bluuebunny/crossref_metadata_2025 huggingface dataset:
Diffusion Behavior of Iron Corrosion Products In Buffer Materials
Authors: Idemitsu Kazuya , Yano Seiji , Xiaobin Xia , Inagaki Yaohiro , Arima Tatsumi , Mitsugashira Toshiaki , Hara Mitsuo , Suzuki Yoshimitsu
Published: April 2011

Carbon steel is one of the candidate overpack materials for high-level waste disposal and is expected to assure complete containment of vitrified waste glass during an initial period of 1000 years in Japan. The lifetime of the carbon steel overpack will depend on its corrosion rate. The corrosion rate of carbon steel is reduced by the presence of buffer material such as bentonite. Buffer material will delay the supply of corrosive materials and discharge of corrosion products through it. Carbon steel overpack will be corroded by consuming oxygen introduced by repository construction after closure of repository and then will keep the reducing environment in the vicinity of repository. The reducing condition will be expected to retard the migration of redox-sensitive radionuclides by lowering their solubilities. Therefore, the diffusion of corrosion products of iron in buffer material is important to discuss the corrosion rate of overpack, migration of redox-sensitive radionuclides and properties of buffer material. The purpose of this paper is to study diffusion behavior of a corrosion product of iron in compacted bentonites under a reducing condition with a carbon steel. The diffusion mechanism of iron in the compacted bentonites were discussed by estimation of iron species in the bentonite pore water. There were two diffusion paths of iron in the compacted bentonites used in this study; the fast path has low capacity of iron, ca. 1wt%, and large apparent diffusion coefficient, ca. 10−12m2/s and the slow path has high capacity of iron, ca. 10wt%, and small apparent diffusion coefficient, ca. 10−14m2/s.
Origins of Discrepancies Between Kinetic Rate Law Theory and Experiments in the Na2O-B2O3-SiO2 System
Authors: McGrail B. P. , Icenhower J. P. , Rodriguez E. A.
Published: April 2011

Discrepancies between classical kinetic rate law theory and experiment were quantitatively assessed and found to correlate with macromolecular amorphous separation in the sodium borosilicate glass system. A quantitative reinterpretation of static corrosion data and new SPFT data shows that a recently advanced protective surface layer theory fails to describe the observed dissolution behavior of simple and complex silicate glasses under carefully controlled experimental conditions. The hypothesis is shown to be self-inconsistent in contrast with a phase separation model that is in quantitative agreement with experiments.
Leaching of Np and Tc From Doped Nuclear Waste Glasses in Clay Media: The Effects of Redox Conditions
Authors: Pirlet Véra , Lemmens Karel , Iseghem Pierre Van
Published: April 2011

Boom Clay is the candidate geologic formation in Belgium for disposal of vitrified high level waste. In the waste glass, 237Np and 99Tc are some of the principal radionuclides. The leaching behaviour of these nuclides has been studied in dissolution tests involving glass doped with 237Np and 99Tc and was found to depend strongly on the redox conditions of the media contacting the glass. Static tests with the reference R7T7 glass and the reference PAMELA SM539 glass were performed in two clay media that may interact with the glass during the geological disposal. The first test medium consisted of FoCa-clay (Fourges-Cahaignes-clay), which is an oxidised clay. The second test medium was a mixture of backfill material, consisting mainly of FoCa-Clay, with metal corrosion products and Boom Clay. Lower Np and Tc concentrations were found in Boom Clay compared to FoCa-clay. In FoCaclay, Np and Tc were predominately in their oxidised form. Although Tc is mostly present in the soluble pertechnetate form, the Np concentrations are lower than expected for the chemistry of Np(V) in the medium. The concentrations of the radionuclides are steady-state concentrations rather than thermodynamic concentrations. Different mechanisms can be invoked to explain these Np concentrations. In Boom Clay, the measured Np concentrations are close to the solubility limit whereas the Tc concentrations are slightly higher than those calculated in Boom Clay at thermodynamic equilibrium. The initial specific activity of the radionuclide in the glass was found to influence the soluble concentration. Np and Tc were not found to be retained in the glass reaction layer for both media.
Corrosion Tests of Lwr Fuels – Nuclide Release
Authors: Finn Patricia A. , Tsai Yifen , Cunnane James C.
Published: April 2011

Two high burnup BWR fuels [64 and 71 (MWd)/kgU], one of which contained 2% Gd, and two low burnup PWR fuels [30 and 45 (MWd)/kgU], are tested by dripping groundwater on the fuel under oxidizing and hydrologically unsaturated conditions for 2.4 and 8.2 yr, respectively, at 90°C. The 99Tc, 129I, 137Cs, 97Mo, and 90Sr releases are presented to show the effects of reaction time and of gadolinium (Gd) on nuclide release. For the PWR fuels, the five nuclides have similar fractional release rates at 8.2 yr. For the BWR fuels, the presence of 2% Gd reduced the 99Tc cumulative release fraction after 2.4 yr by about an order of magnitude from that of a fuel with a similar burnup but without added Gd.
Radiation Effects in Crystalline Oxide Host Phases for the Immobilization of Actinides
Authors: Weber William J. , Ewing Rodney C.
Published: April 2011

Radiation effects from alpha-decay events in crystalline oxides, which are proposed for the immobilization of actinides, often lead to amorphization, macroscopic swelling and order-of-magnitude increases in dissolution rates for all of the phases currently under consideration. However, the results of systematic experimental studies using short-lived actinides and ion-beam irradiations, studies of radiation effects in U- and Th-bearing minerals, and the development of new models of the damage process over the past 20 years have led to a substantial increase in the understanding of the processes of damage accumulation in apatite, zircon, perovskite, zirconolite, and pyrochlore/fluorite structures. This fundamental scientific understanding now provides a basis for predicting the performance of nuclear waste forms in a radiation field. One of the recent successes of these studies has been the discovery of a class of radiation-resistant pyrochlore/fluorite structures that can serve as highly durable, radiation-resistant host phases for the immobilization of actinides.
Performance Assessment of Geological Disposal of High-level Radioactive Waste in a Plastic Clay formation
Authors: Marivoet Jan , Sillen Xavier , Mallants Dirk , Preter Peter De
Published: April 2011

In Belgium the possibilities to dispose of high-level waste in the plastic Boom Clay formation has been studied since 1975. Consequently many results of the site characterisation programme are already available. Various performance assessments have been carried out dealing with the disposal of high-level waste arising from reprocessing and with direct disposal of spent fuel. The performance assessment consists of two main steps: scenario development and consequence analyses. The scenario analysis is based on a catalogue of features, events and processes (FEPs) having the potential to influence the behaviour of the repository system. Two main groups of scenarios are distinguished. The normal evolution scenario, including a number of variants, treats the FEPs that are fairly sure to take place. Altered evolution scenarios focus on FEPs having a probability of occurrence lower than one but that might influence the performance of the repository system. For the impact analyses, a robust concept approach was introduced, which focused the analyses on a limited number of well-characterised barriers and processes. The impact analyses are complemented with sensitivity and uncertainty analyses based on deterministic and probabilistic approaches.
Molecular Dynamics Studies of Ion Distributions around DNA Duplexes and Duplex Dimers: Salt Effects and the Connection to Cooperative DNA Melting
Authors: Long Hai , Schatz George C.
Published: April 2011

We present extensive molecular dynamics simulations of DNA duplexes and duplex dimers based on the Amber force field to determine the distribution of ions as a function of salt (NaCl) concentration over the range 0.2–1.0M. Periodic boundary conditions are used to model an infinite DNA chain, and particle mesh Ewald summation is used to describe long range electrostatic interactions. We have used these simulations to determine the ion distributions associated with a 10 base pair duplex, and we find that the positive and negative ion distributions are identical for distances greater than a radius Rcounter which is on the order of 25 Å from the DNA axis, and which decreases as the bulk salt concentration is varied. Based on the calculated Rcounter, we determine the local counterion concentration as a function of bulk salt concentration. Similar studies of DNA duplex dimers separated by 30–40 Å leads to a determination of the local counterion concentration around these dimers. Here we find that dimerization leads to greatly enhanced counterion concentrations. If this information is combined with the measured results concerning the dependence of DNA melting temperature on bulk salt concentration, we find that dimerization leads to a several degree increase in melting temperature, with the increase being 10°C for a dimer separation of 30 Å. This result provides justification for a recently developed cooperative melting model of DNA duplex aggregates.
Engineered Films of Bombyx mori Silk with Poly(ethylene oxide)
Authors: Jin Hyoung-Joon , Park Jaehyung , Cebe Peggy , Kaplan David L.
Published: April 2011

Phase separation into controllable patterned microstructures was observed for Bombyx mori silkworm silk and poly(ethylene oxide) (PEO) (900,000 g/mol) blends cast from aqueous solution. Solution blending was used to incorporate water-soluble PEO into silk to enhance elasticity and hydrophilicity. The sizes of the globule fibroin phase ranged from 3.1±0.9 μm to 18.2±2.1 μm depending on the ratio of silk/PEO. Optical microscopy and SEM analysis confirmed the micro-phase separation between PEO and silk. Surface properties were determined by contact angle. The PEO can be easily extracted from the films with water to generate silk matrices with definable porosity and enhanced surface roughness. These blend films formed from two biocompatible polymers provide new potential tissue engineering scaffolds and controlled release drug delivery materials.
Human Bone Marrow Stem Cell Responses on Electrospun Bombyx mori Silk Fibroin
Authors: Jin Hyoung-Joon , Chen Jingsong , Karageorgiou Vassilis , Altman Gregory H. , Kaplan David L.
Published: April 2011

Electrospinning for the formation of nanoscale diameter fibers has been explored for high performance filters and biomaterial scaffolds for vascular grafts or wound dressings. Fibers with nanoscale diameters provide benefits due to high surface area. In this study we used electrospinning for protein-based biomaterials to fabricate scaffolds from aqueous regenerated silkworm silk, Bombyx mori,. Adhesion, spreading and proliferation of human bone marrow stem cells (hBMSCs) on electrospun silk was characterized. Scanning electron microscopy (SEM) and MTT analyses demonstrated that the electrospun silk matrices promoted hBMSC attachment and proliferation over 10 days in culture. The responses of the hBMSCs on the electrospun silk matrices, combined with the biocompatibile properties of the silk fibroin protein matrix, suggest potential for use of this biomaterial as scaffolds for tissue engineering.
Electrospinning Nanofibers of PANI/PMMA Blends
Authors: Desai Keyur , Sung Changmo
Published: April 2011

Electrically conducting organic polymers are a novel class of ‘synthetic metals’ that combine the chemical and mechanical properties of polymers with the electronic properties of metals and semiconductors. Electronically conducting polymers have been studied extensively owing to their applications in energy conversion devices, sensors, electro chromic devices, electromagnetic interference shielding (EMI), electronic circuits etc. Polyaniline - an organic conducting polymer - has been blended with poly methyl methacrylate and the blends have been electrospun to produce conducting nanofibers. The electrospun blends have been characterized to study fiber morphology and formulate conditions for nanofiber formation.
Bisperfluorophenyl-Substituted Thiophene Oligomers. Organic Semiconductors with Complementary-Type Carrier Mobility
Authors: Facchetti Antonio , Katz Howard E. , Marks Tobin J.
Published: April 2011

The design, synthesis, and properties of two mixed perfluorophenyl-thiophene oligomers 5,5″′-diperfluorophenyl-2,2′:5′,2″:5″,2″′:5″′,2″″:5″″,2″″′-quaterthiophene (2) and 5,5′-bis{1-[4-(thien-2-yl)-2,3,5,6-tetrafluorophenyl)] }-2,2′-dithiophene (3) are presented. Molecular characterization included the following techniques: multinuclear NMR, DSC and TGA, optical UV-Vis and photoluminescence spectroscopy, and cyclic voltammetry. Thin films can be easily grown by vacuum evaporation and have been characterized by optical UV-Vis and photoluminescence, XRD, and field-effect transistor measurements. Electron and hole mobilities of 0.06–0.08 cm2/(V s) and 0.001–0.003 cm2/(V s) were found for 2 and 3, respectively.
Optical properties of self-assembled InAs quantum dots grown on InAlAs/InP(001)
Authors: Salem B. , Benyattou T. , Guillot G. , Bremond G. , Brault J. , Gendry M.
Published: April 2011

Self-organized InAs quantum islands (QIs) were grown in the Stranski-Krastanov regime, by solid source molecular beam epitaxy (SSMBE), on In0.52Al0.48As layer lattice matched to InP(001) substrate. The growth parameters are chosen to produce dot shaped InAs islands as indicated by the photoluminescence (PL) linear polarization which is about 9%. The PL spectrum reveals several resolvable components. PL versus power excitation and photoluminescence excitation (PLE) measurements show clearly that this multi-component spectrum is related to emission from transitions associated to fundamental and related excited states of quantum dots (QDs) having monolayer-height fluctuations. The integrated PL intensities have been measured as a function of temperature in the 8–300 K range. The PL intensity measured at 300K is only 8 times lower than at 8 K, indicating good carrier confinement in these InAs/InAlAs QDs. An enhancement of the PL intensity in the 8–90 K temperature range has been tentatively attributed to the exciton dissociation from the InAlAs barriers which then recombine radiatively in the InAs QDs.
Patterned Structures of Silicon Nanocrystals Prepared by Pulsed Laser Interference Crystallization of Ultra-Thin A-Si:H Single-Layer
Authors: Wang Xiaowei , Qiao Feng , Zhu Leyi , Li Wei , Li Jian , Huang Xinfan , Chen Kunji
Published: April 2011

We employ the method of phase-modulated KrF excimer pulsed laser interference crystallization to fabricate nanometer-sized crystalline silicon (nc-Si) with the two-dimensional (2D) patterned distribution within the ultra-thin a-Si:H single-layer. The local crystallization occurs after interference laser irradiation under proper energy density. The results of atomic force microscopy, Raman scattering spectroscopy, cross-section transmission electron microscopy and scanning electron microscopy demonstrate that Si nano-crystallites are formed within the initial a-Si:H single-layer, selectively located in the discal regions with the diameter of 350 nm and patterned with the same 2D periodicity of 2.0 μm as the phase-shifting grating. The results show that the present method can be used to fabricate patterned nc-Si films for device applications.
Si Nanoparticle Synthesis and Self – Organization
Authors: Fowlkes J. D. , Pedraza A. J.
Published: April 2011

Si nanoparticle linear arrays have been produced by pulsed KrF laser irradiation in inert atmospheres. The Si nanoparticles have a Gaussian size distribution with a mean diameter of 2.9 nm and a FWHM of 2 nm. The self – organized lines are spaced at a distance approximately equal to the laser beam wavelength, λ. The evolution of this self – organization process and that of laser – induced periodic surface structures (LIPSS) are closely related. The nanoparticles scatter light that interferes with the incident light. Similar to LIPSS, the inhomogeneous deposition of laser light due to this interference pattern created at the surface drives the particle formation and clustering. A detailed study of the clustering formation as a function of the laser pulses is presented.
Characterization of Co-catalyzed Multiwalled Carbon Nanotubes by High-Resolution Transmission Electron Microscopy
Authors: Wang Chih-Chin , Liu Chuan-Pu , Liu Ruo-Mei , Liao Kuen-Hou
Published: April 2011

The dependence of characteristics of multiwalled carbon nanotubes (MWCNT) on the microstructure of cobalt catalysts are intensively investigated by high-resolution transmission electron microscopy (HREM). The cobalt catalysts are prepared by either molecule beam epitaxy (MBE) or by DC magnetron sputtering, followed by MWCNT growth by microwave plasma CVD. The MBE-grown Co thin films consist of large epitaxial grains, whereas the Co nanoparticles of FCC or HCP crystal structures can be directly grown on Si(001) substrates by sputtering. Various HREM technologies are applied to completely characterize the microstructures of those Co catalysts and MWCNT. The results reveal that the morphology and microstructures of MWCNT are greatly controlled by the characteristics of Co catalysts. Better quality of carbon nanotube can be grown by FCC cobalt rather than HCP cobalt. The different effects of cobalt catalysts on MWCNT are discussed in this paper.
Si Nanocrystals by Metal Induced Growth using Different Catalyzing Metals
Authors: Ji Chunhai , Anderson Wayne A.
Published: April 2011

A comparative study of nanocrystalline silicon thin films grown on 25 nm thick catalyzing metals by dc magnetron sputtering from a highly doped Si target has been performed. In our previous study, the growth of Si was catalyzed by the silicide reactant from sputtered Si and Ni. These new experiments compared the effect of two types of catalyzing metals, Ni and Co. The structural and electrical characteristics of nano-Si were examined by scanning electron microscopy (SEM), cross-section SEM (XSEM), transmission electron microscopy (TEM), four-point-probe measurement and Schottky contact I-V measurement. The SEM and XSEM revealed that, for both catalyzing metals, the nano-Si thin films have columnar nano-grains with length of 500 nm in the vertical direction. However, the diameter of grains strongly depends on the catalyzing metals. For Co, the nano-Si grains had a typical diameter of 30 nm, while for Ni, the grains were much larger. TEM analysis showed that this difference in grain size begins at the initial growth stage. In the later-on growth, the Si grains mainly grow in a vertical direction instead of a lateral direction. This implies that the dimensions of Si nanostructures are strongly determined by the initially formed metal silicide nanoparticles. The current-voltage curve of a fabricated Al Schottky diode on P-type Co catalyzed nano-Si exhibited good rectifying characteristics. The dopant has been naturally synthesized in the Si nanocrystals during the growth of nano-Si by using a doped sputtering target. The above measured electrical properties show that metal induced grown nanocrystalline Si is applicable to various electronic and photonic devices.
The Effects of Crystallinity and Catalyst Dynamics on Boron Carbide Nanospring Formation
Authors: McIlroy D. N. , Zhang D. , Kranov Y. , Han H. , Alkhateeb A. , Grant Norton M.
Published: April 2011

The formation of helical nanowires—nanosprings—of boron carbide have been observed and a growth mechanism, based on the work of adhesion of the metal catalyst and the tip of the nanowire, developed. The model demonstrates that the asymmetry necessary for helical growth is introduced when the following conditions are met:

(1) The radius of the droplet is larger than the radius of the nanowire, and

(2) The center of mass of the metal droplet is displaced laterally from the central axis of the nanowire.

Furthermore, this model indicates that only amorphous nanowires will exhibit this unique form of growth and that in monocrystalline nanowires it is the crystal structure that inhibits helical growth. High-resolution transmission electron microscopy and electron diffraction has been used to compare the structure of both amorphous and crystalline nanowires.
Synthesis of SiO2 Nanowires and CdS/SiO2 Composite Nanowires and Investigation of Their Electron Field Emission Properties
Authors: Jiao Jun , Dong Lifeng , Tuggle David W. , Petty Jeremy , Love Logan , Coulter Michael
Published: April 2011

A thermal evaporation method was used to obtain SiO2 and CdS/SiO2 nanowires by heating Si substrates coated with a gold thin film in a quartz tube furnace. During growth, pure CdS powder was placed at the heating zone in the furnace, serving as the CdS source for the CdS/SiO2 composite nanowires. It was found that both non-porous and porous Si substrates served as the Si source for the growth of SiO2 nanowires and the CdS/SiO2 composite nanowires. It was also found that the effect of the temperature gradient in the reaction chamber plays an important role in the density distribution of different nanowires (SiO2 or CdS/SiO2 nanowires). The electron field emission properties of these nanowires were investigated using an electron field emission microscope equipped with a Faraday cup.
Simple Use of SiO2 Film Thickness for the Control of Carbon Nano-Tube Diameter During Ferrocene Catalyzed CVD Growth
Authors: Chopra N. , Kichambare P.D. , Andrews R. , Hinds B. J.
Published: April 2011

Selective growth of carbon nano-tubes (CNT) on micron scale patterned substrates has been accomplished by taking advantage of the non-reactivity of ferrocene catalyst on H-terminated Si surfaces in a CVD process. Demonstrated here is that this phenomenon can be used to control the diameter of CNTs when sufficiently narrow lines of SiO2 surrounded by H-terminated Si are used. Narrow lines of SiO2 (12–60nm) are formed at the etched face of a Si/SiO2/Si multilayer structure. This allows the precisely controllable thickness of an SiO2 film to determine an exposed SiO2 line width. There is no need for e-beam lithography since film thickness determines nm-scale line dimensions. CNTs are then formed by CVD with a ferrocene/H2/Ar mixture at 700°C. CNTs are observed to grow only on the exposed SiO2 surface at the edge of the ‘mesa’ structure. CNT diameters of 13.2, 20.5, 34.2, 64.3nm are observed for SiO2 film thickness of 12, 19, 35, and 65 nm. The larger distribution of CNT diameter with increased line width is consistent with wider SiO2 linewidths not being able to affect smaller nucleation centers. These results are consistent with the use of self-assembly chemistry of iron catalyst onto nano-particles of catalyst support.
Fabrication of Perforated Film Nanostructures
Authors: Elias A. L. , Harris K. D. , Brett M. J.
Published: April 2011

We have demonstrated the fabrication of perforated thin films (PTFs), comprised of thin coatings perforated with unusual pore shapes such as helices or chevrons. PTFs are fabricated using a template of nanohelices or nanochevrons produced using the Glancing Angle Deposition (GLAD) technique. PTFs can be produced by filling GLAD films with a variety of substances, etching back the coating to reveal the tips of the helices or chevrons, and etching out the template film. A process for fabricating nickel PTFs has been developed, and a nickel PTF of helical pores with nominal diameters of 100nm has been produced.
Metal-Induced Low-Temperature Crystallization of Amorphous SiGe on Insulating Films
Authors: Miyao M. , Kanno H. , Tsunoda I. , Sadoh T. , Kenjo A.
Published: April 2011

Metal-induced low temperature (≤ 550 °C) crystallization of a-Si1-xGex (0 ≤ × ≤ 1 ) layers on SiO2 films has been investigated. For low Ge fractions below 20 %, Ge-doping enhanced plane growth was observed. This realized strain-free poly-Si0.8Ge0.2 films with large grains (18 μm). On the other hand, dendrite growth was dominant for intermediate Ge fractions with 40–60 %. Directions and widths of dendrites became straight and narrow with decreasing annealing temperature. As a result, very sharp needlelike crystals (width: 0.05 μm, length: 10 μm) were obtained at the optimized growth conditions (x: 0.4, annealing: 450 °C, 20 h). These new polycrystalline SiGe films on insulators should be used for the advanced system-in-displays and novel one-dimensional wires.
Implant isolation of ZnO epitaxial layers
Authors: Kucheyev S. O. , Jagadish C. , Williams J. S. , Deenapanray P. N. K. , Yano Mitsuaki , Koike Kazuto , Sasa Shigehiko , Inoue Masataka , Ogata Ken-ichi
Published: April 2011

The formation of highly resistive films of single-crystal ZnO as a result of irradiation with MeV Li, O, and Si ions is demonstrated. Results show that the ion doses necessary for electrical isolation close-to-inversely depend on the number of ion-beam-generated atomic displacements. Results show that an increase in the dose of 2 MeV O ions (up to ∼ 2 orders of magnitude above the threshold isolation dose) and irradiation temperature (up to 350 °C) has a relatively minor effect on the thermal stability of electrical isolation, which is limited to temperatures of ∼ 300 — 400 °C. For the case of multiple-energy implantation with keV Cr, Fe, or Ni ions, the evolution of sheet resistance with annealing temperature is consistent with defect-induced isolation, with a relatively minor effect of Cr, Fe, or Ni impurities on the thermal stability of isolation. Based on these results, the mechanism for electrical isolation in ZnO by ion bombardment is discussed.
Ultraviolet Emitting SrS:Te Thin Films
Authors: Fitz-Gerald J.M. , Hoekstra J. , Fowlkes J.D. , Rack P.D.
Published: April 2011

In the bulk SrS has an indirect bandgap of ∼ 4.32 eV. When SrS is doped with tellurium, ultraviolet emission occurs at 360 nm (for singlet) and 400nm (for Te-Te dimers) due to recombination from bound exciton states. In this paper we discuss the ultraviolet emission of pulsed laser deposited thin films of SrS:Te grown at room temperature on Si. Deposited film thickness ranged from 0.1 – 1.5 mm, with optimized films grown at ∼0.5 mm to avoid peeling and cracking. Te doping was incorporated by both ion implantation and conventional diffusion of deposited Te capping films. The characteristics of the ultraviolet emission will be discussed along with results from microstructural, chemical and optical characterization techniques.
Intersubband Transitions in Proton Irradiated InGaAs/InAlAs Multiple Quantum Wells Grown on Lattice Matched InP Substrate
Authors: Zhou Qiaoying , Manasreh M. O. , Weaver B. D. , Missous M.
Published: April 2011

Radiation hardness on intersubband transition in proton-irradiated InGaAs/InAlAs multiple quantum wells is investigated using Fourier transform infrared absorption (FTIR) technique and compared to the results observed for the GaAs/AlGaAs multiple quantum wells. It is observed that the intersubband transition remains almost unchanged in samples irradiated with 1 MeV protons and with doses as high as 1×1014 cm-2. This dose on the other hand, was found to completely deplete the intersubband transition in GaAs/AlGaAs multiple quantum wells samples. The intersubband transition in InGaAs/InAlAs multiple quantum wells was almost washed out in samples irradiated with doses as high as 3×1015 cm-2. The partial thermal annealing recovery of the depleted intersubband transition in the proton irradiated InGaAs/InAlAs multiple quantum wells will be reported.
1.5 μm Range Self-Organized In0.65Ga0.35As/In0.52Al0.48As Quantum Wire Structures Grown on (775)B-Oriented InP Substrates by Molecular Beam Epitaxy
Authors: Hyodo K. , Ohno Y. , Kanamori H. , Kitada T. , Shimomura S. , Hiyamizu S.
Published: April 2011

High quality quantum wire (QWR) structures with an emitting wavelength in the 1.5-μm range were self-organized in an In0.65Ga0.35As/In0.52Al0.48As quantum well layer grown on a (775)B-oriented InP substrate by molecular beam epitaxy. Photoluminescence (PL) from the (775)B In0.65Ga0.35As/In0.52Al0.48As QWRs with a nominal well width of 4.8 nm was observed at 1.43 μm at 12 K, which corresponds to a PL wavelength of about 1.5 μm at room temperature. The PL peak was considerably polarized along the wire direction with a polarization degree of P [= (I∥ - I⊥) / (I∥ + I] ⊥)] = 0.14, indicating its good one-dimensionality. The FWHM of the PL peak was as small as 17 meV, which is the best value for InGaAs QWRs on InP substrates.
Noise Sources in Polycrystalline Silicon Thin-Film Transistors
Authors: Han Il Ki , Park Young Ju , Cho Woon Jo , Choi Won Jun , Lee Jungil , Chovet Alain , Brini Jean
Published: April 2011

Sources for low frequency noise in polycrystalline silicon thin-film transistors are analytically investigated. The grain boundary is modeled as symmetric Schottky barrier and a new device equation for current conduction in thin-film transistors is presented. At lower currents where barrier height is large enough to provide necessary distribution of time constants for 1/f noise, the number fluctuation via barrier height modulation at the grain boundary is found to be the main noise generation mechanism. At higher currents, mobility and diffusivity fluctuation are found to be dominant
Photoreflectance study of hydrogenated (InGa)(AsN)/GaAs heterostructures
Authors: Geddo M. , Guizzetti G. , Pezzuto R. , Polimeni A. , Capizzi M. , Bissiri M. , Baldassarri Höger von Högersthal G. , Gollub D. , Forchel A.
Published: April 2011

We report on photoreflectance measurements performed in the 0.8–1.6 eV photon energy range in as grown and hydrogenated InxGa1-xAs1-yNy/GaAs single quantum wells grown on GaAs substrates by molecular beam epitaxy. In the hydrogenated samples, a blue-shift of all the QW spectral features and a surprising change with temperature in the nature of the lowest energy transition are found. These features are related to the interaction of H with N atoms. An increase in the binding energy of the heavy-hole exciton upon N introduction into the InxGa1-xAs lattice has been measured also and explained in terms of an increase in the electron effective mass.
Improved Device Performance of In0.5Ga0.5P/In0.22Ga0.78As/GaAs MOS p-HEMT using a Selective Liquid Phase Oxidation
Authors: Kang I-H , Lee J-W , Kang S-J , Jo S-J , In S-K , Song H-J , Kim J-H , Song J-I
Published: April 2011

The DC and RF characteristics of In0.5Ga0.5P/In0.22Ga0.78As/GaAs MOS p-HEMTs with different gate oxide thickness were investigated and compared with those of Schottky-gate p-HEMT without the gate oxide layer. The oxide layer was implemented by using a liquid phase oxidation technique. It was found that transconductance (gm), threshold voltage and breakdown voltage characteristics of MOS p-HEMTs depended strongly on the gate oxide thickness. The MOS p-HEMTs showed superior DC and RF performances compared with those of GaAs-based MOSFET having oxide/n-GaAs or oxide/InGaAs interface.
Oxygen incorporation into MBE-grown AlGaAs layers
Authors: Naritsuka S. , Kobayashi O. , Mitsuda K. , Maruyama T. , Nishinaga T.
Published: April 2011

The incorporation mechanism of oxygen into MBE-grown AlGaAs layers was systematically studied by changing the growth temperature and AlAs mole fraction. It was found that segregation of oxygen atoms strongly influences oxygen incorporation. By taking into account the surface segregation of oxygen, all of the particular characteristics observed in the oxygen incorporation into MBE-grown AlGaAs layers can be explained including a peak and a dip formation in the profile. Oxygen atoms accumulate on the surface of the substrate due to surface segregation and the number multiplied by the coefficient of surface segregation determines the oxygen incorporation.
Thermal Stability in HgCdTe IR Photodiodes
Authors: Dell J. M. , Nguyen T. , Musca C. A. , Antoszewski J. , Faraone L. , Pal R.
Published: April 2011

Packaging of HgCdTe photodiode detector arrays in a dewar involves degassing at elevated temperatures for several days so as to achieve vacuum integrity. This sustained exposure to relatively high temperatures can influence the HgCdTe bulk material properties, p-n junction integrity, and the passivant-HgCdTe interface. This work investigates the effects of bake-out treatment on the performance of HgCdTe based photodiodes formed using a new plasma induced type conversion process. Experimental results of a series of experiments in both long-wavelength infrared (LWIR) and mid-wavelength infrared (MWIR) devices are presented.

Bulk lifetime was used as an indicator of the change in the bulk material resulting from baking in vacuum and was measured by photoconductive decay. These measurements did not show any appreciable changes as a result of baking. Modification of the doping profile in the n-p junction may also result from high temperature baking. Doping profiles of the photodiodes were studied by measuring the junction capacitance-voltage relation before and after baking. The results of these tests after baking showed no changes to C-V measurements from those before bake.

The effect of baking on the passivant/HgCdTe interface was also examined by carrying out surface recombination velocity measurements by photoconductive decay on samples with different passivation layers.

Variable area HgCdTe photodiodes have also been fabricated and studied to understand the effect of the surface condition of the performance of the devices. Initial bake tests on LWIR devices show that the technology is stable when employing a double layer passivation technique. Bake tests on the more advanced MWIR technology indicates that the plasma induced type conversion process produces stable photodiodes with state of the art performance.
Ferromagnetic Single-Electron Transistor with RC Gate
Authors: Shirakashi Jun-ichi , Takemura Yasushi
Published: April 2011

Ferromagnetic single-electron transistors coupled to the controlling gate potential by the gate resistance and gate capacitance in series are studied quantitatively. In this type of the device, several metastable charge states are possible within the Coulomb blockade range. The enhancement and hysteresis of tunnel magnetoresistance on drain and gate voltages are predicted. Inelastic macroscopic quantum tunneling of charge and existence of several charge states play an important role for the unique behavior of the tunnel magnetoresistance. This implies that RC-coupled ferromagnetic single-electron transistors have a new functionality as novel magnetoresistive nanostructure devices.
Annealing of CoxCu1-x / Cu Multilayers
Authors: Ebert Jörg , Ghafari Mohammad , Stahl Branko , Hahn Horst
Published: April 2011

In the multilayer system cobalt / copper at the second antiferromagnetic coupling maximum (2. AFM) with a copper thickness of dCu = 2,2 nm it is possible to reduce magnetoresistive hysteresis by the use of either very thin Co-layers or by alloyed magnetic layers Co1-xCux. It was possible to achieve values for the giant magnetoresistance effect of GMR ≈ 20 % for as prepared samples. A heat treatment was applied to study the degeneration of the system. For annealing at moderate temperatures (Tanneal ≤ 250°C) an increase up to GMR ≈ 25 % was observed. Annealing at slightly higher temperatures lead to an rapid decrease in the GMR effect. To study the structural changes the method of x-ray reflectivity was utilized showing changes in interface roughness as well as in bilayer thickness.
Observation of the Verwey Transition in Fe3O4 Nanocrystals
Authors: Markovich Gil , Fried Tcipi , Poddar Pankaj , Sharoni Amos , Katz David , Wizansky Tommer , Millo Oded
Published: April 2011

The electronic properties of arrays and isolated magnetite nanocrystals were studied using tunneling spectroscopy. Macroscopic tunnel junctions were used to study stacked arrays of the nanocrystals. The temperature dependent resistance measurements showed an abrupt increase of the resistance around 100 K, attributed to the Verwey metal-insulator transition, while the current-voltage characteristics exhibit a sharp transition from an insulator gap to a peak in the density of states near the Fermi energy. This conductance peak was sensitive to in-plane magnetic field showing large magnetoresistance. The tunneling spectra obtained on isolated particles using a Scanning Tunneling Microscope exhibit a gap-like structure below the transition temperature that gradually disappeared with increasing temperature, ending with a small peak structure around zero bias.
Inert Gas Condensation of Iron and Iron-Oxide Nanoparticles
Authors: Baker C. , Ismat Shah S. , Hasanain S. K. , Ali B. , Shah L. , Li G. , Ekiert T. , Unruh K. M.
Published: April 2011

An inert gas condensation technique has been used to prepare nanometer-sized particles of metallic iron by evaporation and agglomeration in a flowing inert gas stream. The resulting Fe nanoparticles were protected from complete oxidation either by the formation of a thin Fe-oxide surface passivation layer or by immersion in an oil bath. X-ray diffraction and transmission electron microscopy measurements indicated that the nanoparticles were typically between 10 and 20 nm in size, that the thickness of the Fe-oxide surface passivation layer was between 3 and 4 nm, and that the oil immersed samples exhibited a significant smaller volume fraction of Fe-oxides than did the surface passivated samples. Room temperature magnetization measurements were also carried out and the coercivity and saturation magnetization of the surface passivated and oil immersed samples determined. Although the coercivities and saturation magnetization values of both samples were very similar, the Fe/Fe-oxide samples exhibited a single component hysteresis loop while the Fe/oil samples exhibited a two component loop.
Chemically Functional Alkanethiol Derivitized Magnetic Nanoparticles
Authors: Fleming David A. , Napolitano Michael , Williams Mary Elizabeth
Published: April 2011

Chemically functional magnetic nanoparticles, comprised of an Fe core encased in a thin Au shell, have been prepared by sequential high temperature decomposition of organometallic compounds in a coordinating solvent. A novel approach to encapsulate the Fe core in Au has been developed. TEM analysis confirms that the nanoparticles are monodisperse (∼20%) with average diameters of 8nm. The nanoparticles were subsequently functionalized with alkanethiolate ligands, which prevent aggregation, enable solubility in a range of solvents (both hydrophobic and hydrophilic), and permit subsequent derivatization (e.g., via ligand exchange reactions). The functionalized particles are characterized using high-resolution transmission electron microscopy (HRTEM), X-ray powder diffraction (XRD) and ultraviolet-visible (UV-Vis) absorption spectroscopy.

We have utilized place-exchange to impart chemical functionality to the nanoparticles by attaching either (1) thiol-derivatized redox moieties (e.g., ferrocene) or (2) alkanethiols with terminal reactive groups such as alcohols, amines and carboxylic acids. This paper presents our preliminary investigations of the voltammetry of the former class of these magnetic core/shell nanoparticles.
Epitaxial Growth and Magnetic Behavior of (Ni,Zn)Fe2O4 Thin Films on Si Substrate Using Designed Buffer Layers for Novel Memory Application
Authors: Wakiya Naoki , Shinozaki Kazuo , Mizutani Nobuyasu
Published: April 2011

Epitaxial nickel zinc ferrite (Ni,Zn)Fe2O4 (NZF) thin films were successfully deposited on (MgO-Al2O3)/CeO2/YSZ/Si(001) substrates, where (MgO-Al2O3) is MgO doped with Al2O3. The crystallographic orientation and magnetic properties (saturation magnetization: Ms, and squareness: Mr/Ms where Mr is remanent magnetization) of NZF thin films were considerably changed with the amount of Al2O3 addition. If the amount of Al2O3 addition was less than 7 mol%, (001)-oriented epitaxial NZF thin films were obtained and the films had low squareness (around 45%). If the amount of Al2O3 addition was more than 7 mol%, (111)-oriented epitaxial NZF thin films were obtained and the films had high squareness (around 60–81%). Maximum squareness (81%) was obtained if the amount of Al2O3 addition was 26 mol%. For the sample with this Al2O3 content, the lattice mismatch between NZF and (MgO-Al2O3) buffer layer was 3.2%. The fact that high squareness was not obtained if lattice mismatch was very small (-0.3% on MgO) but obtained if lattice mismatch was 3.2% suggests that lattice mismatch to a certain content is important to avoid the formation of antiphase boundaries (APBs). This consideration was confirmed by examining other buffer layers having various lattice mismatches with NZF.
SiO2 Formation at the Aluminum Oxide/Si(100) Interface
Authors: Chowdhuri A. Roy , Takoudis C. G. , Klie R. F. , Browning N. D.
Published: April 2011

Thin films of aluminum oxide were deposited on clean Si(100) substrates using trimethylaluminum and oxygen at 300°C. Infrared spectroscopic and x-ray photoelectron spectroscopic analyses of these films showed no aluminum silicate or SiO2 phase formation at the film/substrate interface. The O/Al ratio in the as deposited film was found to be higher than that in stoichiometric Al2O3. On annealing the as deposited samples in Ar at higher temperatures, a peak due to the transverse optical phonon for the Si-O-Si stretching mode appeared in the infrared spectra. A combination of Z-contrast imaging and electron energy loss spectroscopy in the scanning transmission electron microscope confirmed that the annealed samples developed a layer of silicon dioxide at the aluminum oxide-Si interface. Z-contrast images and electron energy loss spectra, obtained while heating the sample inside the scanning transmission electron microscope were used to follow the interfacial SiO2 formation.
In situ investigation of the stress evolution during deposition of Ti/Al-multi layer films as a function of layer thickness and substrate temperature.
Authors: Lackner St. , Abermann R.
Published: April 2011

In order to further investigate the origin of growth instabilities in aluminium rich Ti/Al-alloy films, formed by simultaneous deposition of the two alloy components, from separate evaporation sources, we have investigated the growth stress of multilayer-films under UHV-conditions, formed by a variable number of double layers of Ti and Al, by in situ internal stress measurements. The thickness of the respective Ti/Al-double layer was varied between 6.25 nm and 25 nm and the thickness of the respective titanium and aluminium layer was chosen to achieve an overall composition of Ti25Al75in a 150 nm thick film. The multilayer films were deposited on 10 nm thick alumina substrate films at substrate temperatures of 350°C and 450°C. Microstructure and phase formation was investigated by TEM/TED-experiments.

In summary, these experiments show diffusion of aluminium (compressive stress) into the underlying film during deposition of the first monolayers and then formation (stress free or small tensile stress) of aluminium precipitates on the surface of the multilayer film during each aluminium deposition. During the subsequent titanium deposition the aluminium surface precipitates spread in a circular region under alloy formation (tensile stress) (see also accompanying paper). The respective stress contributions are strongly dependent on the double-layer thickness and substrate temperature. The increasing magnitude of the different stress contributions in the early growth stage are interpreted to indicate that the various processes are limited to specific surface regions, which get larger as the number of double-layers increases. The average film stress built up in the respective multilayer film by superposition of the stress contributions mentioned above, is also strongly dependent on double layer thickness and substrate temperature.
Dehydrogenation and Polymerization of TiOxHy Films in Obtaining Anatase Coating at Low Temperature
Authors: Takayama Kouichi , Ohshio Shigeo , Saitoh Hidetoshi
Published: April 2011

Chemical-vapor-deposition of titanium tetra-isopropoxide (TTIP) under the atmosphere at low temperature has been conducted. The structure of the obtained films was assessed using Fourier transform infrared spectroscopy, X-ray diffractometry and Raman spectroscopy. These analyses indicated that amorphous TiOxHy films were obtained at gas temperatures in the range of 150–300 °C, and crystalline anatase-TiO2 film was formed at 350 °C. This distinction is accounted for by plausible chemical reactions as follows; the hydroxyl reaction of TTIP below 350 °C promotes the formation of the amorphous TiOxHy. As the temperature goes up to 350 °C, dehydrogenation of the TiOxHy films promotes to form crystalline TiO2. Also the obtained amorphous films were annealed for 10 min under the atmosphere in assessing the transformation proceeding in the solid state. The structural change is shown at 350 °C, indicating that the crystalline phase would be formed via dehydrogenation and polymerization on the surface of the amorphous phase under the atmosphere. The crystal size of the annealed films was evaluated in assessment for the transformation.
Adatom Diffusion on Strained Si(001)-(2×1) Surface
Authors: Kuronen Antti , Henriksson Krister , Kaski Kimmo
Published: April 2011

The effects of a buried germanium island inside silicon substrate on the silicon adatom diffusion on the substrate surface have been studied by kinetic Monte Carlo simulations. The confinement of adatoms caused by the strain field of the germanium island can clearly be seen. Moreover, due to the anisotropy in adatom diffusion the confinement in directions parallel and perpendicular to the dimer rows of the surface take place in different temperatures.
Deposition Mechanism of Oxide Thin Films Manufactured by a Focused Energetic Beam Process
Authors: Wanzenboeck H.D. , Harasek S. , Langfischer H. , Bertagnolli E.
Published: April 2011

Chemical vapor deposition (CVD) is a versatile deposition technique for both dielectrics and metals. CVD is based upon the adsorption of a volatile species from the gas phase and the decomposition of the adsorbed molecules on the sample surface resulting in the deposition of solid material. In contrast to thermal CVD or plasma assisted CVD used for large area coatings this work focuses on a method for locally confined deposition. A focused energetic beam is used to provide the necessary activation energy for CVD. With a focused beam material could be deposited locally within a strictly confined area down to the nanometer range. The deposition of silicon oxide microstructures utilizing two precursor gases - siloxane and oxygen - was performed by direct-write nanolithography. For initiating the CVD process energy is introduced by local ion exposure utilizing a scanning focused ion beam (FIB). The influence of the different ion fluxes and the effect of the mixture ratio of precursors were studied. Deliberate changes in the process parameters allowed adjusting the physical properties and the chemical composition of the solid silicon oxide. Process control allows tailoring of material properties according to requirements of the application.
Nanocluster Epitaxy by Annealing: Ag on H-terminated Si (111) Surfaces
Authors: Li B.Q. , Shi Y.F. , Bording J. , Zuo J.M.
Published: April 2011

We report an experimental investigation on the morphology and orientation of Ag nanoclusters by RT deposition and subsequent annealing. We show that epitaxial Ag clusters of 2 ∼ 6 nm in diameter can be synthesized in this way. The RT self-assembled Ag clusters grow as mostly single-crystal crystallites with Ag(111)//Si(111), but the in-plane orientation has a dispersion of ∼ 9° centering at Si[110] direction. Upon annealing, the Ag clusters drastically rotated to the epitaxial configuration with the in-plane orientation aligned to the Ag[110] //Si[110] direction. The rotation and epitaxy of the Ag nanoclusters are explained based on a coincident site lattice model and interface energy minimization.