bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kinetic and Thermodynamic Properties of Nanocrystalline Materials
Authors: Averback R.S. , Hahn H. , Hö;fler H.J. , Logas J.L. , Shen T.C. 
Published: March 2011

AbstractA new class of materials with ultra small grain size has recently been synthesized by combining the methods of inert gas condensation of metal vapors and in situ powder compaction. These ‘nanocrystalline’ materials, with grain sizes of 5-10 nm, can have over 30% of their atoms lying in the highly disordered interfaces or grain boundaries. Because of their unique atomic structure, nanocrystalline materials often have properties far different from their bulk counterparts. In addition, kinetic processes can be rapidly accelerated due to the short diffusion distances between grains. In this review, we will report on the thermodynamic properties and reaction kinetics of nanocrystalline metals and on such kinetic properties as sintering and grain growth in nanocrystalline ceramics.
Measurement of Bond Strength at Metal/Ceramic Interfaces
Authors: Nutt Gerald L. , Lai William , Froeschner Kenneth E. , King Wayne E. 
Published: March 2011

AbstractWe report on a novel method for measuring the bond strength of metal/ceramic interfaces. Test specimens are created by vapor depositing a metal film on a ceramic substrate. The specimen is impacted with a thin metal flyer sending a short planar shock pulse into the ceramic. If the shape and amplitude of the wave is properly controlled the interface will spontaneously debond creating new free surfaces.Measurements indicate the debonding process occurs in less than 1.0 ns, which we believe is too short for crack propagation along existing flaws. Therefore, we conclude that simultanious breaking of atomic bonds rather than propagation and coalescence of cracks is the means by which the film and substrate are separated. The free surface velocity of the metal overlayer is monitored during spall by laser interferometry. The data constitute a direct measurement of the bond strength. The measured bond strengths are reproducible and do not show a dependence on shock amplitude for identically prepared specimens.
Continuous-Film Thickness Determination by AES of Cr Overlayers on Cu Surfaces
Authors: Lefakis H. , Ho P.S. 
Published: March 2011

AbstractThe characteristics of Cr coverage of Cu surfaces, including determination of tc, the minimum average film thickness required for formation of a continuous film, have been studied in-situ by Auger Electron Spectroscopy (AES). Auger signal intensities of substrate and deposit were monitored during Cr film growth by vapor deposition in UHV. It was shown that substrate surface morphology (roughness) has a dominant effect on coverage rate and tc. Slower coverage rates and larger tc′s were effected by the presence of native oxides, substrate heating (to 330°C) and H2O-vapor rich (5×10−5 Torr) ambient during Cr deposition. Surface oxides seemed to affect more the coverage of a smooth than a rough surface. Conversely, substrate heating affected more the coverage of a rough surface. The combined effect of substrate heating and water vapor rich atmosphere was pronounced for both smooth and rough surface coverages. Some of the main factors controlling these effects are discussed.
Electron Microscopy Analysis of Aluminous Porcelain-Tin Oxide Coated Platinum Bonds
Authors: Ji Huaxia , Marquis P. M. , Loretto M. H. 
Published: March 2011

AbstractThe structure of the bond between dental aluminous porcelain and tin oxide coated platinum foils, used in dental jacket crowns, has been studied using analytical electron microscopy of crosssectioned specimens. It has been shown that the tin oxide is in the form of stannic oxide (SnO2) and that some of the oxide dissolves into the glass. It has also been demonstrated that the platinum foil is strained immediately adjacent to the interface.
Atomic Matching Across Internal Interfaces
Authors: Merkle Karl L. 
Published: March 2011

AbstractThe atomic structure of internal interfaces in dense-packed systems has been investigated by high-resolution electron microscopy (HREM). Similarities between the atomic relaxations in heterophase Interfaces and certain largeangle grain boundaries have been observed. In both types of interfaces localization of misfit leads to regions of good atomic matching within the interface separated by misfit dislocation-like defects. It appears that, whenever possible, the GB structures assume configurations in which the atomic coordination is not too much different from the ideal lattice. It is suggested that these kinds of relaxations primarily occur whenever the translational periods along the GB are large or when the interatomic distances are incommensurate. Incorporation of low index planes into the GB appears to lead to preferred, i.e. low energy structures, that can be quite dense with good atomic matching across a large fraction of the interface.
The Study of Contamination of Carbon, Boron, and Oxygen in LEC-GaAs
Authors: Itoh Y. , Takai M. , Fukushima H. , Kirita H. 
Published: March 2011

AbstractCarbon in LEC GaAs was found to be introduced as CO from the ambient atmosphere; the oxygen concentration in the crystals decreased with increase in the duration of melting. An equilibrium segregation coefficient of oxygen in GaAs crystals was found by charged particle activation analysis to be 0.1, the value of which was smaller by a factor of 3~4 than that reported before.
Depth Sensitive Imaging of Defects in Epilayers and Single Crystals Using White Beam Synchrotron Radiation Topography in Grazing Bragg-Laue Geometry.
Authors: Dudley M. , Yao G.-D. , Wu J. , Liu H.-Y. 
Published: March 2011

AbstractThe technique of Synchrotron White Beam topographic imaging in grazing Bragg-Laue geometries has been developed at the Stony Brook synchrotron topography station at the NSLS. This technique enables imaging of defects in subsurface regions of thickness which can range from hundreds of Angstroms to hundreds of microns as determined by the penetration depth of the X-rays. This penetration depth, which is shown to be determined by the kinematical theory of X-ray diffraction, can be conveniently varied, in a controlled manner, by simple manipulation of the diffraction geometry, thereby enabling a depth profiling of the defect content.The fundamentals of the technique are described, and its advantages and disadvantages compared to existing techniques are discussed in detail. Examples of application of the technique in the characterization of defects in thin epitaxial films of GaAs on Si, are given, and the general applicability of the technique is discussed.
Formation of Three Red-Shift Emissions in Heavily Germanium-Doped P-Type GaAs Grown By MBE
Authors: Makita Y. , Yamada A. , Shibata H. , Asakura H. , Ohnishi N. , Beye A. C. , Mayer K. M. , Kutsuwada N. 
Published: March 2011

AbstractMolecular beam epitaxy (MBE) of Ge-doped GaAs was made, in which As4 to Ga flux ratio :γ and Ge concentration :[Ge] were used as growth parameters. Photoluminescence (PL) spectra at 2K for slightly Ge-doped GaAs revealed that for γ =1 the emission of excitons bound to neutral Ge acceptors (A°,X) was the dominant one. With increasing γ ,(A°,X) was found to be steeply suppressed and at around γ=1.1, (A°,X) was totally quenched. For γ higher than 1.4, the emission of excitons bound at neutral Ge donors (D°,X) was gradually enhanced and for γ =11, (D°,X) became the principal one. Through van der Pauw measurements, samples with [Ge] around 1×1017cm-3 presented type conversion at around γ=1.7. In this series, the sample with γ =1.0 indicated a strong specific emission, [ g-g], which is formed just below (A°,X) and exhibited a strong energy shift towards lower energy sides (red shift) with increasing [Ge]. [g-g] was theoretically attributed to the pairs between excited-state acceptors. Since [g-g] is known to be easily quenched by small amount of donors, the formation of predominant [g-g] for γ =1 assures that very low-compensated p-type GaAs were grown by using this typically am-photeric impurity. We fabricated a series of p-type Ge-doped GaAs by keeping γ =1 in which the net hole concentration, │ NA-ND │ as high as 1×1020cm-3 was attained. We found four emissions which exhibited significant energy shifts with increasing │ NA-ND │ . From │ NA-ND │ ~1×1016 cm-3, [g-g] begins to appear as a dominant emission and at │ NA-ND │ ~ 1×1017 cm-3, another red shift emission, [g-g]2 begins to be formed parralelly on the higher energy side of [g-g]. It is interesting to note that both [g-g] and [g-g]2 seem to be totally quenched by the further increase of [Ge]. The emission due to band to Ge acceptor,(e,Ge) does not change its central energy until [Ge]= 5×-1018cm-3 and for larger [Ge] it turned into a new broad emission,[g-g]β showing a steep red energy shift. [g-g]α was formed on the higher energy side of (e,Ge) and indicated a systematic blue energy shift with growing [Ge] larger than 1×1019cm-3. [g-g]α was theoretically explained to be the emission due to the pairs between ground-state acceptors.
Photoluminescence Study of GaAs Diffused with Li
Authors: Gislason H. P. , Sveinbjörnsson E. Ö. , Monemar B. , Linnarsson M. 
Published: March 2011

AbstractWe present a detailed study of the photoluminescence (PL) properties of a wide range of GaAs material diffused with the group I element Li. The effects of the Li diffusion are investigated through its effects on existing photoluminescence bands in the as-grown material as well as the appearence of new such bands. Among new PL bands resulting from the Li doping of n-type and semi-insulating material the most pronounced ones are a strong deep band at 1.34 eV and shallower bands at 1.45 and 1.48 eV. The origin of these PL bands will be discussed.
The Role of Oxygen in p-Type InP
Authors: Michel J. , Jeong J. , Lee K.M. , Kimerling L.C. 
Published: March 2011

AbstractWe have studied the influence of oxygen on the optical properties of Be implanted InP. Be implanted p-type InP without oxygen shows a strong deep photoluminescence (PL) band at 0.82 eV following anneal. As the oxygen concentration increases, the 0.82 eV PL-band disappears. We attribute the disappearance of this PL-band to the formation of oxygen complexes with the implantation induced defects. In epitaxial grown, nominally undoped InP a new PL-line is observed at ~1.2 eV. The paramagnetic state of the phosphorus on indium P^ antisite is observed by optically detected magnetic resonance (ODMR) as a modulation of the photoluminescence in all Be implanted samples without oxygen. The antisite resonance is detected as a reduction of the 0.82 eV PL-band and the 1.2 eV PL-band. The observation of the Fe3+ resonance by ODMR spectroscopy is reported for the first time.
Mid-Infrared Spectral Photoresponse of Semi-Insulating GaAs
Authors: Brown G.J. , Mitchel W.C. 
Published: March 2011

AbstractWe have developed a characterization technique using spectral photoconductivity that is capable of identifying deep energy levels in gallium arsenide. Our technique requires less sample processing than deep level transient spectroscopy (DLTS) and can be used on semi-insulating (si) gallium arsenide. The technique uses a mid-infrared fourier transform spectrometer for rapid photoresponse versus wavelength measurements. Using this technique we have observed evidence of several below mid-gap energy levels in undoped si gallium arsenide by the spectral PC technique. Spectral PC measurements were made on si GaAs before and after illuminating the cooled samples with high intensity white light at 8K. The PC spectrum typically showed a broad photoresponse that was attributed to multiple energy levels being present in the material. The observed energy levels were: 0.54 eV, 0.44 eV, 0.25 eV, 0.17 eV, 0.14 eV and ~0.10 eV. The shallow photoresponse from the carbon acceptor was not observed. The most striking spectral feature was a sharp ionization edge at about 0.44 eV in all of the samples studied. This energy level correlates to the 0.43 eV intrinsic defect level that has been observed by temperature dependent Hall effect measurements. The 0.44 eV level was also observed in our PC spectrum of a n-type Bridgman grown sample that had shown the 0.43 Hall effect level. The presence of additional deep levels in concentrations comparable to those of EL2 and carbon indicates that the simple model for compensation in si GaAs which invokes only EL2 and shallow impurities needs revision.
Deep Level Luminescence in InP: Phonon Feature Analysis
Authors: Banerjee S. , Srivastava A.K. , Arora B.M. 
Published: March 2011

AbstractThe phonon features in the deep level luminescence (PL) bands related to Fe and Mn and native defects in InP have been clearly identified and the lineshape of the bands are analysed using configuration coordinate model. A consistent set of phonon parameters are determined for the first time.
The Nature of Native Defects in LEC grown Semi-Insulating GaAs by Thermally Stimulated Current Spectroscopy
Authors: Fang Zhaoqiang , Shan Lei , Schlesinger T. E. , Milnes A. G. 
Published: March 2011

AbstractTraps have been studied by thermally stimulated current spectroscopy (TSC) with intrinsic (1.96 eV) and extrinsic (1.15 eV) light for both In doped and undoped LEC materials grown under various non-stoichiometric conditions. Significant differences are seen in the bulk trap spectra associated with Ga-rich and As-rich material and with isoelectronic In doping. Proximity wafer-annealing at 950° C has been shown to improve minority carrier lifetime in n-type GaAs and we show that in semi-insulating GaAs this causes changes in trap structure. From such thermal studies and the effects of non-stoichiometric growth, the probable nature of the traps commonly seen is inferred.
Comparative Optical Studies of Cu, Mn, and C Impurities in Bulk Lec grown GaAs by Electron Beam Electroreflectance (EBER) and Photoluminescence (PL).
Authors: Herman M. H. , Pearah P. J. , Elcess K. , Ward I. D. 
Published: March 2011

AbstractWe have used 300K Electron Beam Electroreflectance (EBER) and 4. 2K photoluminescence (PL) to measure optical transitions in a series of LEC grown GaAs samples. The contaminants primarily consisted of the individual elements Cu, Mn, and C at levels above 1016/cm3. In unmodified control samples we find evidence of strong excitonic effects in the EBER lineshape even at 300K. For the contaminated samples, we find characteristic impurity transitions below the E0 bandgap of the GaAs in both optical spectroscopies. However, in general the estimated impurity binding energies by EBER are not equivalent to established PL or DLTS values. Specifically, from EBER data we find below E0 (1.424eV at 300K) a Cu peak near 49meV (1.375eV) and a C peak about 39meV (1.385eV) below E0 . An EBER spectrum of the Cu-contaminated sample at 124K shows an asymmetric Cu impurity peak 47meV below E0 . The C feature has been ascribed to either Si or Ge from corresponding PL energies by several earlier researchers. Two samples which had been implanted with Mn and annealed show a peak about 43meV below E0 (1.381eV), and what appears to be a sharp, excitonic transition 10 to 16meV above the E0 . Although these features may be due to Mn alone, the latter observation is suggestive of strain-induced valence band splitting.The correlated appearance of impurity peaks below the split-off E0 +Δ0 band may allow their assignment to either donors or acceptors in modulated reflectance studies [1,2]. None of the present cases showed corresponding transitions below E0 +Δ0 , suggesting that the observed impurity features arise only from acceptor transitions. Alternatively, the reduction of light penetration into the GaAs above the E0 bandgap, reducing the sample interaction volume, may also explain this null observation.
Ge Related Deep Level Luminescence in InGaAs Lattice Matched to InP
Authors: Chandvankar S.S. , Srivastava A.K. , Arora B.M. , Sharma D.K. 
Published: March 2011

AbstractPhotoluminescence and Hall measurements are reported on Ge doped InGaAs layers lattice matched to InP. Ge doping of these samples results in highly compensated material, with the highest Ge content sample giving a p type conductivity with carrier concentration of 5 ×1017 cm-3. Low temperature PL spectra of these samples show a broad peak from 0.55 to 0.77 eV due to Ge. The peak of luminescence shifts to lower energy with increasing Ge content. The peak position shifts to higher energy with increasing excitation like in a D-A pair transition. The PL spectra have been explained on the basis of a model which assumes tail states near the band edges due to disorder produced by the presence of Ge in the lattice.
High Performance Photoluminescence Spectroscopy using Fourier Transform Interferometry
Authors: Thewalt M.L.W. , Nissen M.K. , Beckett D.J.S. , Lundgren K.R. 
Published: March 2011

AbstractWe present recent results on the applications of Fourier transform techniques to photoluminescence spectroscopy as it relates to both basic and characterization-related semiconductor research. The emphasis here is on demonstrating the advantages of these methods in situations requiring very high spectral resolution and/or very high sensitivity. We also provide an example of the utility of interferometry in performing photoluminescence excitation spectroscopy in spectral regions where broadly tunable laser sources are not readily available.
Photoconductivity Study of CrB and CrI in Silicon
Authors: Schlette A. , Klenle R. , Dörnen A. , Kürner W. , Thonke K. 
Published: March 2011

AbstractWe observe in photoconductivity (PC) measurements EMT-like excited states of the pseudodonor CrB, which are responsible for the capture of free electrons due to their short lifetime. The energetic position of the ground state can be located at Ev + (292 ± 5) meV. A finestructure of the (CrB)° transition consisting of at least 15 components is observed in PC and high-resolution Fourier transform photoluminescence. In acceptor-free silicon a step in photoconductivity at 205 ± 10 meV is ascribed to interstitial Cr, whereas a second step at ~ 425 meV could be due to substitutional Cr.
Formation of In-Cu Pairs in Silicon During Chemomechanical Polishing
Authors: Wichert Th. , Keller R. , Deicher M. , Pfeiffer W. , Skudlik H. , Steiner D. 
Published: March 2011

AbstractUsing the perturbed γγ angular correlation technique (PAC) the pairing of Cu with the radioactive acceptor atom 111In in Si is detected. Because of the identity of the electric field gradients the so-called X defect, observed after chemomechanical polishing of Si wafers and known of neutralizing acceptor atoms in Si, is identified as a Cu atom. It is also shown that as-delivered Si wafers already contain Cu atoms which neutralize acceptor atoms if the wafers are annealed at 1173 K.
Strain Induced Intrinsic Quantum wells as the Origin of Broad Band Photoluminescence in Silicon Containing Extended Defects
Authors: Weman H. , Monemar B. 
Published: March 2011

AbstractA new recombination mechanism occuring in semiconductors containing extended defects is presented. The model is based on experimental data both from hydrogen plasma treated silicon, containing extended defects like platelets, and from oxygen precipitated silicon. The broad photoluminescence bands from these samples are attributed to the heavily damaged regions surrounding the extended defects, where electrons and holes can be localized in the strain-induced potential wells. From a theoretical calculation it is shown that the compressive strain field surrounding [111] and [100] platelets are sufficient to cause a local band gap reduction of as much as 0.3 eV, consistent with the experimental data.
Identification of Radiation-Induced Defects in Si:Al
Authors: Latushko Ya.I. , Petrov V.V. 
Published: March 2011

AbstractRadiation-induced defects (RD) in Si.:Al have been investigated by means of infrared absorption (IRA) and photoluminescence (PL) methods. It has been found that the main Al containing RD in electron-irradiated Si is an interstitial Al atom (Al1). In the process of annealing at about 225 °C the production of Al1-Al1 pairs takes place. The activatin energy of this RD production is 0.95 eV, which corresponds to Al1 migration energy along hexagonal interstitials. Al1 is shown to be a two - charge donor with the energy level E(+/++) = Ev + 0.20 eV. Besides the above mentioned defect as well as acceptor type defect with Ev + 0.21 eV level a number of other defects has been revealed in neutron-irradiated Si:Al. These centers give rise to a great number of IRA and PL lines in the spectral range from 0.1 to 1.2 eV. The classification of the observed defects has been done on the basis of the annealing results and uniaxial stress measurements.
Excitoic Recombination at a Transititon-Metal Related Defect in Silicon
Authors: Mcguigan K.G. , Henry M.O. , Lightowlers E.C. , Nazare M.H. 
Published: March 2011

AbstractA new photoluminescence system is reported for copper-doped silicon. The luminescence system consists of two doublet zero phonon lines at 1033.51±.05 meV, 1033.62±.05 meV, 1040.05±.05 meV and 1040.17±.05 meV. We establish from Zeeman studies that the lower energy lines are isotropic magnetic triplets, and the upper energy lines are singlets. From temperature dependence measurements the energy separation between triplet and singlet states is determined to be approximately 6 meV, in agreement with the spectroscopic separation. Also from temperature dependence PL we show that the transition probability ratio for the higher and lower states is 210. We conclude that the main features of the luminescence agree with radiative recombination of excitons bound to an axial isoelectronic defect. The chemical identity of the constituent(s) involved is uncertain although the participation of copper is likely.
Light- and Heavy-Hole Bound Exciton Transitions and Free to Bound Transitions in GaxAl1-xAs/GaAs Quantum Wells
Authors: Reynolds Donald C. , Bajaj K.K. 
Published: March 2011

AbstractExcitons bound to neutral donors in AlxGa1-xAs/GaAs quantum wells were observed by high resolution resonant excitation photoluminescence, and temperature dependent photoluminescence measurements. Changes in the binding energy of excitons are observed when the donors are located in the center of the well, at the edge of the well, or in the center of the barrier. The variations in these binding energies are reported as a function of well size from 75–350Å. The binding energies increased as the well size was reduced to about 100Å, with further reductions in well size they decreased.Light-hole free excitons bound to neutral donors were observed in AlxGa1-xAs/GaAs quantum wells. The transitions were observed, using selective excitation photoluminescence spectroscopy, in the energy region between the light-hole and heavy-hole free exciton transitions where no other intrinsic transitions exist. The neutral donor-bound heavy-hole free-exciton transitions were also observed when the light-hole bound exciton transitions were observed. Quantum well structures which showed no evidence of a heavy-hole donor bound exciton also showed no evidence of a light-hole donor bound exciton.Free to bound transitions, free hole to bound electron, have also been observed in the AlxGa1-xAs/GaAs quantum wells. The diamagnetic shift of these transitions was used to distinguish them from excitonic transitions.
Decay Measurements of Free and Bound Exciton Recombination in Doped GaAs/GaAIAs Quantum Wells
Authors: Bergman J.P. , Holtz P.O. , Monemar B. , Sundaram M. , Merz J.L , Gossard A.C. 
Published: March 2011

AbstractIn this study we present photoluminescence decay measurements of free exciton (FE) and bound exciton (BE) recombination in doped GaAs/AIGaAs quantum wells (QW). It is found that the FE decay time is reduced in the doped QW’s compared to similar undoped samples. The low temperature decay time of the BE is slightly longer than for the FE, with BE decay times from 300 to 600 ps for well widths of 50 to 150 Å, respectively. It is also found that the observed decay of the BE is strongly influenced by the decay time of the FE. This is especially observed in the similarity of the temperature dependence for the FE and BE decay time.