bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Origin Of Light Emission From Porous Silicon
Authors: Ben-Chorin M. , Heckler H. , Kovalev D. , Averboukh B. , Polisski G. , Schwartzkopff M. , Koch F. 
Published: April 2011

AbstractWe report on luminescence hole burning experiments, which prove that radiative recombination between quantum confined states is the only viable model for the mechanism of the light emission from porous silicon. We find that more than 90% of the luminescence originates from quantum confined states inside the Si nanocrystals.
Dispersive Fourier Transform Spectroscopy Of Free-Standing Porous Silicon Films
Authors: Salonen J. , Saarinen K. , Peura J. , Vilnikanoja J. , Salomaa I. , Laine E. , Kauppinen J 
Published: April 2011

AbstractWe have investigated optical constants of free-standing porous silicon films by dispersive Fourier transform spectroscopy (DFTS) in the NIR-VIS range. This allows the spectral variation of both the absorption coefficient and the refractive index of a material to be determined from the measurements of the attenuation and phase shift imposed on an electromagnetic wave by its interaction with a specimen. Using these optical constants, we have studied the complex dielectric function and the complex conductivity. To avoid the additive error in the absorption spectra arising from the pseudocoherence, we measured the transmission spectra by conventional Fourier transform spectroscopy (FTS). Using the refraction spectrum derived from the DFTS measurements, we have corrected for reflection losses in calculation of the absorption spectrum from the FTS transmission spectrum. The changes in the absorption coefficient and the refractive index due to oxidation, which is the most common aging phenomenon in porous silicon, have been studied using samples with different types of oxidization.
Guided Wave Fluorescence In Thin Film Er- Doped Barium Titanate
Authors: Gill D. M. , Ford G. M. , Block B. A. , Wessels B. W. , Ho S. T. 
Published: April 2011

AbstractGuided-wave absorption and fluorescence in epitaxial Er:BaTiO3 thin film channel waveguides on MgO are reported. Guided- wave absorption is strongly dependent on post- growth annealing. Stimulated emission over a 40 nm bandwidth (λcente - 1.54 μm) has been achieved in oxygen-annealed waveguides. At 1.54 μm the absorption is reduced from ∼ -2 dB/cm to -∼-1.3 dB/cm in a 2.2 mm long 5 μm wide channel waveguide due the presence of the pump light.
Photoluminescence Stability Of Silicon Suboxide Thin Films
Authors: Wang F. , Hinds B. J. , Wolfe D. W. , Lucovsky G. 
Published: April 2011

AbstractPhotoluminescence (PL) stability of silicon suboxide (SiOx, 0<x<l.5) under light soaking and thermal processing has been investigated. As the oxygen content increases, the PL peak position shifts to the visible, with improved stability against measurement temperature and light soaking. With increasing annealing temperature, the PL spectra shifted to infrared, characteristic of a- Si:H. With annealing above 550 °C, visible PL is lost while infrared PL can be recovered by rehydrogenation of Si-dangling bond defects. Infrared absorption, transmission electron microscopy, visible absorption, and photocurrent indicate a disproportionation reaction resulting in a-Si phase segregation.
Materials For Monolithic Silicon Microphotonics
Authors: Giovane L. M. , Lim D. R. , Ahn S. H. , Chen T. D. , Foresi J. S. , Liao L. , Oulette E. J. , Agarwal A. M. , Duan X. , Michel J. , Thilderkvist A. , Kimerling L. C. 
Published: April 2011

AbstractThe path for silicon materials development has been charted. By the year 2010 we will have fabricated integrated circuit chips containing 109 transistors with 40 Å thick gate oxides and 1000 Å minimum feature sizes running at 4 GHz clock speeds. It is conceivable that incremental advances on the current chip architecture will satisfy the required materials and process improvements. The interconnection problem is the only challenge without a proposed solution. The signal propagation delay between devices is now longer than the individual device gate delay. The resistance and capacitance associated with fine line Al interconnects limit speed and increase power consumption and crosstalk. High power line drivers are limited by the reliability constraint of electromigration. There is no current paradigm for 4 GHz, electronic clock distribution. Optical interconnection can remove the electronic transmission bandwidth limit. The main challenge is development of a silicon-compatible, microphotonic technology.Rare earth doping has provided a means of sharp-line electroluminescence from silicon at λ = 1.54 μm. Silicon's high index of refraction and low absorption in the near infrared yield an ideal optical waveguide. As with microelectronics, the silicon / silicon-dioxide materials system allows high levels of integration and functionality. The applications of silicon materials to light emission (Si:Er), optical waveguides (Si/SiO2), photonic switching (Si/SiO2) and photon detection (SiGe) are reviewed. These developments are discussed in the context of systems applications to communications and computation.
Visible Photonic Band Gap Waveguide Devices
Authors: Charlton M. D. B. , Parker G. J. 
Published: April 2011

AbstractPhotonic band gap (PBG) structures are multidimensional lattices, formed by a strong modulation of dielectric constant which prevent the propagation of photons over a forbidden energy range1. Since the first demonstration of a PBG at microwave frequencies2-7, it has proved technologically difficult to create a PBG in the optical region of the spectrum8-11 since the band gap centre wavelength is of the order of twice the lattice pitch. Recently, we have succeeded in fabricating novel waveguide designs which incorporate a TE polarised visible photonic band gap12,13 By reducing the band gap to visible wavelengths, we greatly simplify the experimental investigation of the behaviour of these complicated structures.In this paper, we present the fabrication and initial optical testing of devices with band gaps in the visible wavelength range 545nm-632.8nm. These devices demonstrate unusual optical effects dependent upon the number of lattice periods such as: broadband wavelength filtering, wavelength dependent beam splitting, and broadband polarisation selective routing. In contrast to the well known active applications of PBGs, we suggest a host of new passive applications for PBGs in optical computing and wavelength division multiplexed (WDM) communications.
Mineralization of Multilayer Hydrogels as a Model for Mineralization of Bone
Authors: Calvert Paul , Frechette Joelle , Souvignier Chad 
Published: April 2011

AbstractExtrusion freeform fabrication is a 3-D layerwise writing technique for forming objects directly under the control of a CAD program. This method is one of a family of rapid prototyping methods which include stereolithography, selective laser sintering and fused deposition modeling. This system can be used to build shapes, layer by layer, from hydrogels of agarose, polyacrylamide or other cross-linked water-soluble acrylic polymers.Mineralization can be induced in these gels by building a part with alternating layers of gels containing calcium and carbonate or phosphate that can be formed into stacks which then mineralize by cross-diffusion. The write head can be conceived of as a cell which delivers the appropriate minerals to a site within a swollen gel matrix. This diffusive mineralization process can thus be compared with bone mineralization. The gel structure controls the morphology of the mineral. The site of mineralization is controlled by osmotic forces which localize most of the mineral in whichever zone has the higher ionic strength. The mineral content, expressed as a fraction of the polymer content, is similar to that of bone but the water content is much higher than in bone. This raises the question of what process drives the water exclusion during bone mineralization.
Microscale Radiative Effects in Complex Microstructures of Iridescent Butterfly Wing Scales
Authors: Tada Haruna , Mann Seth E. , Miaoulis Ioannis N. , Wong Peter Y. 
Published: April 2011

AbstractThe cellular microstructure of insect scales can be detailed intricately with threedimensional structures and multiple thin-film layers. In butterflies, iridescent scales can reflect bright colors through thin-film interference and other optical phenomena; the balance of radiation is absorbed for thermoregulatory purposes. Results of numerical and experimental investigations into the function, properties, and structure of these scales are presented. Of particular interest are the numerical modeling of the microscale radiative effects in the scales, determining the optical properties of the biological material, and the cellular development of thin-film structures.
Sequence Specific Force Curves Measured by Mechanically Opening the DNA Double Helix
Authors: Bockelmann U. , Essevaz-Roulet B. , Heslot F. 
Published: April 2011

AbstractUsing techniques of molecular biology, we have designed a molecular construction which allows to attach the two complementary strands of one end of a single molecule of bacteriophage λ DNA separately to a glass microscope slide and a microscopic bead. A soft microneedle acting as a force sensor is chemically attached to the bead and its deflection is measured by an optical microscope. Keeping the base of the force lever fixed, the glass slide is displaced slowly, leading to a progressive opening of the double helix. The force measured during the opening process shows a characteristic variation which is related to the sequence of the bases along the DNA molecule. We present a brief summary of the present state of our work.
First Principles Simulations of Glucose in Aqueous Solution
Authors: Molteni C. , Parrinello M. 
Published: April 2011

AbstractWe present an application of first principles molecular dynamics simulations, based on the Car-Parrinello method, to the study of the properties of glucose in aqueous solution. By treating both solute and solvent quantum-mechanically, we provide a reliable description of the hydrogen bonds, which determine the water structure around the glucose. These results show the power of our technique in describing biologically relevant problems, where an accurate microscopic description is essential.
Microscopic Elasticity of DNA from Torsionally-Constrained Stretching
Authors: Moroz J. D. , Nelson P. 
Published: April 2011

AbstractWe investigate the statistical mechanics of a torsionally constrained polymer. The polymer is modelled as an inextensible chain with bend rigidity A, twist rigidity C, and twist-stretch coupling D. In such a model, thermal bend fluctuations couple geometrically to an applied torque through the relation Lk = Tw + Wr. We explore this coupling and find excellent agreement between the predictions of our model and the single λ-DNA molecule stretching experiments of Strick et al. [Science 271 (1996) 1835]. This analysis affords an experimental determination of the microscopic twist rigidity C. Quantitative agreement between theory and experiment is obtained using C = 120 nm and D = 50 nm. The theory further predicts a thermal reduction of the effective twist rigidity induced by bend fluctuations.
Charge Transfer Modeling for Charge-Coupled Devices
Authors: Lavine James P. , Stevens Eric G. , Banghart Edmund K. , Trabka Eugene A. , Burkey Bruce C. , Schneider David J. 
Published: April 2011

ABSTRACTThe three-dimensional Poisson's equation is solved by iterative methods and the resulting electric field is used in Newton's equation to simulate electron transfer in a charge-coupled device (CCD). The time dependence of charge transfer is studied through a random walk simulation of Newton's equation. Potential obstacles of the order of 0.03 V are seen to slow charge transfer. Electron motion is also followed in two spatial dimensions through Newton's equation in order to probe a more varied set of potential obstacles.
Light-Controlled Switching Transients in Mis Silicon Structures with Multichannel Insulator: Physical Processes and New Device Modelling
Authors: Malik A. , Martins R. 
Published: April 2011

ABSTRACTWe present the modelling of a new two-terminal and low-voltage operating optoelectronic device based on MIS silicon structure with multichannel insulator and having as gate a transparent metallic tin-doped indium oxide (ITO) layer deposited by spray pyrolysis technique over the insulator layer. ITO layer has a multiple non-rectifier electrical contact with silicon substrate, in the SiO2 channel's region. Construction details of the process, together with its operating characteristics are given. The devices developed do not require external active electronic components (transistors, microschemes) to execute their functions and to transform analogue input optical signals to digital output form, highly important for a wide range of optoelectronic applications.
The Application of GaAs TCAD in Industry
Authors: Blakey P. A. , Deepak  , Johnson K. , Recker C. , Varadarajan S. 
Published: April 2011

ABSTRACTThe implementation and application of GaAs technology CAD for industrial research and development are described. Existing silicon-oriented software was modified extensively to make it applicable to the simulation of GaAs processes and devices. RF-oriented post-processing capabilities were implemented, and effective applications methodologies were developed. Examples of the practical application of GaAs technology CAD are presented.
Arsenic Deactivation in Silicon
Authors: Berding M. A. , Sher A. 
Published: April 2011

ABSTRACTIn this paper we examine the properties of arsenic in silicon, using ab initio calculations and a statistical theory. Good agreement is found between theory and experiment for the electronic concentration as a function of temperature and total arsenic concentration. We show that for low arsenic concentrations, full activation is the equilibrium condition. In equilibrium, the neutral complex composed of a lattice vacancy surrounded by four arsenic (VAs4) is the dominant means by which high concentrations of arsenic are rendered inactive. Under constrained equilibrium conditions in which VAs4 cluster formation is prohibited, we show that VAs3Si1 cluster populations increase dramatically and can account for nearly the same degree of compensation as the VAs4 clusters. Even VAs2 clusters alone can account for substantial deactivation in the absence of VAs3 and VAs4 clusters. These smaller complexes are essential not only to the establishment of equilibrium, since SiAs4 clusters are extremely rare, but can also explain some degree of deactivation, even if the formation of VAs4 clusters are kinetically inhibited.
Ab Initio Calculation of Tight-Binding Parameters
Authors: Mcmahan A. K. , Klepeis J. E. 
Published: April 2011

ABSTRACTWe calculate ab initio values of tight-binding parameters for the /-electron metal Ce and various phases of Si, from local-density functional one-electron Hamiltonian and overlap matrix elements. Our approach allows us to unambiguously test the validity of the common minimal basis and two-center approximations as well as to determine the degree of transferability of both nonorthogonal and orthogonal hopping parameters in the cases considered.
Efficient Electronic Energy Functionals for Tight-Binding
Authors: Haydock Roger 
Published: April 2011

ABSTRACTGeneralized functionals are constructed from the exchange-correlation energy by a Legendre transformation which makes the new functionals stationary at the electronic charge density, potential, and wave functions for the ground-state. Using generalized functionals, the density, potential, and wave functions can be independently parameterized and varied to determine the ground-state energy-surface for a system of atoms. This eliminates the computationally awkward steps of constructing densities from wave functions or potentials from densities, and is particularly well suited to parameterizations using tight-binding orbitale together with atomic-like densities and potentials. For each choice of parameters, the only quantities which must be computed are the electron-electron energy for the density, the integral of the potential over the density, and the band structure energy for the wave functions. To second order in the density, potential, and wave functions, the energy for a configuration of atoms is given by the generalized functional evaluated at a superposition of atomic densities, a potential made by stitching together the atomic potentials where they are equal, and atomic wave functions. For more accurate stationary energies the densities, potentials, and wave functions can be improved by one or more conjugate gradient steps.
Electronic Structure, Pressure Dependence and Optical Properties of FeS2
Authors: Nguyen-Manh D. , Pettifor D. G. , Sithole H. M. , Ngoepe P. E. , Arcangeli C. , Tank R. , Jepsen O. 
Published: April 2011

ABSTRACTA revisited electronic structure study of iron pyrite, FeS2, has been performed using a new Tight-Binding Linear Muffin-Tin Orbital (TB-LMTO) technique in which the radii of overlapping MT spheres are determined from a full potential construction. The interstitial spheres were chosen to provide an efficient packing of space while ensuring that the overlap between the spheres remain small. We have found that this treatment of interstitial spheres results in a dramatic improvement in the description of the electronic structure and the binding energy curves for FeS2 in comparison with a previous LMTO calculation. In particular, the energy band gap, the equilibrium lattice constant and the bulk modulus are all in much better agreement with experimental observations. Moreover, the calculated equation of state is in excellent accord with recent measured P- V data up to pressures of 15GPa with overall deviations of less than 10%. The predicted reflectivity spectrum of FeS2 as a function of pressure gives the observed behaviour of the optical edge. The bonding behaviour the orthorhombic marcasite phase of FeS2 is also discussed within this new TB-LMTO formalism.
Large Scale Quantum Simulations Using Tight-Binding Hamiltonians and Linear Scaling Methods
Authors: Galli Giulia , Kim Jeongnim , Canning Andrew , Raerle Rainer 
Published: April 2011

ABSTRACTWe describe linear scaling methods for electronic structure calculations and quantum molecular dynamics simulations, which are based on an orbital formulation of the electronic problem. In particular, we discuss some open problems which need to be addressed to improve the performances of these methods, and briefly review some applications to carbon and silicon systems, within a Tight-Binding framework.
Tight Binding Simulations of Disordered Systems
Authors: Rosato V. , Celino M. 
Published: April 2011

ABSTRACTCarbon allotropy allows the formation of a large variety of disordered structures whose properties depend on the density and on the preparation technique. Computer simulations, based on quantum mechanics, can reproduce the essential features of these systems. We first assess the reliability of the amorphous carbon structures generated by molecular dynamics simulations based on a semi-empirical Tight Binding hamiltonian. Then we attempt to understand of the path followed by diamond to reach the amorphous phase via a direct crystalline-to-amorphous transformation. Results concern the large variety of structures which can be obtained and a general adequacy of the semi-empirical Tight Binding hamiltonian to reproduce the essential features of amorphous carbon structure. Moreover, it is shown that the process of direct transformation from the crystalline into the amorphous phase occurs continuously. The formation of three-fold coordinated sites is not followed by an immediate site re-hybridization. When this process takes place, a large strain sites associated with the mis-coordinated sites is released.
A LCAO-OO Approach to the Calculation of Electronic Properties of Materials
Authors: Pou P. , Perez R. , Ortega J. , Flores F. 
Published: April 2011

ABSTRACTWe present a selfconsistent LCAO approach for describing the electronic properties of materials. This method introduces many-body effects by means of a new approach, whereby a local orbital potential is defined by calculating the exchange-correlation energy as a function of the different orbital occupancies. A LCAO-pseudopotential is also introduced, keeping all the calculations within the context of the local orbital basis. We have applied the method to the calculation of simple molecules and crystals, in both cases we find results that confirm the validity of our approach.
Covalent Liquids: Tight Binding Simulation Versus Experimental Results
Authors: Gaspard J.-P. , Bichara C. , Raty J. Y. 
Published: April 2011

ABSTRACTWe show that a simple tight binding model with a repulsive potential describes the Peierls distortions in covalent systems and the well-known octet rule. The existence and the intensity of the Peierls distortion is mainly related to the hardness of the repulsive potential as demonstrated both by theoretical calculations and by the experimental systematic analysis of liquid structures. In particular, As is threefold coordinated and Sb is sixfold coordinated in the liquid, the qualitative difference is explained by the ratio of the distortion energy ΔE to the thermal energy kBT. The Asx Sb1-x alloys show continuously varying average coordination numbers showing: the semiconductor-metal transition is continuous with concentration.In addition, we illustrate in the case of liquid Se that, tight binding Monte Carlo simulations are able to describe quantitatively the structure of liquid elements provided the Van der Waals potential is added.
Structural and Electronic Properties of a-Gaas: A Tight-Binding–Molecular-Dynamics–Art Simulation
Authors: Lewis Laurent J. , Mousseau Normand 
Published: April 2011

ABSTRACTBy combining tight-binding (TB) molecular dynamics (MD) with the recently-proposed activation-relaxation technique (ART), we have constructed structural models of a-GaAs and a-Si of an unprecedented level of quality: the models are almost perfectly four-fold coordinated and, in the case of a-GaAs, exhibit a remarkably low density of homopolar bonds. In particular, the models are superior to structures obtained using melt-and-quench TB-MD or quantum MD. We find that a-Si is best described by a Polk-type model, while a-GaAs resembles closely the mechanical model proposed by Connell and Temkin, which is free of wrong bonds. In this paper, the structural, electronic, and dynamical properties of a-GaAs based on this approach will be reviewed, and compared to experiment and other structural models. Our study provides much-needed information on the intermediate-range topology of amorphous tetrahedral semiconductors; in particular, we will see that the differences between the Polk and Connell-Temkin models, while real, are difficult to extract from experiment, thus emphasising the need for realistic computer models.
Carbon Schwarzites: Properties and Growth Simulation from Fullerene Fragments
Authors: Benedek G. , Colombo L. , Spadoni S. , Gaito S. , Milani P. 
Published: April 2011

AbstractWe investigated by tight-binding molecular dynamics the structure, the bulk modulus and the electronic properties of the smallest four-branched carbon schwarzites fcc-(C28)2, fcc-(C36)2 and fcc-(C40)2 having the shape of a D minimal periodic surface. They are found to have a stability comparable to that of fullerene C60 and to exhibit alternative metallic and insulating characters, with an apparent relationship to their local geometry. We also studied the coalescence of fullerenic fragments and carbon clusters by following the evolution of the topological connectivity. Though different temperature variation protocols lead to irregular structures similar to random schwarzites, their connectivity is found to stabilize at values corresponding either to tubulene or three-branched schwarzites, indicating that long time evolution at constant connectivity is potentially able to yield regular shapes. Experiments on laser-induced transformations of fullerite occasionally yield branched tubular structures with a schwarzite shape.