bluuebunny/crossref_metadata_2025 huggingface dataset:
Phospholipase C activator m‐3M3FBS affects Ca2+ homeostasis independently of phospholipase C activation
Authors: Krjukova Jelena , Holmqvist Tomas , Danis Alexander S , Åkerman Karl E O , Kukkonen Jyrki P
Published: September 2004

In this study, we have investigated responses to the phospholipase C (PLC) activator m‐3M3FBS in SH‐SY5Y human neuroblastoma cells. As measured using fura‐2, m‐3M3FBS caused a slowly developing − full response was obtained within 4–6 min − Ca2+ elevation both in the presence and absence of extracellular Ca2+, indicating Ca2+ release from intracellular stores, putatively from endoplasmic reticulum and mitochondria. PLC activity was also measured using two methods, the classical ion‐exchange separation and the more novel fluorescent real‐time method. In the time frame in which m‐3M3FBS caused Ca2+ elevation (up to 7 min), no PLC activation was detected. Instead, more than 20 min were required to see any inositol phosphate generation in response to m‐3M3FBS. m‐3M3FBS also interfered with store‐operated Ca2+ influx and Ca2+ extrusion. In conclusion, m‐3M3FBS cannot be considered either potent or specific PLC activator.

British Journal of Pharmacology (2004) 143, 3–7. doi:10.1038/sj.bjp.0705911
Nucleoside transporter subtype expression and function in rat skeletal muscle microvascular endothelial cells
Authors: Archer Richard G E , Pitelka Václav , Hammond James R
Published: September 2004

Microvascular endothelial cells (MVECs) form a barrier between circulating metabolites, such as adenosine, and the surrounding tissue. We hypothesize that MVECs have a high capacity for the accumulation of nucleosides, such that inhibition of the endothelial nucleoside transporters (NT) would profoundly affect the actions of adenosine in the microvasculature.

We assessed the binding of [3H]nitrobenzylmercaptopurine riboside (NBMPR), a specific probe for the inhibitor‐sensitive subtype of equilibrative NT (es), and the uptake of [3H]formycin B (FB), by MVECs isolated from rat skeletal muscle. The cellular expression of equilibrative (ENT1, ENT2, ENT3) and concentrative (CNT1, CNT2, CNT3) NT subtypes was also determined using both qualitative and quantitative polymerase chain reaction techniques.

In the absence of Na+, MVECs accumulated [3H]FB with a Vmax of 21±1 pmol μl−1 s−1. This uptake was mediated equally by es (Km 260±70 μM) and ei (equilibrative inhibitor‐insensitive; Km 130±20 μM) NTs.

A minor component of Na+‐dependent cif (concentrative inhibitor‐insensitive FB transporter)/CNT2‐mediated [3H]FB uptake (Vi 0.008±0.005 pmol μl−1 s−1 at 10 μM) was also observed at room temperature upon inhibition of ENTs with dipyridamole (2,6‐bis(diethanolamino)‐4,8‐dipiperidinopyrimido‐[5,4‐d]pyrimidine)/NBMPR.

MVECs had 122,000 high‐affinity (Kd 0.10 nM) [3H]NBMPR binding sites (representing es transporters) per cell. A lower‐affinity [3H]NBMPR binding component (Kd 4.8 nM) was also observed that may be related to intracellular es‐like proteins.

Rat skeletal muscle MVECs express es/ENT1, ei/ENT2, and cif/CNT2 transporters with characteristics typical of rat tissues. This primary cell culture model will enable future studies on factors influencing NT subtype expression, and the consequent effect on adenosine bioactivity, in the microvasculature.

British Journal of Pharmacology (2004) 143, 202–214. doi:10.1038/sj.bjp.0705921
Microcantilever equipped with nanowire template electrodes for multiprobe measurement on fragile nanostructures
Authors: Lin R. , Bøggild P. , Hansen O.
Published: September 2004

We present a technique for fabricating nanoelectrode extensions to microcantilevers for multiprobe electrical characterization. For electrical measurements of fragile samples, such as thin films and nanostructures, it is advantageous to combine a small contact force with a small contact area, which can be done by reducing the dimensions of the electrodes to nanoscale dimensions. Here we report a fabrication method of a nanoscale four-point probe utilizing silicon nanowires as templates for metal electrodes. Using nanomanipulation, we attach 200–300 nm wide silicon nanowires to microfabricated cantilevers. By subsequently covering these nanowires with a metallic coating, they are made conducting and at the same time fixed to the cantilevers. These silicon nanowire four-point probes were tested on 7 and 35 nm thick Au films as well as poorly adhering 16 nm thin Au nanowires deposited on a silicon surface through a nanofabricated shadow mask. It was found that the nanowire extensions dramatically reduce the damage of the studied samples, while nearly reproducing the resistivity measurements of the unmodified, but more destructive micro four-point probes.
Spectroscopic and structural properties of Nd3+ doped strontium lanthanum aluminate laser crystals
Authors: Lupei A. , Lupei V. , Gheorghe C. , Vivien D. , Aka G. , Aschehoug P.
Published: September 2004

Nd 3+ -activated strontium lanthanum aluminate Sr1−xNdyLax−yMgxAl12−xO19 (ASL:Nd) crystals give efficient F43/2→I49/2 laser emission at 900 nm, whose properties depend on the x and y composition parameters. Based on high-resolution spectroscopy and emission decay, this paper demonstrates that the composition dependence of the laser emission is caused by the presence of two structural centers, C1 and C2, whose relative proportion in crystals is determined by composition parameter x. From the spectral data and crystal structure it is inferred that C2 center that prevails at low x, corresponds to a Nd3+ in a Sr2+ (2d) site of D3h local symmetry with no nearby Ln3+ (La3+ or Nd3+) ions. The C1 center lines, prevailing at large x parameter, which are broader and shift with composition, are composite lines of various structural centers of Nd3+ in a Sr2+ site with different occupancy of nearest-neighbor sites by Ln3+. The influence of the spectral and emission dynamics features of these centers on the laser properties is discussed and criteria for the selection of optimal composition is inferred.
A simple time-delay feedback anticontrol method made rigorous
Authors: Zhou Tianshou , Chen Guanrong , Yang Qigui
Published: September 2004

An effective method of chaotification via time-delay feedback for a simple finite-dimensional continuous-time autonomous system is made rigorous in this paper. Some mathematical conditions are derived under which a nonchaotic system can be controlled to become chaotic, where the chaos so generated is in a rigorous mathematical sense of Li–Yorke in terms of the Marotto theorem. Numerical simulations are given to verify the theoretical analysis.
The electron cyclotron resonance coupled to laser ion source for charge state enhancement experiment: Production of high intensity ion beams by means of a hybrid ion source
Authors: Gammino S. , Torrisi L. , Ciavola G. , Andò L. , Celona L. , Manciagli S. , Krása J. , Láska L. , Pfeifer M. , Rohlena K. , Mezzasalma A. M. , Gentile C. , Picciotto A. , Wolowski J. , Woryna E. , Badziak J. , Parys P. , Hitz D. , Shirkov G. D.
Published: September 2004

The experiment concerning the ECLISSE method (ECR ion source coupled to a laser ion source for charge state enhancement) has been carried out by coupling a laser ion source (LIS) to the superconducting electron cyclotron resonance source (SERSE) electron cyclotron resonance (ECR) ion source with the goal to obtain intense beams of highly charged ions (cw or pulsed mode) from metal samples, especially from refractory elements. The coupling efficiency of the ion beam produced by the LIS with the ECR plasma was remarkable and the measured beam intensities were quite high. The maximum charge states, obtained with a good reproducibility, were 38+ for Ta and 41+ for Au. The highest current was obtained for 25+ and 28+ for Ta and Au ions, respectively, and it was in both cases of the order of some tens of microampere, i.e., higher than the current obtained from SERSE with other methods (i.e., evaporation and sputtering). The ion beam stability and reproducibility were both acceptable. The possibility to get a further enhancement of the available charge states was limited by charge exchange processes connected with the target ablation. The main features of the LNS facility based on a Nd:YAG (yag, yttrium aluminum garnet) laser (0.9J∕9ns, laser power densities <5×1010W∕cm2) and on the SERSE superconducting ECRIS working in single frequency mode (18GHz) will be shown in the following. The analysis of the results and the way to get rid of the existing limits will be also presented and discussed.
Effect of ultrathin Cr layers on surface second-harmonic generation from Cr-SiO2-Si(001) structures
Authors: An Yong Qiang , Cundiff Steven T.
Published: September 2004

An ultrathin semitransparent Cr coating layer on oxidized Si(001) significantly alters surface second-harmonic generation (SHG) behavior. The peak locations of the rotational-anisotropy SHG (RA-SHG) signals from Cr coated SiO2-Si(001) surfaces are shifted by 45° from that of uncoated surfaces consistently for several polarizations, but only for specific photon energies. Moreover, for appropriate polarizations, a peak-to-valley transition of the RA-SHG signal by varying photon energy is observed for Cr coated samples but not for uncoated samples. The time-dependent SHG signal decreases with continuous laser illumination for Cr coated surfaces, but it increases for uncoated surfaces. Through these comparisons, we find that the Cr coating introduces an additional SHG. Interference between the additional and original SHG contributions modifies both the phase and amplitude of the net SHG, and thus the measured spectroscopic and time dependence of SHG. To determine the source of this additional SHG, we perform further surface SHG measurements on a thick Cr film and the SiO2-Cr interface. We find that it mainly comes from the outermost surface of the Cr coating layer. In addition, we investigate the effect of the thickness of the SiO2 layer on the SHG response in reflection from Cr-SiO2-Si(001) structures.
A model based on dry friction for modeling hysteresis in ferroelectric materials
Authors: Sebald G. , Boucher E. , Guyomar D.
Published: September 2004

This paper presents a model describing the hysteresis in ferroelectric materials at moderate to high driving levels. Hysteresis and nonlinearities are attributed to the irreversible displacement of domain walls. The model, based on a simple mechanism related to the dry-friction concept, is developed to describe the hysteresis of polarization and strain under electric field and stress. Besides coefficients such as ε33 and d33 also exhibit large hysteresis loops under high electric and/or mechanic level. In this paper it is shown that modeling macroscopic quantities such as P or S hysteresis lead to a reasonable estimate of the coefficients since their behavior depends mainly on polarization. The proposed approach is developed, discussed, and compared with experimental results from Navy II piezoelectric transducer ceramic. Comparisons on hysteresis loops are given and are in good agreement for the polarization and strain versus electric field and, to a less extent, for the coefficients ε33 and d33. The linear and Rayleigh regime are deduced from the proposed approach.
Analytic light—or radiation—induced pn junction photocurrent solutions to the multidimensional ambipolar diffusion equation
Authors: Axness C. L. , Kerr B. , Wunsch T. F.
Published: September 2004

We transform the n-dimensional ambipolar transport equation to the n-dimensional nonhomogeneous heat equation, which has been solved for most common initial and boundary conditions. Thus, general solutions to the nonhomogeneous heat equation, obtained in a robust form through finite Fourier transforms, provide an easy approach to solving the ambipolar transport equation, which previously had been solved with more difficulty through Laplace transform techniques. We then obtain a general analytic one-dimensional time-dependent solution to the excess carrier and current densities in a pn junction diode in response to a transient radiation or light pulse under low-injection conditions. We derive most of the known analytic solutions to this problem and we examine the limiting behavior of these solutions to show that they are consistent. The model includes the effects of a constant electric field in the quasineutral region, a finite diode length, and an arbitrary generation function in terms of space and time. In the area of light communication, we use the model to examine the impact of doping parameters on the buildup of diffusive photocurrent that limits the signal bandwidth. Solutions to the ambipolar diffusion equation assuming more general initial and boundary conditions are easily obtained via the given transformation. The model may be applied to problems involving photodiodes, light-emitting diode or laser communication, transient radiation effects in microelectronics, dosimetry, or the response of solar cells to light.
Ridge waveguide as a near field aperture for high density data storage
Authors: Şendur Kürşat , Challener William , Peng Chubing
Published: September 2004

The performance of the ridge waveguide as a near-field aperture in data storage systems is investigated. Finite element method (FEM) and finite-difference time-domain (FDTD) based software are used in the numerical simulations. To verify their accuracy at optical frequencies, the FEM and FDTD are first compared to analytical results. The accuracy of these techniques for modeling ridge waveguides at optical frequencies is also evaluated by comparing their results with each other for a plane wave illumination. The FEM, which is capable of modeling focused beams, is then used to simulate various geometries involving ridge waveguides. Near-field radiation from ridge waveguide transducer is expressed in terms of power density quantities. Previous studies in the literature consider the performance of the transducer in free space, rather than in the presence of a recording magnetic medium. The effect of the recording magnetic medium on the transmission efficiency and spot size is discussed using numerical simulations. The effect of various geometric parameters on the optical spot size and transmission efficiency is investigated and discussed. Based on our numerical simulations, a promising transducer design is suggested to obtain intense optical spots well below the diffraction limit. Numerical simulations suggest that a full width at half maximum spot diameter of 31nm in the recording magnetic medium can be obtained. The maximum value of the absorbed optical power density in the recording medium is about 1.67×10−4mW∕nm3 for a 100mW input power. In-track and cross-track profiles for this design are compared with Gaussian distributions.
Structural and Mössbauer characterization of the ball-milledFex(Al2O3)100−x system
Authors: Paesano A. , Matsuda C. K. , Cótica L. F. , de Medeiros S. N. , da Cunha J. B. M. , Hallouche B. , Silva S. L.
Published: September 2004

Metal-oxide composites were synthesized by high-energy ball milling of metallic iron (α-Fe) and alumina (α-Al2O3) powders, varying the starting relative concentration and the milling time. The samples were characterized by scanning electron microscopy, x-ray diffraction, and Mössbauer spectroscopy. The results revealed the formation of a FeAl2O3+W spinel phase (hercynite) and of iron (super)paramagnetic nanoprecipitates, in addition to residual magnetic iron and alumina. We also observed that the relative amounts of nanoprecipitates and hercynite for isochronally milled samples were correlated with the sample nominal concentration x, with the precursor iron being relatively more converted in those phases for low x values. Particularly for x=10 milled sample, the relative amounts of the (super)paramagnetic and spinel phases were observed to increase linearly with the milling time. An x=20∕24h milled sample was annealed in H2 atmosphere and revealed the reduction of hercynite, with iron phase separation.
The influence of microstructure on the probability of early failure in aluminum-based interconnects
Authors: Dwyer V. M.
Published: September 2004

For electromigration in short aluminum interconnects terminated by tungsten vias, the well known “short-line” effect applies. In a similar manner, for longer lines, early failure is determined by a critical value Lcrit for the length of polygranular clusters. Any cluster shorter than Lcrit is “immortal” on the time scale of early failure where the figure of merit is not the standard t50 value (the time to 50% failures), but rather the total probability of early failure, Pcf. Pcf is a complex function of current density, linewidth, line length, and material properties (the median grain size d50 and grain size shape factor σd). It is calculated here using a model based around the theory of runs, which has proved itself to be a useful tool for assessing the probability of extreme events. Our analysis shows that Pcf is strongly dependent on σd, and a change in σd from 0.27 to 0.5 can cause an order of magnitude increase in Pcf under typical test conditions. This has implications for the web-based two-dimensional grain-growth simulator MIT/EmSim, which generates grain patterns with σd=0.27, while typical as-patterned structures are better represented by a σd in the range 0.4 – 0.6. The simulator will consequently overestimate interconnect reliability due to this particular electromigration failure mode.
Molecular dynamics simulation for evaluating melting point of wurtzite-type GaN crystal
Authors: Harafuji Kenji , Tsuchiya Taku , Kawamura Katsuyuki
Published: September 2004

A two-phase molecular dynamics simulation of coexisting solid and liquid has been carried out to investigate the melting point of wurtzite-type GaN crystals. The melting point is determined by examining the movement of the interface between the solid and liquid during the simulation. The potential is a two-body interatomic one composed of the long-range Coulomb interaction, the Gilbert-type short-range repulsion, the covalent bonding and covalent repulsion of the modified Morse type, and the van der Waals interaction. The melting point and the interface morphology depend on the crystallization direction. The melting point Tm(K) increases with pressure P(GPa), but there appears a discontinuity in the vicinity of 8–9GPa. This is due to the solid-electrolyte-like behavior of Ga atoms with a partial charge in the high-pressure region. The discontinuity has not yet been confirmed by experiment. The least-squares fitted result is Tm=2538+177P−4.62P2 at pressures lower than 8GPa and Tm=2825+210P−5P2 at pressures higher than 9GPa. The Clausius-Clapeyron relation is confirmed using calculated thermodynamic data.
Effect of temperature cycling on the static fatigue of double-coated optical fibers
Authors: Shiue Sham-Tsong , Shen Ting-Ying , Lin Kun-Ming
Published: September 2004

This study theoretically investigates the effect of temperature cycling on the static fatigue of double-coated optical fibers. The tensile force and temperature cycling induced tensile stresses on the glass fiber of double-coated optical fibers are determined using the viscoelastic theory. Optical fibers lifetime is dominated by the tensile stress on the glass fibers, which is a function of the material properties and thickness of the polymeric coating. To minimize these stresses on the glass fiber, the radius, Young’s modulus, and thermal expansion coefficient of the secondary coating should be reduced, while the relaxation time of the secondary coating should be increased. Additionally, based on strength consideration, the radius and Young’s modulus of the polymeric coating should be sufficiently thick or hard to support the external mechanical stresses. Meanwhile, based on the microbending-insensitivity consideration, the relaxation time of the primary coating should be reduced.
Raman spectroscopic studies of TeO2-BaO-SrO-Nb2O5 glasses: Structure-property correlations
Authors: Murugan G. Senthil , Ohishi Yasutake
Published: September 2004

The structure of technologically important tellurite glasses has been studied by Raman spectroscopy. The present investigation revealed the presence of TeO4 trigonal bipyramid, TeO3 trigonal pyramid, and NbO6 octahedra in these glasses. The influence of a gradual addition of the modifier oxides on the glass structure has been elucidated. The evolution of TeO3 units with the modifier addition was different from the earlier reports on the tellurite glasses. Even at higher modifier concentrations TeO4 units were dominating in the glass network compared to TeO3, though NbO6 octahedra also come into the picture. The ratio of TeO4∕TeO3 structural units was discussed for different series of glass compositions. An attempt has been made based on these structural details obtained via Raman studies to explain the origin of the greatly improved thermal stabilities and refractive indices of these glass compositions.
Modification of exciton binding energy in the horizontal Bridgman–Stockbarger growth of InSe by Ho doping
Authors: Ateş A. , Tüzemen S. , Yildirim M.
Published: September 2004

Undoped InSe and Ho doped InSe single crystals with various Ho concentrations were grown by the horizontal Bridgman-Stockbarger method. The absorption measurements were carried out in the temperature range 10–320K. Exciton binding energies, steepness parameters, and Urbach energies of InSe and InSe:Ho samples were investigated as a function of temperature. Ho doping caused a shift towards longer wavelengths in the absorption edge. In general, Ho doping causes certain increases in the exciton binding energy and Urbach energy, and a decrease in the steepness parameter. An enhancement of exciton binding energy up to about 55meV is observed at 0.0025 mass ratio of Ho.
Oxygen precipitation in nitrogen doped Czochralski silicon wafers. I. Formation mechanisms of near-surface and bulk defects
Authors: Karoui A. , Sahtout Karoui F. , Rozgonyi G. A. , Yang D.
Published: September 2004

Defect size distributions in nitrogen-doped Czochralski (N-CZ) silicon wafers were obtained using an oxygen precipitate profiler and Wright-Jenkins etching. These showed unique depth dependence in low-high and high-low-high cycled N-CZ wafers. Unique phenomena observed include a high defect concentration at the subsurface that decreases within the top 2μm of the so-called denuded zone. In contrast to N-free CZ Si for which the first high step annealing dissolves the grown-in defects, these appeared to be stable in N-CZ Si. As a result, the defect size distribution in the bulk was found to be independent of the annealing cycle. It was also found that the depth dependent defect concentration correlates well with oxygen and strongly with nitrogen secondary ion mass spectroscopy profiles, suggesting that nitrogen is the leading impurity in the defect formation processes even though introduced at very low concentration. Nitrogen appeared to effectively modify the nucleation regime by a drastic increase of the nuclei density. At low temperature under external stress, nitrogen and oxygen cosegregate to the surface where the stress is applied; such a phenomenon is largely increased at high temperature.
Extended-pulse excimer laser annealing of Pb(Zr1−xTix)O3 thin film on LaNiO3 electrode
Authors: Lai S. C. , Lue Hang-Ting , Hsieh K. Y. , Lung S. L. , Liu Rich , Wu T. B. , Donohue P. P. , Rumsby P.
Published: September 2004

Comparing to conventional short-pulse (<30ns) excimer laser annealing, the extended pulse (374ns) can provide sufficient thermal energy and time into the Pb(Zr1−xTix)O3 (PZT) thin film to complete the crystallization, whereas the bulk of the material remains at low temperature. In this study, thermal simulation is presented to illustrate the temperature distribution in the specimen and the benefits of the extended pulse. With extended-pulse laser annealing, we observe a 50% improvement in remanent polarization because of the elimination of the amorphous layer on the PZT surface, which is also confirmed by cross-section transmission electron microscopy analysis. This low temperature process is suitable for embedded capacitor-over-interconnect ferroelectric random access memory for advanced system-on-chip applications.
Structural, magnetic, and transport properties of high-quality epitaxial Sr2FeMoO6 thin films prepared by pulsed laser deposition
Authors: Sánchez D. , García-Hernández M. , Auth N. , Jakob G.
Published: September 2004

We have succeeded in the preparation of a broad set of epitaxial Sr2FeMoO6 thin films by pulsed laser deposition. We have studied the effect of various deposition conditions, on both substrate-induced strain and antisite disorder (ASD), which translate into a variety of magnetic and transport properties of the films. We find that the saturation magnetization and the magnetoresistance are dominated by the degree of cationic order, and the strain effects are clearly evidenced in a lower TC. We characterize the ASD induced magnetoresistance, which arises from a moderate concentration of antisite defects and vanishes for massive ASD levels.
Transient photovoltage in GaN as measured by atomic force microscope tip
Authors: Reshchikov M. A. , Sabuktagin S. , Johnstone D. K. , Morkoç H.
Published: September 2004

We studied restoration of the band bending at the surface of undoped GaN layers after illumination with above-bandgap light. The photovoltage saturated with illumination at about 0.2–0.3eV at room temperature, although the upward band bending for GaN in the dark is of the order of 1eV. We attribute the photovoltage effect to charging of the surface states, the density of which is estimated at about 1012cm−2. Restoration of the barrier after a light pulse is simulated by a phenomenological model whereby the acceptorlike surface states are emptied of electrons under illumination and filled back in dark due to thermionic transfer of free electrons from the bulk to the surface states over the near-surface barrier. Photoinduced desorption of oxygen also affects the value of the photovoltage if the illumination is prolonged.
Fluorescence quenching and excitation transfer between semiconducting and metallic organic layers
Authors: Åsberg Peter , Nilsson Peter , Inganäs Olle
Published: September 2004

Here we present a simple approach to study the interaction of singlet excitons with polarons in conjugated polymers in organic electronic devices. Interlayer quenching constants KIL of 1.5M−1 between a fluorescent molecule and a doped polymer in a layered sample demonstrates the importance of understanding the quenching of excited states in polymeric devices. A combination of Förster resonance energy transfer and quenching of photoluminescence between a fluorescent molecule and a conjugated polymer in its semiconducting and metallic states were studied. The polymer is a chiral 3-substituted polythiophene (POWT) and the fluorescent molecule is fluorescein bound to dextran (D-FITC). Bilayer samples with fluorescein on top of the POWT were fabricated and studied with absorption spectroscopy, fluorescence microscopy, and electrochemical doping methods. When POWT is electrochemically dedoped it is possible to enhance the photoluminescence in the polymer layer by excitation transfer from the fluorescein layer. Our results demonstrate that PL from the polythiophene disappears rapidly as soon as the layer is doped. As the doping of polymer layer increases the fluorescence from the fluorescein on top of the polymer decreases, due to excitation quenching. Models for excitation transfer and excitation quenching in POWT/FITC bilayer devices have been developed. This model predicts a linear relationship between the PL from the two molecules, in agreement with our experimental findings. These results are relevant for the development of electroluminescent devices or solar cells based on conjugated polymers.
Electric transport in a AlGaAs∕GaAs structure from 300Kto4.2K
Authors: Khlil R. , Hdiy A. El , Cavanna A. , Laruelle F. , Jin Y.
Published: September 2004

Some AlGaAs∕GaAs heterostructures with different high electron mobilities were electrically characterized as a function of temperature. Hall measurements were made at 4.2K and current-voltage characteristics were measured from 300Kto4.2K. Experimental results have revealed a saturation of the current at electric fields as low as 5V∕cm at low temperature (<100K). The saturation was linked to the very high mobility combined with the presence of alloy diffusion in the AlGaAs∕GaAs channel. The pinch-off effect was excluded because of the absence of the control gate. Drift velocities were carried out at 4.2K in these experiments.
Amorphous silicon nitride deposited by hot-wire chemical vapor deposition
Authors: Liu Fengzhen , Ward Scott , Gedvilas Lynn , Keyes Brian , To Bob , Wang Qi , Sanchez Errol , Wang Shulin
Published: September 2004

High-quality amorphous silicon nitrides were deposited by hot-wire chemical vapor deposition using SiH4, NH3, and H2 gases. These films show a high deposition rate of 5Å∕s, a low processing temperature of 300°C, an excellent conformal coverage, a low etching rate of 7Å∕min, an index of refraction of 2.1, an optical band gap of 4.0eV, and a high breakdown field of 3MV∕cm. The effects of hydrogen dilution, substrate temperature, chamber pressure, and filament temperature on silicon nitride film property were studied to optimize the process. We found that adding H2 to the processing significantly enhances the silicon nitride films’ properties. The N content in the film increased significantly based on the infrared measurement. Hydrogen dilution is believed to play a key role for the conformal silicon nitride film. Hydrogen dilution also improves the process in that the gas ratio of NH3∕SiH4 has been greatly reduced with the assistance of the H2 gas. With substrate temperatures varying from 23°to400°C, this study showed a best film at near 300°C. However, a good-quality silicon nitride can be grown even if starting with a substrate at room temperature. Furthermore, we found that increasing chamber pressure and a high filament temperature result in higher deposition rate and better quality in the films. The optimized films were grown with hydrogen dilution at about 300°C substrate temperature, 83mTorr pressure, and 2100°C filament temperature.
Bistability in deformed helix ferroelectric liquid crystal
Authors: Kaur S. , Thakur A. K. , Chauhan R. , Bawa S. S. , Biradar A. M.
Published: September 2004

Bistability in deformed helix ferroelectric liquid crystal (DHFLC) has been investigated by electro-optical and dielectric methods and compared with the bistability phenomenon in surface stabilized ferroelectric liquid crystal (SSFLC). Bistability in DHFLC as well as SSFLC is based on different physical phenomena. In SSFLC, it occurs due to surface effect and in DHFLC, by the critical deformation of the helix, under the application of time delayed square voltage pulse of known magnitude and frequency. Memory behavior of DHFLC and SSFLC cells has been compared by optical, electrical, dielectric, and hysteresis methods and the difference has been analyzed. It has been observed that memory effect in DHFLC is independent of surface effect but critically depends on the applied voltage and frequency of time delayed square wave pulse.
Morphology and optical properties of InAs(N) quantum dots
Authors: Schumann O. , Geelhaar L. , Riechert H. , Cerva H. , Abstreiter G.
Published: September 2004

InAs(N) quantum dots (QDs) were grown on GaAs(001) by solid source molecular beam epitaxy. Nitrogen was supplied by a radio-frequency plasma cell. The samples were characterized by atomic force microscopy, photoluminescence (PL) spectroscopy, and transmission electron microscopy. With an increasing amount of nitrogen supplied to the surface, large QDs form and the small QDs typical for nitrogen free growth gradually disappear. For intermediate amounts of nitrogen, small and large QDs coexist in a bimodal distribution. The large QDs contain misfit dislocations and are thus plastically relaxed. These dislocations are already induced in the wetting layer by exposure to the nitrogen plasma and act as nucleation centers for the large QDs. The incorporation of material into relaxed QDs is preferred, which leads to an elimination of the small strained QDs. When increasing the amount of nitrogen, the expected strong redshift in the PL wavelength does not occur. This leads to the conclusion that only a little nitrogen is incorporated into the small coherent QDs.
W
O
3
∕
metal
thin-film bilayered structures as optical recording materials
Authors: Takeda Yasuhiko , Kato Naohiko , Fukano Tatsuo , Takeichi Akihiro , Motohiro Tomoyoshi , Kawai Shoichi
Published: September 2004

Interface reactions in WO3∕metal thin-film bilayered structures were examined for applications to optical recording materials. Decreases in the reflectance of the structures caused by temperature elevation were observed and were attributed to (i) coloration of the WO3 layers, and (ii) decreases in the reflectance of the metal layers resulting from redox reactions between the WO3 and the metals. The reflectance spectra of the structures before temperature elevation showed moderate wavelength dependence over a wide range, from the visible to the near infrared. Decreases in the reflectance due to temperature elevation occurred over a wide wavelength range. Examination of the WO3∕Al–Ti bilayered structures as potential optical disk memories revealed that the redox reactions occurred within submicrosecond time periods during irradiation with the recording laser. The results indicate that these structures possess promising properties for applications to optical recording materials that can be used over a wide wavelength range.
GaN
nanoindentation: A micro-Raman spectroscopy study of local strain fields
Authors: Puech Pascal , Demangeot François , Frandon Jean , Pinquier Claire , Kuball Martin , Domnich Vladislav , Gogotsi Yury
Published: September 2004

We have investigated strain fields around GaN nanoindentations. Stress relaxation around the edges of the nanoindentation was evident in atomic force microscopy images. More detailed information on the strain fields was obtained from Raman scattering, which has been used to analyze the shape of the strain field around the indentation. We find that the Berkovich tip giving a triangular imprint on the sample generates a strain field, which represents a hexagonal pattern. Negative values of the strain indicate that the residual stress is compressive. Strain is larger in the center of the indentation than outside. Analysis of the ratio of the frequency shift of the E2 and A1(LO) modes suggests that the residual strains are close to biaxial state outside the indentation contact zone, and mostly hydrostatic within the indentation center.
Formation of waveguides by implantation of 3.0MeV Ni2+
Authors: Lu Fei , Zhang Tingting , Wang Xuelin , Li Shiling , Wang Keming , Shen Dingyu , Ma Hongji
Published: September 2004

3.0 MeV  Ni2+ in the beam doses from 1×1013to9×1014ions∕cm2 are implanted into LiNbO3 single crystals at room temperature. After 300°C annealing for 30min in air ambient, dark mode measurement is done by the prism-coupling technique. Waveguides from both raised extraordinary index layer and barrier-confined are formed by low and high beam dose implantation, respectively. In the samples implanted by mediate beam doses, a phenomenon of “missing mode” is observed. The experimental results are analyzed and compared with the simulated results from a theoretical model, which is based on the assumption that the change of index induced by implantation is mainly governed by degradation of polarization and reduction of material density. With a fiber probe, the waveguide loss from single transverse magnetic mode is measured, which is about 3dB∕cm.
Optical and electrical properties of highly (100)-oriented PbZr1−xTixO3 thin films on the LaNiO3 buffer layer
Authors: Yu Jian , Meng X. J. , Sun J. L. , Huang Z. M. , Chu J. H.
Published: September 2004

In this paper, using wet chemical solution deposition processes, the (100)-highly oriented LaNiO3 buffer layers were grown on both silicon and platinized silicon wafers and, sequentially, the highly (100)-oriented PbZr1−xTixO3 thin films with various compositions were obtained on them. The misfit elastic strains were found to be critical factors to determine the orientation of PZT thin films, even though the used LaNiO3 buffer layer reduces the lattice mismatch between PZT films and silicon wafers. For the PZT thin films with x=0.5 and 0.6 on the LaNiO3/platinized silicon substrate, the infrared optical constant, ferroelectric, and dielectric properties were characterized and analyzed with relation to the film orientation and the film grain size. It was found that the finite grain size effect here played a key role in determining these optical and electrical properties. With nanoferroelectric thin films, it is the most useful way of controlling both grain size and crystallographic orientation to tune performance of commercial film devices.
Design and fabrication of physical vapor transport system for the growth of SiC crystals
Authors: Dhanaraj G. , Dudley M. , Ma R.-H. , Zhang H. , Prasad V.
Published: September 2004

A physical vapor transport (PVT) system has been designed and fabricated for growing SiC single crystals. Novel multisegmented graphite insulation has been used for improved heat containment in the hotzone. Numerical modeling was applied to obtain the temperature field inside the hotzone, which also helped in predicting various growth parameters. Single crystals of 6H SiC were grown by the modified Lely method using the PVT system developed in the laboratory. The grown crystals were subjected to preliminary characterization.
Photoreflectance evidence of multiple band gaps in dilute GaInNAs layers lattice-matched to GaAs
Authors: Kudrawiec R. , Pavelescu E.-M. , Wagner J. , Sęk G. , Misiewicz J. , Dumitrescu M. , Konttinen J. , Gheorghiu A. , Pessa M.
Published: September 2004

Dilute Ga1−xInxNyAs1−y∕GaAs quantum wells with high In-content, which are under compressive strain, have been shown previously to exhibit multiple band gaps, likely due to the presence of different nitrogen nearest-neighbor environments, i.e., N-Ga4−mInm(0⩽m⩽4) short-range-order clusters. Here, photoreflectance (PR) measurements on lattice-matched dilute GaInNAs-on-GaAs layers with low indium and nitrogen content are reported, which give evidence that these layers also exhibit several distinct band gaps. These distinct band gaps, which were found to coexist, are associated with different nitrogen bonding configurations, as revealed by Raman spectroscopy. Thus, the metastable nature of GaInNAs seems to be a persistent intrinsic property, irrespective of strain and indium content. The annealing-induced blueshift of GaInNAs band gap energy, which is usually observed in this system, has been associated with the change in the intensity of PR resonances related to different N-Ga4−mInm configurations.
Lasing in organic circular grating structures
Authors: Jebali Asma , Mahrt Rainer F. , Moll Nikolaj , Erni Daniel , Bauer Christian , Bona Gian-Luca , Bächtold Werner
Published: September 2004

Optically pumped organic polymer lasers are fabricated by spin coating a thin polymer film onto a nanopatterned SiO2 circular-grating surface-emitting distributed Bragg reflector. For certain grating parameters, we observe a peak inside the stop band that leads to lasing with a reduced threshold. An analytical model, based on the transfer-matrix method, has been developed to investigate the origin of this peak. The theoretical results are in good agreement with the experimental findings.
Energy-level structure and spectral analysis of Nd3+(4f3) in polycrystalline ceramic garnet Y3Al5O12
Authors: Gruber John B. , Sardar Dhiraj K. , Yow Raylon M. , Allik Toomas H. , Zandi Bahram
Published: September 2004

A detailed crystal-field splitting analysis is given for the 26 lowest-energy multiplet manifolds, LJ2S+1, of Nd3+(4f3) in polycrystalline ceramic garnet Y3Al5O12 (YAG). The absorption spectra obtained between 8K and room temperature, and between 1750 and 350nm, and the fluorescence spectrum obtained at 8K and observed between 1450 and 875nm are analyzed for transitions between individual energy (Stark) levels that characterize the energy-level structure of Nd3+ ions in D2 symmetry sites, replacing Y3+ ions in the garnet host lattice. A model Hamiltonian including atomic and crystal-field terms is diagonalized within the complete 4f3SLJMJ basis set which includes 364 states. The calculated splitting of the Nd3+ energy levels by the crystal field is compared with the experimental splitting observed in both the ceramic sample and a single-crystal laser rod. Both samples have approximately the same Nd3+ concentration, about 1at.%. By varying the atomic and crystal-field parameters, we obtain a standard deviation of 18cm−1 between 106 calculated-to-observed Stark levels found between the ground state and the D1∕24 at 28 369cm−1. Within this standard deviation the energy-level structure of Nd3+ is found to be similar in both samples. Low temperature visible and near IR spectra of ceramic Nd3+:YAG show it has comparable properties to the crystalline analog.
Holographic method for a direct growth of three-dimensional photonic crystals by chemical vapor deposition
Authors: Duneau Michel , Delyon François , Audier Marc
Published: September 2004

A method to obtain three-dimensional (3D) photonic crystals by chemical vapor deposition (CVD) is presented. Campbell et al. [N. Campbell, N. Sharp, M. T. Harrison, R. G. Denning, and A. J. Tuberfield, Nature 404, 53 (2000)] have developed a method of holographic lithography for producing 3D periodic structures with photoresists. Their method is adapted in two main directions. First, we optimize the geometry of the interferometer with respect to polarizations and relative intensities of the beams. The construction of an interferometer adapted to a ultraviolet laser source at 355 nm is described and direct observations of the interference field obtained by a video camera are presented. Second, we show that a laser source with short pulses could induce a suitable thermal contrast on a convenient substrate in order to grow a 3D photonic crystal by CVD.
Mid-infrared electroluminescence from coupled quantum dots and wells
Authors: Shields P. A. , Bumby C. W. , Li L. J. , Nicholas R. J.
Published: September 2004

Room temperature electroluminescence between 1.7–2.6μm has been observed from coupled quantum dots and quantum wells in the InAs∕InSb∕GaSb materials system. The samples studied consist of a single narrow InAs quantum well grown below a layer of InSb quantum dots in a GaSb matrix. The thickness of the GaSb spacer layer lowers the energy from that of a quantum well alone but with a dependence that cannot be described solely through electronic coupling of the wave functions. A sharp transition occurs after a single monolayer coverage of GaSb either due to structural changes in the quantum dots or from shrinkage of the quantum well. For slightly thicker layers the emission energy can be explained by segregation during growth or strain-mediated correlation of the localized states in the system.
Electrophoresis of long deoxyribonucleic acid in curved channels: The effect of channel width on migration dynamics
Authors: Ueda Masanori , Hayama Tetsuya , Takamura Yuzuru , Horiike Yasuhiro , Dotera Tomonari , Baba Yoshinobu
Published: September 2004

We investigated the dynamics of long deoxyribonucleic acid (DNA) migrating through curved channels under electric fields. Long DNA exhibits large conformational changes in the curved channels because of the inhomogeneity of the electric fields around curves. Two kinds of channel shapes were used for the examination. One (type I) has the same width in the curved region as in the straight region. The other (type II) is wider in the curved region than in the straight region. The difference in migration rates between long DNA and short DNA was larger in type II than in type I chips. We discuss the separation mechanism of the type II chip.
Influence of microroughness on emissivity
Authors: Ghmari Faouzi , Ghbara Taoufik , Laroche Marine , Carminati Rémi , Greffet Jean-Jacques
Published: September 2004

In this paper we revisit the absorption and thermal emission of electromagnetic radiation by a rough surface. We use a numerical simulation of the absorptivity of a grating to explore the validity of the ray tracing approach. We show that it often predicts correctly the absorptivity and emissivity of a surface with characteristic lengths on the order of a wavelength. Recent advances in the understanding of the microscopic mechanism of thermal emission in the near field are used to discuss the data and to explain this surprising result. We also identify three different regimes depending on the ratio of the period to the wavelength: the homogenization regime, the resonance regime, and the geometrical optics regime.
Thermal and transport properties of the Heusler-type compounds Fe2−xTi1+xSn
Authors: Lue C. S. , Kuo Y.-K.
Published: September 2004

We have studied the thermoelectric properties of the stoichiometric and off-stoichiometric Heusler compounds Fe2−xTi1+xSn between 10K and 400K. It is found that the electrical resistivity and Seebeck coefficient are very sensitive to the off-stoichiometry. Seebeck coefficient (S) measurements indicate that all studied materials are p-type materials with moderate S values of about 20–30μV∕K at room temperature. Broad maximums at around 330K are observed in S for Fe2TiSn and Fe2.05Ti0.95Sn, and this maximum shifts to higher temperatures with replacing more Ti for Fe. These features are consistent with other experimental results and are related to issues raised by band-structure calculations.
Impurity photovoltaic effect with defect relaxation: Implications for low band gap semiconductors such as silicon
Authors: Brown Andrew S. , Green Martin A.
Published: September 2004

The impurity photovoltaic solar cell can, in principle, increase the sunlight to electricity conversion efficiency of a conventional single junction solar cell by the introduction of optically active impurities or defects into the device. These “defects” ideally allow electrons to be excited from the valence band to the conduction band via the mid-gap defect level through the absorption of previously wasted sub-band-gap photons. In this work the maximum efficiency limits for such a device are calculated for the special case where the energy of the partly excited electron relaxes to a lower energy partly through the two-stage excitation process. This relaxation in energy by the electron when occupying the defect state is shown to give an efficiency improvement over the case where no defect relaxation occurs. In the case of silicon, an efficiency limit of 39.7% under the airmass 1.5G solar spectrum is obtained, compared to 33.0% when no defects are present and 30.5% when a defect is present but no relaxation is allowed.