bluuebunny/crossref_metadata_2025 huggingface dataset:
In situ measurement of the rate of H absorption by a Pd cathode during the electrolysis of aqueous solutions
Authors: Algueró M. , Fernández J. F. , Cuevas F. , Sánchez C.
Published: July 2002

An experimental setup to measure “in situ” the amount of H that a Pd cathode absorbs during the electrolysis of aqueous solutions has been built up and tested. The setup implements a volumetric technique, i.e., it involves the measurement of the rate of H2 generation by the cathode. The pros and cons of this type of techniques against other procedures, the measurement of the variation of the cathode electrical resistance or of its dilation during the electrolysis, are briefly discussed. A careful analysis of the setup error sources is done by using two non-H-absorbing Pt electrodes. Neither any significant recombination of the electrolysis gases (H2 and O2), nor any deviation of a 100% electrolysis efficiency have been observed. It has been found that gas (air) release and H2 and O2 absorption by the solution, in the first stage of the electrolysis, seriously affect the measurement of the rate of H absorption by the cathode. Several improvements of the experimental installation and an operation protocol of saturation of H2 and O2 and of exhaustion of air in the solution, before starting the electrolysis, allowed overcoming those limitations. Finally, we present the results obtained in the measurement of the rate of H uptake by a Pd cathode during electrolysis. The reliability of the measurement has been confirmed by electrochemically deloading the Pd cathode.
Avalanche photodiodes operating parameter optimization for the Frascati Tokamak Upgrade Thomson scattering system
Authors: Orsitto F. , Brusadin A. , Giovannozzi E.
Published: July 2002

Measured figures (linearity, avalanche gain, frequency response, and noise) of the avalanche photodiodes (APD) detectors used on the FTU Thomson scattering system (FTU-TS) are reported. This investigation on the APD figures is motivated by the necessity of knowing their values over a wide range of input signals, and also of checking the validity of McIntyre model of APD noise, since using this model the experimental signal-to-noise ratio is calculated. From the noise analysis, a method of optimization of the detection system sensitivity is derived, leading to the optimization of the signal-to-noise ratio over the entire FTU-TS system.
Flow system and 9.5 GHz microwave resonators for time-resolved and steady-state electron paramagnetic resonance spectroscopy in compressed and supercritical fluids
Authors: Dukes Katerina E. , Harbron Elizabeth J. , Forbes Malcolm D. E. , DeSimone Joseph M.
Published: July 2002

An apparatus for the electron paramagnetic resonance (EPR) detection of stable and transient free radicals in pressurized liquids and supercritical fluids is described. The construction of a quartz EPR sample cell capable of withstanding pressures up to 3000 psi (204 atm) and the components of a high pressure flow system are explained and illustrated. In order to accommodate the thick-walled, high pressure sample tube, two X-band (9.5 GHz) microwave cavities were fabricated. One is a brass, cylindrical TE011 cavity for time-resolved (direct detection) EPR experiments where field modulation was not necessary, and the other is a silver wire-wound cylindrical TE011 cavity, mounted in a quartz support tube. The wire-wound cavity allows for simultaneous light excitation and field modulation for steady-state EPR. Both cavities are fitted with tunable end plates to facilitate tuning at X band in the face of large frequency shifts when the sample tube is introduced to the resonator and to allow for operation with smaller sample tubes at ambient pressure. Microwave coupling, flow optimization, and UV-light access for both cavities are described, and sample spectra in both time-resolved and steady-state modes are reported.
Multicusp sources for ion beam projection lithography
Authors: Lee Y. , Gough R. A. , Kunkel W. B. , Leung K. N. , Vujic J. , Williams M. D. , Wutte D. , Zahir N.
Published: July 2002

Multicusp ion sources are capable of producing positive and negative ions with good beam quality and low energy spread. The ion energy spread of multicusp sources has been measured by three different techniques. The axial ion energy spread has been reduced by introducing a magnetic filter inside the multicusp source chamber which adjusts the plasma potential distribution. The axial energy spread is further reduced by optimizing the source configuration. Values as low as 0.8 eV have been achieved.
Operation of the ECR ion source Alice and its platform
Authors: Cavenago M. , Cervellera F. , Kulevoy T. , Marchetti M. T. , Vassiliev A.
Published: July 2002

The operation of the electron cyclotron resonance (ECR) ion source Alice is described, with attention to the improved ion analysis and the new diagnostic equipment. Ion current peaks as small as tens of nA can be measured; resolving power is about 100. Routine operation is still restricted to gases, but prototypes of ovens have passed the first tests. Since currents are still rather limited (about 400 nA for Xe18+132), a new removable plasma chamber with increased inner diameter (63 mm), made in aluminum, is under construction. Preliminary analysis of charge state distribution of xenon isotopes shows good fits with an approximately thermodynamical distribution; a sort of effective chemical potential μc is defined from fit parameters; in the particular case shown here μc≅390 eV. A decision to install a high voltage insulation transformer to allow platform operation up to Vp=350 kV was made, and an adequate location is being found, with proper wall feedthroughs in design.
High resolution reflectivity diffractometer on Station 2.3 (Daresbury Laboratory)
Authors: Tang C. C. , Collins S. P. , Murphy B. M. , Telling N. D. , Wogelius R. A. , Teat S. J.
Published: July 2002

A high resolution reflectivity diffractometer (HRRD) has been recently commissioned on Station 2.3 at the SRS, Daresbury Laboratory. Using the instrument which is x-ray wavelength tunable, the characterization of the interface structure in an ion-assisted deposited Co/Cu multilayer has been carried out. In order to improve the electron density contrast of the sample, we have used an x-ray energy near the Cu K edge of 8.989 keV. By scanning the normal (specular), near normal (off specular), and parallel axes (transverse) of the surface, we have obtained useful reflectivity intensity data. By applying simulations to the data, we have determined a total roughness (rms) of 6.0±0.5 Å with a significant contribution from correlated interfacial roughness (4.2±0.2 Å). Other detailed structural information obtained has successfully demonstrated that the commissioned instrument is a viable tool for reflectivity studies.
In-series combination of a magnetic-sector mass spectrometer with a time-of-flight quadratic-field ion mirror
Authors: Andersen Ulla N. , Colburn Alex W. , Makarov Alexander A. , Raptakis Emmanuel N. , Reynolds David J. , Derrick Peter J. , Davis Stephen C. , Hoffman Andrew D. , Thomson Steven
Published: July 2002

A tandem mass spectrometer consisting of a double-focusing magnetic-sector mass analyzer in series with a time-of-flight (TOF) mass analyzer has been designed and constructed. The TOF analyzer was a quadratic-field ion mirror. The method of ionization used was matrix-assisted laser desorption/ionization. Precursor ions were mass selected with the magnetic-sector analyzer, and time focused by ion bunching prior to fragmentation in a collision cell. The fragment ions were mass analyzed with the TOF analyzer, which possessed the property that residence times (i.e., times of flight) in the mirror were independent of ion velocity. The theoretical background to the instrumental design is presented. Experimental results are presented, showing resolutions of 4000 in fragment ion spectra and demonstrating effective high-energy collision-induced decomposition of peptide molecule ions.
Penetration of electrostatic fields and potentials through meshes, grids, or gauzes
Authors: Read F. H. , Bowring N. J. , Bullivant P. D. , Ward R. R. A.
Published: July 2002

A theoretical, computational, and experimental study has been carried out of the penetration of electrostatic fields and potentials through meshes. When a conducting partially transparent mesh is used to separate two regions of uniform static field of different strengths the potential distribution in the holes of the mesh is altered, causing the effective average potential of the mesh to become different from the potential applied to the mesh itself, which in turn gives rise to long-range changes to the fields and potentials on both sides of the mesh. The magnitudes of the effective changes in potential are investigated computationally for meshes that consist of either round wires or flat strips, in each case in either a parallel or crossed configuration. Semiempirical formulas are presented for the change in potential as a function of the fields on the two sides of the mesh and the size and spacing of the wires or strips. An experimental test using the shift in apparent energy of an electron-atom scattering resonance has been carried out.
Compact multifunctional spectrofluorimeter with a novel design for anisotropy measurements
Authors: Jasny Jan , Waluk Jacek
Published: July 2002

A multifunctional spectrofluorimeter is described, based on double grating monochromators in both excitation and emission paths. Instead of Glan prisms, commonly used in anisotropy measurements, Wollaston prisms were applied. This results in a large increase of light throughput, which significantly increases the sensitivity. Luminescence measurements of various sample types are possible, in a wide and precisely controlled temperature range.
Hydrostatic optical cell for temperatures below 350 K and pressures to 400 MPa
Authors: Johnson J. Bruce
Published: July 2002

A compact optical pressure cell tested at pressures up to 400 MPa is presented. The cell has been used within the temperature range 10–350 K. The cell has a small mass of 0.2 kg which facilitates rapid changes in temperature. A new high-pressure window seal is presented which allows the cell to be mounted directly in vacuum with no leak over its entire temperature and pressure range. A method of attaching the cell to common coldhead-type cryostats and closed-cycle refrigerators is presented.
A new device for contactless studies of dielectrics
Authors: Bacchetta H. , Béghé J.-P. , Berthault A. , Carles P. , Niepce J.-C.
Published: July 2002

A new device, based on force measurements, has been developed for contactless studies of space charges in dielectrics. An electronic microforce balance is used to measure the force exerted on a sphere suspended above the surface of a dielectric sample. The application of a bias voltage to the sphere allows to separate the contributions to the force of the dielectric matrix and of space charges. Furthermore, the well-defined geometry used gives access to a precise modeling of the setup response function. Translation of the sample allows the mapping of charge distributions over large areas, with a lateral resolution limited by the size of the probe. A new type of experiment, taking advantage of the potentialities of the setup to study charge transport phenomena in dielectrics without preliminary implantation of charges, is also presented, and the first results obtained on polyethylene are discussed.
Transient thermography using evanescent microwave microscope
Authors: Tabib-Azar M. , Ciocan R. , Ponchak G. , LeClair S. R.
Published: July 2002

Very high spatial resolution thermography is of great importance in electronics, biology, and in many other situations where local variations in temperature are needed to study heat dissipation or to monitor metabolism rate which can be directly related to the heat production. Infrared imaging techniques probably are the best way of obtaining thermal maps of large structures. However, the spatial resolution of infrared imaging techniques is limited to a few 100 μm and their temperature resolution is usually around 0.1 K. Here we report on a new evanescent microwave method that is capable of mapping temperature distributions with ≈1 μm spatial resolution. The temperature sensitivity of this probe was better than 0.1 V/K with a minimum detectable signal of 0.01 K with a response time faster than 1 μs.
Effect of harmonic rf fields on the emissive probe characteristics
Authors: Lho T. , Hershkowitz N. , Kim G-H.
Published: July 2002

New features of the emissive probe characteristic curves in an inductive plasma source were observed in the E mode operation. More than the two inflection points in the derivative of the I–V characteristic curves are found when the harmonics of the input frequency (13.56 MHz) are present. The pairs of inflection points are symmetric about dc plasma potential.
Electron cyclotron resonance plasma source for ion assisted deposition of thin films
Authors: Vargheese K. Deenamma , Rao G. Mohan
Published: July 2002

An electron cyclotron resonance (ECR) plasma source (10 cm in diameter) has been developed for ion assisted sputter deposition of thin films. Variation of plasma parameters like ion density, electron temperature, plasma potential, and floating potential as a function of pressure and microwave power has been studied using Langmuir probe analysis. The ECR source gives an ion density of 1.01×1011/cm3 at a distance of 8 cm from the source exit at a pressure of 8×10−4 mbar and 400 W of microwave power. The uniformity of the plasma parameters at the substrate position was found to be ±2% over a diameter of 12 cm. Thin films of copper and silicon nitride have been deposited by rf sputtering in the presence of ECR plasma. The properties showed a significant change at an ECR power of 100 W.
Approximation of the plasma inhomogeneity by broad-beam measurements and simulation
Authors: Tartz M. , Hartmann E. , Deltschew R. , Neumann H.
Published: July 2002

In broad-beam ion sources an inhomogeneous plasma distribution has a strong effect on both the maximum extractable ion current and the broad-beam profile. An approximate plasma distribution function is determined by fitting calculated accelerator-grid currents to corresponding experimental data, thus efficiently replacing complicated and expensive plasma probe measurements.
H
−
ion source using a localized virtual magnetic filter in the plasma electrode: Type-I localized virtual magnetic filter
Authors: Oka Y. , Kaneko O. , Tsumori K. , Takeiri Y. , Osakabe M. , Kawamoto T. , Asano E. , Akiyama R.
Published: July 2002

A new multi-cusp H− ion source using a localized virtual magnetic filter of type I in the plasma electrode is investigated. A multi-pole arrangement with a spacing of 10 mm of the magnet bars holds an extraction hole, optimizing the efficient production of high H− current, and at the same time only a small electron component was co-extracted with the H− ions. The local filter arrangement separates the beam electrons at a low energy. It is shown that the coextracted total electron current is determined principally by the integrated magnetic field flux (Gcm) of the local filter with an extraction system at a constant extraction voltage. When the value of the Gcm is increased, the total electron component is reduced, while the H− electrical efficiency had a broad maximum around the optimized value of the Gcm. A thicker plasma electrode should be necessary for sufficient reduction of electron current. In pure hydrogen operation, the achieved current density of H− is 10 mA/cm2. When Cs is seeded in a filter optimized for pure volume mode H− production, the maximum H− current density obtained is 51 mA/cm2 and the ratio Iele/H− is ∼0.4 without applying a bias potential.
Influence of plasma-wall interaction on high charge state production in electron cyclotron resonance ion sources
Authors: Meyer D. , Schmitz H. , Daube Th. , Mannel C. , Wiesemann K.
Published: July 2002

In contrast to the widely accepted model of ion cooling, which is supposed to fully explain the gas mixing effect, we recently presented an alternative model of self-enhanced sputtering of wall material. In order to prove our model further, we numerically simulated different plasma parameters in the vicinity of plasma limiting edges of the discharge chamber (walls) via particle in cell and Monte Carlo methods. Both experimental investigations and simulations give clear evidence that the optimization of an electron cyclotron resonance ion source with respect to the high charge state production is sensitively influenced by the contamination of the plasma with heavy atoms sputtered off the walls. Any optimization of the charge state distribution in physical terms means nothing else than balancing the ratio of hot and cold electrons.
Optimization of the radial magnetic field of an 18 GHz electron cyclotron resonance ion source at the Heavy Ion Medical Accelerator in Chiba
Authors: Kitagawa A. , Muramatsu M. , Sekiguchi M. , Yamada S. , Jincho K. , Okada T. , Yamamoto M. , Biri S. , Uno K.
Published: July 2002

Since the narrowly concentrated ion-density distribution enhances the space charge effects, the extracted beam intensity is lower than case with a uniform distribution. In order to realize the uniform ion-density distribution at the extraction aperture for the higher beam intensity, the radial magnetic field given by the permanent sextupole magnet has been optimized. The ion-density distribution estimated by the TRAPCAD code depends on the magnetic trap configuration. The diameter of the electron cyclotron resonance (ECR) zone determined by the inner diameter of the sextupole magnet was enlarged, and consequently the density of the flux lines running through the ECR zone decreased at the extraction aperture. The ion-density distribution could become more uniform. The inner diameter of the sextupole magnet of an 18 GHz ECR ion source for the Heavy Ion Medical Accelerator in Chiba at the National Institute of Radiological Sciences was increased from 46 to 66 mm, so that the extracted intensities of Ar8+ and Ar9+ ions increased from 250 and 150 e μA to 1100 and 650 e μA, respectively.
Initial growth temperature of crystalline SiC by simultaneous irradiation of energetic Si−28 and C+12
Authors: Tsubouchi Nobuteru , Chayahara Akiyoshi , Kinomura Atsushi , Horino Yuji
Published: July 2002

Initial growth temperature of SiC polycrystalline films by simultaneous irradiation of energetic, isotopical mass-separated Si−28 and C+12 ions was investigated. The kinetic energies of both ions were 200 eV and deposition temperatures were room temperature, 400 °C, and 600 °C. The SiC films deposited at ∼600 °C showed the infrared absorption peak at 802 cm−1 and weak ring patterns on reflection high-energy electron diffraction measurements, characteristics for crystalline SiC. With x-ray photoelectron spectroscopy, transmission electron microscopy, and transmission electron diffraction, the films were nearly stoichiometric and the initial growth of nanocrystalline 3C–SiC at ∼600 °C under ion irradiation was observed.
Calibration of etching uniformity for large aperture multilevel diffractive optical element by ion beam etching
Authors: Fu Yongqi , Bryan Ngoi Kok Ann , Shing Ong Nan
Published: July 2002

Ion beam milling is a suitable technique for manufacturing optical elements. It has the advantages of accurately controlling and maintaining a constant optical index. However, it is very difficult to ensure etching uniformity on large areas due to the instability of the machine during sputtering. In this article, the etching speed is analyzed, and selection criteria of corresponding technological parameters are proposed. An available calibration method is put forth to improve etching depth uniformity. Etching is divided into several steps and the sample is rotated to change its position on the target after each step. It is proved by experiment that this is very practical for actual fabrication with a 5%–15% improvement of depth uniformity from previous results.
Ion sources for large area processing (invited)
Authors: Naito M. , Ando Y. , Inouchi Y. , Tanaka H. , Miyamoto N.
Published: July 2002

Large area ion sources have been used in ion doping systems in the field of LCD production. In these ion sources good uniformity and wide dynamic range in beam current are both required to achieve the good dose uniformity in wide dose range. A new ion source which uses dc arc discharge with three filaments, each of which is controlled individually, is now in the production lines instead of the conventional rf discharge type. Better than 5% of beam uniformity across 600 mm is achieved by an automated feedback control using beam profile data taken by a built-in beam profiler in less than 10 s from arc ignition. Another emerging requirement is high beam purity, for the ion beams from these ion sources are used without mass analysis. The hydrogen ion fraction was successfully reduced by magnetically retarding the hydrogen ions to less than 5%. A large area ion source having a newly designed mass separating structure is developed. The structure is comprised of a permanent magnet array and a beamlet scanner just after the multiple-slot beam extraction electrode system. All the unwanted ion species in the beam can be eliminated to a good level.
Aberrations due to solenoid focusing of a multiply charged high-current ion beam
Authors: Grégoire G. , Kugler H. , Lisi N. , Schnuriger J.-C. , Scrivens R. , Tambini J.
Published: July 2002

At the output of a laser ion source, a high current of highly charged ions with a large range of charge states is available. The focusing of such a beam by magnetic elements causes a nonlinear space-charge field to develop which can induce large aberrations and emittance growth in the beam. Simulation of the beam from the CERN laser ion source will be presented for an ideal magnetic and electrostatic system using a radially symmetric model. In addition, the three dimensional software KOBRA3 is used for the simulation of the solenoid line. The results of these simulations will be compared with experiments performed on the CERN laser ion source with solenoids (resulting in a hollow beam) and a series of gridded electrostatic lenses.
Beam diagnostics extracted from radio frequency driven ion source
Authors: Abdelaziz M. E. , Zakhary S. G. , Ragheb M. S.
Published: July 2002

Lower ignition voltage (50 up to 200 V) and higher plasma intensity feature the characteristics of the rf driven in vacuum arc ion source. The source is considered self-extracted ion current and could deliver ion currents of ∼10 mA for thin beam (φ∼4 mm) and ∼20 mA for broad beam (φ∼6 cm) at ∼200 V extraction voltage. In this work an investigation is made for the beam diagnostics which include: the beam profiles, beam emittance, energy spread and distribution of the ion species in the ion beam. The increase of the anode voltage affects the decrease of the beam emittance, while the energy spread increases with the decrease of the discharge pressure. The beam emittance is found to be around 200 up to 400 mm mrad. and the energy spread of the ions in the ion beam is around 40 up to 80 eV. The Ar ion specie extracted from the source could reach Ar+5. The beam profiles show that the beam is more convergent with the increase of the accelerating voltage and with the use of proper capacitors between the extraction electrodes.
Production of organosilicon ions for SiC epitaxy
Authors: Kiuchi Masato , Matsumoto Takashi , Mimoto Kazuhiko , Takeuchi Takae , Goto Seiichi
Published: July 2002

The production of organosilicon ions in a Freeman-type ion source were studied for SiC heteroepitaxial growth on a Si wafer. One of the possibilities for SiC epitaxy is a low energy deposition of an organosilicon ion beam. The advantage of this technique is that the organosilicon ion already has a binding of Si and C. The organosilicon ion usually also has a dipole moment which is useful for atomic arrangement on a depositing surface. Methylsilane and dimethylsilane were introduced in a Freeman-type ion source and discharged for ionization. Because of fragmentation, methylsilylene ions and methylsilicenium ions were produced. The ions were accelerated and mass selected in order to create a well defined ion beam. The energy distribution, measured by a plasma monitor, was ±1 eV. By using this ion beam, heteroepitaxitial growth of 3C-SiC on Si was successfully created.
Influence of sapphire nitridation on properties of gallium nitride grown by metalorganic chemical vapor deposition
Authors: Keller S. , Keller B. P. , Wu Y.-F. , Heying B. , Kapolnek D. , Speck J. S. , Mishra U. K. , DenBaars S. P.
Published: July 2002

The properties of 1.2 μm thick GaN films were found to be significantly influenced by the duration of exposing the sapphire substrate to ammonia prior to the GaN growth initiation. The different nitridation schemes of sapphire strongly affect the dislocation structure of GaN films resulting in a decrease of the dislocation density from 2×1010 to 4×108 cm−2 for shorter NH3 preflow times. Room- and low-temperature electron transport characteristics of these films are specifically affected by the dislocation structure. A 300 K electron mobility as high as 592 cm2/V s was obtained for a short ammonia preflow whereas a long nitridation caused the mobility to drop to 149 cm2/V s. Additionally, the photoluminescence quality deteriorates for samples with a long sapphire nitridation time.
Passivation of Si(111)-7×7 by a C60 monolayer
Authors: Dunn A. W. , Moriarty P. , Upward M. D. , Beton P. H.
Published: July 2002

C60 monolayers are formed on a Si(111)-7×7 surface under ultrahigh vacuum (UHV) conditions. The effects of exposure to atmosphere (for 30 min) and water (for 30 s) are assessed by comparing images of the surface acquired using an UHV scanning tunneling microscope. Following exposure and/or immersion we are able to resolve the C60 molecules exhibiting hexagonal order in an arrangement which is essentially identical to that formed prior to withdrawal from the UHV system. Our results clearly show that deposition of one monolayer of C60 on a Si surface can inhibit chemical attack by water and atmospheric oxygen.
Textured diamond films growth on (100) silicon via electron-assisted hot filament chemical vapor deposition
Authors: Fu G. S. , Wang X. H. , Yu W. , Han L. , Dong L. F. , Li X. W.
Published: July 2002

Textured (100) diamond films are successfully grown on single-crystalline (100) silicon substrate by electron assisted hot filament chemical vapor deposition from a gas mixture of methane and hydrogen. The effects of various parameters have been studied. The optimal growth conditions are obtained and the oriental growth character is discussed.
Ion beam etching of GaAs: Influence of etching parameters on the degree of radiation damage
Authors: Borzenko T. B. , Koval Y. I. , Kulik L. V. , Larionov A. V.
Published: July 2002

The possibility of decreasing the radiation damage of GaAs during ion beam etching was investigated with the help of a photoluminescence spectra study of GaAs/InGaAs/GaAs heterostructures with near surface quantum wells. It was shown that the change of normal ion incidence to oblique and the decrease of the sample temperature to that of liquid nitrogen cause minimum radiation damage to GaAs.
Coherent control of cyclotron emission from a semiconductor using sub-picosecond electric field transients
Authors: Huggard P. G. , Cluff J. A. , Shaw C. J. , Andrews S. R. , Linfield E. H. , Ritchie D. A.
Published: July 2002

We have demonstrated the excitation and control of coherent cyclotron emission from a semiconductor using a THz beam containing pairs of sub-picosecond electric field pulses closely spaced in time. The source of THz radiation in these experiments is a biased coplanar stripline fabricated on semi-insulating GaAs and edge illuminated with pairs of temporally and spatially separated 70 fs pulses of near infrared light. A GaAs/AlGaAs two-dimensional electron gas was used in the experiments because of its long intraband phase relaxation time. Changes in the amplitude and phase of the cyclotron emission are observed when varying the interpulse delay and are well described within the theoretical framework of a two level system.
Single DNA molecule grafting and manipulation using a combined atomic force microscope and an optical tweezer
Authors: Shivashankar G. V. , Libchaber A.
Published: July 2002

In this letter, we report on spatially selecting and grafting a DNA-tethered bead to an atomic force microscope (AFM) cantilever, using an optical tweezer. To quantify this technique, we measure force versus extension of a single DNA molecule using AFM. For such studies, we have developed a micromanipulation approach by combining an AFM, an optical tweezer, and visualization setup. The ability to select a single DNA polymer and specifically graft it to a localized position on a substrate opens up new possibilities in biosensors and bioelectronic devices.
Rotating-compensator multichannel ellipsometry for characterization of the evolution of nonuniformities in diamond thin-film growth
Authors: Lee Joungchel , Rovira P. I. , An Ilsin , Collins R. W.
Published: July 2002

A multichannel spectroscopic ellipsometer based on the rotating-compensator principle has been applied to obtain the evolution of spectra (1.5–4.0 eV) in the normalized Stokes vector of the light beam reflected from the surface of a nanocrystalline diamond film during growth. Spectra in the ellipsometry angles (ψ, Δ) provide the time evolution of the microstructure and optical properties of the film in thin layers, whereas the spectra in the degree of polarization provide the time evolution of nonuniformities in the growth process attributed to light scattering by diamond nuclei in the initial stage of growth and to thickness gradients over the probed area in thicker layers.
540 mW of blue output power at 425 nm generated by intracavity frequency doubling an upconversion-pumped Er3+:YLiF4 laser
Authors: Möbert P. E.-A. , Heumann E. , Huber G. , Chai B. H. T.
Published: July 2002

We report efficient room-temperature continuous-wave intracavity frequency doubling of an upconversion-pumped Er(1%):YLiF4 laser at 850 nm. A titanium–sapphire laser was used for excitation of the S3/24→I13/24 transition in erbium. The maximum laser output power at 850 nm was 1200 mW. Intracavity frequency doubling the fundamental wave utilizing lithium triborate as nonlinear crystal yielded a maximum second-harmonic output power of 540 mW at 425 nm.
Size-quantized CdS films in thin film CuInS2 solar cells
Authors: Gal Dori , Hodes Gary , Hariskos Dimitri , Braunger Dieter , Schock Hans-Werner
Published: July 2002

Semiconductor quantum dots and wires are the subject of great interest, mainly due to their size-dependent electronic structures, in particular increased band gap and therefore optoelectronic properties. We have electrodeposited films of size-quantized CdS (∼4 to 5 nm cross section by 15 nm height) as a buffer layer on CuInS2. The resulting CuInS2/CdS thin-film solar cells gave increased photocurrents and higher light-to-electricity conversion efficiencies (>11%) than those made with conventional nonquantized CdS films. This was due mainly to the increased band gap of the quantized CdS, allowing more light to reach the active CuInS2 layer.
Organic complementary ring oscillators
Authors: Lin Y.-Y. , Dodabalapur A. , Sarpeshkar R. , Bao Z. , Li W. , Baldwin K. , Raju V. R. , Katz H. E.
Published: July 2002

We report the characteristics of complementary organic ring oscillators. The shortest delay time measured is 38 μs per stage that corresponds to a 2.63 kHz oscillation frequency. The active material in the n-channel transistors is copper hexadecafluorophthalocyanine and that in the p-channel transistors is an oligothiophene/oligothiophene derivative.
Reaction of nanometer-sized Cu particles with a SiO2 substrate
Authors: van den Oetelaar L. C. A. , van den Oetelaar R. J. A. , Partridge A. , Flipse C. F. J. , Brongersma H. H.
Published: July 2002

The thermal stability of nanometer-sized Cu particles on a 400–500 nm thick SiO2 layer on top of a Si(100) substrate was studied after annealing in ultrahigh vacuum up to 620 °C. Atomic force microscopy, low-energy ion scattering, Rutherford backscattering spectrometry, and Auger electron spectroscopy measurements clearly show that Cu-silicide islands are formed. A direct reaction of Cu with the SiO2 support is assumed, which is facilitated by a fairly strong metal-support interaction and by the wetting behavior of the silicide islands. Exposure to air at room temperature results in regeneration of the annealed Cu/SiO2 system.
An ohmic nanocontact to GaAs
Authors: Lee Takhee , Liu Jia , Janes D. B. , Kolagunta V. R. , Dicke J. , Andres R. P. , Lauterbach J. , Melloch M. R. , McInturff D. , Woodall J. M. , Reifenberger R.
Published: July 2002

The formation and characterization of nanometer-size, ohmic contacts to n-type GaAs substrates are described. The nanocontacts are formed between a single-crystalline, nanometer-size Au cluster and a GaAs structure capped with layer of low-temperature-grown GaAs (LTG:GaAs). An organic monolayer of xylyl dithiol (p-xylene-α,α′- dithiol; C8H10S2) provides mechanical and electronic tethering of the Au cluster to the LTG:GaAs surface. The I(V) data of the Au cluster/xylyl dithiol/GaAs show ohmic contact behavior with good repeatability between various clusters distributed across the surface. The specific contact resistance is determined to be 1×10−6 Ω cm2. Current densities above 1×106 A/cm2 have been observed.
Optical absorption edge characteristics of cubic boron nitride thin films
Authors: Chen Guanghua , Zhang Xingwang , Wang Bo , Song Xuemei , Cui Bentao , Yan Hui
Published: July 2002

Boron nitride films with different cubic phase contents were deposited in a radio frequency bias sputtering system by a two-stage deposition process. The Fourier transform infrared spectra and UV-visible transmittance and reflection spectra were measured. The optical absorption edge of BN films consists of a low energy region in which α increases exponentially as incident photon energy hν, and a high energy region, in which α varies as (hν)m, which is the characteristics of amorphous materials. These two regions are fitted by the Urbach tail model and the band-to-band transition model with an effective medium approach, and the Urbach energy and the optical band gap are determined from these fits. With an increase in the cubic boron nitride (c-BN) content, the absorption edge shifts to the higher energy and the optical band gap increases. For a BN film with 88% cubic phase, the optical band gap exceeds 6.0 eV, which is comparable to that of c-BN single crystal.
Photonic stopbands and light transmission characteristics in GaAs-based three dimensional waveguides with large index contrast
Authors: Bhattacharya Pallab , Zhou Weidong , Zhu Donghai , Sabarinathan Jayshri
Published: July 2002

A relatively simple technique to realize a III–V semiconductor based quasi-three-dimensional photonic crystal material with a refractive index contrast ∼2 is described. Fourier transform infrared spectroscopy measurement reveals a stop band between 15 and 20 μm for a sample with scattering center spacing of 6.3 μm. Another narrow transmittance dip is observable in the wavelength range of 1.1–1.58 μm, with an attenuation of 12 dB at 1.18 μm. The relation between transmission T and waveguide length L, as measured by 1.15 μm wavelength light is either T−L−2 or T−exp(−L/L0), indicating photon localization in the weakly disordered system.
Ferroelectricity in sol-gel derived Ba0.8Sr0.2TiO3 thin films using a highly diluted precursor solution
Authors: Cheng Jian-Gong , Meng Xiang-Jian , Li Biao , Tang Jun , Guo Shao-Ling , Chu Jun-Hao , Wang Min , Wang Hong , Wang Zhuo
Published: July 2002

Barium strontium titanate films with good ferroelectricity have been obtained by a developed sol-gel processing, using a highly dilute spin-on solution. X-ray diffraction and scanning electron microscopy investigations show that large grains with the size of 100–200 nm in the films are formed from highly dilute spin-on solutions with layer-by-layer homoepitaxy. Polarization-electric field and dielectric constant-temperature (εr−T) measurements reveal that the ferroelectricity becomes more evident as the grain size increases. The measurements for quality Ba0.8Sr0.2TiO3 ferroelectric films derived from a 0.05 M solution have shown a remnant polarization of 3.5 μC/cm2, a coercive field of 86 kV/cm, and two distinctive phase transitions.
Device degradation of polymer light emitting diodes studied by electroabsorption measurements
Authors: Giebeler C. , Whitelegg S. A. , Lidzey D. G. , Lane P. A. , Bradley D. D. C.
Published: July 2002

We have studied the device degradation of single layer poly(2,5-dialkoxy-p-phenylenevinylene) light emitting diodes by electroabsorption spectroscopy. The applied direct current (dc) bias generates an opposing internal field. This internal field rises as the applied dc bias is increased. The development of the internal field is less pronounced in vacuum than in an ambient atmosphere and is no longer apparent for devices that were prepared and tested under an inert atmosphere in a glovebox. For the devices that were tested in air and under dynamic vacuum conditions we have also observed a change in the flat band voltage of the devices due to an aging effect on the electrodes. The combination of these two processes leads to an increase in the device turn-on voltage with increasing operating time.
Highly balanced long-baseline single-layer high-Tc superconducting quantum interference device gradiometer
Authors: Eulenburg A. , Romans E. J. , Carr C. , Millar A. J. , Donaldson G. B. , Pegrum C. M.
Published: July 2002

We describe a direct-current superconducting quantum interference device (SQUID) first-order gradiometer fabricated from a single layer of YBa2Cu3O7 on a 30×10 mm2 bicrystal substrate. The device has a baseline of 13 mm and an intrinsic balance of ∼10−3. The gradient sensitivity at 77 K and 1 kHz is 50 fT/(cmHz) in magnetic shielding and 260 fT/(cmHz) when operated unshielded in our laboratory. An antiparallel two-SQUID coupling scheme is employed to optimize the device’s balance to at least 3×10−5.
Experimental test for elastic compliance during growth on glass-bonded compliant substrates
Authors: Moran P. D. , Hansen D. M. , Matyi R. J. , Mawst L. J. , Kuech T. F.
Published: July 2002

Highly mismatched films (In0.44Ga0.56As, 3% mismatch) grown well beyond their critical thickness (to 3 μm) on GaAs glass-bonded compliant substrates exhibit surfaces four times smoother and strain distributions twice as narrow as films grown simultaneously on conventional GaAs substrates. The compliant substrates consist of a thin (∼10 nm) GaAs template layer bonded via a borosilicate glass to a mechanical handle wafer. The improvement of highly mismatched films grown well beyond their critical thickness on compliant substrate structures is commonly modeled in terms of an elastic partitioning of strain from the film to the thin (∼10 nm) single-crystal template layer. The present study is a direct test for this mechanism of elastic compliance. A comparison is reported of the strain in 92 nm In0.09Ga0.91As films and 76 nm In0.03Ga0.97As films grown simultaneously on conventional GaAs substrates and the compliant substrates responsible for the improved structural quality of In0.44Ga0.56As films. Elastic partitioning of strain from the mismatched film to the 10 nm template layer prior to the onset of misfit dislocations is not observed for films grown on these glass-bonded compliant substrates.
The effect of anisotropy on the second virial coefficient of H2
Authors: Harvey Allan H. , Hodges Matthew P.
Published: July 2002

We have calculated the second virial coefficient B(T), including quantum corrections, from a pair potential for hydrogen recently developed from ab initio calculations. Previous comparisons with experimental second virial coefficients used an isotropic simplification of the potential. We compute B(T) for the full anisotropic potential in a semiclassical expansion for temperatures above 100 K and compare the results with experiment. We find that the effect of the anisotropy at the temperatures considered is of similar magnitude to the uncertainty in the best data. Even with this more rigorous calculation, the second virial coefficient predicted by the potential is consistently too positive by an amount somewhat greater than the experimental uncertainty.
Gauge-origin independent magneto-optical activity within coupled cluster response theory
Authors: Coriani Sonia , Hättig Christof , Jørgensen Poul , Helgaker Trygve
Published: July 2002

A gauge-origin invariant formulation of the frequency-dependent Verdet constant V(ω) of magneto-optical rotation and of the Faraday ℬ term of magnetic circular dichroism for coupled-cluster wave functions is derived within the framework of variational response theory. Working expressions suitable for implementation in ab initio program packages are presented. These expressions have a structure similar to that of the expressions for the first hyperpolarizability and the two-photon transition moment, respectively, for the Verdet constant and the ℬ term. The approach is general and can easily be extended to other similar frequency-dependent properties as well as to other wavefunction models. Pilot results at the CCSD level are presented for V(ω) of HF and H2.
Temperature effect on the deactivation of electronically excited potassium by hydrogen molecule
Authors: Hsiao Yen-Chin , Liu Dean-Kuo , Fung Hok-Sum , Lin King-Chuen
Published: July 2002

Time-resolved fluorescences from varied K excited states are monitored as a function of H2 pressure. According to a three-level model, the rate coefficients of collisional deactivation for the K 6 2S, 7 2S, and 8 2S states at 473 K have been determined to be 4.94±0.15, 5.30±0.15, and 5.44±0.15×10−9 cm3 molecule−1 s−1. In addition, the collision transfer of S2−D2 transition may be derived to be 5.03±0.21, 4.68±0.30, and 4.89±0.36×10−9 cm3 molecule−1 s−1, showing dominance of the S2-state deactivation processes owing to the effect of near-resonance energy transfer. As the temperature is varied, the activation energies for the collisions of K(6 2S), K(7 2S), and K(8 2S) atoms with H2, respectively, may be estimated to be 5.38±0.33, 4.39±0.16, and 3.23±0.19 kJ/mol. The first two values are roughly consistent with the theoretical calculations of 3.1 and 0.9 kJ/mol in C∞v symmetry predicted by Rossi and Pascale. The obtained energy barriers are small enough to allow for occurrence of the harpoon mechanism, a model applicable to the reactions between H2 and alkali atoms such as K, Rb, and Cs. Among them, K–H2 collisions appear to be the first case to possess a slight energy barrier. This finding of energy barrier may account for the discrepancy for the state reactivity towards H2 observed between K (or Rb) and Cs atoms.
Strong and stable ultraviolet luminescence in porous silicon in situ passivated by manganese
Authors: Chen Qianwang , Zhu D. L. , Zhang Y. H.
Published: July 2002

A strong and stable ultraviolet photoluminescence (PL) band (370 nm) together with a red luminescence band around 670 nm with a 730 nm shoulder were observed in Mn-passivated porous silicon (PS) prepared by the hydrothermal technique. The surface structure is examined by Fourier infrared and x-ray photoelectron spectroscopy analysis. The 670 nm band was confirmed to be the usually observed PL band in PS, and the appearance of the 370 nm band and 730 nm shoulder peak was interpreted based on surface structure characterization and spectroscopy measurements.
Anisotropic polarization memory in thermally oxidized porous silicon
Authors: Koyama Hideki , Fauchet Philippe M.
Published: July 2002

Visible photoluminescence (PL) from thermally oxidized porous silicon (PSi) has been investigated in terms of polarization memory (PM). The PSi samples were prepared by anodization of (100)p+-Si wafers in a HF/ethanol solution, followed by thermal oxidation at 700–1000 °C. These oxidized PSi samples show significantly anisotropic PM which depends largely on the polarization direction of the excitation light with respect to their crystallographic axes. In addition, the anisotropic PM from samples oxidized at 800 and 900 °C shows an anomalous emission-energy dependence. It is also observed that thermal oxidation at 1000 °C results in a significant decrease in the degree of PM, although it increases with increasing oxidation temperatures for ⩽900 °C. These experimental results suggest that the PL from oxidized PSi cannot be explained as a simple extension of the PL from as-anodized PSi and should be attributed to several different origins.
Ultrashallow junctions in silicon formed by molecular-beam epitaxy using boron delta doping
Authors: Thompson Phillip E. , Bennett Joe
Published: July 2002

Low-temperature molecular-beam epitaxy was used to form highly conductive, ultrashallow layers in silicon using boron delta doping. Junction depths, determined with secondary ion mass spectrometry, ranged from 7 to 18 nm. A minimum resistivity of 3×10−4 Ω cm was obtained when the delta-doped layers were spaced 2.5 nm apart. The sheet resistances of the epitaxial layers, plotted as a function of junction depth, followed the theoretical curve for a box-doped layer having a boron doping concentration equal to the solid solubility limit, 6×1020/cm3. At a specific thickness, the minimum sheet resistance obtained by B delta doping was more than a factor of 5 less than that achieved by ion implantation.
Electron-beam-induced reactivation of Si dopants in hydrogenated GaAs: A minority carrier generation effect or an energetic electron excitation effect?
Authors: Silvestre S. , Bernard-Loridant D. , Constant E. , Constant M. , Chevallier J.
Published: July 2002

We study the changes in electronic properties of Si-doped GaAs epilayers exposed to a hydrogen or a deuterium plasma, and then submitted to electron-beams of different injection energies (between 10 and 50 keV). Using Hall effect measurements, we have observed the formation of Si–H or Si–D complexes and their dissociation induced by the electron-beam irradiation. A strong isotope effect is observed in the dissociation rate of these complexes. Moreover, increasing injection energy reduces the dopant reactivation efficiency. Both effects are quite difficult to explain assuming minority carrier induced dissociation and could be understood under the light of recent works on electronic excitation of Si–H complexes in GaAs, and also of Si–H (D) bonds at the surface of silicon.
Dislocations as a source of micropipe development in the growth of silicon carbide
Authors: Cherednichenko D. I. , Khlebnikov Y. I. , Khlebnikov I. I. , Drachev R. V. , Sudarshan T. S.
Published: July 2002

Micropipes are the primary macroscopic defects in silicon carbide single crystals. It is shown that a stable hollow core of dislocation can act as an initial site of micropipe development. The specific strain energy necessary to estimate the thermodynamic stability of a hollow dislocation core is expressed in terms of the macroscopic parameters of the material Young’s modulus and of the Gruneisen constant.
Comment on “A general property of endoreversible thermal engines” [J. Appl. Phys. 81, 2973 (1997)]
Authors: Yan Zijun
Published: July 2002

It is pointed out that one cannot regard the function E=P−T2σ as the best ecological function. The proof of the best ecological function in a recent article is of no significance. Moreover, it is emphasized that the genuine loss power should be considered in the definition of the ecological function.