bluuebunny/crossref_metadata_2025 huggingface dataset:
Edge-driven rotating magnetic field current drive of field-reversed configurations
Authors: Milroy Richard D. , Miller Kenneth E.
Published: January 2004

Field-reversed configurations (FRCs) are created and sustained using a rotating magnetic field (RMF) in the Translation Confinement and Sustainment experiment. Normally this experiment is operated in a manner where the RMF only partially penetrates the plasma column. This method of operation may have significant advantages in producing less disturbances to the bulk of the FRC, but requires driving an overall radially inward flow to maintain Eθ(r)=0 everywhere (through the VrBz term in the generalized Ohm’s law). However, some RMF penetration is still required at the field null R, where Bz=0. For some experimental conditions it appears that the RMF does not even penetrate as far as the null, raising the question as to how Eθ(r=R) can be maintained at zero despite a finite η⊥jθ(r=R). Numerical simulations with a resistivity profile that is sharply peaked near the plasma edge yield similar profiles, and provide insight into this physical process. An inner magnetic structure forms, which rotates at a much lower frequency than the RMF. A tearing and reconnection process produces a torque transfer from the outer RMF to the inner structure, allowing it to act as an RMF downshifted to a lower frequency, and thus provide current drive to the inner region of the FRC. This mode of RMF current drive is being called “edge-driven mode.”
Testing of an edge thermal instability stabilization model for the low-to-high mode power threshold
Authors: Stacey W. M.
Published: January 2004

A test of a new model for the low-to-high (L–H) mode power threshold, based on the stabilization of edge thermal instabilities, is made by comparison with a set of DIII-D [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] discharges at times just prior to a L–H transition. Agreement is found between the measured power crossing the separatrix just prior to the L–H transition and the predicted power threshold for the stabilization of transport enhancing thermal instabilities.
Magnetic versus structural properties of Co nanocluster thin films: A magnetic force microscopy study
Authors: Koch S. A. , te Velde R. H. , Palasantzas G. , De Hosson J. Th. M.
Published: January 2004

Magnetic force microscopy (MFM) has been employed to study thin films consisting of low-energy-deposited cobalt nanoclusters. On continuous cluster layers a clear magnetic stray field pattern can be observed, although measurements on individual clusters are complicated by interference from topography. The magnetic correlation length determined from MFM images is substantially larger than the size of a single cluster. This indicates that the clusters are magnetically coupled to form stable domains associated with the formation of a correlated super-spin-glass state.
Critical current density and magnetic-field irreversibility of Na0.35CoO2⋅1.3H2O superconductor
Authors: Badica P. , Kondo T. , Togano K.
Published: January 2004

Critical current density Jc of Na0.35CoO2⋅1.3H2O superconductor (Tc=4.4 K) has been estimated from magnetization measurements: Jc(1.9 K,0 T)=5×104 A/cm2, Jc (1.9 K,0.4 T)=4×102 A/cm2 and Jc (3.4 K,0 T)=103 A/cm2. Jc versus applied magnetic field H cannot be fitted, as for high-Tc superconductors (HTS), by a power law for any temperature. The temperature dependence for a given H is not of the linear type as for MgB2, but is close to quasiexponential (associated with the thermally activated flux creep) as for HTS. Irreversibility field data points Hirr versus (1−T/Tc) obey a power law with power exponent n=3.4. The irreversibility line is located below, but in vicinity of, the line for Bi-2223. Details of morphology are also presented.
Reduction of threading dislocations in GaN layers using in situ deposited silicon nitride masks on AlN and GaN nucleation layers
Authors: Fang X. L. , Wang Y. Q. , Meidia H. , Mahajan S.
Published: January 2004

We have examined the influence of thin layers of silicon nitride, deposited in situ on AlN and GaN nucleation layers (NLs), on the density of threading dislocations (TDs) in GaN overgrowths. Results indicate that TD density is reduced to 2–4×108 cm−2. In GaN/silicon nitride/AlN–NL/sapphire composites, alternating regions of low and high TD density coexist in the overgrowth, and microstructural features characteristic of epitaxial lateral overgrowth techniques are seen. On the other hand, such features are absent in GaN/silicon nitride/GaN–NL/sapphire composites, and TDs are uniformly distributed.
Surface passivation effects on AlGaN/GaN high-electron-mobility transistors with SiO2, Si3N4, and silicon oxynitride
Authors: Arulkumaran S. , Egawa T. , Ishikawa H. , Jimbo T. , Sano Y.
Published: January 2004

Surface passivation effects were studied on AlGaN/GaN high-electron-mobility transistors (HEMTs) using SiO2, Si3N4, and silicon oxynitride (SiON) formed by plasma enhanced chemical vapor deposition. An increase of IDmax and gmmax has been observed on the passivated (SiO2, Si3N4 and SiON) HEMTs when compared with the unpassivated HEMTs. About an order of magnitude low IgLeak and three orders of magnitude high IgLeak was observed on Si3N4 and SiO2 passivated HEMTs, respectively, when compared with the unpassivated HEMTs. The increase of IgLeak is due to the occurrence of surface related traps, which was confirmed by the observation of kink and hysteresis effect on dc and ac IDS–VDS characteristics, respectively. Though the Si3N4 passivated HEMTs show better dc characteristics, the breakdown voltage (BVgd) characteristics are not comparable with SiO2, SiON passivated and unpassivated HEMTs. The SiON is also a very promising candidate as a surface passivant for AlGaN/GaN HEMTs because it shows better BVgd with low hysteresis width and small ID collapse than Si3N4 passivated HEMTs.
Scaling of the memory function and Brownian motion
Authors: Kneller G. R. , Sutmann G.
Published: January 2004

It has been recently shown that the velocity autocorrelation function of a tracer particle immersed in a simple liquid scales approximately with the inverse of its mass [J. Chem. Phys. 118, 5283 (2003)]. With increasing mass the amplitude is systematically reduced and the velocity autocorrelation function tends to a slowly decaying exponential, which is characteristic for Brownian motion. We give here an analytical proof for this behavior and comment on the usual explanation for Brownian dynamics which is based on the assumption that the memory function is proportional to a Dirac distribution. We also derive conditions for Brownian dynamics of a tracer particle which are entirely based on properties of its memory function.
Quantum dot/substrate interaction in InAs/In0.53Ga0.47As/InP(001)
Authors: Liao X. Z. , Zhu Y. T. , Qiu Y. M. , Uhl D. , Xu H. F.
Published: January 2004

InAs quantum dots grown on In0.53Ga0.47As/InP(001) substrate by low-pressure metalorganic chemical vapor deposition were investigated using high-angle annular dark-field imaging. Results suggest significant mass transport of mainly the large-sized component (InAs) from the In0.53Ga0.47As substrate to InAs quantum dots, an unexpected process that increases the system strain energy. The amount of the transported mass increases with quantum dot size. Two monolayers of GaAs inserted between InAs islands and the InGaAs substrate appears to block or at least effectively slow down this mass transport process.
Photoluminescence study of ZnO nanorods epitaxially grown on sapphire (112̄0) substrates
Authors: Zhang B. P. , Binh N. T. , Segawa Y. , Kashiwaba Y. , Haga K.
Published: January 2004

ZnO nanorods were synthesized on sapphire (112̄0) substrates by metalorganic vapor deposition. The rods exhibited better crystalline and optical properties than those of ZnO rods formed on sapphire (0001) substrates. The emission due to biexcitons is persistent up to ∼200 K, indicating potential for applications in biexciton-based nanoscale short-wavelength light-emitting photonic devices. The exciton–biexciton energy separation is independent of sample temperature. The band edge emission peak at room temperature is a mixture of free exciton and impurity-related transitions.
Two-dimensional photonic crystal Mach–Zehnder interferometers
Authors: Shih M. H. , Kim W. J. , Kuang Wan , Cao J. R. , Yukawa H. , Choi S. J. , O’Brien J. D. , Dapkus P. D. , Marshall W. K.
Published: January 2004

Mach–Zehnder interferometers were fabricated from suspended membrane photonic crystal waveguides. Transmission spectra were measured and device operation was shown to be in agreement with theoretical predictions.
Applicability of the power-law current–voltage characteristics to melt-textured YBa2Cu3O7−δ superconductors
Authors: Fisher L. M. , Kalinov A. V. , Mnatsakanov T. T. , Voloshin I. F. , Levchenko A. A. , Yampol’skii V. A.
Published: January 2004

A simple method is proposed for defining the parameters of current–voltage characteristics (CVCs) of hard superconductors, which is based on measuring the relaxation of magnetization. In this method, the inhomogeneity of the spatial distribution of the electric field and current density is taken into account. The limits of applicability of the power-law CVC are evaluated by comparing the experimental data with the results of numerical calculations.
Ultrasensitive quartz crystal microbalance with porous gold electrodes
Authors: Hieda Mitsunori , Garcia Rafael , Dixon Matt , Daniel Tad , Allara David , Chan M. H. W.
Published: January 2004

The quartz crystal microbalance is a sensitive thickness monitor used in a variety of technological applications. It is also a versatile research tool for chemical sensor, nanotribology, wetting transition, and superfluid transition studies. By replacing the conventional gold electrodes with porous gold electrodes, the effective adsorbing surface area and hence sensitivity was enhanced by a factor of 40 with no sacrifice of the mechanical quality factor or the stability in the resonant frequency.
Reduced 1/f noise in p-Si0.3Ge0.7 metamorphic metal–oxide–semiconductor field-effect transistor
Authors: Myronov M. , Mironov O. A. , Durov S. , Whall T. E. , Parker E. H. C. , Hackbarth T. , Höck G. , Herzog H.-J. , König U.
Published: January 2004

We have demonstrated reduced 1/f low-frequency noise in sub-μm metamorphic high Ge content p-Si0.3Ge0.7 metal–oxide–semiconductor field-effect transistors (MOSFETs) at 293 K. Three times lower normalized power spectral density (NPSD) SID/ID2 of drain current fluctuations over the 1–100 Hz range at VDS=−50 mV and VG−Vth=−1.5 V was measured for a 0.55 μm effective gate length p-Si0.3Ge0.7 MOSFET compared with a p-Si MOSFET. Performed quantitative analysis clearly demonstrates the importance of carrier number fluctuations and correlated mobility fluctuations (CMFs) components of 1/f noise for p-Si surface channel MOSFETs, and the absence of CMFs for p-Si0.3Ge0.7 buried channel MOSFETs. This explains the reduced NPSD for p-Si0.3Ge0.7 MOSFETs in strong inversion.
Nanoscopic electric potential probing: Influence of probe–sample interface on spatial resolution
Authors: Kuntze S. B. , Sargent E. H. , Dixon-Warren St. J. , White J. K. , Hinzer K. , Ban D.
Published: January 2004

Electric potential probing on the nanometer scale elucidates the operation of actively driven conducting, semiconducting, insulating and semi-insulating devices and systems. Spatial resolution of this analysis technique is shown to depend on the time required for the voltage measurement circuit to reach steady state with the local electric potential of the sample. Scanning voltage microscopy on actively biased buried heterostructure lasers reveals this time to be intrinsically long (10−2 s to 1 s) and to depend on material doping type (n- or p-type) and scan direction (to increasing or decreasing sample potential). The bandstructure of the probe–sample interface is examined and is shown to provide high incremental contact resistance to an equivalent circuit model of the measurement circuit. Practical scan speed limits are defined for accurate scanning electric potential measurements given a desired spatial resolution.
V defects of ZnO thin films grown on Si as an ultraviolet optical path
Authors: Yoo Y.-Z. , Sekiguchi T. , Chikyow T. , Kawasaki M. , Onuma T. , Chichibu S. F. , Song J. H. , Koinuma H.
Published: January 2004

V defects were observed in the ZnO films epitaxially grown on the ZnS-buffered Si. Although the defects were located on the surface, strong near-bandedge emission confined to the {101̄1} facets of V defects was observed at room temperature. The near-bandedge emission spreads out over the whole film centering at V defects at 30 K. The detailed optical characterization shows that activation of excitonic absorption is responsible for this unique optical behavior.
Fabrication and electrical properties of grain-oriented 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 ceramics
Authors: Sun Shiwen , Pan Xiaoming , Wang Pingchu , Zhu Lihui , Huang Qingwei , Li Donglin , Yin Zhiwen
Published: January 2004

〈112〉 grain-oriented 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 (PMN–0.3PT) piezoelectric ceramics with a degree of orientation of 0.35 have been produced from melt by a directional solidification method. The dielectric, ferroelectric, and piezoelectric properties were investigated, e.g., εrt∼4800, tan δ<0.6%, d33∼1500–1600 pC/N, kt∼51%, and k33∼82%, some of these values are comparable to those of PMN–PT single crystals. The strain–electric-field curve with a maximum strain of 0.23% at a field of 22 kV/cm and well-saturated hysteresis loops with a Pr∼35 μC/cm2 were recorded. The results demonstrate that the directional solidification method is a promising technique to fabricate high performance grain-oriented PMN–PT ceramics.
Optically controlled electroabsorption modulators for unconstrained wavelength conversion
Authors: Sabnis V. A. , Demir H. V. , Fidaner O. , Harris J. S. , Miller D. A. B. , Zheng J.-F. , Li N. , Wu T.-C. , Chen H.-T. , Houng Y.-M.
Published: January 2004

We introduce a proof-of-concept, optically controlled, optical switch based on the monolithic integration of a surface-illuminated photodetector and a waveguide electroabsorption modulator. We demonstrate unconstrained wavelength conversion over the entire center telecommunication wavelength band (C band) and optical switching up to 2.5 Gbit/s with extinction ratios exceeding 10 dB. Our approach offers both high-speed, low-power, switching operation and two-dimensional array scalability for the fabrication of chip-scale reconfigurable multichannel wavelength converters.
Optical observation of lipid- and polymer-shelled ultrasound microbubble contrast agents
Authors: Bloch Susannah H. , Wan Mingxi , Dayton Paul A. , Ferrara Katherine W.
Published: January 2004

High-speed optical experiments demonstrate that the behavior of a polymer-shelled microbubble contrast agent in response to an acoustic pulse is qualitatively and quantitatively different from that of a lipid-shelled agent. The lipid-shelled agent expands in response to a two-cycle pulse, and at pressures approaching 1 MPa, both the shell and its contents fragment. The polymer-shelled agent remains largely intact at pressures up to 1.5 MPa and exhibits a different destruction mechanism: the polymer shell does not oscillate significantly in response to ultrasound; instead, a gas bubble is extruded and ejected through a shell defect while the shell appears to remain largely intact.
Anisotropic in-plane strains and dielectric properties in (Pb,Sr)TiO3 thin films on NdGaO3 substrates
Authors: Lin Y. , Chen X. , Liu S. W. , Chen C. L. , Lee Jang-Sik , Li Y. , Jia Q. X. , Bhalla A.
Published: January 2004

Anisotropic in-plane strain can be induced in (Pb,Sr)TiO3 (PST) thin film by using orthorhombic NdGaO3 (110) as a substrate. High-resolution x-ray diffraction was used to measure the strain of the PST thin film. A rocking curve with full width at half maximum of ∼0.04° illustrated that the film had nearly perfect single-crystalline quality. Reciprocal space maps around the (001), (103), and (013) reflections of the PST film revealed anisotropic in-plane strain of 485 ppm along [100] and 26 ppm along [010], respectively. Coplanar capacitance measurements also showed systematic changes in the dielectric constant and tunability due to strain; about a 15% difference in tunability at surface field of 50 kV/cm and a 20% difference in the zero-field dielectric constant were observed along [100] and [010], respectively.
Mechanism for bistability in organic memory elements
Authors: Bozano L. D. , Kean B. W. , Deline V. R. , Salem J. R. , Scott J. C.
Published: January 2004

We demonstrate that the resistive switching phenomenon observed in organic semiconductor layers containing granular metal particles conforms to a charge storage mechanism described by Simmons and Verderber [Proc. R. Soc. A 391, 77 (1967)]. The space-charge field due to the stored charge inhibits further charge injection from the electrodes. The equilibrium current–voltage curve is N shaped and the low and high resistance states are obtained by applying voltage close to the local maximum and minimum, respectively.
Binary liquid mixtures in porous solids
Authors: Alnaimi S. M. , Mitchell J. , Strange J. H. , Webber J. B. W.
Published: January 2004

The technique of nuclear magnetic resonance cryoporometry has been used to study the behavior of binary liquid mixtures of water and decane in porous sol–gel silicas. It was observed that the water preferentially adsorbed onto the silica surface and so was able to displace the decane from the pores.
Annealing effects on optical and structural properties of 1.3-μm GaInNAs/GaAs quantum-well samples capped with dielectric layers
Authors: Liu H. F. , Peng C. S. , Pavelescu E.-M. , Jouhti T. , Karirinne S. , Konttinen J. , Pessa M.
Published: January 2004

Effects of thermal annealing on photoluminescence (PL) and x-ray diffraction from metastable GaInNAs/GaAs quantum-well samples covered by dielectric layers have been studied. PL from uncoated samples exhibits a saturable blueshift of 22 meV relative to PL from the as-grown samples in these experiments. The shift is attributable to a change in the nearest neighbors of nitrogen in short-range-order N-InmGa4−m (0⩽m⩽4) clusters at a fixed composition with negligible Ga/In/N interdiffusion. A Si3N4 cap layer effectively prevents the blueshift in the early stage of annealing and improves emission intensity. Under severe annealing conditions (750 °C for 1500 s), the maximum blueshift for the Si3N4-covered samples is 31 meV. A SiO2 cap layer causes a large nonsaturable blueshift, almost 100 meV in these experiments. The large blueshift is assigned to the formation of defects (likely Ga vacancies) at the SiO2/GaAs interface. The defects are believed to diffuse into the bulk at elevated temperatures and to assist Ga/In/N interdiffusion.
Analysis of reverse-bias leakage current mechanisms in GaN grown by molecular-beam epitaxy
Authors: Miller E. J. , Yu E. T. , Waltereit P. , Speck J. S.
Published: January 2004

Temperature-dependent current–voltage measurements have been used to determine the reverse-bias leakage current mechanisms in Schottky diodes fabricated on GaN grown by molecular-beam epitaxy, and two dominant mechanisms are clearly identified. The first mechanism is field-emission tunneling from the metal into the semiconductor, which is dominant at low temperatures and which, at higher temperatures, becomes significant for large reverse-bias voltages. The second mechanism, presumed to be associated with dislocation-related leakage current paths, is observed to have an exponential temperature dependence and becomes significant above approximately 275 K. The temperature dependence of the second mechanism is consistent with either one-dimensional variable-range-hopping conduction along the dislocation or trap-assisted tunneling.
Infrared spectroscopic analysis of an ordered Si/SiO2 interface
Authors: Queeney K. T. , Herbots N. , Shaw Justin M. , Atluri V. , Chabal Y. J.
Published: January 2004

Infrared spectroscopy is used to compare the Si/SiO2 interfaces created by thermal oxidation of a standard Si(100) substrate and of an ordered, (1×1) Si(100) substrate. The thermal oxides (approximately 25 Å) examined in this study are etched in dilute hydrofluoric acid and the resulting films analyzed spectroscopically. The behavior of the dominant optical phonon modes as a function of film thickness provides strong evidence that the ordered Si(100) substrate provides a template for an Si/SiO2 interface with a higher degree of homogeneity in the Si–O bonding environment of the intervening substoichiometric SiOx layer than does the standard Si(100) substrate.
Scanning near-field infrared microscopy based on tapered silver–halide probes
Authors: Ephrat P. , Roodenko K. , Nagli L. , Katzir A.
Published: January 2004

We report on developments in scanning near-field infrared microscopy where the scanning elements are silver–halide tapered fiber probes. These probes showed good transmission efficiency and a transparency over a very wide spectral range (0.6–10 μm), which may prove useful in high-resolution spectroscopy. We performed spatial characterization of the radiation distribution emitted from these probes, using the knife-edge technique. The obtained profiles, measured both for midinfrared and for visible radiation, were consistent with theoretical predictions. Images of subwavelength features, acquired with these probes, validated their potential for super-resolution microscopy, spectroscopy, and radiometry in the midinfrared.
Efficiency enhancement in a light-emitting diode with a two-dimensional surface grating photonic crystal
Authors: Ichikawa Hiroyuki , Baba Toshihiko
Published: January 2004

We demonstrate a light-emitting diode exhibiting 1.7–2.7-fold enhancement in light extraction efficiency compared with that for a planer device. It has a two-dimensional surface grating photonic crystal, which diffracts internal light with a large solid angle into the escape light cone. Due to its shallow grating separated from the active layer and micron order lattice constant, the fabrication process is simple, applicable to arbitrary semiconductor devices, and free from process-induced nonradiative recombinations.
Parallel high-throughput microanalysis of materials using microfabricated full bridge device arrays
Authors: Potyrailo Radislav A. , Morris William G.
Published: January 2004

An array of microfabricated full bridge devices has been implemented for the rapid thermal microanalysis of polymers. In each microelectromechanical system device, four strain gauges were formed in silicon cantilevered microbeams and were configured as a Wheatstone bridge circuit. Glass transition temperatures Tg were measured by the quantitation of the strain produced in the sensor by the stress applied by a polymer layer to the cantilevered microbeams. The measured strain was analyzed as a function of chip temperature for the change in the slope, which was indicative to Tg. Resolution of Tg determinations of amorphous and crystalline polymers was <0.25 °C and <2.0 °C, respectively, being attractive for combinatorial screening of polymers. Our approach is a practical alternative to known methods for Tg determinations because of the immunity to the variations in the amount of deposited material and its viscosity, vapor pressure of employed solvent, and ease of multiplexing into dense sensor arrays.
Impact of current crowding on electromigration-induced mass transport
Authors: Wang H. , Bruynseraede C. , Maex K.
Published: January 2004

To assess the relevance of current crowding to electromigration-induced mass transport, a test structure was designed to structurally induce and accelerate current crowding in Cu damascene lines. Electromigration experiments and quantitative finite element analysis demonstrate how current crowding can substantially enhance local atomic flux along critical diffusion paths. The resulting flux divergence leads to rapid void nucleation and growth. The observed increase in atomic flux and flux divergence is also moderately affected by the presence of Joule-heating-induced temperature gradients.
Blocking thin-film nonuniformities: Photovoltaic self-healing
Authors: Roussillon Y. , Giolando D. M. , Shvydka Diana , Compaan A. D. , Karpov V. G.
Published: January 2004

An approach is developed to block the effects of lateral nonuniformities in thin-film semiconductor structures. The nonuniformity modulates the surface photovoltage distribution. When exposed to light and immersed in a proper electrolyte, this distribution will generate laterally nonuniform electrochemical reactions. Such treatments result in a nonuniform interfacial layer that balances the original nonuniformity. This approach has been implemented for CdTe/CdS photovoltaic devices, in which it improved the device efficiency from 1%–3% to 11%–12%.
III-nitride blue and ultraviolet photonic crystal light emitting diodes
Authors: Oder T. N. , Kim K. H. , Lin J. Y. , Jiang H. X.
Published: January 2004

We present results on enhancement of 460 nm blue and 340 nm UV optical power output in III-nitride light emitting diodes (LEDs) using photonic crystals (PCs) under current injection. Triangular arrays of the PCs with diameter/periodicity of 300/700 nm were patterned using electron-beam lithography and inductively coupled plasma dry etching. The total power at 20 mA of 300×300 μm2 unpackaged LED chips revealed an increase by 63% and 95% for the blue and UV LEDs, respectively, as a result of the PC formation. Possible ways for further improving enhancement of light extraction using PCs are discussed.
Deformation twinning in nanocrystalline copper at room temperature and low strain rate
Authors: Liao X. Z. , Zhao Y. H. , Srinivasan S. G. , Zhu Y. T. , Valiev R. Z. , Gunderov D. V.
Published: January 2004

The grain-size effect on deformation twinning in nanocrystalline copper is studied. It has been reported that deformation twinning in coarse-grained copper occurs only under high strain rate and/or low-temperature conditions. Furthermore, reducing grain sizes has been shown to suppress deformation twinning. Here, we show that twinning becomes a major deformation mechanism in nanocrystalline copper during high-pressure torsion under a very slow strain rate and at room temperature. High-resolution transmission electron microscopy investigation of the twinning morphology suggests that many twins and stacking faults in nanocrystalline copper were formed through partial dislocation emissions from grain boundaries. This mechanism differs from the pole mechanism operating in coarse-grained copper.
Viscous flow of the Pd43Ni10Cu27P20 bulk metallic glass-forming liquid
Authors: Fan G. J. , Fecht H.-J. , Lavernia E. J.
Published: January 2004

The equilibrium viscosity of the Pd43Ni10Cu27P20 bulk metallic glass-forming liquid was measured over a wide temperature range from the equilibrium supercooled liquid state to the glass transition region using parallel-plate rheometry and three-point beam bending. Based on the measured viscosity data, the fragility of this liquid was quantitatively determined. The Pd43Ni10Cu27P20 alloy, despite exhibiting the best glass-forming ability reported thus far, is relatively fragile compared with other bulk glass-forming liquids, such as Vit 1 and Vit 4.
Positional disorder of oxygen ions in ceria at high temperatures
Authors: Yashima Masatomo , Kobayashi Syuuhei
Published: January 2004

Accurate nuclear density distribution of ceria, CeO2 has been studied between 1005 and 1497 °C by the maximum-entropy method-based pattern fitting combined with the Rietveld method using neutron powder diffraction data. The results reveal that the oxygen ions have a complicated disorder spreading over a wide area and shift to the 〈111〉 directions from the ideal fluorite position. This feature is more significant at higher temperatures, which is consistent with the higher ionic conductivity.
Anisotropic structural characteristics of (112̄0) GaN templates and coalesced epitaxial lateral overgrown films deposited on (101̄2) sapphire
Authors: Wang Hongmei , Chen Changqing , Gong Zheng , Zhang Jianping , Gaevski Mikhail , Su Ming , Yang Jinwei , Khan M. Asif
Published: January 2004

a-plane GaN templates and coalesced epitaxial lateral overgrown (ELOG) films on r-plane sapphire substrates were investigated by x-ray diffraction (XRD). The a-plane GaN templates were found to have [0001]-oriented stripe-features, which is related to anisotropic mosaicity. For the mosaic blocks, the mosaicity reached the largest and the smallest values along the [11̄00] and the [0001] directions. The ELOG procedure with the SiO2 mask stripes perpendicular to the [0001] direction limits the preferable growth along this direction, and thereby enhances the [11̄00] growth. This leads to large-area, featureless, a-plane GaN films for which the wing tilt and not the fine mosaic block size becomes the major XRD line-broadening mechanism.
Magnetostriction and anisotropy compensation in TbxDy1−xPr0.3(Fe0.9B0.1)1.93 alloys
Authors: Ren W. J. , Zhang Z. D. , Zhao X. G. , Liu W. , Geng D. Y.
Published: January 2004

Structure and magnetostriction of Dy0.7−xTbxPr0.3(Fe0.9B0.1)1.93 (0⩽x⩽0.70) alloys have been studied. The easy magnetization direction of the Laves phase in the Dy0.7−xTbxPr0.3(Fe0.9B0.1)1.93 alloys with 0⩽x<0.20 lies along 〈100〉 axis, while that of the Laves phase in those alloys with 0.25⩽x⩽0.70 lies along 〈111〉 axis, as determined by means of x-ray crystallography study. When x is increased from 0.15 to 0.25, the change of the easy magnetization direction from 〈100〉 to 〈111〉 axis is detected also by Mössbauer spectra, in good agreement with the results of x-ray crystallography. The Laves phase Tb0.25Dy0.45Pr0.3(Fe0.9B0.1)1.93 has a large spontaneous magnetostriction (λ111≈1850 ppm) and a low anisotropy at room temperature, which could make it a good candidate material for magnetostriction applications.
Strongly cluster size dependent reaction behavior of CO with O2 on free silver cluster anions
Authors: Socaciu Liana D. , Hagen Jan , Le Roux Jérôme , Popolan Denisia , Bernhardt Thorsten M. , Wöste Ludger , Vajda Štefan
Published: January 2004

Reactions of free silver anions Agn− (n=1–13) with O2, CO, and their mixtures are investigated in a temperature controlled radio frequency ion trap setup. Cluster anions Agn− (n=1–11) readily react with molecular oxygen to yield AgnOm− (m=2, 4, or 6) oxide products. In contrast, no reaction of the silver cluster anions with carbon monoxide is detected. However, if silver cluster anions are exposed to the mixture of O2 and CO, new reaction products and a pronounced, discontinuous size dependence in the reaction behavior is observed. In particular, coadsorption complexes Agn(CO)O2− are detected for cluster sizes with n=4 and 6 and, the most striking observation, in the case of the larger odd atom number clusters Ag7−, Ag9−, and Ag11−, the oxide product concentration decreases while a reappearance of the bare metal cluster signal is observed. This leads to the conclusion that carbon monoxide reacts with the activated oxygen on these silver clusters and indicates the prevalence of a catalytic reaction cycle.
Carrier concentration dependence of Ti/Al/Pt/Au contact resistance on n-type ZnO
Authors: Ip K. , Heo Y. W. , Baik K. H. , Norton D. P. , Pearton S. J. , Ren F.
Published: January 2004

Ti/Al/Pt/Au ohmic contacts on n-type ZnO with a range of carrier concentrations (7.5×1015–1.5×1020 cm−3) show as-deposited specific contact resistances in the range from 3×10−4 to 8×10−7 Ω cm2. Temperature-dependent measurements showed that the dominant transport mechanisms were tunneling in the contacts in the most highly doped films and thermionic emission in the more lightly doped films. After annealing at 200 °C, the lowest specific contact resistance achieved was 2.2×10−8 Ω cm2. However, the contacts show evidence of reactions between the Ti and the ZnO film even for this low annealing temperature, suggesting that applications requiring good thermal stability will need metallurgy with better thermal stability.
Amorphous silicon electrostatic microresonators with high quality factors
Authors: Gaspar J. , Chu V. , Conde J. P.
Published: January 2004

Phosphorus-doped amorphous-silicon thin-film micromachined mechanical bridge resonators are processed at low temperatures (⩽110 °C) on glass substrates. The microelectromechanical structures are electrostatically actuated, and the resulting deflection is monitored optically. Resonance frequencies in the megahertz range are observed with quality factors up to 5000 when measured in vacuum. The energy dissipation processes in amorphous-silicon thin-film microbridges are discussed. The dominant intrinsic dissipation mechanism is surface loss.
The effect of mixed Mn valences on Li migration in LiMn2O4 spinel: A molecular dynamics study
Authors: Tateishi Kenji , du Boulay Douglas , Ishizawa Nobuo
Published: January 2004

Previous molecular dynamics (MD) simulations have shown that, with good choice of potential shapes and parameters, the structure and properties of stoichiometric LiMn2O4 can be reproduced to good accuracy. In particular, the experimentally observed self-diffusion of Li ions was shown to occur only for a discrete, mixed Mn valence model. Here, those MD studies have been extended, demonstrating that periodically switching the Mn valence states, reflecting an electron hopping model, greatly facilitates the Li ion self-diffusion. The interaction is mediated by the O atoms, which coordinate both cations and temporarily adopt local distortions based on the three coordinating Mn valences. Although the O atoms continue to vibrate harmonically about a displaced mean, permitting the Li atoms to migrate, the time and spatial average remains that of the ideal spinel with distributed Li.
One-polymer active pixel
Authors: Tzeng K. L. , Meng H. F. , Tzeng M. F. , Chen Y. S. , Liu C. H. , Horng S. F. , Yang Y. Z. , Chang S. M. , Hsu C. S. , Chi C. C.
Published: January 2004

A metal-oxide field-effect transistor (MOSFET) based on an electroluminescent conjugated polymer is fabricated on a glass substrate. It is found that the mobility horizontal to the substrate is two to three orders of magnitude larger than the mobility vertical to the substrate. The high horizontal mobility is attributed to the in-plane chain alignment in amorphous spin-coated films. We demonstrate an active pixel in which the light-emitting diode and the driving MOSFET share the same active polymer.
Practical electron-tunneling refrigerator
Authors: Clark A. M. , Williams A. , Ruggiero S. T. , van den Berg M. L. , Ullom J. N.
Published: January 2004

We demonstrate a thin-film, solid-state refrigerator based on the removal of hot electrons from a metal by quantum-mechanical tunneling. We have reduced the electronic temperature in a metal film from 260 to ∼130 mK. The base temperature of the device is predicted to increase to near 140 mK under a power load of 10 pW. Both the cooling power and temperature reduction of the refrigerator are well matched to practical applications. This refrigerator will make high-performance cryogenic photon sensors more accessible to the astronomical and analytical communities.
Electrochemical potential arrangement of nanoclusters weakly coupled with metal surface
Authors: Ohgi Taizo , Sakotsubo Yukihiro , Ootuka Youiti , Fujita Daisuke
Published: January 2004

We investigated the electrochemical potential arrangement of Au nanoclusters, 1–3 nm in diameter, weakly coupled with bulk Au surface through tunneling junctions. The measurement of the Coulomb staircase by scanning tunneling spectroscopy and the statistical analysis for clusters reveal that [μ(0)+μ(1)]/2, where μ(n) is the electrochemical potential of the cluster when the number of excess electrons changes between n−1 and n, distributes around the Fermi level of the bulk Au electrode with the standard deviation σ of 30–70 meV. The spacing ΔE of the equally spaced electrochemical potentials decreases with increasing cluster size, which leads to the breakdown of the charge neutrality of the clusters below ΔE∼0.3 eV due to the competition between σ and ΔE.
Room-temperature ballistic electron emission luminescence spectroscopy with a scanning tunneling microscope
Authors: Appelbaum Ian , Russell K. J. , Kozhevnikov M. , Narayanamurti V. , Hanson M. P. , Gossard A. C.
Published: January 2004

We present a luminescence spectroscopy for semiconductor heterostructures based on local hot electron injection from a scanning tunneling microscope tip. In addition to a tip voltage bias exceeding the metal-semiconductor Schottky barrier height, this process requires a collector bias voltage to satisfy energy conservation. These results indicate that this method could be used to study local electron transport and simultaneous electroluminescence in buried luminescent layers at depths greater than the ballistic electron mean free path in the collector.
Towards ultranarrow bandwidth polymer-based resonant grating waveguide structures
Authors: Katchalski T. , Teitelbaum E. , Friesem A. A.
Published: January 2004

The needed parameters and configurations that would lead to the achievement of ultranarrow spectral bandwidths in polymer-based resonant grating waveguide structures are presented. These include the addition of an upper polymeric layer to the basic configuration and increasing the waveguide thickness. The results reveal that spectral bandwidths as narrow as 0.15 nm at 1.5 μm can be achieved.
Deposition and electrical properties of N–In codoped p-type ZnO films by ultrasonic spray pyrolysis
Authors: Bian J. M. , Li X. M. , Gao X. D. , Yu W. D. , Chen L. D.
Published: January 2004

The N–In codoped p-type ZnO films have been prepared by ultrasonic spray pyrolysis. X-ray photoelectron spectroscopy analysis confirmed the presence of nitrogen and indium in the codoped films, and the incorporation of indium causes the change in the chemical state of nitrogen, which promotes the formation of p-type conduction. Low resistivity of 1.7×10−2 Ω cm, high carrier concentration of 2.44×1018 cm−3 and Hall mobility of 155 cm2 V−1 s−1 at room temperature for the codoped films were obtained. A conversion from p-type conduction to n type in a range of temperature has been identified by the measurement of Seebeck and Hall effect.
Formation and optical properties of CdTe self-assembled quantum rings with electronic states embedded in ZnTe barriers
Authors: Kim T. W. , Lee E. H. , Lee K. H. , Kim J. S. , Park H. L.
Published: January 2004

Atomic force microscopy (AFM) measurements were carried out to investigate the structural properties of CdTe/ZnTe quantum rings (QRs), and photoluminescence (PL) measurements were performed to determine the electron activation energy. The AFM images showed that uniform CdTe QRs were formed on ZnTe buffer layers. While the excitonic peak corresponding to the transition from the ground electronic subband to the ground heavy-hole band (E1–HH1) in the CdTe/ZnTe QRs was shifted to higher energy in comparison with that in CdTe/ZnTe quantum wires and quantum wells, it was shifted to lower energy in comparison with that in CdTe/ZnTe quantum dots. The activation energy of the electrons confined in the CdTe QRs, as obtained from the temperature-dependent PL spectra, was higher than those in CdTe quantum wires and quantum wells and smaller than that in CdTe quantum dots. The present results can help improve understanding of the formation and optical properties of the CdTe QRs grown on ZnTe buffer layers.
Nonplanar two-dimensional electron gases in InAs heterostructures on GaAs
Authors: Löhr S. , Heyn Ch. , Hansen W.
Published: January 2004

Using transport measurements in tilted magnetic fields we observe direct evidence of a nonplanar electron system in an InAs/InGaAs quantum well. The corrugation results from the lattice-mismatched epitaxial growth of the heterostructure on a GaAs substrate. We argue that the curvature of the electron system may result in an appreciable effective spin-orbit interaction.
Interpretation of Fermi level pinning on 4H-SiC using synchrotron photoemission spectroscopy
Authors: Han Sang Youn , Lee Jong-Lam
Published: January 2004

The Fermi level movements on 4H-SiC were observed in in situ deposited Ni contact using synchrotron radiation photoemission spectroscopy. For n-type SiC, the surface band bending increased about 0.75 eV with the Ni deposition, meaning the shift of Fermi level towards valence band edge. The barrier height was calculated to be 1.61 eV, consistent with the Schottky–Mott theory (1.65 eV). For p-type SiC, however, the barrier height was 0.95 eV, lower than theoretical value (1.61 eV). The large discrepancy is due to the defect level (activation energy=0.96 eV) observed by deep level transient spectroscopy, leading to a major role in pinning the Fermi level in p-type SiC.
Wind-induced roughening of thin liquid films
Authors: Mate C. Mathew
Published: January 2004

A constant wind shear stress is shown to induce roughness on molecularly thin perfluoropolyether films that are susceptible to dewetting. These wind-induced roughening or dewetting features are pinned to the silicon substrate surface, indicating that these perfluoropolyethers have a heterogeneous interaction with the surface. These results highlight the role of chemical heterogeneity in nucleating dewetting phenomena.
Complete magneto-optical waveguide mode conversion in Cd1−xMnxTe waveguide on GaAs substrate
Authors: Zayets V. , Debnath M. C. , Ando K.
Published: January 2004

Complete magneto-optical mode conversion was attained in a waveguide of diluted magnetic semiconductor Cd1−xMnxTe grown on GaAs substrate. Mode conversion ratio 98%±2% under a magnetic field of 5 kG was achieved in the waveguide with graded-refractive-index clad layer. The Cd1−xMnxTe waveguide showed an optical loss below 1 dB/cm, and a high magneto-optical figure-of-merit, 200 deg/dB/kG at λ=730 nm. High efficiency magneto-optical mode conversion in a waveguide grown on a semiconductor substrate shows the feasibility of monolithical integration of an optical isolator with semiconductor optoelectronic devices.
Fabrication and magnetocardiography application of the second-order superconducting quantum interference device gradiometer made from a single-layer of YBa2Cu3O7 film
Authors: Lee Soon-Gul , Park Seung Moon , Kang Chan Seok , Yu Kwon-Kyu , Kim In-Seon , Park Yong Ki
Published: January 2004

We have fabricated single-layer, second-order high Tc superconducting quantum interference device (SQUID) gradiometers on SrTiO3 substrates and investigated their noise properties and performance in magnetocardiography. The gradiometer consists of three parallel pickup loops that are directly coupled to a step-edge junction SQUID, in such a way that the coupling polarity of two side loops is opposite to that of the center loop. The overall size of the device is 17.6 mm×6 mm with a baseline of 5.8 mm. The measured gradient noises are 0.45 and 0.84 pT/cm2/√Hz at 1 Hz for the shielded and the unshielded cases, respectively, which correspond to equivalent field noises of 150 and 280 fT/√Hz, respectively. In spite of the short baseline of 5.8 mm, the high common-mode rejection ratio of the gradiometer, 103, allowed us to record a magnetocardiogram of a human subject, which demonstrates the feasibility of the design in biomagnetic studies.
Thickness and dielectric constant of dead layer in Pt/(Ba0.7Sr0.3)TiO3/YBa2Cu3O7−x capacitor
Authors: Chen B. , Yang H. , Zhao L. , Miao J. , Xu B. , Qiu X. G. , Zhao B. R. , Qi X. Y. , Duan X. F.
Published: January 2004

Pt /( Ba 0.7 Sr 0.3 ) TiO 3  (BST)/YBa2Cu3O7−x capacitors were prepared and investigated for the dead-layer (DL) thickness (td) and the DL dielectric constant (εd). Based on the series capacitor model, the td/εd ratio of 0.066 nm and the bulk BST ferroelectric-layer dielectric constant of 1370 were obtained through the measurements of the capacitance–voltage characteristics. The td×εd value of 120 nm was obtained through the measurements of the current–voltage characteristics. Combining these data, the DL thickness and the DL dielectric constant are respectively estimated to be 2.8 nm and 42.6.
The Turkish Minority in Contemporary Bulgaria
Authors: Warhola James W. , Boteva Orlina
Published: January 2004

Although there is indisputable evidence of hostile perceptions, the gulf between ethnic groups has not yet caused any substantial violence between Turks and Bulgarians. Compared not only with former Yugoslavia but also with Romania, this must be upheld as a genuine success story in the endeavor to cope with ethnic tensions in post-Communist Eastern Europe. (Wolfgang Hoepken)
When Weak Nations Use Strong States: The Unintended Consequences of Intervention in the Balkans
Authors: Marsh Christopher , Heppner Mark
Published: January 2004

In the years that have passed since NATO forcibly compelled Yugoslavia to withdraw its military and police forces from Kosovo and the province was placed under U. N. guardianship, the Kosovo crisis of 1999 has been examined from a variety of angles. Although many insightful analyses have documented the horrific and deplorable events that led up to the crisis, one important factor that has received relatively short shrift is the way in which the U. S. was drawn into the conflict. In particular, it has remained overlooked that the United States,quasuperpower, had a significant impact on the policy formulations of the belligerent parties. This essay is based on the proposition that the United States does not formulate policy and operate in a vacuum, but rather that the U. S. is itself a critical factor in the calculations of other actors in the international system. These actors make strategic calculations based upon their expectations of American actions and reactions. The U. S. policymaking community, on the other hand, seems to formulate policies without considering the implications of the fact that other actors might anticipate U. S. actions or even attempt to provoke a desired response.
Keepers of Order? Strategic Legality in the 1935 Czechoslovak General Elections
Authors: Campbell Michael Walsh
Published: January 2004

Konrad Henlein founded the Sudeten GermanHeimatfront(SHF) in October 1933 and in less than a year and a half it would become the largest party in the First Czechoslovak Republic. This achievement is all the more remarkable in light of the initiative undertaken by the Czech and German Social Democrats, as well as the Communists to have the SHF banned in the year before the elections. This initiative would most likely have succeeded had the matter not been referred to Czechoslovakia's ailing President, Tomáš Masaryk. After the state had banned both the Sudeten German Nazi and Nationalist parties on account of their alleged ties to Hitler, Masaryk concluded one month before the 19 May 1935 general elections that the SHF should be allowed to campaign.1Masaryk, however, mandated that theHeimatfrontmust change its name to the more democratic “Sudeten German Party” (SdP). Despite the specter of a ban that still haunted the party in the month before the election, the SdP succeeded in transforming itself from a political pariah into a majority German party by using the legal protections and security forces of Czech democracy to wage a legalistic campaign against the state. In light of this stunning success, how then did the party leadership perform this act of political alchemy and what strategies did it deploy in campaigning against the state?