Micron-scale Spatial Resolution Research Articles

Multiwire$X$-Pinches at 1-MA Current on the COBRA Pulsed-Power Generator

The rebuilt COBRA pulsed-power generator, which has a variable current-pulse waveform and amplitude (95-150-ns rise time and ~1-MA peak current), has extended the range of the current-pulse parameters that can be used to study the X-pinches. X-pinches with 4-12 wires of several different wire materials (from Al to W) with diameters from 25 to 75 mum have been studied. The influence of the rate of the rise of current and the X-pinch wire mass on the X-pinch plasma formation and pinch implosion dynamics has been studied using a set of diagnostics with spatial and/or temporal resolution. Multiwire X-pinches were placed in the diode center, and/or two four-wire X-pinches were placed in one of the four parallel return-current circuits of the diode. The experiments showed that the most important factor determining the first X-ray burst timing is the linear mass density of the X-pinch wires, and an optimal value for obtaining a single high-energy X-ray burst was found. Radiographic images of the different test objects, wires in wire-array Z-pinches, and the X-pinches, themselves, were obtained using a micrometer-scale spatial resolution

Microwave Current Imaging in Passive HTS Components by Low-Temperature Laser Scanning Microscopy (LTLSM)

We have used the Low-Temperature Laser Scanning Microscope (LTLSM) technique for a spatially resolved investigation of the microwave transport properties, nonlinearities, and material inhomogeneities in an operating coplanar waveguide YBa2Cu3O_{7‐δ}(YBCO) microwave resonator on a LaAlO3 (LAO) substrate. The influence of twin-domain blocks, in-plane rotated grains, and micro-cracks in the YBCO film on the nonuniform radiofre-quency (rf) current distribution was measured with a micrometer-scale spatial resolution. The impact of the peaked edge currents and rf field penetration into weak links on the linear device performance were also studied. The LTLSM capabilities and its future potential for nondestructive characterization of the microwave properties of superconducting circuits are discussed.

Layerwise analysis of vacuum copper-chromium condensates by glow-discharge mass spectrometry

Features are examined of using high-sensitivity mass-spectral layerwise analysis in a glow discharge to examine Cu-Cr composite material made by electron-beam evaporation. A mathematical model is used to calculate the concentrations of molecular ions in the glow-discharge plasma in order to select isotopes free from molecular ions. The argon-ion etching allows one to examine the distributions of the main and impurity elements with a sensitivity of 10−5–10−6% with micrometer-scale spatial resolution. The distributions of Ti, Cr, Mn, Fe, Ni, Cu, and Ag in the layers have been examined to determine the effects of the trace impurities on the condensation of the atomic vapor.

Doppler optical coherence microscopy for studies of cochlear mechanics

The possibility of measuring subnanometer motions with micron scale spatial resolution in the intact mammalian cochlea using Doppler optical coherence microscopy (DOCM) is demonstrated. A novel DOCM system is described that uses two acousto-optic modulators to generate a stable 500-kHz heterodyne frequency. Images and motion measurements are obtained using phase-resolved analysis of the interference signal. The DOCM system permits imaging with micron-scale resolution and 85-dB sensitivity and motion measurements with 100-kHz bandwidth, directional discrimination, and 30-pm/Hz(0.5) noise floor. Images and motion measurements are presented that demonstrate the ability to resolve motions of structures of interest in a mammalian cochlea in vitro including the basilar membrane, reticular lamina, tectorial membrane, and outer hair cells.

Development of a three-dimensional scanning microparticle image velocimetry system using a piezo actuator

A technique for measuring the full field (x,y,z,u,v,w) velocity distribution of fluid flow at a micrometer scale spatial resolution has been developed. To investigate three-dimensional (3D) flow structures on a microscopic scale, a 3D scanning microparticle image velocimetry system was developed by combining a high-speed camera, an epifluorescent microscope, a cw laser, and a piezo actuator. Both numerical simulations and an experiment were carried out in order to validate the measurement accuracy of the system. Optimum measurement conditions were determined by numerical simulations using synthetic images under epifluorescent microscope observation. As a demonstration, the three-dimensional velocity distribution of water flow inside a microround tube having a diameter of 95μm was measured at a spatial resolution of 5.4×2.7×4.2μm.

Micro-Raman Evaluation of Polycrystalline Silicon MEMS Devices

ABSTRACTMicro-Raman spectroscopy is a valuable tool for thermometry of operational polysilicon MEMS devices. By using the temperature-calibrated response of the optical phonon peak of the polysilicon Raman signature and the micron-scale spatial resolution achieved with a 488 nm Ar+ laser Raman probe, we have obtained spatially resolved steady-state thermal profiles of Joule-heated thermal flexure actuators. The measured thermal profiles are further compared to one-dimensional numerical models of the thermal response of the electrically heated devices.

Quantification of single fluid inclusions by combining synchrotron radiation-induced micro-X-ray fluorescence and transmission.

Fluid inclusions represent the only direct samples of ancient fluids in many crustal rocks; precise knowledge of their chemical composition provides crucial information to model paleofluid-rock interactions and hydrothermal transport processes. Owing to its nondestructive character, micrometer-scale spatial resolution, and high sensitivity, synchrotron radiation-induced micro-X-ray fluorescence has received great interest for the in situ multielement analysis of individual fluid inclusions. Major uncertainties associated with the quantitative analysis of single fluid inclusions arise from the inclusion depth and the volume of fluid sampled by the incident beam. While the depth can be extracted directly from the fluorescence spectrum, its volume remains a major source of uncertainty. The present study performed on natural and synthetic inclusions shows that the inclusion thickness can be accurately evaluated from transmission line scans. Experimental data matched numerical simulations based on an elliptical inclusion geometry. However, for one nonelliptical inclusion, the experimental data were confirmed using a computed absorption tomography reconstruction. Good agreement between the imaging and scanning techniques implies that the latter provides reliable fluid thickness values independent of the shape of the inclusion. Taking into consideration the incident angle, the incident beam energy, the inclusion fluid salinity, and the transmission measurement stability resulted in errors of 0.3-2 microm on calculated fluid inclusion thicknesses.

Applications of synchrotron radiation X-ray techniques on the analysis of the behavior of transition metals in solar cells and single-crystalline silicon with extended defects

A high flux, non-destructive X-ray synchrotron-based technique, X-ray fluorescence microscopy (μ-XRF), is able to detect metal precipitates as small as a few tens of nanometers in diameter within a silicon matrix, with micron-scale spatial resolution. When this technique is combined with the X-ray beam-induced current (XBIC) technique, one can acquire, in situ, complementary information about the elemental nature of transition metal precipitates and their recombination activity. Additionally, X-ray absorption microspectroscopy (μ-XAS) analyses yield information about the local environment of the impurity atoms and their chemical state. Model defect structures and photovoltaic-grade multicrystalline silicon (mc-Si) were studied using these techniques, and the effect of transition metal clusters on the electrical properties of good and bad regions of mc-Si are discussed in detail.

The Composition of Zircon and Igneous and Metamorphic Petrogenesis

Zircon is the main mineral in the majority of igneous and metamorphic rocks with Zr as an essential structural constituent. It is a host for significant fractions of the whole-rock abundance of U, Th, Hf, and the REE (Sawka 1988, Bea 1996, O’Hara et al. 2001). These elements are important geochemically as process indicators or parent isotopes for age determination. The importance of zircon in crustal evolution studies is underscored by its predominant use in U-Th-Pb geochronology and investigations of the temporal evolution of both the crust and lithospheric mantle. In the past decade an increasing interest in the composition of zircon, trace-elements in particular, has been motivated by the effort to better constrain in situ microprobe-acquired isotopic ages. Electron-beam compositional imaging and isotope-ratio measurement by in situ beam techniques—and the micrometer-scale spatial resolution that is possible—has revealed in many cases that single zircon crystals contain a record of multiple geologic events. Such events can either be zircon-consuming, alteration, or zircon-forming and may be separated in time by millions or billions of years. In many cases, calculated zircon isotopic ages do not coincide with ages of geologic events determined from other minerals or from whole-rock analysis. To interpret the geologic validity and significance of multiple ages, and ages unsupported by independent analysis of other isotopic systems, has been the impetus for most past investigations of zircon composition. Some recent compositional investigations of zircon have not been directly related to geochronology, but to the ability of zircon to influence or record petrogenetic processes in igneous and metamorphic systems. Sedimentary rocks may also contain a significant fraction of zircon. Although authigenic zircon has been reported (Saxena 1966, Baruah et al. 1995, Hower et al. 1999), it appears to be very rare and may in fact be related to …

A class of boron-rich solid-state neutron detectors

Real-time solid-state neutron detectors have been fabricated from semiconducting boron–carbon alloys, deposited by plasma-enhanced chemical vapor deposition. Single neutrons were detected and signals induced by gamma rays were determined to be insignificant. The source gas closo-1,2-dicarbadodecaborane (ortho-carborane) was used to fabricate the boron–carbon alloys with only the natural isotopic abundance of B10. Devices made of thicker boron–carbon alloy layers enriched in B10 could lead to increased detection efficiency and active diodes could use the inherent micron scale spatial resolution, increasing the range of possible applications.

X-ray beam induced current—a synchrotron radiation based technique for the in situ analysis of recombination properties and chemical nature of metal clusters in silicon

A synchrotron radiation based x-ray microprobe analytical technique, x-ray beam induced current (XBIC), is suggested and demonstrated at the Advanced Light Source at the Lawrence Berkeley National Laboratory. The principle of XBIC is similar to that of electron/laser beam induced current with the difference that minority carriers are generated by a focused x-ray beam. XBIC can be combined with any other x-ray microprobe tool, such as the x-ray fluorescence microprobe (μ-XRF), to complement chemical information with data on the recombination activity of impurities and defects. Since the XBIC signal, which carries information about the recombination activity of defects in the sample, and the μ-XRF signal, which contains data on their chemical nature, can be collected simultaneously, this combination offers a unique analytical capability of in situ analysis of the recombination activity of defects and their chemical origin with a high sensitivity and a micron-scale spatial resolution. Examples of an application of this technique to multicrystalline silicon for solar cells are demonstrated.

Feasibility study of online high-spatial-resolution MOSFET dosimetry in static and pulsed x-ray radiation fields

Improvements have been made in the measurement of dose profiles in several types of X-ray beams. These include 120-kVp X-ray beams from an orthovoltage X-ray machine, 6-MV Bremsstrahlung from a medical LINAC in conformal mode and the 50-200 keV energy spectrum of microbeams produced at the medical beamline station of the European Synchrotron Radiation Facility. Using a quadruple metal-oxide-semiconductor field-effect transistor (MOSFET) sensor chip in "edge on" mode together with a newly developed sensor readout system, the feasibility of online scanning of the profiles of quasi-static and pulsed radiation beams was demonstrated. Measurements of synchrotron pulsed microbeams showed that a micrometer-scale spatial resolution was achievable. The use of several MOSFETs on the same chip gave rise to the correction of misalignments of the oxide films of the sensor with respect to the microbeam, ensuring that the excellent spatial resolution of the MOSFET used in "edge-on" mode was fully utilized.

Measurement and simulation of temperature dynamics under electron beam

An original in situ technique was developed to measure the temperature rise and decay of a material under electron-beam (e-beam) irradiation. The technique uses the effect of temperature rise on the electrical conductivity of high-temperature superconductors that are prefabricated as microbridges. This temperature sensor was measured to have a sensitivity greater than two orders of magnitude more than a thin-film thermocouple. A stroboscopic technique ensured nanosecond temporal resolution, and the size of the microbridge allowed for micrometer-scale spatial resolution. These measurement ranges are important for practical e-beam lithography. Experimental results were compared with results simulated by the TEMPTATION (temperature simulation) software, and qualitative agreement of simulated and measured results was found. Factors influencing the accuracy of the temperature measurement are discussed.

Direct observation of calcium-independent intercellular ATP signaling in astrocytes.

Adenosine triphosphate (ATP) is assumed to be involved in the regulation of many extracellular signaling systems including calcium wave propagation. So far all supportive evidence is indirect, such as monitoring changes in intracellular calcium on application of extracellular ATP or off-site measurement of ATP from superfusates. Furthermore, the causal relationships among the various signaling agents are still unclear. A novel chemiluminescence dynamic imaging method was developed to monitor ATP release from living biological cells. The assay has linear response over 3 orders of magnitude for fixed concentrations of enzyme and cofactors, with a correlation coefficient of 0.999. The detectability of ATP is down to 10(-8) M at millisecond exposure times with an intensified charge-coupled device camera. The direct imaging of ATP waves in astrocyte cultures was performed together with Fluo-3-Ca imaging at millisecond temporal resolution and micrometer-scale spatial resolution. We discovered that extracellular ATP mediates intercellular calcium wave propagation, but surprisingly, release and propagation of ATP are not calcium dependent. Therefore, ATP rather than Ca or IP3 is the primary intercellular signaling messenger.

Variable sample temperature scanning superconducting quantum interference device microscope

We demonstrate a design for a scanning superconducting quantum interference device (SQUID) microscope in which the sample temperature can be varied over a large range. In this design, both sample and SQUID are in the same vacuum space, separated by a few microns. By firmly anchoring the SQUID to a low-temperature bath, the sample temperature can be changed while the SQUID remains superconducting. This allows magnetic imaging at varying sample temperatures with micron-scale spatial resolution and the sensitivity of a low-Tc SQUID. We demonstrate this approach by imaging the temperature dependence of Abrikosov vortices in thin films of the high-temperature superconductor YBa2Cu3O7−δ. We extract the in-plane penetration depth λab(T) in our samples from these measurements.

Magnetic resonance imaging of laser polarized liquid xenon

We demonstrate magnetic resonance imaging ~MRI! of laser polarized liquid xenon, and image exchange between the liquid and vapor phases. The exceptionally large magnetization density of this liquid should allow MRI with micron-scale spatial resolution without signal averaging. Applications may include imaging of density equilibration and convective flow near xenon’s liquid-vapor critical point, low-field imaging of porous media microstructure, and mapping of the dynamics of two-phase ~liquid-gas! flows. @S1063-651X~99!05602-0#

The bioscience nuclear microscopy program at LLNL

Since initiation in mid 1994, a bioscience nuclear microscopy program at Livermore has enabled collaboration with bio-scientists on a variety of projects requiring quantitative elemental microanalysis. For microprobe analysis a combination of PIXE and STIM are typically used, respectively generating element distribution maps with micron scale spatial resolution, and projected densities and histological information with sub-micron spatial resolution. Current studies demonstrate the applicability of nuclear microscopy (particularly when combined with other analysis techniques) in environmental tracing, toxicology, carcinogenesis, and structural biology. The program currently uses ∼ 10 percent of the available time on a 10 MV tandem accelerator that is also applied to a variety of Accelerator Mass Spectrometry and other microprobe programs. The completion of a dedicated nuclear microprobe system, using a 5 SDH NEC 1.7 MV tandem accelerator and employing several energy dispersive X-ray detectors to improve X-ray counting rates, promises increased accelerator access, greater sample throughput and continued expansion of the program.

X-Ray Microdiffraction for VLSI

AbstractWe describe how x-ray microbeam diffraction is being used to measure strain with micronscale spatial resolution. Micron-scale x-ray beams can be obtained using tapered glass capillaries. With the high brightness and broad energy spectrum of synchrotron radiation and the energy dispersive capabilities of commercially available, liquid nitrogen cooled x-ray detectors, spatially resolved strains in a sample can be determined along different directions without having to rotate the sample, in contrast with more conventional methods using monochromatic x-ray diffraction. This is a major advantage in achieving micron-scale spatial resolution. Strain sensitivities on the order of 2×10−4 have been achieved in such measurements. White beam x-ray microdiffraction has been applied for the first time in real-time studies of thermal and electromigration related strain distributions in passivated Al-on-Si conductor lines. Results of measurements on a single 10μm-wide line are described.

Recent developments in the study of bulk GaAs properties by electron microscopy

Recent developments in the assessment of the properties of bulk GaAs crystals by SEM-EBIC and TEM are presented. The capability of EBIC of giving the majority carrier (dopant) concentration with a micron-scale spatial resolution is used to provide information on the electrical parameters of the large impurity atmospheres and gettering regions surrounding the dislocations in Si-doped LEC GaAs. Information on the impurities and point defects in these impurity atmospheres can thus be obtained. Application of EBIC to the determination of dopant density at growth striations is also discussed. The use of TEM to the study of the nature of microdefects in as-grown as well as implanted crystals is shown. These microdefects turn out to be either dislocation loops or precipitates depending on the growth and/or processing conditions. The point deffects, vacancies or interstitials, at their origin are also established. This also allows to explain the formation of surface microroughness that sometimes appears in GaAs after wet chemical etchings.

Hadamard Transform Raman Microscopy of Laser-Modified Graphite Electrodes

In this communication, we describe the application of Hadamard transform Raman microscopy to the imaging of edge plane microstructures in laser-modified highly ordered pyrolitic graphite (HOPG) electrodes. Hadamard transform Raman microscopy is a highly selective method of analysis which can image thermally sensitive materials at micron-scale spatial resolution. The technique is capable of imaging relatively weak Raman scatterers in only a few minutes. The current multichannel microscope generates images having 255 × 256 pixels. In addition, we characterize an imaging artifact present in our current system, as well as apply a first-order correction for the problem.