bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optical and Structural Properties of InAs/GaSb Nanostructures
Authors: Stokes D.W. , Li J.H , Forrest R.L. , Ammu S.L. , Lenzi J.C. , Moss S.C. , Nosho B.Z. , Aifer E.H. , Bennett B.R. , Whitman L.J. 
Published: April 2011

ABSTRACTThe nanostructures self-organized via lateral composition modulation in 140 period (InAs)13/(GaSb)13 superlattices grown by molecular beam epitaxy have been studied by highresolution x-ray diffraction and infrared absorption. Three samples were analyzed in this study; two with lateral composition modulation and one without. X-ray reciprocal space map scans were taken to determine the average morphology of the modulated structures. Both vertical and lateral satellite peaks were observed for the samples with composition modulation, indicating the formation of two-dimensional nanowire arrays. The vertical wavelength measured for the two samples was twice the period intended by the growers. This is due to the face-centered cubic type stacking of the nanowires. Infrared absorption spectra of these two samples were compared to the spectra of the sample with no lateral composition modulation. Transitions involving the heavy- and light-hole bands in the GaSb hole quantum well and the electron subbands of the InAs electron quantum well were not evident for the samples with lateral composition modulation, indicating that the nanostructure of the lateral composition modulation affects the optical response of the sample, which is important for optoelectronic device applications.
Subwavelength Structured Optical Elements and Resonant Grating Filters
Authors: Kikuta Hisao , Iwata Koichi 
Published: April 2011

ABSTRACTWe developed several optical elements with subwavelength-structured surfaces. Antireflection surfaces were fabricated on a diffraction grating. A micro-retarder array realized by the form-birefringent effect has been made for an application to a polarization camera system. And we developed narrow-band reflection wavelength filters called “guided-mode resonant grating filters”. This filter bases on a coupling of guided mode and radiation mode. After describing some examples of the filters, we mention a grating structure for an optical switch with nonlinear optical material.
Jahn-Teller Effect In Photonic Crystals
Authors: Malkova Natalia , Gopalan Venkatraman 
Published: April 2011

ABSTRACTThe Jahn-Teller effect in photonic crystals as a prototype of photon-phonon interactions is studied. We are interested in removing the degeneracy of a defect state due to coupling with vibronic mode. Two-dimensional square photonic lattice of the dielectric rods in vacuum doped by the defect rod, giving the doubly degenerate E state in the first TM band gap is studied. We show that coming from the Jahn-Teller theorem, the lattice vibration with the symmetry of B1 and B2 modes should result in splitting the degeneracy of the E photon state, the lattice vibration being frozen. The stable configuration in the presence of the Jahn-Teller effect is determined from the dependence of the energy as a function of the rod displacement. Using the value of the vibronic constants, obtained from the suppercell plane wave calculations and the Finite Difference Time Domain simulations, we find the stable configuration of the lattice. We discuss the conditions to observe the effect.
Standing Wave Reflectivity in Photonic Structures Using a Scattering Type Optical Near-Field Optical Microscope
Authors: Bruyant A. , Aubert S. , Lérondel G. , Blaize S. , Bachelot R. , Royer P. , Minier V. 
Published: April 2011

ABSTRACTA method for measuring locally the normalised reflectivity spectrum in waveguiding photonic structures is presented. The latter is obtained by imaging the standing wave pattern upstream of the structure with a scattering type Scanning Near-field Optical Scanning Microscope (s-SNOM) and normalised with a simple Fourier analysis. Two kinds of sample are investigated. The first one is a corrugated integrated waveguide, the second is a fiber Bragg grating. The s-SNOM technique applied to waveguiding structures is first introduced with the case of a straight waveguide.
Creation and Optical Property of Microphotonic Crystals by Electrophoretic Deposition Method Using Micro-counter Electrode
Authors: Hamagami Jun-ichi , Hasegawa Kazuhiro , Kanamura Kiyoshi 
Published: April 2011

ABSTRACTIn order to create micrometer-scale functional optical materials or devices, we have investigated on development of a novel electrophoretic deposition (EPD) method using a microelectrode as a counter electrode: This is so-called “μ-EPD method”. The μ-EPD method was applied to fabricate micro colloidal crystals consisting of monodisperse submicron polystyrene latex spheres for micro photonic application. Scanning electron micrographs of the deposit prepared under the optimized μ-EPD parameters showed a formation of microdot consisting of three-dimensionally ordered polystyrene spheres. As a result of the microscopic transmittance spectra, the microdots exhibited a narrow absorption peak and the optical stopband was observed at 460 nm for 204 nm polystyrene spheres, 675 nm for 290 nm polystyrene spheres, and 755 nm for 320 nm polystyrene spheres, respectively. The observed position is due to the Bragg diffraction of light from (111) plane of face-centered cubic opal lattice.
Anodization Time Dependent Photoluminescence Intensity of Porous Silicon
Authors: Islam Md. N. , Kumar Satyendra 
Published: April 2011

ABSTRACTThe photoluminescence (PL) intensity first increases with anodization time (ta) and then decreases at very large ta. The increase in PL intensity with ta may be understood if the PL intensity is taken to be proportional to the effective volume of porous silicon (PS) layer under the probe laser beam. The effective volume of PS layer will be proportional to its thickness and reciprocal to the porosity. For a fixed anodization condition, the thickness and porosity both increase with ta. The increase in thickness increases the effective PS volume, while the increase in porosity causes the effective volume to decrease. Therefore, the intensity variation is governed by these two parameters: thickness and porosity. The observed results suggest that the thickness dominates the PL intensity initially and then the porosity becomes more important for very long ta. The PS layers prepared under ambient light illumination also exhibited the similar behaviour. The intensity variation with ta was explained as the interplay of thickness and porosity variations with ta.
Room temperature 1.3–1.55 μm laser-like emission from Ge/Si self-assembled islands in Si-based photonic crystals
Authors: Lourtioz J-M. , David S. , El Kurdi M. , Kammerer C. , Li X. , Sauvage S. , Chelnokov A. , Le Thanh V. , Bouchier D. , Boucaud P. 
Published: April 2011

ABSTRACTExperimental results are reported on various guided optic configurations that combine silicon-based photonic crystals (PC) and Ge/Si quantum island emitters. The feasibility of low-refractive-index-contrast PC waveguides by inductively-coupled-plasma (ICP) etching of buried SiGe/Si waveguides is briefly recalled from a previous work. The main body of the paper is focused on experiments that were carried out on the high-refractive-index-contrast silicon-on-insulator (SOI) system. Self-assembled Ge/Si quantum island layers were deposited on a SOI substrate that was further processed to get two-dimensional PC microcavities and waveguides. The room temperature 1.3–1.55 μm emission from Ge/Si islands is shown to be significantly enhanced in PC microcavities, the strongest enhancement being obtained with the smallest (micropillar-like) cavities surrounded by wide pores. In this latter case, the room-temperature photoluminescence amplitude is more than two-orders of magnitude larger than that of Ge/Si islands grown in unprocessed samples. A superlinear (laser-like) dependence with the optical pumping is observed in the same time. This behavior and other experimental trends would incriminate both a high carrier concentration of the photo-created electron-hole plasma and a good vertical coupling efficiency of the micro-structured silicon. A first attempt to characterize linear PC waveguides is also reported using the wideband luminescence of Ge/Si islands embedded in the guides.
Study of the Structural Transformation of Ge2Sb2Te5 Induced by Current Pulse in Phase Change Memory
Authors: Zhao Rong , Chong Tow Chong , Shi Lu Ping , Tan Pik Kie , Meng Hao , Hu Xiang , Li Ke Bin , Du An Yan 
Published: April 2011

ABSTRACTThe electrical induced structural transformation of Ge2Sb2Te5 thin film in phase change memory device was investigated using micro-Raman spectroscopy and transmission electronic microscopy (TEM). Selected area electron diffraction (SAD) pattern showed that the electrical-induced Ge2Sb2Te5 film was crystallized into a face-centered cubic structure. Micro-Raman spectra show that the Ge2Sb2Te5 active layer at the high resistance state exhibited two minor peaks superposed on the broad peak after several switch cycles, which is identical to those of the Ge2Sb2Te5 active layer at the low resistance state. This is most likely due to the accumulation of segregated crystallites. TEM results suggest that the existence of nano-sized nuclei clusters resulted in the reduced resistance for the Ge2Sb2Te5 active layer at the high resistance state after first several switches. The dependence of resistance on the cycle number indicates that the deterioration of the Ge2Sb2Te5 active layer is resulted from the incomplete amorphization process, which is consistent with the micro-Raman results.
Effect of Ionic Bond in Recording Materials on Characteristics of Phase-Change Optical Disk
Authors: Terao Motoyasu 
Published: April 2011

ABSTRACTThis paper discusses a crystallization model that takes difference of covalent bond and ionic bond into consideration. Ionic bond makes crystallization easier than covalent bond because ionic bond is more flexible than covalent bond. The diameter and spaces around large minus-ions should also be taken into consideration. Elements••having electronic negativity far from that of Te or Sb has a tendency to form ionic bonds. For example, Tb and In are considered to make chemical bonds having more ionic characteristics than Ge. In the case of already reported Sn or Bi addition, large ion diameter seems to increase crystallization speed.
Characterization of Ultra-Fast Phase Change Optical Disk with GaSb Material
Authors: Ito Kazunori , Tashiro Hiroko , Harigaya Makoto , Suzuki Eiko , Tani Katsuhiko , Yiwata Noriyuki , Toyoshima Nobuaki , Kitano Akiko , Kato Kenichi 
Published: April 2011

ABSTRACTWe studied the crystallization mechanism of ultra-fast phase change optical disks with recording layers made of GaSb material for digital versatile disk (DVD) systems. The results of a static recording test and an amorphous mark formation simulation suggest that GaSb maintains a high crystal growth rate even at temperatures 150 degrees lower than the material's melting point. Disks with recording layers made of this material have a write speed margin ranging from DVD 3× to 8× or more.
A Study of Magnox Waste Glass Under Conditions of High Temperature, Very Deep, Geological Disposal
Authors: Hyatt Neil C. , Taylor Kathleen J. , Gibb Fergus G.F. , Lee William E. 
Published: April 2011

ABSTRACTThe behaviour of a simulant Magnox waste glass was investigated under the likely conditions of high temperature, very deep, geological disposal, viz. 760°C and 0.15GPa. Under these conditions partial crystallisation of the glass is observed with the formation of LnBSiO5 (Ln = Y, La, Pr, Ce, Nd, Sm and Gd), LiNaZrSi6O15 and a palladium (ruthenium) telluride phase. The significance of these findings is discussed in the context of the high temperature, very deep, geological disposal scheme.
Thermochemical Investigations of Zirconolite, Pyrochlore and Brannerite: Candidate Materials for the Immobilization of Plutonium
Authors: Helean K. B. , Navrotsky A. , Lian J. , Ewing R. C. 
Published: April 2011

ABSTRACTStandard enthalpies of formation, ΔH°f (kJ/mol) at 298 K, were derived for three pyrochlore phases: Ca0.93Ce1.00Ti2.035O7.00 (−3656.0±5.6), Ca1.46U4+0.23U6+0.46Ti1.85O7.00 (−3610.6±4.1), Gd2Ti2O7 (−3822.5±4.9) and two zirconolite phases: CaZr1.03Ti1.97O7 (−3719.4±3.9) and CaHf1.02Ti1.98O7 (−3720.5±3.9). Enthalpies of formation with respect to an oxide phase assemblage, ΔH°f-ox (kJ/mol) at 298 K: CaO + MO2 + 2TiO2 = CaMTi2O7 or Gd2O3 + 2TiO2 = Gd2Ti2O7, and an oxide/perovskite phase assemblage: ΔH°f-pv+ox (kJ/mol) at 298 K: CaTiO3 + MO2 + TiO2 = CaMTi2O7, M = Ce, U, Hf, Zr were also calculated. All of the pyrochlore and zirconolite materials studied were stable in enthalpy with respect to their oxides. ΔH°f-ox: Ca0.93Ce1.00Ti2.035O7.00 (−54.1±5.2), Ca1.46U4+0.23U6+0.46Ti1.85O7.00 (−123.1±3.4), Gd2Ti2O7 (−113.4±2.8), CaZr1.03Ti1.97O7 (−89.6±2.8) and CaHf1.02Ti1.98O7 (−74.8±3.1). With respect to a perovskite plus oxide phase assemblage the hafnium zirconolite was marginally metastable in enthalpy (ΔH°f-pv+ox = +6.0±3.5 kJ/mol) while zirconolite was marginally stable in enthalpy (ΔH°f-pv+ox = −8.8±3.3 kJ/mol). The Ce-pyrochlore was not thermodynamically stable as measured by the enthalpy change relative to perovskite plus oxides: ΔH°f-pv+ox = Ca0.93Ce1.00Ti2.035O7.00 (+21.0±5.5). The U-pyrochlore sample was marginally stable in enthalpy relative to a perovskite plus oxide assemblage: ΔH°f-pv+ox = Ca1.46U4+0.23U6+0.46+Ti1.85O7.00 (−5.1±4.0). A significant field where the proposed waste form for excess weapons plutonium is not thermodynamically stable both at room temperature and at high temperature was defined.ΔH°f (kJ/mol) at 298 K were derived for three brannerite phases: CeTi2O6 (−2948.8±4.3), U0.97Ti2.03O6 (−2977.9±3.5) and ThTi2O6 (−3096.5±4.3). Enthalpies of formation with respect to an oxide phase assemblage, ΔH°f-ox (kJ/mol) at 298 K: MO2 + 2TiO2 = MTi2O6, M = Ce, U, Th were also calculated. ΔH°f-ox: CeTi2O6 (+29.4±3.6), U0.97Ti2.03O6 (−7.7±2.8) and ThTi2O6 (+19.4±1.6). Thus, Ce and Th-brannerite are entropy stabilized and thermodynamically stable only at high temperature.These thermochemical data are correlated to the observed trends in the radiation “susceptibility” of these phases. Thermodynamic data relevant to waste form processing and optimization are also discussed.
A Generic Procedure for the Assessment of the Effect of Concrete Admixtures on the Sorption of Radionuclides on Cement: Concept and Selected Results
Authors: Glaus M. A. , Laube A. , Van Loon L. R. 
Published: April 2011

ABSTRACTA screening procedure is proposed for the assessment of the effect of concrete admixtures on the sorption of radionuclides on cement. The screening procedure focuses on a broad and generic assessment and can thus be used as a tool for the assessment of concrete admixtures possibly used in the future. The experimental feasibility of the screening procedure and the relevance of the results obtained are tested using a selection of superplasticisers and set modifiers. Selected results obtained for these admixtures are presented in this contribution.
Modelling Experimental Results on Radiolytic Processes at the Spent Fuel Water Interface. I. Radiolysis Products and U Release
Authors: Bruno J. , Cera E. , Eriksen T. E. , Grivé M. , Ripoll S. 
Published: April 2011

ABSTRACTExperimental and modelling efforts in the last decade in the frame of nuclear waste management field have been focused on studying the role of the UO2 surfaces in poising the redox state of solid/water systems. For this purpose, an experimental programme was developed consisting on dissolution experiments with PWR spent fuel fragments in an anoxic environment and by using different solution compositions.The collected data so far, indicate that production and fate of radiolysis products follow the same trends independently on the solution composition used in the tests. Hydrogen and oxygen concentrations show an initial increase with time until reaching a constant concentration. The trend observed for hydrogen peroxide is a decrease at short contact times to reach again a constant concentration with time. These steady-states indicate an overall balance of the generated radiolytic species.Modelling work indicates that uranium dissolution is controlled by the oxidation of the spent fuel matrix in 10mM bicarbonate solutions while in the tests carried out at lower or without carbonate concentrations uranium in the aqueous phase is governed by the precipitation of schoepite.These results are determinant to highlight that reducing conditions are restored in the aqueous phase in relatively short periods of time and at short distances away from the dynamic redox spent fuel/water interface.
Corrosion Behavior of Pre-oxidized High Burnup Spent Fuel in Salt Brine
Authors: Loida Andreas , Kienzler Bernhard , Geckeis Horst 
Published: April 2011

ABSTRACTDuring long-term interim storage of spent fuel, pre-oxidation of the UO2-matrix may not be ruled out completely. This can happen if air could find access to the fuel in the case of cladding failure. The aim of this work is to study the impact of pre-oxidation of the fuel surface on the UO2 matrix dissolution rate and the associated mobilization or retention of radionuclides in highly concentrated salt solutions. The tests were performed with samples that suffered pre-oxidation during up to seven years. The dissolution rate of a fuel sample contacted by small quantities of air-oxygen was found to be roughly a factor of 10 higher in comparison to non oxidized samples, but concentrations of radionuclides, especially Pu and U were hardly affected. The majority of dissolved radionuclides, especially Pu, U appear to have been reimmobilized on the fuel sample itself.
Solubility Measurement of Iron-Selenium Compounds under Reducing Conditions
Authors: Kitamura Akira , Shibata Masahiro , Kitao Hideo 
Published: April 2011

ABSTRACTChemical behavior of selenium (Se), which was one of the important elements for performance assessment of geological disposal of high-level radioactive waste, was investigated under reducing and iron-containing conditions. A washing method for an iron diselenide (FeSe2(cr)) reagent with acidic and basic solutions was carried out for the purification of FeSe2(cr) reagent, which was considered to be a solubility limiting solid for Se under the geological disposal conditions. Furthermore, solubility of FeSe2(cr) was measured in alkaline solutions under reducing conditions, and thermodynamic data on equilibrium reactions between Se in solution and Se precipitate were obtained. It was found that the dependencies of solubility values on pH and redox potential (Eh: vs. standard hydrogen electrode) were best interpreted assuming that the solubility limiting solid was not FeSe2(cr) but Se(cr) and the aqueous species was SeO32- in the present experimental conditions. The equilibrium constant between Se(cr) and SeO32- at zero ionic strength was determined and compared with literature values. The chemical behavior of Se under geological disposal conditions was discussed.
EC GASNET Project: Gas Issues in the Safety Assessment of Deep Repositories for Nuclear Waste
Authors: Cool Wim , Cuñado Miguel , Johnson Lawrence , Mäntynen Mia , Müller Wolfgang , Norris Simon , Rodwell William , Sellin Patrik , Snellman Margit , Talandier Jean , Vieno Timo , Vines Sarah 
Published: April 2011

ABSTRACTGASNET is a “thematic network” project supported by the European Commission. Its objectives are to evaluate the present treatment in safety assessments of issues arising from the generation of gas in deep geological repositories for nuclear waste, and to improve the translation of scientific information on these issues into safety arguments for such repositories.An overview is provided of the work that has been undertaken within the project and of the preliminary observations and conclusions that have been assembled.
Modelling the Release of Radionuclides from the Spent Fuel and their Transport in the Near Field: a Coupled Approach
Authors: Merino Juan , Cera Esther , Bruno Jordi , Martínez-Esparza Aurora 
Published: April 2011

ABSTRACTIn this work we have developed a model for the release of radionuclides from the spent fuel coupled with their transport through the near field. A compartmental approach has been used, as this methodology is well suited to model integrated systems. Several processes have been taken into account: oxidative dissolution of the spent fuel matrix, radioactive decay and chains, diffusive and advective transport, retardation by sorption and secondary phase precipitation. Results illustrate the complex evolution of the radionuclide concentrations in the gap and the near field. Hence, the main conclusion from this study is the requirement to model this coupled system using a compartmental integrated approach.
Model for the Microbiological Corrosion of Copper Containers in a Deep Geologic Repository
Authors: King Fraser , Kolar Miroslav , Stroes-Gascoyne Simcha , Maak Peter 
Published: April 2011

ABSTRACTA model has been developed to predict the impact of microbiological processes on the long-term corrosion behaviour of copper containers in a deep geologic repository. The model accounts for a range of aerobic and anaerobic microbial processes. Various factors expected to limit the extent of microbial activity in the repository, such as the lack of water, evolving redox conditions, and the nutrient-poor environment, are taken into account in the model. Amongst other effects, the model predicts that microbial activity will not occur close to the container in the presence of highly compacted bentonite buffer material.
Mineralogy and some Physical Properties of the San José Bentonite - A Natural Analogue to Buffer Material Exposed to Saline Groundwater
Authors: Karnland Ola , Sellin Patrik , Olsson Siv 
Published: April 2011

ABSTRACTBentonite clay has an important buffer function in several of the proposed systems for nuclear waste repositories. Some proposed repository locations have significant concentration of sodium and calcium chloride in the ground-water, and others may be under sea-level for part of their life-time. A crucial question is consequently if there will be any long term effects on the stability of clay minerals due to exposure to saline conditions and thereby also on the desired physical properties.In the present study we used material from a small bentonite habitat at San José, southeastern Spain, as a natural analogue to a bentonite buffer exposed to high saline ground-water. The composition of the bentonite material was determined by use of XRD, ICP/AES, and cation exchange capacity (CEC) analyses both of bulk material and of fine fraction. The important physical properties swelling pressure and hydraulic conductivity were measured for a range of densities and NaCl concentrations. The observed smectite structure and the measured properties of the San José bentonite were similar to those found in Wyoming bentonite and no obvious effects of the harsh saline environment were observed.
MEMS Microresonators Based on Nanocrystalline Silicon
Authors: Gaspar J. , Adrega T. , Chu V. , Conde J. P. 
Published: April 2011

ABSTRACTThis paper describes the fabrication and characterization of thin-film nanocrystalline silicon microresonators processed at temperatures below 110°C on glass substrates. The microelectromechanical structures consist of surface micromachined bridges of boron-doped hydrogenated nanocrystalline silicon (p+-nc-Si:H) deposited at 100°C by hot-wire chemical vapor deposition (HWCVD). The microbridges, which are suspended over an Al gate electrode, are electrostatically actuated and the mechanical resonance is detected in vacuum using an optical setup. The resonance frequency and energy dissipation in p+-nc-Si:H based resonators are studied as a function of the geometrical dimensions of the microstructures. Resonance frequencies between 700 kHz and 36 MHz and quality factors as high as 2000 are observed. A Young's modulus of 160 GPa for the structural bridge film is extracted from the experimental data using an electromechanical model and the main intrinsic energy dissipation mechanisms in nc-Si:H microresonators are discussed.