analysis of ion beam irradiated polymers

Irradiation with heavy ions can produce several modifications in the chain structure of polymers. These modifications can be related to scissioning and cross-linking of chemical bonds. which depend on the ion fluence and the density of energy deposited in the material. Stacked thin film Makrofol-KG (R) samples were irradiated with 350 MeV Au(26+) ions and FTIR absorption spectroscopy was used to determine the bond changes in the samples. Data on the absorption bands as a function of the fluence indicated a higher probability for simple-bonds scissioning than for double-bonds scissioning and no dependence on the number of double bonds breaking with ion fluence. Since sample irradiation was done in a non-track-overlapping regime, a novel process for double bonds formation is suggested: the excitation of a site in the material by only one incident ion followed by a double bond formation during the de-excitation process. (C) 2009 Elsevier B.V. All rights reserved.

Fermion perturbations in string theory black holes

In this paper we study fermion perturbations in four-dimensional black holes of string theory, obtained either from a non-extreme configuration of three intersecting five-branes with a boost along the common string or from a non-extreme intersecting system of two two-branes and two five-branes. The Dirac equation for the massless neutrino field, after conformal re-scaling of the metric, is written as a wave equation suitable to study the time evolution of the perturbation. We perform a numerical integration of the evolution equation, and with the aid of Prony fitting of the time-domain profile, we calculate the complex frequencies that dominate the quasinormal ringing stage, and also determine these quantities by the semi-analytical sixth-order WKB method. We also find numerically the decay factor of fermion fields at very late times, and show that the falloff is identical to those showing for massless fields in other four-dimensional black hole spacetimes.

Quasinormal modes of semiclassical electrically charged black holes

We report the results concerning the influence of vacuum polarization due to quantum massive vector, scalar and spinor fields on the scalar sector of quasinormal modes in spherically symmetric charged black holes. The vacuum polarization from quantized fields produces a shift in the values of the quasinormal frequencies, and correspondingly the semiclassical system becomes a better oscillator with respect to the classical Reissner-Nordstrom black hole.

Phantom accretion by black holes and the generalized second law of thermodynamics

The accretion of a phantom fluid with non-zero chemical potential by black holes is discussed with basis on the generalized second law of thermodynamics. For phantom fluids with positive temperature and negative chemical potential we demonstrate that the accretion process is possible, and that the condition guaranteeing the positiveness of the phantom fluid entropy coincides with the one required by the generalized second law. (C) 2010 Elsevier B.V. All rights reserved.

Quasinormal modes of black holes immersed in a strong magnetic field

We found quasinormal modes, both in time and frequency domains, of the Ernst black holes, that is neutral black holes immersed in an external magnetic field. The Ernst solution reduces to the Schwarzschild solution, when the magnetic field vanishes. It is found that the quasinormal spectrum for massless scalar field in the vicinity of the magnetized black holes acquires an effective ""mass"" mu = 2B vertical bar m vertical bar, where m is the azimuthal number and B is parameter describing the magnetic field. We shall show that in the presence of a magnetic field quasinormal modes are longer lived and have larger oscillation frequencies. The perturbations of higher-dimensional magnetized black holes by Ortaggio and of magnetized dilaton black holes by Radu are considered. (C) 2007 Elsevier B.V. All rights reserved.

Polarizing beam splitter for dipolar molecules

We propose a coherent beam splitter for polarized heteronuclear molecules based on a stimulated Raman adiabatic passage scheme that uses a tripod linkage of electrotranslational molecular states. We show that for strongly polarized molecules the rotational dynamics imposes significantly larger Rabi frequencies than would otherwise be expected, but within this limitation, a full transfer of the molecules to two counterpropagating ground-state wave packets is possible.

August 1999: Financial Black Holes and Other Challenges

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Nanoindentation mechanical properties characterization of glassy polymeric carbon treated with ion beam

Phenolic resins when heat treated in inert atmosphere up to 1000 degreesC become glassy polymeric carbon (GPC), a chemically inert and biocompatible material useful for medical applications, such as in the manufacture of heart valves and prosthetic devices. In earlier work we have shown that ion bombardment can modify the surface of GPC, increasing its roughness. The enhanced roughness, which depends on the species, energy and fluence of the ion beam, can improve the biocompatibility of GPC prosthetic artifacts. In this work, ion bombardment was used to make a layer of implanted ions under the surface to avoid the propagation of microcracks in regions where cardiac valves should have pins for fixation of the leaflets. GPC samples prepared at 700 and 1500 degreesC were bombarded with ions of silicon. carbon, oxygen and gold at energies of 5, 6, 8 and 10 MeV, respectively, and fluences between 1.0 x 10(13) and 1.0 x 10(16) ions/cm(2). Nanoindentation hardness characterization was used to compare bombarded with non-bombarded samples prepared at temperatures up to 2500 degreesC. The results with samples not bombarded showed that the hardness of GPC increases strongly with the heat treatment temperature. Comparison with ion bombarded samples shows that the hardness changes according to the ion used, the energy and fluence. (C) 2002 Elsevier B.V. B.V. All rights reserved.

Nanohardness of a Ti thin film and its interface deposited by an electron beam on a 304 SS substrate

The results of nanohardness measurements at a film surface and film-substrate interface are presented and discussed. An electron beam device was used to deposit a Ti film on a 304 stainless steel (304 SS) substrate. The diluted interface was obtained by thermal activated atomic diffusion. The. Ti film and Ti film-304 SS interface were analyzed by energy dispersive spectrometry and were observed using atomic force microscopy. The nanohardness of the Ti film-304 SS system was measured by a nanoindentation technique. The results showed the Ti film-304 SS interface had a higher hardness value than the Ti film and 304 SS substrate. The Ti film surface had a lower hardness due to the presence of a TiO2 thin layer.

A Beam Search Method to Solve the Problem of Assignment Cells to Switches in a Cellular Mobile Network

Assigning cells to switches in a cellular mobile network is known as an NP-hard optimization problem. This means that the alternative for the solution of this type of problem is the use of heuristic methods, because they allow the discovery of a good solution in a very satisfactory computational time. This paper proposes a Beam Search method to solve the problem of assignment cell in cellular mobile networks. Some modifications in this algorithm are also presented, which allows its parallel application. Computational results obtained from several tests confirm the effectiveness of this approach and provide good solutions for large scale problems.

Beam Search Algorithms for Minimizing Tool Switches on a Flexible Manufacturing System

In the minimization of tool switches problem we seek a sequence to process a set of jobs so that the number of tool switches required is minimized. In this work different variations of a heuristic based on partial ordered job sequences are implemented and evaluated. All variations adopt a depth first strategy of the enumeration tree. The computational test results indicate that good results can be obtained by a variation which keeps the best three branches at each node of the enumeration tree, and randomly choose, among all active nodes, the next node to branch when backtracking.

Mechanics of the maxillary central incisor. Influence of the periodontal ligament represented by beam elements

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)