bluuebunny/crossref_metadata_2025 huggingface dataset:
Surface migration induced self-aligned InAs islands grown by molecular beam epitaxy
Authors: Mui D. S. L. , Leonard D. , Coldren L. A. , Petroff P. M.
Published: July 2002

We utilize the sensitivity of the two- to three-dimensional growth transition of InAs self-assembled islands on InAs coverage to demonstrate the growth of self-aligned InAs islands on etched GaAs ridges by molecular beam epitaxy. The different migration behavior of In adatoms on different crystal planes of etched ridges is used to spatially modulate the supply of In adatoms. The ridges are oriented either along the [011] and [011̄] direction on (100) substrates with grating spacing of 0.28, 1, and 5 μm. Atomic force microscopy reveals that the InAs islands are self-aligned along the ridges and they have a typical size of 400 Å in diameter and 120 Å in height. In samples with [011] oriented ridges, the islands are located on the sidewalls. On the other hand, for [011̄] oriented ridges the islands are on the (100) planes on and at the foot of the mesa. On samples with a grating pitch of 0.28 μm, all the islands are located either on the sidewalls or at the bottom of the ‘‘V groove’’ for both grating orientations.
Comparison of some glass thermometers at low temperatures in a high magnetic field
Authors: Wiegers S. A. J. , Jochemsen R. , Kranenburg C. C. , Frossati G.
Published: July 2002

We have compared the low-frequency capacitance of glass thermometers of various shapes, made of very pure SiO2 doped with ≊1200 ppm OH−, in the temperature range of 4–100 mK in a magnetic field of 9 T. The construction of the electrodes, the way the contacts are made, and the connection of the leads or cables influence both the voltage and the field dependence of the capacitance and of the loss. We have been able to construct capacitive glass thermometers of which the capacitance is not shifted in a field of 9 T at temperatures down to 4 mK, within our temperature accuracy of ≊5%. This has been determined by comparison with a cerium magnesium nitrate (CMN) thermometer in a field-free region, and by comparing ultrasound measurements versus the thermometer capacitance with and without a magnetic field.
Cathodoluminescence study of erbium and oxygen coimplanted gallium nitride thin films on sapphire substrates
Authors: Qiu C. H. , Leksono M. W. , Pankove J. I. , Torvik J. T. , Feuerstein R. J. , Namavar F.
Published: July 2002

The cathodoluminescence (CL) of erbium and oxygen coimplanted GaN (GaN:Er:O) and sapphire (sapphire:Er:O) was studied as a function of temperature. Following annealing, the 1.54 μm intra-4f-shell emission line was observed in the temperature range of 6–380 K. As the temperature increased from 6 K to room temperature, the integrated intensity of the infrared peak decreased by less than 5% for GaN:Er:O, while it decreased by 18% for sapphire:Er:O. The observation of minimal thermal quenching by CL suggests that Er and O doped GaN is a promising material for electrically pumped room-temperature optical devices emitting at 1.54 μm.
A plane-grating monochromator for radiometric calibration
Authors: Sakurai M. , Morita S. , Fujita J. , Yonezu H. , Fukui K. , Sakai K. , Nakamura E. , Watanabe M. , Ishiguro E. , Yamashita K.
Published: July 2002

A new plane-grating monochromator and calibration chamber were constructed for the radiometric calibration of plasma diagnostic devices. The monochromator is designed to cover a wavelength range of 1.8–238 nm with moderate resolving power of 500±200 in λ/Δλ. To check the performance of the monochromator, spectral distribution and resolution were measured by experiments on photoemission from solids and photoionization of rare gases. The characterization of multilayer reflectors by the use of this beamline is demonstrated.
Ion temperature analysis of implosions of DT-filled capsules
Authors: Remington B. A. , Lerche R. A. , Cable M. D.
Published: July 2002

Fuel ion temperatures have been deduced for a series of implosions of defiled capsules by measuring the thermally broadened neutron time-of-flight signals at 10 and 20 m from the target. Typical temperatures were around 1 keV, and the corresponding thermal broadening was comparable to or less than the time response of the detectors. Under these conditions, error minimization is crucial, and we find that the location of the detector and the analysis technique are important. An optimum location exists, but is very sensitive to the yield of the implosion and to the detector response.
Highly reflective, long wavelength AlAsSb/GaAsSb distributed Bragg reflector grown by molecular beam epitaxy on InP substrates
Authors: Blum O. , Fritz I. J. , Dawson L. R. , Howard A. J. , Headley T. J. , Klem J. F. , Drummond T. J.
Published: July 2002

Surface normal optoelectronic devices operating at long wavelengths (≳1.3 μm), require distributed Bragg reflectors (DBRs) with a practical number (≤50) of mirror layers. This requirement implies a large refractive index difference between the mirror layers, which is difficult to achieve in the traditionally used phosphide compounds. We demonstrate a highly reflective AlAsSb/GaAsSb DBR grown nominally lattice matched to an InP substrate by molecular beam epitaxy. Reflectivity measurements indicate a stop band centered at 1.74 μm with maximum reflectivity exceeding 98%, which is well fitted by our theoretical predictions. Atomic force microscopy and transmission electron microscopy indicate reasonable crystal quality with some defects due to an unintentional lattice mismatch to the substrate.
Magnetophotoluminescence of biaxially compressed InAsSb quantum wells
Authors: Kurtz S. R. , Biefeld R. M.
Published: July 2002

Heterostructures with biaxially compressed InAsSb are being considered as active regions for midwave infrared diode lasers. Quantum wells of biaxially compressed InAs1−xSbx (x≊0.09) in unstrained InAs were characterized using magnetophotoluminescence. The quantum size shift of the photoluminescence for a series of quantum wells produced an estimate of the conduction band offset. In magnetic field studies, the holes in the strained quantum wells exhibited a decrease in effective mass, approaching that of the electrons. A type I band offset was observed for these InAsSb/InAs heterostructures. Throughout this study, magnetoexcitonic behavior is observed; our analysis indicates that the exciton binding energy increases with quantum confinement.
Study of surface Fermi level and surface state distribution in InAlAs surface-intrinsic-n+ structure by photoreflectance
Authors: Hwang J. S. , Chou W. Y. , Tyan S. L. , Lin H. H. , Lee T. L.
Published: July 2002

The built-in electric field and surface Fermi level in the InAlAs surface-intrinsic-n+ structures were studied by room-temperature photoreflectance. The samples were grown by molecular beam epitaxy with an undoped layer thickness of 1000 Å. The undoped layer was subsequently etched to 800, 600, 400, and 200 Å. Different chemical solutions were used in the etching process and the built-in electric field is found independent of the etching process. While the surface Fermi level, in general, varies with the undoped layer thickness, there exists, for each Al concentration, a certain range of thicknesses within which the surface Fermi level is weakly pinned. From the dependence of electric field and surface Fermi level on the undoped layer thickness, we conclude that the surface states distribute over two separate regions within the energy band gap and the densities of surface states are as low as 1.02±0.05×1011 cm−2 for the distribution near the conduction band and 2.91±0.05×1011 cm−2 for the distribution near valence band.
A new multichannel soft x-ray framing camera for fusion experiments
Authors: Ze F. , Kauffman R. L. , Kilkenny J. D. , Wielwald J. , Bell P. M. , Hanks R. , Stewart J. , Dean D. , Bower J. , Wallace R.
Published: July 2002

Two-dimensional, time resolved x-ray imaging is a principal technique used to study hot plasmas produced in laser heated targets. It can be used to study laser energy deposition within the irradiation spot, the spatial and temporal dependence of laser to x-ray conversion efficiency, electron transport and density profiles, mass ablation rates as well as x-ray driven implosions in inertial confinement fusion experiments. We have successfully developed a new soft x-ray framing camera which will allow us to record two-dimensional images at different times almost simultaneously. It is a broadband diagnostic (100 eV≤Δhν≤400 eV) having three channels which can obtain x-ray images at four different times from laser driven targets. Its current configuration includes one 500 eV, one 1.0 keV, and one ∼2.5 keV channels. The two low energy channels resulted from pairing transmission filters to grazing x-ray mirrors. Other channel options can be implemented easily to measure other x-ray energies. Four different striplines coated on a microchannel plate are gated at different times. Each strip records three different images taken nearly simultaneously, one image per channel. The result is 12 x-ray images on film, four images per channel taken at four different times, with a nominal resolution of approximately 100 ps per image. The diagnostic’s spatial resolution is approximately 10 μm. We have already fielded this new instrument during x-ray conversion experiments, using both low and high Z targets driven by 1–2 ns, ‘‘flattop’’ laser pulses. We will show the details of the instrument design and sample results from conversion experiments.
High quality InGaN films by atomic layer epitaxy
Authors: Boutros K. S. , McIntosh F. G. , Roberts J. C. , Bedair S. M. , Piner E. L. , El-Masry N. A.
Published: July 2002

InxGa1−xN single-crystal films were grown at 600–700 °C by atomic layer epitaxy (ALE). InGaN films with compositions of up to 27% indium were achieved. The full width at half-maximum (FWHM) of the (0002) InxGa1−xN peak by double crystal x-ray diffraction (DCXRD) was as small as 6 min, the lowest value reported for this ternary alloy. Strong photoluminescence band edge emission between 360 and 446 nm was observed at room temperature. These low temperature ALE grown films were achieved without the need to use excessive flows of the In organometallic source and thus demonstrate the potential for growth of this ternary alloy over the entire composition range.
Electron density profile measurement with a heavy ion beam probe
Authors: Schwelberger J. G. , Aceto S. C. , Connor K. A. , Zielinski J. J. , Baylor L. A. , England A. C. , Isler R. , Ma C. H. , Murakami M. , Uckan T. , Rasmussen D. A.
Published: July 2002

The feasibility of electron density profile measurements using a heavy ion beam probe in high-temperature plasmas has been demonstrated earlier [J. Schwelberger et al., Bull. Am. Phys. Soc. 36, 2292 (1991); Yu. N. Dnestrovskij et al., Sov. J. Plasma Phys. 12, 130 (1986)]. Two algorithms were developed to obtain density profiles from the heavy ion beam probe on the Advanced Toroidal Facility (ATF). A comparison of the algorithms is presented with a detailed study of the errors involved in the measurements. The errors can be due to uncertainties in cross sections, electron temperature, the line average density measurement, and the ion trajectory calculations. The heavy ion beam probe density profile measurement is not very susceptible to errors as long as the electron temperature stays above 30 eV. If the electron temperature is below this value, a small uncertainty in the temperature introduces a large error in the density. Also, important for a good density profile measurement is the calculation of the correct ion trajectories. Examples of density profiles are shown for ECH plasmas on ATF together with a detailed error analysis. The heavy ion beam probe results are in good agreement with multichannel far-infrared laser interferometry and Thomson scattering results.
Inertial tip translator for a scanning tunneling microscope
Authors: Brockenbrough R. T. , Lyding J. W.
Published: July 2002

A two-dimensional micropositioning device for scanning tunneling microscope (STM) probes has been developed. This device uses the principle of piezoelectric inertial translation to produce a controlled stepping motion of the probe along vertical and horizontal axes over distances of several mm. The tip micropositioner is controlled by the same electrical signals that drive the scanning piezoelectric element, thus alleviating the need for additional electronic control elements. This device has been tested on STMs operating in air and in ultrahigh vacuum environments.
Atomic structure of the CdTe(001) C(2×2) reconstructed surface: A grazing incidence x-ray diffraction study
Authors: Veron M. B. , Sauvage-Simkin M. , Etgens V. H. , Tatarenko S. , Van Der Vegt H. A. , Ferrer S.
Published: July 2002

We present a grazing incidence x-ray diffraction surface structure determination on a II–VI compound, namely, the CdTe(001) C(2×2) reconstructed surface, grown by molecular beam epitaxy. The structural analysis leads to a model with cadmium bridges corresponding to a coverage of 0.5 ML Cd, as expected from previous studies. This surface arrangement is accompanied by a significant relaxation of the underlying substrate down to the sixth atomic layer. Moreover, a strong anisotropy of the reconstructed domain dimensions is observed and quantified. This findings may explain the anisotropic behavior observed during homoepitaxial and heteroepitaxial growth on CdTe.
Sensitive detection of optical rotation in liquids by reflection polarimetry
Authors: Zhou G. X. , Schmitt J. M. , Ellicott C. E.
Published: July 2002

We describe a sensitive polarimeter for measuring optical rotation induced by chiral molecules in solution that operates in the reflectance mode. A polarized light beam is made to pass through a liquid sample two or more times before detection by reflecting the beam from the surface of the sample container. The optical activity of the sample is measured using a differential polarization detector. Our results show that, for certain initial polarization states and angular orientations of the beam with respect to the glass interfaces, high sensitivity to changes in the concentration of the sample can be achieved. Results of a theoretical analysis of the technique were confirmed by experiments in which optical rotation of glucose in water was measured using a simple apparatus that employs a light-emitting diode source. Glucose sensing in vivo and on-line monitoring of industrial processes using integrated optoelectronic sensors are discussed as potential applications.
Abruptness of Ge composition at the Si/SiGe interface grown by ultrahigh vacuum chemical vapor deposition
Authors: Tsai W. C. , Chang C. Y. , Jung T. G. , Liou T. S. , Huang G. W. , Chang T. C. , Chen L. P. , Lin H. C.
Published: July 2002

A model is proposed to estimate the interfacial abruptness of the Si/SiGe heterojunction. In this model, a transition region with linearly graded Ge composition is assumed at the Si/SiGe interface. The Ge composition x of Si/SiGe quantum well grown by ultrahigh vacuum chemical vapor deposition at 550 °C is found to increase with the deposition time as deposition at the same gas phase composition. This phenomenon can be explained by this model and the fitting results match the measured data. The thickness of the transition region and the transition time can be extracted from these fittings. The transition thicknesses are found to be about 1.9 nm or thinner as grown at 550 °C or below.
Fiber optic angular displacement sensor
Authors: Wu Chi
Published: July 2002

A reflective type fiber optic angular displacement sensor has recently been developed, which consists of a light source, an optical isolator, a four-port single-mode fiber bidirectional coupler, and a light intensity detection system (two silicon photodetectors and an analog divider). By using a normal He–Ne laser with ±2% stability in light intensity, we have achieved an angle resolution of 10−6 rad. In this paper, its design principle, instrumentation, calibration results, and sensitivity test have been reported. In addition, possible applications of this sensor, such as in an atomic force microscope, and some feasible improvements of this sensor are discussed.
Doping effects on the kinetics of solid-phase epitaxial growth of amorphous alumina thin films on sapphire
Authors: Yu Ning , Simpson Todd W. , McIntyre Paul C. , Nastasi Michael , Mitchell Ian V.
Published: July 2002

The effects of doping on the kinetics of solid-phase epitaxial growth of amorphous alumina have been studied. Amorphous alumina Al2O3) thin films, 200–265 mm thick, were deposited on to (0001) sapphire substrates by electron-beam evaporation. Iron or chromium atoms were uniformly doped into the films during deposition to cation concentrations below 5 cationic %. The kinetics of the epitaxial growth were studied at 800–1050 °C in flowing oxygen gas by in situ time-resolved reflectivity techniques as well as by ion backscattering and channeling techniques. A phase transformation sequence from amorphous through gamma to alpha alumina has been observed in all the undoped and doped films. The transformation from γ to α alumina is a thermally activated process with an activation energy of 5.0±0.2 eV, independent of the presence of dopants. However, the presence of dopants affects the overall transformation rate. Fe enhances while Cr slows the growth rate relative to the undoped case.
In-well screening nonlinearities in piezoelectric multiple quantum wells
Authors: Huang X. R. , Harken D. R. , Cartwright A. N. , Smirl Arthur L. , Sánchez-Rojas J. L. , Sacedón A. , Calleja E. , Muñoz E.
Published: July 2002

The contribution of the in-well screening of the piezoelectric field to the nonlinear optical response of a [111]-oriented strained InGaAs/GaAs multiple quantum well is separated from, and compared to, that associated with the out-of-well screening and with bleaching by using picosecond nondegenerate differential transmission techniques. These measurements demonstrate that the per-carrier nonlinearity associated with the in-well screening is smaller than that associated with the out-of-well screening by a factor roughly equal to the number of wells.
Simple retrofittable long-range x–y translation system for scanned probe microscopes
Authors: Smith W. F. , Abraham M. C. , Sloan J. M. , Switkes M.
Published: July 2002

A simple, reliable system for long-range translation of scanned probe microscopy (SPM) samples is described. This system could easily be retrofitted to many existing SPMs. The sample is held magnetically onto the scan piezo tube, and is translated by stick-slip motion. The system is very reliable, and provides controllable step size ranging from 20 nm to 1 μm. Three stick-slip drive wave forms are described and tested: sawtooth, cycloid, and an ‘‘improved’’ cycloid based on the resonance curve of a harmonic oscillator. Computer simulations of the stick-slip process are presented, and are in good agreement with experiment. Together, the experiments and simulations demonstrate that it is essential to consider the resonant response of the piezo when evaluating drive wave forms.
A new application of the nonlinear dielectric method for studying relaxation processes in liquids
Authors: Górny M. , Ziolo J. , Rzoska S. J.
Published: July 2002

The measurement setup for studying changes of electric permittivity induced in liquids by a strong electric field nonlinear dielectric effect, (NDE) is presented. The construction is based on the idea of frequency modulation of an LC generator (with an inductance L and a capacitance C in resonant circuit), proposed by Malecki [J. Chem. Soc. Faraday Trans. II 72, 104 (1976)]. The strong electric field is applied in the form of rectangular pulses (typically 1–4 ms). The setup enables measurements in a broad range of frequencies (80 kHz–12 MHz) and contains a new calibrating system, minimizing the influence of systematic error on the measured NDE values. We also indicate menthol as a standard, reference liquid in NDE studies. New applications of the NDE technique for studying relaxation processes in critical solution are also presented. They are based on the time resolved analysis of NDE decay after switching off the strong electric field.
Ultrafast energy loss of electrons in p-GaAs
Authors: Rodrigues-Herzog R. , Sailer M. , Hecker N. E. , Höpfel R. A. , Nintunze N. , Osman M. A.
Published: July 2002

We investigated the ultrafast energy relaxation of photoexcited minority electrons in highly doped p-GaAs by means of femtosecond time resolved luminescence (Δt<90 fs). Our experiments allow the first observation of the extremely fast cooling of minority electrons within the Γ-valley. The electron mean energy decreases within 150 fs from 150 meV down to less than 50 meV. The total energy loss rate reaches values higher than 10−7 W per electron, representing the highest energy loss rates of electrons observed to date in monocrystalline semiconductors. Ensemble Monte Carlo simulations show that the electron-hole scattering is responsible for these high energy loss rates.
Heavy ion beam probe systems for tight aspect ratio tokamaks
Authors: Melnikov A. V. , Zimeleva L. G. , Krupnik L. I. , Nedzelskij I. S. , Trofimenko Y. V. , Minaev V. B.
Published: July 2002

We discuss the specific features of the application of heavy ion beam probe (HIBP) systems to tight aspect ratio tokamaks. We present and compare the HIBP projects for the TUMAN-3, GLOBUS, and COMPASS, where the inner part of the plasma is not available for regular chord diagnostics, so the HIBP becomes very desirable. All existing tight aspect ratio facilities and projects have a low (less than 1.9 T) toroidal field that requires a comparatively low beam energy range. The natural elongation and triangularity in tight aspect ratio tokamaks require an accurate calculation of the three-dimensional magnetic field for probing optimization. In comparison with traditional tokamaks, the detector grids have a wider energy interval. In general, the trajectories and detector grids for tight aspect ratio tokamaks become similar to the stellarator ones. Traditional and new probing schemes are suggested and discussed.
A very sensitive microcalorimetry technique for measuring specific heat of μg single crystals
Authors: Riou O. , Gandit P. , Charalambous M. , Chaussy J.
Published: July 2002

A microcalorimetry technique allowing one to measure the specific heat of bulk single crystals of a mass typically 10 μg, with a relative resolution Δc/c of 10−4 is presented. The well known ac steady state technique is employed. The sample holder is a polymer membrane with lithographically patterned thermometer and heaters made out of metallic thin films. The diameter of the useful area is 0.6 mm and the specific heat of the addendum is 1.5 μJ/K at 100 K. The sample is thermally coupled to the membrane through a gold thin film sputtered on its surface. The thermal coupling time constant of the sample is ∼5 ms, allowing to work at frequencies of 10 Hz. The method was applied to small single crystals of YBCO, providing the specific heat jump at the superconducting transition with a relative resolution of 10−2 and a precision of 10−1. The method is optimized at the temperature range 40–160 K, but can easily be modified for lower temperatures.
The construction of a gas aggregation source for the preparation of mass-selected ultrasmall metal particles
Authors: Baker S. H. , Thornton S. C. , Keen A. M. , Preston T. I. , Norris C. , Edmonds K. W. , Binns C.
Published: July 2002

The design and operation of a high temperature gas aggregation source, capable of in situ deposition of mass-selected atomic clusters of transition metals onto a substrate in an ultrahigh vacuum chamber, is described. Mass-selection is achieved by an ultrahigh mass quadrupole filter operating at masses up to 3×104 amu.
Simple heatable Langmuir probe for alkali plasmas
Authors: Strele Daniela , Koepke Mark , Schrittwieser Roman , Winkler Patrick
Published: July 2002

A new type of small, simple, indirectly heatable Langmuir probe for measurements in alkaline plasmas is presented. The heating element of this probe consists of an elogated half-loop of Ta-wire wound helically, around a thin ceramic tube that carries the probe collector. It is situated as closely as possible to the latter. The necessary heating power is a few watts. It is shown that the inevitable alkaline coating of the probe collector can be removed by sufficient heating. Various types of coating and their influence on the probe characteristic are discussed.
Magnetic susceptibility measurements of ultrathin films using the surface magneto-optic Kerr effect: Optimization of the signal-to-noise ratio
Authors: Arnold C. S. , Dunlavy M. , Venus D.
Published: July 2002

The magnetic susceptibility, χ=∂M/∂H, can be determined for ultrathin films using the surface magneto-optic Kerr effect and an ac technique (ac-MOKE) where the response to a small, modulated H field is measured. Optimization of the signal-to-noise ratio is imperative if the measurements are to be used to extract critical scaling exponents from the small tail of χ in the paramagnetic region. These optimal conditions are different than those appropriate for more conventional static H measurements (dc-MOKE) used to generate magnetic hysteresis loops, because the relative noise contributions from the laser stability, sample stability, and detector are changed. A simple method for determining optimum conditions is demonstrated, and the technique is used to show that a 1.8 ML Fe/W(110) film has the critical exponent γ of the 2D Ising model.
Metal ions from the volatile compounds method for the production of metal ion beams
Authors: Koivisto H. , Arje J. , Nurmia M.
Published: July 2002

The metal ions from the volatile compounds (MIVOC) method was developed at the Accelerator Laboratory, University of Jyväskylä, in order to produce metal ion beams with the source material at or near room temperature conditions. It has been used with the JYFL-ECR ion source since 1993 and has turned out to be both simple and reliable. The method was adopted at several laboratories. Up to the present time, at least 17 MIVOC beams were produced (C, Mg, Si, Cl, Ti, V, Cr, Fe, Co, Ni, Ge, Mo, Ru, Sn, I, W, and Os). With the MIVOC technique it was found possible to operate the JYFL-ECR ion source with compounds of metals, either powders or liquids, that have a room temperature vapor pressure of the order of 1E–3 mbar or higher. The MIVOC method has turned out to be very economical in use since a typical material consumption rate is about 0.3 mg/h. This corresponds to the consumption rate of gases. Due to the simplicity of the system the duty-off time of the ion source is minimized. In this article, the basis of the MIVOC method, phenomena related to it and some results will be presented.
Characterization of an optical fiber bundle sensor
Authors: Bergougnoux Laurence , Misguich-Ripault Jacqueline , Firpo Jean-Luc
Published: July 2002

An optical fiber sensor made of a central emitting fiber and two concentric crowns of receiving fibers is presented. This sensor is mainly used to measure high solid volume concentrations in suspension. The aim of this article is to accurately characterize the geometrical properties of this sensor comparing experimental data and simulation. Experimentally, the sensor is used as a displacement sensor with a metallic mirror as a target. This geometrical problem is simulated by a Monte Carlo method, which takes into account: (1) The experimental determination of the angular distribution of light intensity for the emitting fiber; (2) The finite size of fibers by means of a numerical integration procedure; and (3) The multiple reflections of light on the fiber sections with an explicit use of Fresnel’s factors. By fitting the experimental data with the results of the simulation, we can determine the geometrical properties of the probe and photon efficiency (voltage output versus number of launched photons) of the device. Finally, we discuss the use of this sensor as a displacement sensor. In this case a simple electronic device is given to gain a single valued response of the probe when the distance between the target and the sensor is varied. In this framework, the nature of the scattering target is also discussed.
The motional Stark effect: Overview and future development (invited)
Authors: Levinton F. M.
Published: July 2002

As an atomic beam propagates across a magnetic field, an electric field is generated, E=V×B. This results in a spectral splitting and polarization of the emitted radiation, known as the Stark effect. The direction of polarization of the emitted radiation provides a measure of the local magnetic field direction or pitch angle. In addition to the electric field generated by the neutral beam, intrinsic electric fields present in the plasma affect the direction of polarization. This has been exploited to measure both the plasma electric field and the magnetic field. Future development of the motional Stark effect utilizing laser induced fluorescence to access much lower magnetic fields will be discussed.
A highly efficient neutron time-of-flight detector for inertial confinement fusion experiments
Authors: Izumi N. , Yamaguchi K. , Yamagajo T. , Nakano T. , Kasai T. , Urano T. , Azechi H. , Nakai S. , Iida T.
Published: July 2002

We have developed the highly efficient neutron detector system MANDALA for the inertial-confinement-fusion experiment. The MANDALA system consists of 842 elements plastic scintillation detectors and data acquisition electronics. The detection level is the yield of 1.2×105 for 2.5 MeV and 1×105 for 14.1 MeV neutrons (with 100 detected hits). We have calibrated the intrinsic detection efficiencies of the detector elements using a neutron generator facility. Timing calibration and integrity test of the system were also carried out with a Co60 γ ray source. MANDALA system was applied to the implosion experiments at the GEKKO XII laser facility. The integrity test was carried out by implosion experiments.
Porous Si anisotropy from photoluminescence polarization
Authors: Kovalev D. , Chorin M. Ben , Diener J. , Koch F. , Efros Al. L. , Rosen M. , Gippius N. A. , Tikhodeev S. G.
Published: July 2002

We report the observation of the anisotropic linear polarization of porous Si photoluminescence measured in two excitation geometries. In the normal excitation geometry (exciting beam normal to the sample (100) surface) linear luminescence polarization of as much as 20% is seen parallel to the excitation polarization. In the edge excitation geometry (exciting light incident on a cleaved edge of the sample) the luminescence polarization is aligned mainly in the [100] direction (normal to the surface). The effect is described within the framework of a dielectric model in which porous Si is considered as an aggregate of slightly deformed, elongated and flattened, dielectric elliptical Si nanocrystals with preferred orientation in the [100] direction.
A new high transmission infinite range mass selector for cluster and nanoparticle beams
Authors: von Issendorff B. , Palmer R. E.
Published: July 2002

A new mass selection technique has been developed, which allows one to size-select charged particles from atoms to nanoparticles of almost unlimited size. It provides a mass resolution of m/Δm=20–50 and a transmission of about 50% for the selected size, both independent of mass. The technique is based on the time-of-flight principle, but differs fundamentally from time-of-flight mass selection normally used. The basic idea is to use time-limited high voltage pulses to displace laterally a preaccelerated ion beam, without changing its direction or shape. As the movement of the ions perpendicular to their original beam direction is independent of their forward velocity, mass resolution and calibration does not depend on the ion beam energy. A mass selector of this type has been implemented successfully into a cluster deposition experiment and has proven to be reliable and simple to operate.
A compact ultrahigh-vacuum system for the in situ investigation of III/V semiconductor surfaces
Authors: Geng Peter , Márquez Juan , Geelhaar Lutz , Platen Jutta , Setzer Carsten , Jacobi Karl
Published: July 2002

A compact ultrahigh vacuum (UHV) system has been built to study growth and properties of III/V semiconductor surfaces and nanostructures. The system allows one to grow III/V semiconductor surfaces by molecular beam epitaxy (MBE) and analyze their surface by a variety of surface analysis techniques. The geometric structure is examined by scanning tunneling microscopy (STM), low-energy electron diffraction and reflection high-energy electron diffraction. The electronic properties of the surfaces are studied by angular resolved photoemission either in the laboratory using a helium discharge lamp or at the Berlin Synchrotron Radiation Facility BESSY. In order to meet the space restriction at BESSY the system dimensions are kept very small. A detailed description of the apparatus and the sample handling system is given. For the UHV-STM (Park Scientific Instruments, VP2) a new, versatile tip handling mechanism has been developed. It allows the transfer of tips out of the chamber and furthermore, the in situ tip cleaning by electron annealing. In addition, another more reliable in situ tip-preparation technique operating the STM in the field emission regime is described. The ability of the system is shown by an atomically resolved STM image of the c(4×4) reconstructed GaAs(001) surface.
Simulation of interferometric sensors for pressure and temperature measurements
Authors: Golnabi Hossein
Published: July 2002

A Mach–Zehnder type fiber optic sensor is modeled and the phase change for this device as a result of pressure or temperature variation is studied. Different parameters involved in the sensing process such as Young's modulus, Poisson's ratio, light wavelength, index of refraction, and stress–optic coefficients are changed and their effects investigated. Our results show that Young's modulus, Poisson's ratio, light wavelength, and stress–optic coefficients have the major roles for pressure sensing. On the other hand for temperature sensing, light wavelength, thermal expansion coefficient, and temperature dependence of the index of refraction are the important parameters. For a typical silica glass fiber at 0.6328 μm wavelength, the calculated phase change due a pressure change of 1 Pa for the 1 m length is 4.08×10−5 rad. This phase change for 1 m of a similar probe fiber corresponding to 1 °C temperature change is found to be 107 rad.
Optical phonons of hexagonal and cubic GaN studied by infrared transmission and Raman spectroscopy
Authors: Giehler M. , Ramsteiner M. , Brandt O. , Yang H. , Ploog K. H.
Published: July 2002

Using infrared transmission and Raman spectroscopy, we have studied the optical phonon modes of GaN layers grown on GaAs(001) substrates by molecular beam epitaxy. The crystal structure of the GaN layers ranges from predominantly wurtzite to predominantly zincblende depending on the growth conditions. The transverse and longitudinal optical phonons in cubic GaN are found to be at 552 and 739 cm−1, respectively. These frequencies are slightly shifted with respect to the corresponding A1 and E1 phonon modes in hexagonal GaN. The frequency shifts, together with Raman scattering selection rules, can be used for identifying the phase composition of GaN. A more distinct fingerprint of the hexagonal phase is provided by the occurrence of the E2 phonon modes that are spectrally separated from optical phonon modes in the cubic phase and thus uniquely related to the hexagonal phase.
Patterning method for silicides based on local oxidation
Authors: Mantl S. , Dolle M. , Mesters St. , Fichtner P. F. P. , Bay H. L.
Published: July 2002

Oxidation of CoSi2 layers on Si(100) using oxidation masks has been investigated. It is shown that local oxidation can be used to pattern the silicide layer. This method allows the formation of buried interconnects and metallized silicon mesa structures. Epitaxial CoSi2 silicide layers were grown by molecular beam epitaxy on Si(100). The SiO2/Si3N4 oxidation mask was patterned photolithographically with linewidths of typically 1.5 μm. During thermal oxidation, SiO2 forms in the unprotected regions of the silicide layer. The silicide is pushed into the substrate in these regions. At a critical oxide thickness, the oxidized region of the silicide layer separates from the unoxidized, in conformance with the structure of the oxidation mask. The oxide capped silicide maintains its uniform layer structure and its single crystallinity in spite of the large shift into the substrate. The method should be applicable also to polycrystalline silicides, such as TiSi2.
Lateral quantization effects in modulated barrier InGaAs/InP quantum wires
Authors: Kerkel K. , Oshinowo J. , Forchel A. , Weber J. , Zielinski E.
Published: July 2002

We have used a simple approach to fabricate buried InGaAs/InP quantum wires with widths down to 15 nm. Combining high resolution electron beam lithography and selective wet chemical etching only the InP cap layer of an InGaAs/InP quantum well is locally removed. InGaAs surface quantum wells are formed in the etched parts of the samples, where the energy band discontinuity of the quantum well is replaced by the high vacuum barrier. Therefore a lateral potential barrier is induced, which confines the carriers to the InP covered wire regions. In addition, the lateral potential can be strongly increased by a selective thermal intermixing step. The luminescence spectra of the wires show significant lateral quantization effects with energy shifts up to 13 meV and high quantum efficiencies up to room temperature.
X-ray characterization of the domain structure of epitaxial lead titanate thin films on (001) strontium titanate
Authors: Hsu W. -Y. , Raj R.
Published: July 2002

The coherency of the domain walls forming between the a and c domains in epitaxial lead titanate films forces a tilt in the a-domains with respect to the surface normal of the (001)SrTiO3 substrate. It is shown that the measurement of the relative volume fraction of the domains requires mapping of the x-ray diffraction intensity distribution in the reciprocal space. Maps for lead titanate films of different thickness show that a domains are essentially absent in films less than 50 nm thick and approach 25% volume fraction at a thickness of 350 nm. The tilt angle, which lies in the range 2.65±0.5°, remains unchanged with thickness.
Carrier recombination dynamics in a (GaInSb/InAs)/AlGaSb superlattice multiple quantum well
Authors: McCahon S. W. , Anson S. A. , Jang D.-J. , Flatté M. E. , Boggess Thomas F. , Chow D. H. , Hasenberg T. C. , Grein C. H.
Published: July 2002

We have used the 830 nm, subpicosecond output of a mode-locked Ti:sapphire laser, together with subpicosecond 3.55 μm pulses from a synchronously pumped optical parametric oscillator, to perform room-temperature, time-resolved, differential transmission measurements on a multiple quantum well structure with AlGaSb barriers and GaInSb/InAs superlattice wells. From these measurements, we have determined a Shockley–Read–Hall rate of 2.4×108 s−1 and an Auger coefficient of 7×10−27 cm6/s. In addition, we estimate the carrier capture efficiency into the wells to be ∼52% and have demonstrated that carrier cooling, cross-well transport, and capture are complete within ∼10 ps after excitation.
Measurement of index of refraction of InxAl1−xAs epitaxial layer using in situ laser reflectometry
Authors: Baek Jong-Hyeob , Lee Bun , Choi Sung Woo , Lee Jin Hong , Lee El-Hang
Published: July 2002

We report the application of in situ laser reflectometry in measuring index of refraction and other optical properties of InxAl1−xAs (0≤x≤1) epitaxial layers grown on GaAs substrates by low-pressure metal-organic chemical vapor deposition method. Two different lasers were used: One was a He–Ne laser operating at 0.6328 μm and the other was a single mode distributed-feedback (DFB) laser diode operating at 1.530 μm. The two laser beams were simultaneously directed on the growing layer at an angle of 71° from the surface normal. The oscillatory signals showed a variety of patterns depending on the index of refraction of the epitaxial layer of InxAl1−xAs (0≤x≤1). The initial oscillatory signal pattern was found to be reversed at the composition of x=0.75, where the index of refraction of the InxAl1−xAs layer is the same as that of the GaAs substrate. The absorption coefficients and indices of refraction of the InxAl1−xAs epitaxial layers were obtained for the entire range of composition at the growth temperature of 535 °C by in situ laser reflectometry.
Assembling strained InAs islands on patterned GaAs substrates with chemical beam epitaxy
Authors: Jeppesen So/ren , Miller Mark S. , Hessman Dan , Kowalski Bernhard , Maximov Ivan , Samuelson Lars
Published: July 2002

The assembly of strained InAs islands was manipulated through growth on patterned GaAs substrates with chemical beam epitaxy. Conditions were found to selectively place the islands in patterns features but not on surrounding unpatterned fields. Chains of islands having 33 nm minimum periods were formed in trenches, and single or few islands were grown in arrays of holes. When capped with GaAs, the islands behave as quantum dots and are optically active.
Optical second-harmonic probe for silicon millimeter-wave circuits
Authors: Ohlhoff C. , Meyer C. , Lüpke G. , Löffler T. , Pfeifer T. , Roskos H. G. , Kurz H.
Published: July 2002

Electric field-induced second-harmonic generation (EFISHG) is shown to be a very powerful method for contactless sampling of high-speed electrical signals on silicon millimeter-wave devices. We present picosecond resolution EFISHG measurements of 2 GHz sinusoidal signals on a photoconductive silicon-on-sapphire antenna. We further demonstrate the application of the EFISHG technique for spatial mapping of free-running microwave signals in silicon.
Fabrication of 3 nm wires using 100 keV electron beam lithography and poly(methyl methacrylate) resist
Authors: Cumming D. R. S. , Thoms S. , Beaumont S. P. , Weaver J. M. R.
Published: July 2002

We report the fabrication of 3 nm NiCr wires on a solid silicon substrate. The process uses conventional 100 keV electron beam lithography and poly(methyl methacrylate) resist. The wires consist of short, continuous, lengths of metal that are attached at either end to 20 nm wide wires. Instead of exposing continuous lines in the resist, we blank the beam for several pixels to leave a gap. The resist in the gap is therefore exposed only by the secondary electrons from the neighboring regions that are directly exposed by the beam. The technique is repeatable and we demonstrate that it is possible to make 3 nm features on demand.
Photoluminescence study of ZnSe single crystals grown by solid-phase recrystallization
Authors: Tournié E. , Morhain C. , Neu G. , Faurie J.-P. , Triboulet R. , Ndap J. O.
Published: July 2002

We investigate through low-temperature photoluminescence (PL) and selective photoluminescence (SPL) spectroscopies, ZnSe single crystals grown by solid-phase recrystallization. The PL spectra are dominated by the so-called I1deep excitonic line, a neutral–acceptor bound–exciton line I1, the free-exciton emission FX, and the n=2 excited state of FX. We identify the main residual impurities. Donor–acceptor pair bands are hardly detected. A major characteristic of these samples is the quasiabsence of any Cu-related deep emission which generally plagues the PL spectra of bulk ZnSe. Consequently, I1deep is ascribed to an exciton bound to Zn-vacancies related acceptors. Our results indicate that these ZnSe samples are of high quality and that solid-phase recrystallization is a promising technique to prepare ZnSe epitaxial substrates.
Investigation on direct bonding of III–V semiconductor wafers with lattice mismatch and orientation mismatch
Authors: Okuno Yae
Published: July 2002

The direct bonding of various III–V wafers with mismatches in terms of lattice constants and surface orientations was systematically investigated for an In–Ga–As–P system. Many wafer combinations were bonded with sufficient mechanical strength, despite those mismatches. The bonding interface of (001) GaP and (110) InP was observed by transmission electron microscopy and found to be bonded at the atomic level without any defects occurring. The electrical property of the bonding interface was examined for several bonded structures of GaAs and InP. The results support a novel concept ‘‘free-orientation integration,’’ which should be achieved by direct bonding.
Photovoltaic cell of carbonaceous film/n-type silicon
Authors: Yu H. A. , Kaneko Y. , Yoshimura S. , Otani S.
Published: July 2002

A photovoltaic cell with carbonaceous thin film/n-type silicon (C/n-Si) was fabricated. The carbonaceous thin film was deposited on an n-type single-crystal-silicon substrate by chemical-vapor deposition of 2,5-dimethyl-p-benzoquinone at 500 °C. Without light irradiation, the photovoltaic cell displayed an almost perfect rectifying current–voltage characteristic. Under illumination of 15 mW cm−2 light with wavelengths between 400 and 800 nm similar to the solar light, it generated 2.73 mA cm−2 of short-circuit and 325 mV of open-circuit voltage. With the same light condition, a power conversion efficiency of 3.80% and a fill factor value of 0.65 were achieved.
Nanometer scale conductance change in a Langmuir-Blodgett film with the atomic force microscope
Authors: Yano Koji , Kyogaku Masafumi , Kuroda Ryo , Shimada Yasuhiro , Shido Shunichi , Matsuda Hiroshi , Takimoto Kiyoshi , Albrecht Otto , Eguchi Ken , Nakagiri Takashi
Published: July 2002

A nanometer scale metal/Langmuir-Blodgett (LB) film/metal structure is realized with an atomic force microscope combined with scanning tunneling microscope (AFM/STM). Even in this nanometer scale configuration, increase in conductance can be induced at any point in the LB film by application of a voltage pulse. The AFM/STM observation shows little surface modification has occurred by the voltage application, which shows that the conductance of the LB film changes without pit formation in the LB film or metal cluster deposition from the tip of the probe.
Surface adhesion reduction in silicon microstructures using femtosecond laser pulses
Authors: Tien N. C. , Jeong S. , Phinney L. M. , Fushinobu K. , Bokor J.
Published: July 2002

A reduction of the adhesion between polysilicon surface-micromachined structures and its silicon substrate using ultrashort pulse laser irradiation has been demonstrated. Polysilicon cantilevers, which adhered to the silicon substrate after final rinse and dry, were freed after irradiation by a 800 nm wavelength laser with pulse duration of 150 fs (full width at half-maximum) and fluences up to 40 mJ/cm2. Increasing the pulse widths to 2.7 ps resulted in significantly fewer freed cantilevers indicating that the process depends heavily on the presence of high-temperature carriers in the silicon. Adhesion reduction has been observed from exposure to a single pulse which results in minimal lattice temperature increase.
Photoluminescence study of deep etched InGaAs/GaAs quantum wires and dots defined by low-voltage electron beam lithography
Authors: Steffen R. , Koch Th. , Oshinowo J. , Faller F. , Forchel A.
Published: July 2002

Combining low-voltage electron beam lithography (EBL) and wet chemical etching, arrays of deep etched InGaAs/GaAs quantum wires with widths down to 15 nm and dots with minimum diameters of 27 nm have been fabricated. The application of low-voltage EBL strongly reduces the proximity effect during pattern exposure and allows the formation of very homogeneous nanostructure arrays. Low-excitation photoluminescence (PL) spectroscopy of both wires and dots reveals a structure size dependent blue shift of the emission lines up to 14 meV. This energy shift is caused by lateral confinement and shows a clear dependence on the structure dimensionality. The quantization is calculated with a simple model using only standard InGaAs/GaAs material parameters and the geometrical structure widths measured with a scanning electron microscope (SEM).