bluuebunny/crossref_metadata_2025 huggingface dataset:
Optometric correlates of Meares–Irlen Syndrome: a matched group study
Authors: Evans Bruce J. W. , Busby Anne , Jeanes Rebecca , Wilkins Arnold J.
Published: July 2002

People who report visual perceptual distortions, typically when reading, that are alleviated by using coloured filters are described as suffering from ‘Meares–Irlen Syndrome’. A recent double‐masked placebo‐controlled trial showed that this condition cannot be solely explained as a placebo effect and that the beneficial filter is idiosyncratic and sometimes needs to be highly specific. Several mechanisms have been suggested for Meares–Irlen Syndrome including ocular motor (binocular and accommodative) anomalies, a sensitivity to patterned stimuli (pattern glare), and a deficit of the transient visual sub‐system. We investigated these hypotheses by comparing 16 children, who reported the symptoms described above and who showed a sustained benefit from coloured filters, with 25 control children who came from the same school and were matched for age, reading performance and intelligence. The ‘Meares–Irlen Syndrome’ group had slightly, but significantly, reduced vergence and accommodative amplitudes and stereo‐acuity; they also demonstrated significantly more pattern glare. The two groups did not differ significantly in their visual acuities, refractive error, dissociated or associated heterophoria, AC/A ratio, or ability to perceive 20 Hz flicker. It appears that certain ocular motor factors are correlates of Meares–Irlen Syndrome, rather than the primary underlying cause of the symptoms. The results support the hypothesis that pattern glare may be involved in the mechanism of Meares–Irlen Syndrome.
Adaptation model of nearwork‐induced transient myopia
Authors: Hung George K. , Ciuffreda Kenneth J.
Published: July 2002

A nearwork model was developed to determine whether variation in accommodative adaptation gain, KA, can account for the differences in the dynamic decay timecourse following near work in hyperopes (HYP), emmetropes (EMM), early‐onset myopes (EOM), and late‐onset myopes (LOM). The model incorporated a proximal component into a previously‐developed adaptation model of accommodation and vergence. It was used to simulate the nearwork‐induced transient myopia (NITM) response following 10 min of congruent binocular near viewing (5 D, 5 MA). The accommodative adaptation gain, KA, value was varied from 1.0 to 6.0 in increments of 0.5. For the hyperopes, an additional constraint was imposed wherein the accommodative response was biased on the under‐accommodated side of the deadspace operator (i.e., depth‐of‐focus). In addition, the effect of prolonged nearwork was simulated by alternating between 1 hr of congruent near viewing (3 D, 3 MA) and 5 min of congruent far viewing (0.25 D, 0.25 MA) over a 160 hr period representing one work‐month with 40 hours of nearwork per week. The steady‐state rms value of the accommodative error was measured as a function of KA. It was found that the NITM timecourses for HYP, EMM, EOM, and LOM could be simulated accurately using KA values of 2.0, 2.5, 4.0 and 5.5, respectively. The long‐term final steady‐state rms of the accommodative error was found to increase from 0.182 D to 0.188 D as KA increased from 1 to 6. This indicated a small and progressive increase in residual accommodative error for higher KA values, which was associated with EOM and LOM. Thus, NITM for the different refractive groups could be quantified by the accommodative adaptation gain element, with KA for the HYP, EMM, and EOM and LOM groups having lower, intermediate, and higher values, respectively. The larger rms for higher KA values suggests that a myopic individual may have a predisposition to exhibit a slightly larger long‐term accommodative error, which may stimulate axial elongation and in turn promote the progression of axial myopia.
Ecophysiology of Virus‐Infected Plants: A Case Study of Eupatorium makinoi Infected by Geminivirus
Authors: Funayama‐Noguchi S.
Published: July 2002

Abstract: Plant viruses are prevalent in wild plants. However, few studies have been conducted on virus infection in natural plant communities. This paper describes a series of our studies on the Eupatorium makinoi‐geminivirus system in order to consider the role of plant viruses in natural plant communities. Eupatorium makinoi is a short‐lived perennial, which is widely distributed in Japan. Variegated E. makinoi plants caused by geminivirus infection are prevalent in the field. After a virus epidemic in a local E. makinoi population, the number of plants declined and, consequently, the local population nearly became extinct. Inferior performances of virus‐infected plants were attributed to impaired photosynthesis. Photosynthetic rates of virus‐infected leaves were especially lowered under low irradiance. This decrease was caused by a loss of chlorophyll (Chl) proteins, particularly light‐harvesting chlorophyll a/b binding proteins associated with photosystem II (LHCII). The preferential loss of LHCII was caused by a decrease in the activity of Chl synthesis. These studies demonstrate that geminiviruses play an important role in determining fitness of E. makinoi plants and clarify the physiological mechanism of the decrease in fitness of virus‐infected E. makinoi. Lowered fitness of E. makinoi by the infection would underlie the population dynamics observed in the field. Thus, virus infection is one of the most important biotic factors that affect various ecological and evolutionary phenomena in natural ecosystems.
Elimination of pressure-induced fluorescence in diamond anvils
Authors: Eggert Jon H. , Goettel Kenneth A. , Silvera Isaac F.
Published: July 2002

At pressures above one megabar (100 GPa) in high-pressure diamond anvil cell experiments the ruby fluorescence signal needed for pressure calibration is increasingly difficult to measure. A primary cause of this difficulty is the presence of an intense pressure-induced diamond fluorescence. We give a tentative identification of this pressure-induced fluorescence and report on a technique for the elimination of this fluorescence. We demonstrate that weak ruby signals, completely hidden by diamond fluorescence, are now easily measured with our technique.
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u epitaxial growth of Y1Ba2Cu3O7−x films by molecular beam epitaxy with an activated oxygen source
Authors: Kwo J. , Hong M. , Trevor D. J. , Fleming R. M. , White A. E. , Farrow R. C. , Kortan A. R. , Short K. T.
Published: July 2002

Highly oriented, epitaxial Y1Ba2Cu3O7−x thin films were prepared on MgO(100) by molecular beam epitaxy at a substrate temperature of 550–600 °C. The in situ growth was achieved by incorporating reactive oxygen species produced by a remote microwave plasma in a flow-tube reactor. The epitaxial (001) orientation is demonstrated by x-ray diffraction and ion channeling. In situ reflection high-energy electron diffraction showed that a layer-by-layer growth has produced a well-ordered, atomically smooth surface in the as-grown tetragonal phase of an oxygen stoichiometry of 6.2–6.3. A 500 °C anneal in 1 atm of O2 converted the oxygen content to 6.7 to 6.8. Typical superconducting transport properties of an Y1Ba2Cu3O7−x film 1000 Å thick are ρ(300 K)=325 μΩ cm, ρ(300 K)/ρ(100 K)=2.4, Tc(onset)=92 K, and Tc(R=0)=82 K. The transport Jc at 75 K is 1×105 A/cm2, and increases to 1×106 A/cm2 at 70 K.
Growth of n-type heteroepitaxial films of gray tin on (001) CdTe by molecular beam epitaxy
Authors: Tu Li-Wei , Wong George K. , Ketterson John B.
Published: July 2002

We report the molecular beam epitaxy growth of α-Sn films on argon sputter cleaned (001) CdTe substrates on which a buffer layer of CdTe has been deposited. Films thinner than 400 Å are p-type with carrier densities as high as 2×1019 cm−3 ;thicker films are n-type with carrier densities of (4–10)×1017 . The best film had a mobility of 1.3×104 cm2 /V s at 77 K.
Reaction of titanium with germanium and silicon-germanium alloys
Authors: Thomas O. , Delage S. , d’Heurle F. M. , Scilla G.
Published: July 2002

The reaction of Ti with pure Ge and several Ge-Si alloys has been investigated with the double aim of understanding the reaction with Ge and of throwing some light on the still vexing problem of the Ti-Si reaction. With pure Ge one observes first of all the formation of Ti6Ge5 until complete consumption of the Ti is present. This is followed by the clearly identifiable nucleation of TiGe2, initially forming islands that grow laterally. With a 50-50 (at. %) alloy of Si and Ge, one still observes distinct growth steps, but there is overlap between the growth of the initial phase, and the nucleation and growth of Ti(Ge,Si)2.
Anisotropic transport and nonparabolic miniband in a novel in-plane superlattice consisting of a grid-inserted selectively doped heterojunction
Authors: Motohisa J. , Tanaka M. , Sakaki H.
Published: July 2002

Transport properties of electrons in a novel in-plane superlattice structure are studied and the field-effect transistor action has been demonstrated. The structure consists of an n-AlGaAs/GaAs modulation-doped heterojunction in which an array of monolayer-thick AlAs grid is embedded with an average period of 162 Å in the channel region of the heterojunction. This grid has been prepared with molecular beam epitaxy by depositing a half monolayer of AlAs on a GaAs (001) vicinal plane, where periodically spaced atomic terraces are formed. The electron mobilities μ∥,μ⊥ parallel and normal to the grid are measured as functions of electron concentration NS. While the mobility ratio (μ∥/μ⊥) is nearly unity at low NS, the ratio is found to get as large as 2.2 as NS increases. This anisotropic behavior of μ is well accounted for by the calculated nonparabolicity in the miniband structure of in-plane superlattices.
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u observation of molecular beam epitaxy of GaAs and AlGaAs under deficient As4 flux by scanning reflection electron microscopy
Authors: Yamada K. , Inoue N. , Osaka J. , Wada K.
Published: July 2002

The initial stages of molecular beam epitaxial (MBE) growth of GaAs and AlGaAs are directly observed by scanning reflection electron microscopy. Under deficient As4 flux, it is shown that dark areas appear within several layers of growth, but disappear within several seconds of growth interruption, indicating that they are droplets of Ga and Al. The distance between the droplets is approximately 1 μm, which is identical in GaAs and AlGaAs growth. Thus, the diffusion length of Ga and Al on a group III-rich surface at around 600 °C is estimated to be about 5000 Å, which is the largest among previous reports. The role of droplet disappearance in interface flattening in alternating supply MBE is discussed.
Epitaxial growth of metastable SnGe alloys
Authors: Asom M. T. , Fitzgerald E. A. , Kortan A. R. , Spear B. , Kimerling L. C.
Published: July 2002

We have grown homogeneous alloys of Sn1−xGex with 0.01<x<0.1 by molecular beam epitaxy on 〈100〉 InSb substrates. The Sn-Ge system is immiscible due to differing equilibrium crystal structures at the growth temperature. By stabilizing the diamond cubic α-Sn with the InSb template, we have created a metastable miscibility region for alloying Sn and Ge. Pure α-Sn grown on 〈100〉 InSb shows a tetragonal expansion perpendicular to the substrate because of the slightly larger lattice parameter of α-Sn. As the smaller Ge atom is added, the strain converts from compressive to tension resulting in an effective 1.66% tetragonal contraction in the growth direction for Sn0.92Ge0.08.
Effect of energetic bombardment on the magnetic coercivity of sputtered Pt/Co thin-film multilayers
Authors: Carcia P. F. , Shah S. I. , Zeper W. B.
Published: July 2002

Pt/Co multilayers are an attractive candidate for a magneto-optical recording medium. However, films sputter deposited in Ar have coercivities too small (100–350 Oe) to be practical in recording. By sputter depositing multilayers in Kr or Xe instead of Ar, we achieved coercivities ∼1000 Oe, suitable for recording. We attribute the lower coercivity of Ar-sputtered films to interfacial mixing of Pt and Co layers by energetic bombardment from Ar gas atoms that recoil from the Pt target.
Light-induced defect creation in amorphous silicon: Single carrier versus excitonic mechanisms
Authors: Stutzmann Martin
Published: July 2002

A quantitative explanation is derived for the light-induced degradation of compensated amorphous silicon. The analysis suggests that donor levels in compensated hydrogenated amorphous silicon (a-Si:H) lead to an efficient spatial separation of trapped electrons and holes, thereby preventing excitonic tail-to-tail recombination thought to be responsible for metastable defect creation during illumination. This confirms the original defect creation model which has recently been challenged by single carrier mechanisms invoking dispersive hydrogen motion as the rate-limiting step.
Phase-coupled two-dimensional AlxGa1−xAs-GaAs vertical-cavity surface-emitting laser array
Authors: Deppe D. G. , van der Ziel J. P. , Chand Naresh , Zydzik G. J. , Chu S. N. G.
Published: July 2002

Data are presented demonstrating the optically coupled operation of a 3×3 two-dimensional array of AlxGa1−xAs-GaAs vertical-cavity surface-emitting lasers. Room-temperature threshold current for the array is 90 mA, with the device geometry allowing for light emission from the epitaxial side of the device.
Directional etching of Si with perfect selectivity to SiO2 using an ultraclean electron cyclotron resonance plasma
Authors: Matsuura Takashi , Uetake Hiroaki , Ohmi Tadahiro , Murota Junichi , Fukuda Koichi , Mikoshiba Nobuo , Kawashima Tadashi , Yamashita Yoshihiro
Published: July 2002

Using a newly developed ultraclean electron cyclotron resonance plasma etcher, Si wafers masked by SiO2 were etched with a chlorine plasma at pressures of 0.6–4.0 mTorr with a microwave power of 300–700 W. Ultraclean processing under a low ion energy condition at high pressures has revealed that there is an induction period during which time there is no SiO2 etching. This is not observed with Si. During the induction period, perfectly selective etching for Si to SiO2 has been achieved. Under this perfectly selective condition, anisotropic tenth micron patterns of polycrystalline silicon have been obtained with little undercut.
Photoreflectance study of surface Fermi level in GaAs and GaAlAs
Authors: Shen H. , Dutta M. , Fotiadis L. , Newman P. G. , Moerkirk R. P. , Chang W. H. , Sacks R. N.
Published: July 2002

Franz–Keldysh oscillations from GaAs and AlGaAs structures have been studied and we find that the electric field obtained from the oscillations is in agreement with that derived from electrostatic calculations. Our results show that illumination from pump and probe beams in a normal photoreflectance experiment can significantly affect the measurement and thus erroneously lead to a reduced value of the electric field. The Fermi level on the bare surface of AlGaAs with different Al mole fraction has also been determined.
Transport properties of excitons in GaAs quantum wells−time-resolved Raman probe
Authors: Tsen K. T. , Sankey O. F. , Morkoç H.
Published: July 2002

Time-resolved, space-imaged Raman spectroscopy has been employed to study the transport properties of excitons in GaAs quantum wells. For an injected exciton density of nex ≂1.5×1011 cm−2, the experimental results show that exciton transport can be well described by a simple diffusion model. Based on the temperature and well-width dependence of the deduced diffusion constant, we demonstrate that at low temperatures, i.e., T ≤60 K, the transport of excitons in GaAs quantum wells is primarily governed by two dominant mechanisms: acoustic phonon scattering and interface roughness scattering.
Effect of substrate misorientation on surface morphology of homoepitaxial CdTe films grown by organometallic vapor phase epitaxy
Authors: Snyder D. W. , Mahajan S. , Ko E. I. , Sides P. J.
Published: July 2002

The effect of substrate misorientation on surface morphology of CdTe homoepitaxial films deposited by organometallic vapor phase epitaxy was investigated by deposition onto a substrate polished in the shape of a spherical cap that exposed misorientations up to 15° from the [100] pole. Hillock formation was suppressed for misorientations between 2.5° and 4.5° from the [100] pole towards the nearest {111} Te planes, whereas tilt towards the nearest {111}Cd planes resulted in only a slight improvement in surface morphology. A commonly used direction for misorienting substrates, towards the nearest {110} planes, reduced the size and density of the hillocks but did not completely suppress their formation. Double-crystal x-ray rocking curves indicated that high crystalline quality was obtained near the (100) plane, and that misorientations towards the nearest {111}Te planes did not significantly degrade the quality. Arguments have been developed to rationalize these observations.
25 ps pulses from a Nd:YAG laser mode locked by a frequency doubling β-BaB2O4 crystal
Authors: Stankov K. A.
Published: July 2002

We report on the generation of ultrashort light pulses from a Nd:YAG laser, passively mode locked by an intracavity frequency doubler in a nonlinear mirror arrangement. The pulse duration in the range of 20–25 ps is the shortest obtained so far from a Nd:YAG laser mode locked by this technique. In addition, the mode locking with frequency doubling crystal has provided in this experiment second-harmonic radiation amounting up to 38% of the fundamental radiation output and single-pass conversion efficiency of about 80%.
Strain-compensated strained-layer superlattices for 1.5 μm wavelength lasers
Authors: Miller B. I. , Koren U. , Young M. G. , Chien M. D.
Published: July 2002

Strain-compensated strained-layer multiple quantum well structures have been grown by introducing opposite strain into the barrier layers. Such structures show significant improvement in the photoluminescence spectra, i.e., narrower full width half maxima and stronger intensities. Lasers fabricated with such structures have exhibited low current thresholds (12 mA), high quantum efficiencies (28% per facet), which are constant over a wide current range.
Vacancy ordering of Ga2Se3 films by molecular beam epitaxy
Authors: Teraguchi Nobuaki , Kato Fuji , Konagai Makoto , Takahashi Kiyoshi , Nakamura Yoshio , Otsuka Nobuo
Published: July 2002

Ga2Se3 films have been grown by molecular beam epitaxy. Single-crystal Ga2Se3 films were obtained for the first time on (001) GaP substrates at a substrate temperature of 550 °C and at a VI/III flux ratio greater than 15. Extra diffraction spots with weak intensity were observed in reflection high-energy electron diffraction patterns of the Ga2Se3 films grown at a VI/III ratio above 150. These extra spots were also observed in the transmission electron diffraction pattern. The extra points are attributed to the ordering of native Ga vacancies in the defect zinc blende structure.
Submicron probe of polymer adhesion with atomic force microscopy: Dependence on topography and material inhomogeneities
Authors: Mizes H. A. , Loh K.-G. , Miller R. J. D. , Ahuja S. K. , Grabowski E. F.
Published: July 2002

We have used the atomic force microscope as a nanoindenter to both doped and undoped polycarbonate to probe the dependence of adhesion on topography and material inhomogeneities. Adhesion measurements at the same position are repeatable to 2%. The magnitude of the adhesion is found to decrease as the local curvature on the surface increases. Spatial adhesion maps of doped polymers show structure that is not apparent in surface topography. The spatial resolution of the measurement is at least 300 Å.
In situ determination of dielectric functions and optical gap of ultrathin amorphous silicon by real time spectroscopic ellipsometry
Authors: An Ilsin , Li Y. M. , Wronski C. R. , Nguyen H. V. , Collins R. W.
Published: July 2002

We have developed techniques to determine the near-infrared to near-ultraviolet dielectric function and optical gap of ultrathin amorphous silicon [a-Si:(H)] using real-time spectroscopic ellipsometry during preparation and processing. The techniques have been applied to ∼50 Å a-Si:H films prepared by plasma-enhanced chemical vapor deposition, and to ∼250 Å pure a-Si chemically modified by atomic H exposure. For the latter, the time evolution of the bonded H content can be estimated along with the evolution of the gap.
Passive mode locking and Q switching of an erbium 3 μm laser using thin InAs epilayers grown by molecular beam epitaxy
Authors: Vodopyanov K. L. , Lukashev A. V. , Phillips C. C. , Ferguson I. T.
Published: July 2002

Passive mode locking and Q switching has been achieved for the first time in an Er3+:YSGG laser at λ=2.8 μm using ultrathin single-crystal InAs epilayers grown on GaAs substrate which were subsequently bombarded with 15 keV protons at a dose of 1013 cm−2. The bleaching effect was due to a dynamic Moss–Burstein mechanism with a fast (<100 ps) recovery time. In the case of passive mode locking, pulses of 10 MW power were generated at λ=2.8 μm.
New theory of linewidths of radiative transitions due to disordering in semiconductor alloys
Authors: Lee S. M. , Bajaj K. K.
Published: July 2002

A quantum mechanical formalism for the excitonic photoluminescence linewidth in semiconductor alloys due to band gap fluctuations caused by the random distributions of alloy components is presented. Using a quantum mechanical description for the excitonic system, the mean deviation of its transition energy due to the statistical potential fluctuations is calculated using a first-order perturbation theory. We then apply this formalism to calculate the linewidth of the ground state excitonic transition as a function of composition. Specifically, the excitonic linewidth in AlxGa1−xAs alloy as a function of Al concentration is calculated and compared with earlier models and available low-temperature photoluminescence data.
Dielectric functions and critical points of strained InxGa1−xAs on GaAs
Authors: Pickering C. , Carline R. T. , Emeny M. T. , Garawal N. S. , Howard L. K.
Published: July 2002

Dielectric function spectra of strained InxGa1−xAs (x≤0.25) epilayers on GaAs are presented for the first time, together with spectra of relaxed layers of the same compositions. Critical point energies, obtained by line-shape fitting to second-derivative spectroscopic ellipsometry (SE) data, show an increase in the E1, E1+Δ1 splitting with strain, in agreement with theory using GaAs deformation potentials. SE is shown to be capable of determining layer thickness, composition, and strain in this alloy system.
Photoluminescence studies on porous silicon
Authors: Xu Z. Y. , Gal M. , Gross M.
Published: July 2002

We have measured the temperature dependence of the photoluminescence of porous silicon and have found that it disagrees with the expected behavior of crystalline or amorphous silicon. We also found that soaking the samples in oxygen and simultaneously illuminating them with light results in the quenching of the photoluminescence. We propose that luminescence in porous silicon may actually be luminescence from molecules attached to the Si surface, rather than any previously assumed quantum size effect.
High T
c thin films with roughness smaller than one unit cell
Authors: Nakamura O. , Fullerton Eric E. , Guimpel J. , Schuller Ivan K.
Published: July 2002

We have developed a method for the growth of epitaxial high Tc superconducting thin films with roughness smaller than one unit cell using conventional magnetron sputtering. In this method the substrate is positioned above one edge of the target (off axis) to avoid resputtering, and oscillated back and forth between the two symmetrical edges of the target to improve film thickness homogeneity. Finite size peaks in the x-ray diffraction spectra of thin GdBa2Cu3O7−δ films and satellite peaks on a GdBa2Cu3O7−δ/YBa2Cu3O7−δ superlattice show the excellent thickness control and smoothness obtained with this technique.
a-axis oriented growth of YBa2Cu3O7−y films on LaSrGaO4(100) substrates
Authors: Hontsu S. , Mukai N. , Ishii J. , Kawai T. , Kawai S.
Published: July 2002

We have grown a-axis oriented YBa2Cu3O7−y (YBCO) films on LaSrGaO4 (LSGO) (100) substrates with (100) oriented seed layer of PrBa2Cu3O7−x (PBCO) using a pulsed laser deposition technique. PBCO films on LSGO (100) deposited even at ∼800 °C exhibits the a-axis orientation. In this temperature range, PBCO films on SrTiO3 (100) substrate exhibits the c-axis orientation. The YBCO film with a-axis orientation was grown on this PBCO(100) layer at a wide range of 650–800 °C. The YBCO films on PBCO free substrates have, on the other hand, c-axis orientation normal to the surface of the LSGO (100). We found that the preferred orientations of YBCO thin films can be controlled by the presence of PBCO films on LSGO substrate. For the a-axis orientated YBCO films, the resistance perpendicular to the c axis is 1/2 of that parallel to the c axis, suggesting the preferred orientation of c axis along the surface. The zero resistance superconducting transition temperature (Tc) of the films on the LSGO (100) and PBCO (100)/LSGO (100) substrates are 88.0 and 89.0 K, respectively.
Ultrafast chemical reactions between nickel and aluminum powders during shock loading
Authors: Bennett L. S. , Sorrell F. Y. , Simonsen I. K. , Horie Y. , Iyer K. R.
Published: July 2002

A recent investigation of powdered Ni-Al systems subject to shock loading has yielded evidence that reactions occur during the shock front. Time-resolved measurements of normal shock pressure indicate that an ‘‘excess pressure’’ is generated possibly due to an exothermic reaction in the Ni-Al system. These reactions appear to occur during the 100 ns that represent the shock front. A clear reaction threshold is observed and corroborated by micrographs of the recovered samples.
Polarization insensitive multiple quantum well laser amplifiers for the 1300 nm window
Authors: Tiemeijer L. F. , Thijs P. J. A. , van Dongen T. , Slootweg R. W. M. , van der Heijden J. M. M. , Binsma J. J. M. , Krijn M. P. C. M.
Published: July 2002

A polarization insensitive (less than 1 dB gain difference over the 3 dB gain bandwidth) multiple quantum well laser amplifier for the 1300 nm window is reported for the first time. The amplifiers employ a single active layer containing three tensile strained and four compressively strained quantum wells and show a fiber to fiber gain of 16 dB at 1310 nm and 200 mA driving current. Furthermore at the same wavelength these devices have a record low fiber coupled noise figure of 6.5 dB and a conveniently high fiber coupled saturation output power of 13 dBm for both polarizations.
Imaging and blackbody emission spectra of particulates generated in the KrF-laser ablation of BN and YBa2Cu3O7−x
Authors: Geohegan David B.
Published: July 2002

Blackbody emission from ejecta following KrF-laser irradiation of YBa2Cu3O7−x (YBCO) and BN targets in vacuum has been observed for the first time using intensified charge-coupled-device (CCD) photography and gated photon counting. Temporally resolved emission spectra from particulates up to 2 cm from the target and from 10 μs to 1.5 ms after the laser pulse are attributed to blackbody radiation. The spectra are used to estimate temperatures between 2200 and 3200 K for ejecta from both BN and YBCO when irradiated at Φ248=3.5 J and 1.5 J cm−2, respectively. The measured cooling of the particles in vacuum is compared to a radiative cooling model.
Refractive index gradients and light scattering in polymer-dispersed liquid crystal films
Authors: Drzaic Paul S. , Gonzales Anne M.
Published: July 2002

We compare the light scattering properties of polymer-dispersed liquid crystal films incorporating different nematic mixtures. We find that, when powered, the turbidity of these disparate films share a common quadratic dependence on the refractive index difference between the nematic and polymer. In contrast, when we compare the turbidity of powered and unpowered films with the same refractive index difference, we find that the unpowered films scatter much more strongly. These differences show that the scattering cross section for a droplet depends not just on the refractive index of the polymer interface, but also on the structure surrounding the droplet.
Growth of strain-balanced InAsP/InGaP superlattices for 1.06 μm optical modulators
Authors: Chiu T. H. , Cunningham J. E. , Woodward T. K. , Sizer T.
Published: July 2002

Using a strain-balanced growth approach, we show that the pseudomorphic InAsP/InGaP multiple quantum well structures, grown by chemical beam epitaxy, have superior material properties for 1.06 μm modulator application when compared to the strained InAsP/InP or the lattice-matched InGaAsP/InP systems. The broadening in absorption edge due to dislocations in the strained system, or composition fluctuations in the lattice-matched system as a consequence of growth temperature instability, can be greatly minimized. A strong reduction in the nonradiative recombination centers in the strain-balanced InAsP/InGaP system has been observed.
Epitaxial MnGa/NiGa magnetic multilayers on GaAs
Authors: Tanaka M. , Harbison J. P. , Sands T. , Philips B. , Cheeks T. L. , De Boeck J. , Florez L. T. , Keramidas V. G.
Published: July 2002

We have grown a new class of epitaxial metallic multilayers consisting of ultrathin ferromagnetic tetragonal MnGa and nonmagnetic (CsCl-type) NiGa on (001) GaAs substrates by molecular beam epitaxy. Reflection high energy electron diffraction and cross-sectional transmission electron microscopy analyses show that MnGa/NiGa multilayers with atomically abrupt interfaces are formed with the expected epitaxial orientations, and, in particular, that the c-axis of the tetragonal structure of the MnGa film is aligned perpendicular to the substrate. Perpendicular magnetization of the MnGa/NiGa multilayers was evidenced by both vibrating sample magnetometer and extraordinary Hall effect measurements at room temperature, with higher values (Mr=267–302 emu/cm3) of remanent magnetization than those of previously reported MnGa and MnAl thin films. The capability of growing this new class of materials will allow a new degree of artificial materials design on semiconductor substrates.
Partially coherent light generated by using single and multimode optical fibers in a high-power Nd:glass laser system
Authors: Nakano H. , Miyanaga N. , Yagi K. , Tsubakimoto K. , Kanabe T. , Nakatsuka M. , Nakai S.
Published: July 2002

A simple and flexible method is presented for generating a partially coherent light which obtains the highly smooth focused beam pattern. The beam divergence of 32 times diffraction limited light having a spectral width of 1.6 nm has been easily and reproducibly achieved by injecting a laser pulse from an actively mode-locked Nd:YLF oscillator to a single mode optical fiber, coupled to a multimode optical fiber. Temporal evolution of the beam smoothing due to the induced incoherency was examined with temporally resolved measurements of the beam pattern. The partially coherent light was focused through a random phase plate after the amplification. Small-scale intensity perturbation in a focused beam pattern was greatly reduced.
Transport mechanism of X band electrons in AlAs electrode through GaAs/AlAs/GaAs structure by varying GaAs well thickness
Authors: Shieh Tung-Ho , Lee Si-Chen
Published: July 2002

The transport of X band electrons through AlAs/GaAs/AlAs/GaAs/AlAs structure with various GaAs well thickness is investigated. The resonant tunneling of X band electrons through X band double barrier is only observed when the GaAs well thickness becomes smaller than 3 nm. For thicker GaAs, the single tunneling peak is due to X band electrons tunneling through the Γ band confined states in the GaAs well. Its longitudinal optical phonon replica is also observed at temperature below 80 K, but disappears at higher temperature. This replica is due to the scattering of electrons from X band of AlAs electrode to the Γ band of GaAs in order to satisfy the momentum conservation.
Schottky barrier heights of W on Si1−xGex alloys
Authors: Aubry V. , Meyer F. , Warren P. , Dutartre D.
Published: July 2002

The Schottky barrier height of W on p-type Si1−xGex/Si has been investigated as a function of composition (10%≤x≤33%) and Si1−xGex thickness for a given composition. The barrier height decreases with increasing Ge fraction and follows the rate of strain relaxation. These results suggest that the Fermi level at the interface is pinned relative to the conduction band.
Photomechanical stabilization in a polymer fiber-based all-optical circuit
Authors: Welker D. J. , Kuzyk M. G.
Published: July 2002

We report on the demonstration of an all-optical feedback circuit that photomechanically stabilizes the length of a polymer-optical fiber through a photothermal mechanism.
Photoinduced superconductivity and structural changes in high temperature superconducting films
Authors: Lederman David , Hasen J. , Schuller Ivan K. , Osquiguil E. , Bruynseraede Y.
Published: July 2002

The illumination of PryGd1−yBa2Cu3Ox semiconducting and superconducting thin films increases their critical temperatures and decreases their normal state resistivities if and only if the films are oxygen deficient. Moreover, these changes are enhanced near the Pr-induced metal-insulator transition. Light also causes a contraction of the c-axis in YBa2Cu3Ox which is correlated with the observed photoinduced resistivity changes. These changes are similar to those observed when oxygen-deficient YBa2Cu3Ox is enriched with oxygen or annealed at room temperature after quenching from high temperatures.
2000 V 6H-SiC p-n junction diodes grown by chemical vapor deposition
Authors: Neudeck Philip G. , Larkin David J. , Powell J. Anthony , Matus Lawrence G. , Salupo Carl S.
Published: July 2002

In this letter we report on the fabrication and initial electrical characterization of the first silicon carbide diodes to demonstrate rectification to reverse voltages in excess of 2000 V at room temperature. The mesa structured 6H-SiC p+n junction diodes were fabricated in 6H-SiC epilayers grown by atmospheric pressure chemical vapor deposition on commercially available 6H-SiC wafers. The devices were characterized while immersed in FluorinertTM to prevent arcing which occurs when air breaks down under high electric fields. The simple nonoptimized diodes, whose device areas ranged from 7×10−6 to 4×10−4 cm2, exhibited a 2000 V functional device yield in excess of 50%.
Growth of GaAs/AlAs trench-buried multiple quantum wires by metalorganic chemical vapor deposition on V-grooved substrates
Authors: Sogawa T. , Ando S. , Kanbe H.
Published: July 2002

We report the fabrication of GaAs/AlAs multiple trench-buried quantum wires (TBWs) by metalorganic chemical vapor deposition on V-grooved substrates. The shape of AlAs layers grown on the V-grooves can be changed significantly from a V-shape to U-shape by varying growth temperatures and group-V/III ratios. 30-nm-wide and 100-nm-deep AlAs trenches with nearly vertical sidewalls are formed at the growth temperature of 650 °C with the group-V/III ratio of 165, while V-shaped AlAs grooves are formed at 700 °C with the V/III ratio of 110. Vertically stacked double TBWs are formed using the 30-nm-wide trenches. The low-temperature (15 K) photoluminescence spectrum for the double TBWs shows two distinct emission peaks corresponding to the 6.5- and 8.0-nm-thick wires.
Heavily boron-doped silicon membranes with enhanced mechanical properties for x-ray mask substrate
Authors: Lee Ho-Jun , Han Chul-Hi , Kim Choong-Ki
Published: July 2002

Heavily boron-doped silicon membranes which show substantial improvement in mechanical properties have been fabricated for x-ray mask substrate by eliminating the misfit dislocation from the membrane. The measured surface roughness, fracture strength, and residual tensile stress of the membrane are 20 Å peak to peak, 1.39×1010 and 2.7×109 dyn/cm2, while those of the conventional heavily boron-doped silicon membrane with high density of misfit dislocations are 500 Å peak to peak, 8.27×109 and 9.3×108 dyn/cm2, respectively. The differences between the two membranes are due to misfit dislocation. Young’s modulus has been extracted as 1.45×1012 dyn/cm2 for both membranes. Also, the lattice constant of strain-free membrane, the in-plane lattice constant of the conventional membrane, and the density of extra-half plane contained in the conventional membrane have been extracted as 5.424 Å, 5.426 Å, and 2.3×104/cm, respectively.
Silicon field-effect transistor based on quantum tunneling
Authors: Tucker J. R. , Wang Chinlee , Carney P. Scott
Published: July 2002

This letter explores regulation of current flow within a silicon field-effect transistor by gate-induced tunneling through a Schottky barrier located at the interface between a metallic source electrode and the Si channel. The goal here is to forestall short-channel effects which are expected to prevent further size reductions in conventional devices when linewidths reach ∼1000 Å. Control of tunneling appears to be possible at minimum channel lengths L∼250 Å or less while simultaneously eliminating the need for large-area source and drain contacts, so that scaling of Si transistors could be significantly extended if this principle proves technically feasible.
Crystallization behavior of sol-gel derived Pb(Zr,Ti)O3 thin films and the polarization switching effect on film microstructure
Authors: Amanuma Kazushi , Hase Takashi , Miyasaka Yoichi
Published: July 2002

The microstructure of sol-gel derived Pb(Zr,Ti)O3 thin films was investigated using Auger electron spectroscopy (AES) and transmission electron microscopy (TEM). The AES depth profile revealed that the Ti content decreases and the Zr content increases from the bottom through the thickness as a result of the crystallization into perovskite phase. A cross-sectional TEM micrograph showed that the PZT grains are columnar and grow epitaxially from the bottom to the surface. It was also shown that the 2.5-nm-thick interface layer appeared at the top Au electrode-PZT interface after 108 polarization switching cycles, while there was no change at the bottom Pt-PZT interface.
Nonresonant detection of electric force gradients by dynamic force microscopy
Authors: Yokoyama Hiroshi , Inoue Takahito , Itoh Junji
Published: July 2002

A mechanoelectric cross-modulation scheme is proposed to enable direct and nonresonant detection of electric force gradients by dynamic force microscopy. The technique employs an ultrasonic vibration of the sample against a conductive tip, to which an alternating voltage is applied at a frequency near that of mechanical modulation, chosen well above the resonance frequency of the cantilever. The heterodyne mixing between the mechanically and the electrically induced oscillating charge densities on the tip gives rise to low frequency cross-modulation forces, proportional to the electric force gradients. The nonresonant detection of the first- and the second-order electric force gradients has successfully been performed, resulting in a dramatic enhancement of lateral resolution in surface potential imaging.
Epitaxial Fe16N2 films grown by sputtering
Authors: Ortiz C. , Dumpich G. , Morrish A. H.
Published: July 2002

We have been able to obtain α″-Fe16N2 films using an underlayer template to induce the epitaxial growth of this metastable phase. They are epitaxial in the (001) direction and show single crystallinity in plane. Furthermore, they are deposited by simple reactive nitrogen sputtering. They have an average magnetic moment of 250 emu/g, considerably larger than the moment (217 emu/g) for pure bcc iron. Conversion electron Mössbauer spectroscopy gives three hyperfine fields corresponding to three different iron sites, as expected for this structure.
Conjugated polymer light-emitting diodes on silicon substrates
Authors: Baigent D. R. , Marks R. N. , Greenham N. C. , Friend R. H. , Moratti S. C. , Holmes A. B.
Published: July 2002

We report the fabrication of polymer electroluminescent devices on doped silicon substrates. An electron-injecting aluminum electrode is thermally evaporated onto the silicon substrate, and a layer of a high electron affinity conjugated polymer, poly(cyanoterephthalylidene), CN-PPV, is then spin coated onto this. A hole-transporting layer of poly(p-phenylene vinylene), PPV, is formed on top of the CN-PPV layer by thermal conversion of a spin-coated layer of the sulphonium precursor polymer. Finally, a transparent hole-injecting top electrode of indium-tin oxide is formed by rf sputtering. These devices show efficient red electroluminescence, with emission from the CN-PPV layer.
TiCN: A new chemical vapor deposited contact barrier metallization for submicron devices
Authors: Eizenberg M. , Littau K. , Ghanayem S. , Mak A. , Maeda Y. , Chang M. , Sinha A. K.
Published: July 2002

High-quality chemical vapor deposited TiCN films were produced in a single wafer reactor using a metallorganic (TDMAT) precursor. The films have excellent step coverage over high aspect-ratio contacts as well as very low particle content. These properties are obtained because the films are deposited under surface-reaction controlled conditions. The films show also excellent barrier properties against Al and WF6 attack. These properties make this material a superb contact barrier material for ultra-large-scale integrated devices.
Photoluminescence determination of the nitrogen doping concentration in 6H-SiC
Authors: Henry A. , Kordina O. , Hallin C. , Hemmingsson C. , Janzén E.
Published: July 2002

The intensity of impurity and intrinsic luminescence lines reflects the impurity doping concentration. A calibration procedure is presented for the nitrogen impurity in 6H–SiC. The calibration is valid for a large range of n-type doping from 1014 to 1016 cm−3. Effects of excitation density, temperature during the photoluminescence experiments as well as the observation of acceptor related lines are discussed.
Etching of Si(111)-(7×7) and Si(100)-(2×1) surfaces by atomic hydrogen
Authors: Wei Yi , Li Lian , Tsong I. S. T.
Published: July 2002

We present scanning tunneling microscopy (STM) studies of the etching behavior of the surfaces of Si(111)-(7×7) and Si(100)-(2×1) by atomic hydrogen. Etching proceeds via the formation of volatile SiH4 through a two-step mechanism in which the H atoms react with SiH2 and SiH3 species on the surface at room temperature. By measuring the area of etch pits in the STM images taken under the same flux conditions, the etching of Si(100) is determined to be nearly three times faster than that of Si(111) because intermediate hydride products are more readily stabilized on the (100) surface.
Near-surface electronic structure in GaAs (100) modified with self-assembled monolayers of octadecylthiol
Authors: Dorsten J. F. , Maslar J. E. , Bohn P. W.
Published: July 2002

Passivation of the GaAs (100) surface by self-assembled monolayers of octadecylthiol (ODT) has been studied using inelastic light scattering as a probe of the near-surface electronic structure. Application of the ODT self-assembled monolayers reduces the width of the depletion region at the surface of GaAs resulting in a reduction of the surface band bending, and the electron scattering time is increased as well. The ODT passivated surfaces are more stable to environmental degradation, over time and under temperature stress, than inorganic sulfide treated surfaces which have been reported. Organic thiol passivation may provide an attractive alternative to inorganic sulfide protocols for reduction of surface recombination velocities in III–V devices.
Optimized structure for InGaAsP/GaAs 808 nm high power lasers
Authors: Yi H. J. , Diaz J. , Wang L. J. , Eliashevich I. , Kim S. , Williams R. , Erdtmann M. , He X. , Kolev E. , Razeghi M.
Published: July 2002

The optimized structure for the InGaAsP/GaAs quaternary material lasers (λ=0.808 μm) is investigated for the most efficient high-power operation through an experiment and theoretical study. A comparative study is performed of threshold current density Jth and differential efficiency ηd dependence on cavity length (L) for two different laser structures with different active layer thickness (150 and 300 Å) as well as for laser structures with different multiple quantum well structures. A theoretical model with a more accurate formulation for minority leakage phenomenon provides explanation for the experimental results and sets general optimization rules for other lasers with similar restrictions on the band gap and refractive index difference between the active layer and the cladding layers.
Solid phase epitaxial growth of sol-gel derived Pb(Zr,Ti)O3 thin films on SrTiO3 and MgO
Authors: Nashimoto K. , Fork D. K. , Anderson G. B.
Published: July 2002

Pb(Zr0.52Ti0.48)O3 (PZT) thin films were crystallized on SrTiO3 (100) and MgO (100) substrates by a sol-gel process using nonhydrolyzed metal methoxyethoxide precursors, spin coating, and rapid thermal annealing. Solid phase epitaxial growth of PZT on SrTiO3 was observed directly from the amorphous phase even at 425 °C. The PZT had a single (001) orientation and rocking curve full width at half maximum (FWHM) less than 0.1°. High-temperature annealing of MgO substrates improved orientation of PZT thin films. Epitaxial crystallization of PZT with a single (001) orientation on the annealed MgO was observed at temperature above 550 °C after the formation of the pyrochlore phase.
Integrated optical isolator based on nonreciprocal higher-order mode conversion
Authors: Shintaku Toshihiro
Published: July 2002

An integrated optical isolator based on nonreciprocal conversion from a fundamental TM mode to a higher-order TE mode is proposed and experimentally demonstrated. The isolator is realized using a single-mode rib channel waveguide in Ce-substituted yttrium iron garnet which has a very large Faraday rotation. 24 dB isolation is obtained at a wavelength of 1550 nm.
Diamond chemical vapor deposition from a capacitively coupled radio frequency plasma
Authors: Jackman Richard B. , Beckman Judith , Foord John S.
Published: July 2002

Capacitively coupled radio frequency (cc-rf) plasmas offer advantages over microwave (MW) induced plasmas for the growth of large area homogeneous thin films. However, conventionally designed cc-rf sources lead, at best, to extremely poor quality material when diamond growth is attempted. The first complete diamond overlayer to be grown with cc-rf is reported here, where a novel magnetically enhanced source with ring electrodes has been used.
Transparent and opaque Schottky contacts on undoped In0.52Al0.48As grown by molecular beam epitaxy
Authors: Gao Wei , Berger Paul R. , Hunsperger Robert G. , Zydzik G. , Rhodes W. W. , O’Bryan H. M. , Sivco D. , Cho A. Y.
Published: July 2002

The Schottky barrier height was measured for five different materials on undoped In0.52Al0.48As grown by molecular beam epitaxy (MBE). Of the materials tested, two were transparent conductors, indium-tin-oxide (ITO), and cadmium tin oxide (CTO) and for comparison, three were opaque metals (Au, Ti, and Pt). The barrier heights were measured using I–V measurements. Due to the high series resistance created by the undoped In0.52Al0.48As, the Norde method [J. Appl. Phys. 50, 5052 (1979)] was used to plot the I–V characteristics and extract the Schottky barrier height. The Schottky barrier heights were determined to be 0.639, 0.637, 0.688, 0.640, and 0.623 eV for ITO, CTO, Au, Ti, and Pt, respectively. Previously published results for Schottky barriers on In0.52Al0.48As are compared with our measurements.