bluuebunny/crossref_metadata_2025 huggingface dataset:
Automatic rotating element ellipsometers: Calibration, operation, and real-time applications
Authors: Collins R. W.
Published: July 2002

In a typical reflection ellipsometry experiment, one characterizes the polarization state change that a polarized light beam undergoes upon reflection from a specular surface. This measurement provides ρ≡rp/rs, where rp and rs are the complex amplitude reflection coefficients of the surface for p- and s-polarized waves. Nearly 15 years have passed since the development of automatic ellipsometers along with the detailed calibration, error analysis, and data reduction procedures to be used with them. More specifically, these powerful instruments permit (1) determination of bulk dielectric functions and nondestructive depth profiling of static multilayered materials through measurements as a function of photon energy and (2) characterization of dynamic surfaces in adverse environments through measurements as a function of time at fixed photon energy. In the 15 intervening years, the major research thrusts in ellipsometry have been the exploitation of these instruments in materials and process characterization in diverse areas of materials science and electrochemistry. One of the simplest and most popular automatic ellipsometers is a photometric instrument in which one or more of the optical elements (polarizer, compensator, and/or analyzer) is designed to rotate continuously. In this article, the major developments in rotating element ellipsometry are reviewed since the first report of an automatic rotating analyzer instrument by Cahan and Spanier in 1969. The topics covered include rotating element configurations, calibration, characterization of errors and imperfections, absolute accuracy, data reduction, precision, and a review of the real-time applications accessible to these instruments. The sections on calibration, errors, and data reduction include new material and are written from a practical standpoint to assist in instrumentation setup and troubleshooting. The development and improvement of next-generation rotating element instruments that employ optical multichannel detectors to collect spectroscopic data on dynamic surfaces with time resolution as short as 5 ms now defines the forefront of research in this field.
Rogowski coil calibration on a capacitive discharge rig without the use of a current reference
Authors: Podlesak Michael
Published: July 2002

In this article a method of calibrating a Rogowski coil is given, which does not require other current reference devices. The method is based on the intrinsic properties of an LCR circuit, requiring only ringdown measurements using a waveform recorder and a high dc-voltage measuring device. While the Rogowski coil was the main subject of our experimental investigation, the method is quite general and is applicable to the calibration of other types of current sensing devices.
Magnetic shield for wide-bandwidth magnetic measurements for nondestructive testing and biomagnetism
Authors: Ma Yu Pei , Wikswo John P.
Published: July 2002

A magnetically shielded chamber has been designed and constructed for nondestructive testing and biomagnetic measurements with a high spatial resolution SQUID magnetometer. The shield consists of two layers of 1.6-mm-thick, high permeability alloy and two layers of 1.3-cm-thick aluminum, and has interior dimensions of 0.6×1.2×1.7 m. Except at 60 Hz, the noise level above 10 Hz is 12 fT/√Hz. The major noise, due to the 60 Hz power line, has been reduced to 8–36 fT/√Hz. The thermal noise generated by the shield does not affect the measurement inside the shield. At the center of the shield, the shielding factor against the earth’s static magnetic field is 500, and the ac shielding factor at 60 Hz is larger than 3×105. The results have been discussed and compared with the calculations.
A new displacement current measuring system coupled with the Langmuir-film technique
Authors: Majima Yutaka , Iwamoto Mitsumasa
Published: July 2002

The new displacement current measuring system used for detecting the dynamic behavior of monolayers at the air-water interface is described. It basically consists of a film balance, a light source and a pair of electrodes connected to each other through a sensitive ammeter. Here, one electrode is suspended in air and the other electrode is placed in the water. Using the system, displacement current generated from a single monolayer by either the application of surface pressures or the photoirradiation can be detected. Since the displacement current flows due to the dynamic behavior of polar molecules at the air-water interface, the physicochemical properties of monolayers, e.g., dipole moment of the constituent molecules and the molecular structural change due to the photoisomerization, can be investigated without destroying the monolayers themselves.
A study of the parallel energy distribution of lost electrons from the central plasma of an electron cyclotron resonance ion source
Authors: Golovanivsky K. S. , Melin G.
Published: July 2002

The electron loss current from the central plasma of a 10 GHz Caprice ion source is analyzed by using a multigrid electrostatic analyzer. It is found that the plasma potential near the axis is negative in the range −10 to −30 V when the rf power varies from 100 to 450 W. It is also shown that cold electrons having a nearly Maxwellian distribution with T∥ec∼25 eV, and warm electrons nearly Maxwellian with T∥ew of a few hundreds of eV, are the two components of the measured electron population.
Recent experiments with liquid gallium cooling of crystal diffraction opticsa)
Authors: Smither R. K. , Lee W. , Macrander A. , Mills D. , Rogers S.
Published: July 2002

The x-ray beams for the next generation of synchrotrons will contain much more power (1–10 kW) than is available at present day facilities. Cooling the first optical components in these beam lines will require the best cooling technology that one can bring to bear. Argonne continues to pioneer the use of liquid metals as the cooling fluid and has adopted liquid gallium as the liquid metal of choice. Its low melting point, 29.7 °C and its very low vapor pressure make it an easy fluid to handle and its high thermal conductivity and heat capacity make it an excellent cooling fluid. A series of experiments were performed during April 1991 with the wiggler beam at the F2 station of the CHESS facility at Cornell to investigate the cooling of large areas of high power. Two types of cooling crystal geometries were tested. One where the cooling channels were core drilled just below the surface of the crystal and a second where slots were cut into the crystal just below the surface with a diamond saw. Both crystals performed well with photon beam powers up to 1050 W and power densities of up to 14.5 W/mm2 at normal incidence. An infrared camera was used to measure the variation in the temperature of the top layer of the silicon crystals. For the core-drilled crystal the peak temperature measured at the center of the beam at a power density of 12.3 W/mm2 was 15 °C hotter than the crystal surface outside of the beam with a flow of liquid gallium of 2 gpm (gallons per minute) and was 10 °C with a flow of 4 gpm. The maximum distortion of the crystal surface distortion of the core-drilled crystal was about ±2.0 arcsec for the 2 gpm case with a maximum power density of 10.9 W/mm2 and about 5% of the expected beam intensity was lost at peak power of 14.5 W/mm2. For the slotted crystal the peak temperature difference for a peak power of 10.9 W/mm2 was 3.5 °C and 2.0 °C for liquid gallium flows of 1 gpm and 2 gpm, respectively. No intensity loss was measured for the maximum power density of 14.5 W/mm2. The fact that the peak temperature difference on the surface of both crystals was decreasing with increased flow of liquid gallium suggests that even higher power densities can be accommodated with higher flows of liquid gallium.
Radioactive particle tracking technique for investigation of phase recirculation and turbulence in multiphase systems
Authors: Moslemian D. , Devanathan N. , Dudukovic M. P.
Published: July 2002

The development of a noninvasive PC-based computer automated radioactive particle tracking (CARPT) facility for investigation of phase recirculation and turbulence in multiphase systems such as fluidized beds and bubble columns is presented. In this facility, the motion of a single radioactive particle, which is dynamically similar to the recirculating phase, is monitored by an array of scintillation detectors which surround the test section. An on-line computer is used to map the flow field of the recirculating phase. The data acquisition is achieved by commercially available nuclear instrumentation via a modular, high-speed GPIB-CAMAC system through assembly language software. Using CARPT, solids’ motion in gas-fluidized beds and liquid motion in bubble columns have been investigated. The capabilities and versatility of the CARPT facility is described by illustrating some typical results for mean recirculation in gas-fluidized beds with and without internals and in a gas-liquid bubble column. The results include the mean circulation profiles and turbulence parameters such as the Reynolds normal and shear stresses and the turbulent eddy dispersion coefficients. Potential applications of CARPT technique to other recirculating systems are also discussed.
A paraboloidal electrostatic reflector for molecular-beam time-of-flight photoelectron spectrometers
Authors: Steadman Jhobe , Syage Jack A.
Published: July 2002

We describe a design for a paraboloidal electrostatic reflector (PER) adapted for molecular-beam time-of-flight (TOF) photoelectron spectrometers. The PER offers a nearly two orders of magnitude improvement in detection efficiency over standard line-of-sight TOF detection. The energy resolution ΔE/E is nominally about 0.02, but can be improved to about 0.005 (to a current limit of ΔE=10 meV) at some expense in sensitivity. The PER makes possible sensitive measurements for inherently weak ionization experiments. We have used our spectrometer in applications involving low-power picosecond pulses, low-density molecular clusters, and ionization through dissociative states.
Elastic recoil detection for medium-energy ion scattering
Authors: Copel M. , Tromp R. M.
Published: July 2002

Medium-energy ion scattering (MEIS) has been successfully applied for many years as a technique for structural analysis of solids. Advantages over competing techniques include superb depth resolution (5–10 Å), quantitative information (well-known cross sections), and ease of interpretation. A weakness of the technique is the lack of sensitivity to light elements. We have adapted the technique to detect light elements by elastic recoil detection analysis (ERDA). This has been used to analyze samples containing hydrogen and boron, with depth resolution of ≊10 Å, comparable to conventional MEIS. This is an order of magnitude improvement over conventional ERDA.
The ‘‘TITAN’’ ion source
Authors: Bugaev S. P. , Nikolaev A. G. , Oks E. M. , Schanin P. M. , Yushkov G. Yu.
Published: July 2002

TITAN is a new type of ion source capable of generating high current, wide aperture beams of gas and metal ions from a broad range of elements: Mg, Al, Ti, Cr, Fe, Co, Ni, Sm, Zn, W, Pb, Ta, Re, Y, C, He, N, Ar, and Xe. A specific feature of the TITAN ion source is the use of two kinds of arc discharges, each with cold cathodes, to produce plasma for ion beam extraction. Metal ions are generated by means of the vacuum arc in the metal vapor formed in cathode spots. Gas ions, on the other hand, are provided by a low-pressure constricted arc discharge. In a pulsed mode of operation the extraction voltage of the source ranges from 10 to 100 kV. The pulsed beam current for gas and metal ions is on the order of 1 A at pulse repetition rates up to 50 pulses per second and pulse duration of ∼400 μs. For dc operation and at an extraction voltage up to 10 kV, the ion current is as high as hundreds of milliamperes. This work outlines briefly the ion source, its design, and certain physical peculiarities observed when a high current ion beam is generated and transported.
Open source for excited species of alkali atoms and ions using diffusion through a thin metal foil
Authors: Holmlid Leif , Pettersson Jan B. C. , Hansson Tony , Wallin Elisabeth
Published: July 2002

A novel type of source for excited species of cesium is described. It employs an effusive flux to the back of a metal foil, with the excited-state emission from the other side of the covered foil. The foil is kept at a temperature of 1000–1900 K by direct heating with an electric current. From the foil, various excited species of ions and atoms, some of which are rather short lived, are emitted at large densities. Only the species observed at a distance of at least 40 mm from the source emitter are of interest here. Excited species are observed by both steady-state and pulsed field ionization, at current densities up to 10−4 A cm−2, which is several percent of the total beam flux. Positive and negative excited ions can also be observed in the flux from the source, by their ability to emit electrons with energy-independent efficiency at impact on surfaces. The corresponding flux densities are up to 10−5 and 10−4 A cm−2, respectively. Doubly excited atoms can be observed as Cs2+ after field ionization in a mass spectrometer. They also produce ions after energy transfer to small molecules.
Low resonant frequency cantilever spring vibration isolator for gravitational wave detectors
Authors: Ju L. , Blair D. G.
Published: July 2002

An all metal multistage low frequency vibration isolator for a laser interferometer gravitational wave detector has been built and tested with a very sensitive accelerometer. Curved cantilever springs are used to form a low frequency compact form of isolation element. Near center of mass suspension of the isolation stages reduces cross coupling between orthogonal directions. The isolator has a low-pass corner frequency of 6.5 Hz vertically and 1.8 Hz horizontally. The system shows low temperature coefficients and absence of creep. Results demonstrate that steel curved springs near their elastic limit do not generate broadband acoustic noise at the 10−15 m /√Hz level.
Low energy Mott polarimetry of electrons from negative electron affinity photocathodes
Authors: Ciccacci Franco , De Rossi Stefano , Campbell D. M.
Published: July 2002

We present data on the spin polarization P and quantum yield Y of electrons photoemitted from negative electron affinity semiconductors, including GaAs(100), GaAsP(100) alloy, and strained GaAs layer epitaxially grown on a GaAsP(100) buffer. Near photothreshold the following values for P(Y) are, respectively, obtained: 26% (2.5×10−2), 40% (1×10−3), and 60% (1.5×10−4). We describe in detail the apparatus used containing a low energy (10–25 keV) Mott polarimeter. The system, completely fitted in a small volume (∼104 cm3) ultrahigh vacuum chamber, is intended as a test facility for characterizing candidate photocathode materials for spin polarized electron sources.
Nonradiative x-ray resonant Raman scattering from solids (invited) (abstract)
Authors: Drube W. , Treusch R. , Materlik G.
Published: July 2002

High-intensity synchrotron radiation is a powerful tool to study photon-electron-scattering phenomena involving resonantly excited inner-shell electrons. A basic process is the x-ray resonant Raman effect which dominates the radiative and nonradiative emission in the threshold region. The one-step nature of the transition from the initial ground state to the final scattering state results in peculiar characteristics of the emission spectrum, e.g., a Raman-type dispersion of emission lines and lifetime suppression of the intermediate hole states. This has been studied mostly in the radiative channel for atoms, molecules, and solids. Data on the accompanying electron emission, however, are still scarce, especially for solids. We focus on the various aspects of radiationless scattering and present experimental results on resonant Auger electron emission from solid 4d metals at the L3 excitation threshold.
Optical converters for circularly polarized VUV and soft-x-ray radiation (invited)(abstract)
Authors: Höchst Hartmut
Published: July 2002

During the last few years considerable effort was spent at various laboratories to evaluate the possibilities of optical devices to generate circularly polarized synchrotron radiation. These instruments convert linearly polarized radiation by utilizing the phase-shifting properties of multiple reflectors or multilayer transmission optics. In the VUV and soft-x-ray range, the figure of merit TP2, where P is the degree of circular polarization and T the optical transmission, of specially tailored reflection coatings or multilayer structures can be considerably higher than what can be achieved with conventional insertion devices such as the crossed field undulator. In addition to being considerably less expensive, the various optical designs have the great advantage of not being an integral part of the storage ring and, as such, completely transparent to the operation and other users of the storage ring. Various phase-shifter designs will be discussed in terms of their performance, e.g., optical throughput, degree of polarization, and capabilities to modulate between left and right circular light. Recent MCD experiments utilizing optical phase shifters not only demonstrate the proof of principle, but also provide strong evidence of the potential capabilities of ‘‘optical insertion’’ devices as an alternative tool to generate variably polarized synchrotron radiation.
Application of oblique incidence detector to vacuum ultraviolet polarization analyzer
Authors: Saito Terubumi , Yuri Masatada , Onuki Hideo
Published: July 2002

Use of a photodetector placed obliquely to the incident radiation was proposed as a simple polarization analyzer in the vacuum ultraviolet. An ellipsometer using a Au-GaAsP photodiode as an analyzer of this method was constructed and was shown to work successfully. The polarization characteristics obtained in this experiment agreed well with a model calculation.
Soft x-ray scanning microtomography with submicrometer resolution
Authors: McNulty I. , Haddad W. S. , Trebes J. E. , Anderson E. H.
Published: July 2002

Scanning soft x-ray microtomography was used to obtain high-resolution three-dimensional images of a microfabricated test object. Using a special rotation stage mounted on the scanning transmission x-ray microscope at the X1A beamline at the National Synchrotron Light Source, we recorded nine two-dimensional projections of the 3D test object over an angular range of −50° to +55°. The x-ray wavelength was 3.6 nm and the radiation dose to the object per projection was approximately 2×106 Gy. The object consisted of two gold patterns supported on transparent silicon nitride membranes, separated by 4.75 μm, with 100- to 300-nm-wide and 65-nm-thick features. We reconstructed a volumetric data set of the test object from the two-dimensional projections using an algebraic reconstruction technique algorithm. Features of the test object were resolved to ∼100 nm in transverse and longitudinal extent with low artifact in three-dimensional images rendered from the volumetric set.
A newly developed hydraulic modular squeezer for high-pressure experiments using synchrotron radiation
Authors: Will G. , Höffner Ch.
Published: July 2002

For synchrotron diffraction experiments remotely controlled equipment is needed. For diffraction of samples under pressure in the Mbar range we have developed a hydraulic system with a specially modular system which can be adjusted to extreme parallel diamond faces. The system has been used in synchrotron experiments up to 1.1 Mbar for determining the compressibility of iron and gold.
A variable temperature scanning tunneling microscope for the study of surface reactions in ultrahigh vacuum
Authors: Crew William W. , Madix Robert J.
Published: July 2002

The design and performance of a variable temperature, controlled atmosphere ultrahigh-vacuum scanning tunneling microscope (STM) system useful for the study of reactions on surfaces is described. The system incorporates a scanning tunneling microscope of the ‘‘Johnnie Walker’’ type into a versatile UHV system equipped with other diagnostic equipment necessary for studies of surface reactivity. The design is compatible with the combination of a wide variety of surface science measurements with STM. Vibration isolation of the microscope is simply accomplished by use of laminar flow isolation legs and inertial decoupling of the sample from the environment. Atomic resolution on metals can be achieved at temperatures between 125 and 400 K with a combination of continuous liquid–nitrogen cooling and radiative heating of the sample.
Plasma density measurements on COMPASS-C tokamak from electron cyclotron emission cutoffs
Authors: Chenna Reddy D. , Edlington T.
Published: July 2002

Electron cyclotron emission (ECE) is a standard diagnostic in present day tokamak devices for temperature measurement. When the plasma density is high enough the emission at some frequencies is cut off. Of these cutoff frequencies, the first frequency to cut off depends on the shape of the density profile. If the density profile can be described by a few parameters, in some circumstances, this first cutoff frequency can be used to obtain two of these parameters. If more than two parameters are needed to describe the density profile, then additional independent measurements are required to find all the parameters. We describe a technique by which it is possible to obtain an analytical relation between the radius at which the first cutoff occurs and the profile parameters. Assuming that the shape of the profile does not change as the average density rises after the first cutoff, one can use the cutoffs at other frequencies to obtain the average density at the time of these cutoffs. The plasma densities obtained with this technique using the data from a 14 channel ECE diagnostic on COMPASS-C tokamak are in good agreement with those measured by a standard 2 mm interferometer. The density measurement using the ECE cutoffs is an independent measurement and requires only a frequency calibration of the ECE diagnostic.
Behavior of intrinsic Si point defects during annealing in vacuum
Authors: Gossmann H.-J. , Rafferty C. S. , Unterwald F. C. , Boone T. , Mogi T. K. , Thompson M. O. , Luftman H. S.
Published: July 2002

Using B and Sb doped Si(100) doping superlattices (DSL) as tracers of native Si point defect behavior it is shown that vacuum annealing at 810 °C leads to a depletion of Si self-interstitials, with their smallest concentration at the surface, but does not affect the vacancy population. At a fixed depth, the interstitial concentration drops for increasing annealing times; for a given time, the interstitial concentration increases into the sample as a function of depth. Inert anneals of a B-DSL in Ar show flat interstitial profiles. Apparently, the vacuum anneal makes the surface a better sink for interstitials than an inert Ar anneal, leading to an equilibrium interstitial concentration below the value in the bulk and establishing a net outflow of interstitials to the surface. The absence of a response of the vacancy population yields a lower limit on the interstitial-vacancy recombination time of 104 s at 810 °C. Process simulation of this scenario captures the essential trends of the experimental data.
Precision localization of hidden absorbers in body tissues with phased-array optical systems
Authors: Chance Britton , Kang Kyung A. , He Libo , Liu Hanli , Zhou Shoumin
Published: July 2002

The recurrent difficulties of rapidly localizing a small object in a large volume of highly scattering material such as brain and breast has been the ‘‘stumbling block’’ of optical methods for tumor detection. Amplitude cancellation of in- and out-of-phase photon diffusion patterns, used in detection of small objects containing highly absorbing and fluorescing contrast agents provides real time, two- and three-dimensional localization of objects of mg size and picamole contents in models of human breast and brain tumors with positional accuracies of millimeters. A simple robust electronic circuit is described and tested to give a phase accuracy of ∼0.1°. An electro-optical scan rapidly detects small objects in a large volume that simulates the absorption/scattering characteristics of human head or breast.
Recent expansion of the TFTR multichannel neutron collimator
Authors: Roquemore A. L. , Bitter M. , Johnson L. C. , von Goeler S.
Published: July 2002

Radial neutron emission profiles from TFTR DT plasmas are generally narrow and highly peaked. In the past, the neutron profile monitor provided inadequate coverage of the plasma core for these peaked profiles. Four new sight lines were added to improve the view in the central region and better evaluate parameters such as global neutron yields and neutron peakedness and to localize neutron MHD activity. The new sightlines utilize plastic scintillators instead of the original ZnS based NE451 detectors. These new detectors have larger volumes and increased solid angles as compared to the NE451 detectors in order to increase the incident neutron flux, in order to reduce statistical “shot noise” on the signal traces and improve the frequency response. The increased detection capabilities along with recent upgrades in the fast amplifiers and wave form digitizers have extended the frequency response to >50 kHz which allows the study of high frequency MHD activity. Data from DT plasmas illustrating the enhanced spatial and temporal resolution with the new channels are presented.
Runaway electrons in a Tokamak: A free-electron maser
Authors: Kurzan B. , Steuer K.-H. , Suttrop W.
Published: July 2002

In Ohmic divertor plasma discharges of the ASDEX Upgrade tokamak a small population of runaway electrons is purposely generated at the beginning of the discharge. About 1.5 s after the runaways’ generation fluctuating emission in the microwave region with a very narrow bandwidth is observed. The radiation can be explained by relativistic runaway electrons forming a free-electron maser in the tokamak: The dynamics of the runaways is simulated by taking into account the acceleration in the electric field, collisions with the plasma particles, synchrotron radiation losses and the resonances between the gyromotion and harmonics of the magnetic ripple field. According to this the runaways reach a final energy determined by the ripple resonance mechanism and are monoenergetic enough to form a cyclotron autoresonance maser. The guiding of the radiation along the bent path of the runaways is accomplished by nearly resonant runaways around the amplifying runaways. The emission frequency depends on the final energy of the runaways and the observed bandwidth via the maser’s gain on their particle density. Analyzing the emitted fluctuating emission is thus a potentially new diagnostic for runaways.
Application and assessment of multiscale bending energy for morphometric characterization of neural cells
Authors: Cesar Roberto Marcondes , Costa Luciano da Fontoura
Published: July 2002

The estimation of the curvature of experimentally obtained curves is an important issue in many applications of image analysis including biophysics, biology, particle physics, and high energy physics. However, the accurate calculation of the curvature of digital contours has proven to be a difficult endeavor, mainly because of the noise and distortions that are always present in sampled signals. Errors ranging from 1% to 1000% have been reported with respect to the application of standard techniques in the estimation of the curvature of circular contours [M. Worring and A. W. M. Smeulders, CVGIP: Im. Understanding, 58, 366 (1993)]. This article explains how diagrams of multiscale bending energy can be easily obtained from curvegrams and used as a robust general feature for morphometric characterization of neural cells. The bending energy is an interesting global feature for shape characterization that expresses the amount of energy needed to transform the specific shape under analysis into its lowest energy state (i.e., a circle). The curvegram, which can be accurately obtained by using digital signal processing techniques (more specifically through the Fourier transform and its inverse, as described in this work), provides multiscale representation of the curvature of digital contours. The estimation of the bending energy from the curvegram is introduced and exemplified with respect to a series of neural cells. The masked high curvature effect is reported and its implications to shape analysis are discussed. It is also discussed and illustrated that, by normalizing the multiscale bending energy with respect to a standard circle of unitary perimeter, this feature becomes an effective means for expressing shape complexity in a way that is invariant to rotation, translation, and scaling, and that is robust to noise and other artifacts implied by image acquisition.
Self-similarity of plasma networking in a broad range of length scales: From laboratory to cosmic plasmas
Authors: Kukushkin A. B. , Rantsev-Kartinov V. A.
Published: July 2002

A newly developed method of high-resolution processing, called a method of multilevel dynamical contrasting, is applied to analyze numerous data from laboratory electric discharges and observations of cosmic plasmas in a broad spectroscopic range from rf to soft x-ray images. A high degree of self-similarity of plasma structuring is found in a very broad range of length scales, from individual filaments in laboratory discharges to the structures in the universe, which resemble electric currents networking in laboratory plasmas. The results presented illustrate recently suggested [Kukushkin and Rantsev-Kartinov, Laser Part. Beams 16, 445 (1998)] generic features of networking in plasmas: (1) long-living (nonfluctuative) filamentation of electric current; (2) formation of a fractal structure made of single filament and complicated interaction of these “fractal” filaments; (3) formation of a percolating network that includes, in particular, formation of the “stockings” woven by the individual filaments.
Thermal noise in a high Q cryogenic resonator
Authors: Bonaldi Michele , Falferi Paolo , Cerdonio Massimo , Vinante Andrea , Dolesi Rita , Vitale Stefano
Published: July 2002

In order to evaluate the feasibility of a mixed mechanical and electrical multimode matching network for a resonant gravitational wave detector, current noise measurements were performed on a high quality factor inductance–capacitance resonator, based on a superconducting coil, by using a dc superconducting quantum interference device weakly coupled to the coil. We present a method to identify different noise sources in the system by their dependence on the temperature or on the resonator quality factor. Measurements performed at quality factors up to 106 in the temperature range 1.2–4.2 K, show that the total measured noise is only contributed by the resonator thermal noise.
Superconducting and structural properties of in-plane aligned a-axis oriented YBa2Cu3O7−x thin films
Authors: Sung Gun Yong , Suh Jeong Dae
Published: July 2002

We report the superconducting and structural properties of a-axis oriented YBa2Cu3O7−x (YBCO) films as a function of deposition temperature of PrBa2Cu3O7−x (PBCO) template layers. X-ray diffraction (XRD) analysis revealed the orientation relationship in which the b axis of the PBCO template layers and the a axis of the YBCO films were normal to the LaSrGaO4 (100) substrate surface. In-plane aligned a-axis oriented YBCO films having a zero resistance temperature of 88 K and an anisotropy ratio of resistivity of 11.5 at 275 K were obtained on PBCO template layers deposited at 630 °C among the deposition temperatures ranging from 600 to 650 °C at intervals of 10 °C. The degree of in-plane alignment of the a-axis oriented YBCO films which was estimated by the ratio of relative intensity at 90° and 180° in the XRD φ scan of the (102) YBCO peak was 0.5, 0.045, and 0.053 for the films on PBCO templates deposited at 620, 630, and 640 °C, respectively. In conclusion, the deposition temperature of PBCO template layers is critical to fabricate the in-plane aligned a-axis oriented YBCO films on LaSrGaO4 (100) substrates.
Novel physical sensors using evanescent microwave probes
Authors: Tabib-Azar Massood , Akinwande Deji , Ponchak G. , LeClair S. R.
Published: July 2002

Local probes, such as electron and photon tunneling, atomic force, and capacitance probes, are excellent sensing means for displacement and other related sensors. Here we introduce applications of a new local probe using evanescent microwave probe (EMP) in displacement sensing with a very high vertical spatial resolution (0.01 μm at 1 GHz), very high bandwidth (100 MHz), and stability. The EMP has been used in the characterization and mapping of the microwave properties of a variety of materials in the past and its application in gas sensing and thermography was recently explored and reported. The interesting feature of the EMP is that its characteristics can be easily altered for a specific sensing application by changing its geometry and frequency of operation.
Room-temperature synthesis of copper germanide phase by ion beam mixing
Authors: Dhar S. , Som T. , Mohapatra Y. N. , Kulkarni V. N.
Published: July 2002

This letter reports room-temperature synthesis by ion beam mixing of the ε1-Cu3Ge phase which is a promising candidate for interconnect and contact material in very large scale integrated circuit technology. The resistivity of the mixed sample was found to be nearly the same as the one obtained from thermally prepared films. We briefly discuss the likely mechanisms of phase formation and conclude that reaction kinetics dominates over thermodynamic forces during phase formation. The sequence of phase formation is explained by effective heat of formation rule.
Modulated shear–force distance control in near-field scanning optical microscopy
Authors: Brunner R. , Simon A. , Stifter T. , Marti O.
Published: July 2002

The tip–sample distance in near-field scanning optical microscopy is typically controlled by the shear–force interaction between the laterally vibrating tip and sample. In this article, a mode of shear-force feedback is described in which an additional vertical modulation is introduced. Similar to the tapping mode applied in atomic force microscopy, the modulated shear–force technique deals with problem due to the snap to contact and therefore improves the mapping of soft and ductile materials, such as biological samples and soft polymers. The imaging properties of the modulated shear–force mode is demonstrated on structures of a soft polymer blend. Additionally, the modulated shear–force technique allows a simple comparison between effects in the optical far field and in the optical near field.
A high-voltage scanning electron microscopy system for in situ electromigration testing
Authors: Doan J. C. , Lee S. , Lee S.-H. , Meier N. E. , Bravman J. C. , Flinn P. A. , Marieb T. N. , Madden M. C.
Published: July 2002

An apparatus has been constructed to conduct electromigration tests on realistic specimens while simultaneously observing them at relatively high magnification. A scanning transmission electron microscope has been converted into a high-voltage scanning electron microscope (HVSEM) with a large specimen chamber. By imaging with high-energy electrons (120 keV) and detecting backscattered electrons, voids in metal lines can be viewed through passivation layers. The HVSEM has a resolution of 50 nm through 1 μm of passivation. We have constructed instrumentation to heat and pass current through interconnect structures, while they are inside the electron microscope. Presently, the specimen temperature can be as high as 350 °C and is maintained constant to within 0.1 °C. The resistances of interconnects are measured with a precision of 0.05% during an experiment. Testing the lines at moderately accelerated conditions requires great stability of the microscope and instrumentation as well as full automation of the data collection. These requirements have been met, and metallization lines can be tested for several weeks with minimal operator intervention. Digital images of an entire 300-μm-long test structure as well as electrical data are stored automatically every few minutes during a test. The hundreds to thousands of pictures are analyzed using digital image processing techniques to extract void positions and sizes as a function of time. We use this system to characterize electromigration failure in advanced interconnect structures and to test existing theories on electromigration phenomenon.
Surface and bulk point defect generation in Czochralski and float zone type silicon wafers
Authors: Fang Wingra T. C. , Fang Tilden T. , Griffin Peter B. , Plummer James D.
Published: July 2002

The origin of the defects which mediate dopant diffusion in silicon has never been conclusively established. Two primary theories, one favoring bulk generation and the other surface generation, have been proposed to explain the source of point defects. However, the inability to experimentally isolate surface effects from bulk effects has presented experimental determination of the dominant point defect source. An experimental structure employing multiple box-shaped boron marker layers on a variety of silicon substrates has generated strong evidence for separate bulk and surface generation of point defects. A method of using dislocations generated by unstably strained SiGe layers as a sink of interstitials allows a determination of the relative magnitude of surface interstitial generation and bulk interstitial generation. Analysis reveals that the wafer surface under inert anneals is a significant source of point defects and that the interstitial source in the bulk is dependent on the oxygen concentration and precipitate size.
Experimental investigation of dipole-dipole interaction in a water-free glass particle/oil electrorheological fluid
Authors: Wen Weijia , Lu Kunquan
Published: July 2002

An experimental investigation of the dipole interaction in a water-free glass/oil electrorheological fluid under an alternating electric field is presented in this letter. The values of the dielectric constant ε and conductivity σ of glass and oil with respect to the frequency of the external electric field are measured, respectively. Corresponding to the changes in ε and σ, the square of the absolute dielectric mismatch parameter |β| {β=(ε̃p(ω)−ε̃f(ω)]/[ε̃p(ω)+2ε̃f(ω)], where ε̃=ε+σ/iε0ω, and subscripts p and f indicate the glass and oil} decreases as the frequency is increased. After comparing the variation tendency of the |β|2 with the yield stress of the electrorheological (ER) fluid in a measured frequency range we found that they coincide very well. This result confirms that the polarization theory can explain the mechanism of the ER effect not only in a dc electric field but also in that with a wide frequency range. However, the interaction within the multipoles should be considered in an exact calculation.
Deposition and extensive light soaking of highly pure hydrogenated amorphous silicon
Authors: Kamei Toshihiro , Hata Nobuhiro , Matsuda Akihisa , Uchiyama Toyoshi , Amano Shigeru , Tsukamoto Kazuyoshi , Yoshioka Yoshiaki , Hirao Takashi
Published: July 2002

We have developed an ultrahigh vacuum plasma-enhanced chemical-vapor deposition system, and deposited high-purity device-quality hydrogenated amorphous silicon films. High sensitivity secondary ion mass spectrometry measurements show that impurity contents in the bulk of the present films are reduced to 2×1015 cm−3 for O, 7–10×1015 cm−3 for C, and 5×1014 cm−3 for N; these impurities are normally present at fairly high levels. Nevertheless, extensive light soaking of the films resulted in a defect density as high as 5×1017 cm−3, which is well above the impurity content. This result excludes those models of photoinduced degradation that postulate one-to-one correlation between light-induced defects and O, C, or N impurity atoms.
Observation of temperature-insensitive emission wavelength in GaInAs strained multiple-quantum-wire heterostructures
Authors: Wohlert D. E. , Chou S. T. , Chen A. C. , Cheng K. Y. , Hsieh K. C.
Published: July 2002

We report on the photoluminescence (PL) properties of GaxIn1−xAs strained multiple-quantum-wire (MQWR) heterostructures formed in situ by the strain-induced lateral-layer ordering (SILO) process. Samples with moderately strained MQWR active regions demonstrate a negligible variance in emitted PL spectra with respect to temperature. The net temperature dependence of PL wavelength for these samples is less than 0.1 Å/°C between 77 and 300 K. For MQWR samples with stronger lateral composition modulation, the PL peak wavelength blue shifts with increasing temperature. The SILO process induced multiaxial strain in the (GaAs)2/(InAs)2.2 short-period-superlattice active region is responsible for this temperature insensitivity and blueshift of PL wavelength with temperature.
Structural nature of the Si/SiO2 interface through infrared spectroscopy
Authors: Devine R. A. B.
Published: July 2002

The spatial variations of the transverse-optic and longitudinal-optic mode vibrations of the bridging oxygen asymmetric stretch have been studied in the region of the SiO2/Si interface in thermally grown oxides. Comparing the behavior of the two modes it is concluded that vibrational frequency shifts are due primarily to stoichiometry changes and not stress or densification. Fitting to and deconvolution of the measured peak lineshifts as a function of oxide thickness enables us to deduce that the region of stoichiometry variation is ≤1.6 nm.
Temperature-dependent generation of misfit dislocations in In0.2Ga0.8As/GaAs single heterostructures
Authors: Zou J. , Cockayne D. J. H. , Usher B. F.
Published: July 2002

The onset of misfit dislocation generation in [001] In0.2Ga0.8As/GaAs single heterostructures is investigated by transmission electron microscopy using the liftoff technique. To determine the equilibrium critical thickness of misfit dislocation generation for different temperatures, postgrowth annealing was carried out for 2 h at 530 and 600 °C. The equilibrium critical thicknesses are determined as 100–120 Å for 530 °C postgrowth annealing and 60–80 Å for 600 °C postgrowth annealing, respectively. Metastable dislocation structures can be disturbed by sustained elevated temperatures. The variability in the effect is once again due to variations in the extent of dislocation pinning.
Strong photoluminescence in ammonia plasma treated amorphous-SiC thin films deposited by laser ablation
Authors: Ghosh S. , Bhattacharya P. , Bose D. N.
Published: July 2002

Amorphous-SiC films have been deposited by pulsed laser ablation on silicon substrates. Photoluminescence (PL) studies showed two broad bands with peaks at 1.34 and 1.72 eV for these unhydrogenated films. On NH3 passivation the intensity of the 1.34 eV peak increased by a large factor of 40–50 with full width at half-maximum (FWHM) decreasing to 13.5 meV at 12 K. The activation energy of this level was found to be 24 meV. These results are in contrast with those from unhydrogenated a-Si. A possible mechanism responsible for PL enhancement is discussed.
Kinetics of solid phase epitaxy in buried amorphous Si layers formed by MeV ion implantation
Authors: McCallum J. C.
Published: July 2002

The kinetics of solid phase epitaxy have been measured in buried amorphous Si layers produced by ion implantation. Crystallization occurs simultaneously at both amorphous/crystalline interfaces of the buried layer. By collecting time resolved reflectivity data simultaneously at λ=1152 nm and λ=632.8 nm it is possible to accurately determine the crystallization rates at both interfaces. Both interfaces crystallize at a constant rate that is comparable to the intrinsic rate found for thick amorphous surface layers before rate retardation due to H infiltration has occurred. Thus, buried amorphous Si layers provide a suitable environment for studies of the intrinsic growth kinetics of amorphous Si.
Evidence of the role of positive bias in diamond growth by hot filament chemical vapor deposition
Authors: Cui Jingbiao , Fang Rongchuan
Published: July 2002

Diamond films have been deposited on a positively biased silicon substrate by hot filament chemical vapor deposition. It is found that the size distribution of the diamond particle is uniform under bias conditions. The effects of the bias on reactive gas composition were investigated by in situ infrared absorption and in situ optical emission with Ar actinometry. These techniques indicate that the bias does not significantly influence the gas composition. Diamond growth under bias conditions for a small region masked by metal Mo is similar to that without bias. These results confirm that the influence of bias on diamond growth is caused by electron and/or negative ion bombardment on the surface of the substrate and the growing crystallites rather than by the change in gaseous environments.
Synchrotron x-ray diffraction studies of the structural properties of electrode materials in operating battery cells
Authors: Thurston T. R. , Jisrawi N. M. , Mukerjee S. , Yang X. Q. , McBreen J. , Daroux M. L. , Xing X. K.
Published: July 2002

Hard x rays from a synchrotron source were utilized in diffraction experiments which probed the bulk of electrode materials while they were operating in situ in battery cells. Two technologically relevant electrode materials were examined; an AB2-type anode in a nickel–metal–hydride cell and a LiMn2O4 cathode in a Li-ion ‘‘rocking chair’’ cell. Structural features such as lattice expansions and contractions, phase transitions, and the formation of multiple phases were easily observed as either hydrogen or lithium was electrochemically intercalated in and out of the electrode materials. The relevance of this technique for future studies of battery electrode materials is discussed.
Device grade microcrystalline silicon owing to reduced oxygen contamination
Authors: Torres P. , Meier J. , Flückiger R. , Kroll U. , Selvan J. A. Anna , Keppner H. , Shah A. , Littelwood S. D. , Kelly I. E. , Giannoulès P.
Published: July 2002

As-deposited undoped microcrystalline silicon (μc-Si:H) has in general a pronounced n-type behavior. Such a material is therefore often not appropriate for use in devices, such as p-i-n diodes, as an active, absorbing i layer or as channel material for thin-film transistors. In recent work, on p-i-n solar cells, this disturbing n-type character had been successfully compensated by the ‘‘microdoping’’ technique. In the present letter, it is shown that this n-type behavior is mainly linked to oxygen impurities; therefore, one can replace the technologically delicate microdoping technique by a purification method, that is much easier to handle. This results in a reduction of oxygen impurities by two orders of magnitude; it has, furthermore a pronounced impact on the electrical properties of μc-Si:H films and on device performance, as well. Additionally, these results prove that the unwanted donor-like states within μc-Si:H are mainly due to extrinsic impurities and not to structural native defects.
Hysteresis relaxation in (Pb,La)(Zr,Ti)O3 thin film capacitors with (La,Sr)CoO3 electrodes
Authors: Aggarwal S. , Dhote A. M. , Ramesh R. , Warren W. L. , Pike G. E. , Dimos D. , Raymond M. V. , Tuttle B. A. , Evans J. T.
Published: July 2002

We report on the thermally activated hysteresis relaxation effects in (La,Sr)CoO3/ (Pb,La)(Zr,Ti)O3/(La,Sr)CoO3 thin film ferroelectric capacitors. Films cooled in oxygen deficient ambients exhibit a marked voltage offset in the hysteresis loops. Upon the application of a dc bias voltage or unidirectional pulses of the same polarity as the offset, the loops become more symmetric. Subsequently, holding the capacitors in the original preferred polarization state leads to a relaxation of the hysteresis loop towards its original voltage offset condition. The relaxation process is described by a stretched exponential and is thermally activated.