bluuebunny/crossref_metadata_2025 huggingface dataset:
Enhanced pinning and peak effect in overdoped (Hg, Pb)(Sr, Ba)2Ca2Cu3O8+δ superconductors
Authors: Lee Sergey , Akao T. , Suematsu H. , Yamauchi H. , Kiryakov N. P. , Emelyanov D. A. , Kuznetsov M. S.
Published: July 2002

“Peak effect” was observed in the magnetization hysteresis loops of both (Hg, Pb)(Sr, Ba)2Ca2Cu3O8+δ polycrystalline bulks and single crystals, and the influence of postannealing on the peak position (Hs.p.) was studied, where “s.p.” means second peak. It was shown that the Hs.p.–T characteristic curves for a Sr-rich (Hg, Pb)-1223 were located in higher fields than those reported for conventional Hg-1223 and Tl-1223 single crystals, corresponding to reduced lattice parameters and electronic anisotropy of the studied compounds. The Jc (77 K) values of 3×105, 2.8×104, and 1.8×104 A/cm2 were estimated for the present single-crystal sample at H=0, 1, and 2 T, respectively. This confirms the excellent flux-pinning property of (Hg, Pb)(Sr, Ba)2Ca2Cu3O8+δ, making them potential candidates for high current applications.
Simultaneous sampling of optical pulse intensities and wavelengths by four-wave mixing in a semiconductor optical amplifier
Authors: Diez S. , Schmidt C. , Hoffmann D. , Bornholdt C. , Sartorius B. , Weber H. G. , Jiang L. , Krotkus A.
Published: July 2002

An all-optical sampling technique that allows the simultaneous measurement of optical pulse intensities and wavelengths with a temporal resolution of about 1 ps is introduced. Using four-wave mixing (FWM) in a semiconductor optical amplifier, the optical signal under test is cross correlated with nearly transform-limited 1.4 ps optical sampling pulses. While the intensity of the generated FWM signal is used to determine the temporal shape of the signal intensity, the wavelength of the FWM signal yields time-resolved information about the signal wavelength (i.e., the frequency chirp). Using this technique, the correlation of intensity and wavelength dynamics of pulses generated by a self-Q-switched distributed-feedback laser is determined directly.
Performance of high-Tc superconducting quantum interference devices with resistively shunted inductances
Authors: Kang D. J. , Booij W. E. , Blamire M. G. , Tarte E. J.
Published: July 2002

The voltage modulation depths, ΔV of high-Tc direct current superconducting quantum interference devices (SQUIDs) with resistors connected in parallel with their inductances were investigated. Both the junctions and resistors in the SQUIDs were fabricated using focused electron-beam irradiation. The effect of varying the resistor value (using focused ion-beam trimming) and the screening parameter βL (by varying the temperature and hence the junction critical current) were studied. Significant enhancement of ΔV relative to an equivalent unshunted SQUID for βL values up to 50 was observed, and the most effective shunt resistor value was found to be approximately equal to the junction resistance.
Substitutional Ge in 3C–SiC
Authors: Guedj C. , Kolodzey J.
Published: July 2002

The incorporation of substitutional Ge into 3C–SiC alloys is studied theoretically with an anharmonic Keating model specifically adapted to the computation of the structural properties and the lattice dynamics of Si1−x−yGexCy alloys. Basic energy calculations show that the substitution of Si by Ge is more probable than the substitution of C by Ge in the zinc-blende silicon carbide crystal. If Ge replaces only Si, then the lattice parameter equals (0.43593±0.00002)+(0.000337±0.000002)y, where y stands for the Ge content. Hence, Vegard’s law is not applicable. The alloy is characterized by a distinct phonon spectrum whose maximum peak position in cm−1 is best described by the exponential decay (243±1)+(27±2)exp[−y/(7.5±1.2)] up to the zinc-blende GeC compound.
Confirmation of proton beam bending in graded Si1−xGex/Si layers using ion channeling
Authors: de Kerckhove D. G. , Breese M. B. H. , Smulders P. J. M. , Jamieson D. N.
Published: July 2002

A graded composition Si1−xGex/Si [001] layer, which has recently been proposed as a method for bending and extracting protons from high-energy particle accelerators, has been studied by angle-resolved ion channeling analysis using focused MeV proton and He+ beams. Backscattering spectrometry confirms that the composition is linearly graded and a maximum Ge concentration of 0.16 was measured at the epilayer surface. Off-normal planes {111} are curved with respect to the substrate by a total angle of 0.332° and efficient bending of channeled particles along the curved planes and into the substrate is confirmed.
Strong- and nondegrading-luminescent porous silicon prepared by hydrothermal etching
Authors: Li Xin Jian , Zhu De Liang , Chen Qian Wang , Zhang Yu Heng
Published: July 2002

Porous silicon (PS) with strong and nondegrading photoluminescence (PL) is prepared by iron-passivating hydrothermal etching. The PL peak intensity of freshly as-prepared PS is as ∼2 times strong as that of conventionally anodized PS. This peak intensity reaches a saturation after the samples are annealed at 120 °C for ∼3 h, which is ∼2.5 times strong as that of freshly prepared samples. Exposing the annealed samples to air for ten months, no degradation of the PL intensity occurs and the peak energy remains constant all through the period. Microstructural studies disclose that the participation of iron ions in the hydrothermal process is crucial to the generation of the high-density silicon nanocrystallites and the construction of the solid surface passivation. These two structural properties are responsible for the strong and nondegrading PL of as-prepared PS.
Stripe-width dependence of threshold current for gain-guided AlGaInN laser diodes
Authors: Bour D. P. , Kneissl M. , Romano L. T. , Donaldson R. M. , Dunnrowicz C. J. , Johnson N. M. , Evans G. A.
Published: July 2002

The threshold current density of narrow-stripe gain-guided nitride laser diodes increases very rapidly as the stripe width is made narrow. To examine this behavior, waveguide simulations, incorporating the complex refractive indices associated with optical gain, have been used to analyze the lateral optical modes of gain-guided laser diodes. Threshold current was then determined from the gain–current relationship of our laser material, which was obtained experimentally. These evaluations reveal that gain guiding, coupled with a carrier-induced index depression, offer a reasonable explanation for the rapid increase in threshold when the stripe width becomes less than 5 μm.
Observation of coherent phonons in silver nanoparticles embedded in BaO thin films
Authors: Qian W. , Yan H. , Wang J. J. , Zou Y. H. , Lin L. , Wu J. L.
Published: July 2002

Three kinds of coherent phonons (0.30, 1.90, and 3.75 THz) have been observed in silver nanoparticles embedded in BaO thin films by means of the femtosecond time-resolved pump-probe technique. The generation of 0.3 THz coherent phonons is attributed to the resonant excitation of localized surface plasmon of silver nanopaticles, and the resonant impulsive stimulated Raman scattering in silver aggregates is responsible for the generation of 1.90 and 3.75 THz coherent phonons.
Activation volume for boron diffusion in silicon and implications for strained films
Authors: Zhao Yuechao , Aziz Michael J. , Gossmann Hans-J. , Mitha Salman , Schiferl David
Published: July 2002

The diffusivity of B in Si is enhanced by pressure, characterized by an activation volume of V*=−0.17±0.01 times the atomic volume; V* is close to the formation volume of the self-interstitial determined by atomistic calculations. The results for hydrostatic pressure are used to make predictions for the effect of biaxial strain on diffusion. Assuming an interstitial-based mechanism and a range of values for the anisotropy in the migration volume, comparison is made between our results, the atomistic calculations, and the measured dependence of B diffusion on biaxial strain. We find a qualitative consistency for an interstitial-based mechanism with the measured strain effect on diffusion in Si–Ge alloys, but not with the measured strain effect in pure Si. Experiments and calculations to determine the origin of this discrepancy are discussed.
Molecular-beam epitaxial regrowth on oxygen-implanted GaAs substrates for device integration
Authors: Chen C. L. , Mahoney L. J. , Calawa S. D. , Molvar K. M. , Maki P. A. , Mathews R. H. , Sage J. P. , Sollner T. C. L. G.
Published: July 2002

Device-quality layers were regrown on GaAs wafers by molecular-beam epitaxy over conductive pregrown areas and on selectively patterned high-resistivity areas formed by oxygen implantation. The regrowth over both areas resulted in comparable device-quality GaAs. The high resistivity of the oxygen-implanted area was maintained after the regrowth and no oxygen incorporation was observed in the regrown layer. The cutoff frequency of a 1.5-μm-gate metal-semiconductor field-effect transistor fabricated on the regrown layer over the high-resistivity areas is 7 GHz. This demonstration shows that planar technology can be used in epitaxial regrowth, simplifying the integration of vastly different devices into monolithic circuits.
Monte Carlo simulation of reentrant reflection high-energy electron diffraction intensity oscillation observed during low-temperature GaAs growth
Authors: Yasuda Haruyuki , Ohno Hideo
Published: July 2002

Reentrant behavior of intensity oscillation of reflection high-energy electron diffraction (RHEED) observed during low-temperature GaAs homoepitaxy on GaAs (001) substrates is studied by a Monte Carlo simulation using cubic solid-on-solid configuration. By assuming that an excess As overlayer acts as surfactant which enhances the migration of Ga adatoms at low temperature, temperature as well as V/III ratio dependence of step density oscillation (i.e., RHEED intensity oscillation) is successfully reproduced.
Observation of Tomasch oscillations and tunneling-like behavior in oxygen-deficient edge junctions
Authors: Nesher O. , Koren G.
Published: July 2002

Properties of oxygen-deficient edge junctions made of YBa2Cu3O6.6 as the superconductor and YBa2Cu3−xFexOy as the barrier are reported. These junctions show weak-link characteristics when the edge angle is 50°, while tunneling-like behavior is observed when the edge angle is 36°. In all junctions strong peaks in the conductivity are found, which depend on the specific junction geometry. Some series of peaks were identified as due to Tomasch oscillations in the cover electrode, which yield Δ=1.4±0.2 meV and vF′=(4.4±0.2)×107 cm/s.
Dual function hybrid polymer-nanoparticle devices
Authors: Narayan K. S. , Manoj A. G. , Nanda J. , Sarma D. D.
Published: July 2002

Dual properties of photoconduction and electroluminescence (EL) in hybrid devices consisting of a nanocluster semiconductor layer and a polymer are reported. It is observed that the photocurrent spectral response and efficiency in these multilayer devices are similar to that of the semiconductor component, while the EL spectral responses are closer to that of the polymer layer. The results are confirmed using the nanoparticle semiconductor, cadmium sulphide CdS, of different particle sizes and polymers representing a wide spectral range. A general feature of efficient photocurrent spectral response corresponding to nanoparticle and an appreciable EL response corresponding more to the active polymer are observed in all devices and results in wide, separated spectral windows. Current–voltage responses also indicate possibilities of added tunability in these devices.
Power rise in broad-waveguide diode laser with inclined facet
Authors: Kostko Irina A. , Evtikhiev Vadim P. , Kotelnikov Eugeny Yu. , Zegrya Georgy G.
Published: July 2002

A method of transverse mode selection in high-power broad-waveguide separate confinement heterostructure quantum-well lasers by placing the front mirror at the angle other than the normal to the radiation propagation direction is proposed. Optimal values of facet inclination angles and widths and the refractive indices of the dielectric coating at which the fundamental guided mode dominates are found. The possibility of increasing the output power 1.2 times of a broad-waveguide separate confinement heterostructure quantum-well diode laser with inclined facet is shown.
Spatially resolved dopant profiling of patterned Si wafers by bias-applied phase-imaging tapping-mode atomic force microscopy
Authors: Nelson M. W. , Schroeder P. G. , Schlaf R. , Parkinson B. A. , Almgren C. W. , Erickson A. N.
Published: July 2002

Tapping-mode atomic force microscopy was used to spatially resolve areas of different doping types on Si wafers patterned by photolithography and subsequent ion implantation. Application of a direct current dc bias between cantilever and sample during measurement induced a change in the tapping-mode phase contrast depending on the dopant type of the scanned sample area. This allowed the direct identification of areas of different doping types. Additional measurements on Au samples demonstrate a direct correlation between bias-induced Coulomb force and resulting phase change allowing the conclusion that the observed phase contrast results from dc bias-induced band bending changes.
Periodic poling of RbTiOPO4 for quasi-phase matched blue light generation
Authors: Karlsson H. , Laurell F. , Cheng L. K.
Published: July 2002

RbTiOPO 4 has been periodically poled for first-order quasi-phase matching. The poling was monitored using a technique based on the electro-optic effect, which enabled fabrication of high-quality domain gratings for efficient frequency doubling to the blue.
Effect of Be doping on the absorption of InGaAs/AlGaAs strained quantum-well infrared photodetectors grown by molecular-beam epitaxy
Authors: Zhang D. H. , Shi W. , Zhang P. H. , Yoon S. F. , Shi X.
Published: July 2002

We report on the effect of Be doping in the well layers on the absorption of the p-type strained InGaAs/AlGaAs quantum-well infrared photodetectors. It is found that the absorption spectrum originated from the bound-to-bound intersubband transition shifts towards the low-wavelength side as the doping density is increased, due to the band gap shrinkage and widened well width. The full width at half maximum of the absorption spectrum increases with doping density due mainly to the increased roughness at the well–barrier interfaces. The observed results are in good agreement with the estimated values after taking the compressive strain, band gap shrinkage of the well layers, and the increased well width into account.
Observation of change in shape of oxygen precipitates in high-temperature annealed silicon by transmission electron microscopy
Authors: Sakai K. , Yamagami T. , Ojima K.
Published: July 2002

Changes in size and shape of oxygen precipitates in Czochralski silicon after high-temperature annealing in an Ar atmosphere were observed using a transmission electron microscopy. The oxide precipitates introduced by 750 °C after 4 h annealing in an Ar atmosphere had their corners rounded off by thermal annealing at 1200 °C, and disappeared by 1300 °C although we observed no change in shape at 1050 °C.
Scaling laws in annealed LiCoOx films
Authors: Kleinke M. U. , Davalos J. , Polo da Fonseca C. , Gorenstein A.
Published: July 2002

The surface morphology evolution due to the annealing process of LiCoOx thin films deposited by rf sputtering is studied by means of an atomic force microscope. Linear relationships were observed in log–log plots of interface width versus window length, as predicted by scaling laws. For as-grown films, only one growth exponent α is evidenced. For annealed films two different slopes α1 and α2 were observed, indicating distinct growth dynamics in the system. The roughness exponent for the as-grown film and the internal morphology of the crystalline grains for the annealed films can be described by a diffusional process. The macrostructure shows characteristics of a Kardar–Parisi–Zhang system [M. Kardar, G. Parisi, Y. C. Zhang, Phys. Rev. Lett. 56, 889 (1986); J. Krim and G. Palasantzas, Int. J. Mod. Phys. B 9, 599 (1995)]. An activation energy Ed=(0.11±0.01) eV is determined for the diffusion process.
Thermal effect on current gains of an AlGaAs/GaAs heterostructure-emitter bipolar transistor
Authors: Lo H. B. , Yang E. S. , Yang Y. F.
Published: July 2002

The temperature effect on current gains is presented for an AlGaAs/GaAs heterostructure-emitter bipolar transistor (HEBT). Experimental results show that the HEBT has much less temperature sensitivity in current gain than a heterojunction bipolar transistor. The current gains for the HEBT are almost constant with the substrate temperature at a high current regime. This indicates that the HEBT could be a good candidate for power applications.
Epitaxial growth of magnetoresistive (00h), (0hh), and (hhh) La2/3Sr1/3MnO3 thin films on (001)Si substrates
Authors: Fontcuberta J. , Bibes M. , Martínez B. , Trtik V. , Ferrater C. , Sánchez F. , Varela M.
Published: July 2002

We show that suitable choice of the buffer heterostructure allows us to obtain epitaxial (00h), (0hh), and (hhh) La2/3Sr1/3MnO3 thin films on buffered Si(001) substrates. The magnetotransport properties are investigated. Irrespective of the film texture, it is found that the easy-magnetization direction lies within the film plane. The low-field magnetoresistance is mainly controlled by the in-plane misorientation of crystallites while differences associated with the distinct microstructure of the interfaces appear to have only a second-order effect.
Width dependence of giant magnetoresistance in Cu/Co multilayer nanowires
Authors: Katine J. A. , Palanisami A. , Buhrman R. A.
Published: July 2002

Electron beam lithography and ion milling have been used to pattern sputtered Cu/Co multilayer wires ranging in width from 750 to 35 nm. Samples having Cu thicknesses which correspond to the first, second, and third antiferromagnetic coupling maxima have been measured. Contrary to expectation, enhancement in the amplitude of the giant magnetoresistance with decreasing width was not observed.
Acoustic scattering of impulsive geometrical waves by a glass sphere in water
Authors: Latard V. , Merlen A. , Preobazhenski V. , Ahyi A. C.
Published: July 2002

An elastic sphere is acoustically excited in water by a punctual pulse source. A high-speed visualization system allows the identification of the geometrical waves diffused in the fluid. The visualization results are correlated with a time space representation of pressure measurements in the fluid and with a numerical simulation. The experimental technique presented here allows a very accurate description of the acoustic diffusion on elastic bodies even for ultrasonic frequencies.
Light-induced mobility enhancement in delta-doped GaAs/In0.26Ga0.74As/GaAs quantum wells grown by molecular beam epitaxy on GaAs(001)
Authors: Zervos M. , Elliott M. , Westwood D. I.
Published: July 2002

We have studied persistent photoconductivity in 80 Å strained GaAs/In0.26Ga0.74As/GaAs quantum wells grown by molecular beam epitaxy at 480 °C by measuring the Shubnikov de Haas and Hall effects at 4.2 K. Each quantum well was δ doped with Si to 2×1012 cm−2 either (i) at the center of the quantum well, (ii) at the lower interface, or (iii) the bottom barrier. The free-carrier density after exposure to 654 nm red light with above-band-gap energy did not exceed significantly the intended δ-doping level, but the Hall mobility increased dramatically and was accompanied by stronger Shubnikov de Haas oscillations. We attribute this to electron–hole pair generation and separation and/or the photoionization of deep states, which create a positive space charge in the surface depletion region. This leads to electrostatic bandbending, which converts the quantum well from being asymmetric in the dark to square-like after illumination and shifts the charge distribution away from the δ layer, improving the mobility. This hypothesis is corroborated by the light insensitivity of both an identical heterostructure δ doped to 2×1012 cm−2 in the top barrier and an equivalent set of heterostructures δ doped with Si to 4.5×1012 cm−2.
Microstructure of epitaxial α-Fe2O3 grains in Ba-ferrite thin films grown on sapphire (001)
Authors: Cho T. S. , Doh S. J. , Je J. H. , Noh D. Y.
Published: July 2002

We revealed the existence of epitaxial α-Fe2O3 grains in Ba-ferrite thin films on sapphire (001) using synchrotron x-ray scattering. The antiferromagnetic α-Fe2O3 grains were formed during the crystallization of amorphous Ba-ferrite films grown on sapphire (001) by radio frequency sputtering deposition. The crystal domain size of the α-Fe2O3 grains was about 250 Å in the film plane, similar to that of the Ba-ferrite grains. The in-plane crystalline axis of the α-Fe2O3 was aligned to that of sapphire, while the Ba-ferrite film was rotated by 30° in the film plane. We confirm that the existence of these antiferromagnetic α-Fe2O3 grains greatly degraded magnetic properties of the Ba-ferrite films.
Strained Si n-channel metal–oxide–semiconductor transistor on relaxed Si1−xGex formed by ion implantation of Ge
Authors: John S. , Ray S. K. , Quinones E. , Banerjee S. K.
Published: July 2002

Ge implantation followed by high-temperature solid phase epitaxy was used to form a relaxed substrate, eliminating need for the growth of relaxed Si1−xGex layers. Upon this film, a 2000 Å buffer layer of Si0.85Ge0.15 followed by a 200 Å strained Si layer was grown by ultrahigh-vacuum chemical vapor deposition. For comparison, unstrained Si epitaxial films and a 2000 Å thick film of Si0.85Ge0.15 (on unimplanted Si) followed by 200 Å of Si were used. n-channel metal–oxide–semiconductor transistors were fabricated and their dc characteristics were examined. Strained Si devices show a 17.5% higher peak linear μFE than control devices as a result of higher electron mobility in the strained Si channel. This work demonstrates a simple method for the formation of strained Si layers.
Identification of two patterns in magnetic force microscopy of shape memory alloys
Authors: Neves B. R. A. , Andrade M. S.
Published: July 2002

In this work, we report on the observation of two coexisting patterns in magnetic force microscopy (MFM) images of shape memory alloys. The MFM signal of both patterns presents similar behavior with tip–surface separation. An investigation on the origin of these patterns presents strong evidence that both are of magnetic nature only and, furthermore, can be assigned as bulk and surface-related, respectively.
Quantitative analysis of the compositional profile of a single quantum well by grazing incidence x-ray reflectivity and photoluminescence
Authors: Moon Youngboo , Yoon Euijoon
Published: July 2002

A quantitative analysis method, using grazing incidence x-ray reflectivity (GIXR) and photoluminescence (PL), was applied to obtain the As profile of an InAsxP1−x/InP single quantum well (SQW) formed by AsH3 exposure of an InP surface. The profile could be uniquely determined by simultaneously matching of GIXR and PL with the observed ones. It was found that the so-called effective thickness model was not appropriate for the description of the As compositional profile at the SQW interface. Moreover, it underestimated the amount of incorporated As at the interface. However, the Gaussian As profile proposed in this study resulted in a quite well-matched GIXR curve with quantitative information on the total As amount and the grading of As at the interface.
High second-order optical nonlinearities in thermally poled sol-gel silica
Authors: Pruneri V. , Bonfrate G. , Kazansky P. G. , Takebe H. , Morinaga K. , Kohno M. , Kuwasaki K. , Takeuchi T.
Published: July 2002

Silica glass samples prepared by a sol-gel process, the mixture of silica sol for gelation and colloidal silica particles, have been thermally poled in vacuum by continuous high voltage (8–12 kV) at elevated temperature (280 °C). High second-order nonlinearities (>1 pm/V), located under the anodic surface, have been measured and the values are higher than those obtained in fused silica glass, poled under the same conditions. A model for thermal poling is suggested which explains the experimental results in sol-gel silica and the difference between thermal poling of sol-gel and fused silica. The granular structure and the boundaries of sol-gel silica seem to play a major role in establishing the electrical properties of the depletion layer during and after poling.
Optical characterization of visible multiquantum-well semiconductor lasers by collection/excitation modes of scanning near-field optical microscopy
Authors: Lu N. H. , Tsai Din Ping , Chang C. S. , Tsong T. T.
Published: July 2002

Both collection and excitation modes of scanning near-field optical microscopy were used to study a strained AlGaInP/Ga0.4In0.6P low power visible multiquantum-well laser diode. Collection and excitation modes provide the near-field optical propagating intensity distribution and local photoconductivity information, respectively, at the facet of laser diode. Results show highly localized spatial correlation of the laser diode structure and its optical performance at the facet. Defect level in the energy range of 60–380 meV below the conduction band in the highly n-doped (Al0.7Ga0.3)0.5In0.5P cladding layer was found by the excitation mode using the wavelengths of 543.5 and 632.8 nm. Spatially resolved near-field optical spectra of both stimulated and spontaneous emissions were acquired as well. Longitudinal modes of the stimulated emission of laser diode were observed locally.
Magnetic detection of photogenerated currents in semiconductor wafers using superconducting quantum interference devices
Authors: Beyer J. , Matz H. , Drung D. , Schurig Th.
Published: July 2002

A completely noninvasive method is presented for the investigation of semiconductor wafers with high spatial resolution utilizing a superconducting quantum interference device (SQUID) magnetometer system. The method is based on the detection of the magnetic field caused by photocurrents generated in the semiconductor sample using a sensitive SQUID magnetometer. The photocurrents arise when laser light with a photon energy exceeding the band gap of the semiconductor is focused onto the sample surface in a region of a doping gradient. The spatial resolution of this detection method is mainly determined by the size of the excitation focus of about 20 μm. We report on measurements of silicon wafers with small growth-related doping fluctuations.
Small-signal gain and iodine dissociation in a supersonic chemical oxygen–iodine laser with transonic injection of iodine
Authors: Furman D. , Bruins E. , Barmashenko B. D. , Rosenwaks S.
Published: July 2002

Measurements of the gain and temperature in the resonator of a supersonic chemical oxygen–iodine laser (COIL) with transonic injection of I2, using diode laser-based diagnostics, are reported. For conditions corresponding to the maximum chemical efficiency of this type of COIL (11.7 mmole/s of chlorine, no primary buffer gas, and 1.36 mmole/s of the secondary N2), the gain is a nonmonotonous function of the iodine flow rate. Maximum gain of 0.34%/cm is achieved for an iodine flow rate of 0.27 mmole/s. An analytical method is developed which enables the use of these dependencies for calculation of the iodine dissociation fraction F and the number N of O2(1Δ) molecules lost in the region of iodine dissociation per I2 molecule. It is found that F is a nonmonotonous function of the iodine flow rate, its maximum value being small (0.55).
Thermomechanical stress analysis of laminated thick-film multilayer substrates
Authors: Kim Jin S. , Paik Kyung W. , Lim Ji H. , Earmme Youn Y.
Published: July 2002

As an increasing number of polymer dielectric layers were laminated, the maximum bow values were measured layer by layer using a laser profilometry during thermal cycling. In the lamination process, a polymeric film is overlaid on a silicon substrate using a polymeric adhesive. Since the lamination process uses relatively thick polymer films, the classical stress analyses assuming infinitesimally thin films, are no longer effective. In this letter, a simple model based on the composite beam theory is presented to analyze the experimental results, and compared with the well-known Stoney’s formula. The thermomechanical behavior of the laminated multilayer polymer films on a silicon substrate was better described by the proposed model, while an error as much as 30% was involved using Stoney’s formula. The model can be applied for the design and fabrication of multilayer multichip module substrates.
Low-resistance visible wavelength distributed Bragg reflectors using small energy band offset heterojunctions
Authors: Fastenau J. M. , Robinson G. Y.
Published: July 2002

Semiconductor alloy heterojunctions, with compositions selected to achieve small band offset energies, were used in distributed Bragg reflector (DBR) structures for the purpose of lowering the vertical series resistance. The heterojunctions were simple abrupt interfaces without composition grading. 40 period mirrors of AlGaInP/Al(Ga)As layer pairs were grown by gas-source molecular beam epitaxy. Mirror reflectance values were found to be greater than 99% at wavelengths near 650 nm. Measured specific resistance values, 2.8×10−4 Ω cm2 for a p-type DBR and 2.6×10−5 Ω cm2 for a n-type DBR, were comparable to or better than (Al)GaAs/Al(Ga)As DBRs employing various graded interface composition designs.
Secondary electron energy spectra emitted from radio frequency biased plasma electrodes
Authors: Shaw D. M. , Watanabe M. , Uchiyama H. , Collins G. J.
Published: July 2002

The ion-induced secondary electron energy spectra from a radio frequency biased (13.56 MHz) electrically insulating (Al2O3) plasma electrode surface immersed in a separately powered inductively coupled plasma are studied both experimentally and theoretically. Radio frequency (rf) electrode bias voltages of 140 and 285 V (peak to ground) are employed and the complete electron energy spectra emitted from the electrode and accelerated by the rf sheath are measured 14 cm from the rf biased electrode using a differentially pumped retarding potential analyzer. A collisionless radio frequency Child–Langmuir sheath model is used to explain the experimentally measured electron energy spectra.
Electronic states at conducting polymer/conducting oxide interfaces observed using a low-energy photoelectron spectroscopic method
Authors: Nakanishi Naoki , Tada Kazuya , Onoda Mitsuyoshi , Nakayama Hiroshi
Published: July 2002

We have observed the electronic states at conducting polymer/conducting oxide interfaces using a low-energy photoelectron spectroscopic method. The electronic states of conducting polymer/indium tin oxide (ITO) interfaces were different from those of conducting polymer/metal interfaces. The electron transfer from a conducting polymer to ITO occurred at the interfaces, and is not related to the difference of the ionization potential between conducting polymers and ITO. Although the origin of this electron transfer is not clear at this stage, we speculate that the surface states of ITO play a major role. Moreover, the electron transfer at the interfaces is enhanced at higher temperatures. Other conducting oxides such as indium oxide (In2O3) and tin oxide (SnO2) also show a similar tendency to that of ITO.
Hydrogen cleaning and smoothing of semiconductor surfaces: The case of II–VI compounds
Authors: Picard E. , Gentile P. , Martrou D. , Magnea N.
Published: July 2002

Hydrogen radicals produced by a dc plasma cell have been used for cleaning II–VI semiconductor substrates for molecular beam epitaxy. Surface and chemical analysis experiments, including scanning tunneling microscopy, show a clear improvement of the chemical purity and morphology of the surface prior and after epitaxial growth.
Nonlinear electron transport in magnetic multilayers
Authors: Aliev F. G. , Schad R. , Lobotka P. , Vavra I. , Seynaeve E. , Moshchalkov V. V. , Bruynseraede Y.
Published: July 2002

We report on measurements of the second harmonics in the magnetovoltage generated in [Fe(12 Å)/Cr(12 Å)]10 epitaxial multilayers. It is shown that the variation of the amplitude of the second-harmonic signal with magnetic field is up to three times larger compared to the first harmonic. The enhanced “magnetovoltage” second-harmonic effect may be of practical use in systems based on spin electronic phenomena.
Low-temperature anodic oxidation of silicon using a wave resonance plasma source
Authors: Uchikoga S. , Lai D. F. , Robertson J. , Milne W. I. , Hatzopoulos N. , Yankov R. A. , Weiler M.
Published: July 2002

A rf wave resonance plasma (WARP) source has been used to plasma oxidize Si at temperatures below 100 °C. Oxidation under positive substrate bias in constant current mode gives an oxidation rate of 1–8 nm/min for current densities of 0.4–5.5 mA/cm2. This corresponds to an ionic (O−) current of about 10% of the total current, which is 2–5 times higher than previously reported, due to the high plasma density of 1012–1013 cm−3 achieved by the WARP source. The breakdown field of ∼10 MV/cm and the etch rate of 60 nm/min of the oxide are independent of the oxidation rate and similar to those of the thermal oxide. Results from capacitance–voltage measurements, Fourier transform infrared absorbance spectroscopy, null ellipsometry, and Rutherford backscattering spectroscopy suggest that the oxide grown at low rates (<2 nm/min) is very close to stoichiometric SiO2 while the oxide grown at high rates (>3 nm/min) is Si rich (35%–40% atomic Si).
Low-energy electron microscopy observations of GaN homoepitaxy using a supersonic jet source
Authors: Pavlovska A. , Torres V. M. , Bauer E. , Doak R. B. , Tsong I. S. T. , Thomson D. B. , Davis R. F.
Published: July 2002

A study of the homoepitaxial growth of GaN(0001) layers was conducted in situ and in real time using the low-energy electron microscope. The Ga flux was supplied by an evaporative cell while the NH3 flux was supplied via a seeded-beam supersonic jet source. At growth temperatures of 665 °C and 677 °C, smooth GaN(0001) layers with well-defined step structures were grown on GaN(0001) substrates prepared by metalorganic chemical vapor deposition. In general, nonfaceted homoepitaxial layers were achieved when the Ga/NH3 flux ratios exceeded 2, starting with a Ga-covered substrate surface, in the temperature range of 655–710 °C.
Effects of cobalt silicidation and postannealing on void defects at the sidewall spacer edge of metal–oxide–silicon field-effect transistors
Authors: Kim Yeong-Cheol , Kim Jongchae , Choy Jun-Ho , Park Ju-Chul , Choi Hong-Min
Published: July 2002

The void formation at the edge of the sidewall spacer during postannealing is favorable in reducing both the number of excess silicon vacancies generated in the silicon substrate during silicidation, and the tensile stress concentrated at the edge of the metal-oxide-silicon field-effect transistor (MOSFET) sidewall spacer. The observation of void growth with the postannealing time supports this hypothesis. The observed void shape agrees well with a numerical simulation driven by the minimization of the interfacial free energy. The void serves as a resistance in the current–voltage characteristics of MOSFET devices.
Radio frequency discharge excited diffusively cooled kilowatt carbon monoxide slab waveguide laser with a three mirror resonator
Authors: Xin Jianguo , Zhang Wang , Jiao Wentao
Published: July 2002

In this letter, we describe a kilowatt radio frequency discharge excited diffusively cooled slab waveguide carbon monoxide laser, in which the top and bottom electrodes were cooled with liquid nitrogen and which utilized a modified resonator. With this design we obtained a maximum laser power output of 1020 W, which was 10% higher than the same device employing a conventional unstable resonator.
Electron transport in AlGaInP quantum well lasers
Authors: Wood S. A. , Molloy C. H. , Smowton P. M. , Blood P. , Somerford D. J. , Button C. C.
Published: July 2002

By placing a direct-gap monitor layer (or collector) in the p-cladding layer of red-emitting AlGaInP laser diode structures, we have studied the transport of electrons through this layer by observation of spontaneous emission. Pulsed optical excitation superimposed on cw electrical injection has been used to determine the delay time between optical injection of carriers into the well and radiative recombination from the monitor pit. Computer simulations using measured values of minority carrier lifetime for the well and monitor layer show that the transit time for electrons through the p-cladding layer correspond to an electron mobility of 160 cm2/V s.
Radio-frequency SQUID effect due to natural grain-boundary junctions in ErNi2B2C and DyNi2B2C magnetic borocarbide superconductors
Authors: Khare Neeraj , Gupta A. K. , Hossain Z. , Nagarajan R. , Gupta L. C.
Published: July 2002

This letter reports the observation of rf superconducting quantum interference device (SQUID) effects due to natural grain-boundary junctions in ErNi2B2C (TC≈11.5 K, TN≈6.5 K) and DyNi2B2C (TC≈6.5 K, TN≈11 K) bulk borocarbide magnetic superconductors. Voltage–flux SQUID modulations have been observed up to 10 and 5.7 K in ErNi2B2C and DyNi2B2C, respectively. The amplitude of voltage–flux modulations in ErNi2B2C shows a sharp change around 6 K, which has been attributed to the occurrence of magnetic ordering in ErNi2B2C. Such a change is not observed in DyNi2B2C rf SQUID since, in this case, TC<TN. The flux noise density at 4.2 K of these SQUIDs shows a frequency-independent white-noise region down to 1 Hz. A rapid increase in flux noise has been observed in both cases as temperature approaches TC.
Electron microscopy and nanolithography with an integrated low-energy electron beam
Authors: Zlatkin A. , Garcı́a N.
Published: July 2002

We present nanolithographic lines written with a low-energy (300 eV) electron optical system integrated in a microfabricated planar lens. The system is a versatile tool to operate: the lens reaches a resolution of 30 nm in electron microscopy mode, and in lithography mode the written pattern demonstrates a linewidth of less than 100 nm. Successful writing into polymethyl methacrylate and into sensitive chemically amplified resist has been performed. The generalization and advantages of the integrated microlens for high-throughput multibeam lithography is also discussed in comparison with standard electron-beam columns.
Magneto-optical Kerr effect study of the polymorphic crystallization of thin Fe100−xZrx films
Authors: Herr U. , Ippach H. , Samwer K.
Published: July 2002

Thin films of Fe100−xZrx with 0<x<7 at. % condensed on top of a Zr layer at room temperature grow in an amorphous phase up to a critical thickness dc, beyond which polymorphic crystallization of the initially amorphous film sets in. The crystallization is accompanied by a magnetic transition from a paramagnetic amorphous state to a ferromagnetic crystalline state. We report magneto-optical Kerr effect studies on the crystallization of Fe100−xZrx films. In situ measurements, made during the growth of the films, show that the transformation is completed on a time scale of seconds and seems to be limited only by the available excess driving force.
Fabrication of ohmic contacts to buried diamond layers using Pt layer in the diamond chemical-vapor-deposition process
Authors: Wang Chunlei , Ito Toshimichi
Published: July 2002

Electrical contacts to a buried chemical-vapor-deposited (CVD) diamond layer can be accomplished using a process in which Pt columns automatically grow from the buried layer to the diamond surface by diamond overgrown on a thin Pt film. Hall effect measurements were employed in a temperature region from room temperature to 450 °C to investigate and compare transport properties of a buried B-doped homoepitaxial diamond film with such Pt column electrodes before and after the overgrowth of the upper layer. A useful ohmic contact to the B-doped CVD diamond interlayer was formed by this type of buried electrodes.
Atomic order, electron structure, and critical parameters of epitaxial YBaCuO films
Authors: Okunev V. D. , Samoilenko Z. A. , Abal’oshev A. , Gierłowski P. , Klimov A. , Lewandowski S. J.
Published: July 2002

X-ray structural and optical methods were applied to make a detailed investigation of atomic and electronic structure of superconducting YBa2Cu3O7−δ films obtained by pulsed laser deposition. Optical transmission spectrum was found to depend not only on intraband (ℏω<1.2 eV) and interband (ℏω>1.95 eV) transitions, but also on contributions from charge transfer transitions O 2p⇒Cu 3d in the dielectric phase due to local order in a system of crystallographic (11l) planes. Superconducting properties of the films are determined by orientational structural transition (00l)+(11l)⇒(00l) and by Anderson type transition from a charge transfer O 2p⇒Cu 3d insulator to a strongly degenerate semiconductor with metallic conductivity. We show the effects of ordering on transition temperature Tc and demonstrate that at the concentration of (00l) clusters below the percolation threshold (20%) the behavior of Tc has catastrophic character.
Magneto-mechanical rotation of magnetostrictive amorphous wires
Authors: Castaño F. J. , Vázquez M. , Chen D.-X. , Tena M. , Prados C. , Pina E. , Hernando A. , Rivero G.
Published: July 2002

The mechanical rotation of both positive (FeSiB) and negative (CoSiB) magnetostrictive rapidly quenched amorphous wires, when submitted to an alternating axial magnetic field (Hac) with a frequency of a few kHz, has been investigated. Hac was varied from a few A/m to around 21 kA/m and a laser-based method was implemented to accurately determine the wire rotation frequencies. The appearance of such effect was found to be directly related with both the magnetostrictive nature of these materials and the diameter of the inner tube of the alternating current coil, φ, in which the wires were placed. A dynamical equilibrium of the effect of rotation was only reached for small values of φ. Different frictional arrangements yielded modifications of the spectrum obtained on plotting exciting frequency versus wire rotation frequency (typically several tens of Hz). When rotation started, a directionally controlled axial direct current magnetic field was applied, which eventually made the wires stop rotating. According to our experimental results and observations the initial torque, which yields the mechanical rotation of these wires, would be originated on adding the force asserted by a magnetoelastic wave and the friction force.
Substitutional carbon reduction in SiGeC alloys grown by rapid thermal chemical vapor deposition
Authors: Liu C. W. , Tseng Y. D. , Huang Y. S.
Published: July 2002

The substitutional carbon reduction in Si1−x−yGexCy strained layers, annealed at high temperatures, increases the compressive strain in the originally strain-compensated alloys. From the rocking curve simulation, the maximum amount of carbon reduction was below 0.9% for the various samples which were annealed below 1000 °C in the nitrogen flow. The interstitial silicon injection by thermal oxidation of the Si cap on the Si1−x−yGexCy layer enhances the reduction of substitutional carbon to a concentration of 1.3%. Oxidation of Si1−x−yGexCy alloys yields a Ge-enriched Si1−xGex layer with the Ge concentration larger than the initial content, and the formation of 3C silicon carbide precipitate is observed by the Fourier transform infrared spectroscopy.
Violet/blue light-emitting cerium silicates
Authors: Choi Won Chel , Lee Ho Nyung , Kim Eun Kyu , Kim Yong , Park Chong-Yun , Kim Hong Seung , Lee Jeong Yong
Published: July 2002

We observed violet/blue light emitted from cerium silicates which may be useful for silicon-based optoelectronics. The cerium silicate was produced during a rapid thermal annealing at high temperature (>1100 °C) from the interface between silicon substrate and cerium oxide film. Detailed experiments including x-ray diffraction, high-resolution transmission electron microscope, and Auger depth profiling showed that the cerium silicate consists of Ce4.667(SiO4)3O and Ce2Si2O7 phases. The photoluminescence of the cerium silicate is very strong at room temperature. Specifically, the 358 nm luminescence line is attributed to the Ce2Si2O7 phase.
Generation of 290 fs laser pulses by self-seeding and soliton compression
Authors: Huhse D. , Reimann O. , Böttcher E. H. , Bimberg D.
Published: July 2002

Self-seeding with subsequent chirp compensation presents a simple way to generate pulses of a few picoseconds width tunable over more than 30 nm. Further compression of the laser pulses exploiting nonlinear effects in optical fibers (soliton compression) allows the generation of laser pulses with a full width at half maximum of less than 300 fs. Application of these pulses in an electro-optical sampling system is demonstrated.
Nanoscale structure and chemistry of Al0.49In0.51P thermal oxide
Authors: Mathes D. T. , Hull R. , Dupuis R. D. , Heller R. D. , Tinkham B. P.
Published: July 2002

In this letter, the nanoscale structure and chemistry of the III–V thermal oxide formed from Al0.49In0.51P is described. Transmission electron microscopy studies have shown that the oxide is an amorphous compound, which occupies greater volume than the original unoxidized crystalline Al0.49In0.51P layer, and which contains O, Al, In, and P (i.e., none of the species are completely desorbed during the oxidation reaction). Electron energy loss spectroscopy and energy spectroscopic imaging have shown specifically that the oxidation products include Al2O3 and In2O3 and P, either as an oxide or in some other amorphous compound.
Separation of a single cell by red-laser manipulation
Authors: Shikano Shuji , Horio Koji , Ohtsuka Yoshihiro , Eto Yuzuro
Published: July 2002

A single cell of yeast was separated from a bulk sample of yeast without causing damage to the cell. A focused red-laser light beam was used for trapping and transporting the cell. A specially designed microchannel separator played an essential role in the success of the separation.
Efficient polarization insensitive four-wave mixing using a semiconductor optical amplifier and one pump source in an optical loop
Authors: Tang J. M. , Spencer P. S. , Shore K. A.
Published: July 2002

An improved scheme for polarization insensitive four-wave mixing in semiconductor optical amplifiers (SOAs) is proposed, utilizing just one polarization insensitive SOA and one input pump wave, and without compromising the achievable conjugate power compared with that obtained from a conventional dual-pump co-propagating configuration. For frequency detuning larger than ∼300 GHz for a device length of say 500 μm, polarization sensitivity less than ∼0.8 dB can be obtained.
Effects of disorder on the optical gap of (Zn,Mg)(S,Se)
Authors: Saitta Antonino Marco , de Gironcoli Stefano , Baroni Stefano
Published: July 2002

The electronic properties and optical gap of (Zn,Mg)(S,Se) wide-gap solid solutions are studied using ab initio techniques and starting from the previously determined atomistic structure of the alloy. Compositional disorder is shown to close the gap substantially with respect to the predictions of the virtual-crystal approximation. The bowing of the fundamental gap versus composition predicted by our calculations is in very good agreement with experiments available for the Zn(S,Se) pseudobinary alloy. At temperatures typical of molecular-beam epitaxy growth, the quaternary alloy displays a rather large amount of short-range order whose effect is to slightly but unmistakably open the gap. Our results agree well with recent experimental data for the quaternary alloy.