bluuebunny/crossref_metadata_2025 huggingface dataset:
Pulsed laser deposition of relaxor-based PbLu0.5Nb0.5O3–PbTiO3 thin films
Authors: Tyunina M. , Levoska J. , Leppävuori S. , Shorubalko R. , Sternberg A.
Published: July 2002

Ferroelectric thin films of relaxor-based PbLu0.5Nb0.5O3–PbTiO3 solid solution (PLuNT) with compositions near the morphotropic phase boundary were formed by in situ pulsed laser deposition onto La0.5Sr0.5CoO3/(100)MgO (LSCO/MgO). The phase composition of the PLuNT films was sensitive to the deposition temperature (550–710 °C), with single-phase perovskite formation only at 690 °C. The perovskite PLuNT films were pseudocubic and epitaxial, with (001) planes parallel to the substrate surface. At room temperature, capacitors Au/PLuNT/LSCO exhibited ferroelectric behavior (maximum polarization Pm≅29 μC/cm2, remnant polarization Pr≅14 μC/cm2, coercive field Ec≅70 kV/cm), and zero-field dielectric permittivity about ε≅300–450. A broad peak in ε was observed around 350 °C. With increasing deposition temperature, although the volume fraction of the pyrochlore phase decreased, Pm, Pr, and Ec all decreased, while ε remained unchanged. The suppression of polarization in the capacitors, both compared to that in the PLuNT ceramics and under the variation of the deposition temperature, was explained by the presence and evolution of passive layers near the electrodes.
Ceramic microtubes self-formed at room temperature that exhibit a large bending stress
Authors: Akiyama Morito , Shobu Kazuhisa , Xu Chao-Nan , Nonaka Kazuhiro , Watanabe Tadahiko
Published: July 2002

We have investigated the aluminum nitride microtubes made of aluminum nitride thin film. Aluminum nitride thin film deposited on aluminum foil forms microtubes of itself at room temperature when the aluminum foil is dissolved in hydrochloric acid solution. The aluminum nitride microtubes exhibit a large bending stress of 1100±94 megapascals. The bending stress is more than three times larger than the bending strength of aluminum nitride bulk. The diameter of the microtubes is proportional to the film thickness. The bending stress is independent of the film thickness and is fixed.
Comment on “Statistical theory of time-dependent diffusion-controlled reactions in fluids and solids” [J. Chem. Phys. 103, 10201 (1995)]
Authors: Gopich I. V. , Burshtein A. I.
Published: July 2002

The conventional method of statistical mechanics leading to integral kinetic equations for bimolecular energy quenching collapsed when used for evaluation of concentration corrections to the Stern–Volmer constant in the diffusion control limit. These corrections obtained by Felderhof and Jones for uniform quenching within transparent reacting spheres are much larger than in other theories, including exact solution available for irreversible energy transfer from immobile donor to independently moving acceptors. This results in a qualitative distortion of the Stern–Volmer constant dependence on the excitation lifetime at any finite concentration of quenching spheres.
Conduction mechanism in molybdenum-containing diamond-like carbon deposited using electron cyclotron resonance chemical vapor deposition
Authors: Huang Q. F. , Yoon S. F. , Rusli  , Yang H. , Gan B. , Chew Kerlit , Ahn J.
Published: July 2002

The conduction mechanism of molybdenum-containing (Mo) diamond-like carbon films deposited using electron cyclotron resonance chemical vapor deposition was investigated. It is found that there is a conductivity turning point at around 115 K, above which the conductivity is strongly temperature dependent. This indicates that two types of conduction mechanisms, thermal activation and tunneling coexist in the films, and they dominate the conduction behavior in the high and low temperature regimes, respectively. Within the temperature range investigated, the Poole–Frenkel effect is to be expected for thermal activation. However, due to the low concentration of Mo in the films, this effect was not observable. Tunneling is thought to occur between the Mo clusters or the sp2 clusters. A conductivity model, based on the thermal activation and tunneling, is proposed, and showed good agreement with the results obtained at low field. The conduction behavior at high field is also discussed and some possible mechanisms are proposed.
Omegatron ion mass spectrometer for the Alcator C-mod tokamak
Authors: Nachtrieb R. , LaBombard B. , Thomas E.
Published: July 2002

A new ion mass spectrometry probe that operates at high magnetic field (∼8 T) has been recently commissioned on the Alcator C-Mod tokamak. The probe combines an omegatron E(t)×B ion mass spectrometer and a retarding field energy analyzer. The probe samples the plasma in the far scrape-off layer, on flux surfaces between 25 and 50 millimeters from the separatrix. Radio-frequency (rf) power is used to collect ions with resonant cyclotron frequency on the side walls of an rf cavity. Scanning the frequency results in a spectrum ordered by the ratio of ion mass to charge, M/Z. Resonances are presently resolved for 1⩽M/Z<12 down to signal levels as low as 5×10−4 times that of the bulk plasma species. Well-resolved resonances have widths within a factor of two of theoretical values obtained from particle orbit theory. Absolute impurity fluxes and individual impurity charge state temperatures are quantified by varying the applied rf power and recording the change of the amplitude of the resonant ion current. The design of the hardware and electronics design is described, the principles of operation are discussed, and initial experimental results are presented. Sources of noise which presently limit the sensitivity of the device are also discussed along with techniques to improve the signal–to–noise ratio.
Preamplifier and AD converter system for infrared focal plane arrays
Authors: Penegor G. , Wishnow E. H. , Danchi W. C.
Published: July 2002

We describe a precision preamplifier and analog-to-digital (AD) converter system for use with infrared focal plane arrays. The system uses a correlated double sampling integrated circuit which performs an analog subtraction of each full pixel level from its respective reset level prior to digitization by a 14-bit AD converter; this process is also known as “delta-reset” sampling. The system was designed to have good immunity to electrical noise interference and it has a measured dynamic range of better than 16384. A four channel version of this system is used to read out a 128×128 pixel Si:As array at a rate of 2.4 μs/pixel for the Long Wavelength InfraRed Camera a 7–13 μm camera designed and built for the Keck 10 meter telescope.
Phase change in Ge2Sb2Te5 films investigated by coherent phonon spectroscopy
Authors: Först M. , Dekorsy T. , Trappe C. , Laurenzis M. , Kurz H. , Béchevet B.
Published: July 2002

Amorphous and crystalline phases of Ge2Sb2Te5 films are investigated by coherent phonon spectroscopy. By heating amorphous films above specific temperatures, the coherent phonon signatures exhibit pronounced changes due to the crystallization of the amorphous phase into a cubic lattice and the transition from the cubic to a hexagonal crystal structure. The phonon modes observed are identified by comparison with coherent phonon spectra of the binary Sb2Te3 and GeTe constituents.
Magnetic resonance microimaging of pore freezing in cement: Effect of corrosion inhibitor
Authors: Holly R. , Tritt-Goc J. , Pislewski N. , Hansson C. M. , Peemoeller H.
Published: July 2002

Single-point magnetic resonance imaging is applied to study the freezing behavior of white cement paste with and without a Ca(NO2)2 based corrosion inhibitor. Pore size distributions are determined from consideration of the evaporable water content. This represents a unique study into the effect of a corrosion inhibitor on the final cement product. It is found that with the addition of a Ca(NO2)2 based corrosion inhibitor a significant reduction of pores between 3 and 10 nm results, producing a considerably coarser pore structure. A dramatic increase in capillary pores of radii larger than 30 nm is also observed in the cement with the inhibitor and is expected to lead to an increased movement of corrosive agents into the concrete when compared to concrete without the corrosion inhibitor.
Nonadiabatic heat-capacity measurements using a superconducting quantum interference device magnetometer
Authors: Kharkovski A. I. , Binek Ch. , Kleemann W.
Published: July 2002

Nonadiabatic measurements of the heat capacity involving sample-inherent thermometry are proposed. The method is realized with superconducting quantum interference device magnetometry and applied to FeBr2 single crystals by using the magnetization for both thermometry and relaxation calorimetry. When heating with a step pulse of laser light, the magnetization relaxes on a characteristic time scale τ=RC, where C is the heat capacity and R is the heat resistance between the sample and the bath. R is independently determined from the temperature dependence of the magnetic moment measured with and without stationary light irradiation.
Strong blue emission from As doped GaN grown by molecular beam epitaxy
Authors: Winser A. J. , Novikov S. V. , Davis C. S. , Cheng T. S. , Foxon C. T. , Harrison I.
Published: July 2002

Arsenic doped GaN grown by molecular beam epitaxy has been studied by room temperature photoluminescence. In addition to the wurzite band edge transition, luminescence from the cubic phase and very strong blue emission at ∼2.6 eV are observed. The intensities of the blue and the cubic band edge emissions have a power law dependence on the As2 flux. The formation of the cubic phase has been explained by the initial formation of GaAs before substitution of the As by the more reactive N. The intensity of the blue emission at room temperature of the As doped samples is more than an order of magnitude stronger than the band edge emission in undoped samples.
Observation of long photoluminescence decay times for high-quality GaN grown by metalorganic chemical vapor deposition
Authors: Kwon Ho Ki , Eiting C. J. , Lambert D. J. H. , Wong M. M. , Dupuis R. D. , Liliental-Weber Z. , Benamara M.
Published: July 2002

GaN epitaxial layers with different crystalline quality grown on sapphire substrates by metalorganic chemical vapor deposition are investigated using time-resolved photoluminescence at 300 K. It is found that the time-dependent photoluminescence of low-quality GaN decays faster than that of the high-quality GaN films. The time constants for the dual-exponential decay of the photoluminescence are calculated to be 50 and 250 ps for high-quality undoped GaN and 30 ps for low-quality undoped GaN. For high-quality Si-doped GaN, time constants of 150 and 740 ps are extracted while corresponding time constants of 40 and 200 ps are measured for low-quality Si-doped GaN. We believe that the time constant of 740 ps measured for our high-quality Si-doped GaN is the longest ever reported for thin GaN/sapphire films.
Characterization of SrRuO3 thin film grown by laser ablation at temperatures above 400 °C
Authors: Fang Xiaodong , Kobayashi Takeshi
Published: July 2002

Structural and electrical properties of SrRuO3 thin films grown at various temperatures (Td) were investigated. The films grew epitaxially when Td≧350 °C. The dependences of crystallinity, conductivity, and carrier density on temperature were less pronounced when Td was above 400 °C, whereas crystallinity and conductivity were markedly degraded with decreasing Td when Td≦400 °C. Owing to this unique dependence, SrRuO3 thin film deposited at Td as low as 400 °C showed an acceptable quality for application to electronic devices. For the SrRuO3/SrTiO3/SrRuO3 trilayered capacitor structure, when the top SrRuO3 layer was grown at 400 °C, a symmetric permittivity–voltage curve was observed and the SrRuO3 permittivity value of 340 ε0 was obtained. When the top SrRuO3 layer was grown at 600 °C, the permittivity value of SrTiO3 decreased and even a slight asymmetry of the permittivity–voltage curve could ever be observed. This indicates that the lower temperature deposition of SrRuO3 thin film causes less interface degradation.
Exact two-electron wave packet dynamics of H2 in an intense laser field: Formation of localized ionic states H+H−
Authors: Harumiya Kenji , Kawata Isao , Kono Hirohiko , Fujimura Yuichi
Published: July 2002

We have developed an efficient grid method that can accurately deal with the electronic wave packet dynamics of two-electron systems in three-dimensional (3D) space. By using the dual transformation technique, we remove the numerical difficulties arising from the singularity of the attractive Coulomb potential. Electron–electron repulsion is incorporated into the wave packet propagation scheme without introducing any approximations. The exact electronic dynamics of H2 is simulated for the first time. At small internuclear distances (e.g., R=4 a.u.), an ionic component characterized by the structure H+H− is created in an intense laser field E(t) (intensity>1013 W/cm2 and λ≈720 nm) because an electron is transferred from the nucleus around which the dipole interaction energy for the electron becomes higher with increasing |E(t)|. The localized ionic structure is identified with the H− anion at the nucleus around which the dipole interaction energy becomes lower. Tunneling ionization proceeds via the formation of such a localized ionic structure, and direct ionization from the covalent structure is much smaller; the localized ionic structure plays the dominant doorway state to ionization of H2.
Novel instrumentation for spectrally resolved soft x-ray plasma tomography: Development and pilot results on TEXTOR
Authors: Shmaenok L. A. , Golovkin S. V. , Govorun V. N. , Ekimov A. V. , Salashchenko N. N. , Pickalov V. V. , Belik V. P. , Schüller F. C. , Donné A. J. H. , Oomens A. A. M. , Prokhorov K. A. , Andreev S. S. , Sorokin A. A. , Podlaskin B. G. , Khasanov L. V.
Published: July 2002

A novel instrumentation for wavelength- and time-resolved plasma emission tomography in the range 0.1–4 keV has been demonstrated on the Torus Experiment for Technology Oriented Research (TEXTOR). The technique is intended for reconstruction of distributions of local emission coefficients (LEC) for selected spectral lines of impurity ions. Further determination (with additional data on electron density and temperature) of spatial distributions of impurity ions at particular ionization stages will become feasible. Spectrally selective plasma images at several viewpoints around plasma are obtained with miniature pinhole cameras supplemented with multilayer mirrors as dispersion elements. The x-ray image is converted to a visible image and transported by a fiber bundle to a gain enhanced recording camera with an electron bombarded charge coupled device tube. A part of the system has been installed on temporary TEXTOR ports. First demonstration results have been obtained on plasma imaging and on subsequent LEC reconstruction using a modified iterative sinogram restoration tomography algorithm. The complete diagnostics will be operational after the TEXTOR shutdown in 2001.
Novel fabrication method of microchannel plates
Authors: Yi Whikun , Jeong Taewon , Jin Sunghwan , Yu SeGi , Lee Jeonghee , Kim J. M.
Published: July 2002

We have developed a novel microchannel plate (MCP) by introducing new materials and process technologies. The key features of our MCP are summarized as follows: (i) bulk alumina as a substrate, (ii) the channel location defined by a programmed-hole puncher, (iii) thin film deposition by electroless plating and/or sol–gel process, and (iv) an easy fabrication process suitable for mass production and a large-sized MCP. The characteristics of the resulting MCP have been evaluated with a high input current source such as a continuous electron beam from an electron gun and Spindt-type field emitters to obtain information on electron multiplication. In the case of a 0.28 μA incident beam, the output current enhances ∼170 times, which is equal to 1% of the total bias current of the MCP at a given bias voltage of 2600 V. When we insert a MCP between the cathode and the anode of a field emission display panel, the brightness of luminescent light increases 3–4 times by multiplying the emitted electrons through pore arrays of a MCP.
Organic solid-state distributed feedback dye laser with a nonmorphological modification grating
Authors: Nagawa Michifumi , Ichikawa Musubu , Koyama Toshiki , Shirai Hirofusa , Taniguchi Yoshio , Hongo Akihito , Tsuji Shinji , Nakano Yoshiaki
Published: July 2002

We report an organic solid-state distributed feedback laser consisting of an organic active layer and a Bragg grating without morphological change. The active layer consists of 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostryl)-4H-pyran as a laser dye, tris(8hydroxyquinoline) aluminum as a host, and poly(methyl methacrylate) as a binder. The threshold and linewidth of the laser are 400 μJ/cm2 and 1.5 nm, respectively. With this laser, the Bragg grating exists out of the active layer and the grating surface is flat, which are very important for device fabrication and electric driving of the laser.
Selective transmission through very deep zero-order metallic gratings at microwave frequencies
Authors: Went H. E. , Hibbins A. P. , Sambles J. R. , Lawrence C. R. , Crick A. P.
Published: July 2002

Zero-order metal grating structures are found to give extraordinary selective transmission at microwave frequencies through the resonant excitation of coupled surface waves. The metal slat structures with dielectric spacings as small as 250 μm strongly transmit wavelengths of several millimeters. A simple interpretation of these novel results which treats the deep grating structures as “filled” Fabry–Perot cavity systems gives model transmissivities which agree very well with the experimental data.
Electrical properties of shallow p+-n junction using boron-doped Si1−xGex layer deposited by ultrahigh vacuum chemical molecular epitaxy
Authors: Huang Hsiang-Jen , Chen Kun-Ming , Chang Chun-Yen , Chao Tien-Sheng , Huang Tiao Yuan
Published: July 2002

Strained boron-doped Si1−xGex layers with different Ge mole fractions were selectively deposited by ultrahigh vacuum chemical molecular epitaxy to form shallow p+-n junction suitable for raised source/drain metal–oxide–semiconductor field effect transistor applications. Detailed electrical characterizations were performed. Our results show that the reverse leakage current could be optimized by a rapid thermal annealing at 950 °C for 20 s, and a near perfect forward ideality factor (i.e., <1.01) is obtained for the p+-n Si1−xGex/Si junction. By analyzing the periphery and area leakage current components of p+-n Si1−xGex/Si junctions with various perimeter lengths and areas, the degree of misfit dislocations and undercut effect were studied. The specific contact resistance was found to decrease as Ge mole fraction increases. Junction depth measurements also show that the junction depth decreases monotonically with increasing Ge mole fraction. The reduced B diffusion constant is attributed to the increasing Ge gradient in the transition region.
Confluent hypergeometric equations and related solvable potentials in quantum mechanics
Authors: Negro J. , Nieto L. M. , Rosas-Ortiz O.
Published: July 2002

The connection between the Schrödinger and confluent hypergeometric equations is discussed. It is shown that the factorization of the confluent hypergeometric equation gives a unifying powerful algebraic tool in order to study some quantum mechanical eigenvalue problems. That description includes the linear and N-dimensional harmonic oscillators, as well as the Coulomb and Morse potentials.
Magnetostrictive properties of a new type of Tb–Dy–Fe–Zn Laves phase compound
Authors: Ono Hideaki , Shimada Munekatsu , Toma Hideo
Published: July 2002

The magnetostriction of (Tb–Dy)Fe2 Laves phase compounds, which are generally used under compressive prestress, is strongly dependent on prestress in an application range of 0–40 MPa. Magnetostriction shows an especially pronounced decline with increasing prestress in a range of 20–40 MPa. On the other hand, this tendency for magnetostriction to decrease with increasing prestress is suppressed in Tb–Dy–Fe–Zn Laves phase compounds in which Fe has been partially substituted by Zn. Under an applied magnetic field of 80 kA/m, which is the practical operating condition of actuators, magnetorestriction displays a tendency to increase under prestress of 40 MPa compared with that of nonsubstitution compounds. Additionally, the basic properties of this newly found type of Tb–Dy–Fe–Zn Laves phase magnetostrictive compound have also been identified.
Angle-dependent photoluminescence spectra of hydrogenated amorphous silicon thin films
Authors: Marra D. C. , Aydil E. S. , Joo S.-J. , Yoon E. , Srdanov V. I.
Published: July 2002

Multiple sharp peaks were observed in the visible photoluminescence spectra of amorphous silicon thin films, prepared by ultrahigh vacuum electron cyclotron resonance chemical vapor deposition on oxidized silicon substrates. The angular dependence of the photoluminescence, measured by a home-built fiber-optics device, revealed that the origin of these sharp features was due to Fabry–Pérot cavity interference effects. The interference is enhanced by deposition on thermally grown oxide layers with relatively smooth surfaces. We also consider how thin-film interference effects can add to the already existing confusion regarding the photoluminescence (PL) mechanism of porous and other luminescent forms of silicon and propose angle-dependent PL spectroscopy as a remedy for identifying spectral features due to interference effects.
Interface chemistry and electrical properties of SrVO3/LaAlO3 heterostructures
Authors: Kim Dong-Wook , Kim Dae Ho , Noh T. W. , Char K. , Park J.-H. , Lee K.-B. , Kim Hyeong-Do
Published: July 2002

SrVO 3 films were grown by laser molecular beam epitaxy on LaAlO3 substrates. For a 10-nm-thick film, its resistivity could be reduced by a factor of 4 by inserting a single La–O atomic layer on an oxygen-annealed LaAlO3 substrate. X-ray diffraction and x-ray photoelectron spectroscopy measurements revealed that oxygen defect concentrations could be varied significantly by controlling the substrate terminations, i.e., interface chemistry. It was suggested that the interface chemistry could influence formation of extended defects and result in changes in electrical properties.
Atmospheric pressure sample inlet for mass spectrometers
Authors: Dheandhanoo Seksan , Ciotti Ralph J. , Ketkar Suhas N.
Published: July 2002

An inlet for a mass spectrometer has been developed for direct sampling of gases over a wide range of pressure (1–760 Torr). The sample inlet is composed of two small orifices that form a pressure reduction region. These orifices are used to limit the flow of sample gas into the mass spectrometer. The pressure inside the pressure reduction region is regulated by a needle valve and a vacuum pump. The flow of gas through the orifices is viscous. The inlet is made of stainless steel and operated at high temperature to prevent surface adsorption and corrosion. Its adaptability to a wide range of pressures is very useful for monitoring process gases during manufacturing processes of microelectronic devices. This inlet can be used for effluent gas analysis at 760 Torr as well as for in situ monitoring of the semiconductor equipment at pressures less than 5 Torr. The inlet provides a fast response to changes in the constituents of gas samples without memory effects. The sample inlet has been tested extensively in the laboratory as well as in field environments.
Switch-on transient behavior in low-temperature polycrystalline silicon thin-film transistors
Authors: Bavidge N. , Boero M. , Migliorato P. , Shimoda T.
Published: July 2002

We report upon the measurement and simulation of the switch-on transient of polycrystalline silicon (poly-Si) thin-film transistors. The measurement of the switch-on transient reveals an unexpectedly long transient that cannot be explained by the theory adopted for single-crystal silicon-on-insulator (SOI) devices. Contrary to the SOI case, the transient is seen to increase with source–drain voltage. In order to explain the experimental findings, we have performed simulations of the transient and found that the results are heavily dependent upon the density of states in the band gap and their capture cross sections. Only when energy-dependent cross sections are adopted do the calculations correctly reproduce the steady-state and overshoot currents, and also the transient duration. A physical interpretation of this phenomenon is presented.
Alternating current thin-film electroluminescence of GaN:Er
Authors: Heikenfeld J. , Steckl A. J.
Published: July 2002

Thin-film electroluminescence has been obtained from GaN:Er deposited directly on amorphous dielectric layers. Electroluminescent device (ELD) structures consisting of metal/dielectric/GaN:Er/dielectric were fabricated on p+-Si substrates. In contrast to previous GaN:Er ELDs which used epitaxial growth conditions on crystalline substrates and were operated under direct current bias, these ELDs were operated under alternating current bias. Under bias conditions of 170 peak voltage (Vp) and frequencies of 10 and 100 kHz, the ELDs exhibit a luminance of 50 and 300 cd/m2, respectively. The emission spectra, which originate from Er3+ 4f–4f transitions, consist of dominant green emission at ∼537/558 nm accompanied by violet (415 nm) and infrared (1.5 μm) peaks. The violet emission peak indicates that hot carriers can gain up to ∼3 eV energy for a Vp corresponding to 1.5 MV/cm applied field. The emitted intensity initially increases linearly with frequency, followed by a trend towards saturation. The frequency for 3 dB reduction from the linear relation is at ∼65 kHz for the visible emission and ∼8 kHz for the infrared emission.
1.26 μm intersubband transitions in In0.3Ga0.7As/AlAs quantum wells
Authors: Garcia César Pascual , De Nardis Andrea , Pellegrini Vittorio , Jancu Jean Marc , Beltram Fabio , Müeller Bernhard H. , Sorba Lucia , Franciosi Alfonso
Published: July 2002

We observed room-temperature intersubband transitions at 1.26 μm in n-doped type-II In0.3Ga0.7As/AlAs strained quantum wells. An improved tight-binding model was used to optimize the structure parameters in order to obtain the shortest wavelength intersubband transition ever achieved in a semiconductor system. The corresponding transitions occur between the first confined electronic levels of the well following mid-infrared optical pumping of electrons from the barrier X- valley into the well ground state.
Thermodynamic implications of confinement for a waterlike fluid
Authors: Truskett Thomas M. , Debenedetti Pablo G. , Torquato Salvatore
Published: July 2002

A theoretical framework is introduced for studying the thermodynamics and phase behavior of a “waterlike” fluid film confined between hydrophobic plane surfaces. To describe the hydrogen-bonding interactions in the fluid film, an earlier analytical theory for uniform associating fluids is generalized. Two levels of approximation are presented. In the first, the reference fluid is assumed to be homogeneous. Here, the primary effect of the confining walls is to reduce the average number of favorable fluid–fluid interactions relative to the bulk fluid. The implications of this energetic penalty for the phase behavior and, in particular, the low-temperature waterlike anomalies of the fluid are examined. It is shown that the reduction of favorable fluid–fluid interactions can promote strong hydrophobic interactions between the confining surfaces at nanometer length scales, induced by the evaporation of the fluid film. In the second level of approximation, the inhomogeneous nature of the reference fluid is accounted for by a density functional theory. The primary effect of the density modulations is to promote or disrupt hydrogen bonding in distinct layers within the pore. Interestingly, when the reference fluid is treated as inhomogeneous, the theory predicts the possibility of a new low-temperature phase transition in the strongly confined fluid.
Structure and molecular ordering extracted from residual dipolar couplings: A molecular dynamics simulation study
Authors: Stevensson Baltzar , Komolkin Andrei V. , Sandström Dick , Maliniak Arnold
Published: July 2002

A molecular dynamics (MD) simulation, based on a realistic atom–atom interaction potential, was performed on 4-n-pentyl-4′-cyanobiphenyl (5CB) in the nematic phase. The analysis of the trajectory was focused on the determination of molecular structure and orientational ordering using nuclear dipole–dipole couplings. Three sets of couplings were calculated: C13–13C, C13–1H, and H1–1H. These dipolar couplings were used for investigation of the biphenyl and the ring–chain fragments in 5CB. The models employed in the analysis were based on the rotational isomeric state (RIS) approximation and the maximum entropy (ME) approach. The main questions addressed in this article are: (i) How sensitive are the various sets of dipolar couplings to the long-range orientational order and molecular conformation? (ii) Which model predicts a molecular structure that is in best agreement with the true conformation? Computer simulation is an attractive method to address these questions since the answer is provided: we know the true orientational order and the molecular structure. We found that all sets of dipolar couplings analyzed using the two models predict correct orientational order for the biphenyl fragment. The structure of this moiety was unambiguously determined in all analyses except for the ME method applied on the C13–13C couplings. The RIS approximation failed to discriminate between a large range of possible structures of the ring–chain fragment.
Response to “Comment on ‘The viscoelastic response of Brownian suspensions’ ” [J. Chem. Phys. 114, 3339 (2001)]
Authors: Lowe C. P. , Masters A. J.
Published: July 2002

Our original article presented computer simulation results for the viscoelastic response of a simple model colloidal suspension. We compared our results for the viscosity with a theoretical prediction of Verberg et al. [R. Verberg, I. M. de Schepper, and E. G. D. Cohen, Phys. Rev. E 55, 3143 (1997)] and found poor agreement. It is suggested in the previous comment that a comparison with a modified expression is more appropriate. In response we explain the basis of our comparison and expand on how a different interpretation could be made, leading to an expression of the form Felderhof suggests is appropriate. Nonetheless, as stated in the comment, the agreement with simulation is poor, no matter which of the two possible theoretical expressions is used. We also seek to clarify our position concerning the form of the high frequency response at low volume fraction. Our finding is that the ratio of this to the high frequency response in the zero density limit is not the radial distribution function at contact, as predicted by Verberg et al. [R. Verberg, I. M. de Schepper, M. J. Feigenbaum, and E. G. D. Cohen, J. Stat. Phys. 87, 1037 (1997)], but is a rather smaller quantity.
Analysis of phase locking of tearing modes in reversed field pinch plasmas
Authors: Zanca P. , Martines E. , Bolzonella T. , Cappello S. , Guo S. C. , Martin P. , Martini S. , Ortolani S. , Paccagnella R. , Terranova D. , Viterbo M.
Published: July 2002

The reversed field pinch magnetohydrodynamics (MHD) is characterized by a broad spectrum of interacting resistive tearing modes with poloidal mode number mainly m=0,1. According to the nonlinear coupling theory, the modes phase lock together if their amplitudes exceed a critical value. In the Reversed Field Pinch Experiment (RFX) [L. Fellin et al., Fusion Eng. Des. 25, 315 (1995)] they are always locked in phase, determining a global nonaxisymmetric magnetic perturbation. In this work a detailed experimental characterization of the magnetic perturbation is presented. The typical toroidal profiles and spectra, for both the m=0 and the m=1 components, are shown. In particular the phase relationship under locking conditions between the interacting m=0,1 modes is investigated and compared with the theoretical predictions. The results of three-dimensional (3D) MHD numerical simulations are also discussed.
Estimating the model parameters of deep-level transient spectroscopy data using a combined wavelet/singular value decomposition Prony method
Authors: Younan N. H. , Lee H. S. , Mazzola M. S.
Published: July 2002

In this article, a combined wavelet/singular value decomposition-Prony method to estimate the time constants associated with deep-level transient spectroscopy data is presented. A filtering scheme based on wavelet denoising is used to provide a preprocessing technique that allows the singular value decomposition-Prony method to be applied to transient capacitance data to accurately estimate the associated time constants. Results for both simulated multiple exponential model data with additive white-Gaussian noise and real transient spectroscopy data are presented to illustrate the applicability of the presented technique. Furthermore, the concept of detecting multiple time constants is investigated and a statistical analysis is performed to address the constraints associated with the presented technique to achieve effective detection and estimation.
Theoretical prediction of the Cmca phase in Ge under high pressure
Authors: Ahuja R. , Johansson B.
Published: July 2002

We have performed first-principles self-consistent total-energy calculations within the local-density approximation using the full-potential linear-muffin-tin-orbital method to investigate crystal structures at high pressure in Ge. We predict a crystallographic phase transition from the simple hexagonal structure to the Cmca phase, which is similar to the Si–VI phase which has recently been observed by Hanfland et al. [Phys. Rev. Lett. 82, 1197 (1999)]. Our calculated pressure for this phase transition is around 94 GPa in Ge. Further, at the very high pressure of about 150 GPa, the Cmca phase is predicted to transform into the hexagonal-close-packed phase.
Transport and noise characteristics of submicron high-temperature superconductor grain-boundary junctions
Authors: Herbstritt F. , Kemen T. , Alff L. , Marx A. , Gross R.
Published: July 2002

We have investigated the transport and noise properties of submicron YBa2Cu3O7−δ bicrystal grain-boundary junctions prepared using electron beam lithography. The junctions show an increased conductance for low voltages reminiscent of Josephson junctions having a barrier with high transmissivity. The voltage noise spectra are dominated by a few Lorentzian components. At low temperatures clear two-level random telegraph switching signals are observable in the voltage versus time traces. We have investigated the temperature and voltage dependence of individual fluctuators both from statistical analysis of voltage versus time traces and from fits to noise spectra. A transition from tunneling to thermally activated behavior of individual fluctuators was clearly observed. The experimental results support the model of charge carrier traps in the barrier region.
The birth and development of laser heating in diamond anvil cells
Authors: Bassett William A.
Published: July 2002

In 1968 Taro Takahashi and I observed a phase transition that resulted from laser heating under pressure in a diamond anvil cell. Using a ruby laser, we successfully converted graphite to diamond. We soon realized that the ruby laser had such limited capabilities that we acquired a yttrium–aluminum–garnet (YAG) laser that could be used in both continuous and pulsed modes. The road to successfully applying the technique was not without a few bumps. Thirty years later, these seem more amusing than they did at the time. It was with the YAG laser that Ming and Liu investigated a number of silicate phase transitions important to our understanding of the earth’s mantle. Since then it has been gratifying to watch as others have adopted the technique and made many important contributions with it.
Synchrotron radiation and laser heating in a diamond anvil cell
Authors: Andrault Denis , Fiquet Guillaume
Published: July 2002

The last decade has seen the development of very bright third generation x-ray synchrotron sources that have significantly improved x-ray diffraction experiments at high pressure and high temperature. In the same time, focusing optics as well as detectors have been improved in such a way that x-ray diffraction experiments can be routinely carried out on samples in laser-heated diamond anvil-cell, i.e., under extreme static pressure and temperature conditions. It is now possible to obtain from a laser heated sample in a diamond anvil cell (DAC) very high quality powder patterns, needed for accurate in situ phase boundary and pressure-volume-temperature equation of state determinations, as well as for structural refinements. The setup for in situ x-ray investigation at simultaneous high pressure and temperature is complex, since perfect alignment of x-ray path, infrared-laser hot spot, and optical temperature measurement is required. It provides, however, the most accurate information on the structural behavior with step by step increases of pressure and temperature. In addition, a range of experiments can also be realized at room temperature after laser annealing of DAC samples, which has been shown very efficient in releasing stresses build on compression, and/or overcoming phase transitions kinetic barriers.
Effect of dislocations on the photoluminescence decay of 1.54 μm emission from erbium-doped silicon
Authors: Vernon-Parry K. D. , Evans-Freeman J. H. , Hawkins I. D. , Dawson P. , Peaker A. R.
Published: July 2002

The decay of the photoluminescence at 1.54 μm from erbium-implanted silicon has been recorded over nearly three decades of intensity. Two components of the decay are observed at 7.5 K, one with a decay time constant of ∼40–160 μs, and the other with a characteristic time of between 800 and 1200 μs. It is found that the proportions of fast and slow components can vary depending upon the amount of implantation-induced damage, and this variation correlates with a broadening on the high energy side of the erbium related emission. The temperature dependence of the fastest decay is not consistent with it being due to an Auger process involving free carriers, and it is suggested that extended defects in the layers are responsible for this part of the decay curve. The broadening of the erbium line is attributed to the overlap of the dislocation-related line D1 with the erbium emission. Selective chemical etching and scanning electron microscopy show that there are extended defects present in samples with a short fast decay component.
Thermally stimulated luminescence in porous silicon
Authors: Skryshevskii Yu. A. , Skryshevskii V. A.
Published: July 2002

The low-temperature thermally stimulated luminescence (TSL) in both porous silicon (PS) layers on Si substrate and PS powder has been found in the 4.2–300 K temperature range. The dependence of the TSL effect on the wavelength and temperature of an excitation was studied in detail. The shape of TSL glow curves displays the quasicontinuous spectrum of the electron states in the gap of PS and the activation energy is subject to the linear law of E[eV]=0.0029T−0.14 at T>70 K. For the homogeneous PS powder, the TSL glow curves weakly depend on an excitation wavelength. For the PS layer on Si substrate the maximum of the TSL glow curve shifts to the higher temperature both at the excitation by the short wavelength light and by the supplementary exposition to IR illumination. Such behavior is stipulated by the gradient of the PS energy band gap with the depth and, consequently, by the reconstruction of electron states in the band gap. It is shown that the TSL is conditioned by the photoluminescence (PhL) in PS bulk, and the spectral distribution of the TSL signal at 100–120 K is close to its PhL spectrum excited at 546 nm.
Structural, electrical, and low-frequency-noise properties of amorphous-carbon–silicon heterojunctions
Authors: Hastas N. A. , Dimitriadis C. A. , Patsalas P. , Panayiotatos Y. , Tassis D. H. , Logothetidis S.
Published: July 2002

The structural, electrical, and low-frequency-noise properties of heterojunctions of amor- phous-carbon (a-C) films grown on either n- or p-type single-crystal silicon are investigated. The a-C films were deposited by rf magnetron sputtering at room temperature with varying the substrate bias Vb, from +10 to −200 V. The study includes measurements of x-ray reflectivity (XRR), low-frequency noise at room temperature, and dark current–voltage (I–V) and capacitance–voltage (C–V) characteristics over a wide temperature range. Analysis of the XRR data indicates the presence of a thin SiC layer between a-C and Si, with thickness increasing up to about 1.8 nm for Vb=−200 V. The results show that the noise properties of the devices are independent of the SiC interlayer and the a-C film deposition conditions, while the noise of the a-C/n-Si heterojunctions is about four orders of magnitude lower than that of the a-C/p-Si heterojunctions. Analysis of the I–V and C–V data shows that the rectification properties of the a-C/n-Si heterojunctions are governed by conventional heterojunction theory, while multistep tunneling is the current conduction mechanism in a-C/p-Si heterojunctions due to a high density of interface states.
Efficient molecular photorefractive materials based on methine dyes
Authors: Wang Liming , Ng Man-Kit , Yu Luping
Published: July 2002

This letter reports a series of molecular materials that shows efficient photorefractive effect. The materials which consist of monolithic methine dye molecules can form amorphous films. A net photorefractive gain of 215 cm−1 and a diffraction efficiency of 87.6% at a semiconductor laser wavelength of 780 nm are observed. These materials are the simplest molecular materials and possess the best photorefractive performances. Due to the large photorefractive effect, optical self-defocusing and instability of the laser beam are observed in these materials when the applied electric field is above a threshold.
Radio-frequency based monitoring of small supercurrents
Authors: Il’ichev E. , Zakosarenko V. , Fritzsch L. , Stolz R. , Hoenig H. E. , Meyer H.-G. , Götz M. , Zorin A. B. , Khanin V. V. , Pavolotsky A. B. , Niemeyer J.
Published: July 2002

We consider the applicability of the established rf readout technique, which allows to obtain the supercurrent-phase relation of a Josephson element from impedance measurements in the phase-biased regime. In experiments on Nb-based single and double tunnel junctions, we demonstrate that this method holds even if the Josephson coupling energy is smaller than the thermal energy. Compared with conventional current–voltage measurements, we evaluate the rf technique to be favorable in particular for investigations of small supercurrents in low-capacitance Josephson elements.
A calibration system of O2 consumption and CO2 production for premature infants
Authors: Lin Shih-Ching , Luo Ching-Hsing , Yeh Tsu-Fuh
Published: July 2002

An apparatus to calibrate the system of measuring O2 consumption and CO2 production has been developed for premature infants. This system is based on the alcohol combustion principal. The alcohol combustion is used to test the indirect calorimetric system due to its simplicity and reliability. In the previous studies, the O2 consumption rate of alcoholic combustion is too large to simulate the breath of premature infants. A new design is proposed to burn alcohol continuously at a rate as low as 0.004 ml min−1, equivalent to an O2 consumption rate of only 3.9 ml min−1, a level in the breath range of preterms of about 660 g based on the measurement 5.9 ml kg−1 min−1. The alcohol combusts with various steady-state rates to imitate the breath of premature infants, and it is useful for a canopy open-circuit system. The calibration tool proposed here would be helpful in the clinical study of energy expenditure for preterms.
Spatial variation of luminescence in thick GaN films
Authors: Bertram F. , Srinivasan S. , Ponce F. A. , Riemann T. , Christen J. , Molnar R. J.
Published: July 2002

The spatial variation of the optical properties of hydride vapor-phase epitaxial GaN layers of various thickness has been studied using scanning cathodoluminescence microscopy. A strong improvement of these properties with film thickness is observed in plan view. Cross-sectional studies show a strong redshift of the luminescence in the vicinity of the substrate within a typical thickness of about 2 μm, reflecting a high local impurity content. Above this initial growth region, a strong blueshift is observed up to the energy of fully relaxed high-purity GaN, indicating vertical strain relaxation as well as depletion of residual donors. This is accompanied by a sharp increase in the lateral spectral homogeneity, indicative of a significant improvement in crystalline quality.
Electron beam prepatterning for site control of self-assembled quantum dots
Authors: Borgstrom M. , Johansson J. , Samuelson L. , Seifert W.
Published: July 2002

A site-control technique for individual InAs quantum dots (QDs), formed by self-assembling has been developed, using scanning-electron-microscope assisted nanodeposition and metalorganic vapor phase epitaxy. We find that the nanoscale deposits, created at the focal point of the electron beam on a semiconductor surface, act as “nanogrowth masks”. Growth of a thin epitaxial layer produces nanoholes extending down to the deposits. The carbon deposits can be removed by oxygen plasma etching. When a compressively strained layer is deposited on this surface, QDs are self-organized at the hole sites, while no dots are observed in the flat surface region.
Optimization of electronic-band alignments at ferroelectric (ZnxCd1−x)S/Si(100) interfaces
Authors: Hotta Y. , Rokuta E. , Tabata H. , Kobayashi H. , Kawai T.
Published: July 2002

We have obtained ferroelectric characteristics from nonoxide (ZnxCd1−x)S (x=0.1–0.3) thin films. On the basis of x-ray photoelectron and visible–ultraviolet light absorption spectroscopy measurements, the conduction-band discontinuity at the (ZnxCd1−x)S/Si(100) interfaces is found to vary between 0.4 and 1.3 eV with a change in composition x between 0.1 and 0.9. The leakage current density, which strongly depends on the conduction-band discontinuity, is reduced to less than 10−6 A/cm2 at a gate voltage of 4 V.
Photoinduced surface deformations in ion-conducting Ag–As–S glasses. I. Isotropic deformations produced by small light spots
Authors: Gotoh T. , Tanaka K.
Published: July 2002

Prominent surface deformations appear in Ag–As–S chalcogenide glasses when exposed to focused laser beams. Deformation behaviors change with the beam diameter, the photon energy, the temperature at which illumination is provided, and the sample composition. In thin AgAsS2 films exposed at room temperature to a 2.0 eV light spot with a diameter of 2 μm, an isotropic convex structure with a height of ∼0.1 μm appears. The expanded region accompanies an Ag-content enhancement by ∼3 at. %, which suggests that the deformation is caused by photoinduced accumulation of Ag+ ions.
Electro-optical measurements of picosecond bunch length of a 45 MeV electron beam
Authors: Tsang T. , Castillo V. , Larsen R. , Lazarus D. M. , Nikas D. , Ozben C. , Semertzidis Y. K. , Srinivasan-Rao T. , Kowalski L.
Published: July 2002

We have measured the temporal duration of 45 MeV picosecond electron beam bunches using a noninvasive electro-optical (EO) technique. The amplitude of the EO modulation was found to increase linearly with electron beam charge and decrease inversely with distance from the electron beam. The rise time of the temporal signal was limited by our detection system to ∼70 ps. The EO signal due to ionization caused by the electrons traversing the EO crystal was also observed. It has a distinctively long decay time constant and signal polarity opposite to that due to the field induced by the electron beam. The electro-optical technique may be ideal for the measurement of bunch length of femtosecond, relativistic, high energy, charged, particle beams.