bluuebunny/crossref_metadata_2025_split huggingface dataset:
Heteroepitaxy of Strained and Not-Strained Ferroelectric Superlattices and their Electric Properties.
Authors: Tabata Hitoshi , Hamada Masakazu , Kawai Tomoji 
Published: April 2011

AbstractBismuth based artificial superlattices have been formed by a layer-by-layer laser deposition with in-situ monitoring of RHEED. The Bi2O2/WO6, Bi2O2/SrTa2O9, Bi2O2/SrTa2O9 /SrTiO3 and Bi2O2/SrTa2O9/BaTiO3 are constructed epitaxially by a single, double and triple perovskite layers sandwiched by Bi2O2 layers, respectively. The dielectric constant increases with increasing the number of perovskite layers. And the D-E hysteresis loop (ferroelectric properties) appears along the c-axis direction in odd perovskite layers (n=l and 3). We have also formed the SrTiO3/BiWO6/SrTiO3 multi layers. With this combination, the STO layers are isolated by the BWO layers. The dimensionality of STO layer can be controlled by changing the thickness of BWO layers. Below the BWO thickness of 500 Å, the εr increases monotonously with decreasing the BWO thickness. Therefore, the the coulomb force, which is in proportion to inverse of the distance, plays an essential role for the dielectric constant. The formation of “artificially constructed ferroelectric films” by a layer-by-layer deposition method will be discussed ad an essential approach to elucidate the mechanism of ferroelectricity.
Si(001) Homoepitaxial Growth
Authors: Tromp R. M. , Theis W. , Bartelt N. C. 
Published: April 2011

AbstractEpitaxial growth is generally treated as a far-from-equilibrium process, dominated by kinetic restraints rather than thermodynamic driving forces. In this paper we show that homoepitaxial growth, at temperatures exceeding ∼500°C, is a process that can be approached very well from a thermodynamic equilibrium viewpoint, augmented with classical homogeneous nucleation theory.
Brownian Motion and Coarsening of Domain Boundaries on (7×7)-Si(111)
Authors: Atala Pita , Phaneuf R. J. , Barteltl N. C. , Swiech W. , Bauer E. 
Published: April 2011

AbstractWe have used low-energy electron microscopy to investigate the real-time motion of (7×7) out-of-phase domain boundaries in the (7×7) reconstruction on vicinal Si(111), just below the phase transition temperature. As a function of time, the domain boundaries wander and coalesce in one-dimension, parallel to the step edges. We have established that the motion is consistent with the statistical problem of a random walk in the presence of absorbing barriers and have measured the diffusion coefficient for domain boundary wandering. The average distance between domain boundaries becomes large as they coarsen, consequently energetic interactions are not significant in determining their arrangement on this surface.
Potential of Ultra-High Resolution and Low Voltage Sem for Dynamic Experiments
Authors: Boyes E D 
Published: April 2011

AbstractA new generation of ultrahigh resolution scanning electron microscope (UHRSEM) is designed to explore the potential for higher resolution imaging and chemical microanalysis from more representative bulk samples. A <0.5nm probe at 30kV and <2.5nm at 1kV have been integrated with high sensitivity energy dispersive x-ray spectrometry (EDX) [1] and a high vacuum (<3×10−8mbar) heating stage (to >1000°C). The sensitivity of surface imaging is generally enhanced at low beam energies. With low voltages and digitally integrated fast scan techniques, conductive coating of an electrically non-conducting sample, such as a ceramic substrate, is no longer a pre-requisite for SEM, and this opens up new possibilities for minimally invasive dynamic in-situ experiments. This paper focuses on metal particle migration and sintering on a ceramic substrate.
Kinetic Study of the Passive Film on 304 Stainless Steel Using a Scanning Tunneling Microscope
Authors: McKrell T. J. , Galligan J. M. 
Published: April 2011

AbstractThe unique capability of the scanning tunneling microscope, STM, for in situ nanoscale electronic measurements has been utilized to establish the nature of the oxide film on 304 stainless steel under HCI, distilled water, and in air. New insights were obtained concerning the kinetics and electronic surface states of the oxide film as a function of exposure time to these environments: quantitative measurements of the corrosion behavior and the stability of the oxide film, as related to observed defects, have been obtained. These findings have resulted in a model which incorporates these new insights with previously established theories concerning oxidized surfaces.
Dynamic Observation of Vortices in Superconductors Using Electron Waves
Authors: Tonomura A. 
Published: April 2011

AbstractIndividual vortices in superconductors were directly and even dynamically observed by using a “coherent” field emission electron beam. Magnetic lines of force of vortices were quantitatively observed in a holographic interference micrograph and their dynamics were observed by Lorentz microscopy. The interaction of vortices with both line- and point-defects was investigated by direct observation.
Localization Phenomena, Photoluminescence and Raman Scattering in nc-Si and nc-Si/a-SiO2 Composites
Authors: veprek S. , Wirschem T. , Rückschloβ M. , Ossadnik C. , Dian J. , Perna S. , Gregora I. 
Published: April 2011

AbstractWe present evidence for the large increase of the band gap due to the quantum localization in nc-Si imbedded in a-SiO2 matrix, which is in agreement with the original theoretical calculations. This, together with additional experimental data explains the large red shift between the onset of the excitation spectra and the photoluminescence. This also provides strong support for the mechanism of the photoluminescence which originates from radiative centers either at the Si/SiO2 interface or within the SiO2 matrix. The strong decrease of the efficiency of the photoluminescence due to a decrease of the thickness of the a-SiO2 grain boundaries is shown and its origin discussed. Delocalization of the photogenerated charge carriers due to ultra thin a-SiO2 is excluded as the cause of this effect. Microwave absorption is used to study the effect of the grain boundaries on the localization and delocalization of photogenerated charge carriers in pure nc-Si together with concomitant phenomena observed in Raman scattering. Finally we show the strong decrease of the photoluminescence decay time to ≤ 500 ps due to molecular-like radiative centers which are formed in the nc-Si/SiO2 composites by appropriate doping.
Towards a Microscopic Interpretation of the Dielectric Function of Porous Silicon
Authors: Rossow U. , Frotscher U. , Aspnes D. E. , Richter W. 
Published: April 2011

AbstractThe dielectric function of porous silicon layers depends strongly on the electronic properties of the nanostructure of the silicon skeleton. In this paper we discuss the main effects, as determined from spectroscopic ellipsometric measurements of the dielectric function of porous layers formed on p-doped material. Finite-size effects and the high inner surface area of the nanostructure lead to relaxation of k-momentum conservation as defined for infinite crystals and therefore to a broadening of the features in <ε> arising from interband critical points. In addition a small threshold energy shift is observed when the percolation of the structure is reduced. However, this shift is too small to explain red photoluminescence as a consequence of a pseudo-direct gap whose energy is blue-shifted by confinement.
Photoluminescence Properties of Er-Doped Porous Silicon
Authors: Hömmerich U. , Wu X. , Namavar F. , Cremins-Costa A. M. , Bray K. L. 
Published: April 2011

AbstractWe present a photoluminescence study of erbium implanted into porous silicon (Er:PSi) with two different Si porosities, a) Er:PSi with a purple appearance and b) with a green-yellow appearance. Er was implanted with a dose of 1×1015 Er/cm2 at 380 keV and annealed at 650°C for 30 minutes. Room-temperature 1.54μm Er3+ emission was observed from both samples. The emission from purple Er:PSi was four times stronger than that from green-yellow Er:PSi. In contrast, visible luminescence from green-yellow Er:PSi was found to be stronger than that from purple Er:PSi. Temperature quenching and power dependence was investigated to elucidate the excitation mechanisms of Er3+ in porous silicon. The results support a correlation between nanostructures of porous Si and 1.54 μm Er3+ luminescence.
Carrier Transport in Silicon Nanocrystallite-Based Multilayer Electroluminescent Devices
Authors: Burr T. A. , Kolenbrander K. D. 
Published: April 2011

AbstractThe electrical and optical properties of light emitting devices employing silicon nanocrystallites as the active material have been studied. Thin films of silicon nanocrystallites were deposited using a pulsed laser ablation supersonic expansion technique. In order to explore their potential for optoelectronic applications, these films have been incorporated into multilayer light emitting devices, using polymer carrier transport layers to enhance their efficiency. Device performance has been found to be weakly temperature dependent, but strongly dependent on the electrical transport properties of the material and the carrier injection mechanisms at the nanocrystal/electrode interface. A systematic study of simple electrode/nanocrystallite/electrode heterostructures has demonstrated that the electrode material and polarity of the applied bias control whether the devices operate in the interface limited or carrier transport limited regimes.
Control of Silicon Nanocrystallite Luminescence Behavior Through Surface Treatments
Authors: Seraphin A. A. , Ngiam S.-T. , Kolenbrander K. D. 
Published: April 2011

AbstractThe visible photoluminescence from thin films of silicon nanocrystallites produced by a pulsed laser ablation supersonic expansion source has been studied to determine the role of particle surface and size in the emission behavior. Variation of nanocrystallite size and surface through a variety of chemical treatments and processing steps has shown that the visible emission can be explained using only a simple quantum confinement model. Particle size has been reduced through a series of acid etch and reoxidation cycles and compared to sample emission wavelength. The role of surface species in determining emission behavior has been studied by chemically altering the surfaces and comparing their surface properties as determined by x-ray photoelectron spectroscopy to their photoluminescence behavior. Nanocrystallite size controls the emission energy, while surface passivation only determines emission intensity, through control of excited carrier recombination pathways.
Theoretical Modelling of the Surface Oxidation of a Silicon Carbide Nanopowder, Based on the v(SiH) Frequency Evolution
Authors: Baraton Marie-Isabelle , Besnainou Sylvette 
Published: April 2011

AbstractDue to hydrolysis by atmospheric water, the first atomic layer of silicon carbide contains oxygen atoms. The oxygen content on the surface dramatically increases for nanosized SiC powder and strongly affects the overall properties. The presence of SiH groups on the SiC surface, already proven by Fourier transform infrared spectrometry, can be used to investigate the oxidation mechanism. Indeed, the v(SiH) stretching frequency known to strongly depend on the surrounding electronegativity of the silicon atom is directly related to the oxidation degree. Based on our infrared spectroscopic experimental data, ab initio calculations were performed on models representing the SiH surface species in different environments. Using the Hartree-Fock method with 3–21G and 6–31G basis sets, the v(SiH) frequencies were calculated for each model versus the number of substituted oxygen atoms. The comparison with the experimental values led to a discussion of our proposed models and of the SiC surface oxidation mechanism.
Interfacial Defect Control for Infrared Conversion Widening of Silicon Single-Crystal Solar Cells
Authors: Kuznicki Z. T. 
Published: April 2011

AbstractA multi-interface solar cell design exploiting the parts of solar spectrum heretofore never converted by single-crystal silicon devices seems to be possible with local material modifications combined with a superimposition of hetero-interface transition zones. Possible structural modifications by implantation of a silicon single-crystal target causes a series of “secondary” effects of basic importance from the photovoltaic conversion point of view. The 1800 nm divacancy infrared band activity has revealed totally unknown behavior in the built-in strain field of the inserted α-Si/c-Si hetero-interface. First, even an annealing temperature of 770 K is not enough to quench the divacancy absorption. Next, the elimination of useful band-tail and useless divacancy activities is not coincident, i.e. divacancy absorption can be quenched without too much reduction of the band-tail activity. A relatively important infrared current could be observed experimentally up to 2500 nm and by extrapolation up to about 3500 nm.
Transmission Electron Diffraction Techniques for Nm Scale Strain Measurement in Semiconductors
Authors: Vanhellemont J. , Janssens K. G. F. , Frabboni S. , Smeys P. , Balboni R. , Armigliato A. 
Published: April 2011

AbstractAn overview is given of transmission electron microscopy techniques to address strain with nm scale spatial resolution. In particular the possibilities and limitations of (large angle) convergent beam electron diffraction ((LA)CBED) and electron diffraction contrast imaging (EDCI) techniques are discussed in detail. It will be shown by a few case studies that unique and quantitative information on local strain distributions can be obtained by the combined use of both (LA)CBED and EDCI in correlation with three dimensional finite element simulations of the strain distributions in the thinned specimen.
Analysis of Localized Small Defect in ULSIs
Authors: Fukumoto K. , Maeda H. , Mashiko Y. , Sekine M. , Koyama H. 
Published: April 2011

AbstractThe current leakage generated in a localized area that creates a more serious problem to the ULSI devices was investigated. To clarify the origin of such a current leakage generated at a localized small area, an evaluation technique with a high spatial resolution, high sensitivity and a precise positioning is demanded. We have developed the planar point TEM(Transmission Electron Microscope) technique to enable the structure analysis of a localized small area in ULSI devices. Using this technique and AEM(Analytical Electron Microscope), we revealed one cause of current leakage at a small area in a memory device. It was found that one origin of such leakage is caused by heavy metal precipitation on the localized dislocation. The origin of this dislocation generation is a combination of effects from the crystalline damage during the formation of the oxide sidewall spacer by dry etching and the stresses from the oxide sidewall spacer and the field oxide.
Nanocrystallization Studies in Co and Fe-Rich Amorphous Alloys
Authors: Aburto S. , Jiménez M. , Gómez R. , Marquina V. , Marquina M. L. , Ridaura R. , Santiago P. , Rendon L. , Valenzuela R. 
Published: April 2011

AbstractNanocrystallization from Metglas® 2605 SC and Vitrovac® amorphous ribbons were studied by Mössbauer spectroscopy, transmission electron microscopy and differential scanning calorimetry. The spectra showed spin texture. The relative intensities change to a random distribution of spin orientation. New lines appear indicating new magnetic phases. TEM and DSC observations confirmed the crystallization of nanostructured grains.
Evaluation Of Reaction Dynamics Of Film Depositions In Plasma Cvds By Using A Remote Plasma Cvd System
Authors: Wickramanayaka S. , Kitamura K. , Nakanishi Y. , Hatanaka Y. 
Published: April 2011

Abstractdetailed study was carried out in investigating the chemical reaction scheme involved with the deposition of a-SiC:H films by carbosilane sources in a remote hydrogen plasma. As the carbosilane sources, tetramethylsilane (TMS), hexamethyldisilane (HMDS) and tetrakis(trimethylsilyl)silane (TMSS) were used. Depositions were performed in the presence and absence of both UV radiation and H radicals. UV radiation activates only the TMS molecules out of the above three types of molecules in depositing a-SiC:H films. Other two monomers are seen to be activated by hydrogen radicals. It is proposed that the most susceptible bond to be broken at first by hydrogen radical is the Si-Si bond. A reaction model for the formation of a- SiC:H films was presented by considering the Me2Si=CH2 as the film forming precursor.
Diagnostics And Control Of High-Density Etching Plasmas
Authors: Sugai H. , Nakamura K. , Ahn T. H. , Nakamur M. 
Published: April 2011

AbstractAdvanced diagnostics of high-density inductively coupled plasmas (ICPs) are presented supporting the following three proposals of innovative etching modes: First, pulsed plasma etching mode can suppress charge-up on high-aspect-ratio micro-patterns. In order to understand the mechanism, time-resolved measurements of electrons, chlorine atoms and negative ions in a pulsed chlorine ICP are performed. As a result of electron cooling and negative ion yield in afterglow, electrons are found to be accelerated toward a rf-biased electrode, thus neutralizing positive surface charges on that. Second, downstream etching mode using C4F8 gas enables high etch selectivity of SiO2 to Si. The reason for this is qualitatively discussed using comprehensive measurements of spatial distributions of CF3, CF2, CF and F densities in CF4 and C4F8 plasmas. Third, hot wall etching mode also enables high selectibity etching in fluorocarbon plasmas. Radical diagnostics reveal that wall heating dramatically modifies the radical composition of both CF4 and C4F8 plasmas, and it improves the etch selectivity and reproducibility.
Characterization of Materials and Devices by Near-Field Scanning Optical Microscopy
Authors: Goldberg B. B. , Ghaemi H. F. , Ünlü M. S. , Herzog W. D. 
Published: April 2011

AbstractNear field scanning optical microscopy (NSOM) is a recent technique where a tapered single-mode optical fiber probe is scanned over a sample surface at a height of a fraction of the wavelength. The tapered fiber provides a tiny aperture (a, ˜ 70nm) through which light is coupled and can yield resolutions as high as ˜, λ/40. We have used both room and low-temperature NSOM to study the local spectroscopic characteristics of a wide variety of material systems, from quantum dots and wires, to ordered GaInP, to heterojunctions and optoelectronic devices.Low temperature near-field photoluminescence spectroscopy was used to study spectral emission maps of a set of samples of GaInP epilayers with varying degrees of ordering. The samples exhibit two peaks, a low energy (LE) and a high energy (HE) peak. Our data are inconsistent with expectations that the LE peak is due to emission from domain boundaries and alternative models will be discussed. NSOM spectral maps can yield information about the spatial dependence of the local optical matrix elements. NSOM data on the emission mode structure of strained (In, Ga)As quantum well lasers has yielded new information on the source kinks in the light response at high currents, while local photocurrent spectroscopy using the tip as a point source of photons provides analysis of the semiconductor layer composition.
Lineshape Analysis of Intersubband Transitions in Multiple Quantum Wells
Authors: Gumbs G. 
Published: April 2011

AbstractConduction intersubband transitions between the ground and first excited states in Al0.3Ga0.7As/GaAs multiple quantum wells (MQWs) are studied as a function of the twodimensional electron gas density (0.75 × 1012 ≤ σ ≤ 3.75 × 1012 cm−2) and temperature (5 ≤ T ≤ 300 K). There is no electron tunneling between the wells and well regions are uniformly doped with silicon donors. Theoretically, we have solved the Schrödinger equation containing the self-consistent Hartree potential, in which the z-dependencies of both electron effective mass and dielectric constant, as well as the non-parabolicity in the conduction energy subband dispersion have been taken into consideration. By applying many-body theory which includes the depolarization-shift from a collective dipole moment and the excitonicshift from the negative exchange interaction, we calculate the absorption spectrum as a function of the incident photon energy hw for different values of T and σ. From this, we can quantitatively analyze both T- and σ-dependencies of the peak position and the full width at half-maximum (FWHM) of peak values. The blue-shift or red-shift in the absorption peak position are quantitatively reproduced as either T or σ is reduced. The exchange interaction which depends on σ, will modify the energy subband dispersion. Therefore, the absorption peak will be broadened by the exchange interaction. The T-dependence of broadening from the optical-phonon scattering is also taken into account by a phenomenological model. From the calculated absorption spectrum as a function of o, we have successfully reproduced and explained the σ-dependence of FWHM measured in recent experiments.
Reflectivity Difference Spectra of GaAs and ZnSe (100) Surfaces
Authors: Kim C. C. , Sivananthan S. 
Published: April 2011

AbstractUsing a photoelastic modulator in the optical-bridge configuration, the reflectivity difference was obtained for GaAs and ZnSe (100) surfaces over the photon energy range from 1.5 eV to 6 eV with various azimuthal orientations of the surface. The RD data of GaAs (100) are similar to previously reported data. The RD data of ZnSe (100) are larger by an order of magnitude than those of GaAs (100), possibly due to the larger ionicity of Zn and Se atoms. The distinctive critical point structures and interference patterns shown in the RD spectra of ZnSe (100) suggest that the data, if obtained in real time, could be used to determine the alloy composition, thickness and temperature during growth. The RD data are analyzed using models proposed by Aspnes. The results indicate that the major contribution to the RD spectra of ZnSe (100) are from the surface local field unlike the RD spectra of GaAs (110), whose major contribution is from the bulk spatial distribution.
Optical and Electrical Characterisation of Plasma Processed N-GaAs
Authors: Murtagh M. , Herbert P. A. F. , Kelly P. V. , Crean G. M. 
Published: April 2011

AbstractA Photoreflectance (PR), Photoluminescence (PL), Raman scattering and Ellipsometry optical characterisation study of He and SiCl4 reactive ion etched 1018cm−3 n-type GaAs is presented. Ellipsometric and PL data reveal significant modifications to the GaAs substrates for the He plasma as a function of etch power and etch gas pressure. Raman data reveal an increase in the depletion depth while the surface electric field data, extracted from PR spectra, decrease with etch severity. This is accounted for by a plasma etch induced decrease in the near surface net carrier density. Ellipsometric and PL measurements of SiCl4 etching reveal evidence of an improvement in the GaAs surface crystallinity while PR and Raman data are consistent with an increase in the surface carrier concentration. Optical characterisation data are correlated with electrical measurements using capacitance-voltage profiling.