bluuebunny/crossref_metadata_2025 huggingface dataset:
Shock wave compression of the ferroelectric ceramic Pb0.99(Zr0.95Ti0.05)0.98Nb0.02O3: Hugoniot states and constitutive mechanical properties
Authors: Setchell Robert E.
Published: June 2003

Although the particular lead zirconate/titanate composition Pb0.99(Zr0.95Ti0.05)0.98Nb0.02O3 (PZT 95/5–2Nb) was identified many years ago as a promising ferroelectric ceramic for use in shock-driven pulsed power supplies, relatively few studies have been performed to characterize its response under shock wave compression. The current study began when strong interest developed in numerically simulating the operation of pulsed power supplies, which required improved models for dynamic material properties. Experiments were conducted on a gas-gun facility to determine Hugoniot states, to examine constitutive mechanical properties during shock propagation, and to investigate shock-driven depoling kinetics. This article summarizes results from the first two of these areas. A baseline material, similar to materials used in previous studies, was examined in detail. Limited experiments were conducted with other materials to investigate the effects of different porous microstructures. Reverse-impact experiments were used to obtain a Hugoniot curve for the baseline material over the stress range of interest, as well as comparative data for the other materials. Wave profiles recorded in transmitted-wave experiments examined the effects of varying shock strength and propagation distance, poling state and orientation, initial density, porous microstructure at a fixed density, and electric field strength. The collective results identify a complex material behavior governed by anomalous compressibility and incomplete phase transformation at low shock amplitudes, and a relatively slow yielding process at high shock amplitudes. Differences in poling state, field strength, and porous microstructure in common-density materials were found to have a small effect on this behavior, but large effects were observed when initial density was varied. Comparisons with similar studies on other ceramic materials show both similarities and differences, and provide insights into possible yielding mechanisms.
Schottky barrier height and interfacial state density on oxide-GaAs interface
Authors: Hwang J. S. , Chang C. C. , Chen M. F. , Chen C. C. , Lin K. I. , Tang F. C. , Hong M. , Kwo J.
Published: June 2003

Photoreflectance (PR) and Raman spectra were employed to investigate the interfacial characteristics of a series of oxide films on GaAs. The barrier heights across the interfaces and the densities of interfacial states are determined from the PR intensity as a function of the pump power density. The oxide-GaAs structures fabricated by in situ molecular beam epitaxy exhibit low interfacial state densities in the low 1011 cm−2 range. The density of the interface states of the Ga2O3(Gd2O3)–GaAs structure is as low as (1.24±0.14)×1010 cm−2. The Ga2O3(Gd2O3) dielectric film has effectively passivated the GaAs surface. Additionally, Raman spectra were used to characterize the structural properties of the oxide films.
Combined electronic and nuclear dynamics in a simple model system
Authors: Erdmann M. , Marquetand P. , Engel V.
Published: June 2003

We investigate the combined electronic and nuclear motion in a simple model system as proposed by Shin and Metiu [J. Chem. Phys. 102, 9285 (1995)]. A variation of the electron–nuclei interaction energy allows us to study the transition from an adiabatically uncoupled situation to the case where the adiabatic approximation breaks down. Wave-packet calculations illustrate the dynamical changes of electronic and nuclear probability densities for the case of an adiabatic motion and during a nonadiabatic transition. The influence of the coupling on the transport of electron density between different nuclei is characterized with the help of time-dependent Laplacians.
Entropic barriers, activated hopping, and the glass transition in colloidal suspensions
Authors: Schweizer Kenneth S. , Saltzman Erica J.
Published: June 2003

A microscopic kinetic description of single-particle transient localization and activated transport in glassy fluids is developed which combines elements of idealized mode-coupling theory, density functional theory, and activated rate theory. Thermal fluctuations are included via a random force which destroys the idealized glass transition and restores ergodicity through activated barrier hopping. The approach is predictive, containing no adjustable parameters or postulated underlying dynamic or thermodynamic divergences. Detailed application to hard-sphere colloidal suspensions reveals good agreement with experiment for the location of the kinetic glass transition volume fraction, the dynamic incoherent scattering relaxation time, apparent localization length, and length scale of maximum nongaussian behavior. Multiple connections are predicted between thermodynamics, short-time dynamics in the nearly localized state, and long-time relaxation by entropic barrier crossing. A critical comparison of the fluid volume fraction dependence of the hopping time with fit formulas which contain ideal divergences has been performed. Application of the derivative Stickel analysis suggests that the fit functions do not provide an accurate description over a wide range of volume fractions. Generalization to treat the kinetic vitrification of more complex colloidal and nanoparticle suspensions, and thermal glass-forming liquids, is possible.
Infrared spectroscopic ellipsometry study of vinylidene fluoride (70%)-trifluoroethylene (30%) copolymer Langmuir–Blodgett films
Authors: Bai Mengjun , Poulsen Matt , Sorokin A. V. , Ducharme Stephen , Herzinger C. M. , Fridkin V. M.
Published: June 2003

We report the studies of the molecular conformation and chain orientations through characterization of the vibrational modes in crystalline Langmuir–Blodgett films of the polyvinylidene fluoride/trifluoroethylene copolymer. The infrared spectra obtained by polarized reflectometry and ellipsometry showed that the ferroelectric phase has predominantly all-trans conformation and the paraelectric phase has predominantly alternating trans-gauche conformation, as in solvent-formed films of the same copolymer. The results showed that the polymer chains are predominantly parallel to the film plane with a random in-plane orientation and most of the ferroelectric phase vibrational mode behaviors are consistent with the published mode assignments. The ferroelectric phase optical dispersion curves in the infrared range were extracted from the data analysis based on a uniaxial model.
Thermal microstrains measured by atomic force microscopy
Authors: Avilés F. , Ceh O. , Oliva A. I.
Published: June 2003

Microdeformations observed in atomic force microscopy (AFM) images on the surface of metallic films when an electrical current (dc) flows through the film were analyzed on a film–substrate system. The electrical current flow causes an increase in temperature on the thin film and a step in the AFM topography while imaging. Experiments realized with AFM explain the nature of such a step and allow one to quantify these microdeformations. Theoretical bending models mainly derived from modifications of the Stoney equation support our experimental results. Theoretical predictions show reasonable agreement with AFM measurements, and demonstrate that the major contribution to the observed deformation step (about 90%) is due to the thermal bending effect of the AFM cantilever. The remaining deformation is due to the nature of bimaterial effects in the film–substrate system and thermal expansion of the substrate, with the expansion of the film being negligible. The possibility of electric and magnetic effects in the AFM cantilever (due to current flow through the film) is also discussed. The existence of a strong thermal effect on the AFM cantilever is outlined. Hence, a slight variation in temperature during AFM measurements could turn out to be misinterpretation of the results obtained. Consequently, we recommend strict control of the temperature during AFM imaging, in order to improve the reliability and accuracy of the instrument.
High pressure x-ray study on anthracene
Authors: Oehzelt Martin , Heimel Georg , Resel Roland , Puschnig Peter , Hummer Kerstin , Ambrosch-Draxl Claudia , Takemura Kenichi , Nakayama Atsuko
Published: June 2003

The crystalline structure of anthracene (C14H10) under high pressure was studied performing angle dispersive x-ray diffraction experiments using synchrotron radiation in combination with Rietveld refinements and rigid body approximation. High hydrostatic pressure was applied up to 27.8 GPa using a diamond anvil cell. Full structural information (molecular orientations and lattice constants) is given up to a pressure of 20.3 GPa. At the highest pressure of 22.7 GPa the unit cell volume is decreased by 36.8%. Fourier transformation of the diffracted intensities reveals the electron density distribution within the unit cell. A pressure induced increase of the electron densities between adjacent molecules is observed. These findings are shown to be in agreement with theoretical calculations and hint towards the evolution of the anisotropic conductivity with pressure.
Interfacial reactions of Ti/n-GaN contacts at elevated temperature
Authors: Lu C. J. , Davydov A. V. , Josell D. , Bendersky L. A.
Published: June 2003

Interfacial reactions in Ti/GaN contacts have been studied using conventional and high-resolution transmission electron microscopy (TEM), energy-filtered TEM (EFTEM), and x-ray diffraction. The thin film contacts were fabricated by evaporating Ti on n-GaN and subsequent rapid thermal annealing in argon. An x-ray result shows that the as-deposited Ti on GaN is an epitaxial hcp phase, whereas a fcc phase was identified from the as-deposited metal layer in cross-sectional TEM specimens. This phenomenon is interpreted as the transformation of hcp-Ti phase to fcc-TiHx phase by hydrogen incorporation during TEM specimen thinning. At elevated temperature, first gallium and then nitrogen diffused into the metal layer. The reaction front moved into the Ti layer, and after annealing at 700 °C many voids were formed along the Ti/GaN interface at the GaN side. A sequence of phases GaN/TiN/Ti2GaN/Ti3Ga/Ti was identified in annealed contacts, and corresponds to the expected diffusion path. The ternary phase Ti2GaN was confirmed with electron diffraction and EFTEM. A planar TiN layer, which formed in direct contact to the GaN, presumably governs the electrical properties of the alloyed contact.
Effect of tacticity on the local dynamics of polypropylene melts
Authors: Arrighi Valeria , Batt-Coutrot Delphine , Zhang Chuhong , Telling Mark T. F. , Triolo Alessandro
Published: June 2003

We present a quasielastic neutron scattering (QENS) study of the effect of tacticity on the local dynamics of polypropylene (PP). QENS measurements were carried out on different spectrometers. On IN10 (ILL, France) we have measured the decrease of the elastic intensity as a function of temperature for atactic (a-PP), isotactic (i-PP), and syndiotactic (s-PP) PP. The results show that the polyproylene sub-Tg dynamics is independent of tacticity. Measurements of the dynamic incoherent structure factor were carried out on the spectrometers IRIS and OSIRIS (ISIS, UK) and, after Fourier transform, the intermediate scattering functions were computed and analyzed. For all samples investigated, the intermediate scattering functions I(Q,t) show good overlap using shift factors that are close to those reported in the literature. Detailed analysis of the incoherent dynamic structure factor in terms of fast and slow decay processes indicates that in the subpicoseconds regime molecular motion is independent of tacticity. The slower segmental process depends on the sample stereoregularity and, consistently with C13 NMR measurements and molecular dynamics simulations, isotactic PP relaxes faster than the other polymers, while s-PP is the slowest. Correlation times display a non-Arrhenius temperature dependence that is described by a Vogel–Fulcher–Tamman relationship, with parameters that depend on tacticity. Thus the ratio between the correlation times is temperature dependent, and while the dynamic behavior of the samples is very similar at 460 K, considerable differences are observed at lower temperature.
Finite size scaling of structural transitions in a simulated protein with secondary and tertiary structure
Authors: Chapagain Prem P. , Gerstman Bernard S.
Published: June 2003

We present lattice Monte Carlo simulations of unfolding transitions in a protein four-helix bundle, which contains elements of protein secondary and tertiary structure. Various thermodynamic parameters are examined and critical exponents are calculated for different strengths of the hydrophobic interaction by using finite size scaling theory. We find that the order of the transition depends on the strength of the hydrophobic interaction.
Comparative full-band Monte Carlo study of Si and Ge with screened pseudopotential-based phonon scattering rates
Authors: Nguyen Phuong Hoa , Hofmann Karl R. , Paasch Gernot
Published: June 2003

In a previous article [J. Appl. Phys. 92, 5359 (2002)], we presented a combination of a full-band Monte Carlo method using an advanced band structure and a variable Brillouin zone discretization, with phonon scattering rates based on the screened pseudopotential considering the positions of the atoms in the elementary cell. To make the method suitable for sufficiently fast applications, such as device simulations, the simplest wave number dependent approximation was introduced. It contains an average of the cell structure factor, and only two fit parameters: The acoustic and the optical deformation potentials. As the pseudopotential, the Ashcroft model potential is chosen, and screening is taken into account using the Lindhard dielectric function. In the present article, based on the study of the influence of the two deformation potentials on the electron and hole drift velocities in Si and Ge, we show how to select the deformation potentials. Depending on the targeted agreement with experimental results, the pairs of deformation potentials for electrons and holes can be used uniformly for a wide temperature range or separately for different temperatures. For Ge, we achieve remarkable quantitative agreement with the temperature, field, and orientation dependencies of experimental electron and hole drift velocities in the wide temperature range from 77 to 300 K with a single set of the two deformations potentials for each carrier type. A detailed comparative simulation of the transport properties in Ge and Si at different temperatures is presented which is comprised of the steady-state dependence of the drift velocity on the electric field, the low-field mobility, and transient transport. Peculiarities of the drift velocity-field dependencies, such as the anisotropy, and a negative differential mobility are discussed in terms of the different band structures in connection with the field dependence of the simulated distribution functions. For doped materials, ionized impurity scattering is included. The resulting dependencies on the doping level are consistent with experimental values.
Structural and electrical properties of c-axis epitaxial homologous Srm−3Bi4TimO3m+3 (m=3, 4, 5, and 6) thin films
Authors: Zhang S. T. , Chen Y. F. , Sun H. P. , Pan X. Q. , Tan W. S. , Liu Z. G. , Ming N. B.
Published: June 2003

c-axis epitaxial thin films of Bi-layered homologous Srm−3Bi4TimO3m+3 (m=3, 4, 5, and 6) were fabricated on (001) SrTiO3 single crystal substrates by pulsed laser deposition, respectively. Microstructures of the films were systematically characterized by x-ray diffraction (including θ–2θ scans, rocking curve scans and φ scans), atomic force microscopy, and transmission electron microscope. Epitaxial relations were established to be (001)Srm−3Bi4TimO3m+3∥(001)SrTiO3 and [11̄0]Srm−3Bi4TimO3m+3∥[010]SrTiO3 by φ scans and selected area diffraction. A special kind of atomic shift along the [001] direction and a slight atomic vibration of TiO6 octahedra were revealed and discussed. The room-temperature dielectric constants of these epitaxial films measured by using an evanescent microwave probe were 245±23, 237±13, 272±19, and 221±20 for films with m=3, 4, 5, and 6 respectively.
Energy levels of Dy3+(4f 9) in orthoaluminate crystals
Authors: Gruber John B. , Zandi Bahram , Valiev Uygun V. , Rakhimov Sh. A.
Published: June 2003

A detailed crystal-field splitting analysis is reported for the energy levels of Dy3+(4f9) in crystals of YAlO3 and DyAlO3 orthoaluminates. Experimental energy (Stark) levels for the 15 lowest-energy LJ2S+1 multiplet manifolds of Dy3+ are reported and supplemented with values found in the literature. A parameterized Hamiltonian, including Coulombic, spin-orbit, configuration interaction, and crystal-field terms in Cs symmetry, was diagonalized for the HJ6, FJ6, FJ4, IJ4, and GJ4 states. Initial sets of crystal-field parameters were determined from lattice-sum calculations and the three-parameter theory. Considerable J-mixing is found for states having nearly the same energy such as the manifolds F11/26, H9/26, and F9/26, H7/26. Even states that are well separated from each other in energy show sufficient J mixing to explain the polarized absorption and Zeeman effects that involve transitions from the nearly pure (less than 0.2% J mixing) ground state, H15/26 to excited states such as F5/26 and F3/26. The rms for 70 calculated-to-experimental Stark levels for Dy3+ in YAlO3 is 10 cm−1; the rms for 43 calculated-to-experimental levels for Dy3+ in DyAlO3 is 8 cm−1.
Light-induced bias stress reversal in polyfluorene thin-film transistors
Authors: Salleo A. , Street R. A.
Published: June 2003

Gate bias-stress effects in the high-performance semiconducting polymer poly-9,9′ dioctyl-fluorene-co-bithiophene (F8T2) were studied. The bias stress in F8T2 was characterized in devices having various gate dielectric materials—different types of SiO2 and a polymer—and a variety of chemically modified dielectric/semiconductor interfaces. A bias-stress effect was reversed by illuminating the transistor structure with band gap radiation. The recovery rate was directly related to the absorption characteristics of F8T2. We conclude that bias stress in F8T2 is due to hole charge trapping inside the polymer, close to the dielectric interface and not to a structural change in the polymer, or to charge in the dielectric.
Angular truncation errors in integrating nephelometry
Authors: Moosmüller Hans , Arnott W. Patrick
Published: June 2003

Ideal integrating nephelometers integrate light scattered by particles over all directions. However, real nephelometers truncate light scattered in near-forward and near-backward directions below a certain truncation angle (typically 7°). This results in truncation errors, with the forward truncation error becoming important for large particles. Truncation errors are commonly calculated using Mie theory, which offers little physical insight and no generalization to nonspherical particles. We show that large particle forward truncation errors can be calculated and understood using geometric optics and diffraction theory. For small truncation angles (i.e., <10°) as typical for modern nephelometers, diffraction theory by itself is sufficient. Forward truncation errors are, by nearly a factor of 2, larger for absorbing particles than for nonabsorbing particles because for large absorbing particles most of the scattered light is due to diffraction as transmission is suppressed. Nephelometers calibration procedures are also discussed as they influence the effective truncation error.
Permalloy inductor based instrument that measures the sedimentation constant of magnetorheological fluids
Authors: Chen L. S. , Chen D. Y.
Published: June 2003

An instrument, which incorporates a permalloy inductor, an acid buret, a z-axis translating stage, and a multifunctional inductance meter, has been designed and built to measure the sedimentation constant of magnetorheological (MR) fluids. The permalloy inductor is able to sense the tiny settling distance and thus eliminates measurement dependence on the centrifuge. Usage of the device is described and performance of the instrument is validated by measurement on a MRF-132LD MR fluid with a sedimentation constant of about 4.7×10−10 s obtained within 5 h.
Prescription for density profile reconstruction using a heavy ion beam probe
Authors: Fujisawa A. , Kitazawa M. , Shimizu A. , Ohshima S. , Iguchi H.
Published: June 2003

This article presents a method for density profile reconstruction using a heavy ion beam probe. A model calculation is performed to demonstrate the feasibility of the proposed method. The possibility to infer the density profile widely extends the applicability of the heavy ion beam probe by providing fine structural measurements of density profile that is, in principle, continuous in space, with a high temporal resolution of milliseconds.
Crystallization kinetics and dielectric properties in sol-gel derived (Pb,La)(Zr,Sn,Ti)O3 ceramics
Authors: Zhai Jiwei , Chen Haydn
Published: June 2003

Sol-gel derived (Pb,La)(Zr,Sn,Ti)O3 powders and sintered ceramics were prepared; their crystallization kinetics and dielectric properties were studied as a function of temperature. X-ray powder diffraction showed that the pyrochlore phase formed initially from an amorphous gel during low-temperature heat treatment around 200–300 °C. Further heat treatment to 600 °C resulted in the development of the perovskite phase with no significant growth of pyrochlore crystallites. At intermediate temperatures the sol-gel derived powders yielded a mixture of pyrochlore and perovskite phases. The crystallization kinetics of the perovskite phase was analyzed following the Avrami approach, which indicated that the process is diffusion limited. Those fine powders were utilized to prepare compact ceramics after sintering at various temperatures; their dielectric properties were analyzed. The electric field induced transformation from the antiferroelectric to the ferroelectric phase was clearly observed through the polarization reversal experiments. This material holds great promise for high energy density capacitors and microelectromechanical devices.
Work function of MgO single crystals from ion-induced secondary electron emission coefficient
Authors: Lim Jae Yong , Oh Jun Soek , Ko Byung Doc , Won Cho Jae , Kang Seung Oun , Cho Guangsup , Uhm Han Sup , Choi Eun Ha
Published: June 2003

The work functions φω of MgO single crystals with its respective orientation (111), (200), and (220) have been investigated from their ion-induced secondary electron emission coefficient γ, respectively, using various ions with different ionization energies in a γ-focused ion beam system. The work function φω for MgO single crystal with (111) orientation has the lowest value, 4.22 eV, whereas it is 4.94 eV for (200) and the highest value is 5.07 eV for (220). These work functions of MgO single crystals can explain the nonzero values of the ion-induced secondary electron emission coefficient γ for Xe+ ions, whose ionization energy is 12.13 eV.
Enhanced electron emission from carbon nanotubes through density control using in situ plasma treatment of catalyst metal
Authors: Choi Jong Hyung , Choi Sun Hong , Han Jae-Hee , Yoo Ji-Beom , Park Chong-Yun , Jung Taewon , Yu SeGi , Han In-Taek , Kim J. M.
Published: June 2003

We controlled the density of carbon nanotubes (CNTs) through in situ NH3 plasma pretreatment and investigated field emission properties with the density variation. Ni catalytic layer was transformed into small nanoparticles with NH3 plasma pretreatment time and power. As NH3 plasma pretreatment time was increased, the growth rate of grown CNTs was gradually decreased. Also, the density of CNTs reduced from 2×109 to 8×106/cm2 with an increase in NH3 plasma pretreatment time from 10 to 30 min for the Ni layer of 10 Å. With a decrease in the density of CNTs, the emission current density was increased and turn on electric field was decreased. We obtained large and uniform emission current (about 9 mA/emission area of 0.49 cm2) from CNTs film with the density of 8×106/cm2.
Exchange-coupling interaction, effective anisotropy and coercivity in nanocomposite permanent materials
Authors: Gao R. W. , Feng W. C. , Liu H. Q. , Wang B. , Chen W. , Han G. B. , Zhang P. , Li H. , Li W. , Guo Y. Q. , Pan W. , Li X. M. , Zhu M. G. , Li X.
Published: June 2003

The inter-grain exchange-coupling interactions, effective anisotropy, and coercivity in nanocomposite Nd2Fe14B/α−Fe magnets were investigated. The effective anisotropy of nanocomposite magnets has been calculated starting from the statistics of boundaries between magnetically hard-hard, hard-soft, and soft-soft grains. The result shows that the effective anisotropy decreases with reduction in grain size and/or increase in soft phase components. When grain sizes reduce to 4–5 nm, Keff decreases to 1/3−1/4 of the ordinary value of K. The coercivity in nanocomposite magnets demonstrates a similar behavior. The decrement of coercivity is mainly due to the reduction of effective anisotropy. Considering the opposite varying trend the remanence demonstrates with respect to the effective anisotropy and the coercivity, we conclude that the mean grain size should be in the range of 10–15 nm and the volume fraction of soft phase should be less than 50% in order to achieve high energy product magnets.
Collinear Thomson scattering diagnostic system for the detection of relativistic waves in low-density plasmas
Authors: Filip Catalin V. , Tochitsky Sergei Ya. , Narang Ritesh , Clayton Christopher E. , Marsh Kenneth A. , Joshi Chandrashekhar J.
Published: June 2003

A Thomson scattering technique is used to study relativistic plasma waves at plasma densities as low as 2×1015 cm−3. A spatial-spectral filter is utilized to simultaneously attenuate the probe light ∼109 times and collect the weak scattered light which is shifted 3–24 Å from the probe wavelength. The plasma waves, excited by a two-wavelength CO2 laser pulse with intensities up to 1015 W/cm2, are probed by a 532 nm laser pulse in a collinear geometry. Both the red- and blueshifted sidebands of Thomson scattered light are simultaneously resolved in time and frequency.
Scanning Auger microscopy study of W tips for scanning tunneling microscopy
Authors: Ottaviano L. , Lozzi L. , Santucci S.
Published: June 2003

Tungsten tips used in scanning tunneling microscopy (STM) (prepared via electrochemical etching with a 2 N KOH or NaOH solution) have been studied with state of the art scanning Auger microscopy (SAM) with chemical lateral resolution of 10 nm. The experiments were focused on the investigation of the W tips’ apex shape and surface composition, for tips as etched, or after various postetching treatments performed for cleaning, sharpening, and surface oxide removal purposes. Ultrasonic cleaning likely bend the tip apex. Hydrofluoride etching successfully removes the native WO3 oxide layer, but this happens at the expense of the tip sharpness. Ion sputtering in ultrahigh vacuum is not always effective in sharpening and cleaning the tungsten tip apex, and we sometimes observed the formation of needle like nanotips, mostly composed of WO3. Direct resistive annealing of the tip (operated in the STM at 10 V, 50 nA set-point sample bias voltage and current, respectively) to remove the oxide layer, produces a coiling of the tip apex. In this case, atom transfer from the sample to the tip is directly demonstrated with Auger spectra taken at the tip apex.
Instrument and method for measuring second-order nonlinear optical tensors
Authors: Armstrong Darrell J. , Pack Michael V. , Smith Arlee V.
Published: June 2003

We describe an apparatus for measuring the second-order nonlinear tensor of crystals based on the measurement technique of separated-beam, nonphase matched, second-harmonic generation. This method is an improvement over traditional methods based on the analysis of Maker fringes. We illustrate our measurement technique and show some typical data for crystals of potassium dihydrogen phosphate and potassium niobate. We intend to maintain our apparatus to encourage rapid and complete characterization of new nonlinear crystals, and also to improve the nonlinear tensor data base for established nonlinear crystals.
Properties of rf-sputtered indium–tin-oxynitride thin films
Authors: Aperathitis Elias , Bender Marcus , Cimalla Volker , Ecke Gernot , Modreanu Mircea
Published: June 2003

Indium–tin-oxide (ITO) and indium–tin-oxynitride (ITON) thin films have been fabricated by rf-sputtering in plasma containing Ar or a mixture of Ar and N2, respectively. The structural, electrical and optical properties of ITON films were examined and compared with those of ITO films. The microstructure of ITON films was found to be dependent on the nitrogen concentration in the plasma. Increasing the amount of nitrogen in the plasma increased the resistivity and reduced the carrier concentration and mobility of the films. The electrical properties of the ITON films improved after annealing. The absorption edge of the ITON films deposited in pure N2 plasma was shifted towards higher energies and showed reduced infrared reflectance compared to the respective properties of ITO films. The potential of indium–tin-oxynitride films for use as a transparent conductive material for optoelectronic devices is addressed.
Determination of the anisotropic dielectric function for wurtzite AlN and GaN by spectroscopic ellipsometry
Authors: Shokhovets S. , Goldhahn R. , Gobsch G. , Piekh S. , Lantier R. , Rizzi A. , Lebedev V. , Richter W.
Published: June 2003

We demonstrate that variable angle spectroscopic ellipsometry (SE) is capable of determining both ordinary and extraordinary dielectric functions (DFs) in the transparent region of group III nitride wurtzite films even if the optical axis is oriented normal to the surface plane. In contrast to the so far used prism coupling technique, the SE method is neither restricted to layers deposited on lower refractive index substrates nor to available laser wavelengths. Application to AlN and GaN films grown on 6H-SiC substrates yields experimental data which can be represented in simple analytical form. The difference in energy dispersion for ordinary and extraordinary DFs is related to the effective optical band gap depending on the light polarization. Extrapolation of data to lower photon energies allows estimation of the ordinary and extraordinary high-frequency dielectric constants.
Femtosecond time-resolved dielectric function measurements by dual-angle reflectometry
Authors: Roeser C. A. D. , Kim A. M.-T. , Callan J. P. , Huang L. , Glezer E. N. , Siegal Y. , Mazur E.
Published: June 2003

We present a technique to measure the dielectric function of a material with femtosecond time resolution over a broad photon energy range. The absolute reflectivity is measured at two angles of incidence, and ε(ω) is calculated by numerical inversion of Fresnel-like formulas. Using white-light generation, the single-color probe is broadened from the near IR to the near UV, but femtosecond time resolution is maintained. Calibration of the apparatus and error analysis are discussed. Finally, measurements of isotropic, thin film, and uniaxial materials are presented and compared to reflectivity-only studies to illustrate the merit of the technique.
A dynamic compressometer for converse electrostriction measurements
Authors: Yimnirun Rattikorn , Moses Paul J. , Newnham Robert E. , Meyer Richard J.
Published: June 2003

A simple dynamic instrument for measuring very small stress dependence of capacitance is presented in this article. We describe the design and development of a dynamic compressometer for converse electrostrictive measurements on low dielectric constant materials. This redesigned system is capable of resolving a change in capacitance of 10−17 F or smaller. The most important feature is the dynamic stressing system incorporated to improve the accuracy and the reproducibility of the measurements. Furthermore, the uniaxiality and uniformity of the applied stress are found to be critical to the measurements. Therefore, a uniaxial stress delivery scheme using ball bearings is employed in the measurements to improve the accuracy of the experimental results. The converse electrostrictive coefficients obtained from this instrument agree reasonably well with those measured directly by a single-beam interferometer.
Measurement of oxygen atom density employing vacuum ultraviolet absorption spectroscopy with microdischarge hollow cathode lamp
Authors: Nagai Hisao , Hiramatsu Mineo , Hori Masaru , Goto Toshio
Published: June 2003

The compact measurement system for absolute density of oxygen (O) atom has been developed, which employs a vacuum ultraviolet absorption spectroscopy (VUVAS) technique with a high-pressure microdischarge hollow cathode lamp (MHCL) as a light source. The influences of self-absorption, emission line profile of the MHCL, and background absorption of oxygen molecule (O2) on the determination of absolute O atom density were taken into consideration. This system has been applied for measuring absolute O atom densities in an inductively coupled O2 plasma. O atom densities were estimated to be on the order of 1×1012–1×1013 cm−3 at an input power of 100 W and an O2 pressure ranging from 1.3 to 26.7 Pa. The behavior of O atom density measured using VUVAS technique was consistent with that obtained by actinometry technique using O emission intensities of 844.6 nm and 777.4 nm lines. Moreover, the lifetime of O atom in the afterglow plasma has been measured. The decay curves of the O atom density were fitted with exponential functions. The extinction process of O atom in the inductively coupled O2 plasma has been discussed.
In situ photoacoustic investigations of some optically transparent samples like ice and snow
Authors: Kapil J. C. , Joshi S. K. , Rai A. K.
Published: June 2003

A resonant photoacoustic (PA) cell, along with its cooling system in a temperature range of −40 °C to room temperature, has been designed and fabricated at our laboratory for studying samples distilled water, hexagonal ice, and snow. Performance of this cell has been checked by carrying out its parametric studies using the C-black as a sample and nitrogen as a buffer gas. The frequency and spectral responses of the resonant cell were in good agreement with the theoretical results. Thermal diffusivities of distilled water, hexagonal ice, and snow were measured by the phase shift method. In order to see the reliability of the results, thermal diffusivities of other optically transparent samples viz. glass, plexi-glass, and polycarbonate were also measured and the results are in agreement with the reported values. PA spectra of distilled water, hexagonal ice, and snow were also recorded at temperatures of 30, −10, and −10 °C, respectively. Strong absorption bands have been observed having maxima at wavelengths 971 and 983 nm in the case of water and ice and snow, respectively, which are the third harmonics of the fundamental O–H stretching vibrations of the H2O molecule. Our experimental results show a shift to longer wavelengths in the third harmonic of the O–H stretching vibrations, when the state of H2O changes from gaseous state to solid state. This result may be useful in the quantitative estimation of some physical properties of snow viz. hydrogen bond energy, density, heat of sublimation, specific heat, etc. (W. A. P. Luck, Proceedings of the International Symposium on Structure of Water and Aqueous Solutions, Marburg, July 1973) which is expected to be helpful in avalanche forecasting.
A miniature x-ray fluorescence setup
Authors: Ribbing Carolina , Andersson Marit , Hjort Klas , Lundqvist Hans
Published: June 2003

A miniature low-power x-ray fluorescence (XRF) setup has been designed, realized, and tested in vacuum. The experimental setup is centimeter sized and consists of an x-ray source and an electrically cooled silicon detector. The x-ray source has diamond membrane electrodes; the cathode is a field emitting microstructure and the anode is a metal film deposited on a diamond membrane. Anode radiation emergent through one of the diamond membrane electrodes induces characteristic x-ray radiation from a sample. By miniaturization of an XRF setup extremely low power consumption with acceptable yield and signal level is possible because of the small distances involved between source and sample and between sample and detector. The lightweighted XRF setup is intended for in situ materials analysis, e.g., for spacecraft applications, or probe mounted for portable mineralogy, archaeometry, or forensic equipment. In this article an initial test of the fluorescence setup is described and qualitative experimental results are presented and analyzed.
Structure and magnetic properties of thermally annealed (Ni80Fe20)1−xMnx thin films
Authors: Yoon C. S. , Kim S. J. , Kim Suk Jun , Kim C. K.
Published: June 2003

Ni 80 Fe 20 – Mn alloy thin films were fabricated using magnetron sputtering in order to study the microstructural changes that develop in an exchange couple (Ni80Fe20 and Mn). In the process, we discovered that the alloy films phase separated into Ni80Fe20 and Mn when annealed at 400 °C, although bulk Ni80Fe20 and Mn are miscible at room temperature. Moreover, a strong crystallographic texture developed during annealing, especially for films with high Mn content. The increase of texture was attributed to the volume expansion taking place in the phase separation. It was speculated that the as-deposited alloy films had a large coherent interfacial strain, possibly due to inhomogeneous alloying. In turn, this hindered the formation of intermetallic compounds, and instead forced a phase separation to reduce the interfacial energy.
Noise shielding system utilizing a thin piezoelectric membrane and elasticity control
Authors: Mokrý P. , Fukada E. , Yamamoto K.
Published: June 2003

The description and theoretical analysis of a noise shielding system are presented. In this system, the noise and/or sound are transmitted through the piezoelectric curved membrane, which is connected to an external feedback circuit. Using the principle of elasticity control, i.e., utilization of both direct and inverse piezoelectric effects simultaneously, the movement of the membrane as well as the sound pressure of the transmitted wave can be controlled to a large extent. Transmission loss of an audible sound through the membrane in such a system is expressed as a function of a sound frequency, geometrical properties of the membrane, and parameters of the feedback circuit. It is used for the comparison of theoretical predictions and experimental data. Using this technique, the increase of the transmission loss of about 60 dB in a narrow frequency range or about 7 dB in the broad frequency range has been achieved. The performance of this system is discussed.
Development of movable mask system to cope with high beam current
Authors: Suetsugu Y. , Shibata K. , Sanami T. , Kageyama T. , Takeuchi Y.
Published: June 2003

The KEK B factory (KEKB), a high current electron-positron collider, has a movable mask (or collimator) system to reduce the background noise in the BELLE detector coming from spent particles. The early movable masks, however, had severe problems of heating, arcing, and vacuum leaks over the stored beam current of several hundred mA. The cause is intense trapped higher order modes (HOMs) excited at the mask head, where the cross section of the beam chamber changed drastically. The mask head, made of copper–tungsten alloy or pure copper, was frequently damaged by hitting of the high energy beam at the same time. Since the problems of the mask were revealed, several kinds of improved masks have been designed employing rf technologies in dealing with the HOM and installed to the ring step by step. Much progress has come from adopting a trapped-mode free structure, where the mask was a bent chamber itself. Recently the further improved mask with a reduced HOM design or HOM dampers was developed to suppress the heating of vacuum components near the mask due to the HOM traveling from the mask. To avoid damage to the mask head, on the other hand, a titanium mask head was tried. The latest masks are working as expected now at the stored beam current of 1.5 A. Presented are the problems and experiences on the movable mask system for the KEKB, which are characteristic of and common in a high intensity accelerator.
A low cost high resolution pattern generator for electron-beam lithography
Authors: Pennelli G. , D’ Angelo F. , Piotto M. , Barillaro G. , Pellegrini B.
Published: June 2003

A simple, very low cost pattern generator for electron-beam lithography is presented. When it is applied to a scanning electron microscope, the system allows a high precision positioning of the beam for lithography of very small structures. Patterns are generated by a suitable software implemented on a personal computer, by using very simple functions, allowing an easy development of new writing strategies for a great adaptability to different user necessities. Hardware solutions, as optocouplers and battery supply, have been implemented for reduction of noise and disturbs on the voltages controlling the positioning of the beam.
A high-resolution synchrotron-radiation angle-resolved photoemission spectrometer with in situ oxide thin film growth capability
Authors: Horiba K. , Ohguchi H. , Kumigashira H. , Oshima M. , Ono K. , Nakagawa N. , Lippmaa M. , Kawasaki M. , Koinuma H.
Published: June 2003

We have constructed a high-resolution synchrotron-radiation angle-resolved photoemission (ARPES) spectrometer combined with a combinatorial laser molecular-beam epitaxy (laser MBE) thin film growth system in order to investigate the electronic structure of transition metal oxide thin films. An ARPES spectrometer GAMMADATA SCIENTA SES-100 was selected for the high-throughput and high-energy and angular-resolution ARPES measurements. A total energy resolution of 6.3 meV and a momentum (an angular) resolution of 0.02 Å−1 (0.2°) were obtained at a photon energy of 40 eV. The system is installed at the high-resolution vacuum-ultraviolet beamline BL-1C or the soft-x-ray undulator beamline BL-2C at the Photon Factory as an end-station. Another distinctive feature of this system is the direct connection from the spectrometer to a laser MBE chamber. Thin film samples can be transferred quickly into the photoemission chamber without breaking ultrahigh vacuum. Laser MBE is one of the best methods to grow thin films of many different transition metal oxides and to achieve well-ordered surfaces, which are indispensable for the ARPES measurements. The capabilities of the system and the importance of the in situ sample transfer between ARPES and laser MBE are demonstrated by studying the band structure of La0.6Sr0.4MnO3 thin films epitaxially grown on SrTiO3 substrates by laser MBE.
Stress induced magnetic anisotropy and giant magnetoimpedance in Fe-rich glass-coated magnetic microwires
Authors: Zhukova V. , Larin V. S. , Zhukov A.
Published: June 2003

The effect of conventional (CA) and stress annealing (SA) on magnetic properties of Fe74B13Si11C2 glass-coated microwires has been studied. CA treatment does not significantly change the character of the hysteresis loop. Under certain annealing conditions (annealing temperature, Tann>300 °C, applied stress, σ>700 MPa) rectangular hysteresis loop transforms into the inclined with magnetic anisotropy field above 1000 A/m. Such phenomenology has been related to the induction of transverse magnetic anisotropy by SA treatment. Under tensile stress the SA annealed microwire recovers rectangular hysteresis loop. Samples subjected to stress annealing show noticeable magnetoimpedance and stress impedance effects in spite of their large magnetostriction.
Simultaneous measurement of laser-induced shock wave and released particle velocities at Mbar pressure
Authors: Chen J. P. , Li R. X. , Zeng Z. N. , Wang X. T. , Wang W. Y. , Jiang Y. H. , Cheng C. F. , Xu Z. Z.
Published: June 2003

We show the feasibility of simultaneous measurement of shock velocity and released particle velocity after shock at Mbar pressure. The shock wave is driven by a laser pulse of 1.2 ps duration (full width at half maximum), with the intensity of ∼1014 W/cm2 at 785 nm, irradiating a 500-nm-thick aluminum foil. A chirped laser pulse split from the main pulse is applied to detect the shock breakout process at the rear surface of the target based on frequency domain interferometry. The mean shock velocity determination benefits from the precise synchronization (<100 fs resolution) of the shock pump and probe laser pulse, which is calculated from the time the shock takes to travel the 500-nm-thick aluminum. The released particle velocity determination takes advantage of the chirped pulse frequency domain interferometry. The two measured parameters are self-consistent.
Epitaxial growth of yttrium-stabilized HfO2 high-k gate dielectric thin films on Si
Authors: Dai J. Y. , Lee P. F. , Wong K. H. , Chan H. L. W. , Choy C. L.
Published: June 2003

Epitaxial yttrium-stabilized HfO2 thin films were deposited on p-type (100) Si substrates by pulsed laser deposition at a relatively lower substrate temperature of 550 °C. Transmission electron microscopy observation revealed a fixed orientation relationship between the epitaxial film and Si; that is, (100)Si//(100)HfO2 and [001]Si//[001]HfO2. The film/Si interface is not atomically flat, suggesting possible interfacial reaction and diffusion. X-ray photoelectron spectrum analysis also revealed the interfacial reaction and diffusion evidenced by Hf silicate and Hf–Si bond formation at the interface. The epitaxial growth of the yttrium stabilized HfO2 thin film on bare Si is via a direct growth mechanism without involving the reaction between Hf atoms and SiO2 layer. High-frequency capacitance–voltage measurement on an as-grown 40-Å yttrium-stabilized HfO2 epitaxial film yielded an effective dielectric constant of about 14 and equivalent oxide thickness to SiO2 of 12 Å. The leakage current density is 7.0×10−2 A/cm2 at 1 V gate bias voltage.
Self-assembly and magnetic properties of cobalt nanoparticles
Authors: Yang H. T. , Shen C. M. , Su Y. K. , Yang T. Z. , Gao H. J. , Wang Y. G.
Published: June 2003

Two- and three-dimensional superlattices of passivated cobalt nanoparticles were formed by a self-assembly technique. The size and stabilization of the cobalt nanoparticles are controlled by using the combination of oleic acid and triphenylphosphine. The cobalt nanoparticles are stable for at least 90 days without oxidation at room temperature under ambient conditions. The magnetic properties of the cobalt nanoparticles in different forms are compared, which provides helpful information on the magnetostatic interaction of the nanoparticles.
Effect of N incorporation on boron penetration from p+ polycrystalline-Si through HfSixOy films
Authors: Quevedo-Lopez M. A. , El-Bouanani M. , Kim M. J. , Gnade B. E. , Wallace R. M. , Visokay M. R. , LiFatou A. , Chambers J. J. , Colombo L.
Published: June 2003

We demonstrate that incorporating N in Hf-silicate films reduces B penetration through the dielectric film. By modeling the B depth profiles, we calculated the B diffusivities through Hf-silicate (HfSixOy) to be ∼2× higher than the corresponding diffusivities for Hf-silicon oxynitride (HfSixOyNz). B diffusion through grain boundaries after HfSixOy crystallization is believed to be responsible for the enhanced B diffusivity observed. Suppression of crystallization observed in HfSixOyNz films is attributed to the lower Hf content in the films and the incorporation of N. The decreased B penetration observed in HfSixOyNz is a combination of absence of grain boundaries and the fact that N blocks B diffusion by occluding diffusion pathways. The minimum temperatures for B penetration are estimated to be approximately 950 and 1050 °C for HfSixOy and HfSixOyNz, respectively.