bluuebunny/crossref_metadata_2025 huggingface dataset:
Reconvolution analysis in time-resolved fluorescence experiments—an alternative approach: Reference-to-excitation-to-fluorescence reconvolution
Authors: Večeř J. , Kowalczyk A. A. , Davenport L. , Dale R. E.
Published: July 2002

A novel method for reconstructing the apparatus response function required for accurate detailed analysis of nanosecond time-resolved fluorescence decay data is proposed and tested with properly constructed simulated data sets for a variety of pertinent cases, using the high-accuracy convolution algorithm previously developed [J. Večeř, A. A. Kowalczyk, and R. E. Dale, Rev. Sci. Instrum. 64, xxx (1993)]. The veracity of recovery of test mono- and multiexponential decay responses by this method, involving the use of two appropriately chosen monoexponential reference decay responses, is shown to be essentially identical to that attainable with the ‘‘true’’ apparatus response function. The method is also demonstrated to exhibit significant advantages in a variety of situations over currently the most widely employed method of overcoming extant problems in the direct determination of an appropriate apparatus function: indirect analysis against a monoexponential reference decay response (δ-function convolution method, F-F deconvolution).
Ultrahigh-vacuum multichamber apparatus for molecule-surface interaction studies
Authors: Pradère F. , Château M. , Benslimane M. , Bierry M. , Châtelet M. , Clèment D. , Guilbaud A. , Jeannot J. C. , De Martino A. , Vach H.
Published: July 2002

We present a complete apparatus for molecule-surface interaction studies. Three UHV chambers are connected together allowing preparation, characterization, transfer, and experimental investigations with well-defined surface samples under ultrahigh-vacuum conditions. A chopped, supersonic molecular beam with well-controlled profile enters the main UHV chamber where it is scattered by the sample under study. Detection systems have been designed to measure angular and time-of-flight distributions and rotational populations of beam particles scattered off the surface sample giving access to the energy exchange between the internal degrees of freedom of the scattered molecules and the surface. The characteristics of our apparatus are reported and experimental tests for nitrogen and argon molecular beams scattered off a graphite surface are shown.
High critical-current density of Nd(Ba,Nd)2Cu3O7−δ single crystals
Authors: Egi T. , Wen J. G. , Kuroda K. , Unoki H. , Koshizuka N.
Published: July 2002

We have studied the superconducting properties of Nd(Ba1−xNdx)2Cu3O7−δ (Nd123, x≊0.1) single crystals grown by the traveling-solvent floating-zone method under 0.1% O2 in Ar atmosphere. An anomalous peak effect in the magnetization hysteresis (M–B) loop is observed in the Nd123 single crystals as well as in the Nd123 bulk crystals prepared by the oxygen-controlled melt growth (OCMG) method. The critical current density (Jc) of the Nd123 single crystals is 70 600 A/cm2 in 1.0 T at 77 K for the applied field perpendicular to the a-b plane. Uniform flux density distribution with the same shape as the sample is observed in the field perpendicular to the a-b plane by the magneto-optical flux-density observation. Finely dispersed white regions in the dark-field image due to Nd substitutions for Ba are observed in the Nd123 matrix by the transmission electron microscopy. The high Jc value of the Nd123 single crystals in the applied field is explained by the field-induced pinning centers caused by the Nd–Ba substitutions in the Nd123 matrix.
Photon stimulated ion desorption studies using pulsed synchrotron radiation
Authors: Tanaka K. , Tinone M. C. K. , Ikeura H. , Sekiguchi T. , Sekitani T.
Published: July 2002

Photon stimulated ion desorption from small molecules on Si(100) surfaces and from polymer thin films was studied using time-of-flight (TOF) mass spectrometric techniques. The design and operation of a TOF mass spectrometer during single bunch operation of the Photon Factory 2.5 GeV storage ring is described. Experimental results for H2O/Si(100), DCOOD/Si(100), polymethylmethacrylate and polymethylacrylate thin films are demonstrated as examples of the capabilities of the apparatus.
Laser-imploded core structure observed by using two-dimensional x-ray imaging with 10-ps temporal resolution
Authors: Shiraga H. , Heya M. , Fujishima A. , Maegawa O. , Shimada K. , Kato Y. , Yamanaka T. , Nakai S.
Published: July 2002

Core plasmas of laser-imploded ICF targets were observed by using a 10-ps temporally resolved two-dimensional x-ray imaging technique. A multi-imaging x-ray pinhole camera was coupled to an x-ray streak camera, and two-dimensional images were reconstructed by handling the streaked image data. Image distortion of the system was evaluated and nonuniformity in sensitivity was corrected. The spatial resolution was 15 μm and the observed photon energy was 2.2–4.9 keV. Structures in the x-ray image of the core were found to be rapidly changing with 10-ps time scale.
An interleaved comb ion deflection gate for m/z selection in time-of-flight mass spectrometry
Authors: Vlasak Paul R. , Beussman Douglas J. , Davenport Michael R. , Enke Christie G.
Published: July 2002

Modulation of an ion beam is crucial to several applications in time-of-flight (TOF) mass spectrometry, especially for tandem TOF instruments which require selection of a particular precursor m/z (mass to charge) value prior to fragmentation. Here we present a detailed description of an ‘‘interleaved comb’’ ion deflection gate device with suitable electronics which offers a performance advantage over the more commonly used deflection plate devices. We demonstrate unit mass resolution for selection to m/z 167 in the tandem TOF instrument constructed in our laboratory. Calculations suggest that the real time of unit resolution for our experimental arrangement is greater than 300.
A flange-on type low energy electron microscope
Authors: Grzelakowski K. , Bauer E.
Published: July 2002

A small low energy electron microscope in which the specimen is at ground potential and which can be mounted on any ultrahigh vacuum system equipped with a 6 in. Conflat flange is described. It has an all-electrostatic lens system and a magnetic beam separator which does not rotate the electron spin polarization so that the instrument can be used not only for low energy electron microscopy (LEEM) but also for spin-polarized LEEM (SPLEEM). In addition, low energy electron diffraction, mirror electron microscopy, and photoelectron emission microscopy is possible. The theoretical resolution in (SP)LEEM is better than 10 nm at electron energies of a few eV. In the version described here a specimen manipulator with four piezoelectrically and one mechanically controlled degrees of freedom is integrated in the instrument which allows for optimum magnetic shielding.
Earth, soil and environmental science research facility at sector 13 of the Advanced Photon Source. II. Scientific program and experimental instrumentation (abstract)
Authors: Sutton S. , Eng. P. J. , Jaski Y. R. , Lazaraz N. , Pluth J. , Murray P. , Rarback H. , Rivers M.
Published: July 2002

The GSECARS (APS sector 13) scientific program will provide fundamental new information on the deep structure and composition of the Earth and other planets, the formation of economic mineral deposits, the cycles and fate of toxic metals in the environment, and the mechanisms of nutrient uptake and disease in plants. In the four experimental stations (2 per beamline), scientists will have access to three main x-ray techniques: diffraction (microcrystal, powder, diamond anvil cell, and large volume press), fluorescence microprobe, and spectroscopy (conventional, microbeam, liquid and solid surfaces). The high pressure facilities will be capable of x-ray crystallography at P≳360 GPa and T∼6000 K with the diamond anvil cell and P∼25 GPa and T∼2500 °C with the large volume press. Diffractometers will allow study of 1 micrometer crystals and micro-powders. The microprobe (1 micrometer focused beam) will be capable of chemical analyses in the sub-ppm range using wavelength and energy dispersive detectors. Spectroscopy instrumentation will be available for XANES and EXAFS with microbeams as well as high sensitivity conventional XAS and studies of liquid and solid interfaces. Visiting scientists will be able to setup, calibrate, and test experiments in off-line laboratories with equipment such as micromanipulators, optical microscopes, clean bench, glove boxes, high powered optical and Raman spectrometers.
Performance of the beam position monitor for the Advanced Photon Source
Authors: Chung Y. , Kahana E.
Published: July 2002

Performance measurement and analysis of the Advanced Photon Source (APS) beam position monitor (BPM) electronics are reported. The results indicate a BPM resolution of 0.16 μm⋅mA/√Hz in terms of the single-bunch current and BPM bandwidth. For the miniature insertion device (ID) BPM, the result was 0.1 μm⋅mA/√Hz. The improvement is due to the 3.6 times higher position sensitivity (in the vertical plane), which is partially canceled by the lower button signal by a factor of 2.3. The minimum single-bunch current required was roughly 0.03 mA. The long-term drift of the BPM electronics independent of the actual beam motion has measured at 2 μm/hr, which settled after approximately 1.5 hours. This drift can be attributed mainly to the temperature effect. Implications of the BPM resolution limit on the global and local orbit feedback systems for the APS storage ring will also be discussed.
Design and analysis of a photon/safety shutter for CARS sector 14 ID beamline at the Advanced Photon Source (abstract)
Authors: Schildkamp W. , Jaski Y. , Navrotski G.
Published: July 2002

A photon/safety shutter capable of stopping bremsstrahlung, white, pink, and monochromatic radiation from the APS wiggler and undulator sources is described. The shutter consists of two individually actuated but redundant block assemblies. Each block consists of a water-cooled, OFHC block thermal absorber followed by a tungsten block to stop both synchrotron and bremsstrahlung rays. The design presented here is inexpensive and spatially compact. Fatigue analysis and ANSYS thermal and stress analysis are presented.
Possible use of direct silicon-on-silicon bonding for construction of analyzers for inelastic scattering
Authors: Macrander A.T. , Saginuri M. , Yao S. , Hesketh P.J. , Bresloff C.J.
Published: July 2002

Bonding of silicon directly to silicon is possible with proper preparation of the two surfaces to be bonded. The advantage of such a method is that a bonding agent is not required, and direct bonding avoids figure errors introduced by thickness variations in a bonding agent. We have succeeded in bonding a 3-inch-diameter diced (1 mm × 1 mm) silicon(111) oriented wafer to a silicon concave spherical form having a 3-m radius. A very good rms figure error of 0.059 millirad over the entire area of the analyzer was measured. The suitability for x-ray inelastic scattering due to introduced strain is, however, still an open question. Whether or not deleterious strain is unavoidably introduced during the bonding process is a question we will answer with availability of photons on sector 3 of the SRI CAT at the Advanced Photon Source.
XSCAN x-ray data acquisition and analysis software for the MATRIX X-18A x-ray scattering beamline at the NSLS
Authors: Ehrlich S. N. , Schwanof J. A. , Yang X. , Liedl G. L.
Published: July 2002

A versatile and easy-to-use computer software package has been developed for equipment control, data acquisition and analysis at the MATRIX X-18A x-ray scattering beamline at the National Synchrotron Light Source. The software runs on any IBM-compatible personal computer running under MS-DOS and makes use of the GPIB and AT-Bus interfaces. The menu-driven program is user friendly for a wide range of x-ray experiments through control of all aspects of the x-ray beamline. Equipment interfaces include counter-timer, stepping motor controllers, multichannel analyzer, and temperature controller. Real space and reciprocal space scans are possible, as well as an external file scan, which allows control of up to six diffractometer motions plus the energy simultaneously. Orientation matrix calculations, peak fitting routines, and an extensive help file system are included. Plans are presently underway to upgrade the software to run under Windows NT.
Alternative Methods for Sub-eV Resolution Inelastic X-ray Scattering (invited)
Authors: Macrander Albert T. , Platzman Philip M.
Published: July 2002

A synopsis of SRI workshop 9 held on October 20, 1995, is given. Details concerning the oral presentations of speakers not contributing to these proceedings are included. The workshop consisted of the following invited presentations: 1. M. Schwoerer-Boehning (APS), ‘‘Experimental Needs for Milli-eV Resolution Inelastic X-ray Scattering, ’’ 2. E. E. Alp (APS), ‘‘Inelastic Nuclear Resonant X-ray Scattering,’’ 3. A. Baron (ESRF), ‘‘ Inelastic X-ray Scattering via Nuclear Resonant Analyzer,’’ 4. D. E. Moncton (APS), ‘‘ An Exact Backscattering Beamline,’’ 5. A. Caticha (SUNY-Albany), ‘‘X-ray Fabry-Perot Cavities,’’ 6. E. D. Isaacs (AT&T Bell Labs), ‘‘Flux and Resolution Requirements for Studies of Electronic Excitations in Solids,’’ 7. C. K. Stahle (NASA), ‘‘Hard X-ray Detectors with Very High Energy Resolution,’’ 8. A. K. Freund (ESRF), ‘‘Mosaic Crystal Analyzers.’’ These proceedings contain separate papers by Caticha, Isaacs, and Stahle for the above listed presentations, and we will not discuss them further here. The other presentations are summarized below.
Design of the vacuum system for the elliptical multipole wiggler at the Advanced Photon Source
Authors: Den Hartog P. , Grimmer J. , Klippert T. , Trakhtenberg E. , Xu S.
Published: July 2002

A vacuum system for the Advanced Photon Source elliptical multipole wiggler (EMW) that will operate at a pressure of 10−9 Torr with a storage ring current of 100 mA at 7.0 GeV has been designed and is being fabricated. The major part of the system is a stainless steel chamber with a 66.6 mm by 19.6 mm rectangular cross section. The length of the vacuum chamber is 3100 mm, and the wall thickness is 1.2 mm. Two versions of the vacuum chamber will be produced: with and without distributed nonevaporable getter (NEG) pumping. The version with NEG pumping will have slides on the top and bottom walls to accommodate sintered plates available from SAES. To activate these plates, the entire vacuum chamber will be baked from the outside up to a temperature of 350° C–450 °C. Provision for the baking is included in the design of the vacuum system, its support, and in the EMW itself. The complexity introduced into the design by the need for external activation of the NEG plates is eliminated in the design of the second version of the chamber. In this chamber, a sufficiently low outgassing rate may be achieved by extensive surface cleaning and baking in a vacuum furnace (10−6 Torr) up to a temperature of 950 ° C as has been achieved at the ESRF. Both versions are being pursued in parallel.
CHESS upgrade 1995: Improved radiation shielding (abstract)
Authors: Finkelstein K.D.
Published: July 2002

The Cornell Electron Storage Ring (CESR) stores electrons and positrons at 5.3 GeV for the production and study of B mesons, and, in addition, it supplies synchrotron radiation for CHESS. The machine has been upgraded for 300 mA operation. It is planned that each beam will be injected in about 5 minutes and that particle beam lifetimes will be several hours. In a cooperative effort, staff members at CHESS and LNS have studied sources in CESR that produce radiation in the user areas. The group has been responsible for the development and realization of new tunnel shielding walls that provide a level of radiation protection from 20 to ≳100 times what was previously available. Our experience has indicated that a major contribution to the environmental radiation is not from photons, but results from neutrons that are generated by particle beam loss in the ring. Neutrons are stopped by inelastic scattering and absorption in thick materials such as heavy concrete. The design for the upgraded walls, the development of a mix for our heavy concrete, and all the concrete casting was done by CHESS and LNS personnel. The concrete incorporates a new material for this application, one that has yielded a significant cost saving in the production of over 200 tons of new wall sections. The material is an artificially enriched iron oxide pellet manufactured in vast quantities from hematite ore for the steel-making industry. Its material and chemical properties (iron and impurity content, strength, size and uniformity) make it an excellent substitute for high grade Brazilian ore, which is commonly used as heavy aggregate in radiation shielding. Its cost is about a third that of the natural ore. The concrete has excellent workability, a 28 day compressive strength exceeding 6000 psi and a density of 220 lbs/cu.ft (3.5 gr/cc). The density is limited by an interesting property of the pellets that is motivated by efficiency in the steel-making application. The pellets are made to be porous, with about 28% of the volume consisting of connected pores of size typically from 1–10 microns. The porosity may have some useful implications for neutron radiation shielding including the possibility of holding a lot more water than a conventional mix, and the opportunity to impregnate the pellets with a good neutron absorber such as boron. This paper will discuss these developments and report the latest results on the effectiveness of the upgraded shielding at Cornell.
X-ray microfabrication activities at the Center for Advanced Microstructures and Devices (CAMD) (invited)
Authors: Malek C. Khan , Vladimirsky Y. , Vladimirsky O. , Scott J. , Craft B. , Saile V.
Published: July 2002

The x-ray lithography and micromachining facility at CAMD is described. It consists of four dedicated beamlines and exposure stations using the synchrotron radiation delivered by the CAMD storage ring and 230 m2 of fully equipped clean room. The scientific and engineering activities exemplified by results of current studies are reported.
Beamline instrumentation for short-wavelength FELs (invited, abstract)
Authors: Johnson Erik
Published: July 2002

This workshop examine the uniqued requirements of beamlines at short-wavelength FELs, including detector requirements. Additional topics were the heat loads from a short-wavelength FEL, optics for a short-wavelength FEL beamline, and new technologies using short-wavelength FELs.
Use of the program SHADOW in designing a capillary focusing beamline (invited)
Authors: Brown F. C. , Kim K. H. , Heald S. M. , Barg B. M. , Stern E. A.
Published: July 2002

In this report we consider the use of the program SHADOW for ray tracing different configurations of the PNC-CAT mircrofocus beamline. The emphasis is on the final design, which will include crystal and grazing incidence optics focusing onto the entrance of a long tapered glass capillary whose outlet diameter is of the order of one micron or less. The ray-tracing program has been especially valuable in comparing different configurations, determining the required stability of components, and optimizing the capillary profile. It has also been useful in evaluating the results of actual measurements on the throughput of long tapered capillaries fabricated of silica glass. Suggestions for improvements to SHADOW are given. We also present results of a compact pc-based capillary ray-tracing program for comparison. It allows us to use different profiles with minimal programming effort.
Report on the SRI ’95 workshop on the timing structure of the Advanced Photon Source (invited)
Authors: Alp E. E.
Published: July 2002

The workshop on the timing structure of the Advanced Photon Source (APS) brought synchrotron radiation experimentalists and accelerator physicists together to discuss the potential experiments and capabilities of this new machine. The discussions represented only a small subset of possibilities, those that use the built-in time structure of the synchrotron radiation. Similarly, the capabilities of the APS machine, beyond the design parameters, reflect the limited experience the accelerator physicists have had with this machine, which is currently going through a commissioning period. Therefore, projections based on this report may be premature. However, we hope that some of the experimentalists’ needs are better understood by the accelerator physicists and that the limitations of the machine are better understood by the synchrotron radiation experimentalists.
A 2D smart pixel detector for time-resolved crystallography
Authors: Beuville E. , Cork C. , Earnest T. , Mar W. , Millaud J. , Nygren D. , Padmore H. , Turko B. , Zizka G. , Datte P. , Xuong Nguyen-Huu
Published: July 2002

A smart pixel detector is being developed for time-resolved crystallography for biological and material science applications. Using the pixel detector presented here, the Laue method will enable the study of the evolution of structural changes that occur within a protein as a function of time. The x-ray pixellated detector is assembled to the integrated circuit through a bump bonding process. Within a pixel size of 150×150 mm2, a low-noise preamplifier-shaper, a discriminator, a 3-bit counter and the readout logic are integrated. The readout, based on the column architecture principle, will accept hit rates above 5×108/cm2/s with a maximum hit rate per pixel of 1 MHz. This detector will allow time-resolved Laue crystallography to be performed in a frameless operation mode, without dead time. Target specifications, architecture, and preliminary results on a 8×8 prototype are presented.
Recent advances in synchrotron-based Mössbauer experiments (invited)
Authors: Siddons D. P. , Hastings J. B.
Published: July 2002

As the field of nuclear resonant scattering using synchrotron radiation matures, we see a shift from experiments designed to verify theoretical predictions towards those designed to use the phenomenon to elucidate the behavior of a sample. In parallel with this trend towards applications, we have seen further instrumental developments that extend the range of possible applications. This paper will review the recent work in this field with an emphasis on new sources, new isotopes, and new instrumentation.
Soft x-ray interferometry (abstract)
Authors: Trebes James E. , Barbee T. W. , Cauble R. , Celliers P. , Da Silva L. , Decker C. , London R. , Moreno J. C. , Ress D. , Wan A. S. , Weber F.
Published: July 2002

The development of soft x-ray mirrors and large aperture soft x-ray beamsplitters now allows the near routine operation of soft x-ray interferometers with high brightness x-ray sources. Mach-Zehnder and Fourier transform interferometers utilizing a soft x-ray laser light source operating at 80 eV will be described. Results from high density, long scale-length plasma probing measurements, x-ray laser coherence measurements, and materials properties measurements will be presented.
Experimental station for inelastic scattering spectroscopy of electronic excitations
Authors: Kushnir V.I. , Macrander A.T.
Published: July 2002

An experimental station for inelastic x-ray scattering spectroscopy (IXSS) of phonons and electronic excitation is being built on the undulator beamline of Sector 3 at the Advanced Photon Source. The subject of the present article is a description of the instrumentation for the spectroscopy of electronic excitations. The goal of this program is to provide users with the possibility to study IXSS in low- and middle-Z materials with an energy resolution from 1 eV (with a beam coming directly from the high-heat-load monochromator to the specimen) to 100 meV (with a second channel-cut monochromator) in the energy transfer range of 200 eV. The optical scheme of the station is described, and status of the station is reported.
Smart x-ray beam position monitor system for the Advanced Photon Source
Authors: Shu Deming , Kuzay Tuncer
Published: July 2002

In third-generation synchrotron radiation sources, such as the Advanced Photon Source (APS), the sensitivity and reliability requirements for the x-ray beam position monitors (XBPMs) are much higher than for earlier systems. Noise and contamination signals caused by radiation emitted from the bending magnet become a major problem. The regular XBPM calibration process can only provide signal correction for one set of conditions for the insertion devices (ID). During normal operation, parameters affecting the ID-emitted beam, such as the gap of the ID magnets and the beam current, are the variables. A new smart x-ray beam position monitor system (SBPM) has been conceived and designed for the APS. It has a built in self-learning structure with EEPROM memory that is large enough to ‘‘remember’’ a complete set of calibration data covering all the possible operating conditions. During the self-learning mode, the monitor system initializes a series of automatic scan motions with information for different ID setups and records them into the database array. During normal operation, the SBPM corrects the normalized output according to the ID setup information and the calibration database. So that, with this novel system, the SBPM is always calibrating itself with the changing ID set up conditions.
Beam size measurement of the stored electron beam at the APS storage ring using pinhole optics
Authors: Cai Z. , Lai B. , Yun W. , Gluskin E. , Legnini D. , Illinski P. , Srajer G.
Published: July 2002

Beam sizes of the stored electron beam at the APS storage ring were measured using pinhole optics and bending magnet x-rays in single-bunch and low-current mode. A white-beam pinhole of 25 μm and a fast x-ray imaging system were located 23.8 m and 35.4 m from the source, respectively. The x-ray imaging system consists of a CdWO4 scintillation crystal 60 μm thick, an optical imaging system, and a CCD detector. A measurement time of a few tenths of a second was obtained on a photon beam of E≳30 keV produced from a 7-GeV electron beam of 2-mA current. The resolution of the pinhole imaging system was evaluated to be 16 μm. The measured vertical and horizontal sizes of the electron beam were in reasonable agreement with the expected values.
A practical direct current discharge helium absorption cell for laser frequency locking at 1083 nm
Authors: Lu Weijian , Milic Dragana , Hoogerland Maarten D. , Jacka Marcus , Baldwin Kenneth G. H. , Buckman Stephen J.
Published: July 2002

We report the construction of a low pressure (∼0.5 Torr) helium direct current discharge cell to lock a 1083 nm InGaAs diode laser to the 2 3S–2 3P transition in helium using saturated absorption spectroscopy. The direct current discharge cell has the advantage of being radio frequency noise free.
Poiseuille geometry shear flow apparatus for small-angle scattering experiments
Authors: Cloke Veronica M. , Higgins Julia S. , Phoon C. Lin , Richardson Stephen M. , King Stephen M. , Done Robert , Cooper Trevor E.
Published: July 2002

A new apparatus to investigate the structure of fluids under Poiseuille shear flow using small-angle neutron or light scattering techniques is described. Important features of the design include low sample volumes, area average shear rates of up to 5000 s−1, accurate temperature control over the range of 10–125 °C, and the ability to study the development of flow-induced alignment phenomena. Small-angle neutron scattering data are presented for two example systems: the well-characterized surfactant system C16E6/D2O, used to contrast the effects of Poiseuille and Couette flow, and the block copolymer Synperonic P-85/D2O system.
The PNC-CAT insertion device beamline at the Advanced Photon Source
Authors: Heald S.M. , Stern E.A. , Brown F.C. , Kim K.H. , Barg B. , Crozier E.D.
Published: July 2002

The PNC-CAT is a consortium of Pacific Northwest institutions formed to instrument a sector (number 20) at the Advanced Photon Source (APS). Research is planned in a variety of areas, with an emphasis on environmentally based problems. The insertion device beamline is based on the APS undulator A and will be optimized for producing microbeams as well as for applications requiring energy scanning capabilities. This paper describes the basic layout and some special features of the beamline. Two experimental stations are planned: one general purpose and one dedicated to MBE and surface science problems. Both tapered capillaries and Kirkpatrick-Baez optics will be used for producing microbeams, and a large optical bench is planned for the main station to allow for easy accommodation of new optics developments. Design calculations and initial capillary tests indicate that flux densities exceeding 1011 photons/sec/mm2 should be achievable. All major components are under construction or in procurement, and initial testing is planned for late 1996.
First results from the high brightness x-ray spectroscopy beamline 9.3.1 at ALS
Authors: Ng W. , Jones G. , Perera R. C. C. , Hansen D. , Daniels J. , Hemmers O. , Glans P. , Whitfield S. , Wang H. , Lindle D. W.
Published: July 2002

Beamline 9.3.1 at the Advanced Light Source (ALS) is a windowless beamline, covering the 1–6 keV photon energy range. This beamline is designed to achieve the goal of high brightness at the sample for use in the x-ray atomic and molecular spectroscopy (XAMS) science, surface and interface science, biology and x-ray optical development programs at ALS. X-ray absorption and time-of-flight photoemission measurements in 2–5 keV photon energy range along with the flux, resolution, spot size and stability of the beamline will be discussed. Prospects for future XAMS measurements will also be presented.
Polarization device employing the combination effect of double refraction and diffraction
Authors: Liu Shangqing , Li Chengxiang , Chen Yansong
Published: July 2002

Upon the combination of double refraction and diffraction effects, a new kind of polarization device is proposed, which is made of the birefringent plate with the grooves of a sawtooth profile on its surface. This device may separate an incident light beam into two polarized beams spatially with a high extinction ratio and large beam-splitting angle, moreover it has a sheet form, large aperture, and low cost, thus being suitable for practical use.
Neutron activation for ITER
Authors: Barnes Cris W. , Loughlin Michael J. , Nishitani Takeo
Published: July 2002

There are three primary goals for the Neutron Activation system for ITER: to maintain a robust relative measure of fusion power with stability and wide dynamic range (seven orders of magnitude), allow an absolute calibration of fusion power production, and provide a flexible and reliable system for materials testing. The nature of the activation technique is such that stability and wide dynamic range can be intrinsic properties of the system. It has also been the technique that demonstrated (on JET and TFTR) the most accurate neutron measurements in DT operation. Since the detectors for assaying the radioactivity are not located on the tokamak and are therefore amenable to accurate characterization, and if the activation samples are placed very close to the ITER plasma with minimal scattering or attenuation, high overall accuracy in the fusion energy production (7%–10%) should be achievable on ITER. In the paper, a conceptual design is presented. A system is shown to be capable of meeting these three goals, and unresolved design issues are identified.
Current initiation in low-density foam z-pinch plasmas
Authors: Derzon M. S. , Nash T. J. , Allshouse G. O. , Antolak A. J. , Deeney C. , Hurst M. , McGurn J. S. , Muron D. J. , Seaman J. F. , MacFarlane J. , Demiris T. , Hrubesh L. , Lewis H. , Ryutov D. , Barber T. , Gilliland T. , Jobe D. , Lazier S.
Published: July 2002

Low density agar and aerogel foams were tested as z-pinch loads on the Saturn accelerator to study current flow initiation. In these first experiments, we studied the initial plasma conditions by measuring the visible emission at early times with a framing camera and a streaked one-dimensional imaging system. Later, near the stagnation when the plasma is hotter, x-ray imaging and spectral diagnostics were used to characterize the plasma. Filamentation and arcing at the current contacts were observed. Bright implosion features were also observed. Increasing the early time conductivity, by coating the target with a high-z layer and by providing a low-current prepulse, is the most important factor in obtaining good coupling to the machine. None of the pinches were uniform along the z axis. The prime causes of these problems are believed to be the electrode contacts and the current return configuration. Solutions are discussed.
Windows and photocathodes for a high resolution solid state bandpass ultraviolet photon detector for inverse photoemission
Authors: Schedin F. , Thornton G. , Uhrberg R. I. G.
Published: July 2002

We have measured the absolute quantum yield for alkali halides and the spectral transmission for alkaline earth fluoride windows to find an optimized bandpass combination for a solid state ultraviolet (UV) photon detector for inverse photoemission. The best resolution achieved is 0.33 eV (full width at half-maximum), being obtained with the NaCl photocathode–BaF2 window combination. This, however, leads to a rather low quantum efficiency of 0.3%. The combination NaCl–SrF2 chosen for our detector offers a resolution of 0.42 eV (full width at half-maximum) with a maximum quantum efficiency of 2.5% at 9.50 eV photon energy.
Compact grating spectrometer for inverse photoemission spectroscopy
Authors: Kipp L. , Boehme M. , Carstensen H. , Claessen R. , Skibowski M.
Published: July 2002

We report on a normal incidence grating spectrometer for angle-resolved inverse photoemission spectroscopy covering a photon energy range from 10 to 40 eV. Following diffraction from a spherical grating with 201.4 mm radius and 3600 lines/mm the photons are recorded by a position sensitive detector. The compact mounting of the grating and detector on a single 150 mm CF flange is established by displacing detector and sample from the Rowland circle. The performance of the spectrometer concerning energy calibration, spectral efficiency, optical resolution, and count rates was experimentally investigated and found to match the design goals well. Operated together with a low energy electron gun using a low temperature BaO cathode a typical total energy resolution of 360 meV at hν=15 eV is obtained in inverse photoemission spectroscopy. It is shown that due to its compactness the spectrometer unit can be effectively combined with other components for surface analysis.
Indirectly heated cathode arc discharge source for ion implantation of semiconductors
Authors: Horsky Thomas N.
Published: July 2002

We describe an indirectly heated cathode ion source which has several times the lifetime of commercial Bernas sources which incorporate a bare filament cathode. In addition, much higher multiply charged beam currents are attainable using this source due to its ability to operate safely at higher arc discharge power. In addition to an overall system description, we present typical lifetimes and ion species fractions, and the latter’s dependence on source operating parameters such as arc voltage and source magnetic field. Data are presented for boron, arsenic, and phosphorus beams. Cathode lifetime ranges from 70 h at the highest discharge power levels to over 500 h for moderate operation. At high discharge power levels (≈1 kW), the ions are predominantly atomic, rather than molecular, species. Multiply charged beam production also increases with discharge power and plasma density. Doubly charged fractions of 15% for phosphorus, and 2% for boron, have been demonstrated during ion implant.
Time-resolved study of the negative ion density in a volume H− ion source by photodetachment
Authors: Hamabe M. , Oka Y. , Tsumori O. , Kuroda T. , Bacal M.
Published: July 2002

Time-resolved measurements of the negative ion density and of other plasma parameters in a pure hydrogen Tandem source have been effected using the laser photodetachment technique. The study was made for hydrogen filling pressures in the range 7–11 mTorr and an arc current of 120 A. We found a strong time variation in negative ion density was present during the discharge pulse (0.5 s). The maximum negative ion density was observed at the beginning of the pulse, at the lowest filling pressure studied, followed by a rapid decrease. An improvement of the current distribution during the pulse was obtained by increasing the filling pressure. The electron density is highest at 7 mTorr and stays almost constant during the pulse. The increase in filling pressure leads to electron density values lower by a factor of 4 which are constant during the discharge pulse. The highest relative negative ion density during the pulse is obtained at 9 mTorr. The time variation of the negative ion density does not follow that of the electron density at the same discharge conditions. This indicates that the negative ion density is affected not only by the electron density, but also by the neutral particle density, as assumed by the mechanism of volume production of H− ions in a plasma. We attribute the time variation of the negative ion density during the discharge pulse to the ion pumping of hydrogen.
Mass spectroscopy using a rotating electric field
Authors: Clemmons J. H. , Herrero F. A.
Published: July 2002

A mass spectrograph using a rotating electric field and position-sensitive detection is described. Its principles of operation are explained, and a prototype instrument and its test results are presented and discussed. Examination of how the instrument’s properties vary under changes of its parameters (e.g., geometry) shows how it can be tailored to specific measurement requirements. The general case utilizing detection in two (polar) dimensions is discussed, and limiting cases employing one-dimensional imaging in each direction, azimuthal and radial, are presented. Applications are suggested and courses for further development are put forth.
A bimorph based dilatometer for field induced strain measurement in soft and thin free standing polymer films
Authors: Su J. , Moses P. , Zhang Q. M.
Published: July 2002

A bimorph based dilatometer has been developed which enables one to characterize the electric field induced strain response in the out-of-plane direction in thin and soft free standing polymer film samples conveniently over a relatively wide frequency range (1 Hz to 1 kHz). The test results demonstrate that the newly developed dilatometer is capable of detecting displacement down to sub-angstrom range. The agreement between the test results from the bimorph dilatometer, the results from a laser dilatometer, and the model analysis indicates that the device can indeed be used reliably for these measurement with high sensitivity.
Inductive measurement of magnetic field gradients for magnetic resonance imaging
Authors: Senaj Viliam , Guillot Geneviève , Darrasse Luc
Published: July 2002

A simple device for highly accurate and real-time measurement of magnetic field gradient pulses is presented. It uses analog integration of the differential voltage induced in a pair of sensor coils placed along the investigated gradient direction. By this principle, the method is insensitive to static magnetic field inhomogeneities. It does not need either a main field or imaging apparatus and hence can be used in the process of gradient system design and optimization. Two different solutions for analog integration are suggested. The measurement accuracy is analyzed, taking into account errors due to the sensor coils and to both analog integration schemes. Sensor coils and integrators have been built to perform measurements on various gradient systems. Measurements of an actual whole-body gradient system are presented. The measurement accuracy is in the 5–10−4 range, and the reproducibility is better than 10−4, relative to the maximum gradient amplitude. These performances are better than any other presented in literature. They have allowed precise adjustment of a preemphasis unit so as to suppress eddy currents influence below 0.01%, and placed into evidence the thermal drift of standard power amplifier.
New high-temperature rotational rheometer for silicate melts, magmatic suspensions, and emulsions
Authors: Stein D. J. , Spera F. J.
Published: July 2002

A new wide-annulus Couette-type viscometer/rheometer has been designed, fabricated, and tested with the objective of measuring the shear flow properties of silicate melts and magmatic suspensions containing vapor bubbles and/or solid particles at 10−4 GPa and temperatures from 600 to 1500 °C. The goal of this development has been to advance the precision of high-temperature multiphase silicate rheometry in the viscosity regime of 104–1010 Pa s, and to attempt experiments on multiphase magmatic mixtures that have heretofore been difficult to perform in the concentric cylinder geometry. With this instrument, fluids with viscosities in the design viscosity range may be tested at shear rates from 10−5 to 1 s−1, employing a series of interchangeable torque transducers capable of measurements from 0.003 to 3 N m, preserving precision of the stress measurement across the entire dynamic span. A microprocessor-controlled motor drive enables precisely specified rotational motions (position and/or speed of the sample container) for accurate constant-shear-rate or finite-strain experiments. Use of high-purity cast ceramic components rather than platinum alloy for the rotating sample container (cup) and fixed cylindrical bob permit sectioning of the sample following an experiment to inspect and analyze textural characteristics of the magmatic suspensions. Computerized data acquisition is accomplished via a standard microcomputer interface and commercially available software system that allows data to be recorded, visualized, and statistically modeled as an experiment progresses. The instrument has been tested using NIST (NBS) reference material 717 (a borosilicate glass) at viscosities from 104 to 109 Pa s. Value of the standard viscosity has been recovered within the published precision (0.03 log units) at temperatures between 650 and 850 °C.
High-resolution constant length Rowland circle monochromator at BESSY
Authors: Schwarzkopf O. , Eggenstein F. , Flechsig U. , Kalus C. , Lammert H. , Menthel U. , Reichardt G. , Rotter P. , Senf F. , Zeschke T. , Peatman W. B.
Published: July 2002

The working principle, the layout and the performance data of a simple Rowland circle soft x-ray monochromator of constant length are described. By translating the grating while scanning the photon energy, defocus, coma and some spherical aberrations vanish, yielding excellent resolution in the optimized energy range between 270 and 590 eV. This result is obtained while using all optical elements at full illumination. The achieved resolution ranks among the best worldwide.
A slit grating spectrograph for quantitative soft x-ray spectroscopy
Authors: Wilhein T. , Rehbein S. , Hambach D. , Berglund M. , Rymell L. , Hertz H. M.
Published: July 2002

In this article we describe a new slit grating spectrograph which is based on an e-beam written 10 000 linepairs/mm freestanding transmission diffraction grating. In combination with a thinned, back-illuminated charge coupled device (CCD), the spectrograph allows for real-time spectroscopy of laser-produced plasma x-ray sources within the wavelength region λ=1–20 nm. Calibration of grating and CCD allow for the possibility to measure absolute photon fluxes, currently within the wavelength region λ=1–6 nm. The compact spectrograph is easy to align and flexible in its use. Absolutely calibrated spectra were obtained from a liquid-jet laser-plasma source in the water window, with a spectral resolution λ/Δλ⩾330 at λ=3.37 nm. A simple change in experimental geometry allowed single-shot spectra to be recorded with λ/Δλ⩾60 at the same wavelength. In addition, spectra from this laser-plasma source were measured within the range λ=9–20 nm.
Transport characterization of in-plane gate devices fabricated by direct epitaxial growth on patterned substrates
Authors: Dilger M. , Haug R. J. , Eberl K. , Kurtenbach A. , Kershaw Y. , Klitzing K. v.
Published: July 2002

Direct molecular-beam epitaxial growth of GaAs/AlxGa1−xAs heterostructures on bow-tie shaped constrictions, prepatterned on GaAs substrates is used to fabricate in-plane gate transistors. The fabricated devices can be tuned by applying voltages to in-plane gates, which are also realized during the epitaxial growth. In this way, complete in-plane gate transistors are fabricated in a single growth process. Transport measurements of the devices at 1.3 K show conductance quantization or Coulomb blockade depending on the width of the constriction. The Coulomb blockade effect in the narrowest structures is caused by the formation of a self-assembled quantum dot in the center of the constriction.
Reactive ion etching of ferroelectric SrBi2TaxNb2−xO9 thin films
Authors: Desu Seshu B. , Pan Wei
Published: July 2002

Ferroelectric SrBi2TaxNb2−xO9 thin films were patterned using reactive ion etching. Considering the environmental impact effect, CHClFCF3, a special etching gas, known to be less environmentally hazardous compared to the other hydrofluorocarbons, was employed in this study. The etch rates as a function of etching parameters were investigated. An etch rate of 20 nm/min was obtained. Surface compositional change during etching was monitored by x-ray photoelectron spectroscopy. Surface residues were removed by a postetching cleaning process.
Growth and characterization of heteroepitaxial CdTe and ZnTe on Ge(001) buffer layers
Authors: Smith David J. , Tsen S.-C. Y. , Chen Y. P. , Sivananthan S. , Posthill J. B.
Published: July 2002

The microstructure of heteroepitaxial CdTe (001) and ZnTe(001) epilayers grown on Ge(001) buffer layers by molecular beam epitaxy has been characterized using electron microscopy. Apart from occasional {111} stacking faults originating at the interfacial region, the prevailing defects present in both systems are identified by high-resolution imaging as perfect Lomer edge dislocations with Burgers vectors of the type a/2〈110〉 parallel to the interface plane, which are indicative of well-relaxed material. Double-crystal rocking-curve measurements using Ge(001) buffer layers give full-width-at-half-maximum values of 210 arc-sec for a 7.5μm thick ZnTe film and 125 arc-sec for a 12μm thick CdTe film. Use of the Ge buffer layers on Si(001) substrates represents a valuable precursor for eventual growth of mercury cadmium telluride since this allows the substrate orientation to be maintained. The buffer layer also permits a substantial reduction of the in situ annealing temperature needed for substrate oxide removal.
Cleaved cavity optically pumped InGaN–GaN laser grown on spinel substrates
Authors: Asif Khan M. , Sun C. J. , Yang J. W. , Chen Q. , Lim B. W. , Zubair Anwar M. , Osinsky A. , Temkin H.
Published: July 2002

We report an optically pumped multiple-quantum-well laser of InGaN–GaN grown on cubic, (111)-oriented spinel substrates. The laser cavity is formed by cleaving. Atomic force microscopy shows that the cleaved GaN and spinel facets are of similar flatness. The onset of lasing is clearly demonstrated by the saturation of spontaneous emission, abrupt line narrowing, and the highly polarized light output. A lasing threshold power of 140 kW/cm2 is measured in a 400-μm-long cavity at 150 K.
Extremely high-frequency self-pulsations in chirped-grating distributed-feedback semiconductor lasers
Authors: Liao Yuan-Hwang , Winful Herbert G.
Published: July 2002

We show that an asymmetrically chirped, single-section distributed-feedback (DFB) laser is capable of sustained self-pulsations at frequencies in excess of 200 GHz. These pulsations arise from mode beating and are absent in uniform or symmetrically chirped DFB lasers. For sufficiently large coupling constants, the pulsation frequency can approach a terahertz.