bluuebunny/crossref_metadata_2025 huggingface dataset:
Postnatal regression of glucose transport in a patient with glycogen storage disease type 1b
Authors: Levy J. , Abu‐Ras M. T. , Berenstein T. , Potashnik R. , Meisner I. , Moses S. W. , Bashan N.
Published: December 2004

Decreased 2‐deoxyglucose (2‐DOG) uptake is well described in the neutrophils of patients with glycogen storage disease type 1b (GSD 1b). We report a patient with GSD 1b who presented with a normal antenatal and perinatal 2‐deoxyglucose uptake that showed a slow regression during the first months of life. These indicate limitations of 2‐deoxyglucose uptake in the diagnosis of GSD 1b. While it appears that low uptake rate below 0.25 nmol/min in 106 cells is of significance, normal uptake does not rule out the presence of the disease. It seems that antenatal diagnosis of GSD 1b cannot be made by measurement of 2‐deoxyglucose uptake in the fetal neutrophils.
Resistance to erucic acid as a selectable marker for peroxisomal activity: Isolation of revertants of an infantile Refsum disease cell line
Authors: El Bioukar Bachir , Straehli F. , Ng K. Heng , Rolland M. ‐O. , Hashimoto T. , Carreau J. ‐P. , Deschatrette J.
Published: December 2004

A system based on the ability of cells to oxidize very long‐chain fatty acids (VLCFA) was developed to selectin vitro normal human fibroblasts from fibroblasts of patients suffering from peroxisomal disorders with multienzymatic deficiencies: Zellweger syndrome, neonatal adrenoleukodystrophy, infantile Refsum disease (IRD). Cells treated with various concentrations of erucic acid (C22:1 n‐9) revealed an enhanced toxicity of this fatty acid for the fibroblasts of patients compared with normal cells. This differential toxicity is correlated with variable accumulations of C22:1 n‐9 and the absence of β‐oxidation products in the mutants.

Revertants from clonal IRD cell lines were isolated in the selective medium at frequencies ranging from 3×10−7 to 4×10−6 depending on the line. After six weeks of growth in the absence of selective pressure, the variants exhibited a resistance level to C22:1 n‐9 identical to that of normal cells. Furthermore, β‐oxidation of VLCFA is re‐established in these selected cells as well as dihydroxyacetone phosphate acyltransferase activity. Immunoblot experiments also demonstrated a restored pattern of acyl‐CoA oxidase molecular forms. Last, immunofluorescence studies revealed the presence of cytoplasmic structures that were absent in the original IRD cells. Thus, both the deficiencies in metabolic pathways and paucity of the organelle are at least partially corrected in the selected clones.
Production and disposal of medium‐chain fatty acids in children with medium‐chain acyl‐CoA dehydrogenase deficiency
Authors: Heales S. J. R. , Thompson G. N. , Massoud A. F. , Rahman S. , Halliday D. , Leonard J. V.
Published: December 2004

The effect of fasting on plasma concentrations of fatty acids has been determined in four children with medium‐chain acyl‐CoA dehydrogenase (MCAD) deficiency. In addition, thein vivo rate of octanoate oxidation was measured, using [1‐13C]octanoate. In the three older children (1.5–11.2 years), fasting for up to 18 h stimulated lipolysis, as reflected by the increasing concentration of free fatty acids, but with little rise in concentrations of medium‐chain fatty acids, octanoate, decanoate andcis‐4‐decenoate. In an infant (0.5 year), lipolysis was greater and was accompanied by rising concentrations of medium‐chain fatty acids. After 13.5 h there was a rapid increase in the concentration of decanoate andcis‐4‐decenoate. The calculatedin vivo rate of octanoate oxidation was substantial in all patients studied (6.4–13.1 µmol/kg per h) despite very low MCAD activityin vitro. It is concluded that under basal conditions thein vivo oxidation rate of medium‐chain fatty acids is near normal in the four children studied with MCAD deficiency.
High‐resolution loading tests in the study of genetic heterogeneity in gangliosidosis fibroblasts
Authors: Akhunov V. S. , Mirenburg T. V. , Krasnopolskaya X. D.
Published: December 2004

GM1‐ and GM2‐gangliosides were isolated from brain and radio‐labelled. The labelled moieties were localized by hydrolysis with lysosomal enzymes, followed by thin‐layer chromatography of the products. High‐resolution loading tests with labelled gangliosides were developed and found to differentiate infantile and juvenile forms of GM1‐ and GM2‐gangliosidoses as well as the identification of B, O and AB types of GM2‐gangliosidosis.
The b1 isoform of protocadherin‐gamma (Pcdhγ) interacts with the microtubule‐destabilizing protein SCG10
Authors: Gayet Odile , LaBella Vincenzo , Henderson Christopher E. , Kallenbach Sacha
Published: December 2004

Due to their structural characteristics and their diversity, the 22 members of the protocadherin‐gamma (Pcdhγ) family have been suggested to contribute to the establishment of specific connections in the nervous system. Here, we focus on a single isoform, Pcdhγ‐b1. Its expression is found in different brain regions and in developing spinal cord it is restricted to scattered cells, whereas all cells are labeled using an antibody that recognizes all Pcdhγ isoforms. As a first step to understanding the signaling mechanisms downstream of Pcdhγ, we identify the microtubule‐destabilizing protein SCG10 as a cytoplasmic interactor for Pcdhγ‐b1 and other isoforms of the Pcdhγ‐b subfamily, and show that SCG10 and Pcdhγ‐b1 are found together in certain neuronal growth cones.
A model of a transmembrane drug‐efflux pump from Gram‐negative bacteria
Authors: Fernandez-Recio Juan , Walas Fabien , Federici Luca , Venkatesh Pratap J. , Bavro Vassiliy N. , Miguel Ricardo Nunez , Mizuguchi Kenji , Luisi Ben
Published: December 2004

In Gram‐negative bacteria, drug resistance is due in part to the activity of transmembrane efflux‐pumps, which are composed of three types of proteins. A representative pump from Escherichia coli is an assembly of the trimeric outer‐membrane protein TolC, which is an allosteric channel, the trimeric inner‐membrane proton‐antiporter AcrB, and the periplasmic protein, AcrA. The pump displaces drugs vectorially from the bacterium using proton electrochemical force. Crystal structures are available for TolC and AcrB from E. coli, and for the AcrA homologue MexA from Pseudomonas aeruginosa. Based on homology modelling and molecular docking, we show how AcrA, AcrB and TolC might assemble to form a tripartite pump, and how allostery may occur during transport.
Redox behaviour of the haem domain of flavocytochrome c3 from Shewanella frigidimarina probed by NMR
Authors: Pessanha Miguel , Rothery Emma L. , Louro Ricardo O. , Turner David L. , Miles Caroline S. , Reid Graeme A. , Chapman Stephen K. , Xavier António V. , Salgueiro Carlos A.
Published: December 2004

Flavocytochrome c
3 from Shewanella frigidimarina (fcc3) is a tetrahaem periplasmic protein of 64 kDa with fumarate reductase activity. This work reports the first example of NMR techniques applied to the assignment of the thermodynamic order of oxidation of the four individual haems for such large protein, expanding its applicability to a wide range of proteins. NMR data from partially and fully oxidised samples of fcc3 and a mutated protein with an axial ligand of haem IV replaced by alanine were compared with calculated chemical shifts, allowing the structural assignment of the signals and the unequivocal determination of the order of oxidation of the haems. As oxidation progresses the fcc3 haem domain is polarised, with haems I and II much more oxidised than haems III and IV, haem IV being the most reduced. Thus, during catalysis as an electron is taken by the flavin adenosine dinucleotide from haem IV, haem III is eager to re‐reduce haem IV, allowing the transfer of two electrons to the active site.
Oxidized LDL triggers phosphatidylserine exposure in human monocyte cell lines by both caspase‐dependent and ‐independent mechanisms
Authors: Baird Sarah K. , Hampton Mark B. , Gieseg Steven P.
Published: December 2004

Monocytic cell lines have been extensively used to characterize and model various features of the atherogenic process. We found striking differences in the apoptotic pathways of U937 cells and THP‐1 cells exposed to copper‐oxidized LDL. While phosphatidylserine exposure occurred in both lines, caspase activation was only apparent in the THP‐1 cells. OxLDL caused caspase activity to decrease below that seen in untreated U937 cells, and this corresponded with a loss in intracellular thiols. In conclusion, exposure of U937 cells to oxLDL did not trigger a conventional apoptosis response, but still resulted in phosphatidylserine externalization.
Arbeitersteuerung, Klientenberatung
Authors: Meskill David
Published: December 2004

Zusammenfassung. Die angewandte Psychologie diente von circa 1920 bis 1960 als Hilfsmittel in einem System der “Totalerfassung“ und Steuerung aller Berufseingänge. Man wollte “den richtigen Mann an die richtige Stelle“ bringen. Gleichzeitig boten die örtlichen Arbeitsämter psychologische Eignungsprüfungen an, um die Arbeitgeber an sich zu binden. Trotz der ehrgeizigen Pläne für die angewandte Berufspsychologie wuchs die Zahl der Psychologen nur langsam an; die Organisation der Anwendung wurde kaum zentralisiert; die Methoden, die aus einer Mischung aus Fähigkeits- und Intelligenzprüfungen und Charakterdiagnosen bestanden, ermangelten einer Standardisierung und wissenschaftlichen Kontrollen. Nach 1960 ließen das Wirtschaftswunder und die Vollbeschäftigung eine “Totalerfassung“ der Arbeitsmarktvorgänge immer unrealistischer erscheinen. Diese Bedrohung der Rolle der Berufsberatung bewirkte einen grundlegenden strategischen Wechsel im Denken der Bundesanstalt für Arbeit: sie verwandelte sich jetzt in einen Dienstleister, der weniger Kunden - oft die Weniger-Erfolgreichen des Wirtschaftswunders - jetzt intensiver beraten würde. Von diesem Umdenken profitierte der Psychologische Dienst am meisten.
An ultrasonic frequency sweep interferometer for liquids at high temperature: 1. Acoustic model
Authors: Ai Yuhui , Lange Rebecca
Published: December 2004

A general acoustic model for a frequency sweep rod‐liquid‐rod interferometer applicable to high‐temperature silicate liquids is presented. The wave propagations in the acoustic model are solved according to the accurate elastic wave equation and the acoustic wave equation. The solutions indicate that when a pulsed wave is sent down a buffer rod, which is partially immersed in a silicate liquid, the return signal consists of a series of plane waves (mirror reflections from the liquid) and two series of interfering pulses (modes A and B), which are propagating disturbances guided by the cylindrical surface of the upper rod. The acoustic model gives mathematical expressions for the time delays between the various interfering pulses and between the mirror reflections, which are predicted to vary according to the material and dimensions of the upper buffer rod and liquid. These predictions are verified by experiments on molybdenum and aluminum rods of varying dimensions in air, water, and silicate liquid. These results demonstrate that mirror reflections from the liquid can be isolated from the interfering pulses in the return signal by appropriate choice of the dimensions and material of the upper rod. This theoretical model provides a critical foundation for construction of an acoustic interferometer that is uniquely able to measure relaxed sound speeds in silicate liquids at high temperature and high pressure by the frequency sweep method.
Eastward propagating surface anomalies at ocean gyre boundaries
Authors: Sinha Bablu , Topliss Brenda , Harle James
Published: December 2004

Inspection of animations and time‐distance (Hovmoller) plots of unfiltered data from a state‐of‐the‐art coupled climate model (HadCM3) reveals eastward propagating surface temperature‐salinity anomalies at subpolar/subtropical gyre boundaries throughout the world ocean. Maximum anomalies are ∼4°C and ∼0.3 practical salinity units. Horizontal length scales are ∼1000 km. The anomalies travel at a speed consistent with advection by mean near‐surface currents. Generation regions are located at western boundaries and possess an order of magnitude higher variability than all other regions. In some cases, surface heat fluxes are shown to cause anomaly generation; in other cases, surface current anomalies are likely to be responsible. Eastward anomaly propagation also occurs in the Estimating the Circulation and Climate of the Ocean model. The coarser resolution Fast Ocean Rapid Troposphere Experiment (FORTE) coupled model shows no propagating anomalies. Sea surface anomalies in the instrumental record are investigated, using ship‐based sea surface temperature (SST) and heat fluxes, and satellite SST and altimetry. Unlike the models, Hovmoller plots and animations of the unfiltered observational data showed no evidence of eastward propagation. By applying a decadal‐timescale band‐pass filter to the SST time series, we identify underlying propagation of basin‐scale anomalies in both HadCM3 and observations. Maximum anomalies are ∼1°C and length scales are ∼2500 km. These anomalies travel at speeds significantly slower than mean near‐surface currents. Ten anomalies are identified during the period 1870–2002, mostly in the eastern Atlantic basin (east of 45°W). HadCM3 displayed only one propagating anomaly of this type in a typical 100 years of data. We discuss possible reasons for the range of results in models and observations.
Simulations of surface acoustic wave devices built on stratified media using a mixed finite element/boundary integral formulation
Authors: Ballandras S. , Reinhardt A. , Laude V. , Soufyane A. , Camou S. , Daniau W. , Pastureaud T. , Steichen W. , Lardat R. , Solal M. , Ventura P.
Published: December 2004

The demand for high frequency surface acoustic wave devices for modern telecommunication applications imposes the development of devices able to answer the manufacturer requirements. The use of high velocity substrates for which a piezoelectric layer is required to excite and detect surface waves has been widely investigated and requires the implementation of accurate theoretical tools to identify the best combinations of material. The present paper proposes a mixed formulation combining finite element analysis with a boundary integral method to accurately simulate the capability of massive periodic interdigital transducers to excite and detect guided acoustic waves in layered media. The proposed model is exploited for different typical configurations.
Plasma oscillations in a slot diode structure with a two-dimensional electron channel
Authors: Ryzhii V. , Satou A. , Khmyrova I. , Chaplik A. , Shur M. S.
Published: December 2004

We calculate the spectrum of plasma oscillations in a diode structure with a two-dimensional electron channel in a slot between strip-like short circuited contacts. Hydrodynamic electron transport equations coupled with a two-dimensional Poissons equation for the self-consistent electric potential area used. The obtained results can be useful in designing of devices operating at terahertz frequencies based on two-dimensional electron systems and device optimization.
Tungsten bronze type dielectrics in SrO-Sm2O3-TiO2-Nb2O5 system and their dielectric anomaly
Authors: Sun Y. H. , Chen X. M. , Zheng X. H.
Published: December 2004

The dielectric behavior and the features of the diffused phase transition of the SrpSm6−pTi8−pNb2+pO30(p=4,5) ceramics were investigated together with their structure. Both Sr5SmTi3Nb7O30 and Sr4Sm2Ti4Nb6O30 had tungsten bronze structure and weak ferroelectric nature. Though Sr5SmTi3Nb7O30 showed the diffused ferroelectrics phase transition, it was concluded that the transition was mainly the displacive ferroelectric phase transition. In Sr4Sm2Ti4Nb6O30, the Sr2+ ions and Sm3+ ions did not form an order structure and it showed a typical displacive ferroelectric phase transition. The dielectric anomaly was attributed to the different BO6 octahedral distortion.
Photorefractive properties of undoped lithium tantalate crystals for various composition
Authors: Holtmann F. , Imbrock J. , Bäumer Ch. , Hesse H. , Krätzig E. , Kip D.
Published: December 2004

Lithium tantalate crystals of compositions ranging from 48.3mol%to50.0mol% lithium oxide are fabricated by vapor transport equilibration. Light-induced refractive index changes of the crystals are investigated with holographic methods at usual cw-laser intensities (≈105W∕m2) and with a single focused laser beam at high light intensities up to 2×107W∕m2. In stoichiometric crystals the index changes are reduced by more than two orders of magnitude when compared with congruently melting ones. Simultaneously, the normalized photoconductivity σph∕I, where I is the light intensity, increases by nearly two orders of magnitude. Therefore, stoichiometric lithium tantalate is an attractive material for applications such as frequency conversion via quasi-phase matching.
A charge-coupled-device-based heterodyne technique for parallel photodisplacement imaging
Authors: Nakata Toshihiko , Ninomiya Takanori
Published: December 2004

A heterodyne interferometry technique for parallel photodisplacement imaging is presented. In the parallel photodisplacement technique, a linear region of photothermal displacement is excited using a line-focusing intensity-modulated laser beam and is detected with a parallel heterodyne interferometer in which a charge-coupled device linear image sensor is used as a detector. The integration and sampling effects of the sensor provide spatiotemporally multiplexing of the interference light. To extract the spatially resolved photodisplacement component from the multiplexed sensor signal for heterodyne interferometry, a scheme of phase-shifting light integration under an undersampling condition is developed. The frequency relation for the heterodyne beat signal, modulation signal, and sensor gate signal is optimized so as to eliminate undesirable components, allowing only the displacement component to be extracted. Preliminary experimental results using a point-focused laser beam demonstrate that the technique is effective, making it possible to accurately extract photodisplacement components from the multiplexed interferogram. Subsurface structures and defects in silicon wafers are clearly imaged with a detection time of 5.3μs∕pixel. In combination with a line-focusing laser beam, this technique is very promising for high-throughput subsurface imaging with detection speeds more than 10 000 times faster than conventional photoacoustic microscopy.
Oxygen nonstoichiometry and dielectric evolution of BaTiO3. Part II—insulation resistance degradation under applied dc bias
Authors: Yang G. Y. , Lian G. D. , Dickey E. C. , Randall C. A. , Barber D. E. , Pinceloup P. , Henderson M. A. , Hill R. A. , Beeson J. J. , Skamser D. J.
Published: December 2004

The microchemical and microstructural origins of insulation-resistance degradation in BaTiO3-based capacitors are studied by complementary impedance spectroscopy and analytical transmission electron microscopy. The degradation under dc-field bias involves electromigration and accumulation of oxygen vacancies at interfaces. The nonstoichiometric BaTiO3−δ becomes locally more conducting through increased oxygen vacancy concentration and Ti ion reduction. The symmetry across the dielectric layer and locally across each grain is broken during the degradation process. Locally, the nonstoichiometry becomes so severe that metastable lattice structures are formed. The degradation in insulation resistance at the grain boundaries and electrode interfaces is associated with the double Schottky-barrier potential lowering and narrowing. This may correlate with an effective decrease in net acceptor charge density at the grain boundaries.
The initial, thermal oxidation of zirconium at room temperature
Authors: Lyapin A. , Jeurgens L. P. H. , Graat P. C. J. , Mittemeijer E. J.
Published: December 2004

Angle-resolved x-ray photoelectron spectroscopy (ARXPS) and in situ spectroscopic ellipsometry have been used to investigate the initial oxidation of polycrystalline zirconium at room temperature in the partial oxygen pressure range of 1.3×10−7–1.3×10−4Pa. Detailed quantitative analysis of the measured Zr3d ARXPS spectra of the oxidized metal allowed separation of the intrinsic and extrinsic metallic and oxidic contributions to the spectra. It was shown that, in addition to the metallic contribution from the substrate and the oxidic contribution from stoichiometric ZrO2, two additional suboxidic components are contained in the measured Zr3d spectra of the oxidized Zr metal. As evidenced by angle-resolved XPS and in situ ellipsometry, both of these components can be attributed to a gradient of Zr enrichment in the region of the oxide film adjacent to the metal∕oxide interface (with the highest Zr enrichment at the metal∕oxide interface). Investigation of the oxide-film growth kinetics at various pO2, as determined independently using both techniques, showed the occurrence of an initial regime of very fast, electric-field-controlled growth, followed by a much slower oxidation stage. As a result, an, on average, nonstoichiometric oxide film develops. The observed effect of the pO2 on the low-temperature oxidation of Zr has been discussed in terms of the relationship between the fraction of coverage of the surface with physi- and chemisorbed oxygen and the applied pO2.
Effect of the surface adsorbed water on the studying of ferroelectrics by scanning nonlinear dielectric microscopy
Authors: Ohara Koya , Cho Yasuo
Published: December 2004

The effect of adsorbed water on the signal of scanning nonlinear dielectric microscopy (SNDM) is reported. By measuring SNDM image variation under various measurement conditions and by computing the theoretical SNDM signal corresponding to these conditions, we verified that the adsorbed water strongly affects the signal strength, depth sensitivity, and resolution of SNDM. From this study, we find that it is necessary to consider adsorbed water for detailed measurement of the surface polarization state by SNDM. In addition, we also confirmed that the surface paraelectric layer on a LiTaO3 single crystal grows upon heat treatment.
Chemical image generation with a grid-gate device
Authors: Filippini D. , Gunnarsson J. , Lundström I.
Published: December 2004

Scanning light pulse technique generating distinctive chemical images of diverse gases is demonstrated using a sensing arrangement that allows unrestricted choice of sensing materials, disregarding its conductivity or morphology. The present device, a metal oxide semiconductor structure, disentangles biasing from chemical functions by providing an inert grid as a gate that supplies the proper biasing, while functional materials even in the form of disconnected clusters can be used for sensing. The reading of conductimetric chemical responses of clustered materials, in nominal operating conditions, is demonstrated by the generation of chemical images acquired for inversion biasing conditions.
Geometric linewidth and the impact of thermal processing on the stress regimes induced by electroless copper metallization for Si integrated circuit interconnect technology
Authors: McNally P. J. , Kanatharana J. , Toh B. H. W. , McNeill D. W. , Danilewsky A. N. , Tuomi T. , Knuuttila L. , Riikonen J. , Toivonen J. , Simon R.
Published: December 2004

Mechanical strains and stresses are a major concern in the development of copper-based on-chip metallization. Synchrotron x-ray topography (SXRT), micro-Raman spectroscopy, finite element modeling (FEM), and atomic force microscopy (AFM) have been used to examine the strain fields imposed by electroless Cu metallization on the underlying Si. As expected, we have observed enhanced strain regions close to the metal line edges. These strain fields tend to zero at annealing temperatures approaching 200°C, and thereafter the magnitudes of the strain fields at 300°C and 400°C are much higher, implying a return to a higher strain regime. Although the strain transition point is slightly different from the SXRT result, the FEM results confirm the existence of a zero-strain transition point as a function of thermal anneal. We have also examined the generated stress in Si as a function of Cu linewidth L. We have found that the stress σXX due to the electroless copper metallization is empirically related to the Cu linewidth in terms of an exponential distribution. For Cu linewidths less than 20μm, the stress magnitudes increased with decreasing Cu linewidth due to the thermal stress in the absence of self-annealing, whereas the stress decreased with increasing linewidths in the range of 60–100μm due to a relief of the thermal stress possibly via the self-annealing effect. This self-annealing phenomenon was observed using AFM. It is observed that the stresses in the Si shifted to a compressive state after annealing at 400°C.
Microstructural properties and atomic arrangements in GaN/sapphire and AlxGa1−xN∕AlN∕GaN∕sapphire heterostructures
Authors: Kim T. W. , Lee D. U. , Lee H. S. , Lee J. Y. , Lee Jae-Hoon , Lee Jung-Hee
Published: December 2004

Microstructural and atomic structure studies of GaN/sapphire and AlxGa1−xN∕AlN∕GaN heterointerfaces have been performed by using bright-field transmission electron microscopy (TEM) and selected area electron diffraction pattern (SADP) measurements. TEM and SADP results from the GaN/sapphire and the Al0.4Ga0.6N∕AlN∕GaN∕sapphire heterointerfaces showed that GaN epilayers and Al0.4Ga0.6N, AlN, and GaN active layers, respectively, had been grown on the sapphire substrates. The values of the strain and the stress in the Al0.4Ga0.6N, the AlN, and the GaN layers were determined. Possible schematic diagrams of the two heterostructures, as well as diagrams of the [21¯1¯0] projections of the GaN epilayer and the Al0.4Ga0.6N∕AlN∕GaN heterostructure, are presented based on the TEM and SADP results. These results can help improve the understanding of the microstructural properties of the strained AlxGa1−xN∕AlN∕GaN∕sapphire heterostructures for applications in the high-speed and high-power electronic devices.
Analysis of the GaN-rich side of GaNP using x-ray diffraction
Authors: Tsuda Yuhzoh , Mouri Hirokazu , Araki Masahiro , Yuasa Takayuki , Taneya Mototaka
Published: December 2004

We investigated the growth of the GaN-rich side of GaNP films using metal-organic chemical-vapor deposition. The results of Auger electron spectroscopy suggest that phosphorus atoms incorporated into the film would be substituted on gallium sites rather than on nitrogen sites. Using x-ray diffraction, we have revealed that such GaNP films belong to a hexagonal system and that the relationship of the orientation between the GaNP film and its underlying GaN layer is [0001]GaNP‖[0001]GaN and [101¯0]GaNP‖[101¯0]GaN. Moreover, it was found that the lattice constants of GaNP were smaller than those of bulk GaN and there was no phase separation. We have also confirmed that the changes in these lattice constants were almost proportional to the phosphorus concentration included in the entire GaNP film thickness and that they decreased with an increase in the phosphorus concentration.
Magnetization reversal of CrO2 nanomagnet arrays
Authors: Zhang Qiang , Li Y. , Nurmikko A. V. , Miao G. X. , Xiao G. , Gupta A.
Published: December 2004

We report on fabrication techniques and the study of magnetic behavior of submicron-sized ferromagnetic CrO2 arrays. Periodic rectangular arrays composed of circular dots with diameters ranging from 100nmto2μm were fabricated by electron-beam lithography and reactive ion etching of CrO2 epitaxial thin films. The magnetization reversal of the nanomagnet arrays was measured by the magneto-optical Kerr effect, with hysteresis characteristics found to be sensitively dependent on array details, film thickness, and its built-in strain. A rich variety of behaviors such as single domain, probable multidomain, as well as magnetization reorientation transition were observed, with magnetostatic interaction between the neighboring dots affecting the collective behavior of the nanomagnet arrays.
Electrical transport properties of microcrystalline silicon grown by plasma enhanced chemical vapor deposition
Authors: Pinto Nicola , Ficcadenti Marco , Morresi Lorenzo , Murri Roberto , Ambrosone Giuseppina , Coscia Ubaldo
Published: December 2004

The dark conductivity and Hall mobility of hydrogenated silicon films deposited varying the silane concentration f=SiH4∕(SiH4+H2) in a conventional plasma enhanced chemical vapor deposition system have been investigated as a function of temperature, taking into account their structural properties. The electrical properties have been studied in terms of a structural two-phase model. A clear transition from the electrical transport governed by a crystalline phase, in the range 1%⩽f⩽3%, to that controlled by an amorphous phase, for f>3%, has been evidenced. Some metastable effects of the dark conductivity have been noticed.
Characterization of high temperature deposited Ti-containing hydrogenated carbon thin films
Authors: Shi B. , Meng W. J. , Evans R. D.
Published: December 2004

A detailed structural and mechanical characterization was performed on Ti-containing hydrogenated amorphous carbon (Ti-C:H) thin films deposited at ∼600°C by plasma assisted hybrid chemical/physical vapor deposition. The structural and mechanical characteristics of these specimens were compared to those deposited at the lower temperature of ∼250°C. The results indicated that Ti-C:H consisted of a nanocrystalline TiC phase and a hydrogenated amorphous carbon (a-C:H) phase, and that Ti atoms were incorporated into Ti-C:H predominantly as B1-TiC. Deposition at ∼600°C promoted TiC precipitation, resulting in little Ti dissolution within the a-C:H matrix. High temperature deposited Ti-C:H specimens were found to possess lower modulus and hardness values as compared to low temperature deposited specimens, especially at low Ti compositions. This is rationalized by electron microscopy evidence of increased short and medium range graphitic order within the a-C:H matrix of high temperature deposited Ti-C:H, and supported by additional Raman spectroscopic observations. Heat treatments at 600 °C combined with Raman scattering measurements showed that the a-C:H matrix in high temperature deposited Ti-C:H specimens appears to be less structurally sensitive to additional annealing.
Optical studies of zero-field magnetization of CdMnTe quantum dots: Influence of average size and composition of quantum dots
Authors: Gurung T. , Mackowski S. , Jackson H. E. , Smith L. M. , Heiss W. , Kossut J. , Karczewski G.
Published: December 2004

We show that through the resonant optical excitation of spin-polarized excitons into CdMnTe magnetic quantum dots (QD), we can induce a macroscopic magnetization of the Mn impurities. We observe very broad (4-meV linewidth) emission lines of single dots, which are consistent with the formation of strongly confined exciton magnetic polarons. Therefore, we attribute the optically induced magnetization of the magnetic dots to the formation of spin-polarized exciton magnetic polarons. We find that the photoinduced magnetization of magnetic polarons is weaker for larger dots which emit at lower energies within the QD distribution. We also show that the photoinduced magnetization is stronger for quantum dots with lower Mn concentration, which we ascribe to weaker Mn–Mn interaction between the nearest neighbors within the dots. Due to particular stability of the exciton magnetic polarons in QDs, where the localization of the electrons and holes is comparable to the magnetic exchange interaction, this optically induced spin alignment persists to temperatures as high as 160K.
Ohmic contacts to p-type Al0.45Ga0.55N
Authors: Hull B. A. , Mohney S. E. , Chowdhury U. , Dupuis R. D.
Published: December 2004

Ni, Pd, and Au Ohmic contacts to p-Al0.45Ga0.55N have been examined. We have observed that annealing the contacts in excess of 800°C is required to minimize the contact resistivity. However, the Pd and Au contacts annealed in excess of 700°C, which showed much better transport properties than Ni contacts annealed at the same temperatures, suffered from a rapid photoinduced degradation of both the current-voltage characteristics of the contacts and of the sheet resistance of the p-Al0.45Ga0.55N itself. This degradation was greatly reduced by passivating the p-Al0.45Ga0.55N surface with a SiNx film. A hypothesis is presented to describe the observed degradation.
Deep-level-transient spectroscopy of heavily Al-doped ZnSe layers grown by molecular-beam epitaxy
Authors: Oh D. C. , Takai T. , Hanada T. , Cho M. W. , Yao T. , Song J. S. , Chang J. H. , Lu F.
Published: December 2004

Using deep-level-transient spectroscopy, we have investigated deep levels in heavily Al-doped ZnSe layers grown by molecular-beam epitaxy. The Al concentration of the ZnSe layers lies in the range of 5×1018–9×1018cm−3. The ZnSe:Al layers exhibit two electron-trap centers with the thermal activation energies of 0.16eV (ND1) and 0.80eV (ND2). ND2 is a dominant trap center with a trap density of 3×1016cm−3, while the trap density of ND1 is estimated to be 2×1015cm−3. However, ND2 shows anomalous behaviors, different from isolated point defects, in the following points: (1) the emission peak of ND2 moves to the low temperature side with increasing filling pulse duration; (2) the emission peak of ND2 is broader than theoretically calculated one for an isolated point defect; and (3) the capacitance-transient curve is nonexponential. It is observed by high-resolution x-ray diffraction that heavy Al doping results in the relaxation and plastic deformation of the ZnSe lattice. These behaviors can be ascribed to extended defects with a broad energy spectrum. By assuming a Gaussian distribution of deep levels due to extended defect, the broad emission peak is successfully simulated.
High-resolution synchrotron-radiation photoemission characterization for atomically-controlled SrTiO3(001) substrate surfaces subjected to various surface treatments
Authors: Kobayashi D. , Kumigashira H. , Oshima M. , Ohnishi T. , Lippmaa M. , Ono K. , Kawasaki M. , Koinuma H.
Published: December 2004

The chemical properties and electronic structures of atomically flat SrTiO3(001) substrates with various surface treatments have been investigated by high-resolution synchrotron-radiation photoemission spectroscopy. We have found that an annealing process causes the segregation of Sr oxides at the TiO2-terminated surface and that the TiO2-terminated surface is more stable than the SrO terminated one. We demonstrate that the use of chemical etching process is effective as a removal technique for Sr oxides accumulating on TiO2-terminated surfaces and that the adding of a reetching process after annealing in an O2 environment is one of the best methods to obtain well defined and nearly perfect substrate surface.
Spectroscopic properties of Tm3+ ions in PbO–PbF2–Bi2O3–Ga2O3 glasses for S-band optical amplifications
Authors: Yamauchi Hiroki , Murugan Ganapathy Senthil , Ohishi Yasutake
Published: December 2004

The spectroscopic properties of Tm3+ ions in (57−x)PbO–xPbF2–25Bi2O3–18Ga2O3(mol%) glasses were investigated through measurements of absorption, emission, and lifetime measurements. The PbF2 substitution in this glass system raised the lifetime of the 1.48μm emission. The lifetime for the H43 level was changed from 272to416μs when the PbF2 content increased from x=0to15. In a 47PbO–15PbF2–25Bi2O3–18Ga2O3 glass, the phonon-assisted energy transfer involving two phonons with the energy of 550cm−1 dominated the cross relaxation of the Tm3+: H43, H63→F43, F43 route in spite of the presence of the overlap between the H43→F43 emission and H63→F43 absorption spectra. As a result, PbO–PbF2–Bi2O3–Ga2O3 glasses were thought to be useful for the S-band optical fiber amplifiers.
Determination of densities and energy levels of donors in free-standing undoped 3C–SiC epilayers with thicknesses of 80μm
Authors: Matsuura Hideharu , Nagasawa Hiroyuki , Yagi Kuniaki , Kawahara Takamitsu
Published: December 2004

The densities and energy levels of donors in free-standing undoped 3C–SiC epilayers with the thicknesses of ∼80μm are investigated from the temperature dependence of the electron concentration n(T) obtained by Hall-effect measurements. Although in the analysis of n(T) many researchers usually assume that only one type of donor species is included in n-type 3C–SiC, no one knows whether this assumption is correct or not. In order to determine the densities and energy levels using n(T) without any assumptions regarding donor species, the graphical peak analysis method called free carrier concentration spectroscopy is applied. Three types of donor species are detected in these epilayers. These donor densities can be reduced to <5×1015cm−3 by growing 3C–SiC epilayers on undulant Si substrate. Moreover, the dependence of each donor level on a total donor density is investigated, which is used in 3C–SiC device simulation.
Nitrogen surfactant effects in GaInP
Authors: Chapman D. C. , Stringfellow G. B. , Bell A. , Ponce F. A. , Lee J. W. , Seong T. Y. , Shibakawa S. , Sasaki A.
Published: December 2004

The addition of surfactant nitrogen during the growth of GaInP on (001)GaAs substrates produces significant and interesting changes in the optical and morphological properties of GaInP. In particular, multiple peaks are seen in the low temperature photoluminescence (PL) spectra of GaInP∕GaInP:N heterostructures. The origin of these multiple peaks is investigated using transmission electron microscopy, energy dispersive spectroscopy, and cathodoluminescence. It is found that a discontinuous In-rich layer forms at the GaInP∕GaInP:N interface leading to a 1–6nm thick GaInP layer that is ≈70% In and has a PL peak energy of <1.7eV. Cross-sectional cathodoluminescence experiments confirm the existence and composition of the interface layer. The cathodoluminescence experiments also show that the GaInP:N epilayer produces emission at a higher energy than the GaInP epilayer. Cathodoluminescence monochromatic images of surface pyramids indicate that the pyramids emit at higher energy than the surrounding GaInP:N epilayer. Atomic force microscopy of the pyramids reveals the formation of facets with angles of up to 23°. The large misorientation of the pyramids leads to GaInP material that is more disordered than the top epilayer.
Electrostatic cross-talk between quantum dot and quantum point contact charge read-out in few-electron quantum dot circuits
Authors: Zhang L.-X. , Leburton J. P.
Published: December 2004

We investigate by numerical simulation the effect of electrostatic coupling between a quantum point contact (QPC) detector of various geometries and a planar double quantum dot in a few-electron quantum dot circuit. Our simulation is based on solving coupled Kohn-Sham and Poisson equations self-consistently by the finite element method. We use the Slater formula to determine the first electron charging bias point of the plunger gate, and give the corresponding variation of the QPC conductance as a function of the QPC gate bias at that particular point, which we interpret as the detector sensitivity. For all QPC designs, we show that the charging bias point of the plunger gate decreases with increasing QPC gate bias. This effect is enhanced for designs wherein large QPC detection sensitivity is found.
Effect of electrical bias on spin transport across a magnetic domain wall
Authors: Deutsch M. , Vignale G. , Flatté M. E.
Published: December 2004

We present a theory of the current-voltage characteristics of a magnetic domain wall between two highly spin-polarized materials, which takes into account the effect of the electrical bias on the spin-flip probability of an electron crossing the wall. We show that increasing the voltage reduces the spin-flip rate, and is therefore equivalent to reducing the width of the domain wall. As an application, we show that this effect widens the temperature window in which the operation of a unipolar spin diode is nearly ideal.
Polarization-selective waveguide bends in a photonic crystal structure with layered square symmetry
Authors: Roundy David , Lidorikis Elefterios , Joannopoulos J. D.
Published: December 2004

We demonstrate single-mode horizontal and vertical waveguides in a recently proposed photonic crystal having layered square symmetry. The vertical waveguide supports two degenerate polarizations, and thus light can be selectively steered into horizontal waveguides oriented at 90° based on its polarization. We calculate the transmission of 90° bends, both from horizontal waveguide to horizontal waveguide and from horizontal waveguide to vertical waveguide. In the case of the horizontal-horizontal bend, we show a transmission of 83% for a simple (“zero” radius of curvature) bend, and a peak transmission of 100% for a bend which has been optimized by moving one rod from the inner corner to the outer corner of the bend. For the vertical to horizontal bend, we find a transmission of 95% for the allowed polarization, but with a much smaller bandwidth than in the case of the optimized horizontal bend.
Emission of an intense large area electron beam from a slab of porous dielectric
Authors: Friedman M. , Myers M. , Hegeler F. , Swanekamp S. B. , Wolford M. F. , Sethian J. D. , Ludeking L.
Published: December 2004

Inserting a thick slab of porous dielectric (e.g., ceramic honeycomb) in front of the emitting surface of a large-area planar diode improves the electron beam emission uniformity, decreases the beam current rise and fall times, and maintains a more constant diode impedance. Particle-in-cell simulations of the first few nanoseconds of diode operation show that initially numerous secondary electrons and ions load the ceramic honeycomb. The electrons and ions were confined within the ceramic pores, redistributing the electric field by reducing it within the ceramic pores and increasing it on the cathode surface (by a factor of 2–3). After the initial stage, plasma fills the ceramic pores and the space between the cathode and the ceramic. A space-charge-limited electron beam was then emitted from the ceramic honeycomb. No surface plasma was detected outside the pores inside the diode vacuum. The introduction of dielectric into the diode solves two additional problems associated with large-area planar diodes: (1) Space-charge-limited flow in large-area planar diodes is susceptible to the transit time instability. Feeding the instability are growing transverse electromagnetic (TEM) waves that propagate along the anode-cathode gap. By inserting the slab of honeycomb ceramic in front of the emitting cathode these TEM waves are suppressed. (2) A planar diode emits an electron beam with an enhanced current density at the edges (edge effect). The ceramic slab can be easily machined and contoured so as to reduce this effect. The insertion of ceramic honeycomb into the diode had little affect onthe postshot diode pressure. However, deposition of gamma alumina on the ceramic reduced the postshot diode pressure by 80%. This enables the diode to be repetitively pulsed (rep-rated mode). The modified diode was fielded on Electra, a high-power, rep-rated, electron-beam pumped KrF laser. It operated for 50 000 shots at 1Hz and 8000 shots at 5Hz with little or no degradation in the pulse shape and with undetectable loss of cathode material.
Vapor-liquid-solid growth of germanium nanostructures on silicon
Authors: Dailey J. W. , Taraci J. , Clement T. , Smith David J. , Drucker Jeff , Picraux S. T.
Published: December 2004

The pressure and temperature dependencies for vapor-liquid-solid (VLS) growth of Ge nanostructures on Si using chemical vapor deposition are reported. Gold nanodots self-assembled by evaporation on clean hydrogen-terminated and heated Si substrates are used to seed the liquid eutectic VLS growth. Digermane pressures are varied from 4×10−5 to 1×10−2Torr and substrate temperatures from 400 to 600°C for heteroepitaxial growth on Si(111). Two types of nanostructures are identified, nanowires and nanopillars, with a transition from nanopillar growth to nanowire growth occurring with increasing pressure. Nanowires are characterized by rapid vertical growth, long-aspect-ratio structures, and linear dependence of the growth rate on pressure. At lower pressures a transition to nanopillars is observed; these exhibit both vertical and lateral growth with typical aspect ratios of 1:2. For Si(111) substrates nanowires grow epitaxially with their growth axis along the ⟨111⟩ direction. High-resolution transmission electron microscopy shows that the Ge nanowires are relaxed to their equilibrium lattice spacings a short distance from the Si substrate interface.
Exchange-enhanced g-factors in an Al0.25Ga0.75N∕GaN two-dimensional electron system
Authors: Cho K. S. , Huang Tsai-Yu , Huang Chao-Ping , Chiu Yi-Hsing , Liang C.-T. , Chen Y. F. , Lo Ikai
Published: December 2004

Low-temperature magnetotransport measurements were performed on an Al0.25Ga0.75N∕GaN two-dimensional electron system. In this system, we observe Shubnikov-de Haas (SdH) oscillations in a perpendicular magnetic field B. By measuring the positions of a pair of spin-split SdH maxima, we are able to estimate the g-factors at different Landau level (LL) indices. We find the g-factor is enhanced over its bulk value in GaN (≅2) due to many-body exchange interactions. Moreover, the measured g-factor increases with decreasing LL index, indicating that many-body electron–electron interactions become stronger as the number of occupied LLs decreases. Our results suggest that the exchange energy Eex shows an approximately linear B dependence.
Trap-assisted hole injection and quantum efficiency enhancement in poly(9,9′ dioctylfluorene-alt-benzothiadiazole) polymer light-emitting diodes
Authors: Seeley Alexander J. A. B. , Friend Richard H. , Kim Ji-Seon , Burroughes Jeremy H.
Published: December 2004

We report a reversible many-fold quantum efficiency enhancement during electrical driving of polymer light-emitting diodes (LEDs) containing poly(9,9′ dioctylfluorene-alt-benzothiadiazole) (F8BT), developing over several minutes or hours at low applied bias and recovering on similar time scales after driving. This phenomenon is observed only in devices containing F8BT as an emissive layer in pure or blended form, regardless of anode and cathode choices and even in the absence of a poly(styrene-sulphonate)-doped poly(3,4-ethylene-dioxythiophene) (PEDOT:PSS) layer. We report detailed investigations using a standardized device structure containing PEDOT:PSS and a calcium cathode. Direct measurements of trapped charge recovered from the device after driving significantly exceed the unipolar limit, and thermally activated relaxation suggests a maximum trap depth around 0.6eV. Neither photoluminescence nor electroluminescence spectra reveal any change in the bulk optoelectronic properties of the emissive polymer nor any new emissive species. During the quantum efficiency (QE) enhancement process, the bulk conduction of the device increases. Reverse bias treatment of the device significantly reinforces the QE enhancement. Based on these observations, we propose a simple model in which interfacial dipoles are generated by trapped holes near the anode combining with injected electrons, to produce a narrow tunneling barrier for easy hole injection. The new injection pathway leads to a higher hole current density and thus a better charge injection balance. This produces the relatively high quantum efficiency observed in all F8BT LEDs.