bluuebunny/crossref_metadata_2025 huggingface dataset:
Powder x-ray diffraction system with a curved monochromator for high-pressure and low-temperature use
Authors: Suzuki Eisuke , Endo Shoichi
Published: July 2003

A powder x-ray diffraction system operated at high pressure and low temperature has been developed for a conventional x-ray generator. An incident x ray is focused by a curved monochromator on a sample in a diamond anvil cell coupled with a cryostat with a helium gas closed-cycle refrigerator. We demonstrated a high-quality diffraction pattern with sufficient signal-to-noise ratio obtained for sodium chloride at 12 GPa and 6 K by this system using an imaging-plate detector.
Time-division superconducting quantum interference device multiplexer for transition-edge sensors
Authors: de Korte Piet A. J. , Beyer Joern , Deiker Steve , Hilton Gene C. , Irwin Kent D. , MacIntosh Mike , Nam Sae Woo , Reintsema Carl D. , Vale Leila R. , Huber Martin E.
Published: July 2003

We report on the design and performance of our second-generation 32-channel time-division multiplexer developed for the readout of large-format arrays of superconducting transition-edge sensors. We present design issues and measurement results on its gain, bandwidth, noise, and cross talk. In particular, we discuss noise performance at low frequency, important for long uninterrupted submillimeter/far-infrared observations, and present a scheme for mitigation of low-frequency noise. Also, results are presented on the decoupling of the input circuit from the first-stage feedback signal by means of a balanced superconducting quantum interference device pair. Finally, the first results of multiplexing several input channels in a switched, digital flux-lock loop are shown.
Real-time fringe correction algorithm for the JET interferometer
Authors: Innocente P. , Mazon D. , Joffrin E. , Riva M.
Published: July 2003

On the JET facility, the line-integrated electron density is measured by a multichannel far-infrared (FIR) interferometer. The basic source of radiation is a deuterium cyanide laser (λ=195 μm) measuring the density along four vertical and four nearly horizontal (lateral) channels. During high-density discharges the system suffers from fringe jumps that are manually partially corrected by an off-line program. This intermittent phenomenon prevents reliable usage of the measured line-integrated density in a real-time feedback controller. To solve this problem we have developed a method to correct the fringe jumps on the lateral channels in real time. The method uses the additional methyl alcohol laser (λ=118.8 μm) interferometer present on the lateral channels to compensate the vibrations. The method has been successfully tested with off-line test data, before implementation on a VERSA Module Eurocard system for the real-time control of the JET discharges.
Square root data compression
Authors: Gowen Robert A. , Smith Alan
Published: July 2003

Square root data compression is particularly suited to compression of scientific data where there shall be no reconstruction data artifacts, and reconstruction errors are required to be less than specified Poisson statistical noise levels. Its fixed compression ratio also makes it particularly suitable for real-time engineering implementation where telemetry rates and computer memory capacities are constrained. The compression scheme is described together with formulas that determine optimized control parameters to allow any input and compressed dynamic ranges to be accommodated, including joining to uncompressed data regions where zero data errors are desired to protect low count information. Further formulas are presented that allow optimized reconstruction values and maximum reconstruction error limits to be determined. Finally, some examples are presented that demonstrate its particular suitability for scientific applications.
Investigation of microfabrication of diamond-like film via focused ion beam milling
Authors: Fu Yongqi , Bryan Ngoi Kok Ann , Xie Dongzhu
Published: July 2003

Optical properties (transmission and refractive index) and chemical structure (x-ray photoelectron spectroscopy) of a diamond-like coating (DLC) before and after focused ion beam milling (FIBM) process were investigated in this article. We find no influence of FIBM on optical properties and chemical structure of the DLC in the near-infrared region. The film can be used for optical applications. As an application example, a diffractive optical element (DOE) was directly fabricated on the film by FIBM. The measured diffraction efficiency of the DOE is 73%, which is acceptable for conventional use.
High frequency pulser-sustainer for preionization in dc excited continuous wave CO2 lasers
Authors: Mokhariwale Anagha , Bahadur Ram , Deshmukh S. V.
Published: July 2003

Slow flow diffusion cooled CO2 lasers mostly use dc electrical discharge for excitation. Preionization in the discharge tubes of such a laser helps to initiate and maintain the dc discharge at voltages below breakdown voltage. A high frequency pulser using an insulated gate bipolar transistor as switching device is developed for preionization of the 20 discharge tubes of the 1 kW multibeam CO2 laser that we have developed. This pulser produces positive pulses of 10 kV peak voltages; frequency variable from 1 to 5 kHz and its pulse width is variable from 1 to 10 μs. The rise time of the pulses is between 600 and 700 ns. Preionization allows dc discharge excitation simultaneously in all discharge tubes of the multibeam CO2 laser even at high operating pressures. Other advantages of the preionization technique, such as the discharge stability at lower discharge currents with lower ballast resistance and the shorter inactive zone in the discharge tubes, are discussed. This pulser can also be used with dc excited fast axial flow CO2 lasers and other discharge devices.
Method for designing a temperature measurement system using two phase-locked loops
Authors: Huang S. S. , Young M. S.
Published: July 2003

A method using two phase-locked loops (PLLs) for a temperature measurement system (TMS) is described. In the system, a time-domain temperature sensor can convert the temperature into the duty cycle. The PLL circuit developed to emulate the Vernier caliper to measure the duty cycle is able to eliminate the measuring error and obtain higher resolution without increasing the clock frequency. Then, a single-chip microprocessor is designed to get and compute the duty cycle. Thus, the temperature can be easily computed with the duty cycle, and then sent to a liquid crystal display (LCD) to display. The experimental results show that the resolution of the duty cycle is 1/65280, and the range of the measured temperature is from −25.5 to 102 °C with maximum error ±0.05 °C in the TMS. Therefore, the main advantages of this system are high resolution, high accuracy, and low cost.
Room-temperature electroluminescence of ion-beam-synthesized β-FeSi2 precipitates in silicon
Authors: Martinelli Lucio , Grilli E. , Guzzi M. , Grimaldi M. G.
Published: July 2003

A simple silicon-based electroluminescent device has been realized, embedding β-FeSi2 precipitates in the depletion region of a Si p–n junction by ion-beam synthesis, a process fully compatible with microelectronics technologies. Light emission peaked at about 1.6 μm has been observed up to room temperature. The luminescence signal is shown to be due to interband recombination in the crystalline nanoprecipitates.
Defect reduction in (112̄0) a-plane gallium nitride via lateral epitaxial overgrowth by hydride vapor-phase epitaxy
Authors: Haskell B. A. , Wu F. , Craven M. D. , Matsuda S. , Fini P. T. , Fujii T. , Fujito K. , DenBaars S. P. , Speck J. S. , Nakamura Shuji
Published: July 2003

This letter reports on the reduction in extended-defect densities in a-plane (112̄0) GaN films achieved via lateral epitaxial overgrowth (LEO) by hydride vapor phase-epitaxy. A variety of dielectric mask patterns was used to produce 8–125-μm-thick, fully coalesced nonpolar GaN films. The nanometer-scale pit densities in the overgrown regions were less than 3×106 cm−2 compared to ∼1010 cm−2 in the direct-growth a-plane GaN. Cathodoluminescence revealed a fourfold increase in luminous intensity in the overgrown material compared to the window material. X-ray rocking curves indicate the films were free of wing tilt within the sensitivity of the measurements. Whereas non-LEO a-plane GaN exhibits basal plane stacking fault and threading dislocation densities of 105 cm−1 and 109 cm−2, respectively, the overgrown LEO material was essentially free of extended defects. The basal plane stacking fault and threading dislocation densities in the wing regions were below the detection limits of ∼5×106 cm−2 and 3×103 cm−1, respectively.
Fabrication of semiconductor Kagome lattice structure by selective area metalorganic vapor phase epitaxy
Authors: Mohan Premila , Nakajima Fumito , Akabori Masashi , Motohisa Junichi , Fukui Takashi
Published: July 2003

Artificial two-dimensional semiconductor Kagome lattice structures formed by quantum wires can show ferromagnetism when the flatband is half filled, even though it does not have any magnetic elements. Experimental realization of such a Kagome lattice structure is reported. The structure, with different pattern periods, was formed with GaAs quantum wires by selective area metalorganic vapor phase epitaxy on GaAs (111)B substrates. To overcome the lateral overgrowth and to improve the shape of smaller period pattern, flow rate modulation epitaxy was employed and a GaAs Kagome lattice structure with 1 μm period was effectively grown.
Fabrication and coupling to planar high-Q silica disk microcavities
Authors: Kippenberg T. J. , Spillane S. M. , Armani D. K. , Vahala K. J.
Published: July 2003

Using standard lithographic techniques, we demonstrate fabrication of silica disk microcavities, which exhibit whispering-gallery-type modes having quality factors (Q) in excess of 1 million. Efficient coupling (high extinction at critical coupling and low, nonresonant insertion loss) to and from the disk structure is achieved by the use of tapered optical fibers. The observed high Q is attributed to the wedged-shaped edge of the disk microcavity, which is believed to isolate modes from the disk perimeter and thereby reduce scattering loss. The mode spectrum is measured and the influence of planar confinement on the mode structure is investigated. We analyze the use of these resonators for very low loss devices, such as add/drop filters.
High-resolution domain imaging on the nonpolar y-face of periodically poled KTiOPO4 by means of atomic force microscopy
Authors: Canalias C. , Pasiskevicius V. , Fragemann A. , Laurell F.
Published: July 2003

The inverse piezoelectric effect is used to produce high-resolution images of ferroelectric domains in periodically poled KTiOPO4 crystals on their nonpolar y-face using atomic force microscopy. We demonstrate that the technique is convenient for studying the nucleation and growth of domains in a periodically poled KTiOPO4 sample.
An irrecoverable change in the refractive index of plasma self-channeled silica fibers caused by femtosecond optical pulses
Authors: Park I.-W. , Ju H. , Avilov A. , Choh S. H. , Koh E. K. , Cho S. H. , Kumagai H. , Midorikawa K.
Published: July 2003

We have investigated the physical properties of modified optical fibers through which 110 fs Ti:sapphire laser beam is self-focused down to 5 μm at 790 and 395 nm. The optically modified region in the fiber core exhibits the refractive index greater than that in the undamaged region. Electron diffraction measurements for the damaged region reveal that the enhancement of index from 1.457 to 1.480 is induced by the crystallization of amorphous SiO2 into a cristobalite structure. During the optical damaging, silicon and oxygen plasma preferably recombine to result in new bonds responsible for the crystallization. Some of the remnant silicon plasma lead to defects of the well-known E′-center, whose density increased parabolically with the input light intensity.
Experimental observation of photonic-crystal emission near a photonic band edge
Authors: Lin Shawn-Yu , Fleming J. G. , El-Kady I.
Published: July 2003

A three-dimensional tungsten photonic crystal is realized with a photonic band edge at λ∼4 μm wavelength. Its thermal emission is suppressed in the band gap regime and, at the same time, exhibits sharp peaks near the band edge. It is further observed that energy conversion efficiency from one side of the sample reaches η∼40%. This finding is attributed to a complete metallic photonic band gap in the infrared (λ⩾6 μm) and the enhanced density of photon states near the band edge of our tungsten photonic crystal.
Dissolution kinetics of boron-interstitial clusters in silicon
Authors: Mirabella S. , Bruno E. , Priolo F. , De Salvador D. , Napolitani E. , Drigo A. V. , Carnera A.
Published: July 2003

In this work, we have investigated the stoichiometry of boron-interstitial clusters (BICs) produced in a molecular-beam-epitaxy-grown B box by Si implantation and annealing, and their dissolution during further prolonged annealing cycles. Low-concentration B delta doping was used to quantitatively monitor the interstitial (I) flux. A stoichiometric ratio of about 1.2 between I and B was found for the BICs formed at 815 °C. The BIC dissolution kinetics was investigated by analyzing the concentration profiles at different times and temperatures (in the range 815–950 °C) with a simulation code able to deconvolve the processes of B diffusion and B release from clusters. We found that the main mechanism for cluster dissolution is the release of interstitial boron atoms, with a thermal activation energy of 3.2±0.4 eV. These data are discussed and compared with existing literature data.
Transport characteristics of InAs/GaAs quantum-dot infrared photodetectors
Authors: Lin Shih-Yen , Tsai Yao-Jen , Lee Si-Chen
Published: July 2003

A ten-stacked self-assembled InAs/GaAs quantum dot (QD) infrared photodetector is investigated. A wide detection window of 2–10 μm is observed with a peak responsivity of 187 mA/W at 7 μm under an applied voltage of 1.1 V. The observed negative differential conductance (NDC) of the photocurrent at low temperature is attributed to the formation of high-field domains and the resultant intervalley scattering in the GaAs barrier layer. The disappearance of the NDC and the increase of single-QD photoluminescence intensity with increasing temperature below 100 K are attributed to the thermally assisted electron redistribution with increasing temperature.
Electromagnetic properties of the lower-hybrid drift instability in a thin current sheet
Authors: Daughton William
Published: July 2003

The linear and nonlinear properties of the lower-hybrid drift instability are examined in a thin current sheet with thickness comparable to a thermal ion gyroradius ρi∼L. The linear Vlasov stability is calculated using a formally exact technique in which the orbit integrals are treated numerically and the eigenvalue problem for the resulting system of integrodifferential equations is solved using a finite element representation of the eigenfunction. For the fastest growing lower-hybrid modes with wavelength on the electron gyroscale (kyρe∼1), the resulting mode structure is localized on the edge of the current sheet. However, for modes with wavelengths intermediate between the electron and ion gyroscale kyρiρe∼1, the lower-hybrid instability has a significant electromagnetic component to the mode structure which is localized in the central region of the sheet. The addition of a weak guide field complicates the mode structure and gives rise to fluctuations in all three components of the magnetic field. These new predictions from linear Vlasov theory are confirmed using fully kinetic particle-in-cell simulations which indicate the modes saturate at large amplitude in the central region of the sheet. These results suggest the possibility that the electromagnetic fluctuations may potentially influence the development of magnetic reconnection.
Dynamical analysis of carrier concentration in inelastic resonant tunneling
Authors: Chan K. S.
Published: July 2003

An analytic expression for the buildup process in inelastic resonant tunneling is obtained using a tight-binding Hamiltonian. The buildup process is described by the summation of a number of oscillation terms which are guided by an exponential buildup envelope. The relative importance of these terms depends on the incident energy and resonant lifetime. Interesting interference patterns can be obtained by varying these parameters. A nonexponential buildup process is found near the resonant peak, with a buildup rate faster than that of the exponential envelope. Electron–phonon interaction can extend this nonexponential behavior to a wider range of energy by opening up additional resonance channels.
Intense visible light emission from stress-activated SrMgAl6O11:Eu
Authors: Akiyama Morito , Nishikubo Keiko , Nonaka Kazuhiro
Published: July 2003

We have investigated deformation luminescence phenomena and the constituent phases of SrMgAl6O11:Eu. The deformation luminescence is clearly visible to the naked eye in air, and the luminescence intensity is the highest among the materials reported. Using x-ray diffraction the constituent phases of SrMgAl6O11:Eu are determined to be SrAl2O4, SrMgAl10O17, and MgAl2O4. The deformation luminescence center has been identified as the Eu2+ ion from the deformation and photoluminescence studies of the three-phase composite. The thermoluminescence glow curve of the composite indicates the trapping levels around room temperature. This result means that the three-phase structure of the composite influences the high deformation luminescence intensity.
Scaling limits of hafnium–silicate films for gate-dielectric applications
Authors: Takeuchi Hideki , King Tsu-Jae
Published: July 2003

The scaling limits of hafnium–silicate (Hf–silicate) films for use as the gate dielectric material in complementary metal–oxide–semiconductor field-effect transistors are investigated. Scalability is gauged by a figure of merit taken from the analytical model for direct tunneling leakage current. Based on the compositional dependence of this figure of merit, pure HfO2 is more scalable than Hf–silicates. However, the formation of intermediate oxide layers at the Si interface can limit the scalability of HfO2 to ∼1.0 nm equivalent SiO2 thickness (EOT). The use of Si3N4 as a diffusion barrier can prevent the formation of these interfacial layers and thereby yield lower EOT. Alternatively, 20% Hf–silicate may be more scalable than pure HfO2 with interfacial oxide layers.
Transmission electron microscopy observation of high-temperature γ-FeSi2 precipitates formed in Si by iron implantation using a metal vapor vacuum arc ion source
Authors: Gao Y. , Wong S. P. , Cheung W. Y. , Shao G. , Homewood K. P.
Published: July 2003

This work reports the observation of high-temperature γ-FeSi2 precipitates of tens of nanometers in diameter embedded in silicon formed by iron implantation using a metal vapor vacuum arc ion source followed by a dual step annealing process. It was found that the implantation temperature and annealing conditions played important roles on the shape and phase formation of the FeSi2 precipitates. When the implantation temperature was high (about 380 °C), only β-FeSi2 precipitates were formed. When the implantation temperature was low (about −100 °C), after the dual step annealing, in addition to β-FeSi2, γ-FeSi2 precipitates coherent with the silicon substrate were formed.
Deformation mechanism in nanocrystalline Al: Partial dislocation slip
Authors: Liao X. Z. , Zhou F. , Lavernia E. J. , Srinivasan S. G. , Baskes M. I. , He D. W. , Zhu Y. T.
Published: July 2003

We report experimental observation of a deformation mechanism in nanocrystalline face-centered-cubic Al, partial dislocation emission from grain boundaries, which consequently resulted in deformation stacking faults (SFs) and twinning. These results are surprising because (1) partial dislocation emission from grain boundaries has not been experimentally observed although it has been predicted by simulations and (2) deformation stacking faults and twinning have not been reported in Al due to its high SF energy.
Thermodynamic argument about SnO2 nanoribbon growth
Authors: Beltrán A. , Andrés J. , Longo E. , Leite E. R.
Published: July 2003

Calculations based on density functional theory at Becke’s three-parameter exchange functional combined with the Lee–Yang–Parr correlation functional (B3LYP) level and periodic slab models have been done to obtain: (i) the surface energy per unit area of different stoichiometric SnO2 surfaces, and (ii) by using a simple Wulff construction equation-type, the thermodynamic stability associated to the formation of nanoribbons from these surfaces has been obtained. In agreement with previous theoretical studies, the (110) face is the thermodynamically most stable surface. The present theoretical results and high-resolution transmission electron microscopy data reveal that the nanoribbons preferentially grow along the [101] crystal direction.
Structural and magnetic properties of ultrathin epitaxial La0.7Ca0.3MnO3 manganite films: Strain versus finite size effects
Authors: de Andrés A. , Rubio J. , Castro G. , Taboada S. , Martı́nez J. L. , Colino J. M.
Published: July 2003

We present a structural and magnetic study of La0.7Ca0.3MnO3 epitaxial films (the thickness ranges from 2.4 to 80 nm) on SrTiO3. Their structure, as obtained by x-ray diffraction, is orthorhombic with a 45° rotated 2×2 square lattice, referred to the SrTiO3 substrate, in the film plane. The 2.4 nm film adopts a different structure as evidenced by the extinction of particular diffraction peaks and supported by the behavior of the size of the in-plane structural domains. While no important structural changes are detected for the other films as the layer thickness is reduced, Tc decreases drastically while the remanent magnetization is constant. Tc follows the functional dependence of a mean field approximation for the limitation of the divergence of the spin–spin correlations by the film thickness.
Component spatial pattern analysis of chemicals using terahertz spectroscopic imaging
Authors: Watanabe Y. , Kawase K. , Ikari T. , Ito H. , Ishikawa Y. , Minamide H.
Published: July 2003

We demonstrated the separation of the component spatial patterns of chemical samples in transillumination terahertz (THz) images using known spectral curves. The images and spectral data were measured between 1.3 and 1.8 THz, using a widely tunable coherent THz-wave parametric oscillator source. This method could be effective for analyzing spatial patterns and the concentrations of components with various chemical compositions.
Si doping effect on strain reduction in compressively strained Al0.49Ga0.51N thin films
Authors: Cantu P. , Wu F. , Waltereit P. , Keller S. , Romanov A. E. , Mishra U. K. , DenBaars S. P. , Speck J. S.
Published: July 2003

Evaluation of the structural properties of 200-nm-thick Si-doped Al0.49Ga0.51N films, grown on nominally relaxed 1-μm-thick Al0.62Ga0.38N buffer layers on sapphire, revealed that increased Si doping promoted the relaxation of the compressively strained layers. The degree of strain relaxation R of the Al0.49Ga0.51N films, as determined by x-ray diffraction (XRD), increased from R=0.55 to R=0.94 with an increase in disilane injection from 1.25 nmol/min to 8.57 nmol/min. Transmission electron microscopy analysis showed that the edge threading dislocations (TDs) in the Al0.49Ga0.51N layers were inclined, such that the redirected TD lines had a misfit dislocation component. The calculated strain relaxation due to the inclined TDs was in close agreement with the values determined from XRD. We propose that the TD line redirection was promoted by the Si-induced surface roughness.
Observation of the transition of coherent/sequential electron tunneling in a resonant tunneling regime of a GaAs/AlAs three-terminal quantum-well heterostructure
Authors: Kim Gyungock , Roh Dong Wan , Paek Seung Won
Published: July 2003

We observe the coherency of electron tunneling preserved up to the resonant peak voltage by measuring scattered electrons in a GaAlAs/GaAs three-terminal heterostructure. The abrupt increase of the scattered electron current, which onsets at the resonant peak voltage, indicates the breakdown of the coherency of electron tunneling. The experimental result indicates that the abrupt nature of the electron scattering in the resonant tunneling regime can be utilized in switching and logical devices.
Negative differential resistance effects of trench-type InGaAs quantum-wire field-effect transistors with 50-nm gate-length
Authors: Jang Kee-Youn , Sugaya Takeyoshi , Hahn Cheol-Koo , Ogura Mutsuo , Komori Kazuhiro , Shinoda Akito , Yonei Kenji
Published: July 2003

The effects of negative differential resistance (NDR) have been clearly observed in 50-nm-gate InGaAs/InAlAs trench-type quantum-wire (QWR) field-effect transistors (FETs), which are fabricated by atomic hydrogen-assisted molecular-beam epitaxy. The NDR onset voltage is as low as 0.1 V, and the highest peak-to-valley current ratio is 6.2 at 40 K. The equilateral symmetry of the NDR effect in a QWR FET is also observed. The pronounced NDR effects in a trench-type QWR FET are advantageous for high-speed and low power-consumption devices.
Effect of hydrogen dilution on the open-circuit voltage of hydrogenated amorphous silicon solar cells
Authors: Yan Baojie , Yang Jeffrey , Guha Subhendu
Published: July 2003

The open-circuit voltage (Voc) of hydrogenated amorphous silicon solar cells has been studied experimentally and by computer simulation. We find that band gap and defect states affect Voc significantly. Hydrogen (H2) dilution widens the band gap and reduces density of defect states; both contribute to larger Voc and better fill factor in H2 diluted solar cells. Valence band tail narrowing could affect Voc, but is not included in this study due to lack of available data.
Structural and optical characterization of nonpolar GaN/AlN quantum wells
Authors: Ng H. M. , Bell A. , Ponce F. A. , Chu S. N. G.
Published: July 2003

We have grown nonpolar GaN/AlN multiple quantum wells by plasma-assisted molecular-beam epitaxy on R-plane sapphire substrates. X-ray diffraction and selected-area diffraction data show that the III-nitride epilayers are oriented in the [11 2̄0] direction with the [0001] axis lying in the plane of the substrate. The 18-Å GaN quantum wells exhibit luminescence at 326 nm, which is in agreement with the transition energy calculated using a flat-band model; that is, without the presence of a built-in electric field.
On the extraction of positive and negative ions from electron-beam-generated plasmas
Authors: Walton S. G. , Leonhardt D. , Fernsler R. F. , Meger R. A.
Published: July 2003

The results of investigations using pulsed, electron-beam-produced plasmas in Ar/SF6 mixtures are reported. Positive and negative ions were extracted during the active phase of plasma production using a low-frequency, low-voltage bias applied to the sampling electrode. Time-averaged energy distributions, accumulated over several extraction periods, were employed to investigate the flux of both the positive and negative ions. The extraction of negative ions in large quantities suggests the formation of ion–ion plasmas, and the time-averaged energy distributions are in agreement with estimates of sheath formation at the biased electrode.
Temperature dependence of field emission from cupric oxide nanobelt films
Authors: Chen Jun , Deng S. Z. , Xu N. S. , Zhang Weixin , Wen Xiaogang , Yang Shihe
Published: July 2003

Films of aligned cupric oxide nanobelts have been prepared in an aqueous solution at room temperature. Field-emission characteristics, including emission-current–applied-field plot and emission site distribution, have been studied using the transparent anode technique. In addition, the temperature dependence of the field-emission characteristics has been studied from room temperature to 750 K. The threshold field for obtaining a current density of 10 μA/cm2 is ∼11 MV/m. This decreases with increasing temperature, and at 700 K it is ∼6 MV/m. At a fixed field of 10 MV/m, about a three-orders-of-magnitude increase of the emission current level has been observed. The results show that the cupric oxide nanobelt is a promising candidate for cathode material in a thermoelectric conversion device based on field emission.
Electric-field-induced reversible avalanche breakdown in a GaAs microcrystal due to cross band gap impact ionization
Authors: Klappenberger F. , Renk K. F. , Summer R. , Keldysh L. , Rieder B. , Wegscheider W.
Published: July 2003

We report on a reversible avalanche breakdown due to free-carrier multiplication caused by cross band gap impact ionization in a GaAs microcrystal. The n GaAs microcrystal (length 1 μm, diameter 1 μm) was embedded between n+ GaAs layers serving as electric contacts. We guided an electric pulse to the sample and determined, from the reflected and transmitted pulse, the I(V) characteristic. The breakdown was indicated by a sudden current rise and voltage drop and a hysteresis effect and, furthermore, by electron-hole recombination radiation. We reached the threshold field for ionization by making use of a high-field domain whose formation was based on the Gunn effect. The microcrystal could reproducibly be switched into the nonequilibrium avalanche state. Our analysis indicates that the effect provides a basis for the development of an ultrafast electric switch.
Bipolar cascade lasers at emitting wavelengths near 2 μm
Authors: Yang Rui Q. , Qiu Yueming
Published: July 2003

Broad-area InGaAs/InP-based bipolar cascade lasers were demonstrated at emitting wavelengths near 2 μm and their spectral characteristics were investigated. These broad-area lasers operated at temperatures up to 205 K in continuous wave mode and up to room temperature in pulsed mode. Distinct spectral features were observed at high temperatures with larger currents and bias, which may result from significant Stark effects and increased excited state transitions.
Green electroluminescence of EuGa2S4 thin films
Authors: Tanaka Katsu , Okamoto Shinji
Published: July 2003

Green electroluminescence (EL) was observed in europium thiogallate (EuGa2S4) thin films, which is a stoichiometric phosphor material. The peak wavelength of the EL spectrum measured at 300 K was 536 nm. The spectrum’s color coordinates were (0.29,0.67), which is the pure green region. Simulated EL spectra at 77 and 300 K indicated that the green EL originates not from the host band transition but from an intra-atomic transition of the Eu2+ ion. From the transient EL wave form, the EL was observed at the leading edge of a rectangular applied voltage. This suggests that the Eu2+ centers are directly excited by the impact of hot carriers.
InGaN quantum dots grown by metalorganic vapor phase epitaxy employing a post-growth nitrogen anneal
Authors: Oliver Rachel A. , Briggs G. Andrew D. , Kappers Menno J. , Humphreys Colin J. , Yasin Shazia , Rice James H. , Smith Jonathon D , Taylor Robert A.
Published: July 2003

We describe the growth of InGaN quantum dots (QDs) by metalorganic vapor phase epitaxy. A thin InGaN epilayer is grown on a GaN buffer layer and then annealed at the growth temperature in molecular nitrogen inducing quantum dot formation. Microphotoluminescence studies of these QDs reveal sharp peaks with typical linewidths of ∼700 μeV at 4.2 K, the linewidth being limited by the spectral resolution. Time-resolved photoluminescence suggests that the excitons in these structures have lifetimes in excess of 2 ns at 4.2 K.
Nonlinear optical effect of organic crystal heterostructures of benzylidene-aniline derivatives by two-step molecular-beam heteroepitaxy
Authors: Yamashiki Tomoya , Fukuda Seiji , Tsuda Keiji , Gotoh Tetsuya
Published: July 2003

A nonlinear optical waveguide with organic crystals based on 4′-nitrobenzyliden-3acetamino-4-methoxyaniline (MNBA) and its derivative was fabricated by organic molecular-beam epitaxy and operated as an electro-optic (EO) device. It has been proved that an EO coefficient r11 of MNBA significantly depends on the thickness of the 4′-nitrobenzyliden3-ethylcarbonylamino-4-methoxyaniline (MNBA–Et) homoepitaxial layer. Insertion of a thicker MNBA–Et homoepitaxial layer enlarges r11 of MNBA heteroepitaxial layer from 30 to more than 150 pm/V.
Nb/yttria-stabilized-zirconia/Nb nonhysteretic Josephson junctions
Authors: Lam S. K. H. , Gnanarajan S.
Published: July 2003

Yttria-stabilized zirconia (YSZ) is used as an insulating barrier for the fabrication of niobium edge junctions. Using the ion beam assisted deposition technique, Nb/YSZ/Nb edge junctions with YSZ thin film of a few nanometers in thickness have been fabricated. The junctions are nonhysteretic with critical current densities up to 4 mA/μm2 and critical current normal resistance products of ∼1 mV.
Enhanced initial growth of atomic-layer-deposited metal oxides on hydrogen-terminated silicon
Authors: Frank Martin M. , Chabal Yves J. , Green Martin L. , Delabie Annelies , Brijs Bert , Wilk Glen D. , Ho Mun-Yee , da Rosa Elisa B. O. , Baumvol Israel J. R. , Stedile Fernanda C.
Published: July 2003

A route is presented for activation of hydrogen-terminated Si(100) prior to atomic layer deposition. It is based on our discovery from in situ infrared spectroscopy that organometallic precursors can effectively initiate oxide growth. Narrow nuclear resonance profiling and Rutherford backscattering spectrometry show that surface functionalization by pre-exposure to 108 Langmuir trimethylaluminum at 300 °C leads to enhanced nucleation and to nearly linear growth kinetics of the high-permittivity gate dielectrics aluminum oxide and hafnium oxide.
Photofabrication of wood-pile three-dimensional photonic crystals using four-beam laser interference
Authors: Shoji Satoru , Sun Hong-Bo , Kawata Satoshi
Published: July 2003

We present a method for fabricating three-dimensional photonic crystal structures by means of an interference pattern of laser beams. Two orthogonal square lattice rod-arrays which compose the wood-pile photonic crystal structure are fabricated by interference of four laser beams into photopolymerizable resin. The lattice constant of the photonic crystal can be selected freely by incident angles of laser beams without any deformations of the lattice symmetry and the lattice elements. The proposed method does not require complicated multiple processes compared with the layer-by-layer fabrication method, and thick wood-pile photonic crystals are immediately produced with high precision.
Effect of BN coatings on oxidation resistance and field emission of SiC nanowires
Authors: Tang Chengchun , Bando Yoshio
Published: July 2003

We compare the effects of BN coatings on antioxidation ability and field emission properties of SiC nanowires. Under oxidizing condition, SiC nanowires without BN coatings are cracked into nanoparticles or almost fully converted into SiO2 nanowires at the temperature above 800 K, depending on the crystallization degree of SiC nanowires. The BN coatings effectively improve the antioxidation ability of SiC nanowires due to the excellent chemical stability of BN at high temperature. At a temperature higher than 1273 K, the coated SiC nanowires still exhibit strong oxidation resistance. For the effect on electron emission, the BN coatings also reduce the turn-on field of SiC nanowires from larger than 10 V/μm to lower than 6 V/μm. The explanation for the improvement of field emission characteristics has been presented.
High performance sensing of nitrogen oxides by surface plasmon resonance excited fluorescence of dye-doped deoxyribonucleic acid thin films
Authors: Nagamura Toshihiko , Yamamoto Misato , Terasawa Michiyo , Shiratori Koji
Published: July 2003

Highly sensitive, fast responsive, and highly reversible sensing of nitrogen dioxide, nitric oxide, and nitrous oxide at a ppm-to-sub-ppm level has been achieved by fluorescence measurements upon excitation of various dye-doped deoxyribonucleic acid (DNA) or hydrophobic DNA thin films spincoated on a thin silver film by electric-field-enhanced evanescent light at surface plasmon resonance. The response time, sensitivity, or selectivity was controlled by combination of dyes and matrices. The present result will make a great many contributions to environmental and medical applications.
Spherical micromirrors from templated self-assembly: Polarization rotation on the micron scale
Authors: Coyle S. , Prakash G. V. , Baumberg J. J. , Abdelsalem M. , Bartlett P. N.
Published: July 2003

We demonstrate a fabrication route to individual micron-scale metallic spherical mirrors. The mirrors are prepared by electrochemical growth through the interstitial voids of a self-assembled latex sphere template. Excellent spherical mirrors of Au and Pt are obtained with unusual polarization properties in which multiple reflections with distinct anisotropies are found due to geometric polarization rotation. Such micromirrors can form the basis of low-cost microcavity structures and microlasers.
Three-color reconfigurable organic light-emitting devices
Authors: Wu Chung-Chih , Chen Chieh-Wei , Cho Ting-Yi
Published: July 2003

This report reveals utilization of phase transitions and corresponding changes in physical properties of organic semiconductors for implementing reconfigurable organic optoelectronic devices, i.e., a device whose configurations and characteristics can be programed after fabrication. Specifically, glass transitions of amorphous molecular materials have been exploited to demonstrate reconfigurable organic light-emitting devices (OLEDs) capable of generating any of the three primary colors. The capability to pattern such devices into fine color pixels with thermal imaging renders it attractive for applications in high-resolution full-color OLED displays and as active optical memory devices.
Gibb’s free energy for the crystallization of glass forming liquids
Authors: Mondal K. , Chatterjee U. K. , Murty B. S.
Published: July 2003

This letter gives an approximation for the Gibb’s free energy change for the crystallization of undercooled liquid (ΔG). The present ΔG expression is arrived at by the modification of existing models. Calculations based on the present expression have shown that the ΔG values obtained for seven glass forming alloys (Au81.4Si18.6, La50Al30Ni20, Mg65Cu25Y10, Mg50Ni30La20, Pd40Ni40P20, Zr65Cu17.5Ni10Al7.5, and Zr41.2Ti13.8Cu12.5Ni10Be22.5) compare well with the experimental ones in all the cases with a maximum deviation of 6% up to the glass transition temperature (Tg). The present expression is able to calculate the ΔG values accurately in a variety of glass forming alloys ranging from binary to quinary systems with a wide range of reduced glass transition temperature (Trg=Tg/Tm) of 0.45–0.75.
Ionic transport in polycrystalline zirconia and Frenkel’s space-charge layer postulation
Authors: M’Peko Jean-Claude , de Souza Milton Ferreira
Published: July 2003

Various physical and chemical techniques have been applied elsewhere to get insight into the peculiarities of conduction processes in zirconia-based ionic conductors. Although Frenkel’s space-charge model is popularly accepted to describe well the capability of grain boundaries for limiting ion transport throughout these materials, validating this model has generally resulted to be a difficult task provided substantial restrictions to access the subgrain nanometer-sized regions involved. The present work reports a simple but consistent method to also approach this important question, and consists of studying the bulk and grain-boundary electrical responses of these materials while they are subjected to external mechanical loads.
Electric-field-induced dielectric anomalies in C-oriented 0.955Pb(Zn1/3Nb2/3)O3–0.045PbTiO3 single crystals
Authors: Shen Mingrong , Han Jiaping , Cao Wenwu
Published: July 2003

Electrical-field-induced dielectric anomalies in C-oriented 0.955Pb(Zn1/3Nb2/3)O3–0.045PbTiO3 single crystals were observed in both the dielectric constant and loss variations with temperature. Three distinct ordered phases are revealed, which are distinguished by their frequency dispersion behavior. We propose the existence of a medium-range ordered phase between the long-range and the short-range ordered phases, resulting from the competing features of the relaxor and ferroelectric constituents, Pb(Zn1/3Nb2/3)O3 and PbTiO3. Some dispersion is evident in this medium-range ordered phase but global polarization is still present. The assumption is rationalized by the measured relationship between the remnant polarization and temperature.
Sputter deposited GaN doped erbium thin films: Photoluminescence and 1550 nm infrared electroluminescence
Authors: Kim Joo Han , Shepherd Nigel , Davidson Mark , Holloway Paul H.
Published: July 2003

Erbium doped gallium nitride (GaN) thin films were deposited on Si substrates by reactive rf magnetron cosputtering of a commercial GaN target, together with a metallic erbium target. Nitrogen was employed as the reactive sputtering gas. The gallium nitride doped erbium (GaN:Er) films thus obtained, exhibited the characteristic 525, 540, 660, and 1550 nm photoluminescence emission associated with the Er+3 ion 4f–4f intraband transitions. In addition, 1550 nm IR electroluminescence (EL) emission was observed from the sputter deposited GaN:Er phosphor films. The EL device was an inverted half-stack ac thin-film EL device structure. The 1550 nm EL emission is consistent with impact excitation and subsequent I13/24→4I15/2 radiative relaxation of Er+3 ions. Impact excitation requires conduction electrons with sufficient energy from electrical field acceleration, to excite the transition.
Sensitivity of amorphous silicon-germanium solar cells to oxygen impurity atoms
Authors: Ganguly G. , Carlson D. E.
Published: July 2003

The performance of thin-film solar cells based on amorphous silicon germanium alloys (a-SiGe:H) are shown to be relatively sensitive to the contamination level of oxygen and/or nitrogen impurity atoms. Both a-SiGe single-junction solar cells and amorphous silicon (a-Si:H)/a-SiGe:H tandem solar cells were fabricated using a calibrated leak during deposition of individual layers. After light soaking, the tandem cells with a-SiGe layers deposited with an air leak, and observed to incorporate ∼4 (2.3)×1019 cm−3 oxygen (nitrogen) atoms, have significantly (10%) lower performance. The efficiency of a-SiGe:H single junction cells fabricated with varying air leak rates are found to improve systematically by ∼20% as the incorporated oxygen (nitrogen) concentration decreased by a factor of ∼3 (23) down to 1.3 (0.1)×1019 cm−3.
1.47–1.49-μm InGaAsP/InP diode laser arrays
Authors: Gourevitch A. , Belenky G. , Donetsky D. , Laikhtman B. , Westerfeld D. , Trussell C. W. , An H. , Shellenbarger Z. , Martinelli R.
Published: July 2003

Continuous-wave power of 25 W at 1.47-μm was obtained from a 20-element, 1-cm-wide, one-dimensional diode laser array mounted in a microchannel water-cooled heat sink. The coolant temperature was 16 °C. A two-dimensional array comprising four laser bars achieved a quasi-cw output of 110 W at a wavelength of 1.49 μm, with an 8–9-nm full width at half-maximum spectrum width. The coolant temperature was 18 °C. We developed a theoretical model that describes array heating. Thermal resistances of 0.56, 0.4, and 0.34 K/W were experimentally and theoretically determined for arrays with fill factors of 10%, 20%, and 40%, respectively.
On the influence of hydrogen on the erbium-related luminescence in silicon
Authors: Kocher-Oberlehner G. , Jantsch W. , Palmetshofer L. , Ulyashin A.
Published: July 2003

Erbium- and oxygen-doped silicon was additionally doped with hydrogen, using plasma-enhanced chemical vapor deposition. Samples treated with solid-phase epitaxy (SPE) before hydrogenation and annealing at 900 °C afterwards show a large enhancement of the photoluminescence (PL) yield. A change in local concentration leads to a dominance of the cubic center in the PL. Controlled etching shows that the PL stems from a deeper region with lower erbium concentration. The luminescence yield in the hydrogenated samples is significantly higher, even compared to samples optimized for cubic center luminescence. We thus conclude that hydrogen enhances the solubility of the cubic center in Si:Er,O.
Effect of magnetic field on random telegraph noise in the source current of p-channel metal–oxide–semiconductor field-effect transistors
Authors: Baron Filipp A. , Zhang Yaohui , Bao Mingqiang , Li Ruigang , Li Jinmin , Wang Kang L.
Published: July 2003

Drain leakage current in accumulated metal–oxide–semiconductor field-effect transistors (MOSFETs) is pumped out completely by the body, while the source current should be zero due to the barrier of the p/n junction between the source and the accumulated channel. In this letter, we observe a fraction of drain current flowing into the source terminal in accumulated p-channel MOSFETs at low temperature. Under a certain gate bias region, the random telegraph noise (RTN) with an amplitude of 30% is observed in the source current of the devices. The source-current RTN disappears completely when the measured temperature exceeds 4.2 K. The source-current RTN is strongly affected by applied magnetic field, which causes the large decrease of the average switching time of the source RTN. We believe that the random charging and discharging of single defects at the SiO2/Si interface of the gate–source overlap region may strongly disturb the band-to-band tunneling process, and thereby result in the source-current RTN.
Spin-polarized injection into YBaCu3O7 grain boundary junctions
Authors: Ireland J. , Chakalov R. , Colclough M. S. , Muirhead C. M.
Published: July 2003

YBa 2 Cu 3 O 7 / SrTiO 3 / La 0.67 Ca 0.33 MnO 3 trilayer thin films grown on bicrystal substrates were patterned into a structure that allows the injection of spin-polarized current into the region of a grain boundary junction (GBJ). The transfer length LT was determined to ensure that injection was over the entire device width, in contrast to previously reported experiments. Currents up to some 100 times the junction critical current I0 and area density 108 A m−2, have been injected into the GBJ region by using an offset current method. The I0(B) characteristics of the GBJ under injection suggest that the suppression of I0 can be explained by a combination of heating and self-field effects, without any need to invoke the spin-polarized nature of the injected current. We find no evidence of direct injection into the junction.
Systematic analyses of anomalous torque curves in granular BaFe12O19/SiO2/Si thin films
Authors: Lisfi A. , Lodder J. C. , Williams C. M.
Published: July 2003

An anomaly has been observed in the magnetic torque curve of BaFe12O19 films grown on a SiO2/Si substrate. The kink in the torque curve has a strong dependence on the film thickness and appears when the field direction is close to the film plane. Structural analyses together with the support of magnetic loop measurements reveal a polycrystalline structure, with magnetic properties strongly dependent on film thickness. At low thicknesses, a granular structure with a perpendicular c-axis is dominant, whereas, at large thicknesses, a new texture with a tilted c-axis (61° from the film plane) is well developed. By considering the contribution of both types of grains, the shape of torque curve is well predicted and the kink origin is attributed to the tilt of the c-axis.