bluuebunny/crossref_metadata_2025 huggingface dataset:
Hemispherical total emissivity and specific heat capacity of deeply undercooled Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 melts
Authors: Busch R. , Kim Y. J. , Johnson W. L. , Rulison A. J. , Rhim W. K. , Isheim D.
Published: July 2002

High-temperature high-vacuum electrostatic levitation (HTHVESL) and differential scanning calorimetry (DSC) were combined to determine the hemispherical total emissivity εT, and the specific heat capacity cp, of the undercooled liquid and throughout the glass transition of the Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 bulk metallic glass forming alloy. The ratio of cp/εT as a function of undercooling was determining from radiative cooling curves measured in the HTHVESL. Using specific heat capacity data obtained by DSC investigations close to the glass transition and above the melting point, εT and cp were separated and the specific heat capacity of the whole undercooled liquid region was determined. Furthermore, the hemispherical total emissivity of the liquid was found to be about 0.22 at 980 K. On undercooling the liquid, the emissivity decreases to approximately 0.18 at about 670 K, where the undercooled liquid starts to freeze to a glass. No significant changes of the emissivity are observed as the alloy undergoes the glass transition.
Influence of preparation on resistivity behavior of epitaxial Nd0.7Sr0.3MnO3−δ and La0.67Ba0.33MnO3−δ thin films
Authors: Xiong G. C. , Li Q. , Ju H. L. , Greene R. L. , Venkatesan T.
Published: July 2002

The influence of sample preparation on the resistivity and magnetoresistance (MR) behavior of doped manganese oxides has been studied. Two systems, Nd0.7Sr0.3MnO3−δ and La0.67Ba0.33MnO3−δ thin films, have been chosen for this study. The former has the largest reported MR ratio at 60 K and the latter has a large MR ratio at room temperature. Two processes, deposition at a high temperature and annealing at a high temperature, have opposite influences on the resistivity behavior of these films. The results suggest that oxygen stoichiometry and diffusion are important factors in causing the behavior observed in doped manganese oxide films.
Evolution of electronic properties at the p-GaAs(Cs,O) surface during negative electron affinity state formation
Authors: Alperovich V. L. , Paulish A. G. , Scheibler H. E. , Terekhov A. S.
Published: July 2002

The evolution of surface band bending and surface photovoltage was monitored in situ by photoreflectance spectroscopy during activation of the surface of epitaxial GaAs to the state of negative electron affinity by successive deposition of cesium and oxygen in a standard ‘‘yo-yo’’ technique. Considerable variations of the band bending (by approximately 0.3 eV) and surface photovoltage (by three orders of magnitude) were observed. It was found that the maximum of photoemission quantum yield corresponded to unexpectedly small value of the band bending φs=0.3 eV, as compared to widely accepted value of approximately 0.5 eV.
Second-harmonic generation from GaAs/AlAs vertical cavity
Authors: Nakagawa S. , Yamada N. , Mikoshiba N. , Mars D. E.
Published: July 2002

We have demonstrated second-harmonic generation in a GaAs/AlAs vertical cavity grown on a (311)B GaAs substrate. Second-harmonic light of 492 nm was observed and its efficiency was measured to be 1.4×10−4 %/W. The cavity confines high intensity of fundamental field, resulting in efficient second-harmonic generation. Quasiphase matching was realized with the stacked GaAs/AlAs layers inside the cavity, which was designed taking into account the strong absorption of second-harmonic power in GaAs layers. We show that conversion efficiency of the GaAs/AlAs vertical cavity could be more than 10%/W if the optimization is completed.
SIMION PC/PS2 electrostatic lens design program
Authors: Dahl D. A. , Delmore J. E. , Appelhans A. D.
Published: July 2002

SIMION PC/PS2 4.02 is a personal computer program for designing and analyzing charged particle (ions and electrons) lenses, ion transport systems, and various types of mass spectrometers and surface probes that utilize charged particles. The modification of an existing design or the generation of a completely new one is performed interactively with a graphics screen and mouse. Once the geometry has been defined, the operating conditions (electrode voltages and magnetic field configuration) can be quickly changed and the resultant fields viewed in several different 2D and 3D modes. The trajectories of charged particles moving in these fields are calculated utilizing sophisticated ‘‘look-ahead’’ algorithms that dynamically control the time step to optimize speed and accuracy. A unique graphics display of the electrostatic fields and ion trajectories gives the user an intuitive, easily understood view of the performance characteristics. simion also includes a totally integrated capability for users to easily construct subprograms, which are automatically compiled and integrated into the main program, for defining and controlling all of the major functions of trajectory calculations. This makes it possible to model dynamic electric fields (e.g., rf), including ion-molecule collisions or neutralizations, etc. Operational experience with specific ion lenses designed with simion and tested in several different applications are discussed. SIMION PC/PS2 is available upon written request for the cost of distribution.
A piezoelectric droplet generator for use in wind tunnels
Authors: Warnica W. D. , Van Reenen M. , Renksizbulut M. , Strong A. B.
Published: July 2002

This article describes a compact piezoelectric droplet generator. A unique feature of this instrument is the small size of its nozzle assembly which includes a cylindrical piezoelectric ceramic transducer, an interchangeable orifice, a charging ring, and deflection plates. The nozzle assembly is housed in an acrylic tube, 19 mm in outside diameter and 150 mm in length, which can be placed inside a wind tunnel without causing a significant blockage. The main mechanical components consist of a pressurized system which discharges liquid through the orifice to create a free liquid jet in the nozzle assembly. The transducer causes this jet to break up into uniform droplets by exciting the instability mechanism of symmetric varicose deformations. Droplets tend to be closely spaced because of this method of generation so increased separation is obtained by selectively charging and deflecting some of the droplets from the main stream to a drain. One droplet out of 1–9999 droplets can be selected to exit from the nozzle assembly. The electronic circuitry consists of a transducer driver, and circuits for charging and deflecting the droplets. Power metal-oxide-semiconductor field-effect transistors are used in an H bridge and a push-pull configuration to provide rapid operation of the transducer-driver and droplet-charging circuitry. A transient analysis is performed to obtain the gain factor between the applied voltage and the corresponding flow modulation of the liquid jet. This analysis provides operating characteristics of the transducer and may be used to calculate the breakup length of the jet for a typical applied voltage. Uniform droplets can be produced reliably with this instrument over a large range of size and speed. For the current research application, involving droplet drag in turbulent flows, droplets with diameters from 150 to 1000 μm are required at speeds from 3 to 20 m/s. For other studies, the range of size can be changed by using different orifices.
Construction and applications of a dual mass-selected low-energy ion beam system
Authors: Qin Fuguang , Wang Xiangming , Liu Zhikai , Yao Zhenyu , Ren Zhizhang , Lin Lanying , Su Shijun , Jiang Weisheng , Lau W. M.
Published: July 2002

A direct ion beam deposition system designed for heteroepitaxy at a low substrate temperature and for the growth of metastable compounds has been constructed and tested. The system consists of two mass-resolved low-energy ion beams which merge at the target with an incident energy range 50–25 000 eV. Each ion beam uses a Freeman ion source for ion production and a magnetic sector for mass filtering. While a magnetic quadrupole lens is used in one beam for ion optics, an electrostatic quadrupole lens focuses the other beam. Both focusing approaches provide a current density more than 100 μA/cm2, although the magnetic quadrupole gives a better performance for ion energies below 200 eV. The typical current of each beam reaches more than 0.3 mA at 100 eV, with a ribbon beam of about 0.3–0.5×2 cm2. The target is housed in an ultrahigh vacuum chamber with a base pressure of 1×10−7 Pa and a typical pressure of 5×10−6 Pa when a noncondensable beam like argon is brought into the chamber. During deposition, the target can be heated to 800 °C and scanned mechanically with an electronic scanning control unit. The dual beam system has been used to grow GaN using a Ga+ and a N+ beam, and to study the oxygen and hydrogen ion beam bombardment effects during carbon ion beam deposition. The results showed that the simultaneous arrival of two beams at the target is particularly useful in compound formation and in elucidation of growth mechanisms.
Compact, inexpensive, visible diode laser source of high repetition rate picosecond pulses
Authors: Tatum J. A. , Jennings J. W. , MacFarlane D. L.
Published: July 2002

We discuss the techniques and describe the circuitry to build a visible diode laser picosecond light source. The rf circuitry is easy and inexpensive to build, and the final package is quite compact. Stable, low jitter, 108-Hz trains of ∼100-ps, 670-nm optical pulses are therefore readily attainable.
A new Cs sputter ion source for accelerator mass spectrometry
Authors: Höpfl R. , Bretschneider T. , Buchler A. , Charasse Y. , Ernst W. , Finckh E. , Goblirsch R. , Gumbmann F. , Haller M. , Karschnick R. , Kretschmer W. , Rauscher A. , Schielein H. , Schleicher M.
Published: July 2002

At the Erlangen tandem accelerator facility, a new Cs sputter ion source for accelerator mass spectrometry (AMS) has been developed and installed. Since cross talk between the different AMS samples in the ion source must be avoided, the sample magazine is stored in a separate vacuum chamber, which is opened to the source chamber only for exchanging the targets between the AMS measurements. To achieve large negative beam currents and a small beam emittance, a spherical shape of the Cs ionizer was chosen. The geometry of the ionizer, the target region, and the electrostatic lenses have been optimized by extensive ion optical computer simulations. A microcomputer system was developed, which controls the exchanging of the sputter targets, the high voltage supplies, the heating elements, the wobbling of the target, and which allows adjusting of the gap between ionizer and target. Behind the 90° injection magnet, the different isotopes are well separated, and the beam currents (e.g., 20 μA 12C−) are stable. For further optimization of the ion source parameters, an emittance measuring device has been constructed. The measured beam emittance is 2.5 π mm mrad MeV1/2.
Determination of thermal diffusivity of polymers by means of multivariate calibration of mirage data
Authors: Skagerberg Bert , Jaarinen Jussi , Rantala Jukka
Published: July 2002

In this paper we describe how multivariate calibration techniques including experimental design and partial least-squares regression, PLS, can be used to determine thermal diffusivity from mirage data. In order to illustrate the utility of the theory a case study is presented where photothermal mirage data were simulated for a series of polymeric film samples. A PLS model was calculated that predicts thermal diffusivity with high precision.
Near-field optical beam induced current measurements on heterostructures
Authors: Ünlü M. S. , Goldberg B. B. , Herzog W. D. , Sun D. , Towe E.
Published: July 2002

We report near-field optical beam induced current (NOBIC) measurements on semiconductor quantum well (QW) structures. A subwavelength fiber tip is coupled with a tunable laser source and scanned over a sample surface. The induced photocurrent reveals the compositional profile of quantum structures. Semiconductor QW structures were designed and fabricated by molecular beam epitaxy (MBE) to study the wavelength dependence and resolution capability of NOBIC. We demonstrated that the resolution of this technique strongly depends on the aperture size. For aperture sizes that allow for coupling of evanescent fields from the tip into the semiconductor as propagating fields, the resolution strongly depends on the excitation wavelength due to the variation of the optical penetration depth. For smaller apertures, the optical field remains evanescent in the semiconductor and resolution is essentially independent of the wavelength.
A new pressure sensing method by use of magnetic fluid
Authors: Komiya K. , Itoh I. , Gashi Y. H.
Published: July 2002

This article deals with a new pressure sensing method by use of magnetic fluids. In a magnetic fluid placed in a magnetic field, fluid-magnetic pressure appears, which is a function of magnetic field. When a differential pressure is applied to the ends of such a magnetic fluid plug, and the differential pressure is in equilibrium with the fluid-magnetic pressure so that the plug cannot move, then the magnitude of the magnetic field maintaining the fluid-magnetic pressure becomes a measure of the differential pressure. We made a small setup and measured differential pressures up to about 100 Pa by measuring the coil current of an electromagnet.
High aspect ratio submicron silicon pillars fabricated by photoassisted electrochemical etching and oxidation
Authors: Lau H. W. , Parker G. J. , Greef R. , Hölling M.
Published: July 2002

A technique for fabricating submicron free-standing silicon pillars has been developed. The silicon pillars have a high packing density, and aspect ratios over 50:1 can easily be achieved. Photoassisted electrochemical etching in hydrofluoric acid is used to etch deep macropores in n-type silicon wafers which have been patterned by standard photolithography. The regular macropores can be used for fabricating photonic band-gap structures. The bulk silicon remaining between the close-packed macropores is oxidized. Free-standing pillars are then formed by subsequently wet etching the silicon dioxide. The pillars are the initial structures for forming quantum wires using further oxidation and etch steps.
Band filling at low optical power density in semiconductor dots
Authors: Castrillo P. , Hessman D. , Pistol M.-E. , Anand S. , Carlsson N. , Seifert W. , Samuelson L.
Published: July 2002

We have studied band filling in strained InP dots grown on GaInP. Compared to quantum wells, the dots show band filling at two orders of magnitude lower optical excitation power density. We show that the emission attributed to band filling originates from the dots by using spatially resolved photoluminescence recording emission from single dots with very high spectral resolution. With time-resolved photoluminescence spectra we follow the dynamic relaxation of the charge carriers in the dots.
High-current dc microwave ion sources (invited)
Authors: Taylor T.
Published: July 2002

Microwave-driven ion sources and, in particular, electron cyclotron resonance (ECR) ion sources have customarily been used almost exclusively for the production of multiply charged ions. However, very reliable microwave sources that generate high-current low-emittance beams of singly charged ions have recently been developed for ion implanters and accelerator injectors. In this paper the elementary concepts of high-current microwave ion sources are summarized. The distinction between the ECR and the off-resonance coupling of the microwave power into the plasma is addressed as well as the difficulty of extracting high-quality ion beams in the presence of the large magnetic fields associated with microwave ion sources. The features of a selection of high-current microwave ion sources are reviewed.
A new method of surface resistance measurement with a niobium triaxial cavity working at 2 K
Authors: Liang Changnian , Phillips Larry , Sundelin Ronald
Published: July 2002

A 1.5-GHz superconducting niobium triaxial cavity has been fabricated to study residual surface resistance of superconducting materials at 2 K. Unlike many other structures where the entire test samples have to be placed in strong magnetic field locations, we have the edge of a 25.4 mm or larger diameter sample outside of the strong field region, a procedure which will greatly reduce edge effects and image current losses between the thin film and substrate. A calorimetric method is used to measure the sample losses, and is designed to resolve a 10-μK temperature change using 16 carbon resistor sensors. A detection limit of 0.05-μW power dissipation has been determined with a calibration heater, which corresponds to a surface resistance of 0.02 nΩ at a maximum cavity magnetic field of 250 G. Initial cavity testing was performed in a magnetically unshielded cryostat, yielding a 2.2-μΩ residual resistance which was measured by both the rf measurement and the calorimetric measurement.
Cell design for in situ x-ray scattering studies of metal/solution interfaces under electrochemical control
Authors: Nagy Z. , You H. , Yonco R. M.
Published: July 2002

During the last decade, there has been an increasing use of synchrotron x-ray techniques for the in situ investigation of the structure and composition of metal/solution interfaces under electrochemical control. While a number of experimental cell designs have been utilized in the past, every one of them has exhibited some shortcomings. This paper describes the development of a wide-angle-accessible, transmission-geometry, sandwich-type, x-ray/electrochemical cell. From an x-ray physics standpoint, this cell allows uninterrupted access over a 180° in-plane angle for all incident and scattering angles between 0° and 75° with respect to the sample surface. It is especially advantageous at small scattering angles because of the uniform and insignificant background scattering. From an electrochemical standpoint, this cell provides a uniform current distribution and continuous, precise potential control of the working-electrode surface; at the same time, it permits easy flushing of the working solution and even accommodates operating with flowing solution. Its only disadvantage is its inability to permit in situ cyclic voltammetry of only one surface of the single crystal.
Multiampere negative ion source development at Novosibirsk (invited)
Authors: Belchenko Yu. I. , Dimov G. I. , Kupriyanov A. S.
Published: July 2002

Results on multiampere negative ion (NI) sources with a surface-plasma mechanism of negative ion production are presented. Several types of surface-plasma sources (SPS)—Honeycomb semiplanotrons and hollow-cathode Penning source—are reviewed. The data on SPS H−(D−) production with average NI current density in the beam up to 0.1 A/cm2 is presented. The properties of high-current glow hydrogen–cesium discharge that produces a large-area, thin layer of plasma and provides the necessary components for intense negative ion emission and collecting (low work function coverage, electric and magnetic field distribution across the plasma, current composition to NI emitter) are analyzed. Data on efficiency and contribution of different channels of surface-plasma NI production are presented.
A low-noise wide-band transimpedance amplifier for current noise spectra measurements
Authors: De Geronimo G. , Bertuccio G. , Longoni A.
Published: July 2002

A low-noise wide-band transimpedance amplifier, designed to measure the spectral noise densities of currents in submicroampere range, is presented. The feedback transimpedance amplifier is designed to operate in a frequency range from 10–100 kHz, having an intrinsic noise as low as 3 fA/√Hz up to 1 kHz and less than 20 fA/√Hz at 100 kHz at room temperature, allowing the measurement of the shot noise of currents down to the 100-pA range. The design criteria and experimental test on some devices are described.
The effect of rapid thermal N2O nitridation on the oxide/Si(100) interface structure
Authors: Lu Z. H. , Tay S. P. , Cao R. , Pianetta P.
Published: July 2002

High-resolution x-ray photoelectron spectroscopy (XPS) was used to study the chemical nature and physical distribution of N in oxynitride films formed by rapid thermal N2O processes (RTPs). High-resolution synchrotron Si 2p core level photoemission spectroscopy (PES) was used to study the oxide/Si(100) interface suboxide structures with and without the presence of N. XPS N 1s studies indicated that there are two types of N in the RTP oxynitride films. The chemical bond configuration of the first type of N is similar to that N in Si3N4 and is mainly distributed within the first 1 nm from the interface. The second type of N is distributed mainly outside of the first 1 nm region, and the N is likely bonded to two Si and one oxygen atom. PES studies showed that Si formed suboxides with oxygen at the interface for all oxynitride films. It is found that there is no change in the Si+1 structure while there is a dramatic intensity decrease in the Si+2 and Si+3 peaks with the inclusion of N in the oxide. Both the XPS and PES results are explained in terms of a strain reduction as N is incorporated in the film near the interface region, where Si3N4 functions as a buffer layer which reduces the stress caused by the large Si ‘‘lattice’’ mismatch between the bulk Si and the oxide overlayer. About 1/5 of the Si+2 and 1/3 of Si+3 atoms at the SiO2/Si interface has been replaced by the Si3N4 buffer layer at the oxynitride/Si interface.
Modeling of electron-cyclotron-resonance ion source and scaling laws
Authors: Girard A. , Perret C. , Melin G. , Lécot C.
Published: July 2002

The heating and confinement of electrons in an electron-cyclotron-resonance ion source (ECRIS) plasma is described: the single particle motion in a magnetic beach is presented, showing the role of the rf wave magnetic field in the electron losses. This effect can be approximately modeled by a Fokker–Planck quasilinear equation in velocity space. This modeling is discussed and numerical results are presented. The behavior of the wave close to resonance is analyzed, taking into account the thermal motion of the electrons. The role of the different design parameters (including rf frequency) is shown and the major ingredients for the design of an efficient ECRIS for multiply charged ions production are summarized.
Enhancing the performances of traditional electron cyclotron resonance ion sources with multiple-discrete-frequency microwave radiation
Authors: Alton G. D. , Meyer F. W. , Liu Y. , Beene J. R. , Tucker D.
Published: July 2002

The performances of electron cyclotron resonance (ECR) ion sources, in terms of high-charge-state yields and intensities within a particular charge state, can be enhanced by increasing the physical sizes of the ECR zones in relation to the sizes of their plasma volumes. The creation of a large ECR plasma “volume” permits coupling of more power into the plasma, resulting in the heating of a much larger electron population to higher energies, the effect of which is to produce higher charge-state distributions and higher intensities within a particular charge state than possible in present forms of the ECR source. The ECR plasma “volumes” of traditional B-minimum ECR sources can be increased by injecting broadband microwave radiation (multiple-discrete-frequency, variable frequency, or broad-band-width frequency microwave radiation) derived from standard klystron, gyrotron, or traveling-wave-tube (TWT) technologies (frequency domain). To demonstrate that the frequency domain technique can be used to enhance the performance of a traditional B-minimum ECR ion source, comparative studies were made to assess the relative performances of the Oak Ridge National Laboratory Caprice ECR ion source, in terms of multiply charged ion-beam generation capabilities, when excited with high-power, single-frequency, or multiple-discrete-frequency microwave radiation, derived from standard klystron and/or TWT technologies. These studies demonstrate that the charge-state populations for Ar q+ and Xeq+ move toward higher values when excited with two and three discrete-frequency, microwave power compared to those observed when single-frequency microwave power is used. For example, the most probable charge state for Xe is increased by one charge-state unit while the beam intensities for charge states higher than the most probable are increased by factors of ∼3 compared to those observed for single-frequency plasma excitation. The results of these measurements along with details on the modifications to the injection system required to couple the microwave radiation into the plasma volume of the Caprice source will be presented in this report.
Low cost phase-modulation measurements of nanosecond fluorescence lifetimes using a lock-in amplifier
Authors: Harms Peter , Sipior Jeffrey , Ram Natraj , Carter Gary M. , Rao Govind
Published: July 2002

The use of a 200 MHz lock-in amplifier was demonstrated as a low cost instrument for frequency domain measurements of nanosecond fluorescence lifetimes. The lock-in directly provided both the dc bias and the ac signal used to modulate the intensity of a blue light emitting diode excitation source. The emission was measured by a photomultiplier tube and the resulting signal was sent back through a dc block to the lock-in with no external signal processing or heterodyning required. The system was highly accurate at measuring phase and modulation up to 80 MHz and moderately so up to 100 MHz. The fluorescence lifetimes of several standard fluorophores (Fluorescein, Rhodamine B, and [Ru(bpy)3]2+) were measured by the lock-in, and the results agreed closely with those made on a research grade fluorometer. The entire lock-in based system costs less than US $10,000 to build and can be controlled by any standard computer through a GPIB or serial connection. The system is also portable, consumes little power, and can easily be configured for use with fiber optics, making it ideal for use with fluorescence lifetime based sensors.
Synthesis of nanosize powders of alumina by ablation plasma produced by intense pulsed light-ion beam
Authors: Yatsui K. , Grigoriu C. , Kubo H. , Masugata K. , Shimotori Y.
Published: July 2002

Nanosize powders of alumina have been synthesized by high-density ablation plasma produced by the irradiation of an intense, pulsed, light-ion beam on an aluminum target in oxygen. Diameters of the powders, which are observed to be spherical, are typically 5–25 nm. At 1 Torr of oxygen, nanosize powders of aluminum are synthesized with those of a small amount of γ-alumina. At 10 Torr of oxygen, on the other hand, γ-alumina powders are produced with a small amount of aluminum powders. Annealing characteristics in nitrogen have also been studied on the transition from γ- to α-alumina.
Characterization of SiGe quantum wire structures by cathodoluminescence imaging and spectroscopy
Authors: Higgs V. , Lightowlers E. C. , Usami N. , Mine T. , Fukatsu S. , Shiraki Y.
Published: July 2002

SiGe quantum wire (QWR) structures grown by gas source molecular beam epitaxy have been characterized by cathodoluminescence (CL) imaging and spectroscopy. At T≊5 K, the CL spectra obtained with a focused beam contain SiGe luminescence features associated with electron-hole plasma recombination. When the electron beam is defocused three separate SiGe no-phonon luminescence features and their transverse optic phonon replicas are observed. These features are related to recombination in the SiGe (100) quantum wells (QWs), SiGe (111) QWs, and the SiGe QWRs. The high generation rates associated with the focused electron beam quenches the luminescence and results in electron-hole plasma recombination in the adjacent SiGe (100) QWs, and saturation of the radiative processes. Defocusing the electron beam reduces the injection level and nonradiative processes, enabling the SiGe bound exciton features to be observed. Monochromatic CL imaging of the SiGe (100) QWs show that at low temperatures the CL image is broadened by exciton diffusion and becomes sharper at higher temperatures (T=50–70 K) reflecting nonexcitonic recombination.
Correlations for the thermal expansion coefficients of molten glass forming systems
Authors: Chua L. F. , Yuen C. W. , Kui H. W.
Published: July 2002

The specific volumes of molten Pd40Ni40P20, Pd77Cu6.5Si16.5, Pd82Si18, and Ni80P20, which are all glass formers, and were measured near the liquidus. It was found that the ratio α/Tg, where α is the thermal expansion coefficient and Tg is the glass transition temperature, remains fairly constant for all these systems. The scaling follows from the fact that with a larger thermal expansion coefficient, the free volume of the molten system would be squeezed out faster resulting in a larger Tg. This scaling behavior also allows us to roughly predict the glass transition temperature of a glass forming system. The glass forming ability can also be predicted by a parameter defined as α/T1.
Broadband single-electron tunneling transistor
Authors: Visscher E. H. , Lindeman J. , Verbrugh S. M. , Hadley P. , Mooij J. E. , van der Vleuten W.
Published: July 2002

A single-electron tunneling transistor has been directly coupled on-chip to a high electron mobility transistor. The high electron mobility transistor (HEMT) is used as an impedance matching circuit with a gain close to unity. The HEMT transformed the 1.4 MΩ output impedance of the single electron tunneling (SET) transistor by two orders of magnitude down to 5 kΩ, increasing its bandwidth to 50 kHz. This circuit makes it possible to observe the motion of individual electrons at high frequencies. The requirements for the bandwidth in high frequency applications is discussed.
Optical characterization of waveguide based photonic microstructures
Authors: Krauss Thomas F. , De La Rue Richard M.
Published: July 2002

Third-order, one-dimensional, semiconductor-air gratings have been designed, fabricated, and evaluated by optical waveguide transmission measurements. Gratings with as little as six unit cells show a clear band edge around 840–850 nm. Owing to our approach of semiconductor-rich lattices with small airgaps, the diffractive spreading loss is sufficiently small (∼50% in the passband) for meaningful results to be extracted. The measurements indicate that the optical waveguide approach is a good starting point for the study of photonic microstructures and that practical device concepts can be implemented.
Losses in polycrystalline silicon waveguides
Authors: Foresi J. S. , Black M. R. , Agarwal A. M. , Kimerling L. C.
Published: July 2002

The losses of polycrystalline silicon (polySi) waveguides clad by SiO2 are measured by the cutback technique. We report losses of 34 dB/cm at a wavelength of 1.55 μm in waveguides fabricated from chemical mechanical polished polySi deposited at 625 °C. These losses are two orders of magnitude lower than reported absorption measurements for polySi. Waveguides fabricated from unpolished polySi deposited at 625 °C exhibit losses of 77 dB/cm. We find good agreement between calculated and measured losses due to surface scattering.
Microstructure and deposition rate of aluminum thin films from chemical vapor deposition with dimethylethylamine alane
Authors: Kim Byoung-Youp , Li Xiaodong , Rhee Shi-Woo
Published: July 2002

Deposition of aluminum film from DMEAA in the temperature range of 100–300 °C has been studied. In this temperature range, there is a maximum deposition rate at around 150 °C. The film deposited at 190 °C has elongated blocklike grain shapes, which are ∼600 nm in width and 930 nm in length. Grains in the film deposited at 150 °C showed an equiaxed structure with grain size in the range of 100–300 nm in a film with 600 nm thickness. Aluminum oxide particle inclusion was observed especially at high deposition temperature. Plausible reaction pathways of DMEAA dissociation were suggested to explain the experimental observations.
Improving the plasma immersion ion implantation impact energy inside a cylindrical bore by using an auxiliary electrode
Authors: Zeng Xuchu , Tang Baoyin , Chu Paul K.
Published: July 2002

We propose a method to improve the impact energy of ions implanted into the interior sidewalls of cylindrical specimens during plasma immersion ion implantation. Our idea is based on a zero potential conductive auxiliary electrode positioned at the axis of the implanted cylindrical bore. We calculate the structure of the ion-matrix sheath in an infinitely long cylindrical bore with an auxiliary electrode and analyze the dependence of the radius of the auxiliary electrode on the electric field in the bore. Our results show that the auxiliary electrode improves significantly the distributions of the potential and the electric field inside the cylindrical bore. In addition, because the auxiliary electrode improves the potential drop from axis to sidewalls of the bore and introduces an electric field component which does not vary when the ions are implanted into the sidewalls, the impact energy can be improved in a cylindrical bore during plasma immersion ion implantation.
Electromigration damage due to copper depletion in Al/Cu alloy conductors
Authors: Lloyd J. R. , Clement J. J.
Published: July 2002

The problem of damage nucleation due to electromigration-induced copper depletion in an Al/Cu alloy is treated. The diffusion of aluminum in thin-film lines is sharply reduced by alloying with small amounts of copper. In this model, copper is depleted in a region at the cathode end of an Al/Cu alloy line. Assuming that the aluminum diffusion in this copper-deficient region is much faster than the diffusion of the copper, a quasisteady-state stress profile is established between the blocking boundary at the cathode and the copper front moving at the drift velocity. The time to reach a critical stress to initiate failure is shown to depend on the inverse of the square of the current density as observed experimentally. The model is appropriate for failure at contacts and vias, and at the end of long polycrystalline clusters in near-bamboo lines.
The capacitive origin of the picosecond electrical transients detected by a photoconductively gated scanning tunneling microscope
Authors: Groeneveld R. H. M. , van Kempen H.
Published: July 2002

We present experimental results and numerical calculations on the detection of picosecond electrical transients by a photoconductively gated scanning tunneling microscope. We show that the transient signal detected in the tunneling regime is coupled by the 5 fF geometric capacitance between tip and sample leading to a correlation current that is linearly proportional to the tunnel conductance.
Nanostructure fabrication using the selective thermal desorption of SiO2 induced by electron beams
Authors: Fujita S. , Maruno S. , Watanabe H. , Ichikawa M.
Published: July 2002

It has been found that selective thermal desorption of SiO2 on Si (111) substrate is induced by electron-beam irradiation. By using this selective thermal desorption, a nanofabrication technique has been realized by focused electron beams. Open windows of 10 nm width in a SiO2 film have been fabricated by this technique. A pattern transfer from the open windows to thin Si films has also been performed by Si growth and subsequent heating. This has produced Si wires of 10 nm width.
A nonvolatile ferroelectric memory device with a floating gate
Authors: Chen F. Y. , Fang Y. K. , Sun M. J. , Chen Jiann-Ruey
Published: July 2002

An adaptive ferroelectric field-effect transistor (FET) with a floating gate has been developed using a thin film of lead titanate ( PbTiO3) deposited on a n/p+ substrate by rf sputtering. This device utilizes the charge storage on the floating gate to control the n layer conductivity of a n/p+ Si substrate and performs a memory function, in which the drain conductance changes in proportion to the charge storage density on the floating gate. The device is a bulk channel field transistor structure and different from the conventional surface channel-type floating gate memory device. Thus, it possesses higher mobility and fast access time (<160 ns). The FET has low write/erase voltages (≤10 V) and its write/erase cycles are more than 106.
GaInAsSb/AlGaAsSb multiple-quantum-well diode lasers grown by organometallic vapor phase epitaxy
Authors: Wang C. A. , Choi H. K.
Published: July 2002

A GaInAsSb/AlGaAsSb multiple-quantum-well diode laser structure consisting of Al0.6Ga0.4As0.05Sb0.95 cladding layers, Al0.3Ga0.7As0.02Sb0.98 confining layers, and four 15-nm-thick Ga0.87In0.13As0.12Sb0.88 quantum wells with 20-nm-thick Al0.3Ga0.7As0.02Sb0.98 barrier layers was grown by organometallic vapor phase epitaxy. These lasers, emitting at 2.1 μm, have exhibited pulsed threshold current densities as low as 1.2 kA/cm2.
Study of composition and critical-point broadening in InAs/Ga1−xInxSb superlattices using spectroscopic ellipsometry
Authors: Wagner J. , Schmitz J. , Herres N. , Tränkle G. , Koidl P.
Published: July 2002

InAs/(GaIn)Sb superlattices (SL) grown by solid-source molecular-beam epitaxy were studied by spectroscopic ellipsometry. The pseudodielectric function of InAs/GaSb SLs could be fitted using modified bulk dielectric functions of InAs and GaSb with pronounced energy shifts and broadening of critical-point resonances. These changes in the dielectric functions of the constituent layers can be explained only in part by pseudomorphic strains, therefore providing evidence for thin-layer critical-point broadening and quantum confinement effects. For InAs/(GaIn)Sb SLs, the extremum in the pseudodielectric function derived from the E1 critical point of (GaIn)Sb was found to shift to lower energies with increasing In content, and thus can be used as a probe for the composition of the (GaIn)Sb SL layers.
Polarization anisotropy in the electroabsorption of ordered GaInP
Authors: Greger E. , Gulden K. H. , Moser M. , Schmiedel G. , Kiesel P. , Döhler G. H.
Published: July 2002

The polarization dependence of the Franz–Keldysh effect (FKE) in metalorganic vapor phase epitaxially grown AlGaInP/GaInP/AlGaInP p-i-n double heterostructures was investigated for samples with different ordering parameters. We determine an ordering induced shift of the FK spectra of up to 13 meV between light polarized along the [011] and [01-1] crystal directions. Due to the FKE the transmitted light intensity ratio between the respective polarizations was changed from 0.2 to 2.8 dB by applying an electric field of 335 kV/cm.
Noise properties and epitaxial quality in low-noise integrated YBa2Cu3O7 magnetometers
Authors: Scharnweber R. , Dieckmann N. , Schilling M.
Published: July 2002

Temperature dependent flux-locked loop noise measurements have been performed on low-noise integrated multiloop pickup coil magnetometers using ramp-type Josephson junctions with PrBa2Cu3O7 barriers. We show that the noise properties of such multilayer devices depend on the epitaxy of the YBa2Cu3O7 top film as analyzed by micro-Raman spectroscopy. At high epitaxial film quality the low-frequency noise is dominated solely by fluctuations of the critical currents of the Josephson junctions and is suppressible by additional bias-current modulation. The noise and the epitaxial properties of different samples are correlated to details in the laser-deposition process of the insulating SrTiO3 layer.
Direct band gap structures on nanometer-scale, micromachined silicon tips
Authors: Shealy J. R. , Macdonald N. C. , Xu Y. , Whittingham K. L. , Emerson D. T. , Pitts B. L.
Published: July 2002

The selective deposition of compound semiconductors on single crystal silicon tip arrays produces optical quality, direct band gap materials on the silicon nanostructures. We demonstrate using the organometallic vapor phase epitaxy of GaInP that the direct band gap semiconductor nucleates selectively on the silicon tips. The structural properties of the tips (whose radius of curvature is approximately 10–20 nm) are unaltered by this chemical vapor deposition process. Furthermore, intense band edge emission from the GaInP is observed with an external electron beam or laser stimulation indicating a good crystal quality for the three dimensional epitaxial structures.
Fe-doped InGaAs/InGaAsP photorefractive multiple quantum well devices operating at 1.55 μm
Authors: De Matos C. , Le Corre A. , L’Haridon H. , Gosselin S. , Lambert B.
Published: July 2002

Results on semi-insulating photorefractive multiple quantum well (MQW) devices operating without trapping layers are reported. The device structure consists of a MQW doped with Fe (1017 cm−3) isolated from the doped contact by intrinsic standoff layers. The photocarriers generated by the pump pulse are trapped in the MQW and screen the applied electric field in the MQW. Output diffraction efficiency of 0.2% is measured in a nondegenerate four-wave-mixing configuration and the rise time of the diffraction signal reaches 200 ns.
Critical change of magnetoresistance with bandwidth and doping in perovskite manganites
Authors: Tomioka Y. , Kuwahara H. , Asamitsu A. , Kasai M. , Tokura Y.
Published: July 2002

To explore the optimized colossal magnetoresistance (MR), i.e., higher MR with lower field, magnetotransport properties of single-crystalline perovskite manganites have systematically been investigated. Near x=1/2 with intrinsic instability of charge ordering (a 1/1 ordering of Mn3+/Mn4+), the one-electron bandwidth (W) is varied by reducing the radius of R-site cation in R1−xSrxMnO3. For R=Nd, the MR behavior is rather canonical, while for R=Sm, the field-induced nonmetal-to-metal transition of the first order shows up accompanying a change in resistivity by several orders of magnitude as a result of an enhanced antiferromagnetic interaction.
A new protective AlN film for organic photoconductors
Authors: Miao X. S. , Chan Y. C. , Pun E. Y. B.
Published: July 2002

AlN film with high transmissivity was deposited onto organic photoconductor (OPC) surface and the surface hardness was increased by between 31.9% and 61.5%, and the surface roughness was also decreased. The electrophotographic properties of the OPC coated with AlN film were also improved, thus confirming the suitability of AlN film for enhancing the operating life of OPC.
Time-resolved photoluminescence studies of InGaN/GaN single-quantum-wells at room temperature
Authors: Sun C.-K. , Chiu T.-L. , Keller S. , Wang G. , Minsky M. S. , DenBaars S. P. , Bowers J. E.
Published: July 2002

We present a room-temperature study of the well-width-dependent carrier lifetimes in InGaN single-quantum wells. At room temperature, carrier recombination was found to be dominated by interface-related nonradiative processes. The dominant radiative recombination at room temperature was through band-to-band free carriers. For the sample grown at a higher growth rate, we observed a longer luminescence lifetime, which was attributed to an improved quantum well interface.
Thin films of layered-structure (1−x)SrBi2Ta2O9−xBi3Ti(Ta1−yNby)O9 solid solution for ferroelectric random access memory devices
Authors: Desu S. B. , Joshi P. C. , Zhang X. , Ryu S. O.
Published: July 2002

We report on the thin films of solid–solution material (1−x)SrBi2Ta2O9−xBi3Ti(Ta1−yNby)O9 fabricated by a modified metalorganic solution deposition technique for ferroelectric random access memory devices. Using the modified technique, it was possible to obtain the pyrochlore free crystalline thin films at an annealing temperature as low as 600 °C. The solid–solution of layered perovskite materials helped us to significantly improve the ferroelectric properties, higher Pr and higher Tc, compared to SrBi2Ta2O9; a leading candidate material for memory applications. For example, the films with 0.7 SrBi2Ta2O9–0.3Bi3TiTaO9 composition and annealed in the temperature range 650–750 °C exhibited 2Pr and Ec values in the range 12.4–27.8 μC/cm2 and 68–80 kV/cm, respectively. The leakage current density was lower than 10−8 A/cm2 at an applied electric field of 200 kV/cm. The films exhibited good fatigue characteristics under bipolar stressing.
Gettering of iron in silicon-on-insulator wafers
Authors: Beaman Kevin L. , Agarwal Aditya , Kononchuk Oleg , Koveshnikov Sergei , Bondarenko Irina , Rozgonyi George A.
Published: July 2002

Gettering of Fe in silicon-on-insulator material has been investigated on both the bonded and separation by implantation of oxygen (SIMOX) platforms. Reduction of electrically active iron in intentionally contaminated and annealed wafers has been measured by deep level transient spectroscopy. These data, coupled with structural characterization techniques, such as transmission electron microscopy and preferential chemical etching, provide evidence that structural postimplantation damage below the buried oxide (BOX) in SIMOX wafers is an effective site for gettering of iron with the iron gettering efficiency varying with the SIMOX processing. Gettering was not observed in bonded wafers, and the lower BOX interface did not provide any iron gettering in either bonded or SIMOX wafers.
Compensating defect in deep buried layers produced by MeV heavy ions in n-silicon
Authors: Giri P. K. , Mohapatra Y. N.
Published: July 2002

Buried damaged layers in n-silicon created by implantation of MeV heavy ions (Ar+) have been studied by capacitance and current measurements, and spectroscopic techniques such as deep level transient spectroscopy and constant capacitance time analyzed transient spectroscopy. We have isolated a new midgap acceptor level responsible for carrier compensation in samples irradiated with doses below amorphization threshold. This defect level is demonstrated to control hysteresis in capacitance-voltage characteristics, space charge limited current conduction, and premature termination of emission transients. The emission energy of the defect is observed to be sensitive to degree of disorder in the damaged layer controlled by irradiation dose, and relaxation induced by heat treatment.
n
-type high-conductive epitaxial diamond film prepared by gas source molecular beam epitaxy with methane and tri-n-butylphosphine
Authors: Nishimori Toshihiko , Nakano Koji , Sakamoto Hitoshi , Takakuwa Yuji , Kono Shozo
Published: July 2002

An n-type phosphorous (P) doped epitaxial diamond film with high conductivity was grown on a C(001) substrate by gas source molecular beam epitaxy using methane and tri-n-butylphosphine. The electrical conductivity of the diamond film was measured to be 0.33 (Ω cm)−1 at 23 °C with its activation energy to be 0.12 eV. The Hall measurements showed n-type conduction and a carrier concentration of 1.6×1018 cm−3 at 400 °C, which is comparable to the P concentration determined by secondary-ion-mass spectroscopy. These indicate the formation of shallow P donors with high electrical activation efficiency. A p-n junction diode was fabricated by growing a P-doped epitaxial film on a boron-doped C(001) substrate, which showed for the first time a rectification ratio of ∼103 at 10 V.
Determination of the Al mole fraction and the band gap bowing of epitaxial AlxGa1−xN films
Authors: Angerer H. , Brunner D. , Freudenberg F. , Ambacher O. , Stutzmann M. , Höpler R. , Metzger T. , Born E. , Dollinger G. , Bergmaier A. , Karsch S. , Körner H.-J.
Published: July 2002

Al x Ga 1−x N alloys were grown on c-plane sapphire by plasma-induced molecular beam epitaxy. The Al content x was varied over the whole composition range (0⩽x⩽1). The molar Al fraction was deduced from x-ray diffraction and for comparison by elastic recoil detection analysis. The composition of the alloys calculated from the lattice parameter c underestimates x. This is due to a deformation of the unit cell. The exact Al mole fraction and the biaxial strain of the alloys can be calculated by an additional determination of a, using asymmetric reflections. The results obtained by x-ray diffraction and elastic recoil detection provide evidence for the validity of Vegard’s law in the AlGaN system. In addition, the deviation of the band gap from a linear dependence on x was investigated. We found a downward bowing with a bowing parameter b=1.3 eV.