214 research outputs found
Fully integrated three-axis Hall magnetic sensor based on micromachined structures
No full textIn this work we propose a new technological approach to fabricate a fully integrated three-axis Hall magnetic sensor. The three axial device fabrication process exploits microfabrication technologies applied to a GaAs-based heterostructure to obtain at the same time three mutually orthogonal sensors: an in-plane Hall sensor and two out-of-plane Hall sensors. A two dimensional electron gas (2DEG) AlGaAs/InGaAs/GaAs multilayered structure constitutes the sensing medium of the micromachined devices, whereas an underlying strained InGaAs/GaAs bilayer allows the self-positioning of the out-of-plane devices by virtue of sacrificial layer removal and strain release. The in-plane and out-of-plane Hall sensors, show an excellent linearity versus the magnetic field with an absolute sensitivity as high as 0.03 V/T at 0.6 V bias voltage
Protein-ligand docking using a multi-objective genetic algorithm.
No full textLigand docking is the computational prediction of the bound conformation of a small molecule in a complex starting from its atomic coordinates. A docking procedure is composed of two contributions: a scoring function determining the relative score of different configurations of the ligand and a search procedure exploring the space of the possible ligand orientations and conformations. Scoring functions are often based on calculation of binding energies between ligand and receptor; the search procedures have to find the ligand pose that this corresponds to the absolute minimum of the binding energy landscape. Binding energies are sums of different contributions. Search procedures generally look for the minimum of the global scoring function neglecting the possibility to optimize the search towards each single member or a group of them (for example bonded and non-bonded energies). This work describes the application of a Multi-Objective Genetic Algorithm (MOGA) as a search procedure for a protein-ligand docking problem. The MOGA implementation in modeFRONTIERTM is used to optimize the docking towards each of the different contributions of the docking program Autodock v. 3.05 (http://autodock.scripps.edu) scoring function. MOGA results give a set ofsolutions, each one representing a compromise between the different objectives (the so called Pareto frontier). This could be useful, for example, to get a docked complex that exalts one of the contributions to the total binding energy. The results consist of a set of docked ligand conformations within the 2-objectives Pareto frontier (minimization of bonded energy and minimization of non-bonded energy) having a root mean squared deviation from the crystal structure smaller than 1.5 Å. From the inspection of the Pareto frontier results that the non-bonded interactions effectively have a greater influence than bonded interactions in guiding the search
Long wavelength emission in In[sub x]Ga[sub 1 - x]As quantum dot structures grown in a GaAs barrier by metalorganic chemical vapor deposition
No full textA method was proposed to obtain room temperature ground state emission from InGaAs quantum dots (QD) growth directly into a binary GaAs matrix. The wavelength was tuned from 1.26 up to 1.33 μ by varying the V/III ratio during growth of the GaAs cap layer, without using a seeding layer of InGaAs wells. The morphology and density of the dots were studied by atomic force microscopy. Significant redshifting of the emission wavelength and narrowing of the full width half maximum (FWHM) are obtained by reducing the V/III ratio for growth of the GaAs cap layer
FEM design and modeling of χ(2) second-harmonic enhancement in circular photonic crystal
No full textIn this paper, we analyze the enhancement of X^(2) nonlinear process in membrane-type circular photonic crystal (PhC) based on GaAs. This unconventional kind of PhC is well suited for the generation of whispering gallery modes (WGMs) due to the circular symmetric periodic pattern. By using a laser Gaussian beam at 1.55 m as pump signal, a WGM at 1.55 um and a second-harmonic (SH) mode at 0.775 um are obtained. The SH will be generated in the center of the missing-hole microcavity. The periodic pattern and the microcavity are tailored and optimized providing an SH efficiency conversion as high as 50%. We predict the resonances by an accurate 2-D time-domain model including X^(2) nonlinearity and by a 3-D finite-element method. Finally, by using a 3-D membrane configuration, we found a total quality factor of the SH mode of the order of 35 000
Second Harmonic Generation from multilayer structures.
No full textWe present experimental results on second harmonic generation from multilayer structures, including metallo/dielectric and III-V nitrides, and discuss the collinear and noncollinear configuration. Measurements obtained as a function of incidence angle and polarization state of both fundamental and generated beams are reported
Structural and piezoelectric properties of DC-sputtered AlN films deposited on different Si-based substrates
No full textWe study the DC magnetron sputtering deposition of AlN on different substrates: (100) resistive Si, Si3N4 on Si and SiO2 on Si. The growth conditions of such films have been analysed to obtain the best structural and piezoelectric properties on each substrate. We show that, while AlN follows a columnar growth from the early stage of deposition on Si, the non—crystalline nature of Si3N4 and SiO2 induces an amorphous early growth stage on such substrates. Despite this structural difference, high performances have been obtained by AlN delay lines realised on both Si3N4/Si and pure resistive Si, providing further flexibility in the development of Si-based technological applications
Optical properties of InGaAs QDs grown in a GaAs matrix by MOCVD, emitting at 1300 nm at room temperature
No full textPhotomodulated reflectance studies of quantum dot in MCLED structures: monitoring cavity-ground state exciton resonance
No full textSelf-assembled quantum dots emitting around 1.3 μm and embedded in a microcavity structure are analysed by photo-reflectance (PR) measurements performed at different temperatures. The temperature dependence of the PR spectra line-shape and amplitude allows us to determine the tuning condition of the quantum dot ground state transition with the cavity mode. We found that in our structure the perfect tuning is obtained around 250 K
Scalar time domain modeling and coupling of second harmonic generation process in GaAs discontinuous optical waveguide
No full textWe present in this work the scalar potential formulation of second harmonic generation process in χ(2) nonlinear analysis. This approach is intrinsically well suited to the applications of the concept of circuit analysis and synthesis to nonlinear optical problems, and represents a novel alternative method in the analysis of nonlinear optical waveguide, by providing a good convergent numerical solution. The time domain modeling is applied to nonlinear GaAs asymmetrical waveguide with dielectric discontinuities in the hypothesis of quasi phase matching condition in order to evaluate the efficiency conversion of the second harmonic signal. The accuracy of the modeling is validated by the good agreement with the published experimental results. The effective dielectric constant method allows to extend the analysis also to 3D optical waveguides
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