bluuebunny/crossref_metadata_2025 huggingface dataset:
Rydberg electron transfer to SF6: Product ion lifetimes
Authors: Liu Y. , Suess L. , Dunning F. B.
Published: June 2005

The lifetimes of SF6− ions produced by Rydberg electron transfer in K(np)∕SF6 collisions at high n, n≳30, are examined using a Penning ion trap. The data point to the formation of ions with a range of lifetimes that extends from ∼1to≳10ms. Sizable numbers of ions remain in the trap even 40ms after initial injection and at least part of this signal can be attributed to radiative stabilization. Measurements of free low-energy electron attachment to SF6 in the trap show that the product ions have lifetimes similar to those of SF6− ions formed by electron transfer in high-n collisions.
Surface reorganization accompanying the formation of sulfite and sulfate by reaction of sulfur dioxide with oxygen on Ag(111)
Authors: Alemozafar Ali R. , Madix Robert J.
Published: June 2005

On the Ag(111)-p(4×4)-O surface SO2(g) reacts with oxygen according to SO2(g)+O(a)→SO3(a). Sulfite forms in a (2√3×2√3)R30° structure. The restructuring of the surface atoms during sulfite formation is indicative of the deconstruction of the p(4×4)-O structure. Heating the sulfite-covered surface to 700 K affects the disproportionation of SO3 to SO4 in a (4√3×√3)R30° structure accompanied by the desorption of SO2(g) and smoothing of the surface. Continued heating beyond 700 K affects the complete decomposition of sulfate to SO2(g) and O2(g).
Fourier transform microwave spectroscopy of HSiBr: Exploring the Si–Br bond through quadrupole hyperfine coupling
Authors: Tackett Brandon S. , Clouthier Dennis J. , Landry Jennifer N. , Jäger Wolfgang
Published: June 2005

The 101-000(9–10GHz) and 202-101(18–19GHz) rotational transitions of HSiBr79 and HSiBr81 have been measured in a pulsed discharge jet expansion to an experimental uncertainty of ∼1kHz using Fourier transform microwave spectroscopy. The data have yielded an effective rotational constant, the centrifugal distortion constant Dj, the bromine nuclear quadrupole coupling constants, and the bromine nuclear spin-molecular rotation interaction parameter for both isotopomers. The derived parameters have been compared to their values calculated ab initio, and the nuclear quadrupole coupling tensor has been used to investigate the Si–Br bond, giving a σ bond ionic character of 0.60, a π bond character of 0.22, and a total Si–Br ionic character of 0.38. These bond characteristics have been compared to trends in other halosilylenes, silanes, and the analogous carbenes.
Enhanced temporal resolution in femtosecond dynamic-grating experiments
Authors: Hsieh Hung-Te , Psaltis Demetri , Beyer Oliver , Maxein Dominik , Buse Karsten , Sturman Boris
Published: June 2005

Recording of gratings by interference of two pump pulses and diffraction of a third probe pulse is useful for investigating ultrafast material phenomena. We demonstrate, in theory and experiment, that the temporal resolution in such configurations does not degrade appreciably even for large angular separation between the pump pulses. Transient Kerr gratings are generated inside calcium fluoride (CaF2) crystals by two interfering femtosecond (pump) pulses at 388nm and read out by a Bragg-matched probe pulse at 776nm. The solution to the relevant coupled-mode equations is well corroborated by the experimental results, yielding a value of the Kerr coefficient of ≈4.4×10−7cm2∕GW for CaF2.
Electronic state characterization of SiOx thin films prepared by evaporation
Authors: Barranco A. , Yubero F. , Espinós J. P. , Groening P. , González-Elipe A. R.
Published: June 2005

Si O x thin films with different stoichiometries from SiO1.3 to SiO1.8 have been prepared by evaporation of silicon monoxide in vacuum or under well-controlled partial pressures of oxygen (P<10−6Torr). These thin films have been characterized by x-ray photoemission and x-ray-absorption spectroscopies, this latter at the Si K and L2,3 absorption edges. It has been found that the films prepared in vacuum consists of a mixture of Si3+ and Si+ species that progressively convert into Si4+ as the partial pressure of oxygen during preparation increases. From this spectroscopic analysis, information has been gained about the energy distribution of both the full and empty states of, respectively, the valence and conduction bands of SiOx as a function of the O∕Si ratio. The characterization of these films by reflection electron energy-loss spectroscopy (REELS) has provided further evidences about their electronic structure (band gap and electronic states) as a function of the oxygen content. The determination of the plasmon energies by REELS has also shown that the films prepared by evaporation in vacuum consist of a single phase which is characterized by a density (1.7gcm−3) lower than that of SiO2 (i.e., 2.2gcm−3) or Si (i.e., 2.4gcm−3). The optical properties (n and k) of the films as a function of the O∕Si content have been deduced from the analysis of REELS spectra in the energy range from 4to20eV. It has been also shown that the O∕Si ratio in the films and several spectroscopic parameters such as the Auger parameter or the energy of bulk plasmons present a linear relationship and that this linear dependence can be used for a rapid characterization of SiOx materials. By contrast, the band-gap energy changes differently with the O∕Si ratio, following a smooth linear increase from about 3.8eV for SiO1.3 to ca. 5.0eV for SiO1.7 and a jump up to 8.7eV for SiO2. These results indicate that the random-bonding model does not apply to thin films prepared by evaporation under our experimental conditions. Other distributions of Sin+ states can be induced if the films are excited with an external source such as heat or photon irradiation. In this case the electronic properties vary and the previous linear correlations as a function of the oxygen content do not hold any longer.
Ultrafast electron microscopy in materials science, biology, and chemistry
Authors: King Wayne E. , Campbell Geoffrey H. , Frank Alan , Reed Bryan , Schmerge John F. , Siwick Bradley J. , Stuart Brent C. , Weber Peter M.
Published: June 2005

The use of pump-probe experiments to study complex transient events has been an area of significant interest in materials science, biology, and chemistry. While the emphasis has been on laser pump with laser probe and laser pump with x-ray probe experiments, there is a significant and growing interest in using electrons as probes. Early experiments used electrons for gas-phase diffraction of photostimulated chemical reactions. More recently, scientists are beginning to explore phenomena in the solid state such as phase transformations, twinning, solid-state chemical reactions, radiation damage, and shock propagation. This review focuses on the emerging area of ultrafast electron microscopy (UEM), which comprises ultrafast electron diffraction (UED) and dynamic transmission electron microscopy (DTEM). The topics that are treated include the following: (1) The physics of electrons as an ultrafast probe. This encompasses the propagation dynamics of the electrons (space-charge effect, Child’s law, Boersch effect) and extends to relativistic effects. (2) The anatomy of UED and DTEM instruments. This includes discussions of the photoactivated electron gun (also known as photogun or photoelectron gun) at conventional energies (60–200 keV) and extends to MeV beams generated by rf guns. Another critical aspect of the systems is the electron detector. Charge-coupled device cameras and microchannel-plate-based cameras are compared and contrasted. The effect of various physical phenomena on detective quantum efficiency is discussed. (3) Practical aspects of operation. This includes determination of time zero, measurement of pulse-length, and strategies for pulse compression. (4) Current and potential applications in materials science, biology, and chemistry. UEM has the potential to make a significant impact in future science and technology. Understanding of reaction pathways of complex transient phenomena in materials science, biology, and chemistry will provide fundamental knowledge for discovery-class science.
Synchronized firing of FitzHugh–Nagumo neurons by noise
Authors: Kitajima Hiroyuki , Kurths Jürgen
Published: June 2005

We investigate the influence of noise on synchronization between the spiking activities of neurons with external impulsive forces. We first analyze the dependence of the synchronized firing on the amplitude and the angular frequency of the impulsive force in the noise-free system. Three cases (regular spiking, traveling wave, and chaotic spiking) with low synchronized firing are chosen to study effects due to noise. In each case we find that small noise can be a promoter of synchronization phenomena in neural activities, by choosing an appropriate noise intensity acting on some of the neurons.
Magnetoelectric effect in hybrid magnetostrictive-piezoelectric composites in the electromechanical resonance region
Authors: Filippov D. A. , Bichurin M. I. , Nan C. W. , Liu J. M.
Published: June 2005

An expression for the description of the frequency-dependent magnetoelectric response in hybrid magnetostrictive-piezoelectric multiferroic composites is presented by using constitutive and motion equations. The calculations show that the values of the magnetoelectric voltage coefficient of the composites in the region of an electromechanical resonance sharply increase and exceed a low-frequency value by more than two orders of magnitude, which is in reasonable agreement with recent experimental data. The enhanced magnetoelectric response at the electromechanical resonance is dependent on the interface losses.
On the beneficial impact of tensile-strained silicon substrates on the low-frequency noise of n-channel metal-oxide-semiconductor transistors
Authors: Simoen E. , Eneman G. , Verheyen P. , Delhougne R. , Loo R. , Meyer K. De , Claeys C.
Published: June 2005

The low-frequency noise in n-channel metal-oxide-semiconductor field-effect transistors, fabricated on strained silicon (SSi) substrates has been investigated and compared with the results obtained on silicon reference wafers. The strained silicon was deposited on a thin strain-relaxed SiGe buffer layer. A 2-nm SiO2 layer was used as a gate dielectric. It is shown that a factor of 2–3 lower noise can be found in the SSi devices at a frequency f=10Hz, which appears to be correlated with the low-field mobility. This is interpreted in terms of the impact of the biaxial tensile strain on the gate oxide defectiveness.
Demonstration of undoped quaternary AlInGaN∕GaN heterostructure field-effect transistor on sapphire substrate
Authors: Liu Y. , Jiang H. , Arulkumaran S. , Egawa T. , Zhang B. , Ishikawa H.
Published: June 2005

Undoped AlInGaN∕GaN heterostructure field-effect transistors (HFETs) have been demonstrated on sapphire substrate. The maximum drain current of 758mA∕mm and extrinsic transconductance of 123mS∕mm were obtained from the device with 2μm gate length and 15μm gate width. Such performance was comparable to that of a conventional modulation-doped (MOD) AlGaN∕GaN HFET fabricated at same the condition. In spite of the high-density two-dimentional electron gas formed at the heterointerface, the AlInGaN∕GaN HFET structure showed relatively low Hall mobility (689cm2∕Vs at 300K), which was due to the high concentration background doping in the undoped AlInGaN barrier region. Encouragingly, both the gate leakage current and drain current collapse showed lower values than that of the MOD-AlGaN∕GaN HFET, which implied the potential application of quaternary AlInGaN to high-power and high-frequency devices.
Magnetic resonance signatures of grown-in defects in GaInNP alloys grown on a GaAs substrate
Authors: Vorona I. P. , Mchedlidze T. , Izadifard M. , Buyanova I. A. , Chen W. M. , Hong Y. G. , Xin H. P. , Tu C. W.
Published: June 2005

Dilute-nitride Ga0.44In0.56NyP1−y alloys with y=0–0.02, grown on a GaAs substrate using gas-source molecular beam epitaxy, are studied by the optically detected magnetic resonance (ODMR) technique. Grown-in paramagnetic defects were found to act as centers of nonradiative recombination. Resolved hyperfine structure for one of the detected ODMR signals suggests involvement of a Ga-interstitial or an As-antisite in the structure of the related defect.
Magnetoelectric interactions in bilayers of yttrium iron garnet and lead magnesium niobate-lead titanate: Evidence for strong coupling in single crystals and epitaxial films
Authors: Srinivasan G. , De Vreugd C. P. , Bichurin M. I. , Petrov V. M.
Published: June 2005

The nature of low-frequency magnetoelectric (ME) coupling has been investigated in bilayers of single crystal lead magnesium niobate-lead titanate (PMN-PT) and yttrium iron garnet (YIG). Samples with (001) PMN-PT and polycrystalline, single crystal, or epitaxial thin films of YIG were studied. The ME coupling is the weakest in bilayers with polycrystalline YIG. A dramatic strengthening of ME interactions occurs in samples with single crystal (111) YIG. The strongest ME coupling occurs in bilayers with (110) epitaxial YIG film. The voltage coefficients show significant variation with the orientation of the bias magnetic field H; it is maximum for H‖⟨1i¯1⟩ and is minimum for H‖⟨001⟩. The transverse coefficient increases linearly with increasing thickness of YIG film. Data analysis reveals that strong magnetomechanical coupling in thin film YIG is the cause of enhancement in the ME coupling.
Reverse-bias electroluminescence imaging to diagnose failures of vertical-cavity surface-emitting lasers
Authors: McElfresh D. K. , Vacar D.
Published: June 2005

The charge flowing through the junction of vertical-cavity surface-emitting lasers (VCSELs) under reverse-bias gives rise to electroluminescence (EL) when breakdown conditions are satisfied. We collected the reverse-bias EL of VCSEL devices that had been subjected to accelerated stress. We observed distinctly different spatial distributions of the reverse-bias EL: for survivor (nondegraded) devices the breakdown current appears to be confined to one well-defined filament while for dark (degraded) VCSELs the reverse-bias EL pattern is a disordered network of filaments. We show that the line dislocation network that renders the VCSELs dark is directly imaged as the spatial distribution of the reverse-bias EL.
Kinetically controlled thin-film growth of layered β- and γ-NaxCoO2 cobaltate
Authors: Son J. Y. , Kim Bog G. , Cho J. H.
Published: June 2005

We report growth characteristics of epitaxial β-Na0.6CoO2 and γ-Na0.7CoO2 thin films on (001) sapphire substrates grown by pulsed-laser deposition. Reduction of the deposition rate could change the structure of the NaxCoO2 thin film from a β phase with an island growth mode to a γ phase with a layer-by-layer growth mode. The γ-Na0.7CoO2 thin film exhibits spiral surface growth with multiterraced islands and highly crystallized texture compared to that of the β-Na0.6CoO2 thin film. This heterogeneous epitaxial film growth can give an example of the strain effect of physical properties and growth dynamics of NaxCoO2 as well as the subtle nature of structural change.
Epitaxial growth of CoSi2 in a decanano contact opening on a (100) silicon substrate
Authors: Sun Ho-Jung , Lee Young-Jin , Kim Soo-Hyun , Lee Joo-Wan , Ku Ja-Chun , Sohn Hyun-Chul , Kim Jin-Woong , Kim Uisik , Sung Nak-Kyun
Published: June 2005

The behavior of cobalt silicidation was investigated in a 45-nm-wide contact opening on (100) silicon substrate. A Co film was deposited using sputtering techniques with elongated target-to-wafer spacing and a CoSi2 phase was developed after being annealed using rapid thermal processing at 750 °C for 30 s. It was revealed that the CoSi2 was grown epitaxially both on {111} and (100) Si at the same time, resulting in a faceted single crystal. Type A epitaxy on {111} Si was developed due to the coepitaxial growth. It was suggested that the tendency for the epitaxial growth of CoSi2 was strong in such a highly confined contact opening.
Stacking faults in Si nanocrystals
Authors: Wang Y. Q. , Smirani R. , Ross G. G.
Published: June 2005

Si nanocrystals (Si nc) were formed by the implantation of Si+ into a SiO2 film on (100) Si, followed by high-temperature annealing. High-resolution transmission electron microscopy has been used to examine the microstructure of the Si nc produced by a high-dose (3×1017cm−2) implantation. It is shown that there are only stacking-fault (SF) defects in some nanocrystals; while in others the stacking faults (SFs) coexist with twins. Two kinds of SFs, one being an intrinsic SF, the other being an extrinsic SF, have been observed inside the Si nc. More intrinsic SFs have been found in the Si nc, and the possible reasons are discussed. These microstructural defects are expected to play an important role in the light emission from the Si nc.
Cu-Si bilayers as storage medium in optical recording
Authors: Kuiper A. E. T. , Vullers R. J. M. , Pasquariello D. , Naburgh E. P.
Published: June 2005

Instead of a phase change or a dye layer, a Cu∕Si bilayer can be applied as the recording medium in a write-once Blu-ray Disc. The write process basically comprises the formation of a CuSi alloy containing 25–30at.% Si, while any excess of Si is left behind as unreacted film. Auger analyses of the laser-written layers indicate that recording consists primarily of the diffusion of Si into Cu. The data allow for discrimination between the various models presented in literature for Cu∕Si-based recording and to optimize the stack. Very low jitter levels of typically 4% proved to be achievable with equally thick films of Cu and Si as recording medium.
Intrinsic carrier effects in HfO2–Ge metal–insulator–semiconductor capacitors
Authors: Dimoulas A. , Vellianitis G. , Mavrou G. , Evangelou E. K. , Sotiropoulos A.
Published: June 2005

Germanium metal–insulator–semiconductor capacitors with HfO2 or other high-κ gate dielectrics show unusual low frequency behavior of the high frequency (1 kHz or higher) capacitance-voltage characteristics when biased in inversion. Here, we provide evidence that this effect is partly due to the high intrinsic carrier concentration ni in Ge. We show in particular that the ac conductance in inversion is thermally activated and it is governed either by generation-recombination processes in depletion, varying proportional to ni or by diffusion-limited processes varying as ni2, depending on whether the temperature is below or above 45 °C, respectively. From these measurements, we also show that the minority carrier response time in Ge is very short, in the microsecond range (much shorter than in Si), depending inversely proportional to ni at room temperature. This means that due to high ni, the inversion charge is built fast in response to high frequency signals at the gate, inducing the observed low frequency behavior.
n
-type doping of (001)-oriented single-crystalline diamond by phosphorus
Authors: Kato Hiromitsu , Yamasaki Satoshi , Okushi Hideyo
Published: June 2005

n -type doping of (001)-oriented single-crystalline diamond has been achieved using PH3 as doping gas and applying a newly optimized homoepitaxial growth technique based on plasma-enhanced chemical vapor deposition. Hall-effect measurements indicate n-type conductivity with highest mobilities of ∼350cm2∕Vs. Phosphorus doping is confirmed by secondary-ion mass spectroscopy.
Temperature stable LiNbO3 surface acoustic wave device with diode sputtered amorphous TeO2 over-layer
Authors: Dewan Namrata , Tomar Monika , Gupta Vinay , Sreenivas K.
Published: June 2005

Amorphous TeO2 thin film, sputtered in the O2+Ar(25%+75%) gas environment using a metallic tellurium target, has been identified as an attractive negative temperature coefficient of delay (TCD) material that can yield a temperature stable device when combined with a surface acoustic wave (SAW) device based on positive TCD material such as LiNbO3. The influence of amorphous TeO2 over-layer on the SAW propagation characteristics (velocity and temperature coefficient of delay) of the SAW filters (36 and 70 MHz) based on 128° rotated Y-cut X-propagating lithium niobate (128° Y-XLiNbO3) single crystal has been studied. It is found that 0.042λ thick TeO2 over-layer on a prefabricated SAW device operating at 36 MHz centre frequency, reduces the TCD of the device from 76ppm°C−1 to almost zero (∼1.4ppm°C−1) without deteriorating its efficiency and could be considered as a suitable alternative for temperature stable devices in comparison to conventional SiO2 over-layer.
Microdroplet deposition by laser-induced forward transfer
Authors: Willis David A. , Grosu Vicentiu
Published: June 2005

Laser-induced forward transfer was used to deposit aluminum and nickel microdroplets onto a substrate using a Q-switched neodymium:Yttrium-aluminum-garnet laser. The droplets have diameters of a few microns, much smaller than the laser spot diameter, and are transferred at fluences slightly above the melting threshold. Scanning electron microscopy shows that the original donor film is deformed after laser irradiation, such that the film protrudes outward from the center of the laser spot. The film expands during laser heating, but is constrained until the melt interface reaches the free surface. When this occurs, the film is no longer constrained, allowing the melt to rapidly expand, forming the protrusions from which droplets are ejected.
Effect of threading dislocations on the Bragg peakwidths of GaN, AlGaN, and AlN heterolayers
Authors: Lee S. R. , West A. M. , Allerman A. A. , Waldrip K. E. , Follstaedt D. M. , Provencio P. P. , Koleske D. D. , Abernathy C. R.
Published: June 2005

We develop a reciprocal-space model that describes the (hkl) dependence of the broadened Bragg peakwidths produced by x-ray diffraction from a dislocated epilayer. We compare the model to experiments and find that it accurately describes the peakwidths of 16 different Bragg reflections in the [010] zone of both GaN and AlN heterolayers. Using lattice-distortion parameters determined by fitting the model to selected reflections, we estimate threading-dislocation densities for seven different GaN and AlGaN samples and find improved agreement with transmission electron microscopy measurements.
Fabrication of large area two- and three-dimensional polymer photonic crystals using single refracting prism holographic lithography
Authors: Wu Lijun , Zhong Yongchun , Chan Che Ting , Wong Kam Sing , Wang Guo Ping
Published: June 2005

We demonstrate an approach for easy fabrication of two-dimensional (2D) hexagonal and three-dimensional (3D) face-centered-cubic (fcc)-type photonic crystal (PhC) microstructures in a photosensitive polymer by applying a simple single refracting prism. This prism enables the splitting and recombining of a single incoming laser beam to form multiple-beam interference pattern simultaneously. Thus, antivibration equipment and complicated optical alignment system are not required, leading to a much more simple optical setup than previously reported laser holographic lithography techniques. Large-scale (over 1cm2) 2D hexagonal and 3D fcc-type PhCs have been produced. Reflection/transmission measurements performed on the fabricated 3D fcc-type PhC structures agree well with the corresponding band structure calculation.
Effects of electromigration-induced void dynamics on the evolution of electrical resistance in metallic interconnect lines
Authors: Cho Jaeseol , Gungor M. Rauf , Maroudas Dimitrios
Published: June 2005

The effects of void dynamics under electromigration conditions on the electrical resistance evolution in metallic thin-film interconnects are examined based on self-consistent dynamical simulations. Changes in the interconnect line resistance are found to depend strongly on electromigration-induced void morphological changes and are explained on the basis of void extension across the linewidth and void surface area evolution at constant void volume. The void morphological evolution may lead to stable steady or time-periodic line resistance response or to abrupt resistance increase associated with failure. Our computational results imply that electrical resistance increases should not be attributed only to void formation or void growth and that electrical resistance oscillations are not due to alternating defect generation and annihilation. The results are in excellent agreement with analytical scaling theories and qualitatively consistent with a large set of experimental electrical resistance measurements.
Enhanced annihilations of self-interstitial clusters by vacancies transported through vehicle action of Cu in Cu-implanted silicon crystals
Authors: Nakamura Minoru , Murakami Susumu
Published: June 2005

Thermal behaviors of intrinsic defect clusters (self-interstitials and vacancies) in silicon crystals implanted with several metals including Cu were observed by photoluminescence measurements to investigate the influences of the metals on the diffusion of the intrinsic defects. Enhanced annihilations (EAs) of the defect clusters were observed only for an oxygen-lean floating zone (FZ) crystal implanted with Cu and annealed at temperatures between 400 °C and 600 °C, while they were not observed for any types of crystals (n- and p-type FZ and Czochralski crystals) implanted with Fe and Cr. The EAs of the defect clusters were well explained by a vehicle action of fast diffusing Cu for vacancy transportation.
Nanocrystal-based microcavity light-emitting devices operating in the telecommunication wavelength range
Authors: Roither J. , Kovalenko M. V. , Pichler S. , Schwarzl T. , Heiss W.
Published: June 2005

Highly luminescent colloidally prepared HgTe nanocrystals (NCs) are used to fabricate microcavity light-emitting devices operating around 1.5μm. They consist of a Bragg interference mirror from standard optical materials deposited on glass substrates, an active layer embedding the nanocrystals, and a metallic top mirror. These devices give highly directional narrow single-mode emission with a beam divergence below 3° and a spectral width smaller by a factor of 8 than that of a NC reference sample. The emission wavelength can be tuned between 1.4 and 1.75μm by changing the cavity length and thus, the cavity finesse. The influence of the latter on output power and beam divergence is discussed. Furthermore, operation up to 75 °C is demonstrated without degradation of the NCs, which is promising for potential applications.
Optical properties of a transparent CaF2:Er3+ fluoropolymer nanocomposite
Authors: Kumar G. A. , Chen C. W. , Riman R. , Chen S. , Smith D. , Ballato J.
Published: June 2005

We report the observation of Er3+ fluorescence in an optically transparent CaF2:Er3+ perfluorocyclobutyl-based fluoropolymer composite. Under 980 nm excitation, fluorescence was observed at 1560 nm with a bandwidth of 93 nm. A quantitative analysis of the radiative properties yielded a radiative quantum efficiency of 29% corresponding to a measured lifetime of 4 ms and theoretical radiative decay time of 13.8 ms. Further, the estimated stimulated emission cross section was calculated to be 3×10−20cm2, and the maximum optical gain from the composite was estimated to be 1.78 dB∕cm with a pump threshold of 1.1 mW. This estimate demonstrates that it is possible to use polymer nanocomposites for active optical devices.
Measure of disorder in tetrahedrally bonded semiconductors
Authors: Sundari S. Tripura , Raghavan G.
Published: June 2005

A measure of crystalline order in tetrahedrally bonded semiconductors is proposed based on optical response. This measure is obtained from the ⟨111⟩ critical point structure in the dielectric spectra. This descriptor is sensitive to the nature and extent of disorder in specimens and distinguishes differences in medium and short-order present in amorphous materials. Application to Ar+-irradiated Si specimens yields the threshold amorphization dose and this technique is sensitive to structural changes which occur as a function of irradiation fluence both above and beyond the amorphization threshhold. Systematic variations are also obtained in hydrogenated amorphous-Si. The general validity of the method is indicated.
High-electric-field quantum yield roll-off in efficient europium chelates-based light-emitting diodes
Authors: Kalinowski J. , Stampor W. , Cocchi M. , Virgili D. , Fattori V.
Published: June 2005

The europium chelates-based light-emitting-diodes (LEDs) have been fabricated showing the maximum electroluminescence (EL) quantum efficiency (QE) up to 5%photons∕carrier at electric fields slightly below F=1MV∕cm and current density j≅0.01mA∕cm2. Their line-like emission QE drops, however, rapidly within the high drive voltage range. This roll-off effect, exceeding one order of magnitude at F≅1.6MV∕cm(j≅15mA∕cm2), is shown to be underlain by the electric field-assisted dissociation of electron-hole pair precursors of europium ion-localized emissive states. The high field dependence of EL QE fits the Onsager model of geminate recombination well. This is at variance with triplet-triplet annihilation mechanism assumed previously to reduce QE in such LEDs.
Synthesis and field emission properties of TiSi2 nanowires
Authors: Xiang B. , Wang Q. X. , Wang Z. , Zhang X. Z. , Liu L. Q. , Xu J. , Yu D. P.
Published: June 2005

TiSi 2 is a high-melting compound with excellent conductivity ∼severalμΩcm. TiSi2 nanowires were fabricated in large scale by a simple vapor phase deposition method. The as-synthesized TiSi2 nanowires were investigated using x-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Raman scattering. Field emission property of TiSi2 nanowires was studied and an emission current density of 5mA∕cm2 was obtained and no obvious degradation was observed in a life stability experiment period for over ∼40h. The cathodoluminescence images were very bright and homogenous. The remarkable performance reveals that the TiSi2 nanowires can serve as a good candidate for commercial application in vacuum microelectronic devices, particularly flat panel displays.
Surface acoustic wave-induced electroluminescence intensity oscillation in planar light-emitting devices
Authors: Cecchini Marco , Piazza Vincenzo , Beltram Fabio , Gevaux D. G. , Ward M. B. , Shields A. J. , Beere H. E. , Ritchie D. A.
Published: June 2005

Electroluminescence emission from surface acoustic wave-driven light-emitting diodes (SAWLEDs) is studied by means of time-resolved techniques. We show that the intensity of the SAW-induced electroluminescence is modulated at the SAW frequency (∼1GHz), demonstrating electron injection into the p-type region synchronous with the SAW wave fronts.
Depth-resolved analysis of ferroelectric domain structures in bulk LiNbO3 crystals by scanning force microscopy
Authors: Jungk T. , Soergel E.
Published: June 2005

Ferroelectric domains were written in congruently melting lithium niobate crystals (LiNbO3) by electrical field poling using a mask with circular openings. For the surface sensitive detection of the domains, we used scanning force microscopy. Thinning the crystal step-by-step reveals that the domains evolve from circular shape at the very surface to hexagonal shape at a depth of around 30μm, demonstrating the impact of the crystal symmetry on the domain shape.
Organizing Diversity: Scales of Demographic Change and Neighborhood Organizing in St Paul, MN
Authors: Martin Deborah G , Holloway Steven R
Published: June 2005

Neighborhood involvement in urban governance remains a pressing goal in an era of globalization. Cities have instituted a variety of structures to facilitate this involvement, including quasi-formal neighborhood or district councils. At the same time, urban populations are changing rapidly because of multiple dynamics operating at multiple scales. Immigration, for example, continues to transform inner-city neighborhoods despite the emergence of suburban immigrant enclaves. Existing research inadequately addresses the interaction between efforts to organize neighborhood political involvement and the dynamic nature of urban populations. We examine St Paul, Minnesota—a locale with a well-established neighborhood district-council system and a vibrant and rapidly growing immigrant community. Indeed, immigrants from Southeast Asia and East Africa are moving into neighborhoods that up until the early 1990s were predominantly white. Using a multimethod empirical analysis, we argue that the district-council system, while recognizing and empowering local-level organization, fails to provide adequate resources for neighborhoods to address social dynamics that operate at much broader scales. An index of ethnic and racial diversity computed with census data shows that St Paul experienced a significant overall increase in diversity during the 1990s. Although inner-city neighborhoods remained the most diverse, residential areas developed after World War 2 also diversified considerably. Interviews with neighborhood organizers based in part on tabular and cartographic displays revealed a wide variety of strategies and responses to changing ethnic and racial diversity. Predominant, however, was a mismatch between the scale at which demographic change occurs, and the scale of ‘neighborhood’ action embedded within the district-council system.
Interrupting the Telos: Locating Subsistence in Contemporary US Forests
Authors: Emery Maria R , Pierce Alan R
Published: June 2005

People continue to hunt, fish, trap, and gather for subsistence purposes in the contemporary United States. This fact has implications for forest policy, as suggested by an international convention on temperate and boreal forests, commonly known as the Montréal Process. Three canons of law provide a legal basis for subsistence activities by designated social groups in Alaska and Hawaii and by American Indians with treaty rights in the coterminous forty-eight states. A literature review also presents evidence of such practices by people from a variety of ethnic backgrounds throughout the nation. Teleological notions of development espoused by both neoliberal and Marxist scholars suggest that subsistence activities should not persist in a First World setting except as failures of the officially sanctioned economic system. However, alternative economic perspectives from peasant studies and economic geography offer a conceptual framework for viewing at least some subsistence activities as having a logic and values outside of, if articulated with, market structures. Meeting the Montréal Process goal of providing for subsistence use of forests will require research focused on local practices and terms of access to resources as well as their relationship to state and capital processes. We outline the basics of a research agenda on subsistence for an emerging First World political ecology.
Devolution in the Woods: Community Forestry as Hybrid Neoliberalism
Authors: McCarthy James
Published: June 2005

This paper explores the remarkable congruence between the proliferation of community forestry initiatives in North America in recent years and the ascendance of particular forms of neoliberalism. In it I argue that, in the United States in particular, such initiatives are best understood as hybrids between ‘rollout’ neoliberalism and contemporaneous trends in the management of protected areas and state-owned forests. This interpretation contributes to recent arguments that the environment has been understudied as an arena through which neoliberalism has been actively constituted, rather than simply a passive recipient of ‘impacts’. Moreover, surprisingly little academic work has explored the imbrications of specific changes in environmental governance and evolving neoliberalism in the latter's ‘First World’ geographic hearths, such as the USA and the United Kingdom. In this paper I undertake such an investigation with respect to community forestry in the United States. The paper traces the major antecedents, introduction, and institutionalizations of community forestry in the United States, and shows how their conceptualizations and enactments of ‘community’ are structured by hegemonic neoliberal ideas, making community forestry in this context supplementary, rather than oppositional, to neoliberal restructurings. Exploration of the current Bush administration's enthusiastic adoption of central elements of community forestry bolsters this interpretation. Finally, the conclusion draws implications from this case for debates in political ecology.
Mapping Economic Diversity in the First World: The Case of Fisheries
Authors: Martin Kevin St.
Published: June 2005

Fisheries are understood within a binary frame that is both spatialized into the First and Third Worlds and founded upon a developmentalist discourse of fisheries that produces the conditions for capitalism. The result is an inevitable march toward privatization of resources abstractly understood and their utilization by individuals as capital. The Third World is allowed to diverge from this inevitability because of its inherent characteristics of subject and space read as fisheries-based community and territory. These different imaginaries of subject and space produce very different prescriptions for economic development; the First World must choose capitalism whereas the Third World might explore other options, albeit at a local scale. Producing alternative forms of fisheries management in the First World, then, requires both a strategy of valuing that which has been relegated to the periphery (for example, community, cooperation, and participation) as well as a blurring of binary categories generally. Undermining the presence of capitalism in the First World and making space for that which has been excluded (for example, community-based and territorial fisheries) requires a new economic and spatial imaginary.
The Making of an Innovative Region from a Centrally Planned Economy: Institutional Evolution in Zhongguancun Science Park in Beijing
Authors: Zhou Yu
Published: June 2005

Literature on innovation regions has focused mostly on case studies in mature capitalist economies in North America and Europe, generating little knowledge of how innovation may take place in alternative institutional settings or how institutional transformation occurs in regions other than advanced capitalist economies. This paper traces the institutional evolution of Zhongguancun (ZGC), China's most prominent science and technology park, in the northwestern part of Beijing, in its pursuit of becoming China's own ‘Silicon Valley’. Created during the planned economy, ZGC has traveled a radically different trajectory compared with most high-tech regions in advanced countries. Since the mid-1980s, the area has been able to transform itself from a quiet Beijing suburb designated for scientific research and higher education into a bustling hub of global high-tech business. In this paper I examine the changing patterns of behavior and interaction among the Chinese state, Chinese technology firms, and multinational technology corporations during three different stages of ZGC's development, illustrating the possibility of alternative institutional arrangements and the intricacy of institutional transformation. The paper then compares the formal and informal institutional characteristics of ZGC with those of California's Silicon Valley, signifying its strengths and weaknesses for fostering an innovative environment.
The Geographies of Political Ecology: After Edward Said
Authors: Wainwright Joel
Published: June 2005

This paper offers theoretical reflections on a series of questions raised by the shift in political ecology from the Third World to the First: what precisely constitutes a context for political ecology? How does something come to be a space or region that calls for political ecology? To respond to these questions, I argue for a turn to the thought of Edward Said, who articulates a Gramscian approach to geography that calls into question the constitution of the world.
Dynamic Effects within a Regional System: An Empirical Approach
Authors: Márquez Miguel A , Ramajo Julián , Hewings Geoffrey J D
Published: June 2005

In this paper we focus on the dynamic effects under which the regional economic growth processes are accomplished, breaking them down into two broad types: neighborhood and economy-wide effects. By means of a proposed dynamic space–time empirical model, the competition structure within a multiregional economic system is developed. Cointegration and error-correction modeling techniques are used to support the existence of this competition structure over both the short and long term. As an application, we show the dynamic effects on the evolution of the regional performance of Spanish regions over the period 1972–2000. Our results indicate that some macroeconomic forces are operating through time on this Spanish system because positive and negative effects are detected both at economy-wide and at neighborhood levels. Further, the findings show that a new taxonomy of the Spanish regions could provide some guidance for the development of appropriate measures for regional economic policy.
Identification of coexpressed gene clusters in a comparative analysis of transcriptome and proteome in mouse tissues
Authors: Mijalski T. , Harder A. , Halder T. , Kersten M. , Horsch M. , Strom T. M. , Liebscher H. V. , Lottspeich F. , de Angelis M. Hrabě , Beckers J.
Published: June 2005

A major advantage of the mouse model lies in the increasing information on its genome, transcriptome, and proteome, as well as in the availability of a fast growing number of targeted and induced mutant alleles. However, data from comparative transcriptome and proteome analyses in this model organism are very limited. We use DNA chip-based RNA expression profiling and 2D gel electrophoresis, combined with peptide mass fingerprinting of liver and kidney, to explore the feasibility of such comprehensive gene expression analyses. Although protein analyses mostly identify known metabolic enzymes and structural proteins, transcriptome analyses reveal the differential expression of functionally diverse and not yet described genes. The comparative analysis suggests correlation between transcriptional and translational expression for the majority of genes. Significant exceptions from this correlation confirm the complementarities of both approaches. Based on RNA expression data from the 200 most differentially expressed genes, we identify chromosomal colocalization of known, as well as not yet described, gene clusters. The determination of 29 such clusters may suggest that coexpression of colocalizing genes is probably rather common.
The dense core transmembrane vesicle protein IA-2 is a regulator of vesicle number and insulin secretion
Authors: Harashima Shin-ichi , Clark Anne , Christie Michael R. , Notkins Abner Louis
Published: June 2005

IA-2 is an enzymatically inactive member of the transmembrane protein tyrosine phosphate family located in dense core secretory vesicles and a major autoantigen in type 1 diabetes. Recent studies showed that targeted disruption of the IA-2 gene in mice resulted in impairment of insulin secretion and glucose intolerance. Insulin homeostasis, however, is a complex process involving a cascade of regulatory factors, and IA-2 is widely expressed in neuroendocrine cells throughout the body. Consequently, it is uncertain whether the impairment of insulin secretion in IA-2 knockout mice is a direct result of the knockout of IA-2 in beta cells or to counter regulatory alterations resulting from IA-2 knockout in other neuroendocrine cells. To define the function of IA-2, we studied the secretion of insulin in a single cell type, MIN-6, by overexpressing and knocking down IA-2. Our experiments showed that overexpression of IA-2 resulted in a 6-fold increase in glucose- or K
+
-induced insulin secretion and a ≈3-fold increase in the number of secretory vesicles and the insulin content of cells. In contrast, knockdown of endogenous IA-2 by short interfering RNA resulted in nearly a complete loss of glucose-induced insulin secretion and a 50% decrease in basal insulin release. The half-life of insulin in cells overexpressing IA-2 was nearly twice as great as that in mock-transfected cells, suggesting that IA-2 was stabilizing the insulin-containing vesicles. From these results we conclude that in beta cells, IA-2 is an important regulator of dense core vesicle number and glucose-induced and basal insulin secretion.
Two CD1 genes map to the chicken MHC, indicating that CD1 genes are ancient and likely to have been present in the primordial MHC
Authors: Salomonsen Jan , Sørensen Maria Rathmann , Marston Denise A. , Rogers Sally L. , Collen Trevor , van Hateren Andrew , Smith Adrian L. , Beal Richard K. , Skjødt Karsten , Kaufman Jim
Published: June 2005

CD1 molecules play an important role in the immune system, presenting lipid-containing antigens to T and NKT cells. CD1 genes have long been thought to be as ancient as MHC class I and II genes, based on various arguments, but thus far they have been described only in mammals. Here we describe two CD1 genes in chickens, demonstrating that the CD1 system was present in the last common ancestor of mammals and birds at least 300 million years ago. In phylogenetic analysis, these sequences cluster with CD1 sequences from other species but are not obviously like any particular CD1 isotype. Sequence analysis suggests that the expressed proteins bind hydrophobic molecules and are recycled through intracellular vesicles. RNA expression is strong in lymphoid tissues but weaker to undetectable in some nonlymphoid tissues. Flow cytometry confirms expression from one gene on B cells. Based on Southern blotting and cloning, only two such CD1 genes are detected, located ≈800 nucleotides apart and in the same transcriptional orientation. The sequence of one gene is nearly identical in six chicken lines. By mapping with a backcross family, this gene could not be separated from the chicken MHC on chromosome 16. Mining the draft chicken genome sequence shows that chicken has only these two CD1 genes located ≈50 kb from the classical class I genes. The unexpected location of these genes in the chicken MHC suggests the CD1 system was present in the primordial MHC and is thus ≈600 million years old.
Concurrent use of transgenic plants expressing a single and two
Bacillus thuringiensis
genes speeds insect adaptation to pyramided plants
Authors: Zhao Jian-Zhou , Cao Jun , Collins Hilda L. , Bates Sarah L. , Roush Richard T. , Earle Elizabeth D. , Shelton Anthony M.
Published: June 2005

Transgenic plants expressing insecticidal proteins from the bacterium
Bacillus thuringiensis
(Bt) were grown on over 13 million ha in the United States and 22.4 million ha worldwide in 2004. Preventing or slowing the evolution of resistance by insects (“resistance management”) is critical for the sustainable use of Bt crops. Plants containing two dissimilar Bt toxin genes in the same plant (“pyramided”) have the potential to delay insect resistance. However, the advantage of pyramided Bt plants for resistance management may be compromised if they share similar toxins with single-gene plants that are deployed simultaneously. We tested this hypothesis using a unique model system composed of broccoli plants transformed to express different Cry toxins (Cry1Ac, Cry1C, or both) and a synthetic population of the diamondback moth (
Plutella xylostella
) carrying genes for resistance to Cry1Ac and Cry1C at frequencies of ≈0.10 and 0.34, respectively. After 24–26 generations of selection in the greenhouse, the concurrent use of one- and two-gene plants resulted in control failure of both types of Bt plants. When only two-gene plants were used in the selection, no or few insects survived on one- or two-gene Bt plants, indicating that concurrent use of transgenic plants expressing a single and two Bt genes will select for resistance to two-gene plants more rapidly than the use of two-gene plants alone. The results of this experiment agree with the predictions of a Mendelian deterministic simulation model and have important implications for the regulation and deployment of pyramided Bt plants.