bluuebunny/crossref_metadata_2025 huggingface dataset:
Computerized analytical electron microscope for elemental imaging
Authors: Gorlen K. E. , Barden L. K. , Del Priore J. S. , Fiori C. E. , Gibson C. C. , Leapman R. D.
Published: March 2003

A computer system has been interfaced to an analytical scanning transmission electron microscope (STEM) to form an integrated system for high-resolution mapping of the elemental constituents of a specimen. The system controls the electron beam position, acquires data from electron energy-loss spectroscopy (EELS) and energy dispersive x-ray spectroscopy (EDS) detectors, and constructs elemental images by analyzing EELS and EDS spectra taken at each pixel. Data also are acquired and digitized from conventional STEM bright-field and dark-field detectors. Since image registration errors are eliminated by acquiring data from all detectors concurrently, elemental distribution images obtained from energy-loss and x-ray detectors can be correlated with morphological images taken from bright-field and dark-field detectors. Energy-loss and x-ray spectra of user-defined target areas can also be obtained. Data can be acquired, processed, and displayed at the same time because a satellite microcomputer interfaced to the microscope does much of the data acquisition, freeing the host computer to subtract the spectral background from the electron energy-loss and x-ray data ‘‘on the fly,’’ and also to display dynamically the background corrected energy-loss spectrum at each image pixel. Such a display is important for correct operation of the instrument and interpretation of the results. Images are displayed on a color display system equipped with a digital video array processor, where they can be enhanced, compared, measured, annotated, and photographed. Operation of the system is simplified by using menus for function selection and by filling out forms displayed on a video terminal to enter data-acquisition and processing parameters. The computer-controlled analytical electron microscope is used to provide elemental distributions from thin specimens in biology and materials science. Results show that concentrations of a few atomic percent can be mapped at a resolution of 10 to 20 nm with our system. The importance of real-time data processing is demonstrated in the case of EELS imaging by accurate subtraction of the spectral background at each pixel, and by the correction for spectrum drift during the course of data acquisition.
High-temperature substage for a scanning electron microscope
Authors: Lakhani Amir A. , Urech David , Mattingly Mike
Published: March 2003

The construction and operation of a high-temperature substage for a scanning electron microscope (SEM) is described. The substage is designed to be inexpensive, compatible with a wide variety of electron microscopes, and provide for a wide range of heating and cooling rates in the 25°–800 °C range. The advantages of this substage over commercially available models are discussed. The substage was used to observe morphological and metallurgical changes during the formation of ohmic contacts to GaAs.
Electrostatic–magnetostatic hybrid probe for measuring the electron distribution function in a magnetized plasma
Authors: Hayes M. A. , Brown M. R. , Kasevich M. A. , McCowan R. B.
Published: March 2003

A probe has been developed which measures the density (in a magnetized plasma) of electrons with a given parallel energy and also with a given ratio of perpendicular energy to parallel energy. This is done by imposing two noninteracting criteria for electron collection. The electron must first pass an adjustable magnetostatic barrier (a magnetic mirror) which selects electrons according to perpendicular to parallel energy ratio; then the electron must surmount an electrostatic barrier which is well removed behind the mirror, this discriminates on the basis of the electron’s original parallel energy. This probe is straightforward to build and easy to use. A simple formula for obtaining a distribution function map from the data provided by this probe is derived.
Determination of charge centroids in two-side metallized electrets
Authors: von Seggern H. , West J. E. , Kubli R. A.
Published: March 2003

A method of determining the centroid of space in two-side metallized, thin polymer films is discussed. The method is a generalization of the well-known thermal pulse method and allows the determination of the mean depth without knowledge of the sample history. Results for electron-beam charged Teflon FEP films (25 μm thick) are shown and are in good agreement with results obtained for one-side metallized samples by the conventional thermal pulse method. Further agreement is obtained with results, published by Gross et al. [J. Appl. Phys. 48, 563 (1982)], obtained by a different measuring technique. Application of the method is shown by monitoring the charge centroid during a short circuit thermally stimulated discharge experiment.
Experimental time domain electromagnetic induction system
Authors: McFee J. E. , Chesney R. H. , Das Y. , Toews J. , Turnbull M. , Pinnell R. , Bell M.
Published: March 2003

An automated system which measures, coherently averages, and stores time domain electromagnetic induction responses of conductive objects and allows on-line analysis of the data is described. The sensor portion of the system consists of a set of coils, transmit and receive circuitry situated in a remote nonmetallic laboratory. The circuitry is controlled by a specialized high-speed data-acquisition system which communicates, through a microcomputer, with a distant mainframe computer. Advanced inductive load switching techniques are employed and errors due to temperature variations in the coils are minimized by suitable sensor design. The user can change date-collection parameters, such as pulse length, dwell time, and transmitter waveform shape, under program control to tailor the system to a particular application. The design also allows for easy replacement of the sensor elements; i.e., coils, receive and transmit circuitry as different applications require. This flexibility allows the system to be readily adapted for research in a number of areas that rely on measurement of electromagnetic induction responses. A typical response may be obtained in less than 1 min. The minimum time resolution of the system is 4 μs. Noise levels of 3 to 5 mV standard deviation are obtainable for 500 averages. Data are presented to demonstrate the capabilities of the system.
Amplification of picosecond pulses using a copper vapor laser
Authors: McDonald Daniel B. , Jonah Charles D.
Published: March 2003

This paper describes a novel laser system which can give picosecond pulses with greater than 1 MW of power and at a repetition rate of 5 kHz.
Performance evaluation of the NBS long-wave acoustic flowmeter
Authors: Potzick James
Published: March 2003

The NBS long-wave acoustic flowmeter has been tested on room-temperature airflow in a closed pipe to 1.4 kg/s and found to have a sensitivity error of −0.8% and an offset of 2.3 g/s.
Improving the energy-transfer efficiency of opening switch tokamak Ohmic heating transformers
Authors: Bellan P. M.
Published: March 2003

It is shown that the energy-transfer efficiencies of opening switch and closing switch Ohmic heating transformers differ significantly, and that the efficiency of an opening switch transformer can be optimized by using an iron core with a substantial air gap (gap comparable to the plasma minor radius). A demonstration on the Caltech Encore gapped iron core tokamak is cited.
Low-jitter, low-inductance, electrically triggered spark gap
Authors: Small L. L. , McKen D. C. D. , Offenberger A. A.
Published: March 2003

This investigation is concerned with the development of a low-inductance, low-jitter, electrically triggered, high-voltage annular rail spark gap. Three trigger electrode geometries—blade, dull, and sawtooth edge—are tested for the effects of different field stresses on the spark gap switching performance. All possible polarity combinations are applied to the high-voltage and trigger electrodes of the rail gap, and the switching inductance and jitter is measured for each case. Finally, the effects of photopreionization from bare sparks on the spark gap switching performance is explored. A switch inductance of 4 nH and jitter of 0.6 ns have been achieved. A practical application of the rail gap is also described.
Laser Doppler velocimeter for multicomponent measurements using an electro-optical modulator demonstrated for a two-component optical configuration
Authors: Bahnen R. H. , Koeller K. H.
Published: March 2003

For a multidimensional velocity measurement in fluids laser Doppler optics were developed which permit the switching of the measuring volume during the transit time of a particle by using an electro-optical modulator. This enables a multidimensional measurement of the flow velocity from only one Doppler burst. The so-called multicomponent Doppler burst can be detected and processed by only one photomultiplier and one conventional counter. The new measuring technique is demonstrated for an optical configuration which permits a quasisimultaneous two-component measurement of flow velocity. Experimental results are presented to verify this measuring principle. This new measuring technique reduces the number of optical components and electronic devices compared with a conventional two-dimensional measuring system using two colors. The range of detectable velocity vectors for usual fringe numbers is shown. Finally, factors limiting the application of this system are discussed.
Traveling-wave excitation of helical electrode TE N2 laser
Authors: Chang S. H. , Matsumura S. , Teii S.
Published: March 2003

The traveling-wave excitation method has been applied to a helical electrode-type TE N2 laser to increase the laser output as well as to obtain good beam quality. The traveling-wave excitation was achieved by dividing the discharge into ten sections. The discharge time interval between sequent section can be controlled by the length of coaxial cables. Primary experimental results show that the beam cross section is circular and the output in the direction of the traveling wave is 2.2 times that in the other direction. The laser output with a reflecting mirror is approximately two orders of magnitude larger than that without a mirror. The decrease of laser output with increasing pulse repetition rate has been explained and discussed in connection with the long-lived nitrogen afterglow phenomena.
Evaluation of Hamamatsu R1635 photomultiplier
Authors: Lo C. C. , Leskovar B.
Published: March 2003

Characteristics of the Hamamatsu R1635 10-mm-diam photomultiplier have been measured. Some typical photomultiplier characteristics—such as gain, dark current, transit, and rise times—are compared with data provided by the manufacturer. Photomultiplier characteristics, generally not available from the manufacturer, such as the single photoelectron time spread and pulse response for full photocathode illumination were measured and are discussed.
Precision measurement of nuclear susceptibility by pulsed NMR
Authors: Gibson A. A. V. , Kirk W. P.
Published: March 2003

Random and systematic uncertainties in pulsed NMR measurements of nuclear susceptibility are discussed. Methods for minimizing these uncertainties were developed with special reference to ultralow-temperature applications. Compensation of spectrometer drift and the temperature dependence of the sample circuit using a precision calibrator technique is described. The calibrator was able to compensate for simulated two-fold reductions in sample coil Q and in receiver gain to within accuracy of 1/2%, and to within 1% for 3-dB changes in the transmitter output at low levels. Some data-processing methods are discussed which allow the use of very small rf field pulses to reduce heating.
Construction and application of a novel combination glove box deposition system to the study of air-sensitive materials by tunneling spectroscopy
Authors: Hipps K. W. , Mazur Ursula
Published: March 2003

The construction and application of a high-vacuum deposition system housed in a recirculating, catalytically scrubbed, inert-atmosphere glove box is reported. This system is specifically applied to the fabrication of tunnel diodes used in a surface vibrational spectroscopy called inelastic electron tunneling spectroscopy or IETS. Through the use of this inert-atmosphere adsorption/fabrication system, tunneling spectra have been obtained from a variety of air-sensitive compounds adsorbed on aluminum oxide. Up to now, spectra of some of the species reported here have been unattainable by the adsorption techniques used in IETS. The test molecules employed in this study included TCNE (tetracyancethylene), TCNQ (tetracyanoquinodimethane), and Co2(CO)8. TCNE adsorbed reactively on thin-film alumina under nitrogen to form a species with a vibrational spectrum similar to that of the TCNE−2 ion, while TCNQ appears to form the monoanion under the same adsorption conditions.
Rapid measuring system for contrast thresholds
Authors: Horvath H.
Published: March 2003

The determination of contrast thresholds for a human observer was performed by a new method. To the observer targets having increasing contrasts from left to right are presented. The luminances of the targets are chosen such that some of the targets are invisible to the observer. The observer counts the number of visible targets. From this number the contrast threshold can be derived. This method is objective, faster than traditional methods, and gives comparable results. The photometry for the determination of the contrasts is described.
Electron beam induced current technique using a scanning Auger microprobe
Authors: Rao T. V. , Dutta V. , Sastry O. S. , Chopra K. L.
Published: March 2003

A scanning Auger microprobe (SAM) has been modified to detect and process electron beam induced currents (EBIC). The EBIC mode is incorporated as an integral part of the analytical instrument and operates in conjunction with secondary electron detection (SED) and Auger electron spectroscopy (AES) modes. A minicomputer scans the electron beam and acquires the EBIC data. Using the built-in software designed for Auger data analysis, the data are processed, displayed on a graphics terminal, and plotted on a graphics plotter. The technique has been applied to the study of a grain boundary region of a polycrystalline Si solar cell by extracting a noise-free signal and obtaining cell parameters such as diffusion length and surface recombination velocity in the vicinity of the grain boundary has been demonstrated.
Device for rapid transfer of condensable gases into a capillary
Authors: Halas S. , Krouse H. R.
Published: March 2003

An inverted bellows-sealed vacuum valve was modified by replacing the Teflon pad on its stem by a stainless-steel dish with a knife-edge circumference and a capillary attached through its center. A Teflon cup for containing liquid air was threaded on top into the valve outlet. With the dish down, condensable gases could be frozen on a small surface area on the bottom of the cup. By pushing the dish upwards so the knife edge pushed into the Teflon, the gas was quantitatively transferred into the capillary upon warming.
Polarization scrambling by the glass windows of a Raman cell up to 18 kbar
Authors: Ikawa S. , Whalley E.
Published: March 2003

The scrambling of the polarization of a light beam by the glass windows of a 25-kbar hydrostatic Raman cell increases quadratically with the pressure up to 18 kbar, as expected from the theory of the photoelastic effect. When the laser beam passes along the cylinder axis of the window, the degree of scrambling by one window is 0.0022 at 18 kbar, but increases greatly as the laser beam shifts from the center of the window. The theory of the photoelastic effect was specialized to small depolarizations, and from it the mean stress distribution in the window was determined empirically from the degree of scrambling as a function of the radius. The effect of the scrambling on a Raman measurement, which needs a much larger aperture for the exit window than for the exciting laser beam, was estimated for two 90°-scattering geometries by using the empirical stress distribution. The geometry Z(YZ)Y is particularly suitable because the inlet window produces a weak X-polarized signal, which is largely rejected by the analyzer, and the strong Y-polarized signal produces no scattering along the Y direction. The calculated degree of scrambling is <10−3 at 18 kbar. The depolarization of the symmetric stretching bands of carbon tetrachloride up to 1 kbar and of carbon disulphide up to 10 kbar has been measured and confirms this conclusion.
Capacitance transducer with a point-like probe for receiving acoustic emissions
Authors: Boler F. M. , Spetzler H. A. , Getting I. C.
Published: March 2003

A high-sensitivity capacitance transducer for the detection of ultrasonic signals has been developed. The transducer incorporates capacitance pickup circuitry designed by Radio Corporation of America (RCA) for their VideoDisc player. We use a 0.1-mm-diam platinum wire tip as the capacitance probe. This diameter is small compared to ultrasonic wavelengths. The wire forms part of a transmission line resonant circuit whose center frequency (910 MHz) is modulated by the signal capacitance. The signal capacitance is generated by the distance fluctuations between the probe and the vibrating sample surface. The probe is maintained in position at ∼0.1 μm from the sample surface by feedback control (with a 0.3-s time constant) of current supplied to a coil and magnet positioner. The frequency response has been measured between 100 kHz and 6 MHz and is flat in this range. Calibration tests using a step-function point source on an elastic half-space indicate a sensitivity of 7 mV/nm and a minimum displacement resolution of ∼10−11 m, limited by pickup circuit noise.
Detection of free surface motion using a masked aperture technique
Authors: Winkler M. A. , Hixson R. S. , Shaner J. W.
Published: March 2003

A new noncontacting technique for measuring the arrival of a stress wave at the free surface of a very hot fluid metal has been developed. By use of an optical lever arm and a coded aperture, the new technique avoids the extreme sensitivity of optical interferometers, while allowing accurate measurement of rapid surface motions.
Applications of cineradiography to nuclear-reactor safety studies
Authors: DeVolpi A.
Published: March 2003

Nuclear and non-nuclear applications of cineradiography are reviewed, with emphasis on fuel-motion diagnostic instrumentation that is used for in-pile nuclear-reactor safety studies. The primary instrument for this purpose has been the fast-neutron hodoscope, which achieves quantitative monitoring of time, location, mass, and velocity of fuel movement under the difficult conditions associated with experiments in transient reactors. Nominal 1-ms, 0.1-g, 1-mm resolution have been accomplished during reactor transients of over 104 in power. Although alternative diagnostic devices—such as coded apertures, flash radiography, and pinhole imaging—have been developed, they have not matched the performance of the hodoscope; the evaluation of the relevant parameters appears in the paper. Because discriminating detectors can be placed in tandem in hodoscope channels, other test material constituents—such as cladding steel and sodium coolant—can be dynamically distinguished. Material-motion diagnostic systems can also be used for time-integrated radiography and direct time- and space-resolved fuel-pin power monitoring. High-resolution diagnostic systems are now operating at two reactors, and studies and tests have been carried out for application to several others.
Production of plasma with variable, radial electric fields
Authors: Kustom Brittan , Merlino Robert L. , D’Angelo Nicola
Published: March 2003

A steady-state discharge device is described suitable for plasma physics experiments requiring relatively large, variable, radial electric fields perpendicular to a static magnetic field. Two independent, coaxial discharge plasmas are produced consisting of a very-low-density annular plasma surrounding a denser plasma core. By separately adjusting the potentials of these two plasmas, we have been able to produce plasmas with a radial electric field Er ≲5 V/cm.
Microwave photoconductivity lifetime measurements: Experimental limitations
Authors: Deri R. J. , Spoonhower J. P.
Published: March 2003

An analysis of the cavity bandwidth-limited time response of a typical microwave photoconductivity apparatus is presented. Simple methods of measuring this time limit for such contactless conductivity methods are also described.
Simple, fully isolated, pulse transformer
Authors: Kaplan Z.
Published: March 2003

A broadband noninverting pulse transformer, which provides a fully isolated low impedance signal suitable for various applications, was constructed by winding two coaxial cables in a special configuration around a toroidal magnetic core.
Simple UHV offset manipulator with independent θ and φ rotations
Authors: Jamison K. D. , Dunning F. B.
Published: March 2003

A simple UHV offset manipulator is described that not only allows a target crystal to be moved to any point on a circle centered on the manipulator axis but also provides indepedent θ and φ rotations at each position.
Polygonal fitting for linearization
Authors: Han Chong-Soo , Bernasek Steven L.
Published: March 2003

A novel approach to the linearization of transducer outputs is presented based on polygonal fitting of the transducer function. A circuit for realizing this approach is included. Use of this circuit with the type K thermocouple results in excellent linearization.
Multielement, fluid ballasted cylindrical cathode for a coaxial laser discharge system
Authors: Seguin V. A. , Seguin H. J. J. , Capjack C. E.
Published: March 2003

Extensive experimental work has revealed that multielement electrodes are required to provide uniform current distribution in cw coaxial laser discharge configurations. Cylindrical pin electrodes have demonstrated good plasma uniformity, but are vulnerable to damage by high plasma temperatures. This paper describes the design and electrical charcteristics of a new hollow button cathode, which combines excellent discharge performance with greatly improved cooling features.
Streak camera recording of shock wave transit times at large distances using laser illumination
Authors: Tyburczy J. A. , Blayney J. L. , Miller W. F. , Ahrens T. J.
Published: March 2003

A pulsed laser illumination system for streak camera recording of impact-induced shock wave transit times (∼1 μs) during impact experiments is described. Laser illumination of centimeter-sized subjects offers many advantages over diffuse illumination techniques for streak photography. Source-to-sample and sample-to-camera distances of ∼100 to 102 m can be employed. Light filtering, and simultaneous recording of both the impact event and the camera streak rate calibration, can be carried out easily. For use in such a system we describe a Pockels cell controller in which the reference 10-MHz oscillator signal is synchronously divided down to 38 Hz to provide a trigger signal for laser and streak camera testing.
Simple and inexpensive laser wavelength calibrating system with a 0.01-Å accuracy over all the visible range
Authors: Pelletier-Allard N. , Pelletier R.
Published: March 2003

We describe a laser wavelentgh calibration system based on a grating spectroscope used with the method of overlapping orders. Illuminated by a neon spectral lamp it gives about 1500 reference lines. A small mirror, put on the grating axis, is lightened by a He–Ne laser and gives an angular measurement which helps in the identification of the lines. Calibration of the laser wavelength is obtained by linear interpolation between two neighboring reference lines.
New method for the measurement of the power consumption of a guarded hot plate
Authors: Holcombe B. V.
Published: March 2003

A method has been developed, to modify the way power is applied to the test plate of a guarded hot plate, which enables continuous and accurate measurement of the power consumption of the test plate. It is very simple to produce and offers significant advantages in cost and flexibility over methods used in existing systems. The output of the temperature controller is converted into bursts of precisely regulated pulses of power, and these are counted against a time base. This enables digital manipulation of the power consumption data and interfacing of the guarded hot plate to a data processor.
Shielded four-conductor magnetic field assembly
Authors: Morris D.
Published: March 2003

In some cesium frequency standards and clocks, the uniform, static magnetic field (C field) is generated by an assembly consisting of four conducting rods carrying equal currents and symmetrically placed at the corners of a rectangle inside concentric cylindrical magnetic shields. The spacing of the rods and their location within the shield to give minimum variation of the magnetic field within an area of rectangular cross section close to the axis of symmetry are calculated for the case of the National Research Council cesium clocks CsV and CsVI.
Insert for rapidly producing temperatures between 300 and 1 K in a helium storage Dewar
Authors: Engel B. N. , Ihas G. G. , Adams E. D. , Fombarlet C.
Published: March 2003

A simple device is described for rapidly cycling apparatus between 300 and ∼1 K within a helium storage Dewar. The arrangement is useful for testing components or conducting experiments over this temperature range when the apparatus to be cooled is less than 5 cm in diameter and 50 cm long. Helium evaporation on inserting the device is ∼0.2 l, with consumption ∼0.1 l/h during operation.
Wavelength selective modulation in femtosecond pump–probe spectroscopy and its application to heme proteins
Authors: Rosca Florin , Kumar Anand T. N. , Ionascu Dan , Sjodin Theodore , Demidov Andrey A. , Champion Paul M.
Published: March 2003

We demonstrate novel lock-in detection techniques, using wavelength selective modulation of ultrafast pump and probe laser pulses, to discriminate between vibrational coherence and electronic population decay signals. The technique is particularly useful in extracting low frequency oscillations from the monotonically decaying background, which often dominates the signal in resonant samples. The central idea behind the technique involves modulating the red and/or blue wings of the laser light spectrum at different frequencies, ΩR and ΩB, followed by a lock-in detection at the sum or difference frequency, ΩR±ΩB. The wavelength selective modulation and detection discriminates against contributions to the pump–probe signal that arise from degenerate electric field interventions (i.e., only field interactions involving different optical frequencies are detected). This technique can be applied to either the pump or the probe pulse to enhance the off-diagonal terms of the pump induced density matrix, or to select the coherent components of the two-frequency polarizability. We apply this technique to a variety of heme-protein samples to reveal the presence of very low-frequency modes (∼20 cm−1). Such low-frequency modes are not observed in standard pump–probe experiments due to the dominant signals from electronic population decay associated with resonant conditions. Studies of the diatomic dissociation reaction of myoglobin (MbNO→Mb+NO), using wavelength selective modulation of the pump pulse, reveal the presence of an oscillatory signal corresponding to the 220 cm−1 Fe–His mode. This observation suggests that the spin selection rules involving the ferrous iron atom of the heme group may be relaxed in the NO complex. Mixed iron spin states associated with adiabatic coupling in the MbNO sample could explain the fast time scales and large amplitude that characterize the NO geminate recombination.
Ground state electronic structures and spectra of zinc complexes of porphyrin, tetraazaporphyrin, tetrabenzoporphyrin, and phthalocyanine: A density functional theory study
Authors: Nguyen Kiet A. , Pachter Ruth
Published: March 2003

Density functional theory (DFT) electronic structure calculations were carried out to predict the structures and ground-state spectra for zinc complexes of porphyrin (ZnP), tetraazaporphyrin (ZnTAP), tetrabenzoporphyrin (ZnTBP), and phthalocyanine (ZnPc). All four porphyrins are found to have stable D4h structures. Structurally, meso-tetraaza substitutions significantly reduce the central hole in ZnTAP and ZnPc compared to ZnP. The excitation energies and oscillator strengths, computed by time-dependent DFT, provide a good account of the observed spectra of all four compounds. The TDDFT spectrum of ZnPc has a number of bands in the Soret region, in agreement with the experimental spectra that have been determined through spectral deconvolution. The low energy n→π* transition (Q′) reported for ZnPc, however, was not found in the computed spectrum. The effects of meso-tetraaza substitutions and tetrabenzo annulations on the spectrum of ZnP are discussed.
A universal formula for dispersion coefficients between alkali atoms
Authors: Ahna C. J. , Tang K. T.
Published: March 2003

A universal formula is developed for dispersion coefficients between alkali atoms. It gives values for C2n for n=3, 4, 5 and depends only on the static multipole polarizabilities and the corresponding first excitation energies. Comparison with available literature values shows that the foumula is highly accurate.
Theoretical study on electronic excitation spectra of Mo and Re cluster complexes: [(Mo6Cl8)Cl6]2− and [(Re6S8)Cl6]4−
Authors: Honda Hiroaki , Noro Takeshi , Tanaka Kiyoshi , Miyoshi Eisaku
Published: March 2003

We report here on the electronic structures of [(Mo6Cl8)Cl6]2− and [(Re6S8)Cl6]4− obtained by the Tamm–Dankoff configuration interaction approximation, where Darwin and mass-velocity terms are taken into account through the model core potentials, and the spin–orbit interaction term is included in a semiempirical manner. These complexes have absorption spectra ranging from the visible to the near-ultraviolet energy region and have the long-lived luminescence. The calculated results of the transition moments roughly reproduce the experimental absorption and emission spectra. Especially for the absorption spectra, the theoretical strong intensity for the region higher than 4.5 eV in the two complexes is in good agreement with the experimental results. The obtained intense peak at 3.9 eV may correspond to the experimental broad peak at approximately 3.6 eV for the Mo complex. For the Re complex, the calculated intensity distribution gives one broad peak at around 3.1 eV. This peak may correspond to the experimental peak at 2.9 eV. In the experimental emission spectra, the maxima are located at 1.62 eV for the Mo complex and approximately 1.8 eV for the Re complex. Theoretically, 12 and eight states are found in the energy range between 1.5 and 2.0 eV for the Mo and Re complexes, respectively. At least one, if not more, of these states would be responsible for each emission maximum. To determine the character of the above transitions, the absorption and emission transitions were experimentally shown to be ligand-to-metal charge-transfer transitions and metal-localized transitions, respectively. Theoretically, absorption transitions were characterized as a mixture of metal-localized transitions and ligand-to-metal charge-transfer transitions, and emission transitions a mixture of metal-localized transitions and metal-to-ligand charge-transfer transitions.
Self-consistent field algorithms for Kohn–Sham models with fractional occupation numbers
Authors: Cancès Eric
Published: March 2003

The calculations of electronic ground state energies, following either the Hartree–Fock or the Kohn–Sham schemes, are major issues in quantum chemistry. In a recent publication, we have proposed a new numerical method, namely the relaxed constrained algorithms (RCA), to solve the Hartree–Fock problem. The purpose of the present paper is to discuss the extension of this method to the case of the Kohn–Sham problem. It is shown that RCA seems to be more robust than other self-consistent field algorithms currently used and that they provide in addition a natural way to solve the extended Kohn–Sham problem, obtained by allowing fractional occupancy of the single-particle orbitals.
Electronic structure studies of six-atom gold clusters
Authors: Omary Mohammad A. , Rawashdeh-Omary Manal A. , Chusuei Charles C. , Fackler John P. , Bagus Paul S.
Published: March 2003

Combined theoretical and experimental studies of the hexagold phosphine-stabilized complex [Au6(PPh3)6][BF4]2 (1) and of related systems are reported. The goal of these studies is to gain a better understanding of how 1 interacts with the TiO2(110) substrate to yield finely dispersed supported Au particles that are effective for practical catalytic reactions. The experimental efforts involved the measurement of the visible-ultraviolet (UV) absorption spectra of 1 and Au(PPh3)Cl in solution. The theoretical efforts involved the determination of the electronic structure of molecular models of 1 based on density functional theory (DFT), Hartree–Fock (HF), and configuration interaction (CI) methods. The CI wave functions and energies were obtained for a range of excited states and were used to simulate the absorption spectra of Au6 and Au62+ clusters. The theoretical CI absorption spectra for Au6 can be correlated with the visible-UV absorption spectra while the theoretical spectra for Au62+ cannot be correlated with the experiments. This suggests, even though the [Au6(PPh3)6] unit of 1 carries a +2 charge, that the Au6 portion is essentially neutral. More direct evidence for this distribution of the ionized charge has been obtained from HF and DFT calculations of the double ionization energies of models of 1. It is found that the energy required to remove two electrons from a bare Au6 cluster is much larger than that from an Au6 cluster with phosphine ligands present; this is again consistent with the +2 charge in 1 being delocalized onto the triphenylphosphine ligands. It is possible that this delocalization of positive charge is responsible for facilitating the adhesion of the gold cluster as finely dispersed particles onto the metal oxide support.
Configuration interaction of Pr3+ in PrCl63−
Authors: Tanner Peter A. , Mak Chris S. K. , Faucher Michèle D.
Published: March 2003

The low-temperature electronic spectra of Pr3+ at an octahedral site of symmetry in the PrCl63− moiety, in crystals of Cs2NaPrCl6, Cs2LiPrCl6, and Cs2NaMCl6:Pr(M=Gd, Y) have been measured and interpreted. Together with the results from d–f emission spectra and resonance electronic Raman spectra, these new data permitted the assignment of symmetry representations of up to 39 out the possible 40 crystal field levels of the 4f2 configuration. The inclusion of configuration interaction with the next highest even parity configuration, 4f6p, into the energy level parametrization reduced the mean deviation of the energy level fit using the single 4f2 configuration model alone, by a factor of 2.9 (i.e., from 32.7 to 11.6 cm−1). In particular, the interaction mechanism for the “anomalous” multiplets D21 and G41 was shown to arise from crystal field mixing with 4f6p states. This leads to the inclusion of up to about 0.5% of fp-orbital character for these 4f2 eigenvectors. In the 4f2 single-configuration fits to triplet levels alone, the fourth-degree crystal field parameter turned out to be larger than in the fits to singlet terms, which is the reverse of the expected order if correlation crystal field effects are important.
Electronic structure and chemical bonding of 3d-metal dimers ScX, X=Sc–Zn
Authors: Gutsev G. L. , Jena P. , Rao B. K. , Khanna S. N.
Published: March 2003

The electronic and geometrical structures of the ground and excited states of the homonuclear Sc2, mixed ScTi, ScV, ScCr, ScMn, ScFe, ScCo, ScNi, ScCu, and ScZn 3d-metal dimers and their anions have been calculated using the density functional theory with generalized gradient approximation for the exchange-correlation potential. The ground states of the neutral dimers are found to be Σu−5 (Sc2), Σ+6 (ScTi), Σ+7 (ScV), Σ+4 (ScCr), Σ+3 (ScMn), Δ2(ScFe), Σ+1 (ScCo), Σ+2 (ScNi), Δ3(ScCu), and Σ+4 (ScZn). A natural bond analysis reveals an antiferrimagnetic spin coupling in the ground states of ScCr, ScMn, and ScFe. This is due to the electron transfer from Sc to the opposite atom and specific bond formations. While each dimer has a unique chemical bonding pattern, most curious is the localization of two 4s electrons at both atomic sites in the ground Σu−5 state of Sc2, which leads to formation of two lone pairs and the bonding scheme: (3d+3d)α3(4s+4s)β1. No appreciable sd hybridization is found for the ground states of the ScX dimers except for ScNi. Even though the electron affinities of the ScX dimers are relatively low and do not exceed 1 eV, each ScX− (except ScCo−) possesses at least two states stable towards detachment of an extra electron.
Phase transitions in mixed adsorbed layers: Effect of repulsion between “hard squares” and “point particles”
Authors: Liu Da-Jiang , Evans J. W.
Published: March 2003

It is shown that repulsive interactions between larger “hard squares” and smaller “point particles” in a mixed adlayer model modify the hard-square order–disorder transition and can produce phase separation.
Exact three-dimensional quantum mechanical calculation of ozone photodissociation in the Hartley band
Authors: Lin Shi Ying , Han Ke Li , He Guo Zhong
Published: March 2003

Exact three-dimensional time-dependent wave packet calculation for ozone photodissociation in the Hartley band has been carried out for total angular momentum J=0. Fully converged absorption spectrum, autocorrelation function, and O2(a 1Δg) photofragment rovibrational state distributions over wide range of wavelengths are obtained using the Sheppard–Walker potential energy surface (PES). Excellent agreements as well as some deviations have been found in comparison to the various experimental results. From these successes and failings, the ways for further improving the PES have been suggested, and the dynamics has been discussed in some detail in conjunction with time-dependent pictures of the wave packet.
Structures, energies, and vibrational spectra of water undecamer and dodecamer: Anab initiostudy
Authors: Lee Han Myoung , Suh Seung Bum , Kim Kwang S.
Published: March 2003

Ab initio calculations have been carried out to study the water clusters of undecamer [(H2O)11] and dodecamer [(H2O)12]. At the level of Møller–Plesset second-order perturbation theory using TZ2P++ basis set, the lowest-energy conformer of the undecamer has the skeletal structure of Prism56 that a cyclic pentamer and a cyclic hexamer are fused into a prism shape with 16 hydrogen bonds (HBs). In this case, there are quite a number of nearly isoenergetic conformers with different hydrogen orientations. Among these, more stable conformers tend to have dangling H atoms separated (i.e., less clustered). The lowest energy conformer of the undecamer is different in hydrogen orientation from any previously suggested structure (including the ones obtained from various minimization algorithms). A second lowest energy skeletal structure is of Prism56B that a cyclic pentamer and an open-book hexamer are fused into a prism shape with 17 HBs. The most stable dodecamer is a fused cubic or tetragonal prism skeletal structure (Prism444) with 20 HBs. The lowest energy structure among these skeletal conformers has HB orientations with opposite helicities between adjacent tetragonal rings. The second lowest-energy skeletal structure is the hexagonal prism structure (Prism66) with 18 HBs fused by two cyclic water hexamers. The OH stretching vibrational spectra and electronic properties of several low energy conformers of (H2O)11,12 are also reported.
Scaling of classical rate constants on scaled potential-energy surfaces
Authors: Soo Kim Myung , Tae Park Sang , June Sung Bong , Hee Moon Jeong
Published: March 2003

The scaling relation for the classical rate constants on the scaled potential-energy surfaces has been derived using the scaling theorem in classical dynamics reported previously. This applies to the classical rate constants, both for unimolecular and for bimolecular reactions, that can be obtained by the classical trajectory method and the transition state theory. Validity of the theory has been tested for the prototype reactions, H2CO→H2+CO and Cl+H2→HCl+H. Exact scaling of the rate constants obtained by the classical trajectory calculations has been demonstrated. The rate-energy relations for the former reaction calculated with the statistical Rice–Ramsperger–Kassel–Marcus theory also displayed excellent scaling in the high-energy limit. The scaling relation does not hold rigorously near the reaction threshold due to the quantum mechanical zero-point energy effect. Regardless, the order of magnitude prediction of the threshold rate constant by scaling was possible even in extreme cases. The present method may allow reliable prediction of the classical rate constant by using potential energy data obtained at moderately high levels of electronic structure calculation.
The spectrum of an octahedral molecule in a degenerate electronic state: The ν6 fundamental band of jet-cooled V(CO)6
Authors: Rey M. , Boudon V. , Loëte M. , Asselin P. , Soulard P. , Manceron L.
Published: March 2003

The jet-cooled FTIR spectrum of the ν6 fundamental band (C–O stretch) of vanadium hexacarbonyl, V(CO)6, is studied for the first time. The spectrum shows a very unusual structure consisting of three well-defined broad subbands, without the usual PQR structure. V(CO)6 being an open-shell system this is attributed to a dynamical F2g⊗F1u Jahn–Teller coupling which considerably complicates the analysis. A new theoretical model based on group theory and tensorial algebraic techniques is developed in this paper for the very first attempt to analyze such a rovibronic spectrum. The assumption of a negligible spin–orbit coupling is validated by the overall agreement between predicted and observed band profiles. The rovibronic Hamiltonian and dipole moment operators have been expanded in order to enable a simultaneous treatment of the four vibronic sublevels. We were able to satisfactorily reproduce the band profile and thus to give the first estimation of some rovibronic parameters for this molecule.
Interaction induced effects in the nonlinear Raman response of liquid CS2: A finite field nonequilibrium molecular dynamics approach
Authors: Jansen Thomas l. C. , Snijders Jaap G. , Duppen Koos
Published: March 2003

The third- and fifth-order time-domain Raman responses of liquid carbon disulfide have been calculated, taking local field effects into account through the dipole-induced dipole approximation to the polarizability. The third-order response is shown to be in excellent agreement with experimental data. The calculated two-dimensional shape of the fifth-order response is compared with recently reported experimental observations of what is claimed to be pure fifth-order response. Considerable discrepancies are observed which might be explained by contamination of the experimental results with sequential and especially parallel third-order cascaded Raman response. A new choice of polarization conditions is proposed, which increases the discrimination against these unwanted cascading effects, as compared to the previously discussed fully polarized and magic angle conditions.
Normal-incidence spectroscopic ellipsometry for critical dimension monitoring
Authors: Huang Hsu-Ting , Kong Wei , Terry Fred Lewis
Published: March 2003

In this letter, we show that normal-incidence spectroscopic ellipsometry can be used for high-accuracy topography measurements on surface relief gratings. We present both experimental and theoretical results which show that spectroscopic ellipsometry or reflectance-difference spectroscopy at near-normal incidence coupled with vector diffraction theory for data analysis is capable of high-accuracy critical dimension (CD), feature height, and sidewall angle measurements in the extreme submicron regime. Quantitative comparisons of optical and cross-sectional scanning electron microscopy (SEM) topography measurements from a number of 350 nm line/space reactive-ion-etched Si gratings demonstrate the strong potential for in situ etching monitoring. This technique can be used for both ex situ and in situ applications and has the potential to replace the use of CD-SEM measurements in some applications.
Rapid ordering of Zr-doped FePt alloy films
Authors: Lee Seong-Rae , Yang Sanghyun , Kim Young Keun , Na Jong Gab
Published: March 2003

The magnetic properties and microstructural evolution of Zr-doped FePt alloy films prepared by dc-magnetron sputtering were investigated. Compared to an undoped Fe59Pt41 binary film, Zr-doped FePt alloy films showed accelerated ordering transformation kinetics accompanying smaller grains: we were able to fabricate a Zr-doped FePt film [e.g., (Fe59Pt41)97Zr3] possessing very fine grain size (5 nm in average) and high coercivity (7.3 kOe) within 10 min annealing at 500 °C. It is thought that the point defects and lattice strain introduced by Zr-doping activated the nucleation rate of the ordered phase. In particular, for Zr-doped FePt films containing less than 45 at. % Pt, the ordered L10 phase was decomposed into a disordered phase after excessive annealing due to the formation of a Pt–Zr compound, most likely Pt3Zr, that reduces the effective Pt content in the ordered phase.
Thermal activation-induced sweep-rate dependence of magnetic switching astroid
Authors: Sun J. Z. , Slonczewski J. C. , Trouilloud P. L. , Abraham D. , Bacchus Ian , Gallagher W. J. , Hummel J. , Lu Yu , Wright G. , Parkin S. S. P. , Koch R. H.
Published: March 2003

We examine the sweep-rate dependence of magnetic switching field, Hs, in submicron magnetic tunnel junctions where shape anisotropy is dominant. Experimental data support the use of a single-domain thermal activation model for description of activated magnetic reversal in junctions 0.2 by 0.5 μm or less in size. A scaling law is obtained for the thermal activation energy which varies as the cube of junction size.
White light emission from exciplex using tris-(8-hydroxyquinoline)aluminum as chromaticity-tuning layer
Authors: Feng Jing , Li Feng , Gao Wenbao , Liu Shiyong , Liu Yu , Wang Yue
Published: March 2003

We demonstrate efficient organic white light-emitting devices (LEDs), using N,N′-diphenyl-N,N′-bis(1-naphthyl)–(1,1′-biphenyl)-4,4′-diamine (NPB) as the hole-transporting layer, 1,6-bis(2-hydroxyphenyl)pyridine boron complex [(dppy)BF)] as the emitting layer, tris-(8-hydroxyquinoline)aluminum (Alq) as the electron-transporting and chromaticity-tuning layer. The white light comes from exciplex emission at the solid-state interface between (dppy)BF and NPB in addition to the exciton emission from NPB and (dppy)BF, respectively. The chromaticity of white emission can be tuned by adjusting the thickness of the Alq layer. The white LEDs with an Alq thickness of 15 nm exhibit a maximum luminescence of 2000 cd/m2 and efficiency of 0.58 lm/W, and the Commission Internationale De l’Eclairage coordinates of resulting emission vary from (0.29,0.33) to (0.31,0.35) with increasing forward bias from 10 to 25 V. The region is very close to the equienergy white point (0.33,0.33).
Femtosecond switching with semiconductor-optical-amplifier-based Symmetric Mach–Zehnder-type all-optical switch
Authors: Nakamura Shigeru , Ueno Yoshiyasu , Tajima Kazuhito
Published: March 2003

We investigate the effect of intraband carrier dynamics on a nonlinear phase shift induced in a semiconductor optical amplifier (SOA) in terms of its applicability to the Symmetric Mach–Zehnder (SMZ) all-optical switch. Nonlinear phase shifts in an SOA and a passive semiconductor waveguide are compared under control-pulse durations ranging from 3.2 to 0.4 ps. The results show that femtosecond switching with higher efficiency is still possible by using the SOA. We experimentally achieve femtosecond (670 fs), femtojoule (140 fJ) switching with the SOA-based SMZ all-optical switch.