bluuebunny/crossref_metadata_2025 huggingface dataset:
Implantation damage in GaAs-AlAs superlattices of different layer thickness
Authors: Dobisz E. A. , Fatemi M. , Dietrich H. B. , McCormick A. W. , Harbison J. P.
Published: July 2002

We report that two GaAs-AlAs superlattices of different layer thickness show dramatically different crystal damage when ion irradiated under identical conditions. The samples, held at 77 K, were implanted with 100 keV 28Si at doses of 3×1013 cm−2 to 1×1015 cm−2. Ion channeling results show amorphization threshold doses of 1×1015 cm−2 for the 7.0 nm GaAs-8.5 nm AlAs superlattice and 4×1014 cm−2 for the 3.5 nm GaAs-5.0 nm AlAs superlattice. At low doses, the shorter period superlattice was more robust, with no damage peak observed in ion channeling spectra for doses as high as 1×1014 cm−2. For a dose of 7×1013 cm−2, double crystal x-ray diffraction measurements show a 6 arcsec broadening of the (004) peak, relative to that of the unimplanted sample, for both superlattices. However, only the finer period superlattice exhibits a broadening (10 arcsec) of the (224) diffracted peak indicating a distortion in an additional direction. A mechanism involving the formation of slightly misaligned crystal domains is suggested to describe the behavior of the finer period superlattice.
Diffusion of manganese in GaAs and its effect on layer disordering in AlxGa1−xAs-GaAs superlattices
Authors: Wu C. H. , Hsieh K. C. , Höfler G. E. , EL-Zein N. , Holonyak N.
Published: July 2002

Several diffusion runs of Mn in GaAs are performed in sealed quartz ampoules with four different Mn-containing sources: (a) solid crystal granules of Mn, (b) Mn3As, (c) MnAs, and (d) Mn thin films coated on GaAs substrates. Among these, only MnAs results in a smooth GaAs surface and uniform doping distributions. For the others interactions between the source materials and GaAs substrates give rise to poor surface morphologies and inhomogeneous distributions of new-phase (Mn,Ga) crystals. For diffusion at 800 °C, surface p-type carrier concentrations as high as 1020/cm3 are obtained. Diffusion profiles determined by C-V techniques resemble those obtained for Zn diffusions. A substitutional-interstitial mechanism is suggested as the primary diffusion mechanism for Mn in GaAs. Data are also presented showing that layer disordering in AlGaAs-GaAs superlattices can be induced by Mn impurities.
Transistor action based on field-effect controlled current injection into an insulator/SrTiO3 interface
Authors: Tamura Hirotaka , Yoshida Akira , Hasuo Shinya
Published: July 2002

Transistor action with both voltage and current gain exceeding 1 was observed in structures consisting of metal electrodes, insulating barriers, and high-dielectric-constant insulating SrTiO3. These structures were made on insulating (100) single-crystal SrTiO3 substrates having a dielectric constant of 2×104 at 4.2 K. A Nb emitter and collector electrodes were placed on the substrates, with Si or SiO2 barriers between the emitter and substrate. Base leads were made with silver paste on the back of the SrTiO3 wafers. Devices both with and without barrier layers between the collector and substrate showed transistor action at 4.2 K. Essentially no current was required to control the collector current, which ranges from a few microamperes to a few milliamperes. For devices with a 30-μm-diam circular emitter having a minimum emitter-collector spacing of 15 μm, the voltage gain was 2.5–4 and the maximum transconductance 1.4 mS.
Diffusive base transport in narrow base InP/Ga0.47In0.53As heterojunction bipolar transistors
Authors: Ritter D. , Hamm R. A. , Feygenson A. , Panish M. B. , Chandrasekhar S.
Published: July 2002

The common emitter current gain of InP/Ga0.47In0.53As heterojunction bipolar transitors having a base doping level of 7×1019 cm−3 is found to increase monotonically with decreasing base thickness in the range of 200–1000 Å. The variation of the gain with base thickness WB is proportional to 1×W2B, as expected for diffusive base transport, and a high injection efficiency.
Structural investigation of aromatic polyimide films modified by ion beams: A comparative study
Authors: Xu Dong , Xu Xinglong , Zou Shichang
Published: July 2002

X-ray photoelectron (XPS) and Raman spectroscopy were employed in the structural investigation of the modified polyimide films irradiated with boron ion beams. XPS discloses the formation of graphite bonding especially when irradiation comes up to a dose around 3×1016 B+/cm2. Raman spectroscopy, together with the calculation of its reduced spectra as well as the one-phonon state density of amorphous graphite, is inclined to demonstrate a structural similarity between modified polyimide films and amorphous graphite in short range order. The degree of this similarity depends on the irradiation condition. From this view point, the effects of dose and beam current density upon the final microstructures of the irradiated polyimide films were also investigated.
Material dependence of positron implantation depths
Authors: Baker J. A. , Chilton N. B. , Jensen K. O. , Walker A. B. , Coleman P. G.
Published: July 2002

New experiments and Monte Carlo simulations of positron implantation in gold are presented which, when compared with earlier work on aluminum, clearly demonstrate that the material dependence of positron implantation profiles is not adequately described by the simple mass density scaling factor in the widely used expression for median implantation depths. There is excellent agreement between the experimental results and the simulations which use the Penn dielectric formalism to describe inelastic scattering.
Threshold and saturation effects for photosignals in an amorphous silicon waveguide structure
Authors: Zelikson M. , Weiser K. , Salzman J. , Kanicki J.
Published: July 2002

We report on a novel photosignal effect when laser light enters an amorphous hydrogenated silicon (a-Si:H) core waveguide and an external voltage is applied. Above a threshold voltage, the electric field separates the photocarriers in the a-Si:H layer so that the voltage across it is reduced. For larger voltages or high light intensities, this screening effect saturates. Analysis of the results yields electron and hole drift mobilities of 0.6 and 0.2 cm2/V s), respectively.
Large nonlinear phase shifts in low-loss AlxGa1−xAs waveguides near half-gap
Authors: Ho S. T. , Soccolich C. E. , Islam M. N. , Hobson W. S. , Levi A. F. J. , Slusher R. E.
Published: July 2002

We study the instantaneous nonlinear index change in Al0.2Ga0.8As waveguides below the two-photon absorption edge and find π phase shifts with 80 pJ, 0.4 ps pulses at wavelengths near 1.6 μm. These large phase shifts are obtained with less than 1 dB of loss from multiphoton absorption. Our results indicate that AlGaAs waveguides, which have a mature fabrication technology, can be used as compact nonlinear elements in switching and quantum optics applications in the near-infrared. Further optimization of the waveguide geometry should result in useful nonlinear phase shifts and low losses for pulse energies approaching a picojoule.
Simultaneous occurrence of multiphases in interfacial reactions of ultrahigh vacuum deposited Ti thin films on (111)Si
Authors: Wang M. H. , Chen L. J.
Published: July 2002

High resolution transmission electron microscopy in conjunction with optical diffractometry have been applied to identify the formation of an amorphous interlayer as well as to detect the presence of Ti5Si3, Ti5Si4, TiSi, and C49-TiSi2 in the interfacial reactions of ultrahigh vacuum (UHV) deposited Ti thin films on atomically clean (111)Si. The discovery of the formation of an amorphous interlayer and as many as four different silicide phases in the initial stages of interfacial reactions of UHV deposited Ti thin films on silicon by high resolution techniques necessitates a modification of the existing theory of the silicide formation in thin-film reactions.
Analysis of the elastic wave excitation in solid plates by phase velocity scanning of a laser beam
Authors: Tsukahara Yusuke
Published: July 2002

A theory is presented for the propagation of elastic waves in a plate excited by scanning a laser beam at a constant velocity. A formula for the excitation by scanning a line-focused laser beam is deduced from a general formula and analyzed extensively in a two-dimensional model. It is derived that such modes of Lamb waves are selectively excited whose phase velocities match the scanning velocity. It is also shown that major characteristics of experimental observations previously made are explained with the present model.
Formation of misfit dislocations during Zn-diffusion-induced intermixing of a GaInAsP/InP heterostructure
Authors: Park Hyo-Hoon , Nam Eun Soo , Lee Yong Tak , Lee El-Hang , Lee Jeong Yong
Published: July 2002

The microstructural degradation of a lattice-matched Ga0.28In0.72As0.61P0.39/InP heterointerface induced by Zn diffusion has been investigated using transmission electron microscopy. The localized interfacial stress caused by intermixing appears to create stacking faults in the Ga-mixed InP substrate, and dislocation tangles in the In-mixed GaInAsP layer. The observed results are attributed to the contrasted effect of tensile and compressive stresses upon the nucleation of dislocations from both sides of the GaInAsP/GaInP interface. As an evidence of the interface nucleation, we find a stacking fault at the tensile interface, which is bounded by a pair of partials having opposite Burgers vectors. A model is proposed to explain the strain relaxation in the intermixed region in terms of nucleation and splitting mechanisms of the paired dislocations.
New technique for investigating ferroelectric phase transitions: The photoacoustic effect
Authors: Tocho Jorge O. , Ramírez Rafael , Gonzalo J. A.
Published: July 2002

Measurements of the photoacoustic (PA) effect in properly oriented triglycine sulfate (TGS) crystals from 30 to 60 °C show clearly the ferroelectric phase transition in this crystal manifested by the pronounced thermal expansion anomalies. The same method is generally applicable to similar phase transitions.
Mechanism of forming ohmic contacts to GaAs
Authors: Holloway Paul H. , Yeh Liu Lu-Min , Powell David H. , Brown Alan
Published: July 2002

The distribution of Si dopant at the Au/GaAs interface after heat treatment has been studied using spatially resolved secondary-ion mass spectrometry. Previously it has been shown that heat treatment changes as deposited Au thin film from Schottky contacts to ohmic contacts. The present study shows that the transition to an ohmic contact results from segregation of dopants in areas where GaAs is decomposed by reacting with the Au overlayer. Thus the ohmic contact is spatially very inhomogeneous at the metal/semiconductor interface. The mechanism leading to concentrations of the Si and nonuniform ohmic contacts is discussed, and segregation to the solid during decomposition of the GaAs is the most likely mechanism.
Direct observation of BaTiO3 microcrystallites in thin amorphous BaTiO3 films
Authors: Li P. , Lu T.-M.
Published: July 2002

Well separated BaTiO3 microcrystallites were observed by transmission electron microscopy (TEM) in rapidly annealed, amorphous BaTiO3 thin films. The crystallization temperature for amorphous BaTiO3 is between 400 °C and 500 °C.
Magnetless Faraday rotator of (BiY)3Fe5O12 waveguide with stripe magnetic domains
Authors: Matsuda Kaoru , Narusawa Tadashi
Published: July 2002

We propose and demonstrate a magnetless Faraday rotator of a (BiY)3Fe5O12 waveguide with stripe magnetic domains. It has a potential application to compact optical isolators. The specific Faraday rotation angle of −150 deg/cm and the extinction ratio of 13 dB are obtained without a magnet.
Electron focusing with a double grid in AlGaAs/GaAs heterostructures
Authors: Nakazato K. , Hornsey R. I. , Blaikie R. J. , Cleaver J. R. A. , Ahmed H. , Thornton T. J.
Published: July 2002

Electron focusing has been observed in single- and double-grid structures. The magnetoresistance shows strong maxima and minima with values both above and below the zero field resistance. These are interpreted in terms of electron trajectories which are either backscattered from or transmitted through the grids, with a good match between the measured and calculated magnetic field values for the position of these peaks. The difference in magnetoresistance between the two structures is explained by an internal scattering mechanism which is present only for the double-grid system.
Measurements of Al-AlInAs Schottky barriers prepared in situ by molecular beam epitaxy
Authors: Gueissaz F. , Gailhanou M. , Houdré R. , Ilegems M.
Published: July 2002

Aluminum was deposited in situ on high crystalline quality n-doped AlInAs grown by molecular beam epitaxy. The current versus voltage characteristics yielded an ideality factor better than 1.05. A barrier height of 0.55±0.01 eV was found, as determined from capacitance versus voltage and current versus temperature (I-T) measurements. The agreement between the two measurements was excellent. Furthermore, evidence is given here that inhomogeneities of the crystal matrix, as observed by four crystal-six reflection x-ray diffraction, result in anomalous I-T characteristics.
Effects of radiation-induced oxide-trapped charge on inversion-layer hole mobility at 300 and 77 K
Authors: Zupac D. , Galloway K. F. , Schrimpf R. D. , Augier P.
Published: July 2002

The effects of radiation-induced interface-trapped charge and oxide-trapped charge on the inversion-layer hole mobility in p-channel double-diffused metal-oxide-semiconductor transistors at 300 and 77 K are reported. The mobility degradation is more pronounced at 77 than at 300 K, due to an increased importance of Coulomb scattering from trapped charge when phonon scattering is significantly reduced. The mobility degradation is primarily due to interface-trapped charge, but the effects of oxide-trapped charge must be taken into account in order to properly describe the mobility behavior, particularly at cryogenic temperatures.
Synthesis of SmCo5 by chemical reduction during mechanical alloying
Authors: Liu Yinong , Dallimore M. P. , McCormick P. G. , Alonso T.
Published: July 2002

The synthesis of SmCo5 by the chemical reduction of Sm2O3 during mechanical alloying has been investigated using x-ray diffraction, electron microscopy, and magnetic measurements. The mechanical alloying of Sm2O3 with Co and Ca resulted in the formation of CaO and an amorphous Sm-Co phase. The SmCo5 phase formed during subsequent heat treatment exhibited coercivity greater than 33 kOe.
X rays in electron-cyclotron-resonance processing plasmas
Authors: Castagna T. J. , Shohet J. L. , Denton D. D. , Hershkowitz N.
Published: July 2002

Electron-cyclotron-resonance processing plasmas have been shown to produce low-energy x rays. X radiation was detected in nitrogen and CF4 plasmas from energies of 1–17 keV for microwave powers up to 1000 W. The x-ray flux decreased with increasing pressure over the range of 0.5–3.5 mTorr. Temperatures of the hot electrons responsible for creating the x rays were estimated from the slopes of the x-ray spectra and decreased with increasing pressure. The measured x-ray flux decreased substantially when the magnetic field configuration was changed. Measurable x radiation is produced whenever a field line that passes through the cyclotron resonance surface intersects the vacuum chamber walls and/or other solid surfaces inside the source chamber.
Electronic properties of Se-treated SiO2/GaAs interfaces
Authors: Kikawa Takeshi , Takatani Shinichiro , Tezen Yuta
Published: July 2002

GaAs metal-insulator-semiconductor diodes with a Se-treated interface and photochemical-vapor-deposited SiO2 are investigated. The diodes show little frequency dispersion in the capacitance at any accumulation bias, only a few percent between 1 kHz and 1 MHz. Analysis using Terman’s method shows that the density of interface states near the midgap is drastically reduced. In addition, insertion of a Se-treated AlGaAs thin layer at the insulator/semiconductor interface is found to reduce the number of interface states near the conduction band minimum. These improved characteristics are preserved after annealing to 400 °C.
Gain measurements of Mn5+(3d2) doped Sr5(PO4)3Cl and Ca2PO4Cl
Authors: Capobianco J. A. , Cormier G. , Moncorgé R. , Manaa H. , Bettinelli M.
Published: July 2002

We report the room-temperature near-infrared emission (1.0–1.4 μm), the fluorescence lifetimes, and the gain measurements of the tetraoxo manganese specie MnO3−4(Mn5+,3d2) in single crystals of Sr5(PO4)3Cl and Ca2PO4Cl. The relatively long fluorescence lifetimes, 100 and 425 μs for MnO3−4 doped Ca2PO4Cl and MnO3−4 doped Sr5(PO4)3Cl, respectively, are consistent with the emission originating from 1E level. The stimulated emission cross section of Ca2PO4Cl:Mn5+ at around 1.15 μm is found to be 3.2×10−20 cm−2.
Twin formation in Ag seeded Co/Pt multilayers grown on GaAs by molecular beam epitaxy
Authors: Cho N.-H. , Krishnan Kannan M. , Lee C. H. , Farrow R. F. C.
Published: July 2002

Molecular beam epitaxy was used to grow ultrathin Co-Pt multilayers on GaAs (111) substrates with 200 Å thick Ag layer as a buffer. Magnetic properties (B-H loop) of the multilayers, measured by a vibrating sample magnetometer, confirmed that these samples exhibit strong anisotropy perpendicular to the film surface. Reflection high energy electron diffraction and low-energy electron diffraction showed that twin-related Ag grains nucleated on the substrates. The epitaxial relationship of the multilayers with respect to the substrate was investigated by high-resolution transmission electron microscopy. Twin-related grains, 30–40 nm in diameter, are present in the multilayers. These twins are generated either by propagation of existing twin boundaries in the Ag layer into the multilayers or by nucleation of twin-related Pt grains on the Ag buffer surface.
Hysteretic, high T
c Josephson junctions using heterostructure trilayer films grown by molecular beam epitaxy
Authors: Virshup G. F. , Klausmeier-Brown M. E. , Bozovic I. , Eckstein J. N.
Published: July 2002

Hysteretic Josephson junctions have been fabricated by growing c-axis oriented trilayer Bi2Sr2CaCu2O8/Bi2Sr2(Ca,Bi, Sr)7Cu8O20/Bi2Sr2CaCu2O8 single-crystal thin films and patterning them into devices. To our knowledge, these are the first cuprate superconductor junctions to exhibit current-voltage characteristics with substantial hysteresis. Current flow in the devices is in the vertical (c axis) direction, through an ultrathin (∼30 Å) barrier layer. The current-voltage response shows large, sharp Shapiro steps under microwave illumination.
Versatile waveguide polarizer incorporating an ultrathin discontinuous silver film
Authors: Bloemer Mark J. , Haus Joseph W.
Published: July 2002

We demonstrate the first transverse magnetic (TM) pass waveguide polarizer suitable for integrated optic or fiber optic geometries. The polarizing properties of waveguides incorporating an ultrathin discontinuous silver film are due to excitation of a localized surface plasmon mode. The polarizers have a large bandwidth (≳100 nm), high extinction ratios, and do not rely on sensitive phase matching conditions. We illustrate these novel polarizing properties on ion-exchanged planar waveguides overlayed with a 5-nm-mass thick silver film. The measured extinction ratio was 35 dB/mm at 836 nm with 2 dB/mm loss for the TM polarization. The theoretical analysis of the film properties and waveguide propagation losses is compared with the experiments.
Two-photon absorption and nonresonant nonlinear index of refraction in the intersubband transitions in the quantum wells
Authors: Khurgin J. B. , Li S.
Published: July 2002

A simple theory for the two-photon intersubband absorption and, associated with it, nonlinear refraction in multiple quantum wells (QWs) is developed. Using it, the third-order nonlinear susceptibility is evaluated for QWs of different shapes. It is shown that χ(3) of as much as 10−7 esu can be achieved below the two-photon resonance where the absorption is small. Thus, it is preferable to use multiple QWs in nonlinear devices at frequencies less than half of the intersubband frequency.
Electric field dependence of exciton spin relaxation in GaAs/AlGaAs quantum wells
Authors: Vinattieri A. , Shah Jagdeep , Damen T. C. , Goossen K. W. , Pfeiffer L. N. , Maialle M. Z. , Sham L. J.
Published: July 2002

We report measurements of the dependence of exciton spin relaxation in quantum-well structures on an external electric field along the growth direction and on the well thickness. The results show that exciton spin relaxation is dominated by electron-hole exchange interaction, and provide a quantitative understanding of various spin-relaxation rates and their dependence on electric field and well thickness.
Demonstration of quantum dots and quantum wires with removable impurities
Authors: Feng Y. , Sachrajda A. S. , Taylor R. P. , Adams J. A. , Davies M. , Zawadzki P. , Coleridge P. T. , Landheer D. , Marshall P. A. , Barber R.
Published: July 2002

We present the first demonstration of a nanostructural device with a central electrode (diameter ≊300 nm) which is contacted independently. This structure is used to create a quantum wire into which an ‘‘impurity’’ of variable size can be introduced. With additional confining gates the structure can also be used to create a quantum dot which can be converted continuously into a quantum ring. Experimental results of magnetoresistance in both low and high magnetic fields are presented which demonstrate the effect of introducing the artificial impurity to a quantum wire.
Anisotropic Josephson effect in all (103)-oriented YBa2Cu3O7−δ /PrBa2Cu3O7−δ′/YBa2Cu3O7−δ junctions
Authors: Sato Hiroshi , Akoh Hiroshi , Takada Susumu
Published: July 2002

We report a demonstration of the anisotropic Josephson effect in all (103)-oriented junctions consisting of YBa2Cu3O7−δ /PrBa2Cu3O7−δ′/YBa2Cu3O7−δ film sandwiches. The junction shows a resistively shunted junction-like current-voltage characteristics with hysteresis and clear Shapiro steps under the microwave radiation. Depending on the direction of external magnetic field H, the junction exhibits anisotropic Fraunhofer interference patterns with different critical magnetic fields Hc0 and periods in the oscillation of critical current. The agreement between experimental and expected values by the Owen–Scalapino analysis for anisotropic Hc0 confirms that this anisotropic property comes from the anisotropy in the magnetic penetration depth of (103)-oriented YBaCuO films.
Investigation of carrier heating and spectral hole burning in semiconductor amplifiers by highly nondegenerate four-wave mixing
Authors: D’Ottavi A. , Iannone E. , Mecozzi A. , Scotti S. , Spano P. , Landreau J. , Ougazzaden A. , Bouley J. C.
Published: July 2002

A highly nondegenerate (up to 1 THz) four-wave mixing experiment is performed in a bulk semiconductor amplifier. The simultaneous presence of carrier heating and spectral hole burning shows up in a four-wave mixing experiment. A simple physical picture is given that explains the relative weight of the two saturation mechanisms in active semiconductor devices.
Double-disk structure for output coupling in microdisk lasers
Authors: Chu D. Y. , Chin M. K. , Bi W. G. , Hou H. Q. , Tu C. W. , Ho S. T.
Published: July 2002

We report our experiment on the use of a double-disk structure to couple light output from a microdisk laser which allows us to maintain a high Q value of the microdisk resonator. The small photon leakage rate from the lower lasing disk to the top waveguiding disk can be carefully controlled by choosing the distance between the two disks. Various structures can be fabricated on the top disk to couple the light out. In this letter, a simple opening in the top disk is used for output coupling.
The S-passivation of Ge(100)-(1×1)
Authors: Anderson G. W. , Hanf M. C. , Norton P. R. , Lu Z. H. , Graham M. J.
Published: July 2002

The treatment of Ge(100) in an aqueous ammonium sulfide solution is investigated by means of x-ray photoelectron spectroscopy, Auger electron spectroscopy, low-energy electron diffraction, scanning electron microscopy, and atomic force microscopy. This treatment is shown to produce an S-passivated Ge(100)-(1×1) surface, where the S atoms appear to be bridge bonded to the Ge atoms. Desorption of the S is observed to occur between 460 and 750 K and results in a Ge(100)-(1×1) surface with a surface morphology similar to that of the initial sample.
Improved helium cryostat for a vibrating sample magnetometer
Authors: Landee C. P. , Greeney R. E. , Lamas A. C.
Published: July 2002

The design and operating characteristics of a helium cryostat for a vibrating sample magnetometer are described. The cryostat incorporates an exchange gas enclosure for the sample and a carbon-glass resistance thermometer. The design permits a reduced background signal, increased temperature stability, and longer operating times than previous commercially available cryostats.
Horizontal field magnet cryostat and specimen positioning assembly for neutron scattering experiments
Authors: Tennant D. C. , Kerley N. , Killoran N.
Published: July 2002

The basic design concepts and performance of a horizontal field magnet cryostat and specimen drive assembly are described. Specimens can be studied at any controlled temperature between 1.4 and 300 K and in any selected symmetric horizontal field between 0 and 3 T in the sample volume. The unique feature of the cryostat is that it permits almost 360° access for a neutron beam incident on the specimen. In addition, the magnets may be run in asymmetric mode to pull the field nodes out of the scattering plane so as to avoid depolarization of the neutron beam. A drive assembly attached to the top flange of the cryostat has been designed that positions the specimen to an accuracy of ±0.01°, even in the presence of a magnetic torque on the specimen. The drive mechanism design and horizontal field configuration is readily adaptable to other top loading cryostats.
Microwave heating and dielectric diagnosis technique in a single-mode resonant cavity
Authors: Jow Jinder , Hawley Martin C. , Finzel Mark C. , Asmussen Jes
Published: July 2002

A single-mode microwave heating and dielectric measurement technique has been developed. The single- and swept-frequency methods were used to simultaneously heat the material and measure its complex permittivity in this single-mode technique. A cylindrical cavity and Nylon 66 rods were used in this study. The cavity was always resonated in the TM012-mode at 2.45 GHz. The measured changes in the resonant frequency and cavity Q factor of the cavity with and without the sample were related to complex permittivity of the sample using material-cavity perturbation. Temperature measurement was made using a fluoroptic thermometer. On-line measurements of complex permittivity and temperature were made during single- and swept-frequency microwave heating of the sample. Complex permittivity of Nylon 66 as a function of temperature using the single-frequency method was compared to that using the conventional swept-frequency method during microwave heating. It shows that dielectric measurements using the single- and swept-frequency methods are repeatable and consistent. However, the resolution in resonant frequency shifts and cavity Q factor measurements is higher in the single-frequency method. The measurement errors for permittivity and dielectric loss factor are less than ±4% and ±10% for the single-frequency method and less than ±5% and ±15% for the swept-frequency method. Therefore, the single-frequency method is more accurate than the swept-frequency method.
Development of metallic ions in the ECR sources
Authors: Bourgarel M. P. , Bisch M. , Lehérissier P. , Pacquet J. Y. , Rataud J. P.
Published: July 2002

The production of metallic ions compared to gaseous ones is generally obtained with smaller charge states, less current, and a not so good long-term stability. This paper presents the thinking to obtain more comparable results in the two situations and the corresponding measurements; studies undertaken Ca, Zn, Mg, Ni, Ag, Ta, and Pb on the 10 GHz/CAPRICE.
Improvement of hydrogenated amorphous silicon germanium alloys using low power disilane–germane discharges without hydrogen dilution
Authors: Matsuda Akihisa , Ganguly Gautam
Published: July 2002

We suggest that the role of hydrogen dilution in the improvement of the quality of hydrogenated amorphous silicon germanium alloys is to alter the relative contribution of the short and long lifetime precursors to film growth which are deleterious and beneficient, respectively. In order to circumvent the preferential depletion of germane when mixed with silane, we have used low power disilane–germane discharges and thereby obtained films with an optical gap <1.5 eV having similar Urbach tail width and defect absorption, with and without hydrogen dilution.
Scaled train tunnel simulator for weak shock wave generation experiment
Authors: Sasoh Akihiro , Onodera Osamu , Takayama Kazuyoshi
Published: July 2002

A scaled train tunnel simulator has been constructed for investigating weak shock waves which are generated in a long tunnel when a high-speed train enters it. The simulator consists of a driver section which can launch a 50 g and 18 mm diam piston (model train) at up to 120 m/s (430 km/h) and a 40 mm diameter and 25 m long tube. The entire tunnel simulator is inclined by 8° so that the decrease of the piston speed is minimized. The performance of the driver section is analyzed and a simple algebraic formulation is obtained. Mainly due to aerodynamic drag force, the piston speed is decreased by at most 10% through the tube. The effect of the decrease of the piston speed on shock wave generation processes is found to be negligible. Using this scaled train tunnel simulator, the overpressure of shock waves which is generated by a high-speed train is well reproduced by laboratory experiments.
Computer controlled in situ radiolysis electron spin resonance spectrometer incorporating magnetic field-microwave frequency locking
Authors: Madden Keith P. , McManus Hugh J. D. , Fessenden Richard W.
Published: July 2002

A lab-built personal computer-based electron spin resonance (ESR) spectrometer is described which incorporates a wide range magnetic field/microwave frequency lock as part of its magnetic field control subsystem. Instrument operation is accomplished by keyboard commands, with important experimental variables logged automatically for reference during subsequent data analysis. The spectrometer features both narrowband field modulation and direct-detection time-resolved ESR modes. The data acquisition system and field/frequency lock operate such that spectrum recordings consisting of multiple magnetic field sweeps are undistorted by long-term klystron frequency drift. The spectrometer features low noise microwave preamplification, balanced mixer detection, automatic reference arm phase control, and a fast automatic frequency control system requiring no klystron frequency modulation. Natural abundance 13C and 33S studies of the terephthalic acid radical trianion and sulfite radical anion are presented as proof of spectrometer performance.
Fiber-coupled optical pyrometer for shock-wave studies
Authors: Holmes N. C.
Published: July 2002

We have developed a new optical pyrometer with unique advantages for shock-wave studies and for measurements of systems that are moving with respect to the detection system. Our pyrometer is fully fiber optic coupled. This completely eliminates any time-dependent imaging or aperture effects common to imaging pyrometers, and is simple to align and calibrate. The sensitivity is also higher than typical imaging systems used for shock experiments. The design is excellent for observations of time-varying phenomena. Detection is done with fast photomultiplier tubes with roughly 1 ns response. In addition, one may also include a streaked spectroscopic system, making this system ideal for fast spectroscopic studies.
The NEXAFS of biological calcium phosphates
Authors: Buckley C. J. , Bellamy S. J. , Zhang X. , Dermody G. , Hulbert S.
Published: July 2002

The absorption cross section of a number of calcium salts has been assessed at the calcium L edge by measuring the total electron yield (TEY) at the NSLS U13UA beamline. TEY was used because of distortions introduced by instrumentation when using a transmission signal. The effect of these distortions has been evaluated and is presented. The TEY signal was normalized to the incident beam using the signal from a new beam monitor which is detailed here. Comparative spectra are presented for some calcium salts associated with osteoarthritis.
Improvement of interferometric measurements on far-infrared polarimeter interferometer systems
Authors: Barry S. , Nieswand C. , Bühlmann F. , Prunty S. L. , Mansfield H. M.
Published: July 2002

On many tokamaks the reconstruction of the magnetic field structure in the plasma is supported by polarimetric measurements. Recent proposed and realized methods are based on a far-infrared laser beam with a rotating polarization ellipse. The same instrument usually performs as an interferometer measuring the line integrated plasma density. It has been shown that the rotating polarization ellipse disturbs the interferometric measurements. A method based on the principle of a rotating polarization in which the interferometric measurement is unaffected is proposed. Bench test results are presented which show the feasibility of this method.
X-ray diffraction and absorption at extreme pressures
Authors: Brister Keith
Published: July 2002

This article presents a review of techniques and instrumentation for using x rays and synchrotron radiation in high-pressure experiments. The review focuses on x-ray diffraction experiments using diamond anvil cells. After a brief introductory passage, details about diamond anvil cells, large volume apparatus, pressure measurement, and simultaneous high-temperature and high-pressure instrumentation are provided, with adequate references to these topics. A section on adapting x-ray methods for use with high-pressure apparatus lists the problems encountered. Examples of studies are presented using energy dispersive diffraction, angle dispersive diffraction, infrared spectroscopy, x-ray absorption spectroscopy, and single-crystal techniques. The current trend indicates that energy dispersive diffraction, so far the mainstay of high-pressure powder diffraction with synchrotron sources, has lost some ground to angle dispersive diffraction, due to advances in instrumentation in the latter method.
Liquid helium cooled sample holder assembly for surface x-ray diffraction
Authors: Taylor J. S. G. , Norris C.
Published: July 2002

A cryogenically cooled sample holder and support assembly has been constructed for surface x-ray diffraction studies in ultrahigh vacuum. The design combines ease of sample replacement in situ with good mechanical stability and temperature control. This is achieved by locating a rectangular pin on the sample holder in a collet which can be closed from outside the vacuum chamber. Samples up to 10 mm square can be held at a constant temperature between 40 and 1300 K.
A computer-based digital feedback control of frequency drift of multiple lasers
Authors: Zhao W. Z. , Simsarian J. E. , Orozco L. A. , Sprouse G. D.
Published: July 2002

We report a method to monitor and control laser frequencies with an optical cavity and a digital feedback system. A frequency-stabilized He–Ne laser provides the reference that is transferred to several other lasers using a scanning Fabry–Pérot cavity. A personal computer-based multifunction data acquisition system generates the scan wave form, and reads the detector outputs synchronously with the cavity scan. The computer determines the positions of all of the peaks in the scan, and generates output signals to control the laser frequencies. It also provides a visual display of cavity spectra. We have successfully used the setup to achieve a long-term lock of the lasers for magneto-optical trapping of radioactive francium atoms.
Temperature dependence of terahertz pulses produced by difference- frequency mixing in InSb
Authors: Howells S. C. , Schlie L. A.
Published: July 2002

Terahertz radiation emitted from (111) InSb illuminated with focused 1.4 μm laser pulses is due to both difference-frequency mixing and depletion field driven current. By rotating an undoped (111) InSb sample at a temperature of 80 K about its surface normal, we were able to separate the relative contribution of the azimuthally dependent difference-frequency mixing (DFM) signal from the total terahertz wave form. Contrary to expectations, it was found that the azimuthally dependent spectrum appears nearly identical to the azimuthally independent spectrum. From this, it is concluded that the spectrum of the current surge signal blue shifts as the pump is focused. Also, a strong similarity exists between the temperature dependence of the DFM and current surge signals.
Contour temperature programmed desorption for monitoring multiple chemical reaction products
Authors: Chusuei C. C. , de la Peña J. V. , Schreifels J. A.
Published: July 2002

A simple method for obtaining a comprehensive overview of major compounds desorbing from the surface during temperature programmed desorption (TPD) experiments is outlined. Standard commercially available equipment is used to perform the experiment. The method is particularly valuable when high molecular mass compounds are being studied. The acquisition of contour temperature programmed desorption (CTPD) spectra, sampling 50-dalton mass ranges at a time in the thermal desorption experiments, is described and demonstrated for the interaction of benzotriazole adsorbed on a Ni(111) surface. Conventional two-dimensional TPD spectra can be extracted from the CTPD by taking vertical slices of the contour.
Falling liquid film thickness measurement by an optical-electronic method
Authors: Zhang J. T. , Wang B. X. , Peng X. F.
Published: July 2002

An optical-electronic method was developed for measurement of falling liquid film thicknesses. The method is based on the postulate that a sheet light beam passing tangentially through a vertical liquid film on a cylinder will be blocked by the falling liquid film. Hence, when the beam is much wider than the film, the output of a photodiode probe which is located on the opposite side of the cylinder from the light source will be reduced by an amount proportional to the film thickness. The shadow of the transient film shape will also appear on a screen behind the falling film. Therefore, the variation of the amplitude of the film waves can be measured from the output of the photodiode and the average film thickness can be measured from pictures of the shadow using computer aided image analysis. The average film thickness measured agrees well with commonly accepted empirical equations. The maximum relative deviation between the experimental and calculated results is 18.5% with a standard deviation of 4.34×10−2 mm. Compared with popular conductance parallel-wire probes, this method has the advantages of convenience, noninvasive, higher spatial and temporal resolution, smaller hysteresis and it does not disturb the model’s surface.
Comparison of high temperature thermal stabilities of Ru and RuO2 Schottky contacts to GaAs
Authors: Kim Yong Tae , Lee Chang Woo , Kwak Sung Kwan
Published: July 2002

Thermal behaviors of ruthenium (Ru) and ruthenium dioxide (RuO2) Schottky contacts have been compared after rapid thermal annealing at 550–900 °C for 30 s without arsenic overpressure or capping layer. Rutherford backscattering measurements and x-ray diffraction indicate that no metallurgical interactions take place between RuO2 and GaAs. I–V characteristics of RuO2 Schottky contacts reveal that barrier height increases from 0.83 to 0.85 eV even after RTA at 900 °C, in contrast with the degradation of barrier height from 0.75 to 0.59 eV for the Ru Schottky diodes. This means that RuO2 Schottky contacts have higher thermal stability than Ru contacts to GaAs. The reason is ascribed to the diffusion barrier property of RuO2 preventing the interdiffusion of Ga and As.
Inverse twisted nematic liquid-crystal device
Authors: Patel J. S. , Cohen G. B.
Published: July 2002

In this letter we demonstrate an inverse twisted nematic device in which the input polarized light is unaffected in the field-off state and produces a polarization rotation in the field-on state. This is done by using a homeotropically aligned sample containing chiral nematic liquid crystal with negative dielectric anisotropy and specially prepared surfaces.
Low temperature characterization of modulation doped SiGe grown on bonded silicon-on-insulator
Authors: Paul D. J. , Griffin N. , Arnone D. D. , Pepper M. , Emeleus C. J. , Phillips P. J. , Whall T. E.
Published: July 2002

Modulation doped pseudomorphic Si0.87Ge0.13 strained quantum wells were grown on bonded silicon-on-insulator (SOI) substrates. Comparison with similar structures grown on bulk Si(100) wafers shows that the SOI material has higher mobility at low temperatures with a maximum value of 16 810 cm 2/V s for 2.05×1011 cm−2 carries at 298 mK. Effective masses obtained from the temperature dependence of Shubnikov–de Haas oscillations have a value of (0.27±0.02) m0 compared to (0.23±0.02) m0 for quantum wells on Si(100) while the cyclotron resonance effective masses obtained at higher magnetic fields without consideration for nonparabolicity effects have values between 0.25 and 0.29 m0. Ratios of the transport and quantum lifetimes, τ/τq=2.13±0.10, were obtained for the SOI material that are, we believe, the highest reported for any pseudomorphic SiGe modulation doped structure and demonstrates that there is less interface roughness or charge scattering in the SOI material than in metal–oxide–semiconductor field effect transistors or other pseudomorphic SiGe modulation doped quantum wells.
Nonlinear optical properties of lanthanum doped lead titanate thin film using Z-scan technique
Authors: Zhao Qingchun , Liu Yun , Shi Wensheng , Ren Wei , Zhang Liangying , Yao Xi
Published: July 2002

Lanthanum doped lead titanate (PLT) thin films with good surface morphology and perovskite structure were fabricated by the metalo-organic decomposition process. Their nonlinear optical property was investigated by Z-scan technique. PLT30 thin films on the quartz substrate display strong nonlinear optical effects. A nonlinear refractive index as high as 3.0×10−7 esu was obtained for the thin film. All the results show that PLT ferroelectric thin films are promising materials for nonlinear optics.
Activator recycling in low voltage cathodoluminescent phosphors
Authors: Stoffers C. , Yang S. , Zhang F. , Jacobsen S. M. , Wagner B. K. , Summers C. J.
Published: July 2002

Cathodoluminescent phosphors excited at low voltages and high current densities often exhibit brightness saturation due to ground state depletion. A two-level model can be used to show that the luminance and saturation behavior of low voltage phosphors can be greatly improved by choosing phosphors with an activator decay time that is considerably less than the excitation dwell time. This is of considerable importance for field emission displays, where saturation due to ground state depletion has been found to be a factor limiting the achievement of the necessary luminance. Thus, fast activators may overcome ground state depletion and can lead to brighter displays.
Electro-optic modulation of laser diode light by mode interference in a multilayer waveguide including a 2-docosylamino-5-nitropyridine Langmuir–Blodgett film
Authors: Palchetti L. , Sottini S. , Grando D. , Giorgetti E. , Ricceri R. , Gabrielli G.
Published: July 2002

A hybrid four layer guide (FLG) including a glass guide and a 2-docosylamino-5-nitropyridine Langmuir–Blodgett film is described, and some tests are reported on an electro-optic modulator based on this FLG. The modulation of laser diode light was obtained by guided mode interference, without a Mach–Zehnder configuration of the device. From the modulated signal the r22 electro-optic coefficient was calculated as 11 pm/V.
In situ growth of highly oriented Pb(Zr0.5Ti0.5)O3 thin films by low-temperature metal–organic chemical vapor deposition
Authors: Bai G.-R. , Tsu I-Fei , Wang A. , Foster C. M. , Murray C. E. , Dravid V. P.
Published: July 2002

Highly oriented, polycrystalline Pb(Zr0.5Ti0.5)O3 (PZT) thin films were successfully grown on RuO2/SiO2/(001)Si using metal–organic chemical vapor deposition (MOCVD) at 525 °C. The orientation of the PZT film was controlled by using MOCVD-deposited highly textured RuO2 bottom electrodes. A (001)-oriented PZT film was observed for growth on (101)-textured RuO2. In contrast, for (110) RuO2, the growth of (001) PZT was greatly suppressed while the growth of both (110) and (111) were enhanced, resulting in a poorly (001)-textured polycrystalline film. The as-grown PZT films exhibited a dense columnar microstructure with an average grain size of 150–250 nm. Both PZT films showed excellent ferroelectric properties without any postgrowth annealing. The (001) highly oriented PZT films showed significantly higher values of remnant polarization (Pr=49.7 μC/cm2) and saturation polarization (Ps=82.5 μC/cm2). In comparison, for the PZT films grown on (110) RuO2, Pr and Ps were 21.5 and 35.4 μC/cm2, respectively.
Nonlinear I–V characteristics and proximity effects for PrBa2Cu3O7−δ/YBa2Cu3O7−δ bilayered structures grown on (001) YBa2Cu3O7−δ single crystal substrates
Authors: Usagawa Toshiyuki , Ishimaru Yoshihiro , Wen Jianguo , Utagawa Tadashi , Koyama Satoshi , Enomoto Youichi
Published: July 2002

We have observed superconductivity induced by proximity effects for 100 nm thick (001) PrBa2Cu3O7−δ films pseudomorphically grown on (001) YBa2Cu3O7−δ single crystal substrates by vertical four-probe measurements. The induced superconductivity disappeared around 28 K and was recovered at around 15 K. The 220 nm thick (001) PrBa2Cu3O7−δ/YBa2Cu3O7−δ bilayers show nonlinear I–V behavior with 0.2 mV built-in potential at low temperature below 50 K. The local maximum of the vertical resistance appears around 25 K.
Reflective mode of a nematic liquid crystal with chirality in a hybrid aligned configuration
Authors: Kim Young Jin , Lee Sin-Doo
Published: July 2002

A reflective type of a liquid crystal (LC) display is proposed in a twisted hybrid aligned configuration with a reflective electrode and a single polarizer. A chiral dopant was introduced into a nematic LC to produce a proper amount of twist in a hybrid aligned geometry. Numerical simulations were performed to optimize the cell parameters so that the electro-optical switching between the black and white states could be easily achieved. It was experimentally demonstrated that this reflective mode gives wide viewing and fast response characteristics. The effect of an optical retardation film on the device performance is also discussed.
Continuous-wave operation of InGaN/GaN/AlGaN-based laser diodes grown on GaN substrates
Authors: Nakamura Shuji , Senoh Masayuki , Nagahama Shin-ichi , Iwasa Naruhito , Yamada Takao , Matsushita Toshio , Kiyoku Hiroyuki , Sugimoto Yasunobu , Kozaki Tokuya , Umemoto Hitoshi , Sano Masahiko , Chocho Kazuyuki
Published: July 2002

InGaN multi-quantum-well-structure laser diodes (LDs) grown on GaN substrates were demonstrated. The LDs showed a small thermal resistance of 30 °C/W and a lifetime longer than 780 h despite a large threshold current density of 7 kA/cm2. In contrast, the LDs grown on a sapphire substrate exhibited a high thermal resistance of 60 °C/W and a short lifetime of 200 h under room-temperature continuous-wave operation.