bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental methods in radioactive ion-beam target/ion source development and characterization
Authors: Welton R. F. , Alton G. D. , Cui B. , Murray S. N.
Published: July 2002

We have developed off-line experimental techniques and apparatuses that permit direct measurement of effusive-flow delay times and ionization efficiencies for nearly any chemically reactive element in high-temperature target/ion sources (TIS) commonly used for on-line radioactive ion-beam (RIB) generation. The apparatuses include a hot Ta valve for effusive-flow delay-time measurements, a cooled molecular injection system for determination of ionization efficiencies, and a gas flow measurement/control system for introducing very low, well-defined molecular flows into the TIS. Measurements are performed on a test stand using molecular feed compounds containing stable complements of the radioactive nuclei of interest delivered to the TIS at flow rates commensurate with on-line RIB generation. In this article, the general techniques are described and effusive-flow delay times and ionization efficiency measurements are reported for fluorine in an electron-beam plasma target/ion source developed for RIB generation and operated in both positive- and negative-ion extraction modes.
Interferometric measurement of high-frequency density fluctuations in Madison symmetric torus
Authors: Jiang Y. , Brower D. L. , Lanier N. E.
Published: July 2002

As a consequence of recent improvements to the far-infrared (FIR) interferometer time response, from bandwidth of 10 kHz up to 1 MHz, high-frequency density fluctuations can now be resolved on the Madison symmetric torus (MST) reversed-field pinch. The phase measurement allows absolute calibration of the fluctuation amplitude while eleven chords generate information on the spatial distribution. Density fluctuations up to 200 kHz are observed. A unique feature of the MST interferometer is that six chords are toroidally displaced 5° from the remaining five. Hence, besides information on the poloidal structure, i.e., m=1, toroidal information is also available. By computing the cross power, coherence, and cross phase between two toroidally displaced chords, one can determine the toroidal rotation speed, dispersion, and correlation length.
Axial diagnostic package for Z
Authors: Nash T. J. , Derzon M. S. , Chandler G. A. , Fehl D. , Leeper R. , Hurst M. , Jobe D. , Torres J. , Seaman J. , Lazier S. , Gilliland T. , McGurn J.
Published: July 2002

We have developed and fielded an axial diagnostic package for the 20 MA, 100 ns, z-pinch driver Z. The package is used to diagnose dynamic hohlraum experiments which require an axial line of sight. The heart of the package is a reentrant cone originally used to diagnose ion-beam-driven hohlraums on PBFA-II. It has one diagnostic line of sight at 0°, two at 4°, four at 6°, and four at 9°. In addition it has a number of viewing, alignment, and vacuum feedthrough ports. The front of the package sits approximately 1.5 m from the pinch. This allows much closer proximity to the pinch, with inherently better resolution and signal, than is presently possible in viewing the pinch from the side. Debris that is preferentially directed along the axis is mitigated by two apertures for each line of sight, and by fast valves and imaging pinholes or cross slits for each diagnostic. In the initial run with this package we fielded a time-resolved pinhole camera, a five-channel pinhole-apertured x-ray diode array, a bolometer, a spatially resolved time-integrated crystal spectrometer, and a spatially and temporally resolved crystal spectrometer. We will present data obtained from these diagnostics in the dynamic hohlraum research conducted on Z.
Bolometry systems for the TJ-II flexible heliac
Authors: Ochando M. A. , Mirones E. , Rueda C. , Rodrı́guez P.
Published: July 2002

Local plasma emissivity of TJ-II plasmas will be determined using pyroelectric detectors. For tomographic reconstructions three fan-like arrays, 20 channels each, will be installed at the top, side, and bottom ports of the same sector. The designed compact in-vessel systems will use folding support structures to introduce the arrays through small diameter flanges and translation and rotary drives to position them at their measuring sites. Special individual “honeycomb-like” collimators (transparency of around 50% and spatial resolution of about 2 cm at the plasma center) have been designed to optimize the signal level and to act as a microwave filter. In the first stage, radial profiles of plasma emissivity will be obtained with a single detector, on the basis of frozen plasma parameters during a few ms. This detector is equipped with a rotary slit that scans the whole plasma cross section from 10–20 times per shot. To perform power balances, global plasma emission is monitored with three pyroelectric detectors. Collimators are movable slits that enable probing either the full plasma cross section or narrow central chords; when fully closed they protect detectors during wall conditioning and permit background noise characterization.
New neutron diagnostics with the magnetic proton recoil spectrometer
Authors: Källne J. , Ballabio L. , Conroy S. , Ericsson G. , Frenje J. , Gorini G. , Prandoni P. , Tardocchi M. , Traneus E.
Published: July 2002

The first magnetic proton recoil type neutron spectrometer has been put to use for diagnosing tokamak plasmas of high neutron yield rates (the range Yn=1015–6×1018 n/s). The spectrometer principles along with the diagnostic installation are presented. Performance and diagnostic capabilities are illustrated based on results obtained at Joint European Torus. The implications for neutron spectrometry diagnostics on the next step tokamak for burning plasmas (Yn→1022 n/s) are discussed.
One-dimensional x-ray microscope for shock measurements in high-density aluminum plasmas
Authors: Workman J. , Tierney T. , Evans S. , Kyrala G. , Benage J.
Published: July 2002

Accurate experimental measurements of the equation of state for strongly coupled plasmas (Γ⩾1), relevant to astrophysical, geologic and inertial confinement fusion applications, have been extremely difficult. In this pursuit, we have designed a one-dimensional dual-crystal x-ray microscope for making high-resolution measurements of shocks launched by laser pulses in high-density aluminum plasmas. Optical ray-tracing analysis of the design is presented including effects of surface aberrations. The spherically bent mica crystals are arranged at near normal incidence to operate at energies of 1.35 and 4.75 keV using the second and seventh order reflections, respectively. With a magnification of 45×, the microscope’s spatial resolution is predicted to be better than 2 μm when coupled to an x-ray streak camera. The addition of a grazing-incidence optic perpendicular to the imaging direction partially compensates astigmatism. This compensation provides an increase in collection efficiency at the streak camera slit by a factor of ∼15.
Performance of Alcator C-Mod core Thomson scattering system
Authors: Mossessian D. A. , Hubbard A. , Irby J.
Published: July 2002

Design of the Alcator C-Mod Thomson scattering (TS) diagnostic is discussed and the results of the measurements are presented. The TS system has six spatial channels with observation volumes evenly distributed between the midplane and the edge of the plasma. Each channel is capable of measuring the electron density in the range Ne=5×1019–5×1021 m−3 and temperature from Te=200 eV to 10 keV. A 30 Hz, 1.5 J per pulse Nd-YAG laser is employed allowing the measurements of evolution of Te and Ne profiles during plasma shot. A laser beam position control and feedback system provides for the beam alignment stability and reliable electron density measurements. Examples of the core density and temperature profiles measured at different stages of the plasma evolution are discussed.
Prospects for charge-exchange-recombination-based measurements on International Thermonuclear Experimental Reactor using a helium diagnostic neutral beam
Authors: Thomas D. M. , Burrell K. H. , Snider R. T. , Wade M. R.
Published: July 2002

Several important measurements in the International Thermonuclear Experimental Reactor (ITER) diagnostic mission, including the primary one of core helium ash density, are expected to be addressed using active spectroscopic techniques. These methods rely on the use of a dedicated diagnostic neutral beam (DNB) which has been optimized for the dual requirements of beam penetration and charge exchange cross section. For hydrogenic beams, this results in an optimal beam energy of ∼100 keV/amu. Signal-to-noise estimates using realistic geometries and the existing ITER profile and equilibrium data have confirmed the stringent requirements on beam quality and intensity to satisfy the stated ITER measurement precisions. In this article we consider the use of a neutral helium DNB for making active spectroscopic measurements on ITER, since helium beams offer better penetration in dense plasma for a given energy, and the prospects for given source performance may also be improved. Drawbacks include the more difficult absolute calibration of the beam density profile as well as the fundamental problem of uniquely identifying the source (fusion-based ash, beam core fuelling, or edge DNB neutralizer/source efflux) of the observed He charge-exchange recombination line in order to unambiguously characterize core helium buildup and confinement on ITER.
Benchmarking atomic physics models for magnetically confined fusion plasma physics experiments
Authors: May M. J. , Finkenthal M. , Soukhanovskii V. , Stutman D. , Moos H. W. , Pacella D. , Mazzitelli G. , Fournier K. , Goldstein W. , Gregory B.
Published: July 2002

In present magnetically confined fusion devices, high and intermediate Z impurities are either puffed into the plasma for divertor radiative cooling experiments or are sputtered from the high Z plasma facing armor. The beneficial cooling of the edge as well as the detrimental radiative losses from the core of these impurities can be properly understood only if the atomic physics used in the modeling of the cooling curves is very accurate. To this end, a comprehensive experimental and theoretical analysis of some relevant impurities is undertaken. Gases (Ne, Ar, Kr, and Xe) are puffed and nongases are introduced through laser ablation into the FTU tokamak plasma. The charge state distributions and total density of these impurities are determined from spatial scans of several photometrically calibrated vacuum ultraviolet and x-ray spectrographs (3–1600 Å), the multiple ionization state transport code transport code (MIST) and a collisional radiative model. The radiative power losses are measured with bolometery, and the emissivity profiles were measured by a visible bremsstrahlung array. The ionization balance, excitation physics, and the radiative cooling curves are computed from the Hebrew University Lawrence Livermore atomic code (HULLAC) and are benchmarked by these experiments. (Supported by U.S. DOE Grant No. DE-FG02-86ER53214 at JHU and Contract No. W-7405-ENG-48 at LLNL.)
Implications of high-energy photons and electrons on target preheat at the Sandia “Z” facility
Authors: Derzon M. , Nash T. , Chandler G. , Cooper G. , Fehl D. , Hall C. , Lash J. , Leeper R. , McGuire E. , Mock R. , Olsen R. , Olson C. , Rochau G. E. , Rochau G. A. , Ruiz C. , Seamen J. , Slutz S. , Stygar W. , Sweeney M. A. , Lazier S. , Droemer D. , Helvin T. , Starbird R.
Published: July 2002

High-energy photons and electrons on the Sandia National Laboratories “Z” accelerator, a z-pinch device, will deposit energy into a capsule and fuel; this may create a potential preheat problem for inertial confinement infusion (ICF). In this article we discuss heating of the capsule and fuel by high-energy photons and electrons. The fuel is heated to <2 eV, in a time-integrated sense, on Z by these particles. Because peak implosion occurs at the peak in the soft x-ray emission on Z, the heating at times of interest is reduced roughly an order of magnitude to ∼0.2 eV for times of interest and fuel preheat from this mechanism is concluded to be small. These estimates are generated from time-integrated bremsstrahlung measurements. The uncertainty in the heating is high because the electron spectrum is not known directly, but inferred. In addition, the influence of photons and electrons at energies between 5 and 60 keV is not known. Given the uncertainties at this point, we do not know the impact on the feasibility of internal dynamic hohlraums for a z-pinch-driven ICF implosion. We discuss these issues and suggest directions for further study.
A heavy ion beam probe for the Madison Symmetric Torus
Authors: Shah U. , Connor K. A. , Lei J. , Schoch P. M. , Crowley T. P. , Schatz J. G. , Dong Y.
Published: July 2002

A heavy ion beam probe (HIBP) is being developed for application on the Madison Symmetric Torus (MST). It will be used to make measurements of the plasma space potential Φ(r), fluctuations in potential Φ̃(r), the electron density ne(r), fluctuating electron density ñe(r), and radial electric field Er(r) from the core to the edge region of the plasma in MST. While information on these quantities can and has been obtained with probes inserted in the surface region, none of the above measurements have been made in the core of a hot reversed field pinch. Measurements of Φ(r), Er(r), and ne(r) have been well established in previous HIBP systems on tokamaks such as Impurities Studies Experiment, Texas Experimental Tokamak (TEXT), and TEXT Upgrade, stellarators such as Advanced Toroidal Facility and Compact Helical System and Bumpy Tori such as Elmo Bumpy Torus and Nagoya Bumpy Torus. Less well developed in terms of HIBP measurements are equilibrium and fluctuating magnetic fields. Because the confining field on MST is determined by plasma conditions, some effort has been made in the design of the MST beam probe to make it possible to characterize B before, during, and after the plasma discharge.
Development and operation of a thin foil Faraday collector as a lost ion diagnostic for high yield d-t tokamak fusion plasmas
Authors: Cecil F. E. , Roy B. , Kern S. , Nowak A. , Takimoto Y. , Jarvis O. N. , van Belle P. , Sadler G. J. , Hone M. , Loughlin M. , Darrow D. , Medley S. S. , Roquemore L. , Barbour C.
Published: July 2002

We are continuing our development of a radiation-hard, charged-particle detector consisting of a series of thin parallel conducting foils as a lost ion diagnostic for high yield d-t tokamak fusion plasmas. Advantages of this detector concept include economy, ability to operate in relatively intense neutron/gamma ray radiation backgrounds and at moderately high temperatures, and a modest degree of energy resolution. A detector consisting of four parallel foils of Ni, each of thickness 2.5 μm, was operated in the Joint European Torus during the recent DTE-1 experiment. During the highest yield pulses of this campaign, (16 MW), the flux of energetic alpha particles at the detector was measured to be less than about 2 nA/cm2. This upper limit is significantly greater than the expected flux assuming classical losses and given the geometry of the detector. During most of the nearly 2500 pulses of the DTE-1 experiment for which the detector response has been inspected, a relatively intense (up to 200 nA/cm2) flux of low energy positively charged particles was observed which appears related to the D-α photon flux at the plasma edge. Similar detector designs have been recently evaluated using monoenergetic helium ion beams from the tandem accelerator at Sandia National Laboratories. One such detector, consisting of six foils of 6 μm thick Al demonstrated an energy resolution of about 7% for 7 MeV alpha particles. Possible improvements to this detector concept include the fabrication of an “integrated circuit” like design consisting of alternately deposited layers of insulator and conductor. Future applications of the detector concept include first wall lost ion diagnostics for the ignition device to test engineering concepts and NSTX.
Automatic evaluation of plasma density profiles from microwave reflectometry on ASDEX upgrade based on the time-frequency distribution of the reflected signals
Authors: Varela P. , Manso M. , Nunes I. , Santos J. , Nunes F. , Silva A. , Silva F.
Published: July 2002

A new data analysis technique has been developed for the evaluation of the density profiles from broadband reflectometry in the presence of plasma turbulence. The method is based on the spectrogram of the reflected signals and uses the complete information of the beat frequency spectrum. The application of the Floyd best path algorithm, that takes into account the history of the beat frequency curve, enables us to extract the slow component due to the plasma profile. The statistics of the group delay data points is also considered to validate (or reject) data with great confidence. The results obtained in a wide range of plasma regimes show that accurate and detailed profiles can be measured automatically. One and two dimensional moving averaging over consecutive sweeps is also available to reduce the variance of the inverted profile while retaining a good temporal resolution.
Runaway electrons control during ramp-up and ramp-down of the magnetic fields in the coils of the TJ-II flexible heliac (abstract)
Authors: Rodrı́guez-Rodrigo L. , López-Fraguas A. , Gabriel A.
Published: July 2002

The main accelerating electric field is induced in TJ-II flexible heliac (Ref. Reference 1) by currents ramping in the central coils, while the current in the vertical coils is kept constant. With this operational protocol in first TJ-II discharges, hard x rays (HXR) measured using NaI detectors during ramp-up seem to be generated by electrons confined about 40 ms. This time is coherent with the existence of closed magnetic surfaces before the steady-state phase. To diminish this runaway electron generation in the large configurational diagram of the device, independently of gas puffing control, two methods acting before the steady-state phase are investigated. One has been designed as a mechanical system interfering poloidally with the magnetic surfaces and the other consists in the study of the magnetic field structure needed to avoid the closed magnetic surface formation and in its possible application to the TJ-II operation.
New shear apparatus for in situ small-angle x-ray scattering experiments
Authors: Münch Ch. , Kalus J.
Published: July 2002

Small-angle scattering is a powerful tool for the investigation of micellar solutions. By applying a shear flow, increased information can be obtained. A new parallel disks shear apparatus for in situ detection of the sheared state by means of small-angle x-ray scattering is described. The steady shear rate Γ may be changed from 0.25 to 200 s−1. If needed transient shear rates Γ having the shape of stop and go, being sinusoidal or a ramp, can be applied. Typical response times of the apparatus are less than 1 s. The path length of the x rays in the shear cell can be continuously changed between 0.5 and 5 mm. The angle α between the incident x-ray beam and the shear gradient vector Γ may be varied from 0° to approximately 55°. As an example, we give a brief report of experiments performed on two sheared aqueous surfactant solutions with differently shaped (disk-like and rod-like) particles: a 30% by weight solution of tetramethylammonium perfluorononanoate in D2O and a 30 mM solution of tetraethylammonium perfluorooctanesulfonate in H2O.
Emittance measurements of the Sub-Picosecond Accelerator electron beam using beam position monitors
Authors: Russell Steven J.
Published: July 2002

In general, the spatial distributions of electron beams from photoinjectors are unknown and are not well approximated by a Gaussian. Therefore, when measuring the emittance, it is important to make no assumptions about the beam’s spatial distribution. A diagnostic that fulfills this requirement uses beam position monitors to measure the second moment of the electron beam’s image charge. This information, coupled with the beam line’s transfer matrix, can be used as an unambiguous measure of the root mean square emittance that is independent of the beam’s spatial distribution. Presented here are the results of the first implementation of this measurement technique on the Sub-Picosecond Accelerator facility at Los Alamos National Laboratory.
Quantitative measurement of x-ray images with a gated microchannel plate system in a z-pinch plasma experiment
Authors: Shan Bing , Yanagidaira Takeshi , Shimoda Katsuji , Hirano Katsumi
Published: July 2002

A multiframe, gated pinhole system capable of quantitative acquisition for pulsed soft x rays is described and tested. The system based on a gated microchannel plate (MCP) is employed to observe the evolution of z-pinch plasma in a plasma focus facility with a time resolution of ∼220 ps. The quantitative relationship between x-ray source intensity and the recorded images has been investigated. To make a quantitative measurement, the phosphor screen current was measured to calculate the total electrons output from the MCP, which is proportional to both the incident x-ray intensity and the intensity of the recorded images. Furthermore, by taking into account the pinhole geometry, MCP gain and system spectral response, a quantitative calibration of the x-ray images has been established. We have employed the system to observe the plasma evolution in a plasma focus facility. An order of ∼1016 photons/(s mm2 mrad2) soft x-ray emission within 6–14 Å was observed in a neon puffed experiment with time resolved four successive frames.
An instrument for performing laser capture microdissection of single cells
Authors: Goldstein Seth R. , Pohida Thomas , Smith Paul D. , Peterson John I. , Wellner Ed , Malekafzali Arash , Suarez-Quian Carlos A. , Bonner Robert F.
Published: July 2002

We have developed a new form of laser capture microdissection (LCM) optimized for isolating and concentrating single cells from a tissue slide for subsequent molecular analysis. In LCM an infrared laser diode is used together with a microscope to locally melt a thin film of ethylene vinyl acetate (EVA) placed in contact or close proximity to microscopically targeted cells. Since the desired cells adhere to the film where it has been melted, they are extracted from their adjacent tissue in the specimen when the film is separated from the slide. In our system the EVA is bonded to a cylindrical substrate resulting in a very small area of contact between the EVA and the slide which minimizes contamination to levels consistent with analyzing a few cells of a selected cell type. By collecting cells at different portions about the cylinder periphery, the novel geometry also allows the concentration of cells from different slides onto a single substrate, enabling very sensitive molecular analysis to be performed on collections of rare cells. A computer controlled mechanism gently lowers the cylinder to either contact the slide with a small preload force, or provide a minute gap between the cylinder and the tissue. In the latter noncontact mode, the possibility of stray contamination is further reduced since EVA/tissue contact is only made at the location of the laser beam at a minute spot. The mechanism also can rotate the cylinder to provide fresh EVA capture surface after it has raised the cylinder off the slide. A method of fabricating the required precision cylinders of EVA capture surface is described which uses a precision mold cavity and a reusable substrate made of polycarbonate and stainless steel. Results are presented for the preload and noncontact modes which demonstrate the capabilities of the system to capture and concentrate targeted single cells from a complex tissue.
Compact optical setup for forward-box degenerate four-wave mixing measurement
Authors: Fukaya Toshio , Iwai Shinichiro , Murata Shigeo
Published: July 2002

We have devised compact optics for the forward-box configuration in degenerate four-wave mixing spectroscopy. The core of the optical setup is the successive use of a pair of polarization-based beam splitters that divide the laser beam into four parallel beams. This setup is compact, easy to assemble, and adaptable for laser light over a wide spectral range. Selection of the combination of beam polarization produces two types of transient grating: either a polarization grating or an intensity grating.
Design and testing of a new magnetorheometer
Authors: Shorey Aric B. , Kordonski William I. , Gorodkin Sergei R. , Jacobs Stephen D. , Gans Roger F. , Kwong Kevin M. , Farny Caleb H.
Published: July 2002

A new, commercially available polishing process called magnetorheological fininshing is used to polish and figure precision optics. To understand and model this process correctly it is important to determine the mechanical properties of the fluid under the influence of the magnetic field. Magnetorheotogical (MR) fluids are commonly modeled as Bingham fluids, so one of the essential properties to measure is the yield stress. Since MR fluids are inherently anisotropic, the yield stress will depend on the mutual orientation of the magnetic field and the direction of deformation. The relative orientation of the field and deformation in polishing does not coincide with common rheological setups, so a new rheometer has been designed and tested. This new magnetorheometer design has been shown to give correct stresses during calibration experiments using Newtonian fluids with a known viscosity. The measured stress has also been shown to have a magnitude consistent with published finite element approximations for magnetic fluids. The design of the instrument was complicated because of the requirements imposed upon the magnetic field, and the difficulty in satisfying the no slip boundary condition. Our results show the importance of having a homogeneous field in the test region during measurements. The solutions to these problems and discussion of the measurements on nonmagnetic and magnetic fluids are given.
Variable geometry two mode levitation trap
Authors: Babič D. , Čadež A.
Published: July 2002

Construction and operation of the electrodynamic levitation trap which can be operated in a passive and an active mode is described. This combination together with variable electrode geometry simplifies the trap’s design and simultaneously gives more flexibility with respect to different kinds of measurements. Sample measurements of mechanocaloric effect caused by nonuniform heating of a single levitated particle are presented and discussed.
Fast two-dimensional potential measurement at the thermal barrier region of the tandem mirror Gamma 10
Authors: Kikuno N. , Ishii K. , Ishibashi N. , Nagasaki M. , Katsuki Y. , Goto T. , Goi Y. , Ono Y. , Yamanashi M. , Nagao A. , Saito T. , Tatematsu Y. , Suzuki A. , Itakura A. , Tamano T. , Yatsu K.
Published: July 2002

A gold neutral beam probe system was improved by adopting a multichannel ion detector and adding sweeping functions of beam energy, deflector voltage, and electrode voltage of the analyzer to the system to measure the fluctuations and time evolution of the two-dimensional space potentials with fast resolving time during one shot. Positions of the beam spot on the multichannel detector corresponding to the ionizing points of the beam in the plasma were simulated precisely as a function of the beam energy and the injection angle. A potential derivation formula was determined taking into consideration both the numerical and experimental results, and the reproducibility of the potential profile was checked. Two-dimensional potential profiles were measured in the optimization experiment of the microwave injection angles for formation of the plug potential.
Elastic mid-infrared light scattering: A basis for microscopy of large-scale electrically active defects in semiconducting materials
Authors: Kalinushkin V. P. , Yuryev V. A. , Astafiev O. V.
Published: July 2002

A method of the mid-IR-laser microscopy has been recently proposed for the investigation of the large-scale electrically and recombination active defects in semiconductors and nondestructive inspection of semiconductor materials and structures in the industries of microelectronics and photovoltaics. The basis for this development was laid with a wide cycle of the investigations on the low-angle mid-IR-light scattering in semiconductors. The essence of the technical idea was to apply the dark-field method for spatial filtering of the scattered light in the scanning mid-IR-laser microscope. This approach enabled the visualization of large-scale electrically active defects which are the regions enriched with ionized electrically active centers. The photoexcitation of excess carriers within a small volume located in the probe mid-IR-laser beam enabled the visualization of the large-scale recombination-active defects like those revealed in the optical or electron beam induced current methods. Both these methods of the scanning mid-IR-laser microscopy are now introduced in detail in the present article as well as a summary of techniques used in the standard method of the low-angle mid-IR-light scattering itself. Besides the techniques for direct observations, methods for analyses of the defect composition associated with the mid-IR-laser microscopy are also discussed in the article. Special attention is paid upon potential applications of the above methods as characterization and testing techniques in the semiconductor science and industry. It is concluded that elastic midinfrared laser light scattering is a basis for the development of a variety of research techniques and instruments which could be useful in different branches of basic and applied research work in the field of defect engineered semiconductors as well as for the development of devices for quality inspections in the semiconductor industry. Being contactless, nondestructive and nonpolluting, techniques based on midinfrared light scattering could also find many applications for automation of the technological process control as well as the process remote monitoring.
Laser-pulse technique for measuring the thermal diffusivity of substrate-supported polymer films
Authors: Hobbie E. K. , De Reggi A. S.
Published: July 2002

We describe a technique for measuring the thermal diffusivity of substrate-supported polymer films based on the early-time electrothermal response following a 100 ns pulse from a Q-switched ruby laser. Data for a polyimide film spin coated on a p-doped Si[111] substrate are used to demonstrate the technique. From the late-time decay of the signal, we also obtain an estimate of the interfacial thermal-transport coefficient of the polymer–semiconductor interface.
Design of a programmable timing unit
Authors: Quine Richard W. , Harbridge James R. , Eaton Sandra S. , Eaton Gareth R.
Published: July 2002

A programmable timing unit (PTU) has been designed and constructed having 1 ns resolution and a generalized matrix-based architecture. Automated measurement and calibration of commercially available programmable delay lines achieve the 1 ns resolution. The matrix architecture allows generalized flexibility in establishing the connections between timing circuits called event markers and output functions that control equipment external to the PTU. The microprocessor-based PTU communicates with a PC through a standard RS-232C serial interface. The PC contains software developed to control specific timing sequences produced by the PTU for control of experimental apparatus. While the PTU was developed for use in an electron paramagnetic resonance laboratory, the architecture is extremely generalized and use in other applications would require only the development of specific application software. The software developed so far has been done in Microsoft Visual BASIC, but other software tools could be used without modification of the PTU hardware.
Pure high dose metal ion implantation using the plasma immersion technique
Authors: Zhang T. , Tang B. Y. , Zeng Z. M. , Kwok T. K. , Chu P. K. , Monteiro O. R. , Brown I. G.
Published: July 2002

High energy implantation of metal ions can be carried out using conventional ion implantation with a mass-selected ion beam in scanned-spot mode by employing a broad-beam approach such as with a vacuum arc ion source, or by utilizing plasma immersion ion implantation with a metal plasma. For many high dose applications, the use of plasma immersion techniques offers a high-rate process, but the formation of a surface film along with the subsurface implanted layer is sometimes a severe or even fatal detriment. We describe here an operating mode of the metal plasma immersion approach by which pure implantation can be obtained. We have demonstrated the technique by carrying out Ti and Ta implantations at energies of about 80 and 120 keV for Ti and Ta, respectively, and doses on the order of 1×1017 ions/cm2. Our experiments show that virtually pure implantation without simultaneous surface deposition can be accomplished. Using proper synchronization of the metal arc and sample voltage pulse, the applied dose that deposits as a film versus the part that is energetically implanted (the deposition-to-implantation ratio) can be precisely controlled.
A method for balancing the paths of a two-photon interferometer
Authors: Spence S. E. , Stoudt D. C. , Swanson N. L. , Parks A. D. , Peterkin F. E.
Published: July 2002

We present and demonstrate a method for balancing the two paths of a two-photon interferometer of the Hong-Ou-Mandel (HOM) variety. This method removes the difficulties of balancing the paths in this type of interferometer where a type-I crystal is used for the generation of the entangled photon pairs. Using this method we show that we are consistently able to balance the ∼2000 mm path lengths in our HOM interferometer on average to within ∼60 μm.
High order quarter-wave plates and analysis of the directions of rotation in the circular polarizations
Authors: Pelletier R. , Pelletier-Allard N.
Published: July 2002

The advent of new research subjects, such as plasmas, optical pumping, and atom cooling, has led to an increased use of quarter-wave plates in order to produce circularly polarized beams with the correct direction of rotation. The recent commercialized quarter-wave plates work in high orders, which leads to a drastic reduction of their pass band. Moreover, the direction of rotation in circular polarization can be affected. The purpose of the present article is to describe new techniques allowing an accurate determination of the optical properties of the used plates.
Measurement of electron bunch timing jitter using wakefield analysis
Authors: Cho Sung Oh , Lee Byung Cheol , Jeong Young Uk , Kim Sun Kook , Cha Byung Heon , Lee Jongmin
Published: July 2002

A wakefield is generated when electron bunches pass through discontinuities of beam pipes, such as rf cavities. We analyze the relation between the timing jitter of the bunches and the wakefield. From the analysis we derive a mathematical expression through which the jitter as well as the amplitude fluctuation of the bunches can be obtained by measuring the power spectrum of the wake. A measurement of the bunch jitter using this frequency-domain based wakefield analysis is compared with that measured by a time-domain based sampling oscilloscope. The two measurement results correspond well each other.
The use of magnetic fields in a partial-coaxial microwave cavity holey-plate ion source
Authors: Yoshida Y. , Takeiri Y.
Published: July 2002

A low-pressure and high-density microwave ion source created and sustained by evanescent waves emitted from a holey plate, and using permanent magnet multicusp fields, has been studied. This source is called a holey-plate ion source. Microwave power at 2.45 GHz is supplied from a coaxial cavity and then converted into an evanescent mode through the use of a holey plate. This source can produce low-pressure and high-density plasma using an octopole magnetic field. The ion current densities are in excess of 4.8 mA/cm2 at an extraction voltage of 3 kV, an argon gas pressure of 0.3 Pa in the plasma chamber, and an input microwave power of 80 W. An 18-mm-diam ion beam is extracted and accelerated from the ion source.
Characterization of an open-loop controlled scanning stage using a knife edge optical technique
Authors: Cronin P. J. , Fekete P. W. , Arnison M. R. , Cogswell C. J.
Published: July 2002

Our experimental confocal microscope project required the construction of a high performance scanning stage. In order to understand the scanning stage behavior we modeled each axis of motion as a damped harmonic oscillator, and measured its mechanical response using an optical knife edge technique. In order to maximize the scan stage accuracy and performance we used the characterization results of the stage to implement first order correction for such influences as the mass, the damping, and the stiffness of the springs of the scanning stage. We show that the stage can be driven over a range of frequencies and motion wave forms, without inducing primary resonant response, and this results in an improved quality of the confocal images. We have constructed a novel scanning motion incorporating the corrected results. The linearity of motion was found to be better than with a ramp or sine wave driving voltage, enabling an order of magnitude increase in speed of acquisition.
Photoconductive frequency-resolved spectrometer for carrier lifetime determination in semiconductors
Authors: Burda Ioan
Published: July 2002

A photoconductive frequency-resolved spectrometer (PCFRS) for the determination of carrier lifetime in semiconductors is described. This PCFRS is designed for operation from 1 up to 1000 Hz (lifetime of 0.159 s–0.159 ms). The PCFRS uses an inexpensive superbright light emitting diode, which can be modulated directly, and a system embedded with a 68HC11 microcontroller, which performs all functions of this spectrometer. A sample of the lifetime distribution for a commercial CdS photoresistor is also presented.
A sample-scanning confocal optical microscope for cryogenic operation
Authors: Segura J.-M. , Renn A. , Hecht B.
Published: July 2002

A sample-scanning confocal optical microscope for single-molecule imaging and spectroscopy working at superfluid helium temperature, liquid nitrogen, and room temperature is described. An optical resolution of 800 nm full width at half maximum as well as a detection efficiency of ≈3.5% are achieved. The sample scanner features an exceptionally large scan range of 23 μm at 1.8 K. A position sensor allows for continuous observation of the scanner motion and for a correction of piezoelectric hysteresis and creep at 77 K and at room temperature. Coarse positioning of the sample in x-y is achieved by an inertia drive with high reproducibility and nanometer precision. We demonstrate combined high–resolution confocal imaging and spectroscopy of single molecules at 1.8 K.
Origin of crystallographic tilt in InGaAs/GaAs(001) heterostructure
Authors: Kang J. M. , Son C. S. , Kim Moo-Sung , Kim Yong , Min Suk-Ki , Kim C. S.
Published: July 2002

X-ray rocking curve measurements showed a significant crystallographic tilt in relaxed InGaAs layer grown on (001) GaAs. Transmission electron microscopy revealed that the origin of tilt is 60° dislocations generated having Burgers vectors of a same vertical edge component. Calculations using anisotropic elasticity show that this configuration of 60° dislocation array is energetically favorable when the tilt of epilayer is present as to remove the long range stress field induced by the vertical edge components at the interface.
Near-field optical characterization of the photoluminescence from partially ordered (GaIn)P
Authors: Gregor M. J. , Blome P. G. , Ulbrich R. G. , Grossmann P. , Grosse S. , Feldmann J. , Stolz W. , Göbel E. O. , Arent D. J. , Bode M. , Bertness K. A. , Olson J. M.
Published: July 2002

The two photoluminescence bands typically observed in partially ordered (GaIn)P are studied with a spatial resolution of 270 nm by use of scanning near-field optical microscopy at low temperature. Local luminescence spectra show a strong spatial variation of the low energetic emission in lineshape and peak position whereas the same attributes of the high energetic emission differ only slightly for all investigated areas of the sample. The intensities of both photoluminescence bands are anticorrelated in space on a 0.5–1.5 μm scale. TEM investigations show that the structure of the sample is inhomogeneous on the same length scale.
Interfacial roughness scaling and strain in lattice mismatched Si0.4Ge0.6 thin films on Si
Authors: Ming Z. H. , Huang S. , Soo Y. L. , Kao Y. H. , Carns T. , Wang K. L.
Published: July 2002

Interfacial roughness parameters and lattice strain of Si0.4Ge0.6 films with varying thickness epitaxially grown on Si(100) were determined using the techniques of grazing-incidence x-ray scattering and diffraction. The roughness of both the buried interface and sample surface follows a similar power-law scaling behavior with an exponent β around 0.71 for films below the critical thickness, and it undergoes a large change above the critical thickness. Observation of such a scaling law thus establishes a quantitative correlation between the interfacial roughness and lattice strain, and also allows the prediction of interfacial roughness as a function of film thickness of this compound.
Hydrogen passivation of Ca acceptors in GaN
Authors: Lee J. W. , Pearton S. J. , Zolper J. C. , Stall R. A.
Published: July 2002

Exposure to a hydrogen plasma at 250 °C of p-type GaN (Ca) prepared by either Ca+ or Ca+ plus P+ co-implantation leads to a reduction in sheet carrier density of approximately an order of magnitude (1.6×1012 cm−2 to 1.8×1011 cm−2), and an accompanying increase in hole mobility (6 cm2/V s to 18 cm2/V s). The passivation process can be reversed by posthydrogenation annealing at 400–500 °C under a N2 ambient. This reactivation of the acceptors is characteristic of the formation of neutral (Ca–H) complexes in the GaN. The thermal stability of the passivation is similar to that of Mg–H complexes in material prepared in the same manner (implantation) with similar initial doping levels. Hydrogen passivation of acceptor dopants in GaN appears to be a ubiquitous phenomenon, as it is in other p-type semiconductors.
High rate melt texturing of Nd1−xBa2+xCu3O7−δ type superconductors
Authors: Salama K. , Parikh A. S. , Woolf L.
Published: July 2002

Melt texturing is one of the most prominent techniques available to fabricate bulk high-temperature superconductors with superior current transport and magnetic properties. In the case of Y1Ba2Cu3Ox, melt textured samples can have a Jc on the order of 105 A/cm2 at 77 K and zero applied magnetic field, and in excess of 103 A/cm2 at 77 K and 30 T. However, a serious drawback of the melt textured Y1Ba2Cu3Ox compound, which severely restricts its application, is the very slow rate (1 mm/h) needed to develop the highly textured planar front necessary for optimum superconducting properties. RE-123 compounds containing the rare earth element neodymium have been recently found to recrystallize much more rapidly, indicating the possibility of their high speed melt texturing. By processing bars (50 mm×5 mm×5 mm) of these compounds through a high-temperature gradient, fully textured microstructures were obtained at rates up to 50 mm/h, which are more than 50 times faster than those employed in Y1Ba2Cu3Ox. After oxygen annealing, these textured bars have a Tc onset of 93 K and a transport Jc, at 77 K and zero applied magnetic field, on the order of 5000 A/cm2. These results are expected to increase significantly as more progress takes place.
Transit-time effect on electronic noise in submicron n +nn+ structures
Authors: Shiktorov P. , Gruz̆inskis V. , Starikov E. , Reggiani L. , Varani L.
Published: July 2002

The voltage noise spectrum associated with velocity fluctuations is calculated for submicron n +nn+ GaAs structures in the framework of a closed hydrodynamic approach based on the velocity and energy conservation equations. Transit-time effects are found to substantially influence the noise spectrum in a wide frequency range. The good agreement found with Monte Carlo simulations validates the proposed theoretical approach. We predict a minimum noise measure at the frequency of 250 GHz for the considered structure.
Atomic force and optical near-field microscopic investigations of polarization holographic gratings in a liquid crystalline azobenzene side-chain polyester
Authors: Ramanujam P. S. , Holme N. C. R. , Hvilsted S.
Published: July 2002

Atomic force and scanning near-field optical microscopic investigations have been carried out on a polarization holographic grating recorded in an azobenzene side-chain liquid crystalline polyester. It has been found that immediately following laser irradiation, a topographic surface grating structure appears. The time development of the grating structure was followed by atomic force microscopy for 20 h by repeatedly scanning the same area of the film. The grating structure disappears after a few hours and a pronounced increase of surface roughness has been found to take place. A near-field optical microscopic scanning of the grating reveals, however, that the bulk of the film remains optically anisotropic.
Regimes of particle trapping in inductively coupled plasma processing reactors
Authors: Hwang Helen H. , Kushner Mark J.
Published: July 2002

Contamination of wafers by particles in plasma processing reactors is a continuing problem affecting yields of microelectronic devices. In this letter, we report on a computational study of particle contamination of wafers in a high plasma density inductively coupled plasma (ICP) reactor. When operating with an unbiased substrate, particles readily contaminate the wafer due to high ion fluxes which produce large ion-drag forces. Biasing the substrate with a radio frequency (rf) voltage counteracts the ion-drag forces by increasing the opposing electrostatic forces in the sheath, thereby shielding the wafer from incoming particles. We have found three regimes of particle contamination for different ICP powers and rf biases. At high rf biases and low ICP powers, particles trap at the edge of the sheath. At low rf bias and high ICP power, ion drag forces dominate, particles do not trap, and wafer contamination is problematic. At intermediate powers and biases, particles quasitrap, leading to moderate particle contamination.
Surface photovoltage spectroscopy of quantum wells and superlattices
Authors: Bachrach-Ashkenasy N. , Kronik L. , Shapira Yoram , Rosenwaks Y. , Hanna M. C. , Leibovitch M. , Ram Prakhya
Published: July 2002

Surface photovoltage spectroscopy (SPS) has been employed to monitor optical transitions in quantum well and superlattice structures at room temperature. Excellent agreement is found between theoretical predictions of heavy hole and electron energy level positions and the observed transitions. The results show that using this technique, the complete band diagram of the quantum structure may be constructed. SPS emerges as a powerful tool capable of monitoring optical transitions above the lowest one in a simple to interpret, contactless, and nondestructive way.
Link-up of 90° domain boundaries with interface dislocations in BaTiO3/LaAlO3
Authors: Dai Z. R. , Wang Z. L. , Duan X. F. , Zhang Jiming
Published: July 2002

Interface microstructures of BaTiO3/LaAlO3 grown by metalorganic chemical vapor deposition (MOCVD) are studied using high-resolution transmission electron microscopy (HRTEM). Interface dislocations in BaTiO3/LaAlO3 have been shown to be directly linked up with the 90° domain boundaries in BaTiO3. This association is a result of strain relief due to a phase transformation when cooled down from the growth temperature. The Burgers vector of the interface dislocations is 〈010〉.