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Possible Estimation Methodologies for Electromagnetic Field Distributions in Complex Environments

Description: Abstract: The problem of measuring and characterizing complicated multiple-source, multiple-frequency electromagnetic environments is becoming more important and more difficult as electrical devices proliferate. This paper outlines three general approaches to the problem which are currently under investigation at the National Bureau of Standards. The three approaches are: 1) a statistical treatment of the spatial distribution of electromagnetic field intensities, 2) a numerical computation using a finite-difference (or lattice) form of the electromagnetic action functional, and 3) use of a directional probe to scan a volume. All three methods are still in the development stage, but each appears promising.
Date: March 1985
Creator: Kanda, Motohisa; Randa, J. & Nahman, N. S.
Partner: UNT Libraries Government Documents Department

Energy Dispersive X-Ray Spectrometry

Description: Abstract: Energy-dispersive x-ray analysis with gas proportional detectors has been used widely in x-ray spectrochemical analysis. It was particularly useful in the detection of low-energy x-ray emission, before the commercial availability of the Blodgett-Langmuir pseudocrystals. With the development of solid-state x-ray detectors of high resolution, and improvement in associated electronics and computers, the interest in energy-dispersive x-ray analysis has increased enormously, to the point where it has replaced Bragg crystal diffraction spectrometry in many instances.
Date: March 1981
Creator: Heinrich, Kurt F. J.; Newbury, Dale E.; Myklebust, R. L. & Fiori, C. E.
Partner: UNT Libraries Government Documents Department

Quantitative X-ray microanalysis of submicron carbide formation in chromium (III) oxide rich scale

Description: This paper discusses the chemical microanalysis techniques adapted to identify the precipitates that form on the surface of, or within, the oxide scale of a Fe-22Cr ferritic steel during exposure to a carbon-monoxide rich environment at 750C for 800 hours. Examination of oxidized test coupons revealed the presence of a fiber like structure at the surface, shown in figure 1. Other studies have reported that these structures are carbon precipitates.
Date: August 1, 2007
Creator: Collins, W.K.; Ziomek-Moroz, M.; Holcomb, G.R.; Danielson, P. & Hunt, A.H
Partner: UNT Libraries Government Documents Department

Symposium on microscale separations and analysis. Final Technical Report

Description: The ''Symposium on Microscale Separations and Analysis'' event, held as a section of the American Chemical Society Annual meeting on 27 August 2001, brought together engineers, physicists, and chemists from both academia and industry to discuss the latest research in the area of biomolecule analysis on microfluidic devices for genomic and proteomic applications.
Date: August 27, 2001
Partner: UNT Libraries Government Documents Department

The role of ALCHEMI in understanding the properties of ordered intermetallic alloys

Description: After one and one-half decades of development, ALCHEMI is approaching the status of an established analytical technique. Many of the problems that have plagued ALCHEMI, especially for the analysis of ordered intermetallic alloys, are now well understood, and accurate site-distributions can be extracted from a variety of intermetallic alloys. This paper begins with an overview of the factors that can lead to large systematic errors or gross misinterpretations of ALCHEMI data, with illustrations from a variety of ordered intermetallic alloys. The paper concludes with a discussion of ALCHEMI in the broader context of understanding the properties of ordered intermetallic alloys. The results of systematic studies are used to illustrate the role of ALCHEMI in determining the competing effects of thermodynamic and kinetic factors during alloy processing and the correlation of alloy properties with the atomic site distributions on which the properties ultimately depend.
Date: November 1, 1998
Creator: Anderson, I.M.
Partner: UNT Libraries Government Documents Department


Description: Understanding magnetic structures and properties of patterned magnetic films at nanometer length-scale is the area of immense technological and fundamental scientific importance. The patterned magnetic films can be used for magnetic sensing . applications, magnetic recording, magnetoelectronics, microactuators and hybrid magneto-superconducting devices. The optimization of film properties is crucially dependent on the understanding of their magnetic properties, which in turn, become sensitive to the specific geometry and, hence, magnetic configurations of a given system when the elements diminish in size. Recent progress in the field of noninterferometric phase retrieval brings the ordinary Fresnel microscopy to a new quantitative level, capable of recovering both the amplitude and phase of the object from the experimental images [1,2], and thus induction mapping of small magnetic elements with known geometry ranging from micro- to few nanometers in size. The key concept behind this approach is the improvement of phase recovery algorithm derived from the transport-of-intensity (TIE) equation with a fast-solution via Fourier transform. A number of quantitative in-situ TEM magnetization experiments can be realized now with the help of magnetic-field calibrated microscope (see, for example [3]). To demonstrate the practical use of the new approach in TEM magnetic imaging with nanoscale resolution we have prepared several films directly on 3mm TEM-grids: (a) square-patterned magnetic films of Co islands with size of 6 pm (Fig. 1), and (b) nano-patterned arrays of Ni-nanodots (Fig.2) with lateral size about 40nm. The Co-films were prepared in UHV system by electron-beam evaporation of Co through an appropriate mask onto 30-nm-thick Si{sub 3}N{sub 4} membrane. The thickness of magnetic elements was approximately 40 nm as determined by EELS. The array of Ni-nanodots on a carbon membrane was prepared by electron-beam TEM-nanolithography followed by oblique angle deposition. Both types of the patterned arrays for Co and Ni films have been characterized ...
Date: August 4, 2002
Partner: UNT Libraries Government Documents Department

Applications of Multivariate Statistical Analysis (MSA) in Microanalysis

Description: Recent improvements in computer hardware and software for the acquisition, storage and analysis of series of spectra and images allow for a change in strategy for quantitative microanalysis. For example, in the area of X-ray microanalysis, whereas compositional analysis and elemental distributions have been traditionally performed using point microanalysis and simple intensity mapping from a ROI, respectively, the two tasks are now routinely performed simultaneously through X-ray spectrum-imaging, where full spectra are acquired from pixels in a two-dimensional array of points on the specimen. Commercially available software now allows for the acquisition and storage of such spectrum-images, perhaps comprising as much as 100 MBytes of data or more. A variety of post-acquisition processing tools are provided by the developer to allow the extraction of both X-ray intensity maps, with or without rudimentary background subtraction, or full spectra from pixels of interest. In order to maximize the extraction of information from these large data sets, a number of linear and nonlinear methods are currently being explored that identify statistically significant variations among the series of spectra without a priori assumptions about the content of the data set. Among these methods, linear multivariate statistical analysis (MSA) has a number of significant advantages, including its comprehensiveness, since all spectral variations distinct from the Poisson noise level are identified, and its broad applicability to a variety of microanalytical techniques.
Date: February 16, 1999
Creator: Anderson, I.M.
Partner: UNT Libraries Government Documents Department

X-ray microprobe: The next step in microcharacterization

Description: The combination of high brilliance of third generation synchrotrons and advanced x-ray microfocusing optics will revolutionize microcharacterization. Kirkpatrick-Baez elliptical mirrors, zone plates, and condensing capillaries have all achieved intense submicron focused beams. Other focusing options are also under study including Bragg-Fresnel optics and compound refractive lenses. The intense micron-scale beams from advanced x-ray optics on third generation sources will provide unique information about the elemental and crystallographic distribution in samples and will enable a variety experiments previously unimaginable. X-ray microbeams can be used to map elemental distributions in two and three dimensions and can be used to study the phase, texture, and strain distributions of inhomogenous samples in two and three dimensions.
Date: June 1, 1997
Creator: Ice, G.E.
Partner: UNT Libraries Government Documents Department

Reactive gas plasma specimen processing for use in microanalysis and imaging in analytical electron microscopy

Description: It has long been the bane of analytical electron microscopy (AEM) that the use of focused probes during microanalysis of specimens increases the local rate of hydrocarbon contamination. This is most succinctly observed by the formation of contamination deposits during focused probe work typical of AEM studies. While serving to indicate the location of the electron probe, the contamination obliterates the area of the specimen being analyzed and adversely affects all quantitative microanalysis methodologies. A variety of methods including: UV, electron beam flooding, heating and/or cooling can decrease the rate of contamination, however, none of these methods directly attack the source of specimen borne contamination. Research has shown that reactive gas plasmas may be used to clean both the specimen and stage for AEM, in this study the authors report on quantitative measurements of the reduction in contamination rates in an AEM as a function of operating conditions and plasma gases.
Date: January 1997
Creator: Zaluzec, N. J.; Kestel, B. J. & Henriks, D.
Partner: UNT Libraries Government Documents Department

Novel micro-calorimetric spectroscopy for mine detection

Description: The authors have developed a novel micro-calorimetric spectroscopy technique that can be used in mine detection applications. In this technique target molecules are allowed to adsorb on the surface of sub-femtojoule sensitive micromechanical thermal detectors. The adsorption of molecules on the thermal detector surface causes a differential surface stress resulting in an initial trigger. By exposing each element in an array of thermal detectors to different photon wavelengths, an extremely sensitive and unique photothermal signature response can be obtained. The authors present their results on target chemicals adsorbed on the detector surface at sub-monolayer coverage levels. They will present infrared photothermal spectra for trace concentrations of diisopropyl methylphosphonate (DIMP), and trinitrotoluene (TNT) over the wavelength region 2.5 to 14.5 microns. They found that in the wavelength region 2.5 to 14.5 microns the photothermal spectra of DIMP and TNT exhibit a number of peaks and are in excellent agreement with infrared absorption spectra found in the literature. Chemical detectors based on micro-calorimetric spectroscopy can be used to sensitively sense small number of molecules adsorbed on a thermal detector surface. The photothermal signature resulting from photon irradiation can be used for improved chemical characterization.
Date: March 1, 1998
Creator: Datskos, P.G.; Rajic, S.; Egert, C.M. & Datskou, I.
Partner: UNT Libraries Government Documents Department

Atom probe field ion microscopy of titanium aluminides

Description: Titanium aluminides have a number of potential high temperature applications due to their good elevated-temperature mechanical properties, low density, and good creep and oxidation resistance. However, fabrication of commercial components of these materials has been impeded by their poor mechanical properties at ambient temperatures. Significant efforts with various degrees of success have been made to improve the mechanical properties of these TiAl alloys by doping them with a variety of different elements including B, C, Cr, Er, Fe, Mn, Mo, Ni, Nb, P, Si, Ta, V and W. One of the optimum analytical tools for investigating the effects of these additions on the microstructure is the atom probe field ion micro scope. However, relatively few studies of titanium aluminides, compared to some other intermetallic compounds, have performed by atom probe field ion microscopy. This lack of attention can be attributed to the brittle nature of the material, in-situ transformations that occur during the field ion microscopy and preferential evaporation problems that were encountered in some of the early studies. The atom probe field ion microscope used for the current experiments has a low base pressure ({approximately} 2 {times} 10{sup 9} Pa) and careful attention was paid to optimizing the experimental parameters. All the examples shown were obtained from specimens prepared by standard electropolishing techniques. To demonstrate the suitability of the technique to these materials, several different titanium aluminides have been characterized in the atom probe.
Date: January 1, 1998
Creator: Larson, D.J. & Miller, M.K.
Partner: UNT Libraries Government Documents Department

A Case Study in Competitive Technical and Market Intelligence Support and Lessons Learned for the uChemLab LDRD Grand Challenge Project

Description: The {mu}ChemLab{trademark} Laboratory Directed Research and Development (LDRD) Grand Challenge project began in October 1996 and ended in September 2000. The technical managers of the {mu}ChemLab{trademark} project and the LDRD office, with the support of a consultant, conducted a competitive technical and market demand intelligence analysis of the {mu}ChemLab{trademark}. The managers used this knowledge to make project decisions and course adjustments. CTI/MDI positively impacted the project's technology development, uncovered potential technology partnerships, and supported eventual industry partner contacts. CTI/MDI analysis is now seen as due diligence and the {mu}ChemLab{trademark} project is now the model for other Sandia LDRD Grand Challenge undertakings. This document describes the CTI/MDI analysis and captures the more important ''lessons learned'' of this Grand Challenge project, as reported by the project's management team.
Date: November 1, 2001
Partner: UNT Libraries Government Documents Department

Mass Sensor

Description: The purpose of this CRADA was to use Honeywell's experience in low temperature cofire ceramics and traditional ceramics to assemble a relatively low-cost, mass-producible miniature mass analyzer. The specific design, given to us by Mass Sensors, LLC, was used to test for helium. The direct benefit for the participant was to have a prototype unit assembled for the purpose of proof of concept and the ability to secure venture capital investors. From that, the company would begin producing their own product for sale. The consumer/taxpayer benefits come from the wide variety of industries that can utilize this technology to improve quality of life. Medical industry can use this technology to improve diagnostic ability; manufacturing industry can use it for improved air, water, and soil monitoring to minimize pollution; and the law enforcement community can use this technology for identification of substances. These are just a few examples of the benefit of this technology. The benefits to DOE were in the area of process improvement for cofire and ceramic materials. From this project we demonstrated nonlinear thickfilm fine lines and spaces that were 5-mil wide with 5-mil spaces; determined height-to diameter-ratios for punched and filled via holes; demonstrated the ability to punch and fill 5-mil microvias; developed and demonstrated the capability to laser cut difficult geometries in 40-mil ceramic; developed and demonstrated coupling LTCC with standard alumina and achieving hermetic seals; developed and demonstrated three-dimensional electronic packaging concepts; and demonstrated printing variable resistors within 1% of the nominal value and within a tightly defined ratio. The capability of this device makes it invaluable for many industries. The device could be used to monitor air samples around manufacturing plants. It also could be used for monitoring automobile exhaust, for doing blood gas analysis, for sampling gases being emitted by volcanoes, for studying ...
Date: January 18, 2001
Creator: Adams, B.E.
Partner: UNT Libraries Government Documents Department

Optimizing the Elemental Sensitivity and Focal Spot Size of a Monolithic Polycapillary Optic Using Micro-X-Ray Fluorescence

Description: A commercial micro-X-ray fluorescence (MXRF) instrument with an aperture X-ray guide was used to compare elemental sensitivities and focal spot sizes with those obtained by focusing the source with a monolithic polycapillary optic retrofitted into the system. The capillary provided an intensity gain of 125 at 4 keV vs. using a pinhole beam collimator; however, this gain advantage declined with increasing analyte line energy as a result of the capillary being designed shorter than its optimal length to fit into the commercial instrument. A minimum capillary focal spot FWHM of 36 {micro}m was achieved, whereas the smallest pinhole aperture available of 50 {micro}m in diameter produced a focal spot width of 69 {micro}m FWHM. Hence, better MXRF lateral resolution could be obtained with the capillary with a simultaneous improvement in elemental sensitivity.
Date: October 1, 1998
Creator: Worley, C.; Havrilla, G.; Gao, N. & Xia, Q.-F.
Partner: UNT Libraries Government Documents Department

Atom probe field ion microscopy of high resistivity materials

Description: Over the last 30 years the atom probe has proved to be a powerful tool for studying nanometer-sized compositional fluctuations in a wide range of metallic alloys but has had only limited applications to semiconductors and ceramics. One of the primary reasons for this difference is the higher resistivity of semiconducting and ceramic specimens. Because of this high resistivity, the high voltage field evaporation pulse is attenuated before it reaches the apex of the specimen thereby making the pulse ineffective for field evaporation. Experiments have demonstrated that both variants of the voltage-pulsed atom probe (i.e., those instruments in which the field evaporation pulse is applied directly to the specimen and those in which the negative pulse is applied to a counter electrode in front of the specimen) are equally affected. In this overview, the limits of applicability of the voltage-pulsed atom probe to high resistivity materials are examined. In this study, a wide range of materials have been examined to determine whether field ion microscopy and voltage-pulsed field evaporation can be achieved and the results are summarized in the report. Field ion microscopy including dc field evaporation was possible for all materials except bulk ceramic insulators and glasses. Field ion microscopy requires some conductivity both to achieve a high electric field at the apex of the specimen, and also to support the field ion current. In contrast, voltage-pulsed field evaporation requires transmission of the pulse to the apex of the specimen. All metallic alloys including high resistance alloys and metallic glasses were successfully field evaporated with a voltage pulse. Specimens that were produced from bulk material of several conducting ceramics including MoSi, TiB and TiC were also successfully field evaporated with a voltage pulse.
Date: February 1, 1998
Creator: Sibrandij, S. J.; Larson, D. J. & Miller, M. K.
Partner: UNT Libraries Government Documents Department

Use of the disk-of-least-confusion in X-ray microanalysis

Description: A Philips XL30/FEG scanning electron microscope equipped with both energy dispersive and wavelength dispersive spectrometers (EDS and WDS) was used in this study. A cleaved GaAs test specimen was used to measure the current distribution in electron probes at 5 and 20 kV as a function of aperture size and objective lens defocus. The generated Ga K{sub {alpha}} x-ray intensity as measured by WDS was used to indicate the integrated current incident on the specimen as a function of distance relative to the specimen edge. Probe diameters can be estimated from profiles of the generated x-rays in the same manner that such diameters can be estimated from the integrated current profiles. Unfortunately, the x-ray intensity is not always proportional to the incident current. When an electron is incident on the GaAs near the cleaved edge, the x-ray yield is reduced when the electron escapes from the edge. Monte Carlo simulations for GaAs at 20 kV indicate that the normalized yield drops from 1 at {approximately}5 {micro}m from the edge to {approximately}0.2 near the edge. Experimental measurements show a similar decrease in normalized x-ray yield near the specimen edge. Both Monte Carlo simulations and measurements show that the magnitude of this effect is reduced at lower accelerating voltage as the spatial extent of the analyzed volume is decreased. X-ray intensities are normalized to that measured on the specimen at 10 {micro}m from the cleaved edge.
Date: February 1, 1998
Creator: Kenik, E.A. & Ren, S.X.
Partner: UNT Libraries Government Documents Department

The self-supporting disc: A specimen geometry exhibiting low secondary characteristic fluorescence

Description: Secondary characteristic fluorescence, when expressed relative to the primary intensity of the fluorescing element, can be written as the product of three factors, which represent the probabilities of the various processes that govern the magnitude of fluorescence and thus have values between zero and one. Two of these factors are characteristic of the material being analyzed. The factor C{sub X}{sup Y} is the likelihood that the primary x ray of Y is absorbed by the element X if it is absorbed in the fluoresced volume of the specimen. The factor P{sub X} is the probability that element X, having absorbed the primary x ray, emits the secondary x ray of interest. The third factor is the likelihood that the primary x ray is absorbed in the fluoresced volume, and is denoted {Omega}{sub eff}/4{pi}. For critical microanalysis studies, thin-flake specimens are most desirable, especially if the size of individual flakes is small relative to the scale, {approximately}10 {mu}m, over which the primary x rays are typically absorbed. However, a specimen comprised of small flakes may be impractical for many studies. Such a geometry may not indicate the relative positions and orientations of important microstructural features. The lack of sampling volume may also inhibit microanalysis of a specific feature of the microstructure, such as an interface, which may not be represented within the small specimen volume. For such analyses, a specimen geometry that leaves the specimen intact, yet minimizes secondary fluorescence by virtue of having a small geometric factor, may be preferable. Because the geometric factor depends only on the absorption properties of the secondary x ray, a rule-of-thumb maximum secondary fluorescence of an elemental line can be calculated by assuming an extreme microanalysis situation: when the entire disc is composed of the fluoresced element.
Date: June 1, 1995
Creator: Anderson, I.M.; Bentley, J. & Carter, C.B.
Partner: UNT Libraries Government Documents Department

The atom-probe field ion microscope: Applications in surface science

Description: The ability to locate an individual atom on a surface, remove it in a controlled fashion, and determine its chemical identity makes the atom-probe field-ion microscope an extremely powerful tool for the analysis of solid surfaces. By itself, the field ion microscope has contributed significantly to the understanding of surface atomic structure, single-atom surface diffusion, and the detailed interactions that occur between atoms and defects on surfaces. When used in combination with the atom-probe mass spectrometer there have been several additional areas within the traditional definition of ``surface science`` where the chemical identification capability of the atom probe has led to new insights. In this paper these applications are reviewed focusing on two specific areas: surface segregation in intermetallic alloys and chemical reactions on metal surfaces.
Date: February 1, 1998
Creator: Kellogg, G.L.
Partner: UNT Libraries Government Documents Department