bluuebunny/crossref_metadata_2025 huggingface dataset:
Laser-induced sputtering of Ga0 and Ga+ from the GaP (110) surface: Its relation to surface imperfection
Authors: Nakai Yasuo , Hattori Ken , Itoh Noriaki
Published: July 2002

We have measured emission of Ga+ ions and neutral Ga0 atoms induced by irradiation of the GaP (110) surface with laser pulses of subband-gap energies. It is found that the Ga+ yield of partially annealed Ar+ ion bombarded surfaces is reduced by thermal annealing and also by repeated irradiation with laser pulses, while the Ga0 yield is not influenced to an important extent by these treatments. The Ga+ emission, which occurs at a lower fluence than Ga0 emission, is ascribed to emission from defect sites at surfaces. We suggest that measurements of laser-induced particle emission for subband-gap energies will be useful for detection and elimination of low-density defects on surfaces.
High sensitivity In0.53Ga0.47As/InP heterojunction phototransistor
Authors: Leu L. Y. , Gardner J. T. , Forrest S. R.
Published: July 2002

We describe both theoretical and experimental investigations of the effects of inserting a thin, low-doped layer into the emitter of an InP/In0.53Ga0.47As heterojunction phototransistor (HPT). This high-low emitter structure has improved sensitivity over conventional structures at low input optical power by decreasing the bulk recombination current at the heterointerface. Experimental data show that the photocurrent gain is independent of the incident optical power at high input powers, corresponding to a heterojunction ideality factor of 1. At low input power, the gain is found to have a small power dependence, with an ideality factor of 1.25. A current gain as high as 260 is obtained at an input power of only 40 nW. These results, which are consistent with numerical simulations of the HPTs, give direct evidence that bulk recombination in the space-charge region at the emitter/base junction is the major source of recombination current for an InP/In0.53Ga0.47As HPT.
Raman scattering from quantum dots of Ge embedded in SiO2 thin films
Authors: Fujii Minoru , Hayashi Shinji , Yamamoto Keiichi
Published: July 2002

Raman measurements were carried out on Ge quantum dots from 6.1 to 15 nm in size embedded in SiO2 thin films. The samples were prepared by rf co-sputtering and post- annealing. In contrast to the amorphous-like broad spectra previously obtained for gas- evaporated Ge microcrystals of comparable sizes, relatively sharp lines around 300 cm−1 were observed, because the present dots satisfy the fixed boundary condition. The increase in the linewidth observed with decreasing the size is in good agreement with the results of the calculation based on the phonon confinement model. However, the downward shift of the line predicted from the calculation was not observed presumably due to the compressive stress exerted on the dots.
Temperature dependence of minority-carrier mobility and recombination time in p-type GaAs
Authors: Beyzavi K. , Lee K. , Kim D. M. , Nathan M. I. , Wrenner K. , Wright S. L.
Published: July 2002

The electron mobility in p-type GaAs, μpe, has been determined as a function of temperature by measuring the common-emitter cutoff frequency, fT, of an AlGaAs/GaAs n-p-n heterojunction bipolar transistor. The base was 0.6 μm thick and it was doped with 4×1018 cm−3 Be. The 300 K value of 1055 cm2/V s and 79 K value of 5000 cm2/V s for μpe are comparable to the previously measured values. The discrepancy with the calculated values is pointed out. The recombination lifetime is also measured as a function of temperature for minority carriers. The results agree reasonably well with the calculated radiative recominbation time.
Fabrication and characterization of planar ion-exchanged KTiOPO4 waveguides for frequency doubling
Authors: Risk W. P.
Published: July 2002

Optical waveguides can be formed in potassium titanyl phosphate (KTiOPO4, KTP) crystals by an ion-exchange process. Waveguides were fabricated in KTP substrates by exchanging rubidium ions for potassium ions. The resulting refractive index profile was measured as a function of diffusion time and temperature. Based on these characterization measurements, the phase-matching properties of the planar waveguide for guided-wave second-harmonic generation were modeled. Second-harmonic generation of blue/green light was observed at wavelengths shorter than the bulk phase-matching limit, in good agreement with the results of numerical modeling.
Spin-polarized secondary electron microscopy of written domains in CoNiCr and its correlation with noise measurements as a function of write current
Authors: VanZandt T. , Browning R. , Lee S. Y. , Khan M. R. , Pressesky J. L. , Duan S. L. , Heiman N.
Published: July 2002

Spin-polarized secondary electron microscope images of tracks of magnetic domains, written in Co62.5Ni30Cr7.5 thin-film longitudinal recording media, are presented as a function of write current. The corresponding modulation noise measurements are also presented for this sample. We observe that the magnetic microstructure visible in the images can be correlated with the modulation noise in each region of write current investigated. Explanations for the possible origins of this microstructure are presented.
Fiber interactions in two-dimensional composites
Authors: Eitan A. , Wagner H. D.
Published: July 2002

A new approach is proposed for assessing the stress concentration factors in two-dimensional undirectional composite materials containing broken fibers. A closed-form expression is derived for the stress concentration factor profiles as a function of materials and geometrical parameters. The model differs significantly from earlier schemes as the local effect of a fiber break on nearest neighbors is much milder than previously assumed, both as a function of the interfiber distance (or fiber content) and of the number of adjacent broken fibers. Comparison with experimental results for SiC/epoxy composites demonstrates the validity of the proposed scheme. The model may help shed light on the (multifilament) fragmentation process [H. D. Wagner and A. Eitan, Appl. Phys. Lett. 56, 1965 (1990)] and on fracture nucleation and growth in composites.
Formation of a thin SiO2 film using synchrotron radiation excited reaction
Authors: Ogawa Taro , Ochiai Isao , Mochiji Kozo , Hiraiwa Atsushi , Takakuwa Yuji , Niwano Michio , Miyamoto Nobuo
Published: July 2002

The possibility of altering an oxygen-adsorbed Si surface to SiO2 using a synchrotron radiation (SR) excited reaction is evidenced for the first time. Oxygen gas is adsorbed on a clean Si surface, and soft x-ray is irradiated on it by SR. As a result, H partly terminated on the oxygen-adsorbed Si surface is eliminated and the surface becomes more SiO2-like. This is proved by x-ray photoelectron spectroscopy (XPS) analysis. Photostimulated desorption (PSD) of H+ ions, which are emitted from the surface, is also detected during SR irradiation. The Si—O bond formation model followed by H+ PSD explains this oxidation.
High-barrier height Schottky diodes on N-InP by deposition on cooled substrates
Authors: Shi Z. Q. , Wallace R. L. , Anderson W. A.
Published: July 2002

Ultrahigh barrier height (φB=0.96 eV) Schottky contacts to n-InP, without an intentionally grown interficial oxide, were formed using metal deposition on a substrate cooled to as low as 77 K [low temperature (LT)]. φB = 0.46–0.52 eV for diodes deposited at room temperature (RT=300 K) agree well with previously published results, and give an ideality factor near unity. For the diodes deposited at LT=77 K, the leakage current density (J0) was reduced by more than 6–7 orders of magnitude with respect to the RT diodes. The φB for the LT diodes was increased from 0.48 to 0.96 eV for Pd metal and from 0.51 to 0.85 eV for Au metal, respectively. An alteration of the metal-induced interface states, inhibition of surface segregation of the released In and P atoms, and very uniform metal coverage may be responsible for the distinct differences between the RT and LT diodes.
Kinetics of silicon-germanium deposition by atmospheric-pressure chemical vapor deposition
Authors: Kamins T. I. , Meyer D. J.
Published: July 2002

The deposition of Si1−xGex alloy layers in an atmospheric-pressure, chemical vapor deposition reactor has been studied by separately examining the silicon and the germanium components of the deposition rate. The overall deposition rate increases approximately linearly with GeH4 partial pressure, but is relatively independent of SiH2Cl2 partial pressure. The silicon component of the deposition rate increases rapidly with increasing temperature for a constant germanium content, but the germanium component changes only slowly above about 675 °C, and is probably limited by mass transport.
End point detection in ion beam milling of YBa2Cu3O7 thin films
Authors: Humphreys R. G. , Chew N. G. , Morgan S. F. , Satchell J. S. , Cullis A. G. , Smith P. W.
Published: July 2002

In the processing of high temperature superconductor thin films into devices, the use of calibrated milling rates has proved unreliable as a means of determining the milled depth. This problem has been solved using in situ secondary ion mass spectrometry for identifying interfaces in multilayers based on YBa2Cu3O7. The depth resolution obtained during routine patterning of typical multilayers was ∼4 nm. Accurate termination of milling at an insulator/superconductor interface has been demonstrated. The presence of water vapor during milling has been shown to affect the proportions of the different secondary ion species, but has only a slight affect on the milling rate.
Epitaxial growth of vanadyl-phthalocyanine ultrathin films on hydrogen-terminated Si(111) surfaces
Authors: Tada Hirokazu , Kawaguchi Takafumi , Koma Atsushi
Published: July 2002

Ultrathin films of vanadyl phthalocyanine (VOPc) have been grown on hydrogen-terminated Si(111) surfaces by molecular beam epitaxy. Epitaxial growth was examined on the two types of substrates. Reflection high energy electron diffraction studies have revealed that VOPc molecules form commensurate lattices [−3[3 1]4], [−1[4 3]3], and [1[4 4]1] on the surface terminated homogeneously with monohydride. On the other hand, epitaxial growth did not occur on the surface terminated with the mixture of polyhydride. Homogeneity and microscopic flatness of the substrate surface seem to be important factors for the epitaxial growth of VOPc on the hydrogen-terminated Si substrate.
High rate epitaxial growth of InP by merged hydride organometallic vapor phase epitaxy in a hot-wall reactor
Authors: Ban V. S. , Rodefeld D. , Flemish J. R. , Jones K. A.
Published: July 2002

A new method which combines features of organometallic vapor phase epitaxy (VPE) with hydride VPE has been demonstrated for the epitaxial growth of InP. In this method trimethylindium is coinjected with HCl into a hot-wall reactor to form volatile InCl, and PH3 is used as the phosphorus source. Layers of InP were grown at approximately 8 μm/h with excellent morphology and good electrical properties. Hall measurements at 77 K show background n-type conductivity with n=7×1015/cm3 and μ=34 000 cm2/V s. This technique should be capable of growing ternary and quaternary heterostructures with thin layers and abrupt junctions.
A comparison of minority electron transport in In0.53Ga0.47As and GaAs
Authors: Kaneto T. , Kim K. W. , Littlejohn M. A.
Published: July 2002

The electron transport properties of heavily doped p-type In0.53Ga0.47As and GaAs have been investigated and the applications in heterojunction bipolar transistors (HBTs) are emphasized. Using the dielectric function formalism, we have characterized minority electron transport in terms of mean-free path and diffusivity. These parameters quantify the nonequilibrium (ballistic) and near-equilibrium (diffusive) transport in the p-type base region of HBTs. Our calculations demonstrate that electron energies above 300 meV provide no benefit for ballistic transport in p-type InGaAs in terms of momentum relaxation mean-free path. Especially for very heavily doped cases (∼1020 cm−3), low-energy electron injection into the p-type InGaAs base is more advantageous for base transport, as well as the succeeding transport in the base-collector depletion region. When diffusive transport is dominant, p-type InGaAs exhibits superior performance over GaAs for a wide range of doping concentrations.
Carrier capture processes in GaAs-AlGaAs quantum wells due to emission of confined phonons
Authors: Weber Gerald , de Paula Ana Maria
Published: July 2002

Carrier capture times are calculated for GaAs-AlxGa1−xAs multiple quantum wells due to the emission of confined longitudinal optical phonons via electron-phonon (Fröhlich) interaction. We compare our results with several capture times measured by optical techniques and we discuss the importance of a knowledge of the carrier excitation details in order to obtain an appropriate interpretation of the experimental results. We show that electrons excited into confined states with a large kinetic energy (which have been ignored in previous works) strongly influence the overall capture times.
Stress-optic effect in ice
Authors: Ravi-Chandar K. , Adamson B. , Lazo J. , Dempsey J. P.
Published: July 2002

It is demonstrated in this letter that single-crystal ice exhibits stress-optic effect or temporary stress-induced birefringence. This effect can be used in the exploration of the stresses using the standard techniques of photoelasticity. The photoelastic sensitivity of ice is quite high compared to glass and thus, should be quite useful in the determination of stresses in polycrystalline materials particularly near grain boundaries and in the vicinity of cracks.
Γ to X
z electron transfer times in type-II superlattices due to emission of confined phonons
Authors: de Paula Ana M. , Weber Gerald
Published: July 2002

We calculate the Γ→Xz electron transfer times due to the emission of confined longitudinal optical phonons in type-II GaAs-AlAs and AlGaAs-AlAs superlattices. A dielectric continuum model is employed to describe the electron-confined-phonon interaction and the electron envelope wave functions are obtained from a Kronig–Penney model. The calculated transfer times compare within order of magnitude, or better, with available experimental results and we obtain a good qualitative description of the transfer time dependence on the layer thicknesses.
Contact resistance of superconductor-semiconductor interfaces: The case of Nb-InAs/AlSb quantum-well structures
Authors: Nguyen Chanh , Kroemer Herbert , Hu Evelyn L.
Published: July 2002

The contact resistances of widely spaced (≫1 μm) superconducting Nb contacts to InAs-AlSb quantum wells indicate a resistive behavior of the interface, with a positive electron transfer length, while narrow-spaced contacts (≤1 μm) exhibit a strong conductance enhancement at low bias with pronounced subgap features. The data are interpreted in terms of a model in which the current across the interface is carried by Andreev reflections. From the measured transfer lengths, we estimate a single-event Andreev reflection probability of about 3.5%, but with a high backplane-enhanced overall reflection probability.
Development of high temperature superconducting Josephson junctions and quantum interference devices using low deposition temperature YBa2Cu3O7−x barriers
Authors: Reagor D. , Houlton R. , Springer K. , Hawley M. , Jia Q. X. , Mombourquette C. , Garzon F. , Wu X. D.
Published: July 2002

We have developed Josephson junctions and superconducting quantum interference devices (SQUIDs) in a superconductor-normal-superconductor edge-junction design. These devices are unusual in that we use YBa2Cu3O7−x for both the superconducting and normal layers. The only difference between the layers is the temperature of the substrate during deposition, 695 °C for the superconductor and 670 °C for the N layer. The lower deposition temperature results in material with a significantly reduced Tc and a higher resistivity. The Josephson junctions produced in this fashion have IcRn products typically greater than 100 μV at 77 K. The SQUIDs are not fully optimized but have produced modulation depths of approximately 10 μV at 76 K. These SQUID results are similar to the best results in the literature.
Gain controlled vertical cavity surface emitting lasers coupled with intracavity in-plane lasers
Authors: Shire D. B. , Tang C. L. , Parker M. A. , Swanson P. D. , Kimmet J. S.
Published: July 2002

We report the observation of optical control of the stimulated emission of a vertical cavity surface emitting laser (VCSEL) by an intra-cavity coupled in-plane laser. Depending on the overlap between the two gain regions, greater than 70% change in threshold current to complete quenching of the VCSEL, is observed. The combined device offers a wide variety of potential applications for integrated, all-optical logic devices and optical interconnects between signal planes.
Interfacial neutral- and charged-dangling-bond densities between hydrogenated amorphous silicon and hydrogenated amorphous silicon nitride in top nitride and bottom nitride structures
Authors: Min Hoonkee , Fukushi Iwao , Masuda Atsushi , Morimoto Akiharu , Kumeda Minoru , Shimizu Tatsuo
Published: July 2002

The bilayer structures composed of hydrogenated amorphous silicon (a-Si:H) and hydrogenated amorphous silicon nitride (a-Si3N4:H) are prepared on fused-quartz substrates and their interfacial Si dangling bonds (DBs) are evaluated by electron spin resonance (ESR). The ESR study reveals that the bottom nitride (BN) structure (a-Si:H/a-Si3N4:H/fused quartz) has a smaller amount of neutral DBs in the interface than the top nitride (TN) structure (a-Si3N4:H/a-Si:H/fused quartz). The photoconductivity measurements also support this finding. A larger amount of charged DBs in the interface, however, exist in the BN structure than in the TN structure. The larger amount of interfacial neutral DBs in the TN structure is likely to be caused by the UV irradiation from the plasma during the deposition of a-Si3N4:H layer.
Molecular beam epitaxial doping of ZnMgSe using ZnCl2
Authors: Ferreira S. O. , Sitter H. , Faschinger W.
Published: July 2002

In this letter we have investigated the n-type doping properties of Zn1−xMgxSe grown by molecular beam epitaxy using a solid ZnCl2 source as dopant. We describe the effect of dopant source temperature on the carrier concentration and show that the optimum doping temperature changes with varying Mg compositions. At the same time, the highest achievable electron concentration decreases as the Mg content in the sample increases, and this behavior can be described by a model that assumes that the Fermi level is pinned 120 meV above the conduction band edge of ZnSe, in an absolute energy scale.
Nonresonant microwave absorption studies of surface passivation of superconducting YBa2Cu3O7−δ thin films
Authors: Rastogi Amit , Sivasubramanian V. , Murthy V. R. K. , Hegde M. S. , Bhat S. V.
Published: July 2002

The surfaces of laser ablated thin films of YBa2Cu3O7−δ have been passivated with about 100 Å thick textured layer of Ca0.95Sr0.025Ba0.025Zr0.98Ta0.01Ti0.01O3. It is shown that this low loss dielectric material preserves the quality of the surface and also prolongs the aging process. The films (both passivated and as-deposited) have been studied for degradation on exposure to atmosphere and also on dipping directly in water. The technique of nonresonant microwave absorption is used to study the effects and extent of degradation in these films.
Small Faraday rotation measurement with a Fabry–Pérot cavity
Authors: Jacob David , Vallet Marc , Bretenaker Fabien , Le Floch Albert , Le Naour Roger
Published: July 2002

The dependence of the eigenstates of a high-finesse Fabry–Pérot cavity on intracavity circular phase anisotropies is shown to provide a very sensitive method to measure small Faraday rotations. The method is experimentally checked by measuring the Verdet constant of the air and a sensitivity of 10−10 rad is reported.
Novel instrument for measurement of multidimensional fluorescence detected circular dichroism
Authors: Thomas Mark , Patonay Gabor , Warner Isiah
Published: July 2002

A new microprocessor-controlled multichannel spectrometer for the measurement of fluorescence detected circular dichroism (FDCD) is presented. Spectra of model steroid compounds are provided to demonstrate the analytical utility of multichannel FDCD over the classical circular dichroism measurement. A detection limit of 3.05×10−8 M was determined for a solution of estrone based on a signal/noise ratio of 2 as a lower limit. The optics and electronics for the rapid acquisition of multichannel FDCD data are described in detail.
Use of manganin stress gauges for determining rarefaction wave velocities at high pressures
Authors: Rosenberg Z.
Published: July 2002

In this paper we suggest and demonstrate the usefulness of thin manganin stress gauges as time-of-arrival sensors to determine the longitudinal sound speed of solids at high shock pressures. We use an experimental configuration which is identical to that recently developed by Los Alamos researchers in which optical analyzers record the thermal radiation emitted by transparent materials at the back of the specimen. In our technique, manganin gauges are placed at the back of a stepped specimen disk and backed by thick epoxy disks. A thin flyer disk is launched towards this instrumented target and the stress-time histories at the various stations are recorded. The overtake distance is determined from the gauges’ records from which we determine the longitudinal sound velocity at high pressures.
dc electric field meter with fiber-optic readout
Authors: Johnston Alan R. , Kirkham Harold , Eng Bjorn T.
Published: July 2002

The design of a dc electric field meter capable of measuring the magnitude and direction of the electric field at an arbitrary location above the ground plane is described. The meter is based on measuring induced charge on a split cylindrical electrode pair which is rotated around its axis of symmetry. Data readout is by fiber-optic cable using pulse frequency encoding. The sensing head is electrically isolated. Initial results are reported from a series of tests at General Electric’s High Voltage Transmission Research Facility, Pittsfield, MA. The electric field was measured in a large test cage and under a dc test line. Measurement of field magnitude and direction around a human subject standing under the conductor was demonstrated.
Electron beam time-of-flight plasma potential diagnostic
Authors: Archer B. T. , Lieberman M. A. , Meuth H.
Published: July 2002

A time-of-flight method for measuring electrostatic potentials in plasmas using a modulated electron beam has been developed. The beam is injected along the magnetic field in a cylindrical plasma geometry. The phase of the electron beam modulation is detected using a Rogowski loop which encircles the beam and plasma, and the phase information is in turn related to the electrostatic potential. Measurements in vacuum and in plasma have been performed.
Spanning short cavity TEM00q frequency spacings by simultaneous excitation of many transverse modes
Authors: Jacobs Stephen F. , Johnston Steve C. , Bass Dan
Published: July 2002

We report simultaneous excitation of at least 19 transverse modes of a curved-plate, degenerate, Fabry–Perot resonator. The usefulness of spanning large free spectral ranges by means of transverse mode excitation is described.
A dedicated soft x-ray beamline for x-ray absorption spectroscopy (abstract)
Authors: Morrison T. I. , Lien N. C. , Bunker B. A. , Sayers D. E. , Heald S. M. , Fareria L. , Scrofani J.
Published: July 2002

We will present the design, capabilities, and characteristics of the recently commissioned Beamline X-11B at the National Synchrotron Light Source. This line has been designed to optimally function in the ‘‘soft’’ x-ray regime (1–5 keV), but can easily be used up to the design limit of the storage ring. The beamline, which shares a common vacuum with the storage ring, is equipped with a double crystal fixed-exit UHV monochromator. The monochromator crystals are mounted on rotating carousels that can each carry four crystals, permitting crystal changes to cover different energy ranges without breaking vacuum. The incident radiation carousel is water cooled and the second carousel can be heated, allowing thermal equilibration of the crystals. The line can be equipped with a UHV backend or a ‘‘fast-turnaround’’ backend. The UHV backend can be used for surface EXAFS and other surface techniques (XPS, Auger) on line. The fast-turnaround backend has been designed to work under less stringent vacuum demands, permitting relatively rapid sample changes for systems that are not oxygen sensitive. We acknowledge the support of the US DOE, Division of Materials Sciences, under Contract No. DE-AS05-ER10742 for its role in the development and operation of Beamline X-11 at the NSLS. The NSLS is supported by the US DOE, Divisions of Materials Sciences and Chemical Sciences, under Contract No. DE-AC02-76CH00016.
Spherically bent crystal spectrometer for inelastic high-energy x-ray scattering experiments
Authors: Nagasawa Hisao
Published: July 2002

The design of a high-resolution spectrometer for the energy analysis of inelastically scattered synchrotron x rays of 40 keV is presented. The spectrometer utilizes a spherically bent Ge crystal in near-backscattering geometry combined with a double-crystal monochromator in order to measure the near edge and extended energy loss fine structure in both the x-ray Raman scattering (low momentum transfer) and the Compton scattering (high momentum transfer) regimes for medium atomic number materials (Z=11–18). A counting rate of a few counts per second can be obtained with a resolution of the order of a few eV measured for the FWHM of the Rayleigh line by optimum utilization of photons from the storage ring at the European Synchrotron Radiation Facility.
Undulator engineering for synchrotron radiation applications
Authors: Slater J. M. , Gottschalk S. C. , James F. E. , Quimby D. C. , Robinson K. E. , Valla A. S.
Published: July 2002

Six undulators have been designed and built by STI since 1980 for synchrotron and FEL applications. Several design concepts, producing successively higher fields, have been developed during this period. A wedged-pole hybrid design has been demonstrated to yield the highest field to date for a given gap-to-wavelength ratio. A simple method of reducing field errors has been demonstrated on the wedged-pole hybrid, and it may lead to significant cost reduction through relaxation of mechanical and magnet tolerances.
Simulation of a magnetic field correction scheme for a Halbach-type undulator
Authors: Isoyama G.
Published: July 2002

An electron-beam trajectory in a Halbach-type undulator with simulated magnetization errors in its component magnet blocks has been calculated using a three-dimensional magnetic field calculation program. The errors taken into account were deviations of the magnetization strength from a nominal value and a deviation of the magnetization direction from a nominal axis. Both uniform and Gaussian distributions of the error magnitudes are assumed for the component magnet blocks of an ideal reference undulator. A simple method for rearranging magnet pairs is discovered. The field integrals are reduced by factors of 4–15 on the average with the method, and the local distortion of the trajectory is strongly corrected. It is found that the distortion of the trajectory in the corrected undulator is almost independent of the magnet gap.
Development of a permanent magnet for a high performance undulator
Authors: Takabayashi H. , Okada S.
Published: July 2002

A new permanent magnet material (NEOMAX-35H) has been designed for generating high brightness synchrotron radiation. Measuring methods of the magnets and their assembly process are also discussed. It has been proved that the NEOMAX-35H magnet is a suitable magnetic material for undulators and wigglers.
Conceptual design of a 1.5-GeV x-ray ring
Authors: Tobiyama M. , Endo I. , Ohta T. , Sugano T. , Taniguchi M.
Published: July 2002

We have designed a 1.5-GeV storage-ring system for a new synchrotron-radiation project at Hiroshima. The storage ring has an achromatic structure with six dispersion-free straight sections for insertion devices. Superconducting horizontal wigglers are used to generate hard x ray. The multipole field of the wiggler causes no problem on beam dynamics. In spite of its small size, 100 m in circumference, the ring can generate excellent synchrotron radiation in a wide wavelength region from VUV up to hard x rays.
Kharkov 3-GeV pulse stretcher ring as a source of synchrotron radiation
Authors: Boldyshev V. F. , Gladkikh P. I. , Grigor’ev Yu. N. , Guk I. S. , Efimov S. V. , Karnaukhov I. M. , Kononenko S. G. , Mocheshnikov N. I. , Popkov Yu. P. , Tarasenko A. S. , Telegin Yu. N. , Chechetenko V. F. , Shcherbakov A. A. , Titov V. A. , Nagaenko M. G.
Published: July 2002

The article discusses the possibility of using the pulse stretcher ring, designed at the Kharkov Institute of Physics and Technology, as a synchrotron radiation source (SRS). Comparison is made between our SRS design parameters and those of other dedicated SRSs.
Laser diode based electro-optic measurement system with high voltage resolution
Authors: Baur G. , Sölkner G.
Published: July 2002

A laser diode based probing system for the electro-optic measurement of fast electrical wave forms has been developed. The system has been optimized to yield a very high voltage sensitivity of 5 mV/√Hz which is only a factor of 1.4 above the shot noise limit. Furthermore, by a proper orientation of the crystal probe the sensitivity to field components parallel to the propagating laser beam are greatly enhanced and absolute voltage measurements are thus made possible which is also verified experimentally. The temporal resolution is limited by the duration of the laser pulses which in our case is below 40 ps. A comparison with electrical sampling measurements shows the good performance of the detection system. Because of its low invasiveness the electro-optic crystal probe can be applied to wave form measurements on lines within integrated circuits as well as for interconnects on board level.
Oxyhydrogen burner for low-temperature flame fusion
Authors: Ueltzen M. , Brüggenkamp T. , Franke M. , Altenburg H.
Published: July 2002

An oxyhydrogen burner as described in this article enables the growth of crystals by Verneuil’s technique at temperatures of about 1000 °C. The powder fed to the crystal passes along a low-temperature pathway through the flame, so that evaporation of volatile components is prevented. Low-temperature flame fusion of superconducting Y-Ba-cuprate is reported.
A detection technique for scanning force microscopy
Authors: Proksch Roger , Dahlberg E. Dan
Published: July 2002

A detection technique for use with noncontact attractive mode force microscopes is described. The technique relies on the accurate measurement of the resonant frequency of a cantilever probe as it rings in response to a very short excitation pulse. The resonant frequency reflects the spatially varying interactions between the probe and the specimen under study. This technique is for cantilevers with relatively high Q values (≳1000) as might be expected with vacuum operation. This technique has the advantage of being relatively easy to implement with commercially available instrumentation, while still providing excellent sensitivity and wide bandwidth operation. A sensitivity of 0.02 Hz at 75 kHz in a bandwidth of 50 Hz is comparable with other techniques. In addition, it is easy to accommodate a wide variety of cantilevers with different vibrational characteristics. A photomicrograph of the stray fields above bits written in a magnetic hard disk is presented, demonstrating the application of the technique to magnetic force microscopy.
System for velocity ratio measurements of an axis-rotating electron beam
Authors: Boulais K. A. , Choe J. Y. , Namkung W. , Chun S. T. , Choi E. H.
Published: July 2002

A novel system to measure the ratio of transverse velocity to axial velocity (α) of a low voltage, axis-rotating electron beam is described herein. With the system, more information about the beam can be obtained than from the usual slit/phosphor screen system. Since most of the beam is undisturbed before the phosphor screen, the beam radius and azimuthal symmetry can be quantified in combination with the beam α along various axial positions. The diagnostic is applied to a Cusptron microwave tube to measure these electron beam parameters which are important for high tube efficiency. Two magnetic field profiles are used to study various causes of low beam quality, while a third profile is used in attempt to maintain a high quality beam. By using the described system, it is shown that the third profile significantly increases beam quality. The system can easily be extended to higher energy beams with an appropriate scintillator.
Calibration technique of time lag between nonsynchronous, ultrafast digitizers for dual homodyne spectroscopy
Authors: Nagatsu Masaaki , Ariga Hiroo , Tsukishima Takashige
Published: July 2002

In situ calibration technique of time lag between nonsynchronous, ultrafast wave form digitizers with a sampling frequency of 1.35 GHz has been developed for application to the dual homodyne receiver system for the ion Thomson scattering experiment. By making use of the proposed calibration technique, time lag between two nonsynchronous digitizers is measured with an accuracy of ±0.015 ns. The present calibration method is applicable to any other multichannel digitizers system for simultaneous measurements, such as cross-correlation diagnostics between high frequency, broadband signals, or measurement of ultrashort pulse wave forms in a single shot.
Symmetric light emitting devices from poly(p-di ethynylene phenylene) (p-di phenylene vinylene) derivatives
Authors: Jeglinski S. A. , Amir O. , Wei X. , Vardeny Z. V. , Shinar J. , Cerkvenik T. , Chen W. , Barton T. J.
Published: July 2002

Light emitting devices were fabricated from 2,5-dialkoxy derivatives of poly(p-di ethynylene phenylene-p-di phenylene vinylene) (PDEPDPV) sandwiched between indium tin oxide (ITO) and Al. The current–voltage (I–V) curve, electroluminescence (EL) intensity-voltage (IEL–V) curve, and the EL spectra were identical in forward and reverse bias. The I–V curves were also symmetric under illumination, with I≊0 and V=0, suggesting a negligibly small internal electric field. At high bias voltage, carrier injection was found to be dominated by tunneling at the interfaces. At low bias voltage, tunneling among localized states at the Fermi level prevailed. The behavior is discussed in relation to Fermi-level pinning at defect states in the interfaces with the ITO and Al.
Signal analysis of transients in pulsed photoacoustic spectroscopy
Authors: Schurig D. A. , Klunder G. L. , Shannon M. A. , Russo R. E. , Silva R. J.
Published: July 2002

A finite difference model was constructed to describe the origin of the complex transients in pulsed photoacoustic spectroscopy signals. With inclusion of boundary conditions and material interfaces, the model is shown to give qualitative agreement with experimental transients. The model provides insight into the results of varying the photoacoustic-cell materials and/or geometric configuration for cell optimization. The transients are found to contain significant information regarding resonant modes in the photoacoustic cell assembly. The transient signal behavior is explained in terms of these resonant cavity modes, and it is determined which cell cavities are relevant to a given time segment of the signal. Analytical detection limits are correlated with each point on the transient signal.
Wavelength dependence of two-beam coupling gain coefficients of BaTiO3:Ce crystals
Authors: Zhang Jiasen , Dou S. X. , Gao Hong , Zhu Yong , Ye Peixian
Published: July 2002

Two-beam coupling gain coefficients of transmission and reflection gratings in BaTiO3:Ce crystals versus wavelength between 570 and 680 nm have been measured. The former decreases more quickly than predicted by theory. The latter was found to vary significantly with wavelength, while theory shows that it should vary little. In order to explain the experimental results we assumed that the effective carrier number density Neff depends on wavelength. By calculating Neff from the measured results we found that Neff is approximately a linearly decreasing function of wavelength. The slopes and intercepts for the linear functions are given for the two crystals studied.
Geometrical optimization of a longitudinal resonant photoacoustic cell for sensitive and fast trace gas detection
Authors: Bijnen F. G. C. , Reuss J. , Harren F. J. M.
Published: July 2002

We present a quantitative discussion of the acoustic transmission line theory pertaining to experimental results from a resonant photoacoustic cell excited in its first longitudinal mode. Window absorption is optimally suppressed by buffer volumes and tunable air columns. The acoustic behavior of an ultrasensitive one inch condenser microphone is quantitatively described. A small and sensitive photoacoustic cell has been developed for intracavity use in a CO2 waveguide laser permitting measurements of ethylene down to 6 pptv (long term stability 20 pptv) with a time response of 2 s at a trace gas flow of 6 1/h. To demonstrate the fast time response within a biological application the instant ethylene release of a single tomato is measured.
Design and performance of a belt-type high pressure, high temperature apparatus
Authors: Venkateswaran C. , Anbukumaran K. , Victor Jaya N. , Natarajan S.
Published: July 2002

A modified belt-type high pressure, high temperature apparatus without tungsten carbide has been designed and constructed based on the theory of multilayered pressure vessels. The calculated interferences seem to give adequate support for reaching a high pressure of 10 GPa and simultaneously temperatures up to 1400 °C. We estimate the highest pressure reached in our experiment to be ∼17 GPa in the sample region, based on the load versus pressure curve calibrated in bismuth, tin, and lead. Talc gaskets were used along with a tubular graphite furnace for high temperatures. This represents a relatively simple and inexpensive device for material synthesis and phase transformation studies.
5.6 tesla Fourier transform ion cyclotron resonance mass spectrometer for analysis of volatile complex mixtures
Authors: Rodgers Ryan P. , White Forest M. , McIntosh Daniel G. , Marshall Alan G.
Published: July 2002

An all-glass heated inlet coupled to a homebuilt 5.6 T Fourier transform ion cyclotron resonance mass spectrometer generates stable mass spectra from a volatile mixture for 2 h from as little as 1 μL of injected sample. A dynamic range of ∼500 and ultrahigh mass resolving power, m/Δm50%≈320 000, are shown for a series of test compounds. A raw diesel fuel sample (with hundreds of components over a wide boiling point range) mass spectrum gave ∼500 resolved peaks over a range, 90⩽m/z<300, from which molecular formulas could be assigned from accurate (⩽±0.8 ppm) mass measurements.
Control of the double pendulum optics suspension system of a 30 m triangular Fabry–Pérot cavity
Authors: Barsuglia M. , Bondu F. , Heitmann H. , Heusse Ph. , Man C. N. , Matone L.
Published: July 2002

We present a technique for the control of a double pendulum suspension system used to carry the optical elements of a 30 m long Fabry–Pérot cavity, a prototype for the mode cleaner of the VIRGO experiment. The movement of the payload is sensed with a charge coupled device camera, and the feedback forces are applied to the intermediate stage of the suspension via coil–magnet systems. The control strategy is explained and the application of the system for the longitudinal locking of the cavity is demonstrated.
Toroidal cross capacitor for measuring the dielectric constant of gases
Authors: Buckley Thomas J. , Hamelin Jean , Moldover M. R.
Published: July 2002

We describe toroidal cross capacitors built to accurately measure the dielectric constant of gases. We tested the capacitors by measuring the dielectric polarizability of helium and argon at 7 and 50 °C at pressures up to 3 MPa. For helium, the results are consistent with the ab initio calculation of the molar polarizability and are limited by the uncertainties of the capacitance measurements. For argon, the results are consistent with the best previously published measurements of the polarizability and are limited by the uncertainties of the pressure measurements. Lessons learned are provided.
Sharp photoluminescence lines from nitrogen atomic-layer-doped GaAs
Authors: Makimoto Toshiki , Kobayashi Naoki
Published: July 2002

We performed nitrogen atomic-layer doping into GaAs grown by molecular beam epitaxy using nitrogen molecules (N2) cracked by a hot tungsten filament. While uniformly nitrogen-doped GaAs layers show relatively weak nitrogen-related photoluminescence lines, nitrogen atomic-layer-doped GaAs layers show a series of sharp and strong photoluminescence lines. The dominant photoluminescence line was observed at 1.4437 eV, where an exciton bound to the nitrogen isotropic traps has the highest binding energy.
Addendum: ‘‘Low noise YBa2Cu3O7−x-SrTiO3-YBa2Cu3O7−x multilayers for improved superconducting magnetometers’’ [Appl. Phys. Lett. 66, 373 (1995)]
Authors: Dantsker E. , Ludwig F. , Kleiner R. , Clarke John , Teepe M. , Lee L. P. , McN. Alford Neil , Button Tim
Published: July 2002

The improvement in performance of superconducting magnetometers is discussed. It is demonstrated that the use of multilayer devices in a flip-chip arrangement, enables one to select the lowest noise SQUID from several made on a single substrate. (AIP)
Effect of interfacial dopant layer on transport properties of high purity InP
Authors: Watkins S. P. , Cheung H. D. , Knight G. , Kelly G.
Published: July 2002

Temperature dependent Hall measurements were used to investigate the role of unintentional interfacial dopant layers on the electrical properties of high purity InP. Secondary ion mass spectroscopy was used to measure the level of Si contamination present in several samples at the substrate-epilayer interface. We show that the presence of interfacial dopant gives rise to two layer conduction whose temperature dependence mimics the freezeout behavior expected for a deep donor. However, the magnetic field dependence of the Hall data at low temperatures shows the expected behavior for the two layer model, including an order of magnitude variation in the apparent sheet concentration and Hall mobility over the range from 0.1 to 0.6 T at 77 K. We show that the true bulk mobility and carrier concentration can be accurately determined in samples with high interfacial contamination by performing Hall measurements at several magnetic fields at 77 K.
Widely tunable single-frequency erbium–ytterbium phosphate glass laser
Authors: Taccheo S. , Laporta P. , Svelto C.
Published: July 2002

A tunable, single-frequency, diode-pumped miniature Er:Yb:glass laser of high power is described. The laser exhibits two intervals of continuous tuning, from 1549 to 1563 nm (Δλ=14 nm) and from 1531 to 1540 nm (Δλ=9 nm), respectively. For an input pump power of 140 mW, a single frequency output power of 20 mW at 1563 nm has been obtained. The tuning characteristics are found to be strictly related to the gain–loss balance of the laser cavity.
Defect characterization of etch pits in ZnSe based epitaxial layers
Authors: U’Ren G. D. , Goorsky M. S. , Meis-Haugen G. , Law K. K. , Miller T. J. , Haberern K. W.
Published: July 2002

Three distinct etch pit features in ZnSe based epitaxial layers have been identified. The features were observed with optical dark field microscopy and confirmed to be pits using scanning electron microscopy. Using transmission electron microscopy, we associated different etch pits with characteristic crystallographic defects which are common in epitaxially grown II–VI materials. Frank-type stacking faults form the largest etch pit followed by a paired configuration of Shockley- type stacking faults. The smallest etch pit is due to a single Shockley-type stacking fault. This study represents one of the first examples of identifying crystallographic defects in II–VI wide bandgap materials using etch pit delineation.
On the role of field-induced polarization in the surface electrification of insulators
Authors: Cunningham Samia
Published: July 2002

The single-point electrification of silicon dioxide, sapphire, and silicon nitride has been studied using noncontact scanning force potentiometry. For all these insulators, the potentiometric signal showed a multicomponent decay which was rapid compared to the charge retention characteristics of the bulk material. The magnitude of the initial signal varied linearly with contact bias voltage: a change from positive to negative bias reversed the sign of the signals without changing their magnitude or decay dynamics. These features suggest that the initial increase in surface potential in single contact electrification may be due to field-dependent polarization rather than net charge transfer.
Formation of ultrathin, buried oxides in Si by O+ ion implantation
Authors: Holland O. W. , Fathy D. , Sadana D. K.
Published: July 2002

A technique is presented for forming a silicon-on-insulator material with an ultrathin buried oxide by utilizing the separation by implantation of oxygen or SIMOX method. It overcomes the problem of oxide continuity encountered during standard SIMOX processing when the O+-implanted dose is scaled down to decrease the thickness of the buried oxide below ∼0.1 μm. To promote the formation of ultrathin buried oxides (during post-implantation annealing), the implantation process was modified to produce a microstructure which promotes coalescence of the oxygen into a continuous layer. This was accomplished by slightly modifying the standard (≳500 °C) process so that the final increment of the dose is implanted near room temperature. This dose is chosen to selectively amorphize the region near the ion’s range which will yield a high-defective layer during subsequent annealing. It is shown that this layer, which can consist of polysilicon, provides a template or guide upon which the oxide forms. Buried oxides prepared in this way are shown to be continuous and without Si inclusions while the standard process yields a broken layer with severe discontinuities.
The characteristics of high-resistance layers produced in n-GaAs using MeV-nitrogen implantation for three-dimensional structuring
Authors: Miao J. , Tiginyanu I. M. , Hartnagel H. L. , Irmer G. , Monecke J. , Weiss B. L.
Published: July 2002

The radiation damage introduced in n-GaAs by 4-MeV N+ implantation at a dose of 1×1015 cm−2 has been analyzed using micro-Raman spectroscopy. Implantation followed by annealing at 600 °C was found to produce a strongly compensated near-surface layer possessing a high crystalline quality. At the same time a pronounced disorder was found underneath the high-resistance layer which enables the fabrication of 2.5-μm thick free-standing membranes using selective electrochemical etching techniques.
A model for optically quenched lasers
Authors: Parker M. A. , Shire D. B.
Published: July 2002

A model is presented for optically controlling the gain of a semiconductor laser by introducing photons from a second coherent source into the side of the laser. We find that the threshold current of the laser increases in direct proportion to the overlap between the two modes and the photon density from the coherent source. An easy-to-use, closed-form expression relates the optical power emitted from the laser to the bias and threshold currents.