bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantum coherent dissipation: A glimpse of the “cat”
Authors: Segale D. , Karavitis M. , Fredj E. , Apkarian V. A.
Published: March 2005

Quantum coherent vibrational relaxation of an impurity strongly coupled to its solid host is demonstrated through four-wave mixing measurements to infer sustained coherence in the bath, which is recognized as a superposition of macroscopically distinct states.
Current fluctuation in single-hole transport through a two-dimensional Si multidot
Authors: Nuryadi Ratno , Ikeda Hiroya , Ishikawa Yasuhiko , Tabe Michiharu
Published: March 2005

Single-hole transport in a two-dimensional Si multidot-channel field-effect transistor is studied. It is found that the single-hole-tunneling current fluctuates in the particular ranges of drain voltage and gate voltage. Such a phenomenon can be explained by a model that the hole transport through the percolation path is sensitively influenced and fluctuates with the time due to charging–discharging and polarity-switching of the dots adjacent to the percolation path. A Monte Carlo simulation using a parallel-double-dot circuit shows good agreement with the experimental characteristics.
Are spin junction transistors suitable for signal processing?
Authors: Bandyopadhyay S. , Cahay M.
Published: March 2005

A number of spintronic analogs of bipolar junction transistors have been proposed for signal processing applications. Here, we show that some of these transistors unfortunately may not have sufficient voltage and current gains for signal processing. They may also have poor isolation between input and output terminals which hinders unidirectional propagation of logic signal from the driver stage to the output. Therefore, these devices may not improve state-of-the-art signal processing capability, although they may provide some additional functionality by offering nonvolatile storage. They may also have niche applications in nonlinear circuits.
High pressure/high temperature cell for x-ray absorption and scattering techniques
Authors: Testemale Denis , Argoud Roger , Geaymond Olivier , Hazemann Jean-Louis
Published: March 2005

A high pressure/high temperature cell dedicated to x-ray absorption spectroscopy, small angle x-ray scattering, and inelastic x-ray scattering techniques is presented. The P and T parameters are controlled independently and their range allow the study of aqueous solutions (T⩽500°C and P⩽2000bar) and liquid metals and glasses (T⩽1700°C and P⩽2000bar). The autoclave technology is inspired from previous high pressure/high temperature equipments but great improvements are achieved. Original high pressure windows have been developed to ensure both pressure resistance and low absorbance combined with large angular aperture. Different configurations are available for the internal cell that contains the sample whether it is aqueous or not. As an example of the efficiency of the set-up, we present preliminary x-ray absorption results on 0.01 m FeCl3 aqueous solutions from ambient to supercritical conditions (375 °C and 300 bar). These low concentrations samples and low energy spectra (Fe K-edge is at 7112 eV) represent challenging experimental conditions.
Infrared grey-field polariscope: A tool for rapid stress analysis in microelectronic materials and devices
Authors: Horn Gavin , Lesniak Jon , Mackin Thomas , Boyce Brad
Published: March 2005

The infrared grey-field polariscope (IR-GFP) has been developed to provide rapid, full-field stress analysis for infrared-transparent materials. Grey-field photoelastic theory is outlined and the advantages of this implementation for microelectronic materials inspection highlighted. The capabilities of this scientific tool are proven using standard sample geometries fabricated from single crystal silicon substrates and the general applicability of the instrument demonstrated on bonded devices and silicon wafer geometries. Stress resolution in silicon wafers is better than 0.1MPa at wafer inspection speeds of 10s for a 100mm wafer. Initial applications of the IR-GFP have shown that the tool provides improvements in defect detection and stress quantification when compared to conventional infrared transmission imaging while also providing several important advantages over other currently utilized inspection technologies.
Instrumentation and calibration methods for the multichannel measurement of phase and amplitude in optical tomography
Authors: Nissilä Ilkka , Noponen Tommi , Kotilahti Kalle , Katila Toivo , Lipiäinen Lauri , Tarvainen Tanja , Schweiger Martin , Arridge Simon
Published: March 2005

In this article, we describe the multichannel implementation of an intensity modulated optical tomography system developed at Helsinki University of Technology. The system has two time-multiplexed wavelengths, 16 time-multiplexed source fibers and 16 parallel detection channels. The gain of the photomultiplier tubes (PMTs) is individually adjusted during the measurement sequence to increase the dynamic range of the system by 104. The PMT used has a high quantum efficiency in the near infrared (8% at 800nm), a fast settling time, and low hysteresis. The gain of the PMT is set so that the dc anode current is below 80nA, which allows the measurement of phase independently of the intensity. The system allows measurements of amplitude at detected intensities down to 1fW, which is sufficient for transmittance measurements of the female breast, the forearm, and the brain of early pre-term infants. The mean repeatability of phase and the logarithm of amplitude (lnA) at 100MHz were found to be 0.08° and 0.004, respectively, in a measurement of a 7cm phantom with an imaging time of 5s per source and source optical power of 8mW. We describe a three-step method of calibrating the phase and amplitude measurements so that the absolute absorption and scatter in tissue may be measured. A phantom with two small cylindrical targets and a second phantom with three rods are measured and reconstructions made from the calibrated data are shown and compared with reconstructions from simulated data.
Variation of lateral tension and a new transition in model bilayers made of chain molecules
Authors: Stecki J.
Published: March 2005

Molecular dynamics simulations of model bilayers made of amphiphilic chain molecules dissolved in a Lennard-Jones solvent, reveal a new transition between a flat tensioned state and a foamy rough thick compressed bilayer. Variation of lateral tension with area per surfactant head undergoes unexpected and dramatic changes when the system size is substantially increased; a new transition is then found. Scaling is discussed and structure factor is reported.
The Ebers–Moll model for magnetic bipolar transistors
Authors: Fabian Jaroslav , Žutić Igor
Published: March 2005

The equivalent electrical circuit of the Ebers–Moll-type is introduced for magnetic bipolar transistors. In addition to conventional diodes and current sources, the new circuit comprises two novel elements due to spin-charge coupling. A classification scheme of the operating modes of magnetic bipolar transistors in the low bias regime is presented.
Variations of surfactant monolayer surface density in induced steady wave regime
Authors: Likhterov L. , Berman A.
Published: March 2005

Fluctuations of an insoluble surfactant concentration along the free liquid surface induced by steady surface waves are considered theoretically. The energy of a waved surface is assumed to consist of surface tension, curvature, and van der Waals energy components. Dependencies of the surface tension and the bending stiffness versus the surfactant concentration are assumed to be linear relative to some reference level. The van der Waals energy is taken in the form of interaction term for a thin film. Minimization of the total energy allows the expression for the deviations of concentration to be obtained. The distribution of a surfactant concentration relative to some reference level has been found to be periodic, with a period that is half of the wave period, and the amplitude of oscillations is a function of a wave number that is very similar to the Landau expansion of the free-energy near the critical point in phase transitions.
Enhanced annealing effect in an oxygen atmosphere on Ga1−xMnxAs
Authors: Malfait M. , Vanacken J. , Moshchalkov V. V. , Van Roy W. , Borghs G.
Published: March 2005

We report on in situ resistivity measurements on Ga1−xMnxAs during post-growth annealing in different atmospheres. A drop in the resistivity is observed when the Ga1−xMnxAs is exposed to oxygen, which indicates that the passivation of Mn interstitials (MnI) at the free surface occurs through oxidation. The presence of oxygen can therefore be an important annealing condition for the optimization of Ga1−xMnxAs thin films, all the more since the oxidation appears to be limited to the sample surface. Annealing in an oxygen-free atmosphere leads to an increase in the resistivity indicating a second annealing mechanism besides the outdiffusion of MnI. According to our magnetization and Hall effect data, this mechanism reduces the amount of magnetically and electrically active Mn atoms.
Dynamics of cross linking fronts in alkyd coatings
Authors: Erich S. J. F. , Laven J. , Pel L. , Huinink H. P. , Kopinga K.
Published: March 2005

The dynamics of the curing process of alkyd coatings is an important aspect for coating performance. The formation of cross links in an alkyd coating film has been followed in time using a microimaging nuclear magnetic resonance setup, having a spatial resolution of 5μm perpendicular to the film. During this cross-linking process a front has been observed inside the coating film. The position of this front varied with the square root of time. With the help of a simple reaction model, we have proven that this dynamics results from the fact that the curing rate is limited by the oxygen flux into the coating. This model can also explain, the differences in curing rates observed for various coatings.
Self-organized nanocolumnar structure in superhard TiB2 thin films
Authors: Mayrhofer P. H. , Mitterer C. , Wen J. G. , Greene J. E. , Petrov I.
Published: March 2005

TiB 2 thin films are well known for their high hardness which makes them useful for wear-resistant applications. Overstoichiometric TiB2 deposited at 300 °C by nonreactive sputtering has been shown to exhibit superhardness (H⩾40GPa), while the hardness of their bulk stoichiometric counterparts is ∼25GPa. We show, using high-resolution transmission electron microscopy, that overstoichiometric TiB2.4 layers have a complex self-organized columnar nanostructure. The ∼20nm wide columns, encapsulated in excess B and oriented along 0001, consist of a bundle of ∼5nm diameter TiB2 subcolumns separated by an ultrathin B-rich tissue phase. The nanocolumnar structure, which is thermally stable to postannealing temperatures up to 700 °C, inhibits nucleation and glide of dislocations during hardness indentation measurements, while the high cohesive strength of the B-rich tissue phase prevents grain-boundary sliding. The combination of these effects results in the observed superhardness of ∼60GPa.
Phase-graded deposition of diamond-like carbon on nanotips by near-field induced chemical vapor deposition
Authors: Shi J. , Lu Y. F. , Chen X. Y. , Cherukuri R. S. , Mendu K. K. , Wang H. , Batta N.
Published: March 2005

Diamond-like carbon (DLC) films were deposited on tungsten (W) tips under the KrF excimer laser in a laser chemical vapor deposition (LCVD) chamber. Raman spectroscopy showed that the deposited DLC films were phase-graded along the tips from the apexes. The DLC films were more diamondlike at or near the tip apexes. From numerical simulation, there is a strongly confined and enhanced optical field at the tip apexes. The simulation also indicates that there is an optical-field gradient from tip apexes to tip bodies. Therefore, the variations in the phases of deposited DLC films were attributed to the corresponding variations in local optical intensities along the tips. Hence, optical local near field was confirmed to be responsible to the DLC deposition.
Growth of Ga-doped ZnO nanowires by two-step vapor phase method
Authors: Xu C. , Kim M. , Chun J. , Kim D.
Published: March 2005

A two-step route is presented to dope Ga into ZnO nanowires and also fabricate heterostructures of Ga-doped ZnO nanowires on ZnO. The content of Ga in ZnO nanowires is about 7 at. % from energy-dispersive x-ray analysis. The single crystal Ga doped ZnO nanowires with the diameter of 40 nm and the length of 300–500 nm are well aligned on the ZnO bulk. The growth direction is along [001]. Raman scattering analysis shows that the doping of Ga into ZnO nanowires depresses Raman E1L mode of ZnO, manifesting that Ga sites in ZnO are Zn sites (GaZn). The formation mechanism of Zn1−xGaxO nanowires/ZnO heterostructures is proposed.
Electronic and vibrational spectra of the low-lying πσ* state of 4-dimethylaminobenzonitrile: Comparison of theoretical predictions with experiment
Authors: Zgierski Marek Z. , Lim Edward C.
Published: March 2005

Comparison of the TD-BP86∕cc-pVDZ electronic excitation energies and the CIS∕cc-pVDZ vibrational frequencies of 4-dimethylaminobenzonitrile with the available experimental data indicates that the picosecond transient absorption at about 700 nm, and the excited-state vibration of frequency 1467cm−1, belong to the lowest-energy πσCN* state of bent geometry (CCN bond angle of about 120° and a large CN bond distance). Consistent with these assignments, the 1467cm−1 Raman band, attributed to the CN stretch, exhibits a large resonance enhancement of intensity when the probe (Raman excitation) wavelength is set to the spectral region of the πσ*←πσ* absorption. The result corroborates the occurrence of an ultrafast state switch from the initially excited ππ*1 (Lb) state to the πσ*1 state of lower energy.
Thin-film alternating current nanocalorimeter for low temperatures and high magnetic fields
Authors: Minakov A. A. , Roy S. B. , Bugoslavsky Y. V. , Cohen L. F.
Published: March 2005

Thin-film nanocalorimeter for low temperatures and high magnetic fields is described. The calorimeter is based on a commercial microchip module (thermal conductivity vacuum gauge TCG 3880 from Xensor Integration, NL). The gauge consists of submicron silicon nitride membrane with a film-thermopile and a resistive film-heater with dimensions of 50×100μm2 located at the center of the membrane. The gauge is mounted in a thermostat filled with helium exchange gas. The method of alternating current (ac) calorimetry is applied for heat capacity measurements. The noise-floor sensitivity of the calorimeter is better than 1nJ∕K below 100K and about 3nJ∕K at 300K. This allows for reliable measurements to be performed on sub-microgram samples. It is proved that the method is applicable for heat capacity measurements at temperatures in the range of 5–300K and in high magnetic fields up to 8T. We present a theoretical analysis of the thermal processes in the gauge-sample-surrounding gas system. On this basis a calibration method has been developed. We demonstrate that the technique yields correct heat capacity for test samples and that in special cases the thermal conductivity and the magnetostriction of the sample can be measured simultaneously with the heat capacity.
Strain-induced formation of K2Ti6O13 nanowires via ion exchange
Authors: Wang R. H. , Chen Q. , Wang B. L. , Zhang S. , Peng L.-M.
Published: March 2005

Nanowires with 10 nm in diameter and several microns in length have been synthesized by ion exchange reaction of Na2Ti3O7 in KOH aqueous solution, and the structure of these nanowires has been determined to be K2Ti6O13. It was shown that the nanowires were formed as a result of strain induced phase transformation from the Na2Ti3O7 structure to K2Ti6O13. The length of the nanowires was determined largely by the size of the raw Na2Ti3O7 crystal along its [010] direction, and the cross section was determined mainly by the competition between the lattice misfit resulted strain energy and the bonding characteristics of the Na2Ti3O7 structure.
Real-time observation of pulse reshaping using Sr0.61Ba0.39Nb2O6 single crystal fiber in a microwave cavity
Authors: Huang Chuanyong , Guo Ruyan , Bhalla Amar S.
Published: March 2005

Ferroelectric single crystal fiber Sr0.61Ba0.39Nb2O6 (SBN) is evaluated for optical pulse engineering in terms of wavelength shifting and pulse compression/expansion through nonlinear optical (Pockels) effect at microwave frequencies. The microwave–photonic interaction was investigated experimentally in a TE103 microwave cavity at 10GHz. It is shown that the frequency component of an optical pulse can be controlled effectively using the SBN single crystal in a microwave cavity without the need of contact electrodes or any interruption to the optical system. The technique may be utilized in several aspects of optical communications such as channel definition and security encoding of the signal, and shows potential for a range of optoelectronic applications.
Phase diagrams of epitaxial BaTiO3 ultrathin films from first principles
Authors: Lai Bo-Kuai , Kornev Igor A. , Bellaiche L. , Salamo G. J.
Published: March 2005

Using a first-principles-based scheme, we determine the qualitative and quantitative effects of surface∕interface, thickness and electrical boundary conditions on the temperature-misfit strain phase diagrams of epitaxial (001) BaTiO3 ultrathin films. The microscopic reasons leading to such effects are also revealed.
Diamond chemical-vapor deposition on optical fibers for fluorescence waveguiding
Authors: Rabeau J. R. , Huntington S. T. , Greentree A. D. , Prawer S.
Published: March 2005

A technique has been developed for depositing diamond crystals on the endfaces of optical fibers and capturing the fluorescence generated by optically active defects in diamond into the fiber. This letter details the diamond growth on optical fibers and transmission of fluorescence through the fiber from the nitrogen-vacancy color center in diamond. Control of the concentration of defects incorporated during the chemical vapor deposition growth process is also demonstrated. These are critical steps in developing a fiber coupled single-photon source based on optically active defect centers in diamond.
Cation intermixing at quantum well/barriers interfaces in aged AlGaAs-based high-power laser diodes bars
Authors: Pommiès M. , Avella M. , Cánovas E. , Jiménez J. , Fillardet T. , Oudart M. , Nagle J.
Published: March 2005

We report an analysis of quantum well (QW) degradation in high-power AlGaAs-based laser bars emitting at 808nm. Using low-temperature spectrally resolved cathodoluminescence (LT-SRCL) we evidenced a redshift of the AlGaAs QW luminescence peak in the less degraded regions and a blueshift in the heavily degraded parts. This blueshift is interpreted as an experimental evidence of cation intermixing between the QW and the barriers. A degradation scenario is proposed where locally higher defects concentration at QW interfaces triggers QW degradation assisted by recombination enhanced defect reactions (REDR) leading to cation intermixing as a final product of the degradation.
Temperature-dependent photoluminescence of nanocrystalline ZnO thin films grown on Si (100) substrates by the sol–gel process
Authors: Zhang Yang , Lin Bixia , Sun Xiankai , Fu Zhuxi
Published: March 2005

Temperature-dependent photoluminescence (PL) of nanocrystalline ZnO thin films grown on Si (100) substrates using a sol–gel method has been investigated. From the PL spectra measured in 83–293K, the excitonic emissions and their multiple-phonon replicas have been observed in ultraviolet region, and their origins have been identified. Moreover, it has been found that the temperature dependence of the free exciton peak position can be described by standard expression, and the thermal activation energy extracted from the temperature dependence of the free exciton peak intensity is about 101meV.
Physical model of InN growth on Ga-face GaN (0001) by molecular-beam epitaxy
Authors: Dimakis E. , Iliopoulos E. , Tsagaraki K. , Georgakilas A.
Published: March 2005

A consistent physical model of the growth of InN on GaN (0001) by radio-frequency plasma-assisted molecular-beam epitaxy is presented. Four distinct regimes of InN growth are observed due to the temperature dependence of indium adatoms’ mobility and of the InN decomposition rate. At substrate temperatures higher than 450°C, indium adatoms are highly mobile and a self-regulating mechanism of InN islands’ diameter takes place, so that a stoichiometric N:In atomic ratio on the top face of the islands is established. As a result, two-dimensional growth is possible only with In∕N atomic ratio on the substrate surface equal to unity. The self-regulating mechanism could be exploited to engineer self-organized nanostructures.
Evidence for nanoindentation-induced phase transformations in germanium
Authors: Jang Jae-il , Lance M. J. , Wen Songqing , Pharr G. M.
Published: March 2005

Nanoindentation experiments were performed using Berkovich and cube-corner indenters to investigate whether nanoindentation-induced phase transformations, such as those observed in silicon, also occur in germanium. Although the indentation load-displacement curves for germanium do not show the unloading pop-out or elbow phenomena observed in silicon, clear evidence for phase transformations was obtained by scanning electron microscopy (SEM) and micro-Raman spectroscopy. SEM showed that there is extruded material around the contact periphery of cube-corner hardness impressions that is metalliclike in its flow characteristics, just as in silicon. Micro-Raman spectroscopy revealed more direct evidence by identifying amorphous and what may be the crystalline BC8 (Ge-IV) phase. The fact that these phenomena are observed primarily and reproducibly only for the cube-corner indenter suggests that the contact geometry significantly affects the transformation behavior. Results are discussed in terms of possible deformation mechanisms and how they may be influenced by the indenter geometry.
Microscope using an x-ray tube and a bubble compound refractive lens
Authors: Piestrup M. A. , Gary C. K. , Park H. , Harris J. L. , Cremer J. T. , Pantell R. H. , Dudchik Y. I. , Kolchevsky N. N. , Komarov F. F.
Published: March 2005

We present x-ray images of grid meshes and biological material obtained using an unfiltered x-ray tube and a compound refractive lens composed of microbubbles embedded in epoxy inside a glass capillary. Images obtained using this apparatus are compared with those using a synchrotron source and the same lens. We find that the field of view is larger than that obtained using the synchrotron source, whereas the contrast and resolution are reduced. Geometrical distortion around the edges of the field of view is also reduced. The experiments demonstrate the usefulness of the apparatus in a modest laboratory setting.
Plasmonically enhanced diffusive and subdiffusive metal nanoparticle-dye random laser
Authors: Dice G. D. , Mujumdar S. , Elezzabi A. Y.
Published: March 2005

We report on surface plasmon (SP)-enhanced random laser emission from a suspension of silver nanoparticles in a laser dye operating at diffusive and subdiffusive scattering strengths. SP resonance enhances the scattering cross section, while the geometrical cross section remains small, thus providing a large gain volume. The localized electromagnetic field near the particle surface leads to enhanced absorption of excitation light and larger amplification of fluorescence. The metal-nanoparticle-based random laser yields larger linewidth narrowing at lower pump fluence threshold than a dielectric-scatterer-based random laser under equivalent conditions. These findings open the door to studies of applications related to light amplification assisted by SP in metallic nanoparticles.
Single-crystalline polytetrafluoroethylene-like nanotubes prepared from atmospheric plasma discharge
Authors: Zhang J. , Guo Y. , Xu J. Z. , Fang X. S. , Xie H. K. , Shi D. L. , He P. , van Ooij W. J.
Published: March 2005

Atmospheric plasma polymerization of perfluorohexane was investigated in this letter. A large quantity of single-crystalline polytetrafluoroethylene (PTFE)-like nanotubes were formed on a simultaneously deposited film at room temperature without any catalysts or templates. The outer diameter of the nanotubes varied from 60 to 1200 nm with a maximum aspect ratio up to 100:1. Transmission electron microscopy and x-ray diffraction results indicated a single crystal close-packed hexagonal (cph) structure in the nanotubes. Polarization optical micrographs of the nanotubes showed their thermal stability comparable to PTFE. It is suggested that the plasma filament played a key role in the rapid formation of the nanotubes. This atmospheric plasma discharge synthesis can serve as a common method for nanofabrication of many other single-crystalline polymer systems.
Liquid-crystal photoalignment by photosensitive fluorinated poly(arylene ether)
Authors: Li Xiang-Dan , Zhong Zhen-Xin , Lee Seung Hee , Ghang Gilson , Lee Myong-Hoon
Published: March 2005

We report a liquid-crystal (LC) photoalignment material with a high photosensitivity based on the fluorinated poly(arylene ether) containing a chalcone unit in the main chain. The fluorinated poly(arylene ether) exhibited defect-free homogeneous alignment of LCs upon irradiation of linearly polarized UV light for 10s. Spectroscopic analyses revealed that [2+2] cycloaddition between the chalcone moieties generated the surface anisotropy to induce an efficient alignment of LCs.
Direct patterning of magnetic media via focusing light by microsphere arrays
Authors: Polushkin Nikolay I.
Published: March 2005

An approach to nanoscale patterning using focused laser beams by two-dimensional lattices of microspheres is presented. The arrays were positioned in a controllable way near the sample surface with submicron accuracy to find the focal plane. This technique has been applied for direct patterning of Fe–Cr layers which exhibit laser-induced modifications in magnetic properties. The obtained data indicate the occurrence of some irregularities in the patterned features. To understand: (1) The reasons for the observed irregularities and (2) how small patterned features can be obtainable, the Mie solution for the intensity of scattered light has been used.
High-resolution second-harmonic optical coherence tomography of collagen in rat-tail tendon
Authors: Jiang Yi , Tomov Ivan V. , Wang Yimin , Chen Zhongping
Published: March 2005

A high-resolution second-harmonic optical coherence tomography (SH-OCT) system is demonstrated using a spectrum broadened femtosecond Ti:sapphire laser. An axial resolution of 4.2μm at the second-harmonic wave center wavelength of 400 nm has been achieved. Because the SH-OCT system uses the second-harmonic generation signals that strongly depend on the orientation, polarization, and local symmetry properties of chiral molecules, this technique provides unique contrast enhancement to conventional optical coherence tomography. The system is applied to image biological tissues of the rat-tail tendon. Highly organized collagen fibrils in the rat-tail tendon can be visualized in recorded images.
Orientation-dependent phonon observation in single-crystalline aluminum nitride
Authors: Bickermann M. , Epelbaum B. M. , Heimann P. , Herro Z. G. , Winnacker A.
Published: March 2005

In this study, we present a microspectroscopic investigation performed on different facets of a self-nucleated aluminum nitride (AlN) single crystal. We show that, apart from evaluating crystalline quality, Raman and Fourier transform infrared spectroscopy can provide means to detect the orientation of any AlN facet. Such local, nondestructive technique is very useful for selecting and evaluating samples of single crystalline AlN.
Electroreflectance studies of InAs quantum dots with InxGa1−xAs capping layer grown by metalorganic chemical vapor deposition
Authors: Chang W.-H. , Chen Hsiang-Yu , Chang H.-S. , Chen W.-Y. , Hsu T. M. , Hsieh T.-P. , Chyi J.-I. , Yeh N.-T.
Published: March 2005

Electroreflectance spectroscopy was used to study the effect of InxGa1−xAs capping layer on InAs quantum dots grown by metalorganic chemical vapor deposition. The optical transitions of the quantum dots and the InxGa1−xAs capping layer were well resolved. The energy shifts in the InxGa1−xAs capping layer show a different trend as compared to a series of referent InxGa1−xAs quantum wells. These results support the concept of strain-driven alloy decomposition during the InxGa1−xAs layer overgrowth.
Low-resistance Al-based reflectors for high-power GaN-based flip-chip light-emitting diodes
Authors: Song June-O , Hong Woong-Ki , Park Y. , Kwak J. S. , Seong Tae-Yeon
Published: March 2005

We report on the formation of high-quality p-type Al-based ohmic reflectors using Ag (3nm)∕indium tin oxide (ITO)(100nm) interlayers for use in high-power flip-chip light-emitting diodes (LEDs). The Ag∕ITO interlayers are first annealed at temperatures of 530 and 630°C for 1min in air, after which Al reflectors (200nm thick) are deposited and subsequently annealed at 330°C for 5min in a vacuum. It is shown that the annealed Ag∕ITO∕Al contacts give specific contact resistances as low as ∼10−5Ωcm−2 and reflectance of ∼85% at a wavelength of 460nm, which are much better than those of oxidized Ni∕Au schemes. LEDs fabricated with the annealed Ag∕ITO∕Al p-type electrodes give forward-bias voltages of 3.29–3.37V at injection current of 20mA.
Nanoscale effects on ion conductance of layer-by-layer structures of gadolinia-doped ceria and zirconia
Authors: Azad S. , Marina O. A. , Wang C. M. , Saraf L. , Shutthanandan V. , McCready D. E. , El-Azab A. , Jaffe J. E. , Engelhard M. H. , Peden C. H. F. , Thevuthasan S.
Published: March 2005

Layer-by-layer structures of gadolinia-doped ceria and zirconia have been synthesized on Al2O3(0001) using oxygen plasma-assisted molecular beam epitaxy. Oxygen ion conductivity greatly increased with an increasing number of layers compared to bulk polycrystalline yttria-stabilized zirconia and gadolinia-doped ceria electrolytes. The conductivity enhancement in this layered electrolyte is interesting, yet the exact cause for the enhancement remains unknown. For example, the space charge effects that are responsible for analogous conductivity increases in undoped layered halides are suppressed by the much shorter Debye screening length in layered oxides. Therefore, it appears that a combination of lattice strain and extended defects due to lattice mismatch between the heterogeneous structures may contribute to the enhancement of oxygen ionic conductivity in this layered oxide system.
Growth and thermal stability of Ga(1−X)CrXN films
Authors: Thaler G. T. , Frazier R. M. , Abernathy C. R. , Pearton S. J.
Published: March 2005

GaCrN thin films were synthesized using gas-source molecular beam epitaxy. No evidence of second-phase formation was observed by powder x-ray diffraction. Magnetic characterization performed using a superconducting quantum interference device magnetometer showed evidence of ferromagnetic ordering at room temperature for all samples. In agreement with theoretical predictions, material with 3% Cr showed the highest degree of ordering. No evidence of segregation was found from secondary ion mass spectroscopy analysis. The oxygen content of the film was found to be ∼1019cm−3. After rapid thermal annealing at temperatures up to 700 °C in a nitrogen ambient for 1 min, the room temperature saturation magnetization of the GaCrN films remained virtually unchanged, in contrast to similarly prepared GaMnN films.
Miniaturized single-crystal silicon cantilevers for scanning force microscopy
Authors: Yang J. L. , Despont M. , Drechsler U. , Hoogenboom B. W. , Frederix P. L. T. M. , Martin S. , Engel A. , Vettiger P. , Hug H. J.
Published: March 2005

We report on a method to reproducibly batch fabricate single-crystal silicon cantilevers with dimensions an order of magnitude smaller than conventional cantilevers, i.e., with lengths between 10 and 35μm, a width of 4μm, and a thickness of 0.2μm. The cantilevers are attached to support chips specially tailored for use in a scanning force microscope. The resonance frequencies are0.2 – 2 MHz, the spring constants about 0.05−1N∕m, and the quality factors 1.5−3.0×104. The resulting thermal force noise is 1−2×10−16N∕Hz at room temperature in vacuum. These cantilevers allow an enhancement of the measurement speed of more than one order of magnitude, and 2−5× better force sensitivity. After annealing in ultrahigh vacuum and measuring at liquid helium temperature, the thermal force noise of these cantilevers is expected to be further reduced down to 10−18N∕Hz.
Intrinsic reoxidation of microwave plasma-nitrided gate dielectrics
Authors: Alshareef H. N. , Niimi H. , Varghese A. , Bevan M. , Kuan R. , Holt J. , Tiner P. , Khamankar R.
Published: March 2005

The impact of nitrogen concentration on nitrided gate dielectric scaling has been found to depend on the process conditions used to incorporate nitrogen. For example, the variation in the nitrogen content of gate dielectrics processed at high pressure (>107Pa) has a strong impact on gate leakage current, but not on equivalent oxide thickness. While this effect allows nearly independent control of gate leakage and drive currents of the device, it prevents scaling of the gate dielectric. In contrast, it is found that at low process pressures (<13Pa) the gate dielectric behaves in a more conventional fashion, where both electrical oxide thickness and film leakage change with film nitrogen content. A model is proposed to explain this behavior based on an intrinsic reoxidation process. Chemical bond analysis results are presented to support the proposed model.
Selective metal electrodeposition through doping modulation of semiconductor surfaces
Authors: Scheck Christian , Evans Paul , Schad Rainer , Zangari Giovanni , Sorba Lucia , Biasiol Giorgio , Heun Stefan
Published: March 2005

We demonstrate selective electrodeposition of magnetic layers on doped semiconductors resulting in a self-aligned pattern which replicates the doping pattern in the semiconductor surface. A Schottky barrier forms at the interface between a semiconductor substrate and the electrolyte, which upon application of a cathodic potential is biased in the forward (reverse) direction for n- or p-type semiconductors, respectively. Electron transfer from an n-type semiconductor is thus possible, while breakdown of the Schottky barrier would be necessary for deposition on a p-type substrate. The process will thus be spatially selective on a lateral modulation of the substrate doping. As an example we demonstrate the deposition of Co on GaAs.
Mechanism for spatial organization in quantum dot self-assembly
Authors: Gao Da , Kaczynski Adam , Jaszczak John A.
Published: March 2005

Inspired by experimental observations of spatially ordered growth hillocks on the (001) surfaces of natural graphite crystals, a mechanism for spatial organization in quantum dot self-assembly is proposed. The regular arrangement of steps from a screw dislocation-generated growth spiral provides the overall template for such ordering. An ordered array of quantum dots may be formed or nucleated from impurities driven to the step corners by diffusion and by their interactions with the spiral’s steps and kinks. Kinetic Monte Carlo simulation of a solid-on-solid model supports the feasibility of such a mechanism.
Pyroelectric effect of a p–n junction in a nonpolar solid
Authors: Sandomirsky V. , Schlesinger Y. , Dashevsky Z.
Published: March 2005

We discuss the possibility of a pyroelectric effect in a nonpolar solid. The built-in electrical field of a p–n junction barrier creates a polar axis in the solid. The electric dipole moment, due to the charge separation at the junction, depends on temperature mainly via the temperature dependence of the dielectric constant, giving rise to the pyroelectric effect. Illustrative estimates have been calculated for two quantum paraelectrics, PbTe and SrTiO3.
Ga
In
As
∕
Al
As
Sb
quantum-cascade lasers operating up to 400K
Authors: Yang Q. , Manz C. , Bronner W. , Mann Ch. , Kirste L. , Köhler K. , Wagner J.
Published: March 2005

Above room-temperature (T⩾400K) operation of GaInAs∕AlAsSb-based quantum-cascade lasers has been demonstrated. The lasers are based on vertical-transition active regions and consist of 25 periods of Ga0.47In0.53As∕AlAs0.56Sb0.44 active∕injection regions grown lattice-matched on InP substrates by molecular-beam epitaxy. They emit at a wavelength of λ∼4.5μm. For a device with the size of 18μm×2.8mm mounted substrate-side down with as-cleaved facets, a maximum peak power per facet of 750mW has been achieved at 300K and remains as high as 30mW at 400K. The characteristic temperature T0 of the threshold current density is 171K in the temperature range between 280K and 400K.
Suppression of hydrogen diffusion at the hydrogen-induced platelets in p-type Czochralski silicon
Authors: Huang Y. L. , Ma Y. , Job R. , Fahrner W. R.
Published: March 2005

Hydrogen diffusion in p-type Czochralski silicon is investigated by combined Raman spectroscope, scanning electron microscope, and spreading resistance probe measurements. Exposure of silicon wafers to rf hydrogen plasma results in the formation of platelets. The increase of hydrogenation duration leads to the growth of the platelets and the reduction of the hydrogen diffusivity. The large platelets grow faster than the small ones. The growth of the platelets is based on the capture of hydrogen. The dependence of the hydrogen diffusivity upon the average size of the platelets suggests that the indiffusion of hydrogen is suppressed by the platelets.
Determination of the piezoelectric field in InGaN quantum wells
Authors: Brown I. H. , Pope I. A. , Smowton P. M. , Blood P. , Thomson J. D. , Chow W. W. , Bour D. P. , Kneissl M.
Published: March 2005

In many studies, the value of the experimentally determined internal piezoelectric field has been reported to be significantly smaller than theoretical values. We believe this is due to an inappropriate approximation for the electric field within the depletion region, which is used in the analysis of experimental data, and we propose an alternative method. Using this alternative, we have measured the strength of the internal field of InGaN p-i-n structures, using reverse bias photocurrent absorption spectroscopy and by fitting the bias dependent peak energy using microscopic theory based on the screened Hartree-Fock approximation. The results agree with those using material constants interpolated from binary values.
From ‘Growth Centre’ to ‘Cluster’: Restructuring, Regional Development, and the Teesside Chemical Industry
Authors: Chapman Keith
Published: March 2005

Agglomeration offers both static, cost-based advantages and dynamic, innovation-related benefits to participating firms. These ideas have informed regional development policy from the growth poles/centres of the 1950/1960s to the contemporary focus on clusters. Although such policies imply the theoretical prospect of regional diversification by exploiting supply-chain and information-based/knowledge-based relationships, in practice they tend to promote regional specialisation. The experiences of many old industrial areas emphasise the risks of specialisation as advantages mutate into liabilities (territorial lock-in). These experiences are ignored in much of the clusters discourse which often lacks historical perspective. This paper provides such perspective by reflecting upon the relationships between the dynamics of industry evolution, agglomeration, and regional development policy with reference to the chemical industry on Teesside in North East England.
Decline of the District, Renewal of Firms: An Evolutionary Approach to Footwear Production in the Pirmasens Area, Germany
Authors: Schamp Eike W
Published: March 2005

Among the variety of old industrial areas, districts involved in the production of light consumer goods are a special case. Taking the single still-surviving footwear-production district in Germany as an example, the author makes an attempt to reflect on the long-term decline of an industrial district and the resulting path dependency of regional development. An evolutionary approach is taken which starts from different institutional bases and reveals a complex mix of temporalities and spatialities in the development path of enterprises and the region. The major empirical findings contrast two dominant types of strategic response to decline: firms either stayed in the industry, but left the region; or stayed in the region, but left the industry. The author concludes by mapping implications for territorial development.
Industrial Restructuring and Early Industry Pathways in the Asian First-Generation NICs: The Singapore Garment Industry
Authors: van Grunsven Leo , Smakman Floor
Published: March 2005

The authors aim to contribute to understanding of the industrial dynamics/evolution of mature export production complexes in the first generation Asian newly industrialised countries (NICs), employing an evolutionary economic perspective. Over the past decade and longer, the first-generation Asian NICs, Singapore included, have been confronted with imperatives necessitating deep restructuring. We observe that the pattern of industrial decline associated with failed restructuring caused by lock-in does not fit these countries, industrial regions, and early industries. Yet research has hardly begun to look at adjustment or to address deeper evolution from tenets in the framework of evolutionary economics, although such an approach is made more rather than less relevant by continued resilience. We analyse the pathway(s) of one early industry, the apparel industry in Singapore, through the 1980s and 90s. The withering away in the Singapore context of an industry such as apparel manufacture is not inevitable. From a juxtaposition of the line of thinking in evolutionary economics in which hindrance and decline due to path dependency and lock-ins are emphasised, with an alternative line in which the possibility of adjusting through renewal and the limited operation of lock-ins is emphasised, we discuss why the latter rather than the former has been the case.
On the Battle between Shipbuilding Regions in Germany and South Korea
Authors: Eich-Born Marion , Hassink Robert
Published: March 2005

Over time we can observe a dramatic global shift in shipbuilding activities, from Great Britain to Continental Europe to Japan to South Korea; most recently China is gaining ground. Every transition is accompanied by institutional and political reactions, leading to protectionism and trade conflicts. The most recent of these battles is being fought out between the European Commission, in particular Germany as a major player in this market, and South Korea, which is accused of illegally supporting its shipyards. As state support has traditionally played an important role, both in establishing and in protecting shipbuilding as a strategic industry within a national economy, the concept of political lock-in appears to provide a promising method for explaining both the rise, through its enabling element, and delayed fall, through its constraining element, of these specific regional economies. Against the background of this theoretical concept, an empirical study comparing two competing shipbuilding regions—Mecklenburg-Vorpommern in eastern Germany and Gyeongnam in South Korea—was conducted; the results are twofold. First, restructuring the shipbuilding industry in these two regions seems less affected by local and regional factors than it is by national and international organisations. National and international organisations are, under globalisation conditions, increasingly responsible for regulating the conditions of competition, but are failing to do so. Second, because of the multiscale involvement of political and economic actors and, hence, the increasing complexity of the restructuring process, the concept of political lock-in needs to be integrated into a much broader explanatory framework—which the authors develop.
Innovation-Oriented Environmental Regulations: Direct versus Indirect Regulations; an Empirical Analysis of Small and Medium-Sized Enterprises in Chile
Authors: Jiménez Orlando
Published: March 2005

It is often suggested that innovation is one of the most desirable environmental policy aims, in that it promises to solve the conflict between environmental regulation and economic growth. Contrary to what is frequently advocated—that in order to foster innovation through regulation, most of the attention should be put on the regulation-setting process, I argue that a cooperative stance in the implementation of regulations also has a crucial impact, especially in small and medium-sized enterprises (SMEs). This argument is assessed looking at innovation effects that both direct regulations (command-and-control) and indirect regulations (negotiated voluntary agreements, called cleaner production agreements) have in this sector. A face-to-face survey questionnaire, with a non-probabilistic matching sampling strategy, was conducted in 322 firms representing four industrial sectors in Chile. The propensity-scores analysis demonstrates that SMEs involved in voluntary agreements innovate significantly more, as expressed through environmental management systems and techniques. In terms of technological innovations, voluntary agreements promoted incremental (rather than radical) multimedia innovations. Nevertheless, they had a significant effect on triggering at least one radical process change in the SMEs engaged in the programme. I conclude by emphasising that a cooperative style in the design and implementation of regulations has a key role to play in environmental capacity building in SMEs, and that this approach can create the appropriate conditions for innovation. However, this potential cannot be fully realised if there are not strong market and regulatory stimuli towards the development of more radical environmental innovations.
Deconstructing State-Owned Enterprises in Socialist China under Reform: A Scalar Examination
Authors: Hu Fox Z Y
Published: March 2005

Studies of economic transformation under socialism in general, and the growth and development of state-owned enterprises (SOEs) in particular, have been based on the assumption that SOEs are a homogeneous entity. With few exceptions, the extant literature tends to compare SOEs as a whole with other economic sectors. Little has been written about the heterogeneous nature of SOEs. The author examines the internal variation of SOEs at different administrative levels in terms of productivity and profitability in China, which remains one of the largest socialist economies undergoing profound structural changes. The performance of SOEs is found to have varied significantly among the administrative hierarchy of the socialist political system. The changing politics of scale from promoting regional self-reliance in the Maoist era toward both expanding SOE autonomy and fiscal decentralization in the post-Maoist era, has resulted in an increase in the disparity between the SOEs affiliated with the national government and those affiliated with local governments. The investigation of SOEs in the Chinese context raises important theoretical questions concerning the growth dynamics of SOEs and suggests the need for a more careful and path-dependent treatment of socialist economies under reform. The growth of SOEs in transitional socialist economies provides an interesting testing ground in which to evaluate the theoretical discourse concerning the politics of scale and the rescaling of politics.
Recent Record Growth in Atmospheric CO2 Levels
Authors: Francey Roger J.
Published: March 2005

Environmental Context.Excessive levels of carbon dioxide are accumulating in the atmosphere, principally from burning fossil fuels. The gas is linked to the enhanced greenhouse effect and climate change, and is thus monitored carefully, along with other trace gases that reflect human activity.The rate of growth of carbon dioxide has increased gradually over the past century, and more rapidly in the last decade. Teasing out fossil emissions from changes due to wildfires and to natural exchange with plants and oceans guide global attempts in reducing emissions.