bluuebunny/crossref_metadata_2025 huggingface dataset:
Activation of ion implanted dopants in α-SiC
Authors: Ahmed S. , Barbero C. J. , Sigmon T. W.
Published: July 2002

In this letter, activation of implanted dopants in 6Hα-SiC using a pulsed excimer laser is reported. Commercially available substrates are implanted with nitrogen or aluminum. A 308 nm pulsed excimer laser is then used to anneal the samples which are held at room temperature. Point contact current-voltage (PCIV) measurements are used to extract the carrier concentration of the annealed layers. Initial results suggest complete activation of the implanted dopants. Pulsed laser annealing of ion implanted SiC appears to be an attractive option as compared to furnace annealing at high temperatures.
Phase-matched frequency doubling in an aluminum nitride waveguide with a tunable laser source
Authors: Blanc D. , Bouchoux A. M. , Plumereau C. , Cachard A. , Roux J. F.
Published: July 2002

Frequency doubling is observed in an aluminum nitride waveguide deposited by dc reactive magnetron sputtering. Phase-matching conditions are obtained by tuning the wavelength of an optical parametric oscillator pumped by a pulsed Nd:YAG laser. The maximum second harmonic generation efficiency is obtained for the TM0(ω)-TM2(2ω) conversion process and is estimated to be around 4×10−8 W−1.
Sources of spin-polarized beams (invited)
Authors: Clegg Thomas B.
Published: July 2002

Sources producing beams of spin-polarized atoms and ions are now widely used in nuclear physics. Modern systems are increasingly expensive and complex. They provide a variety of species and beam polarizations with intensities often sufficient for experimental needs. The laboratory seeking such a device for its program must evaluate a variety of options and match them to its accelerator, experimental program, and expected resources. The major systems and techniques used are surveyed and criteria dictating the choice of source for particular experimental applications are discussed briefly.
Spectroscopy with the MEGA spectrometer, a very-high-resolution grating spectrometer
Authors: Lindblom P. , Meinander N. , Olsson T.
Published: July 2002

A high-resolution grating spectrometer with no moving parts is described. The dispersive element consists of four echelle gratings mounted so that the light is diffracted in series. Wavelength scanning is accomplished by varying the density of the gas filling the monochromator housing. Rayleigh-Brillouin spectra of gases at various pressures recorded with the spectrometer illustrate the performance of the instrument.
Negative ion current measurements with the modified JAERI probe
Authors: Jimbo Kouichi , Iima Masashi
Published: July 2002

The modified JAERI probe, developed to measure negative hydrogen ion current, is a kind of Faraday cup with Nd magnets to distinguish negative ions from electrons. An extractable negative ion current is easily evaluated for extraction voltage less than 2 kV in the grounded negative ion source.
Development of a dc low pressure D− surface-conversion source using a 10-cm-diam solid barium converter
Authors: Kwan J. W. , Anderson O. A. , Chan C. F. , Cooper W. S. , deVries G. J. , Kunkel W. B. , Leung K. N. , Lietzke A. F. , Steele W. F. , van Os C. F. A. , Wells R. P. , Williams M. D.
Published: July 2002

A D− surface-conversion source using a solid barium converter is designed for steady-state operation to produce 200 mA of D−. A similar ion source of twice the size as the one discussed here will meet the requirements set by the present US-ITER neutral beam injector design. Among the possible types of ion sources being considered for the US-ITER neutral beam design, the barium converter surface-conversion source is the only kind that does not use cesium in the discharge. This absence of cesium will minimize the number of accelerator breakdowns.
Performance of a wideband multilayer polarizer for soft x rays
Authors: Yanagihara Mihiro , Maehara Takumi , Nomura Hiroshi , Yamamoto Masaki , Namioka Takeshi , Kimura Hiroaki
Published: July 2002

Performance of a Ru/C multilayer polarizer of double-crystal x-ray monochromator type has been evaluated in the soft x-ray region using synchrotron radiation. The throughput efficiencies for s-polarized light were found to be 11.5% at 100 eV and higher than 4% over an energy range of 80–150 eV without higher-order contamination. Its polarizance was higher than 99.0% at 88 eV and more than 94% over a range of 80–110 eV.
Mott electron polarimetry
Authors: Gay T. J. , Dunning F. B.
Published: July 2002

Electron polarimeters based on Mott scattering are extensively used in atomic and molecular, solid state, nuclear, and high-energy physics. This use stems from the increasing realization that much additional information concerning many physical processes can be obtained through spin-dependent measurements. In this review we discuss the basic physics and application of Mott polarimetry. A number of different Mott polarimeter designs are described that illustrate the wide range of operating energies (10 eV–1 MeV) and geometries that can be used in such instruments. The calibration of Mott polarimeters is discussed together with the potential sources of systematic error that can arise and that can limit measurement accuracies. The aim is to present a comprehensive practical guide to Mott polarimetry and the capabilities of the technique.
Computer correction for distorted STM images
Authors: Cai C. Z. , Chen X. Y. , Shu Q. Q. , Zheng X. L.
Published: July 2002

In quite a few cases, the geometric distortion of a scanning tunneling microscope (STM) image is essentially caused by the nonorthogonal scanning. A physical and mathematical model is proposed to correct such distortion, giving a satisfactory result.
Resolution in surface plasmon microscopy
Authors: Berger Charles E. H. , Kooyman Rob P. H. , Greve Jan
Published: July 2002

In this article we demonstrate how to obtain the ultimate lateral resolution in surface plasmon microscopy (SPM) (diffraction limited by the objective). Surface plasmon decay lengths are determined theoretically and experimentally, for wavelengths ranging from 531 to 676 nm, and are in good agreement. Using these values we can determine for each particular situation which wavelength should be used to obtain an optimal lateral resolution, i.e., where the plasmon decay length does not limit the resolution anymore. However, there is a trade-off between thickness resolution and lateral resolution in SPM. Because of the non-optimal thickness resolution, we use several techniques to enhance the image acquisition and processing. Without these techniques the use of short wavelengths results in images where the contrast has vanished almost completely. In an example given, a 2.5 nm SiO2 layer on a gold layer is imaged with a lateral resolution of 2 μm, and local reflectance curves are measured to determine the layer thickness. The SPM image is compared with an atomic force microscopy image of the same object. We obtain a 3 μm resolution when thickness differences within a lipid monolayer are imaged and measured.
Low-frequency noise in low-T
c multiloop magnetometers with additional positive feedback
Authors: Drung Dietmar
Published: July 2002

The low-frequency noise in multiloop dc superconducting quantum interference device (SQUID) magnetometers fabricated from low-Tc (transition temperature) materials was investigated. The magnetometers are operated in a flux-locked loop based on additional positive feedback (APF). A simple noise reduction scheme for dc SQUIDs with APF is presented that eliminates the influence of critical current and resistance fluctuations without deteriorating the white noise performance. Applying this scheme to a magnetometer with a low-frequency two-level switching due to a single trap in the SixNy tunnel barrier reduced the switching amplitude of ≂10−3 Φ0 by at least two orders of magnitude down to a level below the intrinsic magnetometer flux noise. Using simple direct-coupled readout electronics with a 10 kHz bias reversal, a high bandwidth of ≂1 MHz, a low white flux noise of 1.5×10−6 Φ0/√Hz, and a 1/f noise corner frequency of 4 Hz have been measured.
Technique for the continuous measurement of projectile velocities in plate impact experiments
Authors: Ramesh K. T. , Kelkar N.
Published: July 2002

This paper describes a simple yet accurate technique for the continuous measurement of projectile velocities in plate impact experiments (the impact velocity is a critical parameter in the interpretation of such experiments). The technique, known as the laser line velocity sensor (LLVS), uses a laser line generator to generate a laser sheet of uniform intensity that is incident on a photodiode at the focus of a collecting lens. The amount of light reaching the photodiode diminishes as the projectile intersects the laser sheet, and so a simple calibration procedure in conjunction with a high-bandwidth optoelectronic system provides a measure of the projectile velocity. Since the measurement is continuous, both the projectile velocity and acceleration can be obtained. The LLVS is very stable, does not need reconstruction after impact, does not need frequent recalibration, and is insensitive to rigid body motions. An example of the application of the technique is provided.
First results of collective scattering on JET (invited)
Authors: Hoekzema J. A. , Bindslev H. , Egedal J. , Fessey J. A. , Gatcombe C. P. , Hammond N. P. , Hughes T. P. , Machuzak J. S. , Oosterbeek J. W. , Roberts P. J. , Stevens A. L. , Stott P. E.
Published: July 2002

The fast ion and α-particle diagnostic at JET is based on collective Thomson scattering of high power millimeter-wave radiation. The principal aim of the diagnostic will be the measurement of the spatially resolved velocity distribution of fast α particles when tritium is introduced in JET plasmas, although several other applications are foreseen. The diagnostic uses a 140 GHz, 500 kW, gyrotron as the source of probing radiation and a heterodyne detection system. The diagnostic came into operation during the last JET operational campaign. First measurements were made of the thermal and mildly suprathermal (induced by ion cyclotron resonance heating) ion feature. The results confirmed expectations, indicating that the diagnostic should give the predicted performance for observation of α-particle populations in the DT phase. The signal-to-noise ratio is limited by the noise on the background radiation (electron cyclotron emission), which has a minimum around 140 GHz only when JET is operated at B∼3.4 T. To further improve the S/N and to make the diagnostic suitable for operation at higher field, which is now being considered for some of the DT plasmas, a viewing dump will be installed before the DT phase.
An earth’s field nuclear magnetic resonance apparatus suitable for pulsed gradient spin echo measurements of self-diffusion under Antarctic conditions
Authors: Callaghan P. T. , Eccles C. D. , Seymour J. D.
Published: July 2002

We describe an earth’s field nuclear magnetic resonance apparatus which can be used to carry out pulsed gradient spin echo (PGSE) diffusion measurements. The instrument is portable and incorporates automated process control, allowing direct measurement of the Larmor precession. The use of a common clock for pulse sequencing, excitation pulse synthesis, and detection, results in a phase stability sufficient for accurate signal averaging. The analysis of PGSE data under the conditions of a weak detection field is discussed and measurements of diffusion are presented under both New Zealand and Antarctic conditions. The Antarctic results include an example of restricted diffusion of brine water in McMurdo Sound sea ice.
Midinfrared free electron laser power delivery through a chalcogenide glass fiber
Authors: Awazu Kunio , Ogino Seiji , Nagai Akio , Tomimasu Takio , Morimoto Shozo
Published: July 2002

This article reports on the results of free electron laser (FEL) power transmission measurements through chalcogenide fibers. The FEL power transmission was tested by two types of chalcogenaide NSEG fibers, a normal fiber and a tapered fiber, made by varying the drawing speed from 2 to 17 cm/min. As a result, the tapered NSEG fiber is able to transmit 5–7 μm FEL power with a 10 MW/micropulse without surface damage. Tapered NSEG fibers are useful, therefore, for power transmission to narrow spaces such as the slide glass between the stage and the objective lens in a microscope.
A compact high-current microwave-driven ion source
Authors: Wills J. S. C. , Lewis R. A. , Diserens J. , Schmeing H. , Taylor T.
Published: July 2002

A simple, compact, high-current, 2.45 GHz microwave ion source has been built and tested. The source uses permanent magnets rather than electrical solenoids to provide the required magnetic field. Developed from an earlier microwave-driven ion source, the plasma generator volume has been reduced by a factor of 8 with no discernible change in rf efficiency or feed consumption. A hydrogen beam of over 60 mA has been extracted from a single 5 mm diameter aperture with a proton fraction of 80% at a rf power of 450 W and a gas flow of 1.5 sccm.
A low-temperature dynamic mode scanning force microscope operating in high magnetic fields
Authors: Rychen J. , Ihn T. , Studerus P. , Herrmann A. , Ensslin K.
Published: July 2002

A scanning force microscope was implemented operating at temperatures below 4.2 K and in magnetic fields up to 8 T. Piezoelectric quartz tuning forks were employed for nonoptical tip–sample distance control in the dynamic operation mode. Fast response was achieved by using a phase-locked loop for driving the mechanical oscillator. Possible applications of this setup for various scanning probe techniques are discussed.
A molecular beam apparatus for eigenstate-resolved studies of gas-surface reactivity
Authors: McCabe P. R. , Juurlink L. B. F. , Utz A. L.
Published: July 2002

A new supersonic molecular beam-surface scattering apparatus permits eigenstate-resolved measurements of gas-surface reactivity. Infrared light from a narrow-bandwidth tunable laser intersects a supersonic molecular beam and prepares an ensemble of molecules in a single rotational and vibrational quantum state. The energized molecules, with their well-defined translational, vibrational, and rotational energies, pass into an ultrahigh vacuum chamber and impinge on a single crystal metal surface where their reactivity is quantified. The apparatus provides independent control over translational, vibrational, and rotational degrees of freedom and permits highly detailed studies of gas-surface reactivity. In this article we describe the design and characterization of our apparatus and illustrate its use to study the dissociative chemisorption of methane on Ni(100).
Regional blood flow measurements from fluorescent microsphere images using an Imaging CryoMicrotome
Authors: Kelly Jeffrey J. , Ewen Jon R. , Bernard Susan L. , Glenny Robb W. , Barlow Clyde H.
Published: July 2002

An automated image acquisition and analysis system has been developed that rapidly determines regional blood flow by using the locations of fluorescent microspheres deposited in tissue. A motor-driven microtome removes sections of frozen tissues in steps variable between 10 and 100 μm. Filtered light excites microsphere fluorescence from the exposed surface of the remaining tissue block. A charge coupled device camera records fluorescence images from the tissue block surface after removal of each slice. Approximately 450 images are analyzed from perfused rat hearts providing precise x, y, and z locations of about 10 000 microspheres. Image analysis of fluorescent microspheres is much faster and less labor intensive than traditional indirect microsphere-based flow measurements while providing higher quality data.
Scanning flow cytometry for individual particle analysis
Authors: Maltsev Valeri P.
Published: July 2002

With this work we review the development of theoretical and experimental aspects of the scanning flow cytometry (SFC). The optical and hydrodynamic systems of the SFC provide the measurement of fluorescence and light scattering of individual particles with a typical rate up to 500 particles/s. In addition the optical system of the SFC has the capability of individual particle analysis beyond that of an ordinary flow cytometry. The SFC measures an entire angular dependency of light scattering intensity (flying light scattering indicatrix, FLSI) over angles ranging from 5° to 120°. The fluorescence collection efficiency of the SFC approaches 1/3 of a sphere. Moreover, the optical system of the SFC provides the measurement of fluorescence in a time-resolved mode on a microsecond time scale. The processing of the output data in light scattering is based on a parametric solution of the inverse light-scattering problem, the FLSI method. The FLSI method allows the determination of size and refractive index of spherically modeled particles over a range of diameters from 0.9 to 15 μm and a range of refractive indexes from 1.37 to 1.60. The performance of the SFC in different applications has been demonstrated.
Data acquisition card for fluctuation correlation spectroscopy allowing full access to the detected photon sequence
Authors: Eid John S. , Müller Joachim D. , Gratton Enrico
Published: July 2002

Typically, fluctuation correlation spectroscopy (FCS) data acquisition cards measure the number of photon events per time interval (i.e., bin)—time mode. Commercial FCS cards combine the bins through hardware in order to calculate the autocorrelation function. Such a design therefore does not yield the time resolved photon sequence, but only the autocorrelation of that sequence. A different acquisition method which measures the number of time intervals between photon events has been implemented—photon mode. This method takes advantage of the fact that in FCS the rate of photon counts is much less than the frequency of the clock that is used to determine the temporal location of the photons. By using this new mode of data acquisition, the current card design allows for 25 ns time resolution. The data acquisition card can operate in both time and photon mode and yields the time resolved sequence of photon arrivals in both cases. Therefore, the data is available for analysis by any method(s), such as but not limited to, autocorrelation, photon counting histogram, and higher order autocorrelation.
TRIPS: The high intensity proton source for the TRASCO project
Authors: Celona L. , Ciavola G. , Gammino S. , Gobin R. , Ferdinand R.
Published: July 2002

The TRASCO project (trasmutazione scorie) is a R&D program whose goal is the design of an accelerator driving system for nuclear waste transmutation. The high current continuous wave proton linear accelerator will drive a subcritical system to transmutate nuclear wastes, while producing energy. The proton source TRIPS is a high intensity microwave source, which should be highly reliable and that should provide a minimum proton current of 50 mA with a r−r′ root mean square normalized emittance lower than 0.2 π mm mrad. A program of cooperation has been entered into with CEA-Saclay, where the IPHI project is in progress and the proton source SILHI has been designed and built using goals close to those of TRIPS. The construction of TRIPS is underway and the first beam is scheduled for the first half of 2000. The main features of this source and the results of the optics calculations are presented.
Short-pathlength, high-pressure flow cell for static and time-resolved infrared spectroscopy suitable for supercritical fluid solutions including hydrothermal systems
Authors: Hoffmann Markus M. , Addleman R. Shane , Fulton John L.
Published: July 2002

An optical flow cell for high pressures and temperatures is described. The use of a novel window design allows for a precise, fixed optical pathlength that can be varied by use of spacers that range from a few micrometers to several millimeters. The cell pathlength is not affected by changes in pressure or temperature. The novel window design may be applicable to other high-pressure spectroscopic cells. The flow-cell design has a minimal sample dead volume, which is important for kinetic studies. The design eliminates the need for brazing or for a soft-sealing material for the optical windows, thereby minimizing the number of materials in contact with the sample. Using only diamond and platinum or platinum alloys as the corrosion resistant materials, the design is optimized for the study of aqueous solutions at high temperatures. Infrared spectra of an aqueous sodium tungstate solution up to 400 °C and 380 bar pressure are presented. Time-resolved infrared data are also presented for the ultraviolet photolysis reaction of β-naphthoyl azide in supercritical carbon dioxide.
A continuous motional series resonant frequency monitoring circuit and a new method of determining Butterworth–Van Dyke parameters of a quartz crystal microbalance in fluid media
Authors: Arnau A. , Sogorb T. , Jiménez Y.
Published: July 2002

A new electronic design for continuous monitoring of the motional series resonant frequency of a quartz crystal microbalance either in vacuum or in single-face contact with a fluid medium is presented. The motional resistance is directly measured and a simple method for measuring L and C parameters of the Butterworth–Van Dyke equivalent circuit is described. The results are in agreement with impedance analyzer measurements.
Michelson interferometry with 10 pm accuracy
Authors: Lawall John , Kessler Ernest
Published: July 2002

We demonstrate a new heterodyne Michelson interferometer design for displacement measurements capable of fringe interpolation accuracy of one part in 36 000. Key to this level of accuracy are the use of two acousto-optic modulators for heterodyne frequency generation and digital signal processing demodulation electronics. We make a direct comparison of our interferometer to a commercial interferometer based on a Zeeman-stabilized laser, and show that the residual periodic errors in ours are two orders of magnitude lower than those in the commercial unit. We discuss electronically induced optical cross talk and optical feedback as sources of periodic error. Our new interferometer is simple, robust, and readily implemented.
Role of magnetic anisotropy in the magnetoimpedance effect in amorphous alloys
Authors: Sommer R. L. , Chien C. L.
Published: July 2002

The magnetoimpedance (MI) effect of amorphous Co70.4Fe4.6Si15B10 ribbons, subjected to different annealing conditions with and without an external field, has been measured up to a frequency of 100 kHz. We show that the large MI effect is the result of transverse magnetic anisotropy, which is present in the as-cast and the suitably field-annealed samples.
Photoluminescence of polycrystalline CuInSe2 thin films
Authors: Zott S. , Leo K. , Ruckh M. , Schock H.-W.
Published: July 2002

The photoluminescence of CuInSe2 thin films grown by multisource physical vapor deposition is investigated over a wide composition range with a specially designed sample. Measurements as a function of excitation intensity, and temperature are correlated with the Cu/In ratio x of the films ranging from 1.47≤x≤0.46. All the Cu–rich samples (x≳1.0) show well-defined peak positions independent of the composition. In the slightly In-rich region (x=0.90) where the best absorber layers for high efficiency CuInSe2 solar cells are expected, two broad emission lines are ascribed to donor-acceptor pair transitions. For very In-rich samples (x<0.67), a blue shift of the dominant transition is observed.
Computed laminography for materials testing
Authors: Zhou J. , Maisl M. , Reiter H. , Arnold W.
Published: July 2002

We have developed a computed laminography system for the inspection of large or flat objects using x rays. By this new laminographic method only a translation of the object is necessary. Both the x-ray source and the detector remain stationary. Object cross sections are reconstructed from digital projections taken during the object motions and for the reconstruction well-known algorithms are used. By use of a microfocus x-ray tube and a line detector, objects can be inspected with a slice resolution of about 50 μm independent of the object size.
Room-temperature quantum well infrared modulator using a Schottky diode
Authors: Berger V. , Vodjdani N. , Delacourt D. , Schnell J. P.
Published: July 2002

A reverse biased Schottky diode is used to deplete the population in quantum wells and to modulate the intersubband absorption coefficient. This middle infrared electro-optic modulator works at room temperature. A waveguide geometry is demonstrated, with only six quantum wells. The 14% modulation could easily be enhanced by optimizing the quantum well overlap with the optical guided mode of the waveguide.
Growth-related stress and surface morphology in homoepitaxial SrTiO3 films
Authors: Tarsa E. J. , Hachfeld E. A. , Quinlan F. T. , Speck J. S. , Eddy M.
Published: July 2002

The lattice parameter and surface morphology of homoepitaxial SrTiO3 films were found to depend on the ambient oxygen pressure during growth. The homoepitaxial layers were grown by pulsed laser deposition with static ambient oxygen pressures of 100, 10, and 1 mTorr. The surface roughness of the films increased with increasing ambient growth pressure. In each case, the measured out-of-plane lattice parameter of the film was larger than that of the substrate. The mismatch between film and substrate increased with decreasing growth pressure. Compressive stresses of ∼0.28, 1.2, and 2.0 GPa were determined for homoepitaxial SrTiO3 layers deposited at 100, 10, and 1 mTorr, respectively.
Photoassisted dry etching of GaN
Authors: Leonard R. T. , Bedair S. M.
Published: July 2002

Photoassisted etching of GaN in HCl by a 193 nm ArF excimer laser is reported. A directed stream of HCl etchant with background pressure of ∼5×10−4 Torr, sample temperature between 200 and 400 °C and 1400 mJ/cm2 laser fluence combined to produce etching. Smooth etch features and distinct sidewalls were observed. For the HCl/GaN system, photoassisted etching occurred only when both HCl and laser energy were present.
In situ reflectance monitoring of InP/InGaAsP films grown by metalorganic vapor phase epitaxy
Authors: Lum R. M. , McDonald M. L. , Bean J. C. , Vandenberg J. , Pernell T. L. , Chu S. N. G. , Robertson A. , Karp A.
Published: July 2002

We report the use of in situ reflectance spectroscopy for real-time monitoring of the metalorganic vapor phase epitaxy (MOVPE) growth of InGaAsP films. In situ optical measurements have not been previously reported for this materials system because of its strong absorption in the spectral range of commonly available detectors (λ<1100 nm). To acquire reflectance data beyond the absorption regions of these films we used a grating spectrometer with a Si/PbS dual detector having a wavelength range of 400–2500 nm. Measurements were made during growth of InP/InGaAs/InP double heterostructures and 1.3 μm InGaAsP MQW laser device structures. The multiwavelength reflectance data enabled extraction of the film optical constants, determination of deposition rates to better than 1%, and provided nanometer scale thickness sensitivity for MQW samples.
High-resolution x-ray analysis of InGaN/GaN superlattices grown on sapphire substrates with GaN layers
Authors: Li Wei , Bergman Peder , Ivanov Ivan , Ni Wei-Xin , Amano H. , Akasa I.
Published: July 2002

InGaN/GaN superlattice structures grown on (0001) sapphire substrates with GaN layers were investigated by two-dimensional reciprocal space mapping of high-resolution x-ray diffraction. The results show that InGaN/GaN multi-quantum wells with fairly good crystallinity can be grown coherently on partially relaxed GaN layer irrespective of the large lattice mismatch and thermal incompatibility with the underlying substrate. Narrow and bright band edge related emissions were observed by photoluminescence measurements, indicating high quality of these InGaN/GaN superlattice structures. Our results suggest a larger band-gap bowing coefficient than the value reported in the literature.
Damage to epitaxial GaN layers by silicon implantation
Authors: Tan H. H. , Williams J. S. , Zou J. , Cockayne D. J. H. , Pearton S. J. , Stall R. A.
Published: July 2002

Ion channeling and cross-sectional transmission electron microscopy were used to study the extent and nature of Si ion implantation damage in epitaxial GaN layers at liquid nitrogen temperature. Results indicate that displacement damage produced by the implantation undergoes substantial dynamic annealing during implantation. As a result, at moderate implantation doses residual implantation damage consists of a dense network of secondary defects, such as clusters and loops, which are a consequence of incomplete annihilation of implantation-produced defects. Amorphous layers can be produced, but the doses required are extremely high (≳1016 cm−2) and amorphization appears to ‘‘nucleate’’ at the surface.
Study on the effects of minority carrier leakage in InAsSb/InPAsSb double heterostructure
Authors: Lane B. , Wu D. , Yi H. J. , Diaz J. , Rybaltowski A. , Kim S. , Erdtmann M. , Jeon H. , Razeghi M.
Published: July 2002

InAs x Sb 1−x /InP 1−x−y As x Sb y double heterostructures have been grown on InAs substrates by metal-organic chemical vapor deposition. The minority carrier leakage to the cladding layers was studied with photoluminescence measurements on the InAsSb/InPAsSb double heterostructures. A carrier leakage model is used to extract parameters related to the leakage current (diffusion-coefficient and length) from experimental results. Using the obtained parameters, the temperature dependence of the threshold current density of InAsSb/InPAsSb double heterostructure lasers is predicted and compared with experimental results.
Superior radiation-resistant properties of InGaP/GaAs tandem solar cells
Authors: Yamaguchi Masafumi , Okuda Takeshi , Taylor Stephen J. , Takamoto Tatsuya , Ikeda Eiji , Kurita Hiroshi
Published: July 2002

The observation of minority-carrier injection-enhanced annealing of radiation damage to InGa0.5P0.5/GaAs tandem solar cells is reported. Radiation resistance of InGaP/GaAs tandem solar cells as is similar with GaAs-on-Ge cells have been confirmed with 1 MeV electron irradiations. Moreover, minority-carrier injection under light illumination and forward bias conditions is shown to enhance defect annealing in InGaP and to result in the recovery of InGaP/GaAs tandem solar cell properties. These results suggest that the InGaP/GaAs(/Ge) multijunction solar cells and InGaP-based devices have great potential for space applications.
Spatial variations in oxygen precipitation in silicon after high temperature rapid thermal annealing
Authors: Pagani M. , Falster R. J. , Fisher G. R. , Ferrero G. C. , Olmo M.
Published: July 2002

Spatial variations of oxygen precipitation have been studied in silicon wafers submitted to rapid thermal annealing (RTA) in nitrogen ambients at a temperature above 1150 °C prior to a two-step precipitation treatment. The samples submitted to high temperature preannealing show a consistent enhancement of oxygen precipitation, which is dependent on the RTA time and temperature. Oxygen precipitate density measurements show that oxygen precipitation is not homogeneous inside the wafer, but peaks near the surfaces, with a minimum in the bulk. The high treatment in N2 results in the formation of defects which act as precursors for the subsequent nucleation and growth of oxygen precipitates. There is strong evidence that these precursors are generated by the thermal nitridation of the silicon surface and subsequent vacancy injection into the bulk of the wafer.
Local conduction band offset of GaSb self-assembled quantum dots on GaAs
Authors: Rubin M. E. , Blank H. R. , Chin M. A. , Kroemer H. , Narayanamurti V.
Published: July 2002

GaSb self-assembled quantum dots grown by molecular beam epitaxy on GaAs exhibit a staggered (type II) band lineup with a potential barrier in the conduction band. Traditional methods cannot measure this local band offset because of the small (∼50 nm) lateral dot size. The nanometer resolution of ballistic electron emission microscopy is exploited to image individual dots and measure a local band offset of 0.08±0.02 eV.
High-speed infrared detection by uncooled photovoltaic quantum well infrared photodetectors
Authors: Schneider H. , Schönbein C. , Bihlmann G. , van Son P. , Sigg H.
Published: July 2002

We have investigated the temporal response of uncooled photovoltaic quantum well infrared photodetectors (PV QWIP) using 2 ps pulses from a free electron laser. We measured rise and fall times of 8 ps and 63 ps, respectively. We have also determined the temperature dependence of the voltage responsivity and resistance of the sample from 70 K to 300 K. Based on these measurements, we discuss the figures of merit of PV QWIPs in a high-bandwidth 50 Ω environment.
A new transparent conducting oxide in the Ga2O3–In2O3–SnO2 system
Authors: Edwards D. D. , Mason T. O. , Goutenoire F. , Poeppelmeier K. R.
Published: July 2002

A new transparent conducting oxide (TCO), which can be expressed as Ga3−xIn5+xSn2O16; 0.2⩽x⩽1.6, has been identified. The equilibrium phase relationships of this new material with respect to three other TCOs in Ga2O3–In2O3–SnO2 are reported. The optical properties of this phase are slightly superior to Sn-doped indium oxide (ITO) and depend on composition. A room-temperature conductivity of 375 Ω cm−1 was obtained for H2-reduced Ga2.4In5.6Sn2O16. This value is an order of magnitude lower than commercial ITO films, but comparable to values reported for bulk, polycrystalline Sn-doped In2O3.
“Plastic” lasers: Comparison of gain narrowing with a soluble semiconducting polymer in waveguides and microcavities
Authors: Dı́az-Garcı́a Marı́a A. , Hide Fumitomo , Schwartz Benjamin J. , McGehee Michael D. , Andersson Mats R. , Heeger Alan J.
Published: July 2002

Gain narrowing and lasing from a soluble, highly photoluminescent conjugated polymer, poly(2-butyl, 5-(2′-ethyl-hexyl)-1,4-phenylene vinylene) (BuEH-PPV), are compared using two resonant structures: planar waveguides and microcavities. The gain narrowing and lasing thresholds are comparable, 0.05–0.1 μJ (10 ns pulse focused to ∼1.5 mm). Gain narrowing is not observed in films on indium tin oxide (ITO) unless a cladding layer is placed between the BuEH-PPV and ITO. Single-mode microcavity lasers are obtained when a cavity resonance occurs at the wavelength where the gain of the polymer is maximum.
Experimental demonstration of complete photonic band gap in graphite structure
Authors: Gadot F. , Chelnokov A. , De Lustrac A. , Crozat P. , Lourtioz J.-M. , Cassagne D. , Jouanin C.
Published: July 2002

We experimentally demonstrate the existence of complete photonic band gap in graphite-type photonic crystals, thereby confirming theoretical predictions reported in previous studies. Experiments are performed at microwave frequencies from 27 to 75 GHz using hexagonal lattices of alumina rods. Transmission spectra measured for E (TM) and H (TE) polarizations and for different orientations of the two-dimensional lattice are found to be in excellent agreement with numerical calculations. The complete photonic band gap results from the overlap of E7 and H5 forbidden bands. Attenuations larger than 30 dB are measured for structures comprised of only four rows of alumina rods.
Boron acceptor levels in 6H-SiC bulk samples
Authors: Evwaraye A. O. , Smith S. R. , Mitchel W. C. , Hobgood H. McD.
Published: July 2002

Thermal admittance spectroscopy has been used to determine the ground-state energies of the boron impurity in 6H-SiC. The background doping, NA−ND, of the samples used in this study ranged from 3×1016 to 1×1018 cm−3. From electron spin resonance studies, it is known that boron substitutes for silicon in the silicon carbide lattice occupying three inequivalent sites. Using admittance spectroscopy the ground state energies of Ev+0.27 eV, Ev+0.31 eV, and Ev+0.38 eV were determined for the shallow boron acceptor in 6H-SiC. The free carrier concentration does not appear to be the only determining factor for which the boron acceptor level is observed.
Stability of CdSe and ZnSe dots self-organized on semiconductor surfaces
Authors: Suemune I. , Tawara T. , Saitoh T. , Uesugi K.
Published: July 2002

Several monolayers (ML) of CdSe were deposited on (001) GaAs surfaces to study the stability of the CdSe films. The CdSe film with the 2 ML thickness showed atomically flat surfaces just after the growth. However, in three days after the growth, self-organization into dots at room temperature was clearly observed. This unexpected self-organization of dots observed at room temperature from the once coherently-grown CdSe film will be closely correlated to the enhancement of the heterointerface diffusion observed in this combination of CdSe and GaAs. This correlation between the stability of the dots and the heterointerface diffusion was examined in the common cation case of ZnSe/ZnS, which is known to show low interface diffusion. Self-organization of ZnSe dots was observed with an atomic force microscope on (001) ZnS surfaces. The ZnSe dots were stable as expected and did not show instability such as observed for the CdSe dots on GaAs or on ZnSe.
Smooth n-type GaN surfaces by photoenhanced wet etching
Authors: Youtsey C. , Adesida I. , Romano L. T. , Bulman G.
Published: July 2002

A room-temperature photoelectrochemical wet etching process is described that produces smoothly etched GaN surfaces using KOH solution and Hg arc lamp illumination. Atomic force microscope measurements indicate a root-mean-square etched surface roughness of 1.5 nm, which compares favorably to the unetched surface roughness of approximately 0.3 nm. Etch rates of 50 nm/min were obtained using a KOH solution concentration of 0.02 M and an illumination intensity of 40 mW/cm2. It is shown that the smooth etching occurs under conditions of low KOH solution concentration and high light intensities, which result in a diffusion-limited etch process.
Oxide interfacial phases and the electrical properties of SrBi2Ta2O9 thin films prepared by plasma-enhanced metalorganic chemical vapor deposition
Authors: Seong Nack-Jin , Yang Cheol-Hoon , Shin Woong-Chul , Yoon Soon-Gil
Published: July 2002

Bi-layered ferroelectric SrBi2Ta2O9 (SBT) films were successfully prepared on Pt/SiO2/Si and Pt/Ti/SiO2/Si substrates at 550 °C by plasma-enhanced metalorganic chemical vapor deposition. A BTO (Bi4Ti3O12 or Bi2Ti4O11) phase formed at the interface between SBT films and Pt/Ti/SiO2/Si during the SBT deposition at 550 °C. The BTO phase decreased the leakage current density of the SBT films. The leakage current densities of SBT films deposited on Pt/Ti/SiO2/Si and Pt/SiO2/Si substrates were about 5.0×10−8 and 5.0×10−7 A/cm2 at an applied field of 300 kV/cm, respectively. The SBT films were controlled by Schottky emission. The Schottky barrier heights of SBT films deposited on Pt/Ti/SiO2/Si and Pt/SiO2/Si were about 1.2 and 0.8 eV, respectively.
Metal–oxide bilayer Raman scattering in SrTiO3 thin films
Authors: Merkulov Vladimir I. , Fox Jon R. , Li Hong-Cheng , Si Weidong , Sirenko A. A. , Xi X. X.
Published: July 2002

We have used a metal–oxide bilayer Raman scattering technique to study lattice dynamics in SrTiO3 thin films. The SrTiO3 thin films were epitaxially grown on a conducting metal–oxide layer which reflects the exciting laser beam so that it does not enter the LaAlO3 substrate. Raman scattering from the SrTiO3 thin films was clearly observed, including the first-order Raman peaks forbidden by the cubic symmetry in single crystals. We suggest that strain exists in the films, which changes the crystal symmetry and will affect the dielectric properties of the SrTiO3 thin films.
Visible blind GaN p-i-n photodiodes
Authors: Walker D. , Saxler A. , Kung P. , Zhang X. , Hamilton M. , Diaz J. , Razeghi M.
Published: July 2002

We present the growth and characterization of GaN p-i-n photodiodes with a very high degree of visible blindness. The thin films were grown by low-pressure metalorganic chemical vapor deposition. The room-temperature spectral response shows a high responsivity of 0.15 A/W up until 365 nm, above which the response decreases by six orders of magnitude. Current/voltage measurements supply us with a zero bias resistance of 1011 Ω. Lastly, the temporal response shows a rise and fall time of 2.5 μs measured at zero bias. This response time is limited by the measurement circuit.
Transmission electron microscopy of defects in GaN films formed by epitaxial lateral overgrowth
Authors: Sakai Akira , Sunakawa Haruo , Usui Akira
Published: July 2002

We have investigated by transmission electron microscopy (TEM) defect morphology and structure in GaN films formed using an epitaxial lateral overgrowth (ELO) technique on SiO2-mask/window-stripe-patterned GaN layers in hydride vapor-phase epitaxy. In this experiment, the regions overgrown on the SiO2 masks were thoroughly examined. Cross-sectional TEM clearly revealed characteristic defects along the [0001] direction in the overgrown region, which consisted of arrays of dislocations running along the mask stripe direction. These defects caused crystallographic tilting in that region near the mask with respect to the other region grown from the window area. We also observed, at the coalesced site on the mask, vertical repropagation of dislocations that had propagated laterally during ELO. The origin of the observed defects and their influence on the residual dislocation distribution near the film surface are discussed.
Integrated optical isolator based on efficient nonreciprocal radiation mode conversion
Authors: Shintaku Toshihiro
Published: July 2002

An integrated optical isolator is demonstrated based on efficient nonreciprocal conversion from a fundamental TM mode to a deep TE radiation mode away from the cutoff. The isolator is realized using a single-mode rib channel waveguide in Ce-substituted yttrium iron garnet, which has a very large Faraday rotation. 27 dB isolation is obtained at a wavelength of 1535 nm.
Carbon diffusion in silicon
Authors: Werner P. , Gösele U. , Gossmann H.-J. , Jacobson D. C.
Published: July 2002

Carbon diffusion in silicon has been investigated by using a superlattice structure of carbon spikes (10 nm-wide, carbon concentration >1019 cm−3, spikes spaced 100 nm apart) grown epitaxially by Si molecular beam epitaxy. Samples were annealed in the range between 680 and 850 °C. The diffusive behavior of carbon was monitored by secondary ion mass spectrometry. Carbon diffusion profiles observed at temperatures above 800 °C show highly nonregular behavior. The diffusion results are interpreted in terms of the kick-out mechanism.
Multiphoton-excited luminescence from diamond nanoparticles and an evolution to emission accompanying the laser vaporization process
Authors: Glinka Yu. D. , Lin K.-W. , Lin S. H.
Published: July 2002

The photoluminescence (PL) from 100 nm diamond particles induced by infrared (IR) pulsed excitation [λexc=1064 nm (1.16 eV), τ=10 ns] was observed. The laser light intensity dependence of the PL yield shows that this is the five-photon absorption process (the total energy of excitation 5.8 eV). The PL results from structure defects, impurities, and the graphite-like phase excited by a relaxation of the multiphoton (MP)—produced electron–hole pairs (the band gap of diamond Eg=5.5 eV). By using the ultraviolet one-photon excitation [λexc=354.7 nm (3.48 eV), τ=10 ns], the same PL bands were observed in support of the correctness of interpretation. The typical Swan bands of electronically excited C2 species dominate the spectra at the IR light intensity above the threshold for vaporization. It was concluded that the MP-excited PL precedes the emission accompanying the laser vaporization process.
Corrugated quantum well infrared photodetectors for polarization detection
Authors: Chen C. J. , Choi K. K. , Rokhinson L. , Chang W. H. , Tsui D. C.
Published: July 2002

In this letter, we propose the use of the newly developed corrugated quantum well infrared photodetectors (C-QWIPs) for polarization detection. The corrugated structure, which serves as an optical coupler as well as the polarization-sensitive component, is in this case directly created into the active region of the QWIP, therefore dispensed with the need of an external polarizer. Moreover, four C-QWIPs with differently oriented corrugated patterns can be integrated as one unit, thus allowing a precise, real-time measurement of the polarization state. The polarimetry of this detector unit was characterized using a blackbody source and a metal grating polarizer.
A narrow photoluminescence linewidth of 21 meV at 1.35 μm from strain-reduced InAs quantum dots covered by In0.2Ga0.8As grown on GaAs substrates
Authors: Nishi Kenichi , Saito Hideaki , Sugou Shigeo , Lee Jeong-Sik
Published: July 2002

InAs quantum dots with size fluctuations of less than 4% were grown on GaAs using the self-assembling method. By covering the quantum dots with In0.2Ga0.8As or In0.2Al0.8As, strain in InAs dots can be partly reduced due to relaxation of lattice constraint in the growth direction. This results in low-energy emission (about 1.3 μm) from the quantum dots. The photoluminescence linewidth can be reduced to 21 meV at room temperature. This width is completely comparable to the theoretical limit of a band-to-band emission from a quantum well at room temperature. Because the dots can be uniformly covered by the strain reducing layers, factors that degrade size uniformity during coverage, such as compositional mixing or segregation, will be suppressed, allowing for an almost ideal buried quantum dot structure.
Thermal evolution of impurities in wet chemical silicon oxides
Authors: Gurevich A. B. , Weldon M. K. , Chabal Y. J. , Opila R. L. , Sapjeta J.
Published: July 2002

We have used infrared absorption spectroscopy and x-ray photoelectron spectroscopy to study the thermal evolution (under ultrahigh vacuum conditions) of ultrathin silicon oxide films grown in acid solutions (HCl, HNO3, and H2SO4). We find that adsorbed hydrocarbon contaminants dissociate and become chemically incorporated into the thin oxide as additional silicon oxide, carbide, hydride, and hydroxyl species. These species significantly influence the thermal evolution of the oxide films and persist up to the SiO desorption temperature (850–1000 °C) so that, once formed, these defects will be necessarily present in the final device structure.
Ultraviolet Raman stress mapping in silicon
Authors: Holtz M. , Carty J. C. , Duncan W. M.
Published: July 2002

We report micro-Raman stress imaging in silicon structures using 351 nm excitation. This excitation has an extremely shallow optical penetration depth (≈5 nm) in silicon. It should also ultimately provide higher spatial resolution compared to visible wavelengths used in micro-Raman studies. As a test we examine a wafer which consists of a patterned nitride/polycrystalline silicon/oxide/substrate “stack” with neighboring regions of device-quality silicon covered only by a thin oxide layer. We obtain two-dimensional images with spatial resolutions ranging from 1 to 4 μm. The smallest Raman shift reliably detectable is found to be ±0.07 cm−1, corresponding to a stress magnitude of 35 MPa. Stresses on the order of 140 MPa are observed beneath the stack region. The contrasting linewidths between the substrate and polycrystalline silicon provide a complementary image.
Infrared absorption of Li acceptors and shallow donors in ZnSe
Authors: Nakata H. , Yamada K. , Ohyama T.
Published: July 2002

Using Fourier transform infrared spectroscopy, we have observed the absorption spectra of holes bound to acceptors in bulk ZnSe below 100 K. The absorption is assigned to hole transition of Li acceptors from the 1S3/2 ground state to the 2P3/2 excited state. The obtained transition energy of 72.9±0.1 meV is one order more precise than that obtained by photoluminescence measurements. In addition, absorption lines due to shallow donors are observed below 30 K, and the intensity is enhanced by excitation with a blue light emitting diode. The 1s–2p transition energies of three kinds of donors Al, Cl, and In are estimated at 18.96, 19.64, and 21.67 meV, respectively.