bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling of signal detection by using the photothermal probe beam deflection technique
Authors: Zimmermann Peter , Welsch Eberhard
Published: July 2002

Performing photothermal surface displacement (PTD) technique at λ=10.6 μm in a vacuum chamber, the measured signal is obtained by the change in probe beam deflection at the bulge of the reflecting heated sample surface. The influence of the accuracy-limiting quantities such as angle of incidence of the probe beam as well as its finite lateral extension, and the detector geometry and the temperature-dependent reflection at the sample surface has been investigated by a numerically performed simulation in order to optimize the measuring procedure. The maximum resolution power is achieved for probe beam diameters small compared to the heating beam diameter. An unambiguous measurement may be carried out satisfying the following condition between the quad-cell slit width dslit, the probe beam diameter 2rPB, and the heating beam diameter 2rHB: 2rHB≥2rPB≫dslit keeping the probe beam angle of incidence αPB as small as possible. Moreover, it has been shown that the contribution of the temperature influenced reflection on the change of the probe beam intensity can be also neglected at λ=10.6 μm.
Pressure-jump relaxation apparatus using bipolar-pulse conductivity detection
Authors: Stanley Brett J. , Marshall David B.
Published: July 2002

The theory of bipolar pulse conductivity detection has been successfully applied to the pressure-jump (P-jump) method of relaxation kinetics. This method has distinct advantages over ac bridge detection, including the elimination of capacitance effects which make current balancing significantly easier, the ability to study low-conductance solutions at higher signal-to-noise ratio, and reduction of power input into the cell solutions which decreases heating effects. The P-jump instrument is described, and the electronic circuits for both methods are given. The bipolar pulse circuit diagram is presented and described in detail. Example relaxation curves are shown for single phase and diphasic systems. A signal-to-noise improvement of a factor of 2 is observed for bipolar pulse detection over that observed for the optimal ac bridge detection.
Simple removal method of diffraction peaks in x-ray absorption fine structure spectra from a single crystal in the fluorescence mode
Authors: Emura Shuichi , Maeda Hironobu
Published: July 2002

A simple method has been proposed for the removal of diffraction peaks from x-ray absorption fine structure spectra of a single crystal observed in the fluorescence mode (i.e., excitation spectrum), in which the diffraction peaks inevitably appear. With a patching up of the appropriate spectrum regions from the spectra having many diffraction peaks, it is shown that we can synthesize one spectrum without the diffraction peaks. Here, several spectra are observed in rotating the single crystal within small angles. As an example, this method is successfully applied in finding the local structure around the Cr3+ ion in a single crystal of α-Al2O3:Cr3+. The bond distances of Cr3+–O2− have been determined as r1=2.04 Å and r2=1.95 Å, those are closer to the bond distances in Cr2O3.
High-current plasma lens and focusing of intense ion beams
Authors: Goncharov A. A. , Dobrovolsky A. N. , Kotsarenko A. N. , Protsenko I. M.
Published: July 2002

The static and dynamic characteristics of a high-current plasma lens (PL) with the two-component quasineutral plasma medium formed by a wide-aperture pulse periodical ion beam and secondary ion–electron emission, with the features of focusing and control of a well-formed low-divergent multiaperture ion beam by this lens are investigated experimentally in a wide energy range. It is shown that a careful selection of magnetic field geometry, the fixing electrode number, and the external potential distribution on them, according to theoretical plasmaoptics principles, allow a radial electrical profile in a volume of PL to be modified in a given way. This enables the reduction of the spherical aberration of the beam which is being focused. Experimentally and theoretically it is shown that the controlled introduction of spherical aberrations makes it possible to control a radial beam profile on a target and, in particular, to make it homogeneous. The results of low-energy metal ion beams focused and controlled by PL are obtained. Lens collective processes caused by a principally unremovable magnetic field radial gradient in the ion beam focusing direction are investigated and it is shown that lens electron leakages are connected with these turbulent noises.
Multiple-channel digital lock-in amplifier with PPM resolution
Authors: Probst Pierre-Alain , Jaquier Alain
Published: July 2002

A digital lock-in amplifier built with a couple of input/output boards in a personal computer is described. The use of direct memory access allows the generation of a reference sinewave and the sampling of up to eight channels synchronously with it, leaving enough time for the processor to calculate the in phase and in quadrature responses at and only at selected harmonics (h1,h2,...) of the reference frequency. This digital lock-in is drift free and has the gain stability of the analog-to-digital converter, that is within ±1 ppm for a few minutes, increasing to ±20 ppm for 24 h. Even a simple Mac IIci can monitor in real time h1 at 24 ksamples/s for two channels, corresponding to an upper frequency of 3 kHz, with no limitations on the low-frequency side. Higher sampling rates and processing power are available with more recent hardware.
Streaked shadowgraphy of plasma focus pinch using a coaxial flashlamp-pumped dye laser
Authors: Tou T. Y. , Kwek K. H.
Published: July 2002

Streaked shadowgraphy based on a simple coaxial flashlamp-pumped dye laser as the probing light source is applied to a plasma focus pinch in argon fill gas. This resolves a major problem in using the normal streak photography for capturing the gross dynamics of argon focus pinch, in which its plasma luminosity as a function of time is highly nonuniform.
Superconductivity in epitaxial films of the oxycarbonate Sr2CuO2(CO3) converted from ‘‘infinite layer’’ SrCuO2 by thermal processing
Authors: Feenstra R. , Budai J. D. , Christen D. K. , Kawai T.
Published: July 2002

The conversion of semiconductive SrCuO2 ‘‘infinite layer’’ epitaxial films into a metallic and superconducting (Tc≂30 K) oxycarbonate phase related to Sr2CuO2(CO3) has been induced by thermal processing in oxidizing ambient containing a small amount of CO2. Ion beam analysis using the resonant 12C(p,p)12C elastic backscattering cross section for protons incident at 1.73 MeV confirms the presence of substitutional C in the converted perovskite lattice. Comparison of the threshold CO2 partial pressure with thermodynamic stability data for SrCO3 suggests that the conversion is initiated by the high affinity of Sr(O) for CO2.
A high pressure cell and transfer rod for ultrahigh vacuum chambers
Authors: Ludviksson A. , Yoshihara J. , Campbell Charles T.
Published: July 2002

A novel high pressure cell (or microreactor) and transfer rod for studying surface reaction rates at higher pressures (up to 15 bar) is described in this report. The reactor cell is attached to an ultrahigh vacuum (UHV) chamber for substrate pre- and post-reaction surface analysis. The sample is mounted on a newly designed transfer rod which allows it to be moved between UHV and the microreactor, while being heated resistively or cooled to 100 K. A unique feature of this system is the simple Teflon seal between the high pressure cell and UHV, which is compressed by driving the sample into the high pressure cell but is diffusively separated from the sample. It has been proven that this prevents impurities from the Teflon from reaching the sample during prolonged use.
Pulsed laser deposition of diamond from graphite targets
Authors: Polo M. C. , Cifre J. , Sánchez G. , Aguiar R. , Varela M. , Esteve J.
Published: July 2002

Diamond crystals of 1 μm mean size were grown on (100) silicon substrates by ArF (193 nm) laser ablation of graphite in a hydrogen atmosphere with a laser power density of 1.3×108 W/cm2 at relatively low substrate temperature (450 °C). Raman spectroscopy analysis confirmed the diamond cubic structure of the crystals by the presence of a sharp peak at 1332 cm−1. When a KrF (248 nm) laser was used instead of the ArF no diamond phases were detected in the deposited films and the Raman spectra showed only the two bands centered at 1340 and 1600 cm−1 characteristic of amorphous carbon. The results demonstrated that the laser wavelength is a determinant parameter in the growth of diamond by laser ablation of graphite.
Double-multilayer monochromator using a modular design for the advanced photon source
Authors: Shu D. , Yun W. , Lai B. , Barraza J. , Kuzay T. M.
Published: July 2002

A novel double-multilayer monochromator has been designed for the Advanced Photon Source x-ray undulator beamline at Argonne National Laboratory. The monochromator consists of two ultrahigh-vacuum compatible modular vessels, each with a sine-bar driving structure and a water-cooled multilayer holder. A high precision Y–Z stage is used to provide compensating motion for the second multilayer from outside the vacuum chamber so that the monochromator can fix the output monochromatic beam direction and angle during the energy scan in a narrow range. The design details for this monochromator are presented in this paper.
Strain compensated thin film stress gauges for stress wave measurements in the presence of lateral strain
Authors: Lynch Christopher S.
Published: July 2002

Thin film stress gauges for the measurement of stress waves in solids are calibrated in a uniaxial strain field where the lateral strain components are zero. Frequently, measurements of stress are needed in situations where the lateral strain components are nonzero. The analysis of data often becomes that of best guess, or whatever seems most reasonable. This work is an attempt to quantify the effect of strain on stress gauge output, and to present a technique for strain compensation. To accomplish this, the theories of piezoresistive and piezoelectric films are used to develop equations of the gauge output in terms of normal stress and two components of lateral strain. Thus, with two strain gauges and one gauge that reads stress plus strain, a time-resolved stress history can be accurately determined.
Measurement of hydrogen radical concentration for a hydrogen pressure range from 0.01 to 30 Torr
Authors: Tsuji N. , Akiyama Tomoo , Komiyama Hiroshi
Published: July 2002

A thermocouple method was used to measure the concentration of hydrogen radicals at hydrogen pressures from 0.01 to 30 Torr. The concentration can be calculated from a heat balance at the thermocouple. Under low hydrogen concentration conditions, all terms in the heat balance equation must be estimated accurately. Our results for the measured absolute concentration of the hydrogen radicals at pressures below 1 Torr agreed well with the calculated concentration predicted by a model that is based on the surface dissociation probability at the hot filament and the simulation of diffusion from the filament. With increasing pressure, the hydrogen radical concentration shifted from the surface-dissociation-rate-controlled regime to the diffusion-controlled regime at the hot filament. The agreement between the heat balance at the thermocouple and that at the hot filament shows that the measurement of the hydrogen radical concentration is of the correct order. Our results show that this measurement technique could be used in studying the growth mechanisms in various deposition processes where hydrogen is a main species.
Chemical vapor deposited diamond radiation detectors for ultrahigh radiation dose-rate measurements: Response to subnanosecond, 16-MeV electron pulses
Authors: Han S. , Wagner R. S. , Joseph J. , Plano M. A. , Moyer M. Dale
Published: July 2002

Conductivity modulated devices, similar to photoconductors in operation, for use as radiation detectors were fabricated from polycrystalline chemical vapor deposited diamond films. These detectors were designed to operate under extremely high radiation fields with a large dynamic range in both response and speed. Two types of detectors were studied: a parallel-plate device and a surface device (SDT). The radiation used to excite these detectors was minimum ionizing electrons with an energy of 16 MeV and a nominal pulse width of less than 25 ps. The response time of all detectors was less than 45 ps. The sensitivity of the detectors was in the range 10−5–10−6 A/W. Over the operating range of the detectors, signal saturation was not observed because to the signal size was small in comparison to the applied bias voltage. The detectors appeared to be linear with dose and dose rate over two orders of magnitude, and for dose rates up to 1013 rad/s. Long-lived signal decay tails contributed to much less than 1% of the signal. The response of a SDT detector appeared to be independent of the orientation of the detector to the incident beam direction when the excitation source is minimum ionizing. It appears that the dose-rate linearity may be extended to a range greater than 1013 rad/s.
Gettering of Au to dislocations and cavities in silicon
Authors: Wong-Leung J. , Nygren E. , Williams J. S.
Published: July 2002

The gettering of ion implanted Au to defects in Si has been studied using Rutherford backscattering and channeling and transmission electron microscopy. Damage from a Si implant anneals into dislocations which can efficiently trap diffusing Au. The damage introduced by a H implant evolves during annealing into cavities which getter close to 100% of the Au, leaving very little Au in solution. This process is driven by the diffusion of a supersaturated solid solution of Au to a favorable sink. The internal surfaces of cavities are the most favorable sink, followed by dislocations and then the Si surface.
Electron beam evaporation broad beam metal ion source for material modifications
Authors: Feng Y. C. , Li X. G. , Yang S. T.
Published: July 2002

This paper describes a new type of electron beam evaporation intense beam current broad beam metal ion source. In this ion source, a focusing electron beam is used to bombard and vaporize the metal and other solid elements within the same chamber where the metal and solid element atoms are ionized by arc discharge. It can operate with gaseous and solid elements. Both pure or mixed ions with single or multiple charge states can also be extracted from this source. The performance and the characteristics of this source have tested. Ion beams of a series of elements, which include C, W, Ta, Mo, Cr, Ti, B, Cu, Ni, AI, Ar, N, etc., have been extracted, and the highest beam current is up to 90 mA. By using this ion beam bombardment, a good mixture between substrate and film was observed. Deposition rates as high as 25 Å/s for Mo, 30 Å/s for Ti, and 80 Å/s for C have been obtained. The structure of the ion source and the experimental results will be presented in this paper.
Tomography using neural networks
Authors: Demeter G.
Published: July 2002

We have utilized neural networks for fast evaluation of tomographic data on the MT-1M tokamak. The networks have proven useful in providing the parameters of a nonlinear fit to experimental data, producing results in a fraction of the time required for performing the nonlinear fit. Time required for training the networks makes the method worth applying only if a substantial amount of data are to be evaluated.
Dual purpose diagnostics of edge plasmas of Tokamaks based on a novel spectroscopic effect
Authors: Derevianko A. , Oks E.
Published: July 2002

A significant enhancement of beam-spectroscopy diagnostics is proposed: it is shown that polarization analysis of Lα emission from a neutral hydrogen or deuterium beam allows to measure both the magnetic field pitch angle γp and an effective charge Zeff simultaneously. The suggestion is based on a novel, generalized semiclassical theory of ion impact broadening in high-temperature, magnetized plasmas. A series of generalized theories that the authors had developed recently, represented a significant advancement in accuracy over the standard semiclassical theories. This was achieved by using symmetries of the hydrogenlike quantum systems in electromagnetic fields and treating one component of the dynamic electric microfield much more precisely that the standard theories did. The novelty of the present generalized theory is that the ion impact broadening of magnetically splitted levels of beam atoms is highly anisotropic, resulting in a pronounced angular dependence of widths of π- and σ-components of spectral lines.
Precise total electron yield measurements for impact of singly or multiply charged ions on clean solid surfaces
Authors: Eder H. , Vana M. , Aumayr F. , Winter H. P.
Published: July 2002

Total electron yields γ for impact of singly or multiply charged ions (H+, He+, He2+, N3+, N4+, O5+, O6+) on clean polycrystalline gold have been accurately measured at impact energies from almost zero [exclusive potential emission (PE) range] up to 40 keV times projectile charge state q (dominant kinetic emission range). Impact energies above 10 q keV have been approached by postacceleration of ions via target biasing with up to −30 kV. Total electron yields for γ⩾3 have been derived directly from the related electron number statistics (ES) with total experimental errors of ±3%. Smaller values of γ have been determined from the related ES in conjunction with measurements of the respective primary ion, and ejected-electron currents, which caused somewhat larger experimental errors of typically ±5%. At higher impact velocity discrepancies arise between results from ES-based and current-based measurements of the total electron yield, respectively, because of systematic errors of the latter method due to projectile ion reflection and/or secondary ion emission from the target surface. For differently charged ion species, a difference in γ due to the q-related PE stays almost independent of the projectile impact energy.
Stage for in situ mechanical loading experiments in a scanning electron microscope (Philips 515) with a small chamber
Authors: Yawny A. , Malarría J. , Soukup E. , Sade M.
Published: July 2002

Martensitic transitions involve changes in structure which can be induced thermally as well as under applied mechanical stresses. The thermomechanical characteristics of these displacive transitions are strongly affected by defects which may be introduced in the material by thermomechanical treatments as well as by the transformation itself. To better study the effects of surface defects on these phase transitions high resolution equipment is needed to follow the movement of interfaces. In this work a developed stage is presented. It allows to perform in situ mechanical tests under well controlled temperature conditions and to thermally cycle a sample under controlled stress or strain level in a scanning electron microscope (Philips 515) with small chamber. The test temperature can be easily chosen in the range from −30 to 80 °C. The stage is suitable to be used in bigger chambers of similar equipment. Thermal cycles are obtained using a Peltier thermobattery. The load and deformation are monitored by a load cell and a linear variable differential transformer, respectively. Due to the small space available in the chamber a special port was developed. This port enables the transmission of the mechanical movement generated outside the chamber, the passage of electrical signals, and other commands. Preliminary results of the stage performance obtained with Cu–Zn–Al single crystals are shown.
Direct observation of transferred-electron effect in GaN
Authors: Huang Z. C. , Goldberg R. , Chen J. C. , Zheng Youdou , Mott D. Brent , Shu P.
Published: July 2002

We report the direct observation of transferred-electron effect in unintentionally doped GaN epilayers grown by metalorganic chemical vapor deposition. The negative differential resistivity (NDR) was observed from the current-electric field characteristics in GaN using a metal-semiconductor-metal (M-S-M) system. The threshold field for the onset of NDR was independent of the spacing of M-S-M fingers, and was measured to be 1.91×105 V/cm for GaN with an n-type carrier concentration of 1014 cm−3. This value is very close to the value obtained from theoretical simulation. This observation is an experimental evidence of transferred-electron effects in GaN, which is important in understanding GaN energy band structure and in the application of Gunn-effect devices using GaN materials.
Fabrication of c-oriented HgBa2Ca2Cu3O8+δ superconducting thin films
Authors: Yun S. H. , Wu J. Z. , Kang B. W. , Ray A. N. , Gapud A. , Yang Y. , Farr R. , Sun G. F. , Yoo S. H. , Xin Y. , He W. S.
Published: July 2002

Superconducting Hg-based cuprate thin films have been fabricated on (100) SrTiO3 substrate using rf sputtering and post-Hg-vapor annealing. These films are dominated by c-axis-oriented Hg-1223 phase as indicated by x-ray diffraction and SQUID measurements. Using four-probe technique, the Tc,onset was found to be 130–132 K and Jc was up to 8.5×104 A/cm2 at 77 K and zero field.
A novel computer controlled constant stress lever arm creep testing machine
Authors: Grishaber R. B. , Lu R. H. , Farkas D. M. , Mukherjee A. K.
Published: July 2002

A high speed computer interface and closed-loop feedback control system has been integrated into an existing, mechanical lever-arm, constant load, high temperature creep testing machine to shed load as a function of decreasing cross-sectional area such that a state of constant stress can be obtained throughout the test duration. This allows a computer interface and the custom designed mechanical load shedding apparatus to precisely control the applied stress in response to any changes in the specimen’s measured resistance to deformation during a material evaluation test. A background analysis of typical mechanical creep machines and the design concepts and technical innovations related to the novel apparatus presented in this work will be discussed in detail.
Single molecule spectroscopy in He gas using a highly efficient mirror arrangement
Authors: Heinecke E. , Donovang K. , Müller Ch. , Hese A.
Published: July 2002

We present a new experimental setup for single molecule spectroscopy using a high efficient mirror arrangement with a geometrical efficiency of 0.77. Signal-to-noise (S/N) ratios up to 90 for single pentacene molecules in a p-terphenyl crystal demonstrate that increasing the detection efficiency improves the S/N ratio if the detection geometry ensures a strong stray light suppression. This is realized by the presented mirror arrangement. The experiments were done in a He contact gas cryostat, which is able to work below the lambda point. Temperatures down to 1.7 K at the sample were obtained.
A transmission grating spectrograph and its application in both laser plasma and plasma focus
Authors: Feng X. , Liu M. H. , Lee S.
Published: July 2002

A new transmission grating spectrograph for soft x-ray measurement in pulsed plasmas was designed and studied. The spectrograph has an adjustment system with three degrees of freedom, together with an electronic-controlled camera. This design makes it easy to align and use for laser-produced plasmas or the plasma focus. The spectrograph provides spatially resolved spectrum in two dimensions and has a wavelength range of 0.3–30 nm. A transmission grating was used to obtain spatially resolved spectra from plasmas produced by laser-irradiated solid target and gas filled plasma focus. Such a spectrograph is suitable for coupling with a soft x-ray streak camera or a soft x-ray charge coupled device detector for time-resolved studies.
Thermal imaging with near-field microscopy
Authors: Boudreau B. D. , Raja J. , Hocken R. J. , Patterson S. R. , Patten J.
Published: July 2002

Optical microscopy is an important measurement tool in many industries. This importance is primarily due to the ease-of-use and nondestructive characteristics of optical microscopes. Unfortunately, the far-field optics of conventional microscopes limit their resolution to approximately 200 nm. An imaging technique called near-field microscopy uses a subwavelength aperture to circumvent this limit to obtain images with enhanced resolution without many of the destructive consequences of other techniques. Visible microscopes based on this technique have produced images that demonstrate 10–15 nm resolution. This article describes the extension of these techniques to the infrared regime. A description of an infrared microscope capable of imaging the thermal emissions from micron scale conductors using optical techniques has been given. The microscope has been designed to operate in both the collection mode using an external infrared radiation source and in the self-illumination mode using thermally activated objects. Several infrared images of 2-μm-wide conductors have been provided to demonstrate the resolution capabilities of the microscope. These images clearly show the presence of the conductors and represent a significant increase in resolution over conventional infrared imaging devices.
Growing diamond films from an organic liquid
Authors: Xiao Rong-Fu
Published: July 2002

A pulsed laser deposition technique has been used to grow diamond films from an organic liquid target in the presence of reactive gases H2O2/O2. The technique is simple and safe to operate and the cost of source material is much lower than that in a chemical vapor deposition. The results provide a strong evidence that hydroxyl ions OH−, together with atomic oxygen can indeed promote diamond growth.
Thermo-optical and dielectric constants of laser dye solvents
Authors: El-Kashef Hassan
Published: July 2002

The present work is devoted to the experimental measurements and calculations of thermo-optical and dielectric constants of four commonly used dielectric polar and nonpolar laser dye solvents; toluene, chloroform, carbon disulphide, and benzene. Using a modified high precision laser Mach–Zehnder interferometric technique the refractive index n and its thermal coefficient dn/dT were measured at two different laser wavelengths (514.5 and 632.8 nm). The measured experimental data of n and dn/dT were used in determining about 16 important physical constants and related parameters. On the other hand, the density and molar refraction as a function of temperature for the four solvents are calculated.
Sputtered magnesium as a photocathode material for rf injectors
Authors: Srinivasan-Rao T. , Schill J. , Zvi I. Ben , Woodle M.
Published: July 2002

In this article, we report the investigation of sputtered magnesium as a suitable photoelectron emitter in a rf injector. The measurements were conducted on a 20 μm thick Mg layer, ion sputtered on a copper substrate. UV laser induced damage threshold measurements on this sample indicate that laser energy densities of up to 100 μJ/mm2 at 266 nm, the irradiated surface is indistinguishable from the unirradiated surface. For laser energy densities in the range of 100–300 μJ/mm2, slight roughening of the surface was evident. At 600 μJ/mm2, damage is visible, with the depth estimated to be ∼1 μm. This damage threshold is six times larger than that of the bulk magnesium and approaches that of copper. Systematic laser cleaning has improved the quantum efficiency of the surface from 2×10−5 to 2×10−3. This combination of high quantum efficiency and high damage threshold of sputtered magnesium produces a record current density of 25 kA/mm2 for a metal cathode. The effect of laser cleaning on sputtered Mg, the sample preparation technique for reliable performance, and the parametric dependence of quantum efficiency are reported as well.
Improved low frequency seismic noise isolation system for gravitational wave detectors
Authors: Zhou Z. B. , Fan S. H. , Long F. , Luo J.
Published: July 2002

An improved three-stage low frequency seismic noise isolation system for gravitational wave detectors, based on the cantilever spring, is presented. The measurement results show that the vertical and horizontal displacements of the test mass, at 10 Hz, reach 7×10−13 m/Hz and 1×10−12 mHz, respectively, and the isolation ratios of the system come to about 60 dB vertically and over 50 dB horizontally.
A novel electro-optical probe to diagnose plasma uniformity
Authors: Sarfaty M. , Harper M. , Hershkowitz N.
Published: July 2002

A novel electro-optical probe (EOP) has been developed to characterize the spatial uniformity of various plasma parameters. Spatially resolved electron density and energy distribution function, neutral and charged particle densities, as well as ion flow velocity are determined by the EOP. The design of the EOP combines a Mach probe, back-to-back charge collectors, and a collimated optical fiber. The light collection angle of the optical fiber is limited by recessing the fiber in a ceramic tube. The line-of-sight integration length of the plasma emission is bounded by the charge collector disk. A spatial resolution of 2.4 cm is obtained by the present design of the EOP. The ion flow velocity perpendicular to the charge collector surface is determined by the ratio of the ion saturation currents of the two counter facing charge collectors. Localized actinometry, that combines spatially resolved optical emission spectra and electron energy distribution functions, is used to determine the density of atomic chlorine and fluorine radicals. The spatial distribution is obtained by scanning the EOP across the plasma volume.
Low-pressure organometallic chemical vapor deposition of quantum wires on V-grooved substrates
Authors: Gustafsson A. , Reinhardt F. , Biasiol G. , Kapon E.
Published: July 2002

The structure of GaAs/AlGaAs quantum wires (QWRs) and vertical quantum wells (VQWs) grown by low-pressure organometallic chemical vapor deposition was investigated by conventional and high resolution transmission electron microscopy, and by low-temperature cathodoluminescence. The lower wire boundaries show a much smaller radius of curvature, as compared with atmospheric pressure growth of similar structures, and the upper boundaries show distinct faceting. More abrupt interfaces are obtained due to the kinetically limited growth, with measured interface grading as small as one or two monolayers. The VQW structures formed in the AlGaAs barrier exhibit several branches related to the faceting of the QWR boundaries. These characteristics of the low-pressure nonplanar growth should allow the fabrication of quasi-one-dimensional QWRs with size and shape controlled on the monolayer level.
Calibration of a direct nuclear activation diagnostic which uses boron nitride to measure energetic deuterium ions
Authors: Chambers G. D. , Cooper G. W. , Savage M. E. , Ruiz C. L. , Schmidlapp F. A.
Published: July 2002

A direct nuclear activation diagnostic for the measurement of the kinetic energy of deuterium ions in the energy range of 1–3 MeV has been successfully developed. This diagnostic is based on the fact that the ratio of two different thick-target yields which are generated by the same incident ion species can be a sensitive function of incident ion energy. Targets for this diagnostic are made of α-boron nitride (BN) and use the two reactions: B10(d,n) 11C(β+) and N14(d,n) 15O(β+). The ratio of thick-target yields depends only on the deuterium ion energy and is independent of ion fluence and detector efficiency. The calibrated diagnostic was then fielded to measure the voltage in a plasma opening switch (POS). Electrical measurements of the POS voltage and the voltage inferred from the BN nuclear activation diagnostic were in good agreement.
Deep level transient spectroscopy of InP quantum dots
Authors: Anand S. , Carlsson N. , Pistol M-E , Samuelson L. , Seifert W.
Published: July 2002

We report on the application of deep level transient spectroscopy to the study of electron emission from quantum dots. The results are presented for coherently grown InP dots embedded in Ga0.5In0.5P. We determine an emission activation energy of 220 meV for the one electron ground state of the dots. With increased average electron occupation in the dots we observe a systematic shift of the DLTS peak towards lower temperatures. This we interpret as being due to Coulomb charging of the dots. We extract an average Coulomb charging energy of 8–12 meV per added electron in the dot in agreement with our estimated value of 9 meV.
In-plane-gate transistors fabricated from Si/SiGe heterostructures by focused ion beam implantation
Authors: Többen D. , de Vries D. K. , Wieck A. D. , Holzmann M. , Abstreiter G. , Schäffler F.
Published: July 2002

One-dimensional in-plane-gate (IPG) transistors in the Si/Ge system are fabricated and characterized by focused ion implantation of Ga+ ions on lines into high-mobility two-dimensional electron gases confined in Si/SiGe heterostructures. Transistor operation is demonstrated up to temperatures of T=77 K. The depletion length of the FIB written lines and the saturation drift velocity of the electrons in the Si layer under tensile strain can be estimated from series of samples with different geometric widths of the channel. The IPG transistors presented here are the first based on Si, pushing this elegant transistor concept towards the important Si technology.
Compact neutron generator for diagnostic applications
Authors: Kaschuck Yu. A. , Portnov D. V. , Krasilnikov A. V. , Amosov V. N. , Siromukov S. V.
Published: July 2002

In this article we present the description of compact neutron generators with gas-filled tubes that can be used for neutron detector calibration and stability control. The absolute neutron emission was measured with natural diamond detector and appeared to be in 3% agreement with a standard metrology monitor. Neutron generators design are discussed in regard to neutron emission anisotropy and stability improvement. Data illustrating the neutron spatial and energy distributions are presented.
Improved low-energy, electron-spin-polarized He+4 ion source
Authors: Bixler D. L. , Lancaster J. C. , Kontur F. J. , Popple R. A. , Dunning F. B. , Walters G. K.
Published: July 2002

Recent improvements to a source of electron-spin-polarized He+4 ions based on an optically pumped, rf-excited helium discharge are described that have resulted in ion polarizations P+ of ∼0.18 at currents of ∼1 nA and in an increase of over an order of magnitude in the quality factor P+2I.
An interferometric determination of the refractive part of optical constants for carbon and silver across soft x-ray absorption edges
Authors: Joyeux Denis , Polack François , Phalippou Daniel
Published: July 2002

Interferometric, direct determinations of the f1 scattering factor near absorption edges in the soft x-ray range is demonstrated. The interferometric system, which is based on wave front division (no beam splitter) with plane mirrors only, produces a linear fringe pattern. The principle consists in direct measuring of the fringe shift occurring upon insertion of a sample into one interferometer arm, by means of a dedicated detection system. This provides the optical thickness, which in turn gives the f1 factor, knowing either the sample mass per unit surface, or the sample thickness and density. With the sample being probed in transmission under near normal incidence, the determination of f1 is not perturbed by the absorption part of the complex scattering factor. Therefore, f1 data obtained here can be said new and independent with respect to those obtained previously, in the sense that they are obtained from a new, purely experimental technique, and are neither deduced from nor perturbed by absorption. The interferometer design used can be implemented in a very large spectral range. For demonstrating the ability of this interferometric system to provide such new f1 data, a thin free-standing carbon foil near the K edge (from 4.1 to 4.65 nm, 302–267 eV), and a membrane-supported silver layer near an M edge (from 2.6 to 3.8 nm, 477–326 eV) were used as test objects.
X-ray fluorescence analysis on the base of polycapillary Kumakhov optics
Authors: Nikitina S. V. , Shcherbakov A. S. , Ibraimov N. S.
Published: July 2002

Status of investigations on use of Kumakhov optics in x-ray fluorescence analysis (XRFA) is reported. At present the achieved level of Kumakhov lenses manufacturing technology makes it possible to increase the concentration of x-ray radiation on a sample under investigation by two orders of magnitude or more. Several schemes of the lens used in XRFA are considered. Results of experiments in scheme “x-ray tube–lens–sample detector” are represented. Minimal detection limit in this scheme by using a small 2 W source was on the order of 0.1 pg. Parameters of the lenses with focal spots of micron size (from several tens to several hundreds of microns) used in the experiments are also considered. A brief description of the portable x-ray spectrometer based on Kumakhov optics is given. The next perspectives of use of Kumakhov optics in XRFA are considered.
Design and fabrication of a simple pneumatic loading attachment for diamond anvil cells
Authors: Kumar Ravhi S. , Sekar A. , Jaya N. Victor , Natarajan S.
Published: July 2002

A simple pneumatic pressure attachment has been designed and fabricated for Mao–Bell and National Bureau of Standard type diamond anvil cells (DACs). The assembly can be fitted to the lever arm of the DAC for applying pressure on the diamonds and the pressure at the sample site has been calibrated against the gas dial using the equation of state of silver loaded in the DAC.
Modeling multifrequency eddy current sensor interactions during vertical Bridgman growth of semiconductors
Authors: Dharmasena Kumar P. , Wadley Haydn N. G.
Published: July 2002

Electromagnetic finite element modeling methods have been used to analyze the responses of two (“absolute” and “differential”) eddy current sensor designs for measuring liquid–solid interface location and curvature during the vertical Bridgman growth of a wide variety of semiconducting materials. The multifrequency impedance changes due to perturbations of the interface’s location and shape are shown to increase as the liquid/solid electrical conductivity ratio increases. Of the materials studied, GaAs is found best suited for eddy current sensing. However, the calculations indicate that even for CdTe with the lowest conductivity ratio studied, the impedance changes are still sufficient to detect the interface’s position and curvature. The optimum frequency for eddy current sensing is found to increase as the material system’s conductivity decreases. The analysis reveals that for a given material system, high frequency measurements are more heavily weighted by the interfacial location while lower frequency data more equally sample the interface curvature and location. This observation suggests a physical basis for potentially measuring both parameters during vertical Bridgman growth.
A design of a nanometer size metal particle generator: Thermal decomposition of metal carbonyls
Authors: Huh S. H. , Oh S. J. , Kim Y. N. , Lee G. H.
Published: July 2002

We have developed a method which can produce both pure and alloy nanometer size metal particles in a large scale. This method combines a thermal decomposition of metal carbonyls with a collision induced clustering. Metal carbonyls are thermally decomposed with a hot filament and resultant bare metal atoms undergo collisions to produce nanometer size metal particles. This method requires a very simple experimental setup even though it is a high efficiency production method. Using this method, we have produced, high purity Fe, Mo, and alloy Fe/Mo nanometer size metal particles.
Growth of AlxGa1−xN:Ge on sapphire and silicon substrates
Authors: Zhang X. , Kung P. , Saxler A. , Walker D. , Wang T. C. , Razeghi M.
Published: July 2002

AlxGa1−xN were grown on (00.1) sapphire and (111) silicon substrates in the whole composition range (0≤x≤1). The high optical quality of the epilayers was assessed by room-temperature optical absorption and photoluminescence measurements. Layers with higher Al composition are more resistive. Resistive AlxGa1−xN epilayers were successfully doped with Ge and free-electron concentration as high as 3×1019 cm−3 was achieved.
An acoustic sensor for simultaneous density and viscosity measurements in liquids
Authors: Lévêque G. , Ferrandis J. Y. , Van Est J. , Cros B.
Published: July 2002

We studied theoretically the properties of a vibrating sensor, constituted of a cylindrical tip partly immersed in a liquid. The tip is driven axially by a stepped horn and by a piezoelectric element. Equations of the fluid flow around the tip are solved and show that longitudinal and transverse waves are emitted in the fluid. This allows the device to be sensitive to the density and viscosity of the fluid. It is shown that the properties of the fluid can be deduced by measuring the frequency shift at resonance and the corresponding electric impedance. The precision of the actual device is still low for several reasons, which are discussed. Then our apparatus seems to be more convenient to in situ reaction monitoring rather than for rheological precise measurements.
Study of apparent Faraday rotation of an optically anisotropic system
Authors: Ma Hong-Zhou , Chen Liang-Yao , Zhou Shi-Ming , Zheng Yu-Xiang , Wang Ya-Dong , Qian You-Hua , Chen Chen-Jia
Published: July 2002

We present a formula which can be used to analyze the anisotropic and apparent Faraday effect occurring in a material having an optically anisotropic property. By using the formula the real Faraday parameter can be obtained. For example, we have used the formula to study the anisotropic Faraday effect of a single-crystal Cd0.55Mn0.45Te measured with the spectroscopic ellipsometer and rotating-analyzer-type Kerr apparatus. The calculated data were in good agreement with the experimental results.
Mott ionization of excitons in n-type Zn1−xMnxSe epilayers
Authors: Balchin G. A. , Smith L. M. , Abad H. , Jonker B. T.
Published: July 2002

Recently, the first controlled n-type doping of Zn1−xMnxSe epilayers was reported. Using time-resolved photoluminescence we show that exciton ionization in the moderately doped samples occurs at a significantly lower temperature (50 K) than in undoped material (180 K). This behavior is consistent with Mott ionization of excitons from the increased majority carrier density at higher temperatures. The density and temperature at which the ionization occurs are estimated using calculations of the Mott density and the density-dependent exciton binding energy. No excitons are observed down to 2 K in the samples, which were doped at the highest densities, suggesting that these samples were degenerately doped.
Reactive ion beam etching of aluminum indium antimonide, gallium indium antimonide heterostructures in electron cyclotron resonance methane/hydrogen/nitrogen/silicon tetrachloride discharges at room temperature
Authors: Sendra J. R. , Anguita J. , Pérez-Camacho J. J. , Briones F.
Published: July 2002

Reactive ion beam etching of aluminum indium antimonide, gallium indium antimonide heterostructures in electron cyclotron resonance plasma using methane/hydrogen/nitrogen/silicon tetrachloride (CH4/H2/N2/SiCl4) mixtures has been performed at room temperature. Due to the ratio of chlorine to methane, formation of an indium chloride layer on the etched surface is avoided, thus resulting, in etched surfaces as smooth as the original ones and flat mesa sidewalls. Infrared diodes (2.3μm) have been fabricated using this etching technology.
Theoretical analysis of enhanced electroabsorption related to transition from the second valence subband in wide lattice-matched quantum wells
Authors: Yamanaka Takayuki , Wakita Koichi , Yokoyama Kiyoyuki
Published: July 2002

We formulate on the basis of field-dependent subband structures a design principle for the TE-polarized electroabsorption (EA) effect in quantum wells (QWs) that includes all the possible subband-to-subband and excitonic absorptions. In contrast with trade-off between band-gap-wavelength shift and exciton oscillator strength in enlarged well widths, the transition from the second valence subband dominantly contributes to the EA enhancement. The reason is clarified in conjunction with the nonparabolicity in the valence-subband structures. The enhancement of the EA change through the second-subband transition in lattice-matched wide QWs can be exploited to build highly efficient EA modulators.
Electrochemically induced surface chemistry and negative electron affinity on diamond (100)
Authors: Pehrsson Pehr E. , Long J. P. , Marchywka Michael J. , Butler James E.
Published: July 2002

Hydrogenated single crystal (100) diamond surfaces subjected to an electrochemical (EC) treatment are selectively oxidized at room temperature. Part of the surface remains hydrogenated, except for a narrow transition region between the oxidized and hydrogenated regions. Ultraviolet photoelectron spectroscopy indicates that the transition region has negative electron affinity (NEA), as do the surfaces of hydrogenated crystals. The oxidized and hydrogenated parts of the EC-treated surfaces do not have NEA. A possible explanation is that contaminants eliminate NEA in the hydrogenated parts of the EC treated surfaces, but the transition region remains uncontaminated. None of the oxidized surfaces exhibit NEA.
Limitations of diffusion approximation in describing femtosecond laser transillumination of highly scattering media of biological significance
Authors: Papazoglou Theodore G. , Liu W. Q. , Vasiliou Alex , Grassmel Ralf , Papagiannakis Emmanuel , Fotakis Costas
Published: July 2002

Ultrafast laser pulses transmitted through highly scattering media have been detected by a streak camera. Experimental data, showing the temporal spread of the ultrafast pulse during the transmission through highly scattering media with various optical discontinuities, have been approximated using the diffusion theory. This analysis explicitly shows how the overall optical parameters of the sample (μa,μs′) are influenced by the presence of the discontinuities and proposes the full width at half-maximum as an experimental index of the transition between ballistic and diffusive photon transport.
Thin-oxide charging damage to microelectronic test structures in an electron-cyclotron-resonance plasma
Authors: Friedmann J. B. , Shohet J. L. , McVittie J. P. , Ma S. M.
Published: July 2002

Processing yields in electron-cyclotron-resonance (ECR) and other high-density plasma sources will be increasingly limited by plasma-induced damage. This work investigates the effects of plasma nonuniformities on charging damage to polysilicon-gate MOS capacitor test structures exposed to O2 ECR plasmas. The nonuniformities were produced by independently biasing electrodes located above the wafer. The damage was characterized with ramp-voltage breakdown measurements. Comparison of calculated profiles of the potential difference across the gate-oxide layers of the MOS capacitors with whole wafer maps of the breakdown voltage measurements shows that maximum damage occurs where the oxide potential difference is largest but only in the presence of plasma nonuniformities.
Pyroelectricity in Nylon 7 and Nylon 11 ferroelectric polymers
Authors: Esayan S. , Scheinbeim J. I. , Newman B. A.
Published: July 2002

The temperature and frequency dependences of the pyroelectric current have been studied in Nylon 7 and Nylon 11 ferroelectric polymer films. A remarkable change of value of the pyroelectric currents near the glassy transition temperature (Tg) was observed. Analyses of experimental data show that the temperature behavior of pyroelectric currents can be explained by the competition of the primary and secondary effects. Currents due to these effects have different signs. Below Tg, the dominant component of the pyroelectric current is primary pyroelectricity, and above Tg the secondary effect becomes dominant. Mechanisms producing pyroelectric currents in Nylon 7 and Nylon 11 are discussed.