bluuebunny/crossref_metadata_2025 huggingface dataset:
Relation between the CF2 radical and plasma density measured using LIF and cutoff probe in a CF4 inductively coupled plasma
Authors: Kim Jung-Hyung , Shin Yong-Hyeon , Chung Kwang-Hwa , Yoo Yong-Shim
Published: September 2004

The behavior of the CF2 radical was studied in a CF4 inductively coupled plasma. The CF2 radical was measured using a laser-induced fluorescence method. Absolute electron density was measured using a cutoff probe and the electron temperature was measured using a double probe to study the relationship between these electron properties and the CF2 radical. To examine the relationship between them, the CF2 radical and electron density were measured as a function of the rf power, which is a major external parameter influencing the electron density. As the rf power was increased, the CF2 radical density increased in the range of low electron density, and then decreased beyond a critical electron density. The dependence of the CF2 radical density on the electron density was theoretically analyzed with rate equations. The theoretical result was in good agreement with experiment.
Ultrafast dynamics of the third-order nonlinear response in a two-dimensional InP-based photonic crystal
Authors: Raineri F. , Cojocaru Crina , Monnier P. , Levenson A. , Raj R. , Seassal C. , Letartre X. , Viktorovitch P.
Published: September 2004

We report experimental demonstration of very fast nonlinear response around 1.5μm in an InP-based two-dimensional photonic crystal. The nonlinearity produced by low pump powers via carrier induced nonlinear refractive index, leads to an efficient wavelength shift of a photonic crystal resonance observed in reflectivity. Thus we show that it is possible to obtain round the clock (rise and recovery) switching times shorter than 10ps with contrast ratio higher than 80%.
Low voltage switching of a spin cast ferroelectric polymer
Authors: Naber R. C. G. , Blom P. W. M. , Marsman A. W. , de Leeuw D. M.
Published: September 2004

Employing a conductive polymer as the bottom electrode material of a ferroelectric capacitor is shown to improve the ferroelectric properties of sub-100-nm-thick spin cast poly(vinylidene fluoride/trifluoroethylene) copolymer insulator films. It is demonstrated that a remanent polarization of 65mC∕m2 is switched with only 5.2V (80MV∕m) with a switching time of 80ms. Compared to similar capacitors but with an aluminum bottom electrode the main improvement is a reduction of the switching time with 3 orders of magnitude at this field strength.
Effect of ceria doping on random-field-related polarization reversal in strontium barium niobate ceramics
Authors: Shiue Jyh-Tzong
Published: September 2004

Polarization reversal has been investigated in undoped and Ce3+-doped Sr0.5Ba0.5Nb2O6 in terms of a power-law random-field model. The random fields, excess polarization, and the volume contribution to the excess polarization were evaluated and found to be linearly dependent on the concentration of Ce doping. The origin of the random fields arising form Ce doping is discussed.
Can interface dislocations degrade ferroelectric properties?
Authors: Alpay S. P. , Misirlioglu I. B. , Nagarajan V. , Ramesh R.
Published: September 2004

A thermodynamic analysis has been carried out to investigate the role of dislocations in ferroelectric materials. Due to the coupling of the stress field of the dislocation and the polarization, there is a drastic variation in the polarization near the dislocation. These polarization gradients result in strong depolarizing fields that suppress the polarization in a region that extends over several nanometrers. In epitaxial ferroelectric films, these polarization gradients should result in the formation of dead layers that severely degrade ferroelectric properties. The detrimental effect of such regions will be enhanced in ultrathin ferroelectric thin films, and hence play a critical extrinsic role in size effect studies of ferroelectrics.
Arrays of wirelike microstructures of Ag with visible wavelength transparent plasmonic response at near-ultraviolet and midinfrared regions
Authors: Biswas A. , Kunz R. , Aktas O. C. , Elbahri M. , Adelung R. , Takele H. , Saeed U. , Schürmann U. , Zaporojtchenko V. , Faupel F.
Published: September 2004

We present a simple masked thermal evaporation technique to fabricate arrays of wirelike Ag microstructures of width 8μm with an extremely high aspect ratio on either silicon or glass substrates. In accordance with the theory of periodic arrays of thin wires, the electromagnetic response of Ag microstructures has shown a characteristic low-frequency plasmonic behavior with a transparent visible region. Plasmon absorption is observed to be splitted largely into transverse and predominating longitudinal bands at near-ultraviolet (415nm) and midinfrared wavelengths (2867nm), corresponding to the oscillation of the free electrons perpendicular to and along the long axis of the wires.
Stability of pure electron plasmas on magnetic surfaces
Authors: Boozer Allen H.
Published: September 2004

The electrostatic analog of magnetohydrodynamic stability for a pure electron plasma on magnetic surfaces is examined. Perturbations that conserve the number of particles and the entropy of the plasma as well as maintain force balance and a temperature that is a spatial constant along the magnetic field lines are considered. It is shown that such perturbations require positive external energy and are, therefore, stable.
Structural evolution of dislocation half-loops in epitaxial BaTiO3 thin films during high-temperature annealing
Authors: Sun H. P. , Pan X. Q. , Haeni J. H. , Schlom D. G.
Published: September 2004

BaTiO 3 thin films were grown on (001)SrTiO3 by reactive molecular beam epitaxy. Transmission electron microscopy studies showed that there is a high density of dislocation half-loops inside 8- and 12-nm-thick films. By thermal annealing at 1000°C, the isolated small dislocation half-loops grow and combine to form a self-assembled regular dislocation network at the film/substrate interface. Threading dislocations in the films are removed and the lattice mismatch strain in the film is nearly completely relaxed by annealing at high temperature.
Lack of the critical pressure for weakening of size-induced stiffness in 3C–SiC nanocrystals under hydrostatic compression
Authors: Liu Haozhe , Hu Jingzhu , Shu Jinfu , Häusermann Daniel , Mao Ho-kwang
Published: September 2004

Using in situ high-pressure x-ray diffraction methods, the compressibility of 30nm 3C–SiC nanocrystals was studied under hydrostatic conditions while helium was used as pressure transmitting medium, as well as under nonhydrostatic conditions without pressure medium. No threshold pressure phenomenon was observed for the compressibility of the nanocrystals during compression in hydrostatic conditions, while the critical pressure around 10.5GPa was observed during nonhydrostatic compression. These indicate that the threshold pressure phenomena, recently reported that the nanocrystals initially exhibited much higher bulk modulus below the threshold pressure during compression [Appl. Phys. Lett. 83, 3174 (2003); J. Phys. Chem. 107, 14151 (2003)], were mainly caused by the nonhydrostatic effect instead of a specific feature of nanocrystals upon compression. The bulk modulus of 3C–SiC nanocrystals is estimated as 220.6±0.6GPa based on the hydrostatic compression data.
Tunnel magnetoresistance in GaMnAs: Going beyond Jullière formula
Authors: Brey L. , Tejedor C. , Fernández-Rossier J.
Published: September 2004

The relation between tunnel magnetoresistance (TMR) and spin polarization is explored for GaMnAs∕GaAlAs∕GaMnAs structures where the carriers experience strong spin–orbit interactions. TMR is calculated using the Landauer approach. The materials are described in the 6 band k∙p model which includes spin–orbit interaction. Ferromagnetism is described in the virtual crystal mean field approximations. Our results indicate that TMR is a function of spin polarization and barrier thickness. As a result of the stong spin–orbit interactions, TMR also depends on the the angle between current flow direction and the electrode magnetization. These results compromise the validity of Julliere formula.
Hydraulic jumps and standing waves in gravity-driven flows of viscous liquids in wavy open channels
Authors: Wierschem A. , Aksel N.
Published: September 2004

We experimentally study the flow of a viscous liquid down an inclined channel with a sinusoidal bottom profile of moderate waviness. Depending on the film thickness, we find different flow regimes that are usually not observed in the same system. Besides characterizing these regimes, we study the transition from one regime to the other. At low inclination angles, basins form due to nonmonotonously falling bottom slopes. At the inflow of the basins, we observe the formation of stationary hydraulic jumps as shock fronts and surface rollers. We report on a bistable region in which both phenomena can occur. At the low end of the bistable region, an instationary regime of a shock with a fingering lateral modulation is found. The bistability of shocks and surface rollers is traced back to that of the shock front and the fingering. At higher volume flux or inclination angles, standing waves are created in resonance with the bottom contour. At the rising edge of the resonance curves, we observe humps that seem to be due to higher harmonics of the resonant wave number. There exists a small parameter region where stationary humps and shocks are bistable. At the transition between surface rollers and humps we observe a periodic switching between the two regimes.
High-current-density thin-film silicon diodes grown at low temperature
Authors: Wang Qi , Ward Scott , Duda Anna , Hu Jian , Stradins Paul , Crandall Richard S. , Branz Howard M. , Perlov Craig , Jackson Warren , Mei Ping , Taussig Carl
Published: September 2004

High-performance thin-film silicon n–i–p diodes are fabricated at temperatures below 160°C using hot-wire chemical vapor deposition. The 0.01mm2 diodes have a forward current-density of near 1000A∕cm2 and a rectification ratio over 107 at ±2V. Use of microcrystalline silicon i and n layers results in higher current-density diodes than with amorphous silicon, primarily by lowering a barrier to carrier injection. A 30nm intrinsic Si buffer layer between the i and p layers is needed to reduce the reverse leakage current. Minimizing diode area increases forward current density by reducing the voltage drop across the external series resistances.
Variable range hopping in a C60 field-effect transistor
Authors: Horiuchi Kazunaga , Uchino Shin , Hashii Shinobu , Hashimoto Akira , Kato Tomohiro , Sasaki Takahiko , Aoki Nobuyuki , Ochiai Yuichi
Published: September 2004

A variable range hopping (VRH) has been observed in the low-temperature conductance of a C60 field-effect transistor. We have investigated a thermal annealing (TA) effect at 453 and 498K, on the conductance in various gate voltages and several source-drain separations. VRH analysis shows that density of states in the pseudogap clearly decreases as TA temperature increases. However, there might exist the other charge trapping states at interfaces with electrodes and gate dielectric, which could be modulated also by TA.
Light-induced metastability in hydrogenated nanocrystalline silicon solar cells
Authors: Yan Baojie , Yue Guozhen , Owens Jessica M. , Yang Jeffrey , Guha Subhendu
Published: September 2004

Light-induced metastability in hydrogenated nanocrystalline silicon (nc-Si:H) single-junction solar cells has been studied under different light spectra. The nc-Si:H studied contains a certain fraction of hydrogenated amorphous silicon (a-Si:H). We observe no light-induced degradation when the photon energy used is lower than the bandgap of a-Si:H, while degradation occurs when the photon energy is higher than the bandgap. We conclude that the light-induced defect generation occurs mainly in the amorphous phase. Light soaking experiments on a-Si:H∕a-SiGe:H∕nc-Si:H triple-junction solar cells show no light-induced degradation in the bottom cell, because the a-Si:H top and a a-SiGe:H middle cells absorb most of the high-energy photons.
Microtomography and improved resolution in cathodoluminescence microscopy using confocal mirror optics
Authors: Chan D. S. H. , Liu Y. Y. , Phang J. C. H. , Rau E. , Sennov R. , Gostev A. V.
Published: September 2004

Cathodoluminescence in scanning electron microscopy observed using an ellipsoidal confocal light collector system can offer improved resolution and an implementation of microtomography. With this signal collection system, the resolution limit is no longer determined by the beam and specimen properties but by the system optics. This possibility is demonstrated by the modeling of light transport in cathodoluminescent materials and in the ellipsoidal confocal system which collects the light emission. The conditions for the high-resolution three-dimensional visualization of microstructure within the generation volume of cathodoluminescence emission is described.
A visual acoustic high-pressure cell for the study of critical behavior of nonsimple mixtures
Authors: Aguiar-Ricardo A. , Temtem M. , Casimiro T. , Ribeiro N.
Published: September 2004

A visual acoustic high-pressure cell was constructed for the determination of critical data of multicomponent mixtures. The cell was specially designed to include two piezoelectric transducers and two sapphire windows that make this cell well suited to investigate the critical behavior of mixtures, simultaneously using the acoustic technique and the direct visual inspection of the critical opalescence. Critical data obtained on the binary mixtures of CO2+CHF3 were used for comparison with values given in literature using the traditional methods. The acoustic results are in agreement with those obtained by the conventional methods, within the combined experimental errors. Comparison of visual and acoustic data enabled the evaluation of the applicability of the acoustic technique to study the critical behavior of multicomponent mixtures.
A system of Kerr effect spectroscopy for light absorbing liquids
Authors: Horii Kazuyoshi , Sakai Keiji
Published: September 2004

We developed experimental system of the optical Kerr effect spectroscopy for the light absorbing liquids. To avoid the problems due to the light absorption, such as the thermal lens effect, our new system used a gated rectangular light pulse with the alternative polarization modulation as the pump light. The experimental results of the transient behavior of the signal showed that our system could clearly distinguish the optical Kerr effect from the thermal lens effect. Careful monitoring of the signal enables us to suppress the temperature increase within the experimental latitude. We examined the previous results that the optical anisotropy of the isotropic liquid crystals induced by the external field is enhanced dramatically compared with the pure liquid crystals by doping a small amount of the dye from the viewpoint of relaxation dynamics. The information on the dynamic molecular orientation relaxation obtained by our spectroscopy would help us understand a microscopic interaction among liquid crystals and dye molecules, especially in the vicinity of the transition temperature. The system would be useful widely for the measurement of the nonlinear optical properties in the materials, which show strong light absorption or scattering.
Application of the acousto-optic effect to pressure measurements in ultrasound fields in water using a laser vibrometer
Authors: Buick J. M. , Cosgrove J. A. , Douissard P.-A. , Greated C. A. , Gilabert B.
Published: September 2004

A non-intrusive measuring technique, applied to sensing and measuring acoustic waves at ultrasonic frequencies is considered. The method is optically based and so does not interfere with the ultrasound field. The measurement procedure relies on the acousto-optic effect, that is the change in refractive index which occurs with changing pressure in the ultrasound field. This change in refractive index is detected through the change in the path length of a laser beam propagating through the region of interest. Typically these changes are small corresponding to a physical change of the order of 10−6 m. Fourier analysis is used to separate the component of the signal corresponding to the pressure variation from background noise and vibrations which can be dominant. Application of the technique is illustrated for an underwater ultrasound transducer. Measurements are made using the optical technique and compared to measurements taken with a hydrophone. The effectiveness of the optical measuring technique is discussed. It is shown that the laser vibrometer produces a good estimation of the mean beam pressure provided an estimation of the beam width is available, a restriction which is often satisfied; and the acoustic field can be assumed to be approximately constant across the beam.
Applications of a single-longitudinal-mode alexandrite laser for diagnostics of parameters of combustion interest
Authors: Li Z. S. , Afzelius M. , Zetterberg J. , Aldén M.
Published: September 2004

We report on the applications of a single-longitudinal-mode (SLM) pulsed alexandrite laser system for diagnostics of parameters of flow/combustion interest. The laser system is characterized by its narrow linewidth, high peak power, and broad tunablity. The absolute frequency of the laser output was monitored by a wavelength diagnostic system, which included a high-resolution confocal etalon and a molecular iodine laser-induced fluorescence (LIF) detection system. Different nonlinear frequency conversion schemes were used to cover a large frequency range from the infrared to the deep UV. The versatility of the laser system for flow/combustion diagnostics is demonstrated in three applications, namely filtered Rayleigh scattering, high-resolution Doppler-free two-photon LIF of CO, and infrared LIF and polarization spectroscopy of CO2. The potential impacts of using this SLM laser system in laser flow/combustion diagnostic applications are discussed.
A new plasma potential measurement instrument for plasma ion sources
Authors: Tarvainen O. , Suominen P. , Koivisto H.
Published: September 2004

A very efficient and fast instrument to measure the plasma potential of ion sources has been developed at the Department of Physics, University of Jyväskylä (JYFL). The operating principle of this novel instrument is to apply a decelerating voltage into a mesh located in the beamline of the ion source. The plasma potential is determined by measuring the current at the grounded electrode situated behind the mesh as a function of the voltage. In this article, we will introduce the instrument and the first results. In the experiments, the instrument was connected to the beamline of the JYFL 6.4 GHz electron cyclotron resonance ion source. The plasma potential was measured with different source conditions and it was observed to vary between 30–65 V. The plasma potential tended to increase as the microwave power, or the gas feed rate, was increased. These results are consistent with earlier observations and estimations. It was also noticed that the value of the plasma potential changed when the negative voltage applied to the biased disk at the injection of the ion source was varied. Complementary to optical plasma diagnostics, such an instrument can be used as a very efficient tool to get a precise relationship between plasma conditions and extracted beams.
Contrast and resolution in direct Fresnel diffraction phase-contrast imaging with partially coherent x-ray source
Authors: Han Shensheng , Yu Hong , Cheng Jing , Gao Chen , Luo Zhenlin
Published: September 2004

A general treatment of x-ray image formation by direct Fresnel diffraction with partially coherent hard x rays is presented. Contrast and resolution are the criteria used to specify the visibility of an image, which depend primarily on the spatial coherence of the illumination and the distance from object to the image, with chromatic coherence of lesser importance. The dependence of the quality of phase-contrast images on the parameters of in-line imaging configuration is described quantitatively. The influence of spatial coherence of hard x-ray source on the imaging quality is also discussed based on the partially coherent direct Fresnel diffraction phase-contrast imaging theory. Experimental results are also presented for phase-contrast x-ray images with partially coherent hard x rays.
Versatile fiber-coupled system for simultaneous photon correlation spectroscopy and Fabry–Perot interferometry
Authors: Bogoslovov R. B. , Shelton D. P. , Selser J. C. , Piet G. , Peng S.
Published: September 2004

We demonstrate an experimental setup utilizing fiber-optic detection and coupling of scattered light into existing photon correlation spectroscopy (PCS) and Fabry–Perot (F–P) interferometry systems. The performance of the fiber coupled F–P as a high-resolution interferometer is considered in detail. Several practical issues and limitations are discussed, including the selection of optic and fiber-optic components, collimation, effects of the fiber mode structure and core diameter, and alignment issues. A series of test measurements on standard systems with well known properties shows that the proposed fiber-optic design meets the performance expectations for both PCS and F–P instruments and presents an attractive alternative to the classical pinhole design.
Large-aperture variable-volume view cell for the determination of phase-equilibria in high pressure systems and supercritical fluids
Authors: Licence Peter , Dellar Martin P. , Wilson Richard G. M. , Fields Peter A. , Litchfield David , Woods Helen M. , Poliakoff Martyn , Howdle Steven M.
Published: September 2004

A high-pressure, variable-volume view cell incorporating a custom engineered, optically transparent sapphire piston is described. The view cell has an unbroken field of vision that enables the entire sample volume to be observed at all times. When lit from the rear of the cell, a near perfect view of any physical transition or change in state is available to the experimenter. The system has been shown to be particularly suitable for the determination of phase equilibria and cloud point measurements in supercritical fluid systems and has been rated for experiments up to 400 bar, 200 °C.
Development of thrust stand for low impulse measurement from microthrusters
Authors: Koizumi H. , Komurasaki K. , Arakawa Y.
Published: September 2004

A thrust stand has been developed to accurately measure thrust produced by two types of microthrusters—a liquid propellant pulsed plasma thruster (LP-PPT) and a diode laser ablation microthruster. The impulse of LP-PPT ranged from 20 to 80 μNs. The diode laser microthruster, which is a new type of microthruster, produces much lower impulse range of 1–10 μNs for about 1 s. The mechanical noise induced from the background vibrations becomes a crucial problem for precise estimate of thrust particularly in low impulse measurements. A data analysis method to reduce the effect of mechanical noise is proposed by introducing an additional term in a fitting function. It was verified that the analysis method used in our experimental conditions reduced variance caused by noise down to one-third that of a normal fitting method. The accuracy of the thrust stand is 2.1 μNs in the case of the LP-PPT and 0.7 μNs in the case of the diode laser microthruster.
Low-temperature field emission system for development of ultracoherent electron beams
Authors: Cho B. , Ogawa T. , Ichimura T. , Ichinokawa T. , Amakusa T. , Oshima C.
Published: September 2004

Here, we present the design and test-operation performance of a low-temperature field emission (FE) system which can be employed to image and characterize the FE beam from low-temperature tips. Three radiation shields cooled by liquid helium and liquid nitrogen cryostats surround the FE tips and anodes completely. Once the FE system is cooled down to 5 K, experiments can run for more than 15 h without interruption. The design allows not only for the exchange of tips and anodes by load-lock equipment but also for the adjustment of tip–anode distance using a piezo-tube. Test runs in projection microscopy mode have presented clear diffraction-fringe patterns near the shadows of nano objects at temperatures from room temperature to 5.5 K, indicating that the system is well suited for the investigation of the coherence of electron beam from FE tip.
Fast and adjustable-resolution grazing-incidence x-ray liquid surface diffraction
Authors: Fontaine Philippe , Goldmann Michel , Bordessoule Michel , Jucha Alain
Published: September 2004

We developed a configuration using a two-dimensional detector for grazing incidence x-ray diffraction on Langmuir monolayers and, more generally, for surface diffraction on two-dimensional powders. Compared to the classical setup using a linear detector combined with Soller slits, the acquisition time is reduced by an order of magnitude (from more than 1 h to a few minutes) using the same x-ray source (synchrotron bending magnet) with a comparable signal to noise ratio. Moreover, experimental resolution can be adjusted by varying a vertical slit (horizontal gap) and, for small values of the gap, better resolution can be achieved compared to the one obtained with the Soller slits and linear detector.
Measurements of picosecond lifetimes by time correlated single photon counting method: The effect of the refraction index of the solvent on the instrument response function
Authors: Wróżowa Teresa , Ciesielska Barbara , Komar Dariusz , Karolczak Jerzy , Maciejewski Andrzej , Kubicki Jacek
Published: September 2004

The article concerns the possibility of precise picosecond lifetime measurements by the method of the time correlated single photon counting (TCSPC). The lifetimes (τ) of S2 fluorescence of xanthione measured in different solvents have shown that it is possible to obtain τ as short as a few picoseconds. The values of τ varying from ∼5 to ∼38 ps in solvents whose refraction indices range from 1.34 to 1.50 have been proposed as picosecond standards in lifetime measurements. However, in order to obtain reliable results some conditions must be met: the effect of the absorbing and emitting impurities must be eliminated, the instrument response function (IRF) must be very stable and correctly determined, and because of a much lower time resolution of the TCSPC method relative to that of the upconversion method, the procedure of measurements and numerical analysis of results proposed in our work should be applied. In the study reported the effect of impurities was eliminated by applying high performance liquid chromatography to choose the excitation and emission wavelength for which the emission of impurities is negligible for fluorescence decay measurements of the sample (S) and reference (R). It has been shown that the IRF in TCSPC depends on the refraction index of the solvent used. In order to avoid the systematic errors related to different IRF for S and R, the calculations of fluorescence lifetimes should be performed for S and R in solvents of the possibly most similar refraction indices. The effect of the solvents difference in the refraction indices on the shape of IRF has been shown and then on the fluorescence lifetimes below 20 ps. The proposed procedure of determination of single picosecond lifetimes with the use of TCSPC is particularly suitable when it is necessary to use a very low concentration (⩽10−5 M) of the compound studied in order to avoid dimers and oligomers formation (in the upconversion method concentration >10−4 M is generally used). A very good statistics of the TCSPC method—much better than in the other time-resolved methods—together with the use of the procedure of measurements—the procedure of numerical analysis and procedure of elimination of emission of impurities proposed in our article—permit elimination of the systematic errors (usually ±3 ps) in the lifetimes determined for monoexponential decays and obtaining a highly reliable description of the fluorescence decay kinetics also when the fluorescence decay is nonexponential.
Industrial application of ultrasound based in-line rheometry: From stationary to pulsating pipe flow of chocolate suspension in precrystallization process
Authors: Ouriev Boris , Windhab Erich , Braun Peter , Birkhofer Beat
Published: September 2004

In-line visualization and on-line characterization of nontransparent fluids becomes an important subject for process development in food and nonfood industries. In our work, a noninvasive Doppler ultrasound-based technique is introduced. Such a technique is applied for investigation of nonstationary flow in the chocolate precrystallization process. Unstable flow conditions were induced by abrupt flow interruption and were followed up by strong flow pulsations in the piping system. While relying on available process information, such as absolute pressures and temperatures, no analyses of flow conditions or characterization of suspension properties could possibly be done. It is obvious that chocolate flow properties are sensitive to flow boundary conditions. Therefore, it becomes essential to perform reliable structure state monitoring and particularly in application to nonstationary flow processes. Such flow instabilities in chocolate processing can often lead to failed product quality with interruption of the mainstream production. As will be discussed, a combination of flow velocity profiles, on-line fit into flow profiles, and pressure difference measurement are sufficient for reliable analyses of fluid properties and flow boundary conditions as well as monitoring of the flow state. Analyses of the flow state and flow properties of chocolate suspension are based on on-line measurement of one-dimensional velocity profiles across the flow channel and their on-line characterization with the power-law model. Conclusions about flow boundary conditions were drawn from a calculated velocity standard mean deviation, the parameters of power-law fit into velocity profiles, and volumetric flow rate information.
Indirect optical absorption of single crystalline β-FeSi2
Authors: Udono Haruhiko , Kikuma Isao , Okuno Tsuyoshi , Masumoto Yasuaki , Tajima Hiroyuki
Published: September 2004

We investigated optical absorption spectra near the fundamental absorption edge of β-FeSi2 single crystals by transmission measurements. The phonon structure corresponding to the emission and absorption component was clearly observed in the low-temperature absorption spectra. Assuming exciton state in the indirect allowed transition, we determined a phonon energy of 0.031±0.004eV. A value of 0.814eV was obtained for the exciton transition energy at 4K.
Role of N ions in the optical and morphological properties of InGaAsN quantum wells for 1.3–1.5μm applications
Authors: Miguel-Sánchez J. , Guzmán A. , Muñoz E.
Published: September 2004

In this work, we show the effects of N ions coming from a nitrogen plasma source on the optical and structural properties of InGaAsN quantum wells. The presence of ions in the growth chamber was measured by a modified Langmuir probe method at the substrate position. A magnetic field was applied to deflect charged species from the growing surface, producing a lower concentration of ions in the growth surface that led to an improvement of the optical and structural properties of the InGaAsN layers. The samples grown with an applied magnetic field showed a more intense and narrower photoluminescence emission, as well as a lower surface roughness. Additionally, postgrowth annealing has a smaller impact on the photoluminescence emission when a magnetic field is used, and a much lower blueshift is observed.
Fabrication of three-dimensional photonic crystalsusing silicon micromachining
Authors: Venkataraman Sriram , Schneider Garrett J. , Murakowski Janusz , Shi Shouyuan , Prather Dennis W.
Published: September 2004

We propose a method for the fabrication of three-dimensional photonic-crystal structures using conventional planar silicon micromachining. The method utilizes a single planar etch mask coupled with time-multiplexed, sidewall-passivating, deep anisotropic reactive-ion etching, to create an array of spherical voids with three-dimensional symmetry. Preliminary results are presented that demonstrate the feasibility of the approach.
Ballistic electron emission luminescence spectroscopy of an InAs quantum dot heterostructure
Authors: Yi Wei , Appelbaum Ian , Russell K. J. , Narayanamurti V. , Hanson M. P. , Gossard A. C.
Published: September 2004

We present ballistic electron emission luminescence (BEEL) spectroscopy measurements of an InAs quantum dot (QD) heterostructure based on three-terminal hot electron injection using a scanning tunneling microscope (STM) and a planar tunnel-junction transistor. Due to higher injected current, the planar transistors allow us to perform wavelength spectroscopy of the emitted luminescence, which resolves both quantum-confined Stark-shifted QD luminescence near 1.34eV and bulk GaAs luminescence at 1.48eV. This facilitates interpretation of STM BEEL spectra as a function of collector voltage bias. By freezing out the collector leakage current at low temperatures, consistent collector-current spectra are acquired with both STM and planar transistors.
Thermionic emission from defective carbon nanotubes
Authors: Cox D. C. , Forrest R. D. , Smith P. R. , Silva S. R. P.
Published: September 2004

Using a nanomanipulation system contained within a scanning electron microscope we investigate the thermionic electron emission from multiwall carbon nanotubes. Peak emission currents of 65nA are measured. The carbon nanotubes being grown at low temperature by the chemical vapor deposition method are defective with poor thermal conductivity. We believe it is crucial for the thermal conductivity to be poor in order to obtain significant thermionic emission from the carbon nanotubes. This allows for the carbon nanotube during electron emission to be at high temperatures, and thus give higher emission efficiencies. At the highest emission current levels we estimate the temperature of the nanotubes to be approximately 2900K.
Recombination dynamics of localized excitons in InGaN quantum dots
Authors: Bartel T. , Dworzak M. , Strassburg M. , Hoffmann A. , Strittmatter A. , Bimberg D.
Published: September 2004

Indium-rich fluctuations in ultrathin InGaN layers act at low temperatures as a dense ensemble of quantum dots (QD). This leads to a complex potential landscape with localization sites of widely varying depth for excitons. We report on investigations of the recombination mechanisms of excitons localized in InGaN∕GaN QD structures by time-resolved and spatially resolved photoluminescence (PL) measurements. The structures were grown by metal-organic chemical-vapor deposition on Si (111) substrates. Sharp lines originating from single QDs could be observed. Their PL decays show monoexponential behavior. Similar transition energies have different time constants. Thus, the well-known nonexponential PL decay of the QD ensemble is assigned to the summation of monoexponential decays originating from individual QDs with different exciton lifetimes.
Light-induced instability of PbO-filled single-wall carbon nanotubes
Authors: Hulman Martin , Kuzmany Hans , Costa Pedro M. F. J. , Friedrichs Steffi , Green Malcolm L. H.
Published: September 2004

We investigated single-wall carbon nanotubes filled with lead oxide, PbO, by transmission electron microscopy and Raman spectroscopy. It is concluded that PbO crystallizes in the orthorombic phase forming nanowires inside the nanotubes. The positions of the PbO Raman lines are downshifted as compared to the bulk material as a result of the reduced dimensionality. As a consequence of the filling, nanotubes become sensitive to the laser irradiation. At higher laser power densities, they oxidize and the free PbO nanowires are left in the sample.
Polarized neutron reflectometry of a patterned magnetic film with a He3 analyzer and a position-sensitive detector
Authors: Chen W. C. , Gentile T. R. , O’Donovan K. V. , Borchers J. A. , Majkrzak C. F.
Published: September 2004

We have employed a polarized He3 spin filter in conjunction with a position-sensitive detector (PSD) to perform efficient polarization analysis of neutron diffuse reflectivity. This work was carried out on the NG-1 polarized neutron reflectometer at the National Institute of Standards and Technology Center for Neutron Research. We measured the specular and diffuse reflectivity of a patterned magnetic array that has periodic square holes in a Co film. Analysis of the data yielded spin-analyzed two-dimensional Qx−Qz reciprocal space maps for the sample in magnetized and demagnetized states. We compared the measurements obtained with a 3He analyzer and a PSD with those obtained using a conventional supermirror analyzer and a 3He proportional counter. The results are in good agreement. For this experiment, 3He gas was polarized by the spin-exchange optical pumping method and stored in a uniform magnetic field provided by a shielded solenoid. Improved optical pumping using a spectrally narrowed diode laser array yielded an initial 3He polarization of 70% in a 3He cell volume of 280 cm3.
Fabrication of super-sharp nanowire atomic force microscope probes using a field emission induced growth technique
Authors: Tay A. B. H. , Thong J. T. L.
Published: September 2004

A relatively simple and consistent technique based on field emission induced growth has been developed to grow a single metallic nanowire on an atomic force microscope (AFM) tip. A clamping setup with two micromanipulators ensures that the fabrication of a vertically aligned nanowire probe, which is sharp, robust, and with high aspect ratio, can be achieved on different types of AFM cantilevers with different force constants. The controlled growth technique has been used to produce tungsten nanowire AFM probes with great consistency and high reproducibility. The tungsten nanowires were grown to lengths between 100 nm to 1.5 μm with radius of curvature at the tip end typically between 1–2 nm. Experiments using the fabricated tungsten nanowire AFM probe demonstrate its ability to produce high-resolution AFM images and improved profiling of structures with steep sidewalls due to its very sharp tip and high aspect ratio. The technique can be extended to fabricating other types of metallic nanowire AFM probes or even composite nanowire AFM probes by using different precursor gases. Experiments have been successful in fabricating cobalt nanowire AFM probes which are able to produce good high-resolution AFM images as well.
Compositional dependence of phase separation in InGaN layers
Authors: Rao M. , Kim D. , Mahajan S.
Published: September 2004

Phase separation in InGaN layers grown by metalorganic chemical vapor deposition on GaN epilayers was investigated using transmission electron microscopy. Layer thicknesses of 220 and 660nm were deposited with InN fractions ranging from 3% to 34%. At InN contents of 3%, plan-view TEM images show a homogeneous microstructure and selected area diffraction (SAD) patterns exhibit no evidence of satellite spots. InN contents of 12% result in a speckled contrast. Satellites close to the fundamental spots belonging to the wurtzite structure are present in SAD patterns and they are indicative of composition modulations lying in the (0001) growth plane. No satellites are observed along the [0001] direction, implying that phase separation is two-dimensional in nature. Samples containing InN fractions of between 22% and 28% have microstructures exhibiting much stronger contrast variations. Satellite spots in SAD patterns are further spaced from the fundamental reflections. This trend continues on increasing InN content to 34%. In addition, cross-sectional TEM images show an absence of contrast from InGaN layers with InN contents above 12%, in the vicinity of the InGaN∕GaN interface, indicating that coherency strain inhibits phase separation. Arguments are developed to rationalize these observations.
Microwave SQUID multiplexer
Authors: Irwin K. D. , Lehnert K. W.
Published: September 2004

We describe a superconducting quantum interference device (SQUID) multiplexer operated at microwave frequencies. The outputs of multiple SQUIDs are simultaneously modulated at different frequencies and summed into the input of one high electron mobility transistor (HEMT). The large bandwidth and dynamic range provided by HEMT amplifiers should make it possible to frequency-division multiplex a large number of SQUIDs in one output coaxial cable. We measure low SQUID noise (∼0.5μΦ0∕Hz at 4K) and demonstrate the multiplexed readout of two direct current (dc) SQUIDs at different resonant frequencies. In this work, dc SQUIDs are used, but this approach is equally applicable to radio-frequency SQUIDs.
High-performance diamond/amorphous silicon p-n+ heterojunctions
Authors: Chen Y. G. , Ogura M. , Kondo M. , Okushi H.
Published: September 2004

We have fabricated high-performance p–n+ heterojunctions of homoepitaxial diamond (B-doped film: p type) and hydrogenated amorphous silicon (P-doped a-Si:H film: n type). Current–voltage (I–V) characteristics of the p–n+ heterojunctions at room temperature show excellent rectification properties with an ideality factor n of 1.23 and undetectable leakage current at reverse bias condition. Capacitance–voltage (C–V) characteristics show a large difference of space-charge densities (net acceptor densities) in the bulk and near-surface (interface) regions of the diamond films and a strong frequency dependence in the forward-bias region. The former result indicates that the hydrogen passivation of boron in diamond during the a-Si:H deposition occurs in the near-surface region which gives rise to a reduction of the acceptor density in the depletion region. The latter result indicates an increment of hydrogen-related defect states in the near-surface region of the diamond film. An idealized energy-band diagram for the p–n+ heterojunctions has been constructed on the basis of the negative-electron-affinity model.
Crack-free and conductive Si-doped AlN∕GaN distributed Bragg reflectors grown on 6H-SiC(0001)
Authors: Ive Tommy , Brandt Oliver , Kostial Helmar , Hesjedal Thorsten , Ramsteiner Manfred , Ploog Klaus H.
Published: September 2004

We demonstrate Si-doped n-type AlN∕GaN distributed Bragg reflectors grown on 6H-SiC(0001). The structures are crack-free and have a stopband centered around 450nm with a full width at half maximum between 40 and 50nm. The maximum measured reflectance is ⩾99%. A comparison between Si-doped and undoped structures reveals no degradation of the reflectance due to the Si doping. Vertical conductance measurements at room temperature on the samples show an ohmic I–V behavior in the entire measurement range. The measured resistivity at 77K is only a factor of 2 larger than the resistivity measured at room temperature.
High-performance long-wavelength HgCdTe infrared detectors grownon silicon substrates
Authors: Hall D. J. , Buckle L. , Gordon N. T. , Giess J. , Hails J. E. , Cairns J. W. , Lawrence R. M. , Graham A. , Hall R. S. , Maltby C. , Ashley T.
Published: September 2004

Long-wavelength HgCdTe heterostructures on silicon (100) substrates have been grown using metal-organic vapor phase epitaxy. Test diodes have been fabricated from this material using mesa technology and flip-chip bonding. We have demonstrated excellent resistance-area product characteristics for diodes with a 10.2μm cutoff wavelength. R0A values approaching 103Ωcm2 at 80K have been measured and the resistance-area product maintained above 102Ωcm2 at 1V reverse bias. Variable temperature R0A values correspond to expected generation-recombination loss mechanisms between 60 and 120K. Current-voltage characteristics of two diodes at opposite sides of an array indicate that a very uniform imaging long-wavelength infrared array could be fabricated from this material.
Ultrawide tuning range in doped organic solid-state lasers
Authors: Schneider D. , Rabe T. , Riedl T. , Dobbertin T. , Kröger M. , Becker E. , Johannes H.-H. , Kowalsky W. , Weimann T. , Wang J. , Hinze P.
Published: September 2004

We report on the tunability of 4-(Dicyanomethylene)-2-methyl-6-(julolidin-4-yl-vinyl)-4H-pyran (DCM2)-doped guest-host organic lasers. As host materials Tris-(8-hydroxy-quinoline)aluminum (Alq3), 4,4′-N,N′-dicarbazole-bipheny1 (CBP), and N′N-di(1-naphthyl)-N,N′-diphenyl-1,1′-diphenyl-4,4′-diamine (NPD) are used. The largest tuning range was observed in the Alq3:DCM2 film with 115.3nm between 597.8 and 713.1nm. In CBP:DCM2, a tuning range of 85nm was measured, whereas in NPD:DCM2 only one laser wavelength at 624.4nm could be observed. When comparing the pump energies, we observed considerably lower threshold energy densities in Alq3:DCM2 and CBP:DCM2 compared to NPD:DCM2.
High-quantum-efficiency erbium-doped optical fiber and the effective deactivator
Authors: Peng B. , Qiu X. M. , Jiang L. , Fan Z. C. , Huang W.
Published: September 2004

The optical properties of erbium-doped bismuth-based oxide glasses were studied in this letter. By adding a proper amount of hydroxyl group as the deactivator, the excited state absorption and upconversion of erbium were restrained. The mechanism is explained and some amplifiers with good properties are produced.
Visualization of buried SiGe quantum dots at cleavages by cross-sectional atomic force microscopy
Authors: Dunaevskii M. S. , Titkov A. N. , Krasilnik Z. F. , Novikov A. V. , Lobanov D. N. , Laiho R.
Published: September 2004

Cross-sectional atomic force microscopy (XAFM) is used to visualize in ambient atmosphere SiGe quantum dots (QDs) embedded in Si. Buried QDs are revealed as nanometer high topographic features on cross-sectional cleavages of the samples. Details of the images are used to get information about strain relaxation of the QDs and its relationship with the shape of the surface relief. We propose XAFM as a simple method to check the presence of QDs and to estimate their sizes and surface density. This method also allows detailed investigation of effects related to vertical alignment of the dots in different layers of multilayer QD structures.
Direct evidence for selective impurity incorporation at the crystal domain boundaries in epitaxial ZnO layers
Authors: Bertram F. , Forster D. , Christen J. , Oleynik N. , Dadgar A. , Krost A.
Published: September 2004

A direct correlation of structural properties with the spatial distribution of bound exciton luminescence in ZnO epitaxial layers has been achieved on a microscopic scale using highly spatially and spectrally resolved cathodoluminescence. The morphology of the high quality ZnO layer is characterized by a distinct domain structure. While the laterally integrated cathodoluminescence spectrum shows narrow (full width at half maximum <3meV) I8 luminescence, a pronounced emission line at I0∕I1 emerges in the local spectra taken at domain boundaries. In complete contrast, no I0∕I1 emission is found inside the domains. Monochromatic images further evidence the selective incorporation of impurities at the grain boundaries of domains. Micro mappings of the I8 peak wavelength directly visualize the strain relaxation across the domains toward their very center, where a drop in quantum efficiency indicates enhanced defect concentration.
Electrical transport properties of single ZnO nanorods
Authors: Heo Y. W. , Tien L. C. , Norton D. P. , Kang B. S. , Ren F. , Gila B. P. , Pearton S. J.
Published: September 2004

Single ZnO nanorods with diameters of ∼130nm were grown on Au-coated Al2O3 substrates by catalyst-driven molecular beam epitaxy. Individual nanorods were removed from the substrate and placed between Ohmic contact pads and the current–voltage characteristics measured as a function of temperature and gas ambient. In the temperature range from 25to150°C, the resistivity of nanorods treated in H2 at 400°C prior to measurement showed an activation energy of 0.089±0.02eV and was insensitive to the ambient used (C2H4,N2O,O2 or 10% H2 in N2). By sharp contrast, the conductivity of nanorods not treated in H2 was sensitive to trace concentrations of gases in the measurement ambient even at room temperature, demonstrating their potential as gas sensors.