bluuebunny/crossref_metadata_2025 huggingface dataset:
High performance single emitter homojunction interfacial work function far infrared detectors
Authors: Esaev D. G. , Rinzan M. B. M. , Matsik S. G. , Perera A. G. U. , Liu H. C. , Zvonkov B. N. , Gavrilenko V. I. , Belyanin A. A.
Published: December 2003

Results are reported on p-GaAs homojunction interfacial work function internal photoemission far infrared (HIWIP FIR) detectors with a ∼1019 cm−3 carbon doped single emitter and a barrier layer for three different barrier thicknesses. A remarkably high quantum efficiency with low dark current and an increased responsivity were observed for devices with 1-, 0.1-, and 4-μm-thick barrier regions. The dark current densities for these structures are on the order of 1–10 μA/cm2 at 4.2 K, corresponding to a high dynamic resistance compared with previous HIWIP FIR detectors. A detector with a barrier thickness of 1 μm had a peak responsivity of 18.6 A/W, a peak detectivity D*=9×1011 cmHz/W, and a quantum efficiency of 40% at a wavelength of 58 μm under a reverse bias measured at 4.2 K. Cutoff wavelengths of these detectors vary with bias and are around 70 μm as expected. The main features of the absorption and responsivity spectra are well described based on a model incorporating free carrier absorption, hot hole transport, and emission over the barrier.
Compact submicrosecond, high current generator for wire explosion experiments
Authors: Aranchuk L. E. , Chuvatin A. S. , Larour J.
Published: December 2003

The PIAF generator was designed for low total energy and high energy density experiments with liners, X-pinch or fiber Z-pinch loads. These studies are of interest for such applications as surface and material science, microscopy of biological specimens, lithography of x-ray sensitive resists, and x-ray backlighting of pulsed-power plasmas. The generator is based on an RLC circuit that includes six NWL 180 nF–50 kV capacitors that store up to 1.3 kJ. The capacitors are connected in parallel to a single multispark switch designed to operate at atmospheric pressure. The switch allows reaching a time delay between the trigger pulse and the current pulse of less than 80 ns and has jitter of 6 ns. The total inductance without a load compartment was optimized to be as low as 16 nH, which leads to extremely low impedance of ∼0.12 Ω. A 40 kV initial voltage provides 250 kA maximum current in a 6 nH inductive load with a 180 ns current rise time. PIAF has dimensions of 660×660×490 mm and weight of less than 100 kg, thus manifesting itself as robust, simple to operate, and cost effective. A description of the PIAF generator and the initial experimental results on PIAF with an X-pinch type load are reported. The generator was demonstrated to operate successfully with an X-pinch type load. The experiments first started with investigation of the previously unexplored X-pinch conduction time range, 100 ns–1 μs. A single short radiation pulse was obtained that came from a small, point-like plasma. The following x-ray source characteristics were achieved: typical hot spot size of 50–100 μm, radiation pulse duration of 1.5–2 ns, and radiation yield of about 250–500 mJ in the softer spectral range (hν⩾700 eV) and 50–100 mJ in the harder one (hν⩾1 keV). These results provide the potential for further application of this source, such as use as a backlight diagnostic tool.
Accurate analysis of the bubble formation process in maximum bubble pressure tensiometry
Authors: Fainerman V. B. , Makievski A. V. , Miller R.
Published: December 2003

A method has been developed to determine the characteristic times of bubble formation in maximum bubble pressure experiments. It consists in the analysis of gas flow from a continuous reservoir or pump through a capillary into the system volume attached to the measuring capillary. This method works more reliably than the analysis of the direct pressure signal in the gas volume. A discussion on the optimum choice of the internal gas volume is made with the aim of maximum accuracy of determination of the surface tension and bubble deadtime and lifetime. The findings are compared with conditions given in various commercial instruments.
Europium beta-diketonate temperature sensors: Effects of ligands, matrix, and concentration
Authors: Khalil Gamal E. , Lau Kimberly , Phelan Gregory D. , Carlson Brenden , Gouterman Martin , Callis James B. , Dalton Larry R.
Published: December 2003

Europium beta diketonates are easily synthesized highly luminescent complexes with high temperature sensitivity. We report on the temperature dependence of the luminescence of recently synthesized europium complexes originally prepared for use as light emitting diodes. It has been discovered that when incorporated in a polymer matrix, their decay lifetime can provide accurate measurement of temperature. Their lifetime as a function of temperature depends on three factors: (i) the type and number of ligands in the complex, (ii) the particular polymer used for the matrix, and (iii) the europium chelate to polymer matrix concentration ratio. Various tris and tetrakis europium chelates are used to study ligand effects, while the polymers FIB, polycarbonate, and Teflon© are used to analyze matrix effects. In all cases studied, higher concentrations give rise to shorter lifetimes and higher temperature sensitivities, with sensitivity defined as ΔI/(IrefΔT). We propose to explain this phenomenon by using the following equation: 1/τobs≡Ktotal=kr+knr(T)+kc([Eu]). Here Ktotal is the observed decay rate, which is the inverse of the observed lifetime, while kr and knr(T) are the radiative and nonradiative decay rates, respectively. As well as being dependent on temperature, knr(T) for these complexes is very dependent on the environment, i.e., solvent or polymer, and can be considered as ken(T). The rate kc([Eu]) is the quenching term dependent on the concentration of the europium complex.
A system to damp the free piston oscillations in a two-stage light-gas gun used for hypervelocity impact experiments
Authors: Pavarin D. , Francesconi A. , Angrilli F.
Published: December 2003

Hypervelocity impact experiments that reproduce on-orbit collisions between micrometeoroids or orbital debris and space structures are commonly performed by means of propellant-driven two-stage light-gas guns. Such devices accelerate projectiles using the thrust of a light propellant gas that is compressed to high pressure and temperature by a piston running in a pump tube. Though these guns have the unique capability of accelerating particles up to 9 km/s, many components of the gun must be checked and/or substituted after each shot making test sessions long and expensive. In order to have a lot of and many different types of hypervelocity impact data, the Center of Studies and activities for Space CISAS “G. Colombo” of Padua University developed a high-shot-frequency two-stage light-gas gun that can increase the shot repetition rate of standard facilities by a factor of 5 or more and at the same time reduce the shot cost by a factor of 2 or more. This is made possible through the use of special mechanical and diagnostic solutions that were designed to operate the gun for more than 50 shots in sequence without having to carry out maintenance operations. This article presents the design and operation of the CISAS two-stage light-gas gun damping system, which is one of the subsystems that makes it possible to achieve high-shot frequency. The damping system is in charge of controlling the piston oscillations in the pump tube, making it possible for the piston to withstand more than 100 shots without any damage. In particular, the damping system avoids piston strikes onto the gun head at the end of each compression stroke and allows the piston to be positioned at the base of the pump tube after each shot. The sensitivity of the piston oscillations to the damping operations and main subsystem design parameters were identified using numerical simulations, carried out according to a model that describes every working phase of the gun. Moreover, in this paper, the technical solutions for the damping system implementation are presented and the numerical predictions are compared with experimental results. For the CISAS high-shot-frequency gas gun, an efficient damping system proved to be a fundamental requirement to reliably accelerate 100 mg projectiles above 5 km/s and 70 mg projectiles at 5.5 km/s with a shot frequency of 10 shots per day at least, including the time needed for replacing the target and pumping down the target vacuum chamber.
Nondestructive microwave permittivity characterization of ferroelectric thin film using microstrip dual resonator
Authors: Tan C. Y. , Chen Linfeng , Chong K. B. , Ong C. K.
Published: December 2003

This article presents the use of a microstrip dual resonator for nondestructive permittivity characterization of a ferroelectric thin film at microwave frequencies. The dual-resonator measurement fixture consists mainly of two capacitively coupled microstrip resonators, with the ferroelectric thin film covering the gap between the two resonators. The dielectric constant and loss tangent of the ferroelectric thin film are derived from the resonant frequencies and quality factors of the dual-resonator structure. To study the electric field dependence of the ferroelectric thin film, direct current bias voltage is applied through two electrode pads on the microstrip circuit. The temperature dependence of a ferroelectric thin film was also studied using the hermetic test fixture. The measurement uncertainty of this method comes mainly from the air gap between the microstrip circuit and the ferroelectric thin film. Calibration with a sample of known dielectric constant can be used to compensate for such an error. We demonstrated the use of this method on a piece of the Ba0.5Sr0.5TiO3 thin film deposited on a LaAlO3 substrate.
Ultrasensitive, fast, thin-film differential scanning calorimeter
Authors: Efremov Mikhail Yu. , Olson Eric A. , Zhang Ming , Schiettekatte François , Zhang Zishu , Allen Leslie H.
Published: December 2003

The equipment for an ultrasensitive, fast, thin-film differential scanning calorimetry [(TDSC) or nanocalorimetry] technique is described. The calorimetric cell (∼0.30 cm2) operates by applying a short (∼10 ms) dc current pulse (∼10 mA) to a thin (∼50 nm) patterned metal strip, which is supported by a thin (∼50 nm) SiNx membrane. The calorimeter operates at high heating rates (15–200 K/ms) and is very sensitive (30 pJ/K). The design of the calorimeter, the timing/synchronization methods, as well as the choice of key components of the instrument are discussed. Comparisons are made between two dc pulsing circuits that generate the current, a battery powered system and a system based on discharge of an assembly of charged capacitors (recommended). Design concepts for the differential as well as a simplified nondifferential technique are discussed and evaluated via experiments on thin films of indium. The differential design shows an increase in sensitivity, making it suitable for small samples. The custom made electronic circuits are also described, including the design of a preamplifier with low (28×) and high (700×) gain options, which are also compared using experimental data. Noise considerations are critical for the method. Simple models which describe noise levels in the calorimetric data are given and methods for reducing noise are discussed in detail. The sources of noise in the instrument are discussed in terms of both fundamental factors such as Johnson noise of the metal strip, as well as the limiting attributes of the sensing and pulsing circuits and instrumentation. These limiting attributes include spurious signals generated by desorption of ambient gases from the sensor, ground loops, switching regulators, and missing codes in analog-to-digital converter instruments. Examples of the experimental data of heat capacity Cp(T) of various thin films of indium, tin, and polystyrene are presented. A complete data set of raw experimental values is included for a 20 nm sample of Sn which shows the values of current and voltage of both the sample and reference sensors, as well as the differential voltage and the final values of the heat capacity.
A setup for ultrafast time-resolved x-ray absorption spectroscopy
Authors: Saes Melanie , van Mourik Frank , Gawelda Wojciech , Kaiser Maik , Chergui Majed , Bressler Christian , Grolimund Daniel , Abela Rafael , Glover Thornton E. , Heimann Philip A. , Schoenlein Robert W. , Johnson Steven L. , Lindenberg Aaron M. , Falcone Roger W.
Published: December 2003

We present a setup which allows the measurement of time-resolved x-ray absorption spectra with picosecond temporal resolution on liquid samples at the Advanced Light Source at Lawrence Berkeley National Laboratories. The temporal resolution is limited by the pulse width of the synchrotron source. We characterize the different sources of noise that limit the experiment and present a single-pulse detection scheme.
Measuring the nonlinearity of silicon piezoresistance by tensile loading of a submicron diameter fiber using a microinstrument
Authors: Chen J. M. , MacDonald N. C.
Published: December 2003

This report presents a mechanical loading experiment utilizing a microelectromechanical system microinstrument in which we stretched a 150 nm diameter n-type silicon fiber above 1% strain at room temperature and measured the longitudinal piezoresistive effect. The piezoresistive effect at these strains has not been measured. Piezoresistive coefficients up to the third order are required to fit the 0% to 1% strain measurement data with high statistical confidence. Our first-order coefficient matches results that are published in literature. However, compared with published second-order piezoresistive coefficients, the highest-order coefficient available, our result differs in magnitude and sign. Our analysis suggests that previously published second-order piezoresistive coefficients are not reliable due to limited data measured at small strain values (<0.1%), where the second-order piezoresistive effect is small.
Cryogenic 2 mm wave electron spin resonance spectrometer with application to atomic hydrogen gas below 100 mK
Authors: Vasilyev Sergei , Järvinen Jarno , Tjukanoff Esa , Kharitonov Alexander , Jaakkola Simo
Published: December 2003

We describe a 128 GHz electron-spin-resonance spectrometer based on heterodyne detection with double frequency conversion utilizing cryogenic Schottky-diode mixers. Together with other mm-wave components installed into a dilution refrigerator cryostat, the mixers comprise a bridge operating at 1.5 K. A miniature Fabry–Perot resonator is used to detect samples of bulk and surface-adsorbed atomic hydrogen gas at temperatures below 100 mK. The sensitivity is 2×109 spins/Gauss at the excitation power of 20 pW.
Miniature spectroscopic instrumentation: Applications to biology and chemistry
Authors: Bacon Christina P. , Mattley Yvette , DeFrece Ronald
Published: December 2003

Spectroscopy is a fundamental analytical tool utilized throughout all of the sciences. For chemistry and biology alone, there are thousands of applications. In the past two decades there have been monumental advances in the miniaturization of components used in spectrophotometric systems. The key components include detector arrays, laser diodes, and fiber optics. Currently, there are numerous commercially available miniature spectrometer systems as well as discrete components that are used by researchers in designing their own systems. A comprehensive summary of current instrumentation available for the design and development of miniaturized spectroscopy applications is described, including detectors, wavelength discriminating components, light sources, and sampling assemblies. Recommendations are made for designing spectrometer systems for specific applications. Current literature is reviewed for chemical and biological applications specifically using miniaturized spectrometer systems with the focus being on ultraviolet-visible-near-infrared spectrometers. The applications include laboratory applications, environmental sensing, on-site industrial analyses, botany and ecology applications, and finally clinical and biochemical studies. Additionally, microspectrometers, two-dimensional arrays, and photonics crystals are discussed in regards to their future role in chemistry and biology applications.
Fast-opening, high-throughput gas valve and application for inertial fusion energy R&D
Authors: Combs S. K. , Foust C. R. , Gouge M. J.
Published: December 2003

A fast-opening, high-throughput gas valve and its application to inertial fusion energy (IFE) research and development are described. The valve is a pilot type with two stages of active components. The pilot or first stage section is magnetically driven and equipped with a 4.2-mm-diam orifice. The pilot valve is energized to initiate operations and dumps gas from the upstream section of the second stage to the main valve outlet, and the resultant pressure differential across the large (22.3-mm-diam) output orifice seat causes mechanical activation of the second stage. Both stages are equipped with hard polyimide stem tips and springs for sealing. The valve has been operated reliably with helium gas at pressures in the range of 4–35 bar and frequencies up to 6 Hz, with maximum flow rates of ≈106 Torr l/s. The valve was developed to provide helium propellant gas for accelerating IFE targets to speeds up to 400 m/s in an experimental injector system under construction by General Atomics.
Ultrafast response (∼2.2 ps) of ion-irradiated InGaAs photoconductive switch at 1.55 μm
Authors: Mangeney J. , Joulaud L. , Crozat P. , Lourtioz J.-M. , Decobert J.
Published: December 2003

A 2.2 ps full-width-at-half-maximum impulse response is measured for ion-irradiated InGaAs photoconductive switches triggered by ultrashort 1.55 μm laser pulses. Correspondingly, the −3 dB bandwidth is estimated to be ∼120 GHz. Measurements of the electrical signals delivered by photoconductive switches are performed using an electro-optic sampling technique. As is shown, the ion irradiation reduces the carrier lifetime to less than 1 ps. The sheet resistance is 0.6×105 Ω/square. The photoconductive switch responsivity is found to exhibit a nonlinear dependence with optical power. The results are qualitatively interpreted.
Structural and electrical properties of electron beam gun evaporated Er2O3 insulator thin films
Authors: Mikhelashvili V. , Eisenstein G. , Edelman F. , Brener R. , Zakharov N. , Werner P.
Published: December 2003

We present a detailed study of the evolution with annealing temperature (in an oxygen environment) of the morphological and structural properties of thin erbium oxide (Er2O3) films evaporated in an electron beam gun system. The electrical characteristics of metal-oxide-semiconductor structures are also described. Atomic force microscope and x-ray difractometry were used to map out the morphology and crystalline nature of films ranging in thickness from 4.5 to 100 nm. High-resolution cross-sectional transmission electron microscopy imaging and Auger electron spectroscopy reveal three sublayers: an outer dense nanocrystalline Er2O3 layer, a middle transition layer and amorphous SiO2 film placed close to the Si substrate. The effective dielectric constant depends on the thickness and the annealing temperature. A 1–2.8 nm interfacial SiO2 layer as well as an ErO inclusion with low polarizability are formed during the deposition and the annealing process has a profound effect on the dielectric constant and the leakages. The minimum effective oxide thickness is 2.4–2.8 nm and in the thinnest films we obtained a leakage current density as low as 1–5×10−8 A/cm2 at an electric field of 1 MV/cm. We observe a shift of the flatband voltage to the positive side and significant lowering of the positive charge down to ∼1×1010 cm−2. For a 4.5 nm film, the maximum total breakdown electric field was approximately 1×107 V/cm.
Effects of oxygen related defects on the electrical and thermal behavior of a n+−p junction
Authors: Jiménez Tejada J. A. , Godoy A. , Carceller J. E. , López Villanueva J. A.
Published: December 2003

This study examines the electrical and temperature behavior of two of the levels in Czochralski-grown silicon that are most detected by different authors. A comparison between an analytical expression of the generation recombination noise in p−n junctions with experimental data taken from other authors was used as a tool for determining capture cross sections and densities of oxygen related traps in silicon. The parameters found in the literature for a deep level located at EC−0.43 eV are verified in this work. Parameters for a shallower level, a Coulomb trap with an activation energy of 0.17 eV, are also obtained. To correlate our theoretical results, obtained by noise analysis, with those of other authors, obtained with different techniques, thermally activated and field enhanced transitions between the latter center and the conduction band are considered. A thorough theoretical study of a silicon p−n junction with these levels shows a mutable electrical operation of the shallower center, acting as an electron trap at low temperatures and as a hole trap at room temperatures.
Upconversion luminescence of Eu3+ and Mn2+ in ZnS:Mn2+, Eu3+ codoped nanoparticles
Authors: Chen Wei , Joly Alan G. , Malm Jan-Olle , Bovin Jan-Olov
Published: December 2003

Strong upconversion luminescence of both Mn2+ and Eu3+ is observed in ZnS:Mn2+, Eu3+ codoped nanoparticles. Laser power dependencies and spectroscopic data show that the upconversion emission is due to two-photon excitation of each specific dopant ion. The relative differences in two-photon excitation cross section result in different relative intensities for the Eu3+ and Mn2+ upconversion at different wavelengths. Spectroscopic data and luminescence lifetime data indicate no evidence of energy transfer between the Mn2+ and Eu3+ ions.
Structure and photoluminescence studies on ZnS:Mn nanoparticles
Authors: Karar N. , Singh F. , Mehta B. R.
Published: December 2003

ZnS:Mn was produced in nanocrystalline form by a chemical method using polyvinylpyroledone as a chemical capping agent. Mn was stoichiometrically substituted for Zn in ZnS. The manganese (Mn) concentration was varied over its whole solid solution limit in ZnS, i.e., from 0 to 40%. In the high concentration regime this material formed may be thus written as nanocrystalline (Zn, Mn)S. The material formed is thus a wide gap diluted magnetic semiconductor. The characterized material was in powder form. X-ray diffraction was used to estimate the crystallite size and to confirm formation of the material in single phase. The average crystallite size obtained was about 2 nm. The material remained cubic over the whole Mn solid solution range. The room temperature photoluminescence (PL) when deconvoluted using a Gaussian fit showed two extra peaks in nanocrystalline ZnS:Mn when compared to pure nanocrystalline ZnS, which had only two peaks. Mn incorporation significantly enhanced the PL intensity in nanocrystalline ZnS:Mn (400–850 nm range) thereby suggesting Mn2+ induced PL. The red shift of the two new peaks with increase in Mn2+ concentration can be attributed to the change in band structure due to the formation of ZnS:Mn alloy. These extra peaks were due to (a) various Mn2+ transitions in the ZnS host, (b) related to S as the nearest neighbor of Mn2+ ion in the nanocrystallite (due to the high concentration of Mn2+), or (c) Mn–Mn interactions at high Mn concentrations. However, our prepared pure MnS samples did not show any photoluminescence at room temperature. So it is concluded that the observed PL is Mn2+ induced in the nanocrystalline ZnS host.
Structural, electrical, and optical analysis of ion implanted semi-insulating InP
Authors: Carmody C. , Tan H. H. , Jagadish C. , Douhéret O. , Maknys K. , Anand S. , Zou J. , Dao L. , Gal M.
Published: December 2003

Semi-insulating InP was implanted with MeV P, As, Ga, and In ions, and the resulting evolution of structural properties with increased annealing temperature was analyzed using double crystal x-ray diffractometry and cross sectional transmission electron microscopy. The types of damage identified are correlated with scanning spreading resistance and scanning capacitance measurements, as well as with previously measured Hall effect and time resolved photoluminescence results. We have identified multiple layers of conductivity in the samples which occur due to the nonuniform damage profile of a single implant. Our structural studies have shown that the amount and type of damage caused by implantation does not scale with implant ion atomic mass.
Mechanism for the increase of indium-tin-oxide work function by O2 inductively coupled plasma treatment
Authors: Lee Kwang Ho , Jang Ho Won , Kim Ki-Beom , Tak Yoon-Heung , Lee Jong-Lam
Published: December 2003

The effects of O2 inductively coupled plasma (ICP) treatment on the chemical composition and work function of indium-tin-oxide (ITO) surface were investigated. Synchrotron radiation photoemission spectroscopy showed that the O2 ICP treatment resulted in the increase of the ITO work function by 0.8 eV. Incorporation of oxygen atoms near the ITO surface during the ICP treatment induced a peroxidic ITO surface, increasing the work function. The enhanced oxidation of a thin Ni overlayer on the O2-ICP-treated sample suggests that preventing the migration of oxygen atoms into the active region of organic light-emitting diodes is important for improving device lifetime.
Laser induced surface modes at water–elastic and poroelastic solid interfaces
Authors: Allard J. F. , Henry M. , Glorieux C. , Lauriks W. , Petillon S.
Published: December 2003

A study of acoustic waves propagating along a fluid–solid plane interface, induced by thermoelastic excitation with a laser beam, is performed. The displacement of the interface in the time domain is predicted with an integration over frequency and on different Riemann sheets. The prediction, which includes the effect of the bulk waves induced by the thermoelastic excitation, can be performed at small distances from the heated region. For a bulk velocity in the fluid smaller than the shear wave velocity in the solid (water–glass configuration), and between the velocity of the shear and the compressional wave (water–plexiglass configuration), the poles that contribute to the displacement are identified by comparing the results of the integration in the different paths. A first analysis of the laser induced surface modes for water–porous ceramics configurations is performed in the context of the Biot theory. Measurements are presented.
Dielectric response of graded spherical particles of anisotropic materials
Authors: Dong L. , Huang J. P. , Yu K. W. , Gu G. Q.
Published: December 2003

Anisotropic dielectric response occurs naturally due to the presence of gradation, like in functionally graded materials or graded biological cells. However, these materials with locally anisotropic dielectric responses can have macroscopically isotropic responses. In treating graded particles of anisotropic materials, traditional isotropic gradation methods need to be modified. In this work, we developed a first-principles approach, as well as an anisotropic differential effective dipole approximation, for calculating the dipole moment of these particles. To this end, the two methods are shown in excellent agreement. As a result, these approaches offer convenient and effective ways to investigate the dielectric properties and optical responses of graded spherical particles of anisotropic materials, as well as the electrokinetic phenomena of biological cells.
Formation and charging effect of Si nanocrystals in a-SiNx/a-Si/a-SiNx structures
Authors: Dai Min , Chen Kai , Huang Xinfan , Wu Liangcai , Zhang Lin , Qiao Feng , Li Wei , Chen Kunji
Published: December 2003

The sandwiched structures with a layer of amorphous silicon (a-Si) between two a-SiNx layers have been fabricated by plasma enhanced chemical vapor deposition technique. Si nanocrystal (nc-Si) layer was formed by crystallization of the a-Si layer according to the constrained crystallization principle after thermal annealing at 1100 °C for 30 min. Transmission electron microscopy (TEM) and Raman scattering spectra showed that nc-Si grains were formed in the as-deposited a-Si layer after the annealing with a mean size about the same as the thickness of the as-deposited a-Si layer, and the density of the order of 1011–1012 cm−2. Charge trapping and storage in nc-Si were exhibited in capacitance–voltage (C–V) measurements at room temperature through the hysteresis and shift of the flat-band voltage (ΔVFB) of the nc-Si samples after a dc voltage was imposed. The density of nc-Si grains estimated from the ΔVFB was consistent with the results of TEM observation. The origin of the hysteresis phenomena and mechanism of the charge storage were discussed in detail.
Monte Carlo simulation of nanocrystalline TiN/amorphous SiNx composite films
Authors: Liu Z.-J. , Zhang C. H. , Shen Y. G. , Mai Y.-W.
Published: December 2003

The microstructures of TiN/SiNx films are studied by means of a Monte Carlo method. The simulation results show that nanocomposite films with microstructures comprising nanocrystalline TiN grains in an amorphous SiNx matrix are driven by the energy difference between the TiN grain-boundary energy and TiN/SiNx interfacial energy. The SiNx matrix formed can constrain TiN grain growth and thus causes a remarkable reduction in TiN grain size. The effect of the SiNx fraction on the sizes of TiN grains is also investigated. It is found that the average size of TiN grains decreases with volume fraction of SiNx approximately according to a power law with a time-dependent exponent decreasing with growth time. These simulation results are in reasonable agreement with experimental observations.
CdS quantum dots in hybrid sol–gel matrix; absorption and room-temperature photoluminescence
Authors: Kang K. , Daneshvar K.
Published: December 2003

Strong room-temperature luminescence spectra for cadmium sulfide (CdS) nanometer quantum dots (NQDs) were obtained using a xenon lamp. The samples were fabricated of various concentrations of semiconductor NQDs in the hybrid sol–gel matrix. Concentration dependent total absorption showed a linear relationship following the Beer–Lambert law. An excess H2S source reduced the luminescence intensity, shifted the spectra peak to the red, and broadened the spectra. These excess H2S phenomena disappeared after a certain period of time in ambient conditions. The result showed that strong luminescence in CdS in hybrid-sol–gel matrix can be achieved without any casing.
Backscattering of low energy electrons from carbon films deposited on aluminum: A Monte Carlo simulation
Authors: Dapor Maurizio
Published: December 2003

The low energy backscattering coefficient for the special case of film of carbon deposited on aluminum is investigated. The backscattering coefficient as a function of the primary energy shows an interesting property, i.e., the appearance—for carbon film thicknesses higher than ∼100 Å on aluminum—of relative maxima of absorption (and relative minima of backscattering). It has been noted, for aluminum substrates, that the position of the relative minima of the backscattering coefficient is increasing as the carbon film thickness increases. If experimentally confirmed and quantitatively accurately defined, the results presented—here obtained through a Monte Carlo simulation—can be used as a way to measure the carbon film thickness by a set of measures of the backscattering coefficient.
Schottky barrier height and nitrogen–vacancy-related defects in Ti alloyed Ohmic contacts to n-GaN
Authors: Lin Yow-Jon , Chen Yao-Ming , Cheng Tzyy-Jon , Ker Quantum
Published: December 2003

The relationship between the Schottky barrier height and nitrogen–vacancy-related defects in Ti alloyed Ohmic contacts to n-type GaN (n-GaN) has been investigated using x-ray photoelectron spectroscopy measurements. It is shown that the alloyed Ohmic behavior of the contacts can be attributed to the presence of a large number of nitrogen–vacancy-related defects and not to the formation of lower barriers at the annealed Ti/n-GaN interface. The large number of interface states, related to the nitrogen–vacancy defects has led to the pinning of the Fermi level at 0.5 eV below the conduction-band edge, and has left the GaN surface very heavily n type, thereby forming a tunneling junction.
Fabrication of highly efficient polythiophene-sensitized metal oxide photovoltaic cells
Authors: Senadeera G. K. R. , Nakamura K. , Kitamura T. , Wada Y. , Yanagida S.
Published: December 2003

Poly(3-thiophenylacetic acid)-polymer-sensitized photoelectrochemical cells comprising of either mesoporous TiO2 or SnO2-ZnO electrodes and the electrolyte consisting with redox complex (I3−/I−) were fabricated and characterized. The addition of ionic liquid, 1-methyl- 3-n-hexylimidazolium iodide, into the electrolyte drastically enhanced the cell performance. The cells consisting of the nanoporous TiO2 electrodes showed the incident photon to current conversion efficiency as high as 60% (at 430 nm), while the highest overall power conversion efficiency was ∼2.4% under the irradiance of 100 mW cm−2 (air mass 1.5). The overall efficiency of the cells with nanoporous SnO2-ZnO electrodes was ∼1.5% under the same illumination.
Effect of nitrogen doping into SiO2 studied by photoemission spectroscopy
Authors: Toyoda S. , Okabayashi J. , Kumigashira H. , Oshima M. , Ono K. , Niwa M. , Usuda K. , Hirashita N.
Published: December 2003

Photoemission spectroscopy using synchrotron radiation has been performed on ultrathin Si oxynitride films on Si(001) to investigate a change of the energy-band structure by nitrogen doping. The valence-band spectra obtained by subtracting the contribution of the Si substrate clearly show the difference in nitrogen doping and two valence-band maxima, assigned as SiO2 and Si3N4, are deduced. The chemical analysis in N 1s spectra suggests a possibility that two phases, SiO2 and Si3N4, are separated in the SiOxNy films, since the sample with high nitrogen concentration (1.7×1022 cm−3) shows a valence-band maximum similar to Si3N4. A change of the valence-band maximum by nitrogen doping can be explained by an increase of the Si3N4 domain size in the SiOxNy film.
Optical and magnetic measurements of Mn+-implanted AlN
Authors: Li M. K. , Li C. B. , Liu C. S. , Fan X. J. , Fu D. J. , Shon Y. , Kang T. W.
Published: December 2003

AlN films were prepared by medium-frequency reactive magnetron sputtering and subsequently implanted with 200 keV Mn+ ions with a dose of 5×1016 cm−2. The properties of Mn+-implanted AlN films were investigated by optical and magnetic measurements. Cathodoluminescence (CL) measurements showed a peak at 2.07 eV in AlN and a broad luminescence band around 2.0–3.4 eV in the implanted samples. Fitting of the CL data reveals three peaks, among which the main peak is located at 2.6 eV and attributed to a donor-to-Mn2+ transition. The magnetic measurement showed a transition temperature of 100 K in the implanted AlN annealed at 500 °C for 30 min. Clear ferromagnetic hysteresis was observed at 77 K, with a coercive field of 212.7 Oe.
Peltier current lead experiment and their applications for superconducting magnets
Authors: Yamaguchi Satarou , Yamaguchi Takayuki , Nakamura Kenji , Hasegawa Yasuhiro , Okumura Haruhiko , Sato Ken
Published: December 2003

Many applications of superconductivity are studied because they are basically nondissipative systems; however, electric power is spent to keep them at low temperature. If heat leakage is high, the advantage of the superconductivity will be reduced or disappear, and therefore we must reduce the heat leakage as much as we can in the actual system. The Peltier current lead (PCL) was proposed to reduce heat leakage from the electric circuit of the superconducting magnet system. PCL is composed of thermoelectric semiconductors, metal leads, and high temperature superconducting (HTS) leads. Bismuth–tellurium alloys (BiTe) are used as the thermoelectric semiconductors in the experiment, and these are placed on the room temperature side. Optimum design of the PCL is conducted to solve a heat leakage equation, and depends on the transport parameters such as thermal conductivity, electric resistivity, and Seebeck coefficient of the materials of the PCL. The thermal conductivity of the BiTe is about 0.4% of the copper’s, and we can expect the Peltier cooling by using this material. Therefore, we can expect the large temperature difference of the BiTe and reduce the heat leakage. The experiment has been done and the cold-end temperature of the thermoelectric BiTe is around 200 K both in the experiment and the numerical calculation. The temperature difference of 4 mm thickness of the BiTe exceeds 70 K for 150 A in both the experiment and the calculation. Therefore, the principle was proven in the experiments, and the reduction of the heat leakage is up to 35% for the current lead included in the HTS current lead. Here, we also mentioned and proposed the various types of the PCL for the different kinds of superconducting magnet systems in this article.
Relaxation calorimetry technique for measuring low temperature specific heat
Authors: Newsome R. W. , Andrei E. Y.
Published: December 2003

A rudimentary calorimeter was constructed to measure the temperature dependence of the specific heat of a 10 μ thick (0.62 mg) copolymer film of vinylidene fluoride and trifluoroethylene in the previously unexplored vicinity of 6 K. The data were processed with the algorithm developed by Hwang et al. [Rev. Sci. Instrum. 68, 94 (1997)] as modified for our configuration in which a Cernox thermometer also served as a heater. The measurements extended from 3.75 to 8.5 K, with a temperature resolution of 0.2 K, and the ratios of the statistical uncertainties to the mean values deduced for cp are ± 3% over most of this temperature range. The data taken with the intermediate resolution of this calorimeter provides evidence for the absence of any slowly varying anomaly in the temperature dependence of cp. Such rudimentary systems provide a useful option to gather exploratory information at a comparatively low cost for components.
Deep superconducting magnetic traps for neutral atoms and molecules
Authors: Harris J. G. E. , Michniak R. A. , Nguyen S. V. , Campbell W. C. , Egorov D. , Maxwell S. E. , van Buuren L. D. , Doyle J. M.
Published: December 2003

We describe the design, construction and performance of three realizations of a high-field superconducting magnetic trap for neutral atoms and molecules. Each of these traps utilizes a pair of coaxial coils in the anti-Helmholtz geometry and achieves depths greater than 4 T, allowing it to capture magnetic atoms and molecules cooled in a cryogenic buffer gas. Achieving this depth requires that the repulsive force between the coils (which can exceed 30 metric tons) be contained. We also describe additional features of the traps, including the elimination of trapped fluxes from the coils and the integration of the coils into a cryogenic vacuum environment suitable for producing cold atoms and molecules.
Polarized high-brilliance and high-resolution soft x-ray source at ELETTRA: The performance of beamline BACH
Authors: Zangrando M. , Zacchigna M. , Finazzi M. , Cocco D. , Rochow R. , Parmigiani F.
Published: December 2003

BACH, a soft x-ray beamline for polarization-dependent experiments at the Italian synchrotron radiation facility ELETTRA, was recently completed and characterized. Its performance, in terms of energy resolution, flux and polarization, is presented. Based on two APPLE II undulators, BACH covers the energy range between 35 and 1600 eV with the control of the light polarization. The monochromator is equipped with four gratings and allows one to work either in a high resolution or in a high flux mode. After the monochromator, the beamline is split into two branches with different refocusing properties. One is optimized to exploit the performance of the soft x-ray spectrometer (ComIXS) available at the beamline. Resolving powers between 12000 at 90 eV photon energy and 6600 near 867 eV were achieved using the high-resolution gratings and the smallest available slit width (10 μm). For the high-brilliance grating, which works between 290 and 1600 eV, resolving powers between 7000 at 400 eV and 2200 at 867 eV were obtained. The flux in the experimental chamber, measured with the high-resolution gratings for linearly polarized light at the best achievable resolution, ranges between 4×1011 photons/s at 125 eV and 2×1010 photons/s between 900 and 1250 eV. In circularly polarized mode the flux is two times larger for energies up to 380 eV. A gain of nearly one order of magnitude is obtained for the high-brilliance grating, in accordance with theoretical predictions. Flux beyond 1.3×1011 photons/s was measured up to 1300 eV, and thus over nearly the complete energy range covered by this high-brilliance grating, with a maximum of 1.6×1011 photons/s between 800 and 1100 eV. First results from polarization measurements confirm a polarization above 99.7% for both linearly and circularly polarized modes at low energies. Circular dichroism experiments indicate a circular polarization beyond 90% at the Fe L2/L3 edge near 720 eV.
LabView virtual instrument for automatic plasma diagnostic
Authors: Ballesteros J. , Fernández Palop J. I. , Hernández M. A. , Crespo R. Morales , del Pino S. Borrego
Published: December 2003

This article presents a LabView virtual instrument (VI) that automatically measures the I–V plasma probe characteristic and obtains the electron energy distribution function (EEDF) in plasmas. The VI determines several parameters characterizing the plasma using different methods to verify the validity of the results. The program controls some parameters associated with color coded warnings to verify the fidelity of the measured data and their later numerical treatment. The measurement process and data treatment are very fast, about 0.5 s, so that temporal evolutions of the EEDF can be scanned, to analyze the drift of the plasma. Finally, the program is easily portable since it is developed in the LabView environment, so it can be adapted to any platform using common laboratory instruments.
Optically accessible high-pressure combustion apparatus
Authors: Tse Stephen D. , Zhu Delin , Law Chung K.
Published: December 2003

The design and operation of a novel optically accessible high-pressure combustion apparatus is presented. The apparatus provides optical access for the direct observation of the morphology and development of premixed reaction fronts at elevated pressures. A chamber-in-chamber design with an innovative connecting system allows for safe, constant-pressure measurements, alleviating the extreme overpressures encountered in high-pressure combustion processes within closed bombs. Auxiliary design features include gap-adjustable electrodes for spark ignition and ports for jet stirring. As a result, the apparatus is well suited for the study of laminar premixed flames, flame instabilities, turbulent flames, and detonations. Results from the study of centrally ignited hydrogen and methane fuels in oxygen-inert mixtures up to 60 atm initial pressure demonstrate the suitability of the apparatus for high-pressure combustion experiments.
An axial molecular-beam diode laser spectrometer
Authors: Osthoff Hans D. , Jäger Wolfgang , Walls Johnathon , van Wijngaarden William A.
Published: December 2003

A mid-infrared tunable diode laser molecular-beam spectrometer for the purpose of trace gas sensing and the study of van der Waals complexes is described. The spectrometer employs a Herriott multipass cell with up to 72 passes. The sample gas is injected parallel to the optical axis through a hole at the center of the far mirror. The molecular absorption is Doppler split, resulting from the laser beam propagating parallel and antiparallel to the molecular-beam expansion. The axial expansion leads to narrower line widths and increased sensitivity, compared to the traditional vertical injection method, as a result of selective sampling of the central part of the molecular expansion with reduced Doppler broadening and longer residence time of the molecular sample in the laser beam. The molecular expansion leads also to selective signal enhancement of low-J transitions, as demonstrated for the ν3 antisymmetric stretch vibration of CO2. A microwave horn antenna was implemented into the spectrometer to enable microwave–infrared double-resonance experiments. The spectrometer performance was evaluated by recording spectra of the CO2–Ar, (CO2)2, CO2–He, and CO2–SO2 van der Waals complexes near the R(0) transition of the ν3 band of CO2 around 2349 cm−1. The feasibility of using a pulsed molecular expansion for trace gas sensing is explored.
Irradiation effects on temperature sensors for ITER application
Authors: Van Nieuwenhove R. , Vermeeren L.
Published: December 2003

The effect of neutron and gamma irradiation and magnetic fields on temperature sensors has been reviewed for the particular environment of the International Tokamak Experimental Reactor (ITER). Both Chromel–Alumel and Nicrosil–Nisil thermocouples are expected to be unaffected by neutron irradiation over the entire life time of ITER. Based on the available data, no significant radiation-induced electromotive force effects are to be expected. Magnetic field effects on Chromel–Alumel thermocouples could under certain conditions become important and, in this case, Nicrosil–Nisil thermocouples are recommended. For high temperature measurements (T>1200 °C) in ITER conditions, tungsten–rhenium thermocouples are the most appropriate choice. Resistance thermometers, on the other hand, were found not to be usable in a reactor environment.
Enlargement of the nontransmission frequency range of multiple-channeled filters by the use of heterostructures
Authors: Wang Li , Wang Zhanshan , Wu Yonggang , Chen Lingyan , Wang Shaowei , Chen Xiaoshuang , Lu Wei
Published: December 2003

Transmission characteristics are studied for hybrid structures combining defects and multiple heterostructures. It is shown that the nontransmission frequency range can be substantially enlarged and the phenomenon of multiple-channeled filtering can be realized by adjusting the number, position, and size of the defects. One, two, and three channeled filters are considered in the structures. Examples are studied theoretically by transfer matrix methods.
Enhanced thermoelectric properties of NaxCoO2 whisker crystals
Authors: Peleckis G. , Motohashi T. , Karppinen M. , Yamauchi H.
Published: December 2003

Single-crystalline whiskers of thermoelectric cobalt oxide, NaxCoO2, have been grown by an unconventional method from potassium-containing compositions, and their transport properties, and chemical compositions were determined. The growth mechanism was analyzed and interpreted by means of thermogravimetric analysis. At 300 K, electrical resistivity ρ, and thermoelectric power S of the whisker are 102 μΩ cm and 83 μV/K, respectively. The power-factor, S2/ρ, thus is enhanced up to ∼68 μW/K2 cm.
Epitaxial growth and ferroelectric properties of SrBi2Nb2O9(115) thin films grown by pulsed-laser deposition on epitaxial Pt(111) electrode
Authors: Duclère J.-R. , Guilloux-Viry M. , Bouquet V. , Perrin A. , Cattan E. , Soyer C. , Rèmiens D.
Published: December 2003

Epitaxial SrBi2Nb2O9 thin films have been grown by pulsed-laser deposition on Pt(111) bottom electrode epitaxially grown by dc sputtering on sapphire(0001). Four-circle x-ray diffraction reveals the epitaxial growth of the SrBi2Nb2O9(115)/Pt(111) bilayers. The influence of the Pt bottom electrode on the growth of SrBi2Nb2O9 films is discussed in terms of atomic matching at the SrBi2Nb2O9/Pt interface. The remanent polarization is close to 6 μC/cm2, with a coercive field of 140 kV/cm. The zero-field relative permittivity is about 132 and the dielectric loss less than to 2%. The decay in remanent polarization is only 16% after 2.109 switching cycles, confirming the fatigue resistance of the film.