bluuebunny/crossref_metadata_2025 huggingface dataset:
Neutral beams for ITER (invited)a)
Authors: Hemsworth R. S. , Feist J.-H. , Hanada M. , Heinemann B. , Inoue T. , Kussel E. , Krylov A. , Lotte P. , Miyamoto K. , Miyamoto N. , Murdoch D. , Nagase A. , Ohara Y. , Okumura Y. , Paméla J. , Panasenkov A. , Shibata K. , Tanii M. , Watson M.
Published: July 2002

Neutral beam injection has been the most successful scheme used to heat magnetically confined plasmas studied in controlled nuclear fusion research, and neutral beams are a candidate to heat to ignition the International Tokamak Experimental Reactor (ITER). This article describes the system which is presently being designed in Europe, Japan, and Russia, with coordination by the Joint Central Team of ITER at Naka, Japan. The proposed system consists of three negative ion based neutral injectors, delivering a total of 50 MW of 1 MeV D0 to the ITER plasma for pulse length of ≳1000 s. The proposed injectors each use a single caesiated volume arc discharge negative ion source, and a multigrid, multiaperture accelerator, to produce about 40 A of 1 MeV D−. This will be neutralized in a subdivided gas neutralizer, which has a conversion efficiency of about 60%. The charged fraction of the beam emerging from the neutralizer is dumped onto the water-cooled surfaces making up the electrostatic residual ion dump. A water-cooled calorimeter can be moved into the beam path to intercept the neutral beam, allowing commissioning of the injector independent of ITER.
New photothermal cell equipped with Peltier elements for phase transition studies
Authors: Jalink Henk , Frandas Angela , van der Schoor Rob , Bicanic Dane
Published: July 2002

A new universal cell for studies of phase transitions is proposed and its versatility demonstrated with an intact tomato seed as a sample under investigation. The temperature of the sensor head is regulated by computer controlled Peltier elements. The cell allows fully automated recording of temperature (from −35 to 70 °C) profiles. A diode laser (830 nm) was used to generate thermal waves in the sample to observe phase transitions. Pyroelectric materials such as a 9-μm polyvinylidenefluoride foil and a LiTaO3 single crystal were used as detectors. No influence was observed on the noise behavior of the pyroelectric sensors due to the Peltier elements. An important issue was the thermal isolation of the pyroelectric sensor with respect to the environment, i.e., the temperature of the housing had to be stabilized.
Detecting two components of magnetization in magnetic layer structures by use of a photoelastic modulator
Authors: Jordan S. M. , Whiting J. S. S.
Published: July 2002

A magneto-optic Kerr effect system for the measurement of magnetization in thin ferromagnetic layers based on a photoelastic modulator is described. The use of a quarter wave plate allows light with a variable polarization incident on the sample to be used. The polarization of the light as it passes through the system is treated algebraically using a matrix approach. A procedure for determining both the magneto-optic (MO) rotation presented by the sample and the traditional ellipsometric parameters is described, the consistency of the solutions being demonstrated by experiment. Typical MO rotation versus thickness curves for thin films of Permalloy (Ni79Fe21) deposited on glass for both the longitudinal and transverse field configurations are presented. These results demonstrate that the magnitude and sign (in the transverse case) of the MO rotation is strongly dependent on thickness for films thinner than 200 Å.
A CCD based approach to high-precision size and refractive index determination of levitated microdroplets using Fraunhofer diffraction
Authors: Barnes M. D. , Lermer N. , Whitten W. B. , Ramsey J. M.
Published: July 2002

We describe a fast and convenient method of high precision size and refractive index determination of electrodynamically levitated microdroplets using Fraunhofer diffraction. The diffraction data were obtained with a 16-bit, unintensified charge coupled device (CCD) camera, and converted into angle-resolved elastic scattering intensity patterns by means of a carefully determined set of transformation parameters. The angular scattering patterns were analyzed without any a priori estimate of the droplet size and only a nominal estimate (≈2%) of the refractive index. Experimental angular scattering patterns were fit to calculated patterns from Mie theory using a graded step-size and scaling algorithm and optimized with respect to both droplet diameter and refractive index (real part only) with a precision of ⩽3 parts in 104 and 1 part in 103, respectively. Potential application to quantitative fluorescence and Raman spectroscopy, as well as mixture analysis in microdroplets is discussed.
Design considerations for a three dimensional fiber optic laser Doppler velocimeter for turbomachinery applications
Authors: James Stephen W. , Tatam Ralph P. , Elder Robin L.
Published: July 2002

Single headed three dimensional (3D) laser Doppler velocimetry (LDV) geometries generally rely upon the use of three Doppler difference channels, inclined at differing angles with respect to the mechanical axes of the probe. The transformation between the nonorthogonal measurement coordinate system and the Cartesian system can result in large errors in the calculated velocities. A theoretical analysis of the geometrically induced uncertainties in measurements produced by four single headed 3D LDV configurations is presented. These considerations have lead to the development of a single headed fiber optic 3D LDV probe based on the use of two Doppler difference channels to directly measure the transverse velocity components, and a reference beam channel to measure the on axis velocity component. The f/4 probe head has a working distance of 200 mm, designed to operate within the constraints of the limited optical access available in turbomachinery applications.
Improved dc SQUID read-out electronics with low 1/f noise preamplifier
Authors: Drung Dietmar
Published: July 2002

An improved read-out electronics without flux modulation for dc superconducting quantum interference devices (dc SQUIDs) is presented where the preamplifier is directly coupled to the SQUID. Compared to our previous designs, the 1/f voltage and current noise levels of the preamplifier were reduced by about a factor of 4 (rms) by using bipolar matched transistors instead of operational amplifiers at the input. Three types of flux-locked-loop electronics were developed and successfully tested: a low-power (120 mW) version for large multichannel arrays, a high-speed version with a 15 MHz bandwidth and a very fast (300 ns) reset mode, and a low-noise (0.44 nV/Hz) version with a fast and precise bias reversal circuit. The flux-locked-loop electronics are compatible with each other, so that only one type of low-power (180 mW) control unit is required to operate them. All essential specifications of practical SQUID systems (noise, dynamic behavior, and temperature stability) were determined by using liquid-helium and liquid-nitrogen cooled SQUIDs, respectively.
Using a light-emitting diode as a high-speed, wavelength selective photodetector
Authors: Miyazaki Eiichi , Itami Shin , Araki Tsutomu
Published: July 2002

A light-emitting diode (LED) can function as a wavelength selective photodetector. To evaluate the potential for a LED-based photodetector, we have investigated the stationary and temporal characteristics of two kinds of LEDs: a Zn-doped InGaN blue LED and a GaAlAs red LED. The application of a high current produced two peaks on the emission spectra of the blue LED, at 380 and 450 nm. The extinction profile of the blue LED was consistent with its UV-emission profile. The red LED showed an emission peak at 660 nm and an extinction peak at 620 nm. The LED-based photodetector responded within nanoseconds of the onset of the light impulse. The application of a reverse bias to the LED caused the time spread of the output current wave form to decrease dramatically and was accompanied by an increase in peak height. At a 75 V reverse bias, the resultant pulse widths were 2.6 ns in the blue LED and 7.4 ns in red LED.
Calibration of the JET neutron activation system for DT operation
Authors: Bertalot L. , Roquemore A. L. , Loughlin M. , Esposito B.
Published: July 2002

The neutron activation system at JET is a pneumatic transfer system capable of positioning activation samples close to the plasma. Its primary purpose is to provide a calibration for the time-dependent neutron yield monitors (fission chambers and solid state detectors). Various activation reactions with different high energy thresholds were used including Fe56(n,p) Mn56, Al27(n,α) 24Na, 93Nb(n,2n) 92mNb, and Si28(n,p) 28Al reactions. The silicon reaction, with its short half life (2.25 min), provides a prompt determination of the 14 MeV DT yield. The neutron induced γ-ray activity of the Si samples was measured using three sodium iodide scintillators, while two high purity germanium detectors were used for other foils. It was necessary to use a range of sample masses and different counting geometries in order to cover the wide range of neutron yields (1015–1019 neutrons) while avoiding excessive count rates in the detectors. The absolute full energy peak efficiency calibration of the detectors was measured taking into account the source-detector geometry, the self-attenuation of the samples and cross-talk effects. An error analysis of the neutron yield measurement was performed including uncertainties in efficiency calibration, neutron transport calculations, cross sections, and counting statistics. Cross calibrations between the different irradiation ends were carried out in DD and DT (with 1% and 10% tritium content) discharges. The effect of the plasma vertical displacement was also experimentally studied. An agreement within 10% was found between the 14 MeV neutron yields measured from Si, Fe, Al, Nb samples in DT discharges.
Temperature-compensated meteorological barometer
Authors: Harrison R. G.
Published: July 2002

Meteorological measurements of surface pressure to better than 1 mbar are routinely required in surface pressures of typically 1000 mbar, and detecting small pressure changes is important for forecasting. An inexpensive pressure sensor provides the basis of a barometer suitable for such general meteorological use. Signal-conditioning circuitry has been added to allow typical surface sea-level pressure variations to be resolved to 0.1 mbar using a ±5 V 12-bit analog to digital system. The sensor excitation voltage is shown to track the sensor’s temperature closely, and this is extracted to provide a temperature-compensation signal. When combined with a nonlinearity correction system and a digital display, this gives a portable barometer capable of reading to ±0.5 mbar (over the range of 930–1020 mbar) for temperatures between 0 and 25 °C. The final display reading includes the temperature compensation by using a panel meter in ratio mode.
High-speed atomic force microscopy in liquid
Authors: Sulchek T. , Hsieh R. , Adams J. D. , Minne S. C. , Quate C. F. , Adderton D. M.
Published: July 2002

High-speed constant force imaging with the atomic force microscope (AFM) has been achieved in liquid. By using a standard optical lever AFM, and a cantilever with an integrated zinc oxide (ZnO) piezoelectric actuator, an imaging bandwidth of 38 kHz has been achieved; nearly 100 times faster than conventional AFMs. For typical samples, this bandwidth corresponds to tip velocities in excess of 3 mm/s. High-speed AFM imaging in liquid will (1) permit chemical and biological AFM observations to occur at speeds previously inaccessible, and (2) significantly decrease measurement times in standard AFM liquid operation.
Dynamics of damped cantilevers
Authors: Rast S. , Wattinger C. , Gysin U. , Meyer E.
Published: July 2002

In atomic force microscopy cantilevers are used to detect forces caused by interactions between probing tip and sample. The minimum forces which can be detected with commercial sensors are typically in the range of 10−12 N. In the future, the aim will be to construct sensors with improved sensitivities to detect forces in the range of 10−18 N. These sensors could be used for mass spectroscopy or magnetic resonance force microscopy. Achieving this goal requires smaller sensors and increased quality factor Q. In this article we describe a model to characterize the dynamics of cantilevers of each eigenmode. In contrast to previous models, the damping is treated rigorously in the calculations.
Polarization dependent recordings of surface relief gratings on azobenzene containing polymer films
Authors: Jiang X. L. , Li L. , Kumar J. , Kim D. Y. , Shivshankar V. , Tripathy S. K.
Published: July 2002

Experimental studies on the recording of surface relief gratings on azobenzene containing polymer films using laser beams with different polarizations were carried out. The results indicate that the localized variations of light intensity and alternation of the resultant electric field polarization in the film are essential to the formation of the surface relief gratings.
Noncontact measurement of transport properties of long-bulk-carrier-lifetime Si wafers using photothermal radiometry
Authors: Salnick Alex , Mandelis Andreas , Jean Claude
Published: July 2002

A theoretical model for the photothermal radiometric signal from semiconductors of finite thickness has been used to measure simultaneously the carrier diffusion coefficient, carrier lifetime, and surface recombination velocity of FZ Si wafers with very long bulk carrier lifetimes (industrial microelectronic grade). The results showed the importance of accounting for the finite thickness of the substrate in obtaining accurate measurements of these parameters using the entirely noncontacting radiometric approach.
Minority-carrier injection-enhanced annealing of radiation damage to InGaP solar cells
Authors: Yamaguchi Masafumi , Okuda Takeshi , Taylor Stephen J.
Published: July 2002

The observation of minority-carrier injection-enhanced annealing of radiation-induced defects in InGaP is reported. 1-MeV electron irradiation results demonstrate superior radiation-resistance of InGa0.5P0.5 solar cells compared to GaAs-on-Ge cells. Moreover, minority-carrier injection under forward bias conditions is shown to enhance defect annealing in InGaP and to result in the recovery of InGaP solar cell properties. These results suggest that the radiation-resistance of InGaP-based devices such as InGaP/GaAs(/Ge) multijunction solar cells and InGaP(As) light-emitting devices is further improved under minority-carrier injection condition.
Contrast of microwave near-field microscopy
Authors: Knoll B. , Keilmann F. , Kramer A. , Guckenberger R.
Published: July 2002

Constant-height scanning is demonstrated to improve near-field microscopy by eliminating artifacts connected with topography scanning, hence, to image the inherent electromagnetic contrast. Microwaves are chosen for this study because the long wavelength eliminates coherence artifacts, owing to a scale separation of wave and image frequencies. Measured amplitude and phase images of conductive films are quantitatively analyzed by considering the longitudinal electric near field. The observed spatial resolution of 200 nm equals the probing tip size and proves that the skin depth δ of the tip material (here, 1600 nm) presents no resolution limit to scanning optical microscopy.
III–V based magnetic(GaMnAs)/nonmagnetic(AlAs) semiconductor superlattices
Authors: Hayashi T. , Tanaka M. , Seto K. , Nishinaga T. , Ando K.
Published: July 2002

III–V based magnetic (GaMnAs)/nonmagnetic(AlAs) semiconductor superlattices (SLs) have been grown by low-temperature molecular beam epitaxy. X-ray diffraction measurements show that the SLs have good crystalline quality and abrupt interfaces. The SLs having relatively wide (Ga,Mn)As layers (⩾70 Å) are found to be ferromagnetic at low temperatures, while the SLs with narrow (Ga,Mn)As layers (⩽50 Å) are paramagnetic even at 2.0 K. Magneto-optic spectra have revealed that, due to the quantum confinement effect, the interband transition energy at Γ is blue shifted with decreasing the thickness of the (Ga,Mn)As and some subbands are formed.
Photowritten optical waveguides in various glasses with ultrashort pulse laser
Authors: Miura K. , Qiu Jianrong , Inouye H. , Mitsuyu T. , Hirao K.
Published: July 2002

We show that permanent optical waveguides can be formed in various bulk glasses by photoinduced refractive index change with an ultrashort pulse laser. The waveguides were fabricated by focusing the laser beam through an microscope objective and translating the sample parallel to the axis of the laser beam. From the observations of intensity distributions in the output of guided light by a CCD camera, we demonstrated that permanent optical waveguides can be successfully formed in various glasses. In addition, from the analysis of a near-field pattern, it was confirmed that single mode waveguides of the graded index type can be formed by a writing technique using the ultrashort pulse laser.
Theory of a self-assembled quantum-dot semiconductor laser with Auger carrier capture: Quantum efficiency and nonlinear gain
Authors: Uskov A. V. , Boucher Y. , Le Bihan J. , McInerney J.
Published: July 2002

We analyze a self-assembled quantum-dot laser where lasing levels are pumped purely through Auger carrier capture. Analysis shows that Auger carrier capture and Auger transport of carriers between quantum dots can provide effective laser pumping and fast modulation at least up to 10 GHz. Auger carrier transport decreases spectral hole burning, which together with dot-barrier hole burning can damp relaxation oscillations.
Layered tunnel barriers for nonvolatile memory devices
Authors: Likharev Konstantin K.
Published: July 2002

Fowler–Nordheim tunneling of electrons through “crested” energy barriers (with the height peak in the middle) is much more sensitive to applied voltage than that through barriers of uniform height. Calculations for trilayer barriers, with layer parameters typical for wide-band-gap semiconductors, have shown that by merely doubling the voltage, the tunnel current may be changed by more than 16 orders of magnitude. It is argued that this effect may be used for the implementation of nonvolatile random-access memories combining a few ns cycle time with a few years retention time and for ultradense electrostatic data storage.
Diamond/Ir/SrTiO
3
:
A material combination for improved heteroepitaxial diamond films
Authors: Schreck M. , Roll H. , Stritzker B.
Published: July 2002

Heteroepitaxial diamond films with highly improved alignment have been realized by using the layer sequence diamond/Ir/SrTiO3(001). In a first step, epitaxial iridium films with a misorientation <0.2° have been deposited on polished SrTiO3(001) surfaces by electron-beam evaporation. Using the bias-enhanced nucleation procedure in microwave plasma chemical vapor deposition, epitaxial diamond grains with a density of 109 cm−2 could be nucleated on these substrates. The orientation relationship for this layer system is diamond(001)[100]∥Ir(001)[100]∥SrTiO3(001)[100]. The polar and azimuthal spread for the crystal orientation of a 600 nm thick diamond film is about 1° in each case. For an 8 μm thick diamond film a significantly improved alignment of 0.34° (polar) and 0.65° (azimuthal) has been measured. The latter values, which to the best of our knowledge are superior to those of all former reports about epitaxial diamond films on alternative substrates, indicate the high potential of the substrate Ir/SrTiO3 for the realization of large-area single-crystalline diamond films.
Silicon microcolumn arrays grown by nanosecond pulsed-excimer laser irradiation
Authors: Pedraza A. J. , Fowlkes J. D. , Lowndes D. H.
Published: July 2002

Arrays of high aspect ratio silicon microcolumns that protrude well above the initial surface have been formed by cumulative nanosecond pulsed-excimer laser irradiation of silicon. Microcolumn growth is strongly affected by the gas environment, being enhanced in air or other oxygen-containing ambient. It is proposed that microcolumn growth occurs through a combination of pulsed-laser melting of the tips of the columns and deposition of silicon from the intense flux of silicon-rich vapor produced by ablation of the surface regions between columns. The molten tips of the columns are strongly preferred sites for deposition, resulting in a very high axial growth rate. The growth process is conceptually similar to the vapor–liquid–solid method used to grow silicon whiskers. However, in the present case the pulsed-laser radiation fulfills two roles almost simultaneously, viz., providing the flux of silicon-containing molecules and melting the tips of the columns.
Amorphous silicon transistors on ultrathin steel foil substrates
Authors: Ma Eugene Y. , Wagner Sigurd
Published: July 2002

Thin-film transistors of hydrogenated amorphous silicon (a-Si:H) were fabricated on foils of stainless steel with thickness ranging down to 3 μm, which is less than three times the thickness of the deposited films. Transistors made on foils from 3 to 200 μm thick exhibit comparable electrical performance. Two factors account for the feasibility of such thin device/substrate structures. One is that the built-in stress and the differential thermal contraction stress nearly cancel each other in steel/a-Si:H structures. The other is that on very thin foils the transistor structure offloads part of its strain to the steel foil.
Enhanced room-temperature magnetoresistance in partially melted La0.67Ca0.33MnO3 manganites
Authors: Pradhan A. K. , Roul B. K. , Wen J. G. , Ren Z. F. , Muralidhar M. , Dutta P. , Sahu D. R. , Mohanty S. , Patro P. K.
Published: July 2002

We have performed magnetic and transport measurements on La0.67Ca0.33MnO3 polycrystalline and partially melted samples. The magnetization and resistance decrease as sintering temperature is increased. The insulator-to-metal transition temperature is remarkably enhanced in the partially melted sample, enabling its possible applications at room temperature. The microscopic studies in melt samples show an excellent connectivity between grains, suggesting the enhancement of percolative transport by opening new conduction channels and the disappearance of magnetic phase boundary at elevated temperature by the ordering of Mn spins blocked at the grain boundary of sintered samples.
Dislocation scattering in a two-dimensional electron gas
Authors: Jena Debdeep , Gossard Arthur C. , Mishra Umesh K.
Published: July 2002

A theory of scattering by charged dislocation lines in a two-dimensional electron gas (2DEG) is developed. The theory is directed towards understanding transport in AlGaN/GaN high-electron-mobility transistors which have a large number of line dislocations piercing through the 2DEG. The scattering time due to dislocations is derived for a 2DEG in closed form. This work identifies dislocation scattering as a mobility-limiting scattering mechanism in 2DEGs with high dislocation densities. The insensitivity of the 2DEG (as compared to bulk) to dislocation scattering is explained by the theory.
Mobility enhancement in conjugated polymer field-effect transistors through chain alignment in a liquid-crystalline phase
Authors: Sirringhaus H. , Wilson R. J. , Friend R. H. , Inbasekaran M. , Wu W. , Woo E. P. , Grell M. , Bradley D. D. C.
Published: July 2002

A method is demonstrated by which liquid-crystalline self-organization in rigid-rod nematic conjugated polymers can be used to control the microstructure of the active semiconducting layer in solution-processed polymer thin-film transistors (TFTs). Enhanced charge carrier mobilities of 0.01–0.02 cm2/V s and good operating stability have been achieved in polyfluorene copolymer TFTs by preparing the polymer in a nematic glassy state and by aligning the polymer chains parallel to the transport direction with the help of an alignment layer. Mobility anisotropies of 5–8 for current flow parallel and perpendicular to the alignment direction have been observed that are of the same order of magnitude as optical dichroic ratios.
Precipitation of icosahedral quasicrystalline phase in Hf65Al7.5Ni10Cu12.5Pd5 metallic glass
Authors: Li Chunfei , Saida Junji , Matsushita Mitsuhide , Inoue Akihisa
Published: July 2002

An icosahedral quasicrystalline phase was found in a Hf65Al7.5Ni10Cu12.5Pd5 metallic glass annealed in the supercooled liquid region. Upon annealing at high temperature, the quasicrystalline phase was found to decompose to regular crystalline phases, indicating that it is a metastable phase. The present alloy was compared with the previously reported Zr- and Ti-based alloys with the formation of icosahedral quasicrystalline phases. Hf, Zr, and Ti belong to the same 4A column in the element periodical table. Based on the above comparison, conditions in terms of atomic radius and alloy composition which favor the formation of icosahedral quasicrystalline phase in 4A element based alloys, were suggested.
Time–temperature–transformation diagram and microstructures of bulk glass forming Pd40Cu30Ni10P20
Authors: Löffler Jörg F. , Schroers Jan , Johnson William L.
Published: July 2002

Isothermal crystallization studies were performed on the bulk glass forming alloy Pd40Cu30Ni10P20 in the undercooled liquid region between the glass transition and liquidus temperature, resulting in a complete time–temperature–transformation (TTT) diagram for crystallization. The TTT diagram shows a typical “C” shape with the nose at 50 s and 680 K. Assuming steady state nucleation and a diffusion-controlled growth rate, the TTT diagram was successfully fit over the entire range of the measurement. The microstructure after isothermal crystallization shows a modulation in Cu and P for all degrees of undercooling. The primary solidified phase is Cu3Pd, which forms distinct dendrites at low undercooling. From additional constant cooling experiments, the critical cooling rate to bypass crystallization was determined to be 0.33 K/s.
Extended corresponding-states behavior for particles with variable range attractions
Authors: Noro Massimo G. , Frenkel Daan
Published: July 2002

We propose an extension of the law of corresponding states that can be applied to systems—such as colloidal suspensions—that have widely different ranges of attractive interactions. We argue that the “reduced” second virial coefficient is a convenient parameter to quantify the effective range of attraction. Knowledge of the pair-potential alone allows one to estimate the relative location of the liquid–vapor and solid–fluid coexistence curves.
SmNi
4
B
:
A narrow domain-wall ferromagnet
Authors: Mazumdar Chandan , Nagarajan R. , Gupta L. C. , Padalia B. D. , Vijayaraghavan R.
Published: July 2002

We have investigated magnetic properties of SmNi4B. The material undergoes a ferromagnetic ordering at TC≈39 K, which, surprisingly, is higher than that of isostructural GdNi4B (≈36 K). The saturation magnetic moment is rather small (0.15 μB per Sm at 5 K), suggesting the presence of crystal-field effects. Below TC, the material exhibits a large thermomagnetic irreversibility and also a large magnetic hysteresis at 5 K with a coercive field ≈28 kOe, which is one of the largest observed in a Sm-based material. We suggest that the large coercive field is intrinsic, associated with narrow domain walls of thickness of only one atomic layer, which resembles a ferroelectric wall.
Quantum stochastic differential equation for unstable systems
Authors: Belavkin V. P. , Staszewski P.
Published: July 2002

A semiclassical non-Hamiltonian model of a spontaneous collapse of unstable quantum system is given. The time evolution of the system becomes non-Hamiltonian at random instants of transition of pure states to reduced ones, η⟼Cη, given by a contraction C. The counting trajectories are assumed to satisfy the Poisson law. A unitary dilation of the concractive stochastic dynamics is found. In particular, in the limit of frequent detection corresponding to the large number limit we obtain the Itô–Schrödinger stochastic unitary evolution for the pure state of unstable quantum system providing a new stochastic version of the quantum Zeno effect.
Direct calculation of permeability and permittivity for a left-handed metamaterial
Authors: Smith D. R. , Vier D. C. , Kroll N. , Schultz S.
Published: July 2002

Recently, an electromagnetic metamaterial was fabricated and demonstrated to exhibit a “left-handed” (LH) propagation band at microwave frequencies. A LH metamaterial is one characterized by material constants—the permeability and permittivity—which are simultaneously negative, a situation never observed in naturally occurring materials or composites. While the presence of the propagation band was shown to be an inherent demonstration of left handedness, actual numerical values for the material constants were not obtained. In the present work, using appropriate averages to define the macroscopic fields, we extract quantitative values for the effective permeability and permittivity from finite-difference simulations using three different approaches.
Meyer–Neldel rule in amorphous strontium titanate thin films
Authors: Morii K. , Matsui T. , Tsuda H. , Mabuchi H.
Published: July 2002

In this letter, we report the experimental result indicating that the electrical conductivity in thin films of amorphous strontium titanate (a-STO) is well fit to the Meyer–Neldel (MN) rule over the temperature range 300–470 K. The films were ion-beam sputtered and annealed in two different atmospheres: a vacuum and flowing oxygen. The MN plots for the films show two parallel straight lines depending on the annealing atmosphere, which give the identical MN parameters of about 35 meV with the conductivity prefactors of 9.3×10−10 and 2.3×10−14(Ω cm)−1 for the vacuum- and oxygen- annealed films, respectively.
Efficient photovoltaic energy conversion in pentacene-based heterojunctions
Authors: Schön J. H. , Kloc Ch. , Batlogg B.
Published: July 2002

We have prepared heterojunction devices based on ZnO and both pentacene single crystals and thin films. Their photovoltaic properties have been studied. Bromine doping is found to improve significantly the performance of such devices and solar-energy conversion efficiencies up to 4.5% are achieved for single-crystal devices. In addition, efficiencies exceeding 2% are realized in thin-film devices on flexible plastic substrates. These results demonstrate that efficient photovoltaic energy conversion is possible with organic semiconductors.
Influence of Ti on CoSi2 nucleation
Authors: Detavernier C. , Van Meirhaeghe R. L. , Cardon F. , Maex K. , Vandervorst W. , Brijs B.
Published: July 2002

Evidence is presented that impurities present in the precursor phase may influence the nucleation of a new phase. In case of the CoSi→CoSi2 transition, it is found that the presence of small amounts of Ti (originating from either a Ti capping layer or interlayer) causes an increase in the CoSi2 nucleation temperature. Moreover, for an increasing amount of Ti, we observed a transition from polycrystalline CoSi2 over preferential (220) orientation towards epitaxial (400) CoSi2. The model that we propose entails a new point of view on the mechanism of Ti interlayer mediated epitaxy.
Neutral velocity distribution at a negatively biased electrode in a collisional ion sheath
Authors: Mukherjee S.
Published: July 2002

This paper reports on the planar one-dimensional theoretical estimation of neutral velocity distribution at a negatively biased electrode. The pressure is chosen to be high (∼few Torr) so that the ion sheath is collisional with charge exchange being the dominant collision mechanism. This collision leads to a distribution of ion velocities at the electrode and also generates a large number of energetic neutrals inside the ion sheath that bombards the electrode. Depending on the place of their generation inside the ion sheath, the neutrals have a distribution of velocities at the electrode. The theory indicates that the peak of the neutral velocity distribution shifts to lower velocities as pressure increases. It also indicates that in such collisional ion sheaths, the neutrals deposit more momentum and kinetic energy on the negatively biased electrode than the ions.
Statistical mechanics with three-dimensional particle tracking velocimetry experiments in the study of anomalous dispersion. I. Theory
Authors: Cushman John H. , Moroni Monica
Published: July 2002

Eulerian models developed to simulate dispersion in fluid mechanics often consider the flux of the contaminant species to be proportional to the concentration gradient via a constant or time-dependent dispersion coefficient. These models are crude approximations for systems with velocity fluctuations evolving over a hierarchy of scales on the scale of observation. We say a system behaves in a Fickian fashion if the dispersion coefficient is constant, it is quasi-Fickian if the dispersion coefficient is time dependent, and it is convolution-Fickian if the flux is a convolution. The fractional flux in the sense of fractional derivatives is a special case of a convolution-Fickian flux. More general forms of the flux are possible, and in any case we call all fluxes anomalous if there is not a constant coefficient of proportionality between the flux and the gradient of concentration. In paper I of this two-part sequence we present a theory with statistical mechanical origins for simulating anomalous dispersion. Under appropriate limiting conditions the theory gives rise to Fickian, quasi-Fickian, convolution-Fickian, and fractional-Fickian fluxes. The primary result is a dispersive flux of integral type which in its most general form is not a convolution on time (it is non-Markovian however), but it is always a convolution in space. The concentration is represented by the inverse Fourier transform of the self-part of the intermediate scattering function. In paper II we present an experimental procedure that uses this theory to examine if and when the Fickian limit is reached in porous media homogeneous on the Darcy-scale but heterogeneous on the pore-scale.
Free-standing films of PbSc0.5Ta0.5O3 for uncooled infrared detectors
Authors: Fuflyigin V. , Salley E. , Vakhutinsky P. , Osinsky A. , Zhao J. , Gergis I. , Whiteaker K.
Published: July 2002

Highly textured PbSc0.5Ta0.5O3 (PST) films were grown on (111) Pt/Si by the sol–gel technique. The PST films were subsequently lifted off the silicon substrate using reactive ion etching. A 40%–50% increase in dielectric constant and pyroelectric coefficient was observed for suspended films compared to those properties of the PST films on a Si substrate. Typical values of the pyroelectric coefficient were measured to be 20–45 nC/(cm2 K) for 200–300 nm thick PST films. The loss tangent values were below 0.02 (at 10 kHz), and the leakage current density was as low as 2–3×10−8 A/cm2 at 1 V bias.
Microwave transmission through a two-dimensional, isotropic, left-handed metamaterial
Authors: Shelby R. A. , Smith D. R. , Nemat-Nasser S. C. , Schultz S.
Published: July 2002

We present experimental data, numerical simulations, and analytical transfer-matrix calculations for a two-dimensionally isotropic, left-handed metamaterial (LHM) at X-band microwave frequencies. A LHM is one that has a frequency band with simultaneously negative εeff(ω) and μeff(ω), thereby having real values of index of refraction and wave vectors, and exhibiting extended wave propagation over that band. Our physical demonstration of a two-dimensional isotropic LHM will now permit experiments to verify some of the explicit predictions of reversed electromagnetic-wave properties including negative index of refraction as analyzed by Veselago [Usp. Fiz. Nauk 92, 517 (1964), Sov. Phys. Usp. 10, 509 (1968)].
Solvation in high-temperature electrolyte solutions. III. Integral equation calculations and interpretation of experimental data
Authors: Chialvo A. A. , Kusalik P. G. , Cummings P. T. , Simonson J. M.
Published: July 2002

The solvation of infinitely dilute aqueous Cl−, Br−, I−, Cs+, K+, M+, and the corresponding salts is analyzed by integral equation calculations along three near critical water isotherms according to the recently proposed molecular-based formalism which connects the solvent environment around individual ionic species with their macroscopic solvation behavior. Special emphasis is placed on the temperature dependence of some solvation-related macroscopic properties that are identified as potential candidates for the development of improved engineering correlations. Formal and integral equation calculations are then used to interpret recent experimental data, and some relevant theoretical implications regarding the modeling of high-temperature aqueous electrolyte solutions are discussed.
Neutron confinement cell for investigating complex fluids
Authors: Kuhl Tonya L. , Smith Gregory S. , Israelachvili Jacob N. , Majewski Jaroslaw , Hamilton William
Published: July 2002

We describe an apparatus for measuring the molecular density and orientation of confined, ultrathin complex fluids under static and dynamic flow conditions. The device essentially couples the utility of the surface forces apparatus—ability to control surface separation and alignment under applied loads—with in situ structural characterization of the intervening material utilizing neutron reflectivity measurements. The apparatus is designed such that single crystal substrates of quartz or sapphire with areas up to tens of square centimeters can be kept parallel at controlled and well-defined separations from millimeters to less than 100 nm. The large substrate surface area enables direct structural measurements of the density profile of “soft” material placed between the aligned substrates. In addition, the cell is also designed to enable steady shear rates from 0.001 to 20 Hz to be applied in order to follow the dynamic structural response of the confined material, especially at the solid-solution interface. Faster shear rates of order 104 can be obtained using oscillatory motion. Current design specifications focus on the use of neutron reflectivity to characterize the structure of end-grafted polymer brush layers, but the device can be employed to probe the structure of any complex fluid of interest and is amenable to other characterization techniques.
Directional lasing oscillation of two-dimensional organic photonic crystal lasers at several photonic band gaps
Authors: Notomi M. , Suzuki H. , Tamamura T.
Published: July 2002

We fabricated a series of two-dimensional (2D) hexagonal organic photonic-crystal lasers whose lattice constant varies from 0.18 to 0.44 μm, and observed clear lasing oscillation at the four lowest band gap frequencies (M1, K2, M2, and Γ1). We used in-plane beam propagation analysis to clarify the 2D feedback mechanism at each gap frequency, which differs for different gaps. The observed K1 lasing oscillation is due to coupling of three nonparallel diffracted waves, which has a purely 2D character. This shows that photonic crystal lasers can operate with various feedback essentially different from that of conventional 1D distributed feedback lasers.
Stimulated photon cascade and condensate in a relativistic laser-plasma interaction
Authors: Mima K. , Jovanović M. S. , Sentoku Y. , Sheng Z.-M. , Škorić M. M. , Sato T.
Published: July 2002

The propagation of a linearly polarized relativistic laser pulse in an underdense plasma is studied by fluid-Maxwell and particle-in-cell simulations. A nonlinear interplay between backward and forward stimulated Raman scattering instabilities produces a strong spatial modulation of the light pulse and the down cascade in its frequency spectrum. The Raman cascade saturates by a unique photon condensation at the bottom of the light spectra near the electron plasma frequency, related to strong depletion and possible break-up of the laser beam. In the final stage of the cascade-into-condensate mechanism, the depleted downshifted laser pulse is gradually transformed into a train of ultra-short relativistic light solitons.
Contamination-free sounding rocket Langmuir probe
Authors: Amatucci W. E. , Schuck P. W. , Walker D. N. , Kintner P. M. , Powell S. , Holback B. , Leonhardt D.
Published: July 2002

A technique for removing surface contaminants from a sounding rocket spherical Langmuir probe is presented. Contamination layers present on probe surfaces can skew the collected data, resulting in the incorrect determination of plasma parameters. Despite following the usual probe cleaning techniques that are used prior to a launch, the probe surface can become coated with layers of adsorbed neutral gas in less than a second when exposed to atmosphere. The laboratory tests reported here show that by heating the probe from the interior using a small halogen lamp, adsorbed neutral particles can be removed from the probe surface, allowing accurate plasma parameter measurements to be made.
Automated resonant mechanical analyzer
Authors: Bonetti E. , Campari E. G. , Pasquini L. , Savini L.
Published: July 2002

An automatic vibrating reed apparatus for internal friction and elastic modulus measurements in solids is described. The apparatus is equipped with a resistive heater for measurements up to 1400 K. A magnetic field (up to 250 kAt/m) is also available in the 300–1000 K range. Measurements as a function of temperature and/or magnetic field can be easily carried out. Data acquisition is controlled by a computer and originally written software allows automatic measurements and real time data analysis offering a user-friendly interface. The acquisition rate is nearly two orders of magnitude faster than that achieved manually. The use of the analyzer is straightforward and does not require a prolonged training of particularly skillful personnel.
Rotational dynamics of coumarins: An experimental test of dielectric friction theories
Authors: Dutt G. B. , Raman Sumathi
Published: July 2002

Rotational dynamics of three structurally similar coumarins; coumarin 6, coumarin 7, and coumarin 30 has been studied using a steady-state fluorescence depolarization technique. The idea is to understand how the friction experienced by a polar solute in a polar solvent depends on its dipole moment. Ab initio molecular orbital methods have been used to calculate the ground and excited state dipole moments. Although these coumarins are structurally similar their excited state dipole moments are quite different. Because of their similarity in shape and size they experience almost identical friction in alkanes, which is purely mechanical. However, in alcohols, the observed reorientation times do not follow the trend predicted by the dielectric friction theories of Nee–Zwanzig and van der Zwan–Hynes, based on their dipole moment values. Plausible reasons for the observed trend are discussed.
Quaternionic differential operators
Authors: De Leo Stefano , Ducati Gisele
Published: July 2002

Motivated by a quaternionic formulation of quantum mechanics, we discuss quaternionic and complex linear differential equations. We touch only a few aspects of the mathematical theory, namely the resolution of the second order differential equations with constant coefficients. We overcome the problems coming out from the loss of the fundamental theorem of the algebra for quaternions and propose a practical method to solve quaternionic and complex linear second order differential equations with constant coefficients. The resolution of the complex linear Schrödinger equation, in the presence of quaternionic potentials, represents an interesting application of the mathematical material discussed in this paper.
Optical parametric generation of femtosecond pulses up to 9 μm with LiInS2 pumped at 800 nm
Authors: Rotermund F. , Petrov V. , Noack F. , Isaenko L. , Yelisseyev A. , Lobanov S.
Published: July 2002

We demonstrate direct access to the 4.8–9 μm spectral region with 800 nm, 1 kHz pumping of a femtosecond optical parametric amplifier based on the wide-gap wurtzite-type LiInS2. LiInS2 did not exhibit two-photon absorption at 800 nm and seems applicable at this pump wavelength with intensities of the order of 100 GW/cm2 for down-conversion of high energy ultrashort pulses up to its mid-IR edge at ≈12 μm.
Energetics of vacuum arc cathode spots
Authors: Anders André
Published: July 2002

Vacuum arcs need to generate the current-carrying plasma at cathode spots. The cohesive energy of the cathode material determines the energy the arc needs to provide for the phase transitions of the cathode material. As recent experiments confirm, the greater the cohesive energy the higher the burning voltage (“cohesive energy rule”). This relation is founded in the energy balance of cathode spot operation, regardless of the specific cathode mechanisms involved. A greater power input, as determined by the cohesive energy via the cohesive energy rule, leads to enhanced power output in various forms such as enhanced electron temperature, ion charge states, and ion velocity. Using the Cohesive Energy Rule, secondary relations such as the well known relation between boiling point of the cathode and average ion charge state can be explained.
Optically pumped parametric amplification for micromechanical oscillators
Authors: Zalalutdinov M. , Olkhovets A. , Zehnder A. , Ilic B. , Czaplewski D. , Craighead H. G. , Parpia J. M.
Published: July 2002

Micromechanical oscillators in the rf range were fabricated in the form of silicon discs supported by a SiO2 pillar at the disk center. A low-power laser beam, (Plaser∼100 μW), focused at the periphery of the disk, causes a significant change of the effective spring constant producing a frequency shift, Δf(Δf/f∼10−4). The high quality factor, Q, of the disk oscillator (Q∼104) allows us to realize parametric amplification of the disk’s vibrations through a double frequency modulation of the laser power. An amplitude gain of up to 30 was demonstrated, with further increase limited by nonlinear behavior and self-generation. Phase dependence, inherent in degenerate parametric amplification, was also observed. Using this technique, the sensitivity of detection of a small force is greatly enhanced.
Strain-stabilized charge ordering and magnetorelaxor behaviors in Cr-doped Pr0.5Ca0.5MnO3 epitaxial thin films
Authors: Ogimoto Y. , Izumi M. , Manako T. , Kimura T. , Tomioka Y. , Kawasaki M. , Tokura Y.
Published: July 2002

Thin films of a magnetorelaxor compound, Pr0.5Ca0.5Mn1−yCryO3 were grown on various substrates. Strain-free and polycrystalline thin films on MgO substrates well reproduce the properties reported for the bulk samples. Pseudomorphically strained and atomically smooth epitaxial thin films grown on perovskite substrates show strain-driven modification of the properties. Being consistent with the orbital ordering accompanied with charge ordering, tensile strain anomalously stabilizes the charge-ordered (CO) state. Compressive strain also suppresses ferromagnetism but high-Cr doping (y=0.10) induces magnetorelaxor behaviors, where the volume ratio of coexisting CO and ferromagnetic phases can be tuned and memorized by the history of the magnetic-field application.
Field dependence of thermally stimulated currents in Alq3
Authors: Werner A. G. , Blochwitz J. , Pfeiffer M. , Leo K.
Published: July 2002

The trap properties of the commonly used organic light-emitting diode emitter material tris-8-(hydroxyquinoline) aluminum (Alq3) have been investigated using thermally stimulated currents. Based on a model of the field dependence of the thermally stimulated currents, a trap density of 1.3×1017 cm−3 for depths ranging from 0.05 to 0.7 eV is obtained, indicating considerable influence on charge carrier statistics. A field-induced lowering of trap depth was observed and explained in the framework of the Poole–Frenkel effect.