bluuebunny/crossref_metadata_2025 huggingface dataset:
Localized thermal analysis using a miniaturized resistive probe
Authors: Hammiche A. , Reading M. , Pollock H. M. , Song M. , Hourston D. J.
Published: July 2002

We describe a novel thermal characterization technique based on a differential arrangement, which achieves spatially localized calorimetric analysis. It involves the use of an active probe which acts both as a highly localized heat source and a thermometer. This ability opens the way for the implementation of scanning calorimetric microscopy where image contrast will be created from thermal analysis data. For a number of polymers we have recorded events such as glass transitions, meltings, recrystallizations and thermal decomposition within volumes of material estimated at a few μm3. The data obtained are compared with those obtained from conventional calorimetry and the events registered in both cases are found to match. For a full quantitative analysis of the results obtained, mathematical modelling of the operation of the technique, taking account of physical and other changes in materials, is required.
Tracking real characteristics by multiple-point autocalibration and the tangent method applied to ideal characteristics
Authors: Marić Ivan
Published: July 2002

The measurement system transfer characteristic is an unsteady, nonlinear function that depends upon time and ambient conditions. The article presents a method of tracking the real characteristic by using periodic autocalibration of the real characteristic and by applying a tangent method to the ideal characteristic. The efficiency of the algorithm has been verified for dc current generation. Periodic autocalibration fixes the current state of the measurement system characteristic by measuring internal references. The correction of a quantity at the input of the current generator is calculated from measurement of its output quantity and by using a tangent method applied to the ideal current generator characteristic.
A high spatial resolution in low-temperature microphotoluminescence with far-field optics
Authors: Kasai Jun-ichi , Katayama Yoshifumi
Published: July 2002

We report the results of spatial-resolution measurements on an optical setup for low-temperature microphotoluminescence with far-field optics. The spatial resolution of the optical setup was estimated by observing photoluminescence images of a luminescent line formed in a cleaved face of a quantum-well crystal. A high spatial resolution of 0.43 μm was obtained at a 457.9 nm excitation wavelength.
Multichannel source of synthesized ion-electron flow
Authors: Bizioukov A. A. , Kashaba A. Y. , Sereda K. N. , Tseluyko A. Ph. , Yunakov N. N.
Published: July 2002

In this article, we present a multichannel source with cold electrodes generating spatially combined ion and electron beams with homogeneous profile of current density on 100 mm diam. The source was designed on the basis of a modified Penning cell. The anode configuration provides high current efficiency, reaching 50% under certain conditions. The source has two operating modes: ion beam generation and synthesized ion-electron flow. High current densities 0.5–5 mA/cm2 of ion and electron beams with energies in the range of 0.5–7 keV under low working pressure (1–10)×10−5 Torr are the advantage of this source.
Fabry–Perot interferometer in Brillouin scattering experiments
Authors: Bl/achowicz Tomasz , Bukowski Roman , Kleszczewski Zygmunt
Published: July 2002

The Fabry–Perot interferometer has become a standard spectroscopic tool in scientific laboratories for the study of Brillouin scattering. This article examines some basic properties of the Fabry–Perot interferometer with the student or beginning user in mind in order to demonstrate why it is especially useful for this application. Single and complex Fabry–Perot systems in use for Brillouin scattering studies are discussed starting from elementary equations to show, in particular, how the half-width of the transmission function depends upon the instrumental configuration. The primary results are summarized in graphical form.
Design and characterization of a digital control system for the flow through a microporous membrane
Authors: Molina C. , Arenas A. , Victoria L. , Ibáñez J. A.
Published: July 2002

In many scientific and industrial applications the permeating flow through a membrane separating two fluid phases must be kept constant, either because the flow is feeding another system which requires a constant in-flow, or because membrane fouling is being studied and it is necessary to know what must be done to maintain the flow. We describe a digital proportional-integral controller which makes it possible to maintain a constant permeating flow through a Nuclepore membrane with 8 μm mean pore radius.
Convergent ellipsometry around Brewster angle for quantitative evaluation of Langmuir films
Authors: Hosoda Maiko , Kobayashi Hiroshi , Sakamoto Naoto , Sakai Keiji , Takagi Kenshiro
Published: July 2002

A new technique of Brewster angle ellipsometry was developed for quantitative evaluation of the Langmuir films extended on water surface. A laser beam with P polarization is focused onto the film with its main axis at the Brewster angle θB. The angular distribution of the reflected light is observed by spatial scan of a photodetector. The scan along the direction of P polarization for the reflected light gives the angular dependence of the reflectivity of P-polarized light, which has a minimum at θB. The presence of a Langmuir film causes an increase in the minimum reflectivity, from which the quantities such as thickness or density of the adsorbed molecules are obtained. A Langmuir film of stearic acid in its condensed phase was used as a test specimen. The result showed an increase of 2.0×10−6 in the minimum reflectivity, determined accurately to 10−7. The curve of reflectivity was in very good agreement with a prediction by a theory of geometrical optics made with the assumption that the index of refraction of the film is equal to that of bulk liquid and that the film thickness is equal to the molecular length. The spatial resolution on the film is ∼100 μm determined by the focused spot of the laser. This technique has the potential for optical absorption measurement in monolayer film.
Design and tests of the new partially ionized beam source
Authors: Koh S. K. , Jang H. G. , Choi W. K. , Jung H.-J. , Kondranine S. G. , Kralkina E. A.
Published: July 2002

We developed and evaluated a new partially ionized beam (PIB) source to deposit high quality Cu films. The novelty of the PIB source lies in the fact that the crucible and ionization parts are spaced in one cylindrical shell to make its structure compact and to get a uniform beam profile, but their electric circuits are not separated. In this article, we report the characteristics of the PIB source, such as voltage-ampere characteristics of the crucible and ionization parts, Cu+ ion beam uniformity with a change of the ionization currents, and deposition rate.
Vertical ramp-actuated inertial micropositioner with a rolling-balls guide
Authors: Yakimov V. N.
Published: July 2002

A vertical inertial micropositioner for scanning probe microscopy was developed and tested. The special feature of the micropositioner is the employment of a rolling-balls guide for translation of a slider. The guide and a slider with a clamping mechanism are placed on the base of the micropositioner, and not on a piezoelement. The maximal unloading of the piezodrive allows us to keep its resonance frequencies high. This factor and the large force of the slider clamping permit us to apply a conventional sawtooth voltage for vertical motion. Such a micropositioner design makes it possible to simplify the driver electronics and to increase the mass of the translating part without significant reduction of the eigenfrequencies of the device. Step sizes from 22 to 1340 nm and speeds up to 0.7 mm/s are obtained. The micropositioner is capable of translating loads up to 25 g against gravity. Conditions for the use of the sawtooth wave form as an actuating voltage in the vertical inertial piezopositioner are also discussed.
Performance of the ion source DECRIS-14-2
Authors: Efremov A. , Behterev V. , Bogomolov S. L. , Kutner V. B. , Lebedev A. N. , Loginov V. N. , Yazvitsky Y. Yu
Published: July 2002

The Dubna electron cyclotron resonance ion source DECRIS-14-2 was put into regular operation at the U-400M cyclotron in the beginning of 1995. During the past two years the source has produced a wide range of ion beams for physics experiments as well as for the testing of the beam transport lines and the cyclotron itself. Ions of gases, such as He, N, O, Ne, and Ar were successfully delivered and accelerated in the cyclotron. The ion source has shown good performance especially in the case of middle charge state ions (e.g., 600 eμA of Ar8+) as well as high operational reliability. Significant progress in metal ion production has been achieved by introducing a new microoven for the evaporation of metal samples. This microoven in combination with an additional tantalum sheet installed inside the discharge chamber has made it possible to obtain Li2+ ion beams in excess of 200 eμA.
High-density plasma production for neutralizing negative ion beam
Authors: Tanaka M. Y. , Bacal M. , Sasao M. , Kuroda T.
Published: July 2002

An electron cyclotron resonance (ECR) plasma production method using electron cyclotron wave is presented. This method is not subjected to any cutoff-density scaling, and is capable of generating dense plasmas far beyond the critical density of an ordinary wave. It has been demonstrated that a plasma density more than 1013 cm−3 (argon) is obtained with a low frequency (2.45 GHz) and low power (11 kW) microwave. The experimental results and the application to plasma neutralizer are described. The experimental verification of superpermeability of Nb membrane in a plasma environment is in progress to develop a plasma neutralizer with Nb-membrane wall. The design parameters of Nb-membrane pump are presented.
Some characteristics of moderate energy metal ion beam focusing by a high current plasma lens
Authors: Goncharov A. , Dobrovolsky A. , Protsenko I. , Kaluh V. , Onishenko I. , Brown I.
Published: July 2002

The results of experiments on moderate energy (4–25 keV) metal ion beam focusing by a high current plasma lens (PL) are presented. The ion beam was produced by a two-chamber vacuum–arc metal vapor vacuum arc (MEVVA)-type ion source. Characteristics of the beam passing through the lens have been measured and the PL focusing properties determined for a wide range of ion beam energy and current. Distributions have been determined of the external potential along the lens electrodes that provide maximum increase of the beam current density on axis. Certain features of metal ion beam focusing by the PL are discussed. Some of these characteristics depend on the method of application of the external electric potential to the lens electrodes.
Time-resolving, position-sensitive detection system for scattering and recoiling imaging spectrometry
Authors: Kim C. , Al-Bayati A. , Rabalais J. W.
Published: July 2002

A time-resolving, position-sensitive, single particle detector has been developed for scattering and recoiling imaging spectrometry. A custom designed multiple stop time-to-digital converter is integrated with a commercially available position sensitive detector system utilizing microchannel plates and a resistive anode encoder. The detector system successfully captures images of scattered and recoiled ions and fast neutrals from surfaces in time frames as short as 10 ns.
Design of a laboratory scale fluidized bed reactor
Authors: Wikström E. , Andersson P. , Marklund S.
Published: July 2002

The aim of this project was to construct a laboratory scale fluidized bed reactor that simulates the behavior of full scale municipal solid waste combustors. The design of this reactor is thoroughly described. The size of the laboratory scale fluidized bed reactor is 5 kW, which corresponds to a fuel-feeding rate of approximately 1 kg/h. The reactor system consists of four parts: a bed section, a freeboard section, a convector (postcombustion zone), and an air pollution control (APC) device system. The inside diameter of the reactor is 100 mm at the bed section and it widens to 200 mm in diameter in the freeboard section; the total height of the reactor is 1760 mm. The convector part consists of five identical sections; each section is 2700 mm long and has an inside diameter of 44.3 mm. The reactor is flexible regarding the placement and number of sampling ports. At the beginning of the first convector unit and at the end of each unit there are sampling ports for organic micropollutants (OMP). This makes it possible to study the composition of the flue gases at various residence times. Sampling ports for inorganic compounds and particulate matter are also placed in the convector section. All operating parameters, reactor temperatures, concentrations of CO, CO2, O2, SO2, NO, and NO2 are continuously measured and stored at selected intervals for further evaluation. These unique features enable full control over the fuel feed, air flows, and air distribution as well as over the temperature profile. Elaborate details are provided regarding the configuration of the fuel-feeding systems, the fluidized bed, the convector section, and the APC device. This laboratory reactor enables detailed studies of the formation mechanisms of OMP, such as polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), poly-chlorinated biphenyls (PCBs), and polychlorinated benzenes (PCBzs). With this system formation mechanisms of OMP occurring in both the combustion and postcombustion zones can be studied. Other advantages are memory effect minimization and the reduction of experimental costs compared to full scale combustors. Comparison of the combustion parameters and emission data from this 5 kW laboratory scale reactor with full scale combustors shows good agreement regarding emission levels and PCDD/PCDF congener patterns. This indicates that the important formation and degradation reactions of OMP in the reactor are the same formation mechanisms as in full scale combustors.
A versatile pulsed X-band ENDOR spectrometer
Authors: Shane J. J. , Gromov I. , Vega S. , Goldfarb D.
Published: July 2002

A versatile high power X-band (8.5–9.5 GHz) pulsed EPR/ENDOR (electron-nuclear double resonance) spectrometer which can generate hundreds of microwave (MW) and rf pulses is described. The pulse programmer is constructed from a word generator with 32 channels and 4 ns resolution, coupled to five digital delay generators which can produce a total of ten pulses with a resolution better than 1 ns. The spectrometer contains two MW and two rf channels that allow independent variation of the frequency, amplitude, and phase of the MW and rf pulses. The ENDOR probe head is based on a bridged loop gap (BLG) resonator, coupling is achieved via a coupling loop connected to a waveguide, and the rf coil serves as a MW shield as well. The adjustment of the coupling is done by an up/down motion of the of the resonator assembly with respect to the fixed coupling loop. A flexible and user friendly data acquisition program written in C++ (Borland version 4.5), which uses the Windows-95 Multiple Document Interface (MDI) programming model, was developed to run the spectrometer. This program allows easy programming of any pulse sequence with sophisticated phase cycling. The performance of the spectrometer is demonstrated by two experiments. The first is the triple resonance hyperfine-selective (HS) ENDOR experiment carried out on a frozen solution of the copper protein laccase. The second is the two-dimensional hyperfine-ENDOR (HYEND) correlation experiment performed on a single crystal of γ-irradiated malonic acid.
Scanned perturbation technique for imaging electromagnetic standing wave patterns of microwave cavities
Authors: Gokirmak Ali , Wu Dong-Ho , Bridgewater J. S. A. , Anlage Steven M.
Published: July 2002

We have developed a method to measure the electric field standing wave distributions in a microwave resonator using a scanned perturbation technique. Fast and reliable solutions to the Helmholtz equation (and to the Schrödinger equation for two-dimensional systems) with arbitrarily shaped boundaries are obtained. We use a pin perturbation to image primarily the microwave electric field amplitude, and we demonstrate the ability to image broken time-reversal symmetry standing wave patterns produced with a magnetized ferrite in the cavity. The whole cavity, including areas very close to the walls, can be imaged using this technique with high spatial resolution over a broad range of frequencies.
Reflective optics for cosine-corrected irradiance measurements
Authors: Oppitz Carsten , Heering Wolfgang
Published: July 2002

Most of the detectors commonly used for radiometric measurements have a more or less poor cosine response. By means of a reflective entrance optics in front of the detection system, we have reduced relative cosine errors below 5% up to zenith angles of 75°. Cosine correction is performed by a roughened polytetrafluoroethylene (PTFE) plate which diffusely reflects parts of the incident radiation into a light guide with the detector at its end. It provides for a neglectible wavelength cosine error dependence and a significantly better radiant efficiency. Originally designed for irradiance measurements of solar global radiation and its photobiological effective irradiance, the entrance optics may also be used for determination of radiant flux from lamps by integrating the lamp irradiance over an enveloping surface as it is done in spectrogoniometric measurements.
Silicon avalanche photodiodes as detectors for photon correlation experiments
Authors: Overbeck Ekkehard , Sinn Christian , Flammer Ivo , Rička Jaro
Published: July 2002

In view of time correlated photon-counting experiments using wavelengths at the red end of the electromagnetic spectrum, we developed a simple electronic circuit for periodical gated quenching of silicon avalanche photodiodes. We compare the performance of this device with commercially available passive and active quenching modules and a reference photomultiplier. The detection system’s nonlinearities, i.e., dead time and afterpulsing, lead to direct and indirect distortions of photocount correlation functions. We characterize this nonlinear behavior by measuring intensity auto- and cross-correlation functions and supply nonlinearity parameters for each of the four detection systems. In addition, transfer functions are given which allow an estimate for the highest count rates accessible for each detection system.
Hot plasma production in quasisteady arc discharge for divertor plasma simulator
Authors: Kabantsev A. A. , Reva V. B. , Sokolov V. G.
Published: July 2002

This article describes a type quasisteady arc plasma source developed for investigation of edge plasma physics in a fusion device. The source is a modification of the gas-loaded washer-stack plasma gun [J. Osher, Rev. Sci. Instrum. 53, 1685 (1982)]. One of the principal features of describing the source is the formation of electrostatic thermobarrier for plasma electrons near the output of the plasma source. It has been created by changing the polarity of the voltage applied to the discharge as compared with the conventional case. In a new configuration of electrodes, the electrons are accelerated to the back of the injection direction of the plasma flow. A thermobarrier makes it possible to reach the following plasma parameters: Te≈50 eV, n≈5×1013 cm−3, Ti≈200 eV, and q≈1–10 kW/cm2.
Large scanning area near field optical microscopy
Authors: Wei P. K. , Fann W. S.
Published: July 2002

A near field optical microscope with a scanning area up to 1 mm×1 mm was demonstrated. The scanning element is the tapered fiber probe and a cylindrical lens is used to focus the feedback laser. Instead of the vibrational amplitude, the vibrational angle signal is used to regulate the distance between the probe and sample. The microscope was employed to map out the evanescent wave on a channel waveguide.
Resistive and Hall weighting functions in three dimensions
Authors: Koon D. W. , Knickerbocker C. J.
Published: July 2002

The authors extend their study of the effect of macroscopic impurities on resistive and Hall measurements to include objects of finite thickness. The effect of such impurities is calculated for a series of rectangular parallelepipeds with two current and two voltage contacts on the corners of one square face. The weighting functions display singularities near these contacts, but these are shown to vanish in the two-dimensional limit, in agreement with previous results. Finally, it is shown that while Hall measurements principally sample the plane of the electrodes, resistivity measurements sample more of the interior of an object of finite thickness.
A compact Brewster-angle microscope for use in Langmuir–Blodgett deposition
Authors: Marshall Gary , Dennin Michael , Knobler Charles M.
Published: July 2002

A Brewster-angle microscope designed for use in the preparation of Langmuir–Blodgett films has been constructed. The microscope has a compact vertical design and makes use of inexpensive optics.
High resolution electron cyclotron emission temperature profile and fluctuation diagnostic for Alcator C-Mod
Authors: Heard J. W. , Watts C. , Gandy R. F. , Phillips P. E. , Cima G. , Chatterjee R. , Blair A. , Hubbard A. , Domier C. W. , Luhmann N. C.
Published: July 2002

A new second harmonic heterodyne electron cyclotron emission system with high spatial resolution (⩽15 mm) and a large number of channels (32) for dense profile coverage will be installed on Alcator C-Mod. The system will provide detailed radial electron temperature profiles and core temperature fluctuation measurements. The collection system is composed of elliptical and parabolic mirrors coupled to two overmoded waveguides to provide high poloidal spatial resolution necessary for T̃e measurements. Four radiometer sections cover the frequency range of 234–306 GHz, coupled to four optimized intermediate frequency modules with eight channels of detectors, amplifiers, dividers, and filters providing the profile information. A separate filter arrangement allows for temperature fluctuation measurements utilizing correlation techniques.
Microwave reflectometry diagnostic for density profile and fluctuation measurements on ASDEX Upgrade
Authors: Silva A. , Cupido L. , Manso M. , Serra F. , Nunes I. , Santos J. , Varela P. , Vergamota S. , Meneses L. , Grossman V. , Silva F. , Loureiro C. , Nunes F. , Kurzan B. , Suttrop W.
Published: July 2002

The broadband microwave reflectometry system on ASDEX Upgrade has been recently upgraded with new channels. It has now 12 channels that probe simultaneously the high and low fields plasma, with ultrafast sweeping (20–100 μs). X mode (33–75 GHz) is used for the scrape off layer, and the O mode (16–110 GHz) is reflected from densities between 0.3×1019 and 1.5×1019 m−3. A fast sweeping heterodyne system was developed for the highest frequency channels (50–110 GHz) to cope with higher losses and lower incident power. Fixed frequency operation is employed for fluctuation measurements. A dedicated channel (33–55 GHz) operating in fixed frequency provides a signal to continuously monitor the level of density fluctuations (e.g., L–H transition), during the whole discharge. The diagnostic is fully operated by remote control. The acquisition system is based on specially developed VME boards with up to 1 Gsamp/s sampling rates. Automatic profile inversion was recently implemented using data validation and rejection algorithms. Experimental results are presented to illustrate the profile measurements with O mode and with O and X mode combined operation. We present density profiles measured in a wide range of plasma regimes. Profile modifications due to rotating magnetic islands illustrates the potentialities of the reflectometry to estimate the location of the rational q surfaces.
Implementation of scanning electron microscopy with polarization analysis using high-efficiency retarding-potential Mott polarimeters
Authors: Barnes J. , Mei L. , Lairson B. M. , Dunning F. B.
Published: July 2002

The application of a compact high-efficiency retarding-potential Mott polarimeter in scanning electron microscopy with polarization analysis (SEMPA) is described. Such polarimeters, which combine high-efficiency with large electron optical acceptance and stable long-term operation, are shown to be particularly attractive for use in SEMPA.
Atomic force microscope for operation in high magnetic fields at millikelvin temperatures
Authors: Pelekhov D. V. , Becker J. B. , Nunes G.
Published: July 2002

We report on the design and performance of an atomic force microscope which operates at temperatures down to 20 mK and in magnetic fields up to 9 T. The scan range at low temperatures is 4 μm×4 μm. The instrument features a piezoelectric linear motor for vertical coarse approach, and a horizontal sample translation stage with a 2 mm×2 mm range. A fiber interferometer is used to detect the force-sensing cantilever displacement. The performance demonstrated includes the ability to detect single atomic steps on a graphite surface at 4.2 K and the ability to locate and image nanometer scale electronic devices at millikelvin temperatures.
A simple modification of a commercial atomic force microscopy liquid cell for in situ imaging in organic, reactive, or air sensitive environments
Authors: Wade Travis , Garst John F. , Stickney John L.
Published: July 2002

We describe modifications to a commercial atomic force microscopy (AFM) fluid cell to enable imaging in organic and reactive environments and show initial images obtained with this cell. The fluid cell is constructed of glass and Teflon only, both of which are inert in many organic and corrosive fluids. A flange with a viton “O” ring was fitted around the base of the AFM and an airtight Plexiglas cap was placed on top to cover the AFM. The cap was purged with Ar during scanning and fluid transfer. A commercial oxygen sensor was used to measure the oxygen partial pressure. A flow system was used to introduce the solutions into the cell, minimizing atmospheric contamination. The cell was used to image a Mg surface under aqueous and tetrahydrofuran liquids for hours without leaking.
Single molecule force spectrometer with magnetic force control and inductive detection
Authors: Schemmel A. , Gaub H. E.
Published: July 2002

Mechanical investigations with single molecules have opened a rich spectrum of new experiments, ranging from molecular recognition over polymer elasticity and DNA unzipping to protein unfolding. Here we present the design of a novel instrument, where the force is applied to the molecule via magnetic fields acting on a magnetic cantilever for atomic force microscopy. The performance of this instrument was demonstrated by measuring the binding force of biotin/avidin complexes. A new and technically very appealing detection scheme for measurements of unbinding forces was introduced, which consists of picking up the induced voltage pulse caused by a discontinuous change of the magnet position upon bond rupture.
Level meter for dielectric liquids
Authors: Bruschi L. , Delfitto G. , Mistura G.
Published: July 2002

We describe a novel device which can measure, with low dissipation and high resolution, the level of a dielectric liquid. This device can also be used with cryogenic liquids, in particular with liquid helium. The high degrees of stability and of reproducibility make this apparatus an instrument of performances largely competitive with respect to others commonly used.
Line focus system with a segmented prism array for compact x-ray laser experiments
Authors: Yamaguchi Naohiro , Ohchi Tadayuki , Fujikawa Chiemi , Ogata Asuka , Hisada Yoshiyuki , Okasaka Kazunobu , Hara Tamio , Tsunashima Teruyoshi , Iizuka Yutaka
Published: July 2002

We have designed a new focusing system with a five-segmented prism array in combination with a beam expander and cylindrical lens assembly for compact x-ray laser experiments using a yttrium–aluminum–garnet (YAG) laser. The focusing characteristics were examined from irradiation patterns on a target. It was found that a beam of 25 mm diameter whose intensity profile was not uniform was condensed to a focused line having about 12 mm length and 50 μm width with a flat intensity distribution along the line on average, though the small-scale intensity modulation due to interference among the beamlets was observed. Spectroscopic observation of the plasma produced by irradiating the YAG laser of 2 J energy onto an Al slab target showed that highly ionized ions were produced up to the Li-like ionic stage. The new lens system is useful for compact x-ray laser research.
Production of uniform plasma with surface electromagnetic wave launched by a waveguide-surfatron
Authors: Wu Cong-Feng , Zhan Ru-Juan , Wu Shuai
Published: July 2002

A uniform plasma of large volume is produced by using a new waveguide-surfatron. The plasma is uniform within ±5% in a diameter over 160 mm in the diffusion area. The plasma density is 1010–1011 cm−3 with electron temperature 2–4 eV at a microwave power of 500–900 W and a pressure of 10–50 Pa.
Studies on enhancement of x-ray flux in the compact electron cyclotron resonance plasma x-ray source
Authors: Baskaran R. , Selvakumaran T. S.
Published: July 2002

The electron cyclotron resonance (ECR) plasma x-ray source has a potential application for medical imaging. The plasma and x-ray characterization studies on the ECR x-ray source based on cylindrical cavity operated in TE111 mode were reported earlier by us. In order to enhance the x-ray flux and the effective energy of the x-ray spectrum, the use of rectangular cavity in ECR x-ray source is studied. In this article, the theoretical analysis of electron acceleration in TE101 rectangular cavity used as a cyclotron resonance accelerator is presented. The electron orbital values of rectangular cavity are compared with that of cylindrical cavity (TE111 mode). It is found that there is an increase in final energy of electron (170 keV), reduction in electron transit time, and increase in distance between the successive orbits in the rectangular cavity than the cylindrical cavity. An ECR x-ray source based on rectangular cavity has been designed and constructed and the experimental system is described.
Improved direct bonding of Si and SiO2 surfaces by cleaning in H2SO4:H2O2:HF
Authors: Ljungberg Karin , Söderbärg Anders , Jansson Ulf
Published: July 2002

A method for silicon surface preparation prior to wafer bonding is presented. By cleaning the wafers in a H2SO4:H2O2 mixture in which a small amount of HF is added, and then rinsing in H2O, the bonding behavior of the surfaces is improved, compared to other pretreatments used for bonding. The modified SPM cleaning results in a highly fluorinated chemical oxide on the Si surface. A subsequent water rinse causes substitution of F by OH groups, which increase the initial attraction of the mating surfaces. Higher contact wave velocities and bond strengths than reported for other surface pretreatments have been measured, both for bare and thermally oxidized silicon surfaces.
High-resolution x-ray analysis of compressively strained 1.55 μm GaInAs/AlGaInAs multiquantum well structures near the critical thickness
Authors: Krost A. , Böhrer J. , Dadgar A. , Schnabel R. F. , Bimberg D. , Hansmann S. , Burkhard H.
Published: July 2002

Compressively strained InP/GaInAs/AlGaInAs multiquantum well (MQW) laser structures with up to 15 QWs designed for 1.55 μm emission wavelength were grown by metalorganic chemical vapor deposition (MOCVD) on p-type InP(001) substrates. Crystallographic and optical properties are studied using double crystal x-ray diffraction and photoluminescence measurements. The rocking curves of the complicated MQW structure can be perfectly modeled using dynamical diffraction theory. The critical thickness observed for strain relaxation upon growth and laser processing is found to be in good agreement with that predicted by Matthews and Blakeslee [J. Cryst. Growth 27, 118 (1974)] taking into account the MQW structure and the cap layer.
Stress evolution during the growth of ultrathin layers of iron and iron silicide on Si(111)
Authors: Sander D. , Enders A. , Kirschner J.
Published: July 2002

Using a simple optical deflection technique, we measured continuously the mechanical stress during the growth of Fe films of 0.1–1.5 nm thickness on Si(111) in ultrahigh vacuum (UHV). The stress versus coverage dependence is discussed in view of the different growth modes during the various stages of Fe deposition. The deposition of up to 0.3 nm Fe induces a compressive stress of −1 N/m. We assign this stress to the formation of a reactive Fe–Si interface layer with a silicidelike structure. Subsequent Fe deposition at 300 K leads to a small tensile stress of 0.7 N/m, whereas the deposition at 600 K induces a high tensile film stress of 18 N/m. At 600 K substrate temperature, a solid-state reaction between Fe and Si sets in, and the silicide β-FeSi2 is formed. The decrease of the atomic volume of Si by 7% in this silicide is proposed to be the cause for the tensile stress.
Photoluminescence study of C60 doped polystyrene
Authors: Zhang Chun , Xiao Xudong , Ge Weikun , Loy M. M. T. , Dazhi Wang , Qijin Zhang , Jian Zuo
Published: July 2002

We report here a new phenomenon in photoluminescence of C60 doped in polystyrene. Under 488 nm cw laser radiation, the PL intensity of the sample was found to increase with time. With 10 h of irradiation, the PL signal strength increased by 10 times, comparable to that from porous Si. The peak of the PL was found to shift to high frequency as well. More detailed studies showed that such an irreversible change of the sample might be a result of the lowering symmetry of oxidized C60 fullerene in the polystyrene.
Strongly directed single mode emission from organic electroluminescent diode with a microcavity
Authors: Tokito Shizuo , Noda Koji , Taga Yasunori
Published: July 2002

The strongly directed spontaneous emission along the optical axis of an organic electroluminescent (EL) diode with a typical emitting material, tris(8-quinolinolato) aluminum, is realized with a planner microcavity structure. The structure of the microcavity EL diode is designed to have a resonance condition in which the total optical length is 3/2λ and the resonance wavelength λ is located at shorter wavelength side of a natural emission spectrum of a noncavity EL diode.
Growth of Nd3+-doped LiNbO3 optical superlattice crystals and its potential applications in self-frequency doubling
Authors: Lu Ya-lin , Lu Yan-qing , Xue Cheng-cheng , Ming Nai-ben
Published: July 2002

We have grown Nd:MgO:LiNbO3 crystals with periodic ferroelectric domain structures. Absorption and fluorescence spectra measured on these crystals showed little difference from those from Nd:MgO:LibO3 with uniform domain structures. Green fluorescence was generated by self-frequency doubling in a cavity having great losses and pumped by a pulsed dye laser.
Spontaneous emission of localized excitons in InGaN single and multiquantum well structures
Authors: Chichibu S. , Azuhata T. , Sota T. , Nakamura S.
Published: July 2002

Emission mechanisms of InGaN single quantum well blue and green light emitting diodes and multiquantum well structures were investigated by means of modulation spectroscopy. Their static electroluminescence (EL) peak was assigned to the recombination of excitons localized at certain potential minima in the quantum well. The blueshift of the EL peak caused by the increase of the driving current was explained by combined effects of the quantum-confinement Stark effect and band filling of the localized states by excitons.
Evidence of Γ–X sequential resonant tunneling in GaAs/AlAs superlattices
Authors: Sun Baoquan , Jiang Desheng , Liu Zhenxing , Zhang Yaohui , Liu Wei
Published: July 2002

We have studied the sequential resonant tunneling of doped weakly coupled GaAs/AlAs superlattices under hydrostatic pressure up to 4.5 kbar. The pressure coefficient obtained from the experiment, 15.3 meV/kbar, provides a strong evidence for the formation of the electric field domain due to Γ–X sequential resonant tunneling. At the same time, we have observed the transition between two kinds of sequential resonant tunneling processes within the pressure range from 0 to 4.5 kbar, where the transition pressure between Γ–Γ and Γ–X sequential resonant tunneling is Pt∼1.6 kbar. For P<Pt, the electric field domain is formed by Γ–Γ sequential resonant tunneling, while for P≳Pt, the electric field domain is preferably formed by Γ–X sequential resonant tunneling.
Glass formation in a multicomponent Zr-based alloy by mechanical attrition and liquid undercooling
Authors: Sagel A. , Wunderlich R. K. , Perepezko J. H. , Fecht H.-J.
Published: July 2002

The synthesis of a multicomponent Zr60Al10Ni9Cu18Co3 glass by mechanical alloying has been investigated using thermal and structural analysis and compared with a metallic glass produced by liquid undercooling. The solid-state amorphization reaction is preceded by rapid solution of smaller solute atoms in the Zr matrix with a concomitant reduction in grain size to 10 nm at the amorphization onset. A fully amorphous mechanically alloyed sample shows relaxation compared to a sample synthesized by liquid cooling probably due to removal of residual inhomogeneities on the scale of the nanocrystal size at amorphization. While the kinetic pathways for the two synthesis methods differ, the relaxed amorphous phases from each method exhibit identical thermodynamic properties.
Nanometer scale patterning and pattern transfer on amorphous Si, crystalline Si, and SiO2 surfaces using self-assembled monolayers
Authors: Wang Dawen , Thomas Shawn G. , Wang Kang L. , Xia Younan , Whitesides George M.
Published: July 2002

Microcontact printing was used to form nanometer scale patterns of self-assembled monolayers (SAMs) on amorphous Si, crystalline Si, and SiO2 using octadecyltrichlorosilane (OTS) as the ink and an elastomer as the stamp. The patterns were subsequently transferred into crystalline Si substrates or amorphous Si films using the SAM of OTS as the resist film. Atomic force microscopy was used to characterize the quality of the SAM and the resulting patterns. Using a Si pillar structure as the master, “pancakes” of less than 80 nm in size were formed by over etching of the patterned OTS film on amorphous Si using KOH. The size of the resulting amorphous Si pancakes can be controlled by the etching time.
Low-dispersion thin-film microstrip lines with cyclotene (benzocyclobutene) as dielectric medium
Authors: Heiliger H.-M. , Nagel M. , Roskos H. G. , Kurz H. , Schnieder F. , Heinrich W. , Hey R. , Ploog K.
Published: July 2002

We report on thin-film microstrip lines (TFMSLs) fabricated on low-resistivity Si with polymerized cyclotene as the dielectric between signal and ground conductor, all on top of the wafer. Electro-optic high-frequency characterization of the TFMSLs reveals negligible modal dispersion up to the highest frequencies of 1.0 THz. In spite of the high substrate conductivity, the attenuation is low (⩽1 dB/mm at 100 GHz). Over the full frequency range, it is dominated by conductor losses and not by absorption in the dielectric. With these dispersion and attenuation properties, TFMSLs are an attractive alternative to coplanar waveguides, with the additional advantage of immunity against substrate absorption and radiation losses.
Interstitial defects in silicon from 1–5 keV Si+ ion implantation
Authors: Agarwal Aditya , Haynes Tony E. , Eaglesham David J. , Gossmann Hans-J. , Jacobson Dale C. , Poate John M. , Erokhin Yu. E.
Published: July 2002

Extended defects from 5-, 2-, and 1-keV Si+ ion implantation are investigated by transmission electron microscopy using implantation doses of 1 and 3×1014 cm−2 and annealing temperatures from 750 to 900 °C. Despite the proximity of the surface, {311}-type defects are observed even for 1 keV. Samples with a peak concentration of excess interstitials exceeding ∼1% of the atomic density also contain some {311} defects which are corrugated across their width. These so-called zig-zag {311} defects are more stable than the ordinary {311} defects, having a dissolution rate at 750 °C which is ten times smaller. Due to their enhanced stability, the zig-zag {311} defects grow to lengths that are many times longer than their distance from the surface. It is proposed that zig-zag {311} defects form during the early stages of annealing by coalescence the high volume density of {311} defects confined within a very narrow implanted layer. These findings indicate that defect formation and dissolution will continue to control the interstitial supersaturation from ion implantation down to very low energies.
Determination of the bonding of alkyl monolayers to the Si(111) surface using chemical-shift, scanned-energy photoelectron diffraction
Authors: Terry Jeff , Linford Matthew R. , Wigren Christer , Cao Renyu , Pianetta Piero , Chidsey Christopher E. D.
Published: July 2002

The bonding of alkyl monolayers to Si(111) surfaces has been studied by conventional x-ray photoelectron spectroscopy (XPS) and chemical-shift, scanned-energy photoelectron diffraction (PED) using synchrotron radiation. Two very different wet-chemical methods have been used to prepare the alkyl monolayers: (i) olefin insertion into the H–Si bond on the H–Si(111) surface, and (ii) replacement of Cl on the Cl–Si(111) surface by an alkyl group from an alkyllithium reagent. In both cases, XPS has revealed a C 1s signal chemically shifted to lower binding energy, which we have assigned to carbon bonded to silicon. PED has shown that both preparative methods result in carbon bonded in an atop site with the expected C–Si bond length of 1.85±0.05 Å. Chemical-shift, scanned-energy photoelectron diffraction is a particularly valuable probe of local structure at surfaces that contain the same element in multiple, chemically distinct environments.
Hydrogen abstraction kinetics and crystallization in low temperature plasma deposition of silicon
Authors: Srinivasan Easwar , Parsons Gregory N.
Published: July 2002

Exposing a plasma deposited hydrogenated silicon layer to atomic hydrogen results in hydrogen removal from the silicon/hydrogen surface and a net reduction in the total hydrogen content in the layer. For deposition at low temperature, the crystallization fraction corresponds directly with the extent of hydrogen removal. Silicon films deposited using alternating deposition and hydrogen (or deuterium) plasma exposure are characterized by transmission infrared spectroscopy and Raman spectroscopy. Using mass spectroscopy, hydrogen abstraction and etching are observed and identified as important pathways for hydrogen removal at substrate temperatures between 25 °C and 300 °C. Moreover, the hydrogen abstraction kinetics show that the reaction is first order with an activation barrier of −0.4±1 kcal/mol, consistent with a spontaneous Eley–Rideal abstraction process. Energy barrier values are supported by ab initio calculations.
Alignment of carbon nanotubes in a polymer matrix by mechanical stretching
Authors: Jin L. , Bower C. , Zhou O.
Published: July 2002

We report a method to fabricate polymer-based composites with aligned carbon nanotubes, and a procedure to determine the nanotube orientation and the degree of alignment. The composites were fabricated by casting a suspension of carbon nanotubes in a solution of a thermoplastic polymer and chloroform. They were uniaxially stretched at 100 °C and were found to remain elongated after removal of the load at room temperature. The orientation and the degree of alignment were determined by x-ray diffraction. The dispersion and the alignment of the nanotubes were also studied by transmission electron microscopy.
Thermal mismatch stress relaxation via lateral epitaxy in selectively grown GaN structures
Authors: Zheleva Tsvetanka S. , Ashmawi Waeil M. , Nam Ok-Hyun , Davis Robert F.
Published: July 2002

A reduction in the dislocation density of 104–105 cm−2 has been achieved via lateral epitaxial overgrowth (LEO) of GaN films selectively grown from stripes etched in SiO2 masks deposited on GaN/AlN/6H–SiC(0001) heterostructures. The magnitudes and distribution of stresses generated in the LEO GaN layer and the SiO2, due primarily to differences in the coefficients of thermal expansion, were modeled using finite element (FE) analysis. These calculations showed that localized compressive stress fields of ≈3 GPa occurred at the edges of the LEO GaN in the vicinity of the GaN/SiO2 interface. Localized compression along the GaN substrate/SiO2 interface and tension along the 〈0001〉 direction were responsible for the change in shape of the SiO2 stripes from rectangular with flat sides to an airfoil shape with curved sides. The FE calculations also revealed that an increase in the width of the LEO GaN regions over the SiO2 or the reduction in the separation between the GaN stripes (all other dimensions being fixed) resulted in a slight reduction in the compressive stresses along the LEO GaN/SiO2 interface and an increase in the compressive stress along [0001]. An increase in the shear stress, at the corners of the LEO GaN near the LEO GaN/SiO2 interface, with an increase in the width of the LEO GaN region were also indicated.
Electrical and noise properties of thin-film transistors on very thin excimer laser annealed polycrystalline silicon films
Authors: Angelis C. T. , Dimitriadis C. A. , Farmakis F. V. , Kamarinos G. , Brini J. , Miyasaka M.
Published: July 2002

Thin-film transistors, fabricated on polycrystalline silicon films prepared by combined solid phase crystallization of amorphous silicon and excimer laser annealing processes, have been investigated by electrical and low frequency noise measurements in relation to the active layer thickness and the laser energy density. The device performance is improved with increasing the laser energy density until a critical value where the film is completely melted. By decreasing the active layer thickness from 50 to 25 nm, although the subthreshold characteristics are improved, the electron mobility and the threshold voltage are degraded. The noise data indicate that the degradation is related to electron trapping in both gate and substrate oxide interface traps.
Nanotube self-organization: Formation by step-flow growth
Authors: Louchev Oleg A. , Sato Yoichiro
Published: July 2002

The growth kinetics of carbon nanotubes is considered within the framework of a step-flow kinetics model proposed in 1951 by Burton, Cabrera, and Frank [W. K. Burton, N. Cabrera, and F. C. Frank, Philos. Trans. R. Soc. London, Ser. A 243, 299 (1951)] as a general mechanism for defectless crystal growth. The model reveals that the nucleation of the next layer and its consecutive growth can inhibit the growth of the underlying layers leading to the formation of observed nanotubular “bamboo” structures.
Metal diffusion from electrodes in organic light-emitting diodes
Authors: Lee S. T. , Gao Z. Q. , Hung L. S.
Published: July 2002

Metal diffusion from magnesium–silver cathodes and indium–tin–oxide anodes in organic light-emitting diodes has been investigated. Magnesium showed no substantial diffusion under device operation and had no significant effects on luminance decay with operation time. Indium was immobile in storage at room temperature, while indium penetration into organic layers was observed after device operation. The presence of indium in organic films showed a correlation with performance degradation.