bluuebunny/crossref_metadata_2025_split huggingface dataset:
Influence of Crystallographic Orientation, Chemical Inhomogeneities, Material Transport Anisotropy and Elastic Strain Energy on the Migration of Grain Boundaries in Chromium-Doped Alumina During Internal Reduction
Authors: Backhaus-Ricoult Monika , Peyrot-Chabrol A. , Chiron R. , Hagege S. 
Published: April 2011

AbstractDiffusion-induced grain boundary migration is observed during internal reduction of chromium-doped alumina. It occurs because grain boundary diffusion is fast compared to lattice diffusion of oxygen. The oxygen chemical potential relaxes between grain boundaries and adjacent grains. Migration to either side of the boundary is controlled by multiple factors: chemical composition differences between adjacent grains, elastic strain energy differences on the two sides of the boundary plane or by more rapid oxygen relaxation when the c-axis of a grain is perpendicular to the boundary plane.
Formation and Orientation of Low Energy MgO/Pd, Al2O3/Pd and TiO2/Pd Interfaces
Authors: Cosandey Frederic , Lu Ping 
Published: April 2011

SummaryThe results of this study indicate that oriented α-Al2O3 and TiO2 particles with planar facets suitable for HREM studies can be produced in Pd by internal oxidation. A single high symmetry cube-on-cube orientation relationship has been observed for cubic MgO oxide particles in Pd. Six orientation relationships have been observed for trigonal α-Al2O3 oxide particles in Pd. Parallelism of the low misfit [1100]M// [110]O common direction appears to be the dominant factor for the preferred orientations with facets corresponding to parallelism of low index planes of Pd and α-Al2O3. For the tetragonal TiO2 phase in Pd, eight orientation relationships have been observed with orientations controlled primarily by oxide nucleation on {111} plane of Pd. For this system, the particle shape is controlled by anisotropy in growth kinetics.
Mechanisms of Enhanced Ionic Conduction at Interfaces in Ceramics
Authors: Lubben D. , Modine F. A. 
Published: April 2011

AbstractA large enhancement in the ionic conductivity of certain compounds occurs when the compound is produced as a composite material containing a finely-dispersed non-conductor such as SiO2 or Al2O3 This effect has been reported on for more than 20 years, and it is well established that the enhancement is associated with the presence of interfaces. The popular explanation has been based on a model which contends that the enhancement is due to a space-charge layer which forms to compensate a net charge layer at an interface. A different model proposes that extended defects such as dislocations and grain boundaries, either resulting from or stabilized by the interface, are responsible for the enhancement. This paper describes recent experiments which strongly support the latter model. The ionic conductivities of LiI and CaF2 thin films grown on sapphire(0001) substrates were monitored in-situ during deposition as a function of film thickness and deposition conditions. LiI films grown at 27°C exhibited a region of enhanced conduction within 100 nm of the substrate and a lesser enhancement as the film thickness was increased further. This conduction enhancement was not stable but annealed out with a characteristic log(time) dependence. The observed annealing behavior was fit with a model based on dislocation motion which implies that the increase in conduction near the interface is due to extended defects generated during the growth process. LiI films grown at higher temperatures (100°C) in order to reduce the grown-in defects showed no interfacial conduction enhancement. X-ray diffraction measurements suggest that these high-temperature LiI films nucleate as faceted epitaxial islands with a stable misfit dislocation density defined by the epitaxial relationship between the substrate and film. CaF2 films grown at 200°C showed a behavior similar to the 27°C LiI films, with a region of thermally unstable enhanced conduction that occurs within 10 nm of the substrate. Amorphous Al2O3 films deposited over the CaF2 layers created no additional enhancement but did increase the stability of the conduction, consistent with an extended defect model. Simultaneous deposition of CaF2 and Al2O3 produced films consisting of very-fine-grained CaF2 and particles of amorphous Al2O23 (5-10 nm grain and particle size) and a high defect density which was stable even well above the growth temperature. Measured conduction in the composite at 200°C was approximately 360 times that of bulk CaF2.
Criteria for Misfit Localization at Interfaces
Authors: Lojkowski Witold 
Published: April 2011

AbstractIt is well known that in many cases, the structure of interfaces is well described in terms of “good matching” islands, separated by misfit dislocations. The “0” lattice theory can predict the dislocations' spacing but not their core width. In the present paper, a new physical parameter: p, called further “localization parameter”, is introduced. It permits the assessment of the width of misfit dislocations. p is expressed as p=EAB/E where EAB is the bonding energy of the two crystals and E is their average cohesion energy. The localization parameter was calculated for about 30 interfaces: metal/metal, metal/ceramics, ceramics/ceramics. For p<0.25, misfit dislocations are delocalized.
The Effect of The Space Charge On The Properties of An Inhomogeneous Pyroelectric Ceramic
Authors: Pintilie L. 
Published: April 2011

AbstractThe properties of a series ceramic bimorph structure were studied in this paper. The two components of the bimorph were PLZT ceramics with different transition temperatures. The properties of the series bimorph were strongly influenced by the space charge that appears due to the inhomogenities in resistance and dielectric constant.. Some theoretical considerations were made regarding the electric fields that appear inside the bimorph, when heated. It is shown that the value and the direction of these fields could suffer considerable changes in a bimorph structure, compared with the situation when each of the two components is heated separately. The possibility to obtain structures with improved pyroelectric coefficient was put into evidence.
Defects in Superconductor thin Films
Authors: Nandedkar A. S. , Ganapathi L. 
Published: April 2011

AbstractComputer aided simulations were used to investigate various grain boundary configurations in superconducting (YBa2Cu3O7) thin films. Four angles for tilt grain boundaries were simulated (12.45°, 53.5°, 66.4°, and 74.6°). Energies of unrelaxed configurations were calculated.
Atomic Scale Simulations of Tensile Failure in Metal Oxides
Authors: Streitz F. H. , Mintmire J. W. 
Published: April 2011

AbstractWe describe atomic-scale simulations of the failure under tensile load of an aluminum-alumina heterostructure, comparing the results with similar simulations of failure in metallic aluminum and the ceramic α-alumina. The simulations were performed using a novel computational method which explicitly includes variable charge transfer between cations and anions in an empirical potential. From our simulations we estimate the theoretical limit of yield stress for the interface to be approximately 2 GPa, at a strain of only a few percent. The theoretical limit for yield stress in α-alumina, for comparison, is about 45 GPa.
Electronic States in Cd1−xZnxTe/CdTe Strained Layer Coupled Double Quantum Wells and their Photoluminescence
Authors: Li Tiesheng , Lozykowski H. J. 
Published: April 2011

ABSTRACTExperimental and theoretical investigations of electronic states in a strained-layer CdTe/CdZnTe coupled double quantum well structure are presented. The optical properties of this lattice mismatched heterostructure were characterized by photoluminescence (PL), PL excitation and polarization spectroscopies. The influence of electrical field on exciton states in the strained layer CdTe/CdZnTe coupled double quantum well structure is experimentally studied. The confined electronic states were calculated in the framework of the envelope function approach, taking into account the strain effect induced by the lattice-mismatch. Experimental results are compared with the calculated transition energies.
Luminescence from SiOx Nanoclusters
Authors: wickboldt Paul , Cheong Hyeonsik M. , Pang Dawen , Chen Joseph H. , paul William 
Published: April 2011

ABSTRACTSiOx nanoclusters (7 nm to 17 nm) are produced by evaporation of SiO (or Si) in Ar (+O2) atmospheres. Room temperature photoluminescence (PL) measurements in vacuum reveal a broad band centered at 1.65 eV. Upon exposure to gas this PL band is extinguished in a matter of seconds, and another band centered at 2.12 eV appears. This effect occurs regardless of the gas used (He, Ar, N2, O2, H2O vapor or air) and is entirely reversible upon evacuation.Transmission electron microscopy (TEM), Raman, infrared transmission, and X-ray photoluminescence spectroscopy (XPS) measurements are used to characterize the clusters. They are noncrystalline, and the oxidation state is a suboxide rather than SiO2 The PL spectra are independent of cluster size. The PL does not occur without sufficient oxidation and does not require the presence of bonded hydrogen. We are led to speculate that the radiative recombination occurs in electron states derived from a suboxide.
Blue Light Emission from Germanium Ultrafine Particles by the Gas Evaporation Technique
Authors: Nozaki Shinji , Sato S. , Denda A. , Ono H. , Morisaki H. 
Published: April 2011

ABSTRACTThe ultrafine particles with diameters in the order of 10 nm were deposited onto Si and SiO2 substrates by evaporation of Ge in a pure hydrogen atmosphere. Although the as-deposited Ge ultrafine particles do not show any detectable luminescence, they emit blue light after being exposed to the UV light for a long time. The blue light is strong enough to be seen with the naked eye even under a room light. The photooxidation, unique to the Ge ultrafine particles, has been identified as a major factor contributing to the blue light emission.
Visible Photoluminescence from Silicon Nanoconstrictions formed by Heavy Hydrogen Implantation and Annealing Treatments
Authors: Pavesi L. , Bisero D. , Corni F. , Frabboni S. , Tonini R. , Ottaviani G. 
Published: April 2011

ABSTRACTIon implanted crystalline Si samples show luminescence (PL) in the visible at cryogenic temperatures after annealing treatments. This phenomenon is studied by varying the ion fluences and the sample doping density, and it is discussed considering the damage caused by the H implantation and its evolution with thermal treatments. A working hypothesis about the PL has been formulated which considers the exciton localisation in nanoconstrictions formed in the regions among the different microvoids produced by the implantation.
Control of and Mechanisms for Room Temperature Visible light Emission from Silicon Nanostructures in SiO2 formed by Si+ Ion Implantation
Authors: Komoda T. , Kelly J.P. , Nejm A. , Homewood K.P. , Hemment P.L.F , Sealy B.J. 
Published: April 2011

ABSTRACTImplantation of Si+ ions into thermal oxides grown on silicon has been used to synthesise a two phase structure consisting of Si nanocrystals in a SiO2 matrix. Various processing conditions have been used in order to modify the size and population distributions of the Si inclusions. Photoluminescence spectra have been recorded from samples annealed in nitrogen, forming gas and oxygen. Both red and blue shifts of the luminescence peaks have been observed. It is concluded that the photoluminescence is a consequence of the effects of quantum confinement but is also dependent on the presence of irradiation-induced defects or Si/SiO2 interface states.
Correlation Between Quantum Nanocrystal Particle Size and Photoluminescence Using Raman Scattering
Authors: Forsvthe E. W. , Whittaker E. A. , Pollak F.H. , Sywe B. S. , Tompa G. S. , Khan B. A. , Khurgin J. , Lee H.W.H. , Adar F. , Schaffer H. 
Published: April 2011

ABSTRACTThe PL (photoluminescence) and EL (electroluminescence) demonstrated for porous silicon and silicon rich SiO2 films have provided exciting opportunities for the integration of optoelectronics and Si digital electronics. Recent work has suggested that the porous silicon luminescence results from either quantum size or surface state effects. In this report, we review PL demonstrated in the visible spectral range from quantum nanocrystals (QNC) formed from Si embedded in an SiO2 matrix. We used Raman scattering to estimate the QNC particle size and correlated the shift in the luminescence spectra to the observed change in the Raman spectra. The PL spectrum peak shifted from 7000 to 8000 Å as the average particle size increased from ∼50 to 70 Å, measured from Raman scattering. Further, High Resolution Transmission Electron Microscopy, HRTEM, and X-ray Diffraction, XRD, measurements confirmed the particle size range. PL lifetime measurements and excitation intensity studies are also presented. The stable nature of the QNC embedded in an insulating or semiconducting matrix offers further advances towards the integration of optoelectronics with Si devices.
Influence of the Dispersion of the Size of the Si Nanocrystals on their Emission Spectra
Authors: Khurgin J. B. , Forsythe E. W. , Kim S. I. , Sywe B. S. , Khan B. A. , Tompa G. S. 
Published: April 2011

ABSTRACTA systematic study of the PL spectra of Si quantum nanocrystals in the SiO2 matrix has been performed. The results have been fitted to a quantum-confinement model that includes the nanocrystal size dispersion rather than a specific size of the nanocrystal. This serves as a strong confirmation of the confinement-induced nature of the PL. It has been shown that if the dispersion is taken into account, the position of the emission peak as well as the PL width can always be correlated with the average size of the nanocrystal.
Transparent Sol-Gel Matrices Doped with Quantum Sized PbS Particles
Authors: Gacodin T. , Boilot J.P. , Gandais M. , Ricolleau C. , Chamarro M. 
Published: April 2011

ABSTRACTSol-gel matrices doped with lead sulfide nanoparticles showing a structured absorption spectrum were synthesized by using the procedure previously reported for CdS doped matrices. The morphology of the PbS aggregates was investigated by high resolution electron microscopy, and the observations are correlated with the absorption spectra. Finally, preliminary results concerning some linear optical properties of the materials are presented.
Synthesis of PbS Semiconductor Microcrystallites In Situ in Reverse Micelles
Authors: De Sanctis O. , Kadono K. , Tanaka H. , Sakaguchi T. 
Published: April 2011

ABSTRACTColloid semiconductor particles of PbS have been prepared in reversed micelles of AOT-heptane. The effects of the AOT, water and reactants concentrations have been studied. The initial crystallite size and its growth with the time aging are strongly dependent on the water/AOT ratio and the ionic pool concentration. The absorption spectroscopic characteristics of the PbS particles have been examined. As the particle size decreases the band gap shifts in color from orange-brown to yellow and approaches the transition energy of the first allowed excited state of a PbS molecule. Moreover, the optical nonlinear property of PbS particles was investigated by Degenerate Four-Wave Mixing (DFWM) experiment using a frequency-doubled Nd:YAG laser.
Optical Features of Nanosize Iron and Molybdenum Sulfide Clusters
Authors: Wilcoxon J. P. , Samara G. , Newcomer P. 
Published: April 2011

ABSTRACTIn the bulk state FeS2 and MoS2 are optically opaque, narrow bandgap semiconductors with no optical applications. We demonstrate that nanosize FeS2 and MoS2 have bandgaps that can be adjusted to the visible and even UV region of the spectrum by control of the cluster size. This opens up a host of applications of these materials as inexpensive solar photocatalysts. We demonstrate that the band-gap of both materials shifts to the blue with decreasing size but ceases shifting when a size of ∼ 3 nm (in the case of MoS2) is attained. We interpret this observation as a change from bulk quantum confinement of the hole-electron pair of a tiny semiconductor to a set of discrete molecular-like transitions more characteristic of a large molecule. Room temperature photoemission studies of these clusters demonstrate that, while photoemission shifts to the blue with increasing bandgap for large clusters, small clusters have photoemission exclusively from trapped sub-bandgap surface states. Chemical modification of the surface to introduce hole or electron traps can result in either an enhancement or a decrease in the photoluminescence. In addition, we report our results concerning chemical purification and preliminary surface characterization of MoS2 clusters by chromatography.
Peculiarity of Porous Silicon Formed in the Transition Regime
Authors: Lazarouk S. , Chumash V. , Fazio E. , La Monica S. , Maiello G. , Proverbio E. 
Published: April 2011

ABSTRACTElectrochemical anodization in the transition regime, between porous silicon formation region and electropolishing region, of monocrystalline silicon was investigated. Using this process bright and stable photoluminescence could be obtained on a very large range of substrate resistivities: p=12-0.005 Ωcm for p-type silicon and p = 20-0.001 Ωcm for n-type substrates.Photoluminescence spectra, Fourier Transform IR (FTIR) absorbance and X-Ray Diffraction (XRD) measurements are reported. Investigations showed that anodic silicon suboxide was formed on the surface. The porous structure obtained in the transition regime is suggested to consist of silicon crystallites built inside an anodic oxide.
Effect of Geometrical Irregularities on the Band Gap of Porous Silicon
Authors: Sapoval B. , Russ S. 
Published: April 2011

ABSTRACTWe discuss how the geometrical irregularities of small crystallites, quantum dots or wires may play an essential role in the density of electronic states near the band gap in semiconductors. Assuming a possible irregular structure for porous silicon we show that the irregularity has a strong effect on the value of the band gap and of the density of states in the near band gap region. The effect of the irregularity is essentially to enhance the quantum confinement effect and to screen the fundamental wave-function from the surface.
Investigation of Chemical Adsorbate Effects on Blue and Red Emitting Porous Silicon Samples
Authors: Rehm Julie M. , McLendon George L. , Tsybeskov Leonid , Fauchet Philippe M. 
Published: April 2011

ABSTRACTWe have investigated the sensitivity of blue (PLmax = 480 nm) and red (PLmax = 660 nm) emitting porous silicon samples to various chemical adsorbates. Steady-state and time-resolved photoluminescence measurements and FTIR spectroscopy were employed to characterize the photophysical and optical effects induced by chemical exposure. The red samples, which are hydrogen terminated, exhibit quenching and recovery of photoluminescence intensity and broadening of the Si-Hx stretch bands upon exposure to liquid methanol. This behavior is attributed to the ability of the Si-Hx specie on the surface of the PSI to interact with the solvent molecules which temporarily traps the electrons and causes PL loss and Si-Hx broadening. The blue samples, which are oxygen terminated, display similar sensitivity to methanol. This sensitivity is attributed to the solvent's ability to change the surface passivation and thereby introduce competitive radiative and nonradiative recombination channels. The origin of the blue PL is discussed.
Effective Dielectric Function of Porous Silicon: the Transverse Component
Authors: Lugo J.E. , Del Río J.A. , Tagüeña-Martínez J. , Ochoa-Tapia J.A. 
Published: April 2011

ABSTRACTIn previous works we have obtained an expression for the effective electrical conductivity of a columnar model simulating porous silicon. We used the averaging volume method that has proven to be successful in treating fluid transport in porous media. With this method we can calculate the bulk and the surface contribution to an effective transport property. The axial component can be solved analytically, but in the xY plane the calculation can only be performed numerically. However there is a certain approximation called Chang's cell (valid for high porosities) where the transverse component is also analytical. The extension of our original approach to find the axial component of the effective dielectric function is relatively simple, but the transverse component calculation presents interesting features.
Probing Optical Transitions in Porous Silicon by Reflectance Spectroscopy in the Near Infrared, Visible and UV
Authors: Theiβ W. , Arens-Fischer R. , Arntzen M. , Berger M.G. , Frohnhoff S. , Hilbrich S. , Wernke M. 
Published: April 2011

ABSTRACTReflectance spectroscopy has been used to obtain the dielectric function of the solid phase of porous silicon. The method is based on a fit of a parameterized dielectric function model to measured spectra. A crucial step in the procedure is the 'dielectric averaging' of the microscopic dielectric function of the pore wall material to the macroscopic effective dielectric function which governs the optical properties.Results are given for heavily and moderately p-doped samples of various porosities. For the latter large differences to bulk silicon have been found. The obtained dielectric functions are compared to the results of band structure calculations taken from literature.
Comparison of the Band Gap of Porous Silicon as Measured by Photoelectron Spectroscopy and Photoluminescence
Authors: Van Buuren T. , Eisebitt S. , Patitsas S. , Ritchie S. , Tiedje T. , Young J. F. , Gao Yuan 
Published: April 2011

ABSTRACTThe peak energy of the room temperature photoluminescence of porous silicon is compared with the bandgap determined from photoelectron spectroscopy measurements for a series of porous silicon samples prepared under different conditions. The photoluminescence bandgap is found to be smaller than the photoelectron spectroscopy bandgap, but exhibits the same trend with preparation conditions. The width of both the photoluminescence spectrum and the L-absorption edge increases when the current density during the preparation is increased or the sample is allowed to soak in HF after preparation.
The Spectroscopy of Porous Silicon
Authors: Calcott P. D. J. , Nash K. J. , Canham L. T. , Kane M. J. 
Published: April 2011

ABSTRACTThe spectroscopic evidence that the main visible photoluminescence (PL) band of porous silicon (the 'S' band) originates from quantum confined crystalline silicon is presented, and arguments that claim to invalidate this evidence are analysed in detail. We find that a careful study of all the spectroscopic data provides strong support for the quantum confinement model. Additionally we consider the interesting issue of the luminescence spectrum of a single silicon quantum dot.
Localized Nature of Photoluminescence from Anodically Oxidized Porous Silicon
Authors: Ito T. , Furuta K. , Yoneda T. , Arakaki O. , Hatta A. , Hiraki A. 
Published: April 2011

ABSTRACTPhotoluminescence (PL) properties from anodically oxidized porous silicon (PS) have been investigated. Large temperature coefficients (-0.5 meV/K) of PL peak energy are observed for relatively strongly oxidized PS specimens which show saturation of PL peak blue shift upon further anodic oxidation. Time-resolved PL data show that the PL decay is characteristic of thermal activation process with an energy of 9-27 meV at low temperatures between 80 and 180 K. Those results can be explained using a luminescence model which assumes several PL centers in the energy gap and considers thermally activated and tunneling processes.