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Atom probe tomography (APT)-based isotopic analyses are becoming increasingly attractive for analysis applications requiring small volumes of material and sub-micrometer length scales, such as isotope geochemistry, nuclear safety, and materials science. However, there is an open question within the atom probe community as to the reliability of atom probe isotopic and elemental analyses. Using our proposed analysis guidelines, in conjunction with an empirical calibration curve and a machine learning-based adaptive peak fitting algorithm, we demonstrate accurate and repeatable uranium isotopic analyses, via atom probe mass spectrometry, on U3O8 isotopic reference materials. By using isotopic reference materials, each measured isotopic abundance value could be directly compared to a known certified reference value to permit a quantitative statement of accuracy. The isotopic abundance measurements for 235U and 238U in each individual APT sample were consistently within ±1.5% relative to the known reference values. The accuracy and repeatability are approaching values consistent with measurements limited primarily by Poisson counting statistics, i.e., the number of uranium atoms recorded.

Atom probe tomography (APT) can theoretically deliver accurate chemical and isotopic analyses at a high level of sensitivity, precision, and spatial resolution. However, empirical APT data often contain significant biases that lead to erroneous chemical concentration and isotopic abundance measurements. The present study explores the accuracy of quantitative isotopic analyses performed via atom probe mass spectrometry. A machine learning-based adaptive peak fitting algorithm was developed to provide a reproducible and mathematically defensible means to determine peak shapes and intensities in the mass spectrum for specific ion species. The isotopic abundance measurements made with the atom probe are compared directly with the known isotopic abundance values for each of the materials. Even in the presence of exceedingly high numbers of multi-hit detection events (up to 80%), and in the absence of any deadtime corrections, our approach produced isotopic abundance measurements having an accuracy consistent with values limited predominantly by counting statistics.

In atom probe tomography (APT), some elements tend to field evaporate preferentially in multi-hit detection events. Boron (B) is one such element. It is thought that a large fraction of the B signal may be lost during data acquisition and is not reported in the mass spectrum or in the 3-D APT reconstruction. Understanding the relationship between the field evaporation behavior of B and the limitations for detecting multi-hit events can provide insight into the signal loss mechanism for B and may suggest ways to improve B detection accuracy. The present work reports data for nominally pure B and for B-implanted silicon (Si) (NIST-SRM2137) at dose levels two-orders of magnitude lower than previously studied by Da Costa, et al. in 2012. Boron concentration profiles collected from SRM2137 specimens qualitatively confirmed a signal loss mechanism is at work in laser pulsed atom probe measurements of B in Si. Ion correlation analysis was used to graphically demonstrate that the detector dead-time results in few same isotope, same charge-state (SISCS) ion pairs being properly recorded in the multi-hit data, explaining why B is consistently under-represented in quantitative analyses. Given the important role of detector dead-time as a signal loss mechanism, the results from three different methods of estimating the detector dead-time are presented. The findings of this study apply to all quantitative analyses that involve multi-hit data, but the dead-time will have the greatest effect on the elements that have a significant quantity of ions detected in multi-hit events.

Knowledge of the chemical and physical structure of early soot is useful in the development of sootparticle inception models. This paper examines the hypothesis that soot exiting an inverse diffusion flame is similar in chemical and morphological structure to (1) soot precursor particles and (2) soot that exits underventilated flames. Experiments in volving soot collection from the exhaust of laminar ethylene inverse diffusion flames were performed. Soot samples were analyzed for morphology using transmission electron microscopy, for carbon-to-hydrogen ratio using elemental analysis, for organic fraction using thermaloptical analysis, and for polycyclic aromatic hydrocarbon content using laser microprobe mass spectrometry and gas chromatography/mass spectrometry. Results of these analyses support the validity of the above hypothesis. This finding is significant because exhaust collection from the inverse flame provides an opportunity to gather large samples of young soot without invading the flame with an intrusive probe (a necessary task when collecting precursors low in the center of a normal diffusion flame). Larger samples can then be subjected to more detailed analysis than previously possible. An identification of specific polycyclic aromatic hydrocarbon isomers present in young soot from diffusion flames is reported. The data are available for comparison with polycyclic aromatic hydrocarbon growth, soot inception, and soot growth models.

Cobalt disilicide contacts to silicon–germanium alloys were formed by direct deposition of pure cobalt metal onto silicon–germanium films on Si(001) substrates. Segregation of germanium was observed during the reaction of the cobalt with the silicon–germanium alloy. The nature of the Ge segregation was studied by transmission electron microscopy, energy dispersive spectroscopy, and x-ray diffraction. In the case of cobalt films deposited onto strained silicon–germanium films, the Ge segregation was discovered to be in the form of Ge-enriched Si1−xGex regions found at the surface of the film surrounding CoSi and CoSi2 grains. In the case of cobalt films deposited onto relaxed silicon–germanium films, the Ge segregation was dependent on formation of CoSi2. In samples annealed below 800 °C, where CoSi was the dominant silicide phase, the Ge segregation was similar in form to the strained Si1−xGex case. In samples annealed above 800 °C, where CoSi2 was the dominant silicide phase, the Ge segregation was also in the form of tetrahedron-shaped, Ge-enriched, silicon–germanium precipitates, which formed at the substrate/silicon– germanium film interface and grew into the Si substrate. A possible mechanism for the formation of these precipitates is presented based on vacancy generation during the silicidation reaction coupled with an increased driving force for Ge diffusion due to silicon depletion in the alloy layer.

Polycapillary x-ray optics are gaining increased attention as their transmission characteristics and manufacturing difficulties are better understood. This paper reports experimental results obtained with an optic that was designed for use with both Mo Kα (17.5 keV) and Cu Kα (8 keV). The spectral gain function from 4 to 30 keV was determined from measurements made with an Si(Li) detector, and the results were compared with Monte Carlo simulations. The spatial variation in the spectral transmission was examined with both an Si(Li) detector and a magnifying x-ray CCD camera. The results show that even though the individual capillaries are tapered, their performance is well described by a simple parabolic relationship between the radius of curvature and the maximum energy transmitted derived for capillaries of constant diameter. Copyright © 1999 John Wiley & Sons, Ltd.

Thresholds of visibility for objects in images with random pixel noise are predicted in terms of the signal-to-noise ratio. From trials with volunteers marking test images, we determined visibility thresholds of objects obscured by random pixel noise. The test images had objects with a variety of simple shapes and relatively little internal structure. Aside from the noise, the background of the test images was smooth and featureless. We extend the threshold signal-to-noise ratio measurements of Rose and others to a variety of object sizes and shapes. For objects with areas less than a disc subtending 2 degrees at the eye, visibility depends on the averaged difference in intensity from background, the noise level and the number of pixels in the object. Visibility does not seem to depend on object shape.

Recent work on the magnetic characteristics of nanometer scale materials has suggested that magnetically isolated nanometer magnetic particles would show magnetic behavior different than those found in the bulk. Such behavior could be explored if such materials could be synthesized in sufficient quantities where the magnetic particles could be isolated from each other via encapsulation within a non-magnetic host. We have investigated application of flame technology for the synthesis of this class of materials. A premixed methane/oxygen flame diluted with nitrogen has been used as the reacting environment in which iron pentacarbonyl and hexamethyldisiloxane were added as the magnetic and non-magnetic precursor materials. The results, based on x-ray diffraction, electron microscopy, Mossbauer effect, and magnetization data have shown that: (i) nanometer composite particles are formed containing 5–10 nm Fe2O3, encased in a silica particle whose diameter ranged from 30–100 nm, depending on loading and flame temperature, and (ii) the iron oxide clusters are magnetically isolated and in some cases show superparamagnetic behavior.

Atom probe tomography implant dose measurements are reported for National Institute of Standards and Technology Standard Reference Material 2134 (arsenic implant). Efforts were taken to manufacture specimens with limited variation in size and shape to minimize variation in physical reconstruction parameters. A tip profile reconstruction was utilized where measurements of tip profile, post-analysis specimen radius and sphere-to-cone radius ratio were required as inputs into the reconstruction process. A variation of 4% is observed in the dose measurement under these conditions. Various considerations necessary to narrow the observed variation in measured dose, toward the limit imposed by counting statistics, are discussed.

Replica sections were prepared from a single polycarbonate filter that had chrysotile and several types of non-asbestos particles deposited on its surface. Twenty-seven analysts from 15 laboratories counted a minimum of 3 grid squares and recorded the physical characteristics of the particles and the methods used for identification of the particles

Bulk SiGe wafers cut from single‐crystal boules were evaluated with the electron probe microanalyzer (EPMA) for micro‐ and macroheterogeneity for use as primary standards for future characterization of SiGe thin films on Si that are needed by the microelectronics industry as reference standards. Specimens with nominal compositions of 14 at. %, 6.5 at. %, and 3.5 at. % Ge were rigorously tested with wavelength dispersive spectrometers (WDS) using multiple point, multiple sample, and duplicate data acquisitions. The SiGe14 is a good bulk reference material for evaluation of SiGe thin films.

Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.

Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.

Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.

Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.

Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.

Titanium silicide films grown on silicon were analyzed by transmission electron microscopy (TEM), electron diffraction, scanning transmission electron microscopy (STEM), energy dispersive x-ray spectroscopy, and electron energy loss spectroscopy. The films were prepared by sequential rapid thermal annealing (RTA) at 675 °C and 850 °C of 16-nm-thick sputtered Ti on Si (001) wafers. In some cases, a 20-nm-thick TiN capping layer was deposited on the Ti film before the RTA procedure and was removed after annealing. HRTEM and STEM analysis showed that the silicide films were less than 0.1 μm thick. The capped film was more uniform, ranging in thickness from ∼25–45 nm, while the uncapped film ranged in thickness from ∼15–75 nm. Electron diffraction was used to investigate the titanium silicide phases present in the films; more than one phase was found to exist.

Titanium nitride films are used in a variety of applications in the semiconductor industry, but the stoichiometry and homogeneity of the films can be difficult to control and characterize. The National Institute of Standards and Technology (NIST) is developing a TiN thin film on silicon to be used as a physical and chemical standard for the semiconductor industry. A prototype 100 nm thick film has been manufactured by dual ion beam deposition. NIST is characterizing the film by x-ray interferometry for thickness and density, neutron depth profiling for nitrogen content and homogeneity as a function of depth, neutron activation analysis for titanium content, and x-ray fluorescence spectromety, electron probe microanalysis, grazing incidence x-ray photoelectron spectroscopy, and transmission electron microscopy for homogeneity and composition. The intent of this research is to create a TiN film of known thickness, density, stoichiometry, and homogeneity that can be used by the semiconductor industry as a primary, traceable standard for characterization of industry thin films. The intent of the standard is to promote more accurate characterization and improved TiN manufacturing capabilities as well as to aid manufactures in more easily employing ISO 9000 related traceability and quality assurance practices.

Titanium silicide films grown on silicon were analyzed by transmission electron microscopy (TEM), electron diffraction, scanning transmission electron microscopy (STEM), and energy dispersive x-ray spectroscopy. The films were prepared by sequential rapid thermal annealing (RTA) at 675 °C and 850 °C of 16-nm-thick sputtered Ti on Si (001) wafers. In some cases, a 20-nm-thick TiN capping layer was deposited on the Ti film before the RTA procedure and was removed after annealing. TEM and STEM analyses showed that the silicide films were less than 0.1 μm thick; the capped film was more uniform, ranging in thickness from ∼ 25 – 45 nm, while the uncapped film ranged in thickness from ∼ 15 – 75 nm. Electron diffraction was used to determine that the capped film contained C54-TiSi2, C49-TiSi2, Ti5Si3, and possibly TiSi, and that the uncapped film contained C49-TiSi2, TiSi, Ti5Si3, unreacted Ti, and possibly C54-TiSi2.

The microstructure of highly sp2 bonded amorphous carbon and partially tetrahedrally bonded amorphous carbon deposited on needle-shaped molybdenum field emitters by pulsed laser ablation and cathodic arc deposition techniques was studied using transmission electron microscopy and electron energy loss spectroscopy. Undoped and nitrogen-doped films were included in this study. The undoped laser ablation films were approximately 50% sp2 at the emitter tip and 65% sp2 along the shank, while the N-doped laser ablation films were highly sp2 bonded both at the tip and along the shank. These laser ablation films were continuous and relatively uniform, exhibiting an isotropie microstructure at the emitter tip and a columnar microstructure along the shank. The cathodic arc deposited films were predominantly sp2 bonded both at the tip and along the shank; these films were non-uniform, with an isotropie microstructure at the tip and regions of isotropie, columnar, and mixed microstructure appearing along the shank.

We have constructed an x-ray optical test bench which has been used to characterize transmission and manufacturing artifacts associated with monolithic polycapillary optics of the Kumakhov type. The test bench incorporates a conventional 8 keV x-ray source and a sample holder which is capable of high precision translation and rotation. Both non-imaging and imaging detectors are used, including a magnifying x-ray camera capable of resolving the transmission of individual capillary channels in a polycapillary bundle. We demonstrate the use of the bench to determine imperfections in the fabrication of early prototype capillary optics. The images illustrate the anomalies associated with the forming of the capillary bundles, the effects of extended exposure to synchrotron radiation, and the x-ray transmission lateral uniformity. We also show the intense focused beams obtained with complete optics.

Micro X-ray fluorescence (micro-XRF) is a useful nondestructive technique for multielement analysis of samples from a few hundred to a few micrometers in size. Micro-XRF is usually performed at synchrotron sources where element sensitivities are not compromised by micrometer spatial collimation of high flux beams. Ideally, micro-XRF would not have the burden of transporting samples to a synchrotron facility, but could be performed on a laboratory or portable scale. At the National Institute of Standards and Technology we are developing a micro-XRF system that combines a polycapillary optic with a standalone X-ray tube. This optic not only transmits the X-ray beam over 80 mm, but also focuses the beam to an area smaller than the unfocused beam size. The fine resolution combined with a high intensity produces a tool for laboratory scale micro-XRF analyses.The X-ray focusing optic is a tapered, glass polycapillary optic. This optic, contained in an approximately 5 × 70 mm steel cylinder, transmits and focuses incoming X-rays to a spot 9.5 mm from the optic exit.

For studies of particles suspended in air or water, material is commonly deposited onto membrane filters. Submicrometer particles collected in or on the surface of the filters can be prepared for analysis by TEM by extraction replica methods. To identify the problems and artifacts generated during the preparation process, evaluations were made of replicas prepared internally at NIST and prepared by laboratories involved in the analysis of air-collected asbestos. Problems or artifacts that could affect the counting and analysis of asbestos particles were identified and characterized. Results of evaluations of replicas prepared by eighteen laboratories in an interlaboratory study are summarized.

Cobalt disilicide (CoSi2) is an attractive contact material for Si1-xGex devices due to its low resistivity, low Schottky barrier, and good thermal and chemical stability. Previous studies have shown that blanket Co films on Si0.80Ge0.20 react at annealing temperatures of 700 °C to form CoSi, CoSi2 and a Ge-rich Si1-xGex alloy; no Co-Ge phases were found. The Co preferentially reacts with the Si, which can lead to Ge segregation and island formation. To gain a better understanding of cobalt silicide formation, an electron microscopy investigation of Co/Si1-xGex/Si was performed.Si1-xGex films (x ≤ 0.3) 64 nm to 260-nm thick were grown by molecular beam epitaxy at 550 °C on phosphorus-doped Si substrates. Co films ranging in thickness from 5 nm to 25 nm were electron-beam evaporated (evaporator base pressure < 6.67 x 10-8 Pa) at room temperature on the Si1-xGex films.

Control of electron microscopes by a remote networked computer system has been implemented successfully in a variety of ways including via the World Wide Web (WWW). This approach works well with users who are familiar with the operation of the instrument and are experienced microscopists. However, many of our collaborations involve other scientists or engineers looking to us for analytical expertise. In order to accommodate collaborators with a broad range of skills and to allow them to interact remotely, in near-real time with a scientist operating an instrument, we have implemented a Virtual Collaborative Environment (VCE) based on a WWW server and the use of the server-push protocol.The system developed at NIST is a frames-based WWW page that is presented to the user with an index of instruments on the left side (FIG.l), live video pages to the right side, and a download area (via ftp) toward the bottom for data and high resolution images.

Accurate characterization of electron diffraction patterns can be tedious, which encourages development of computer assisted tools and methods. We developed a spot measurement tool to characterize rapidly arrays of diffraction spots that are characteristic of a single crystal, and to measure precisely the d-spacing values for individual spots. The spot tool determines these vectors for averaged measurements from many spots in a digital image of the diffraction pattern. Previously we developed automated methods for spot pattern analysis. Why make an operator-assisted tool? This tool is faster than either our automated or entirely manual methods, and it allows assessment of the quality of the data at the beginning of the analysis.It is easy to see regular patterns of spots in a zone axis diffraction pattern (Fig. 1.1). An operator guides the initial calculations by adjusting an array of circles to approximately cover the spots in the pattern to be analyzed.

Amorphous carbon coatings, including highly sp3-bonded amorphous diamond (a-D), also referred to as tetrahedral amorphous carbon (ta-C), and diamond-like carbon (DLC), have recently been explored for field emission applications [1-3]. These coatings can be deposited uniformly at low temperatures, and possess chemical and mechanical properties similar to those of diamond. They also can be doped with nitrogen to form n-type semiconductors [4]. Diamond coatings, on the other hand, are microscopically nonuniform, usually require deposition temperatures greater than 600 °C, and cannot be doped to produce shallow donor levels [2]. Diamond, a-D, and DLC coated emitters all show enhanced electron emission properties [1-3].The major emphasis of the work presented here is on the parallel electron energy loss spectroscopy (PEELS) characterization of the sp2 and sp3 bonded carbon in the coatings. PEELS spectra and TEM images were recorded with a Philips CM300 FEG TEM, equipped with a Gatan model 666 parallel acquisition EELS spectrometer. The operating voltage was 300 keV.

Monitoring the performance capabilities of energy dispersive X-ray spectrometers (EDS) and related x-ray analysis electronics and software is important for determining and improving the reliability, sensitivity, and accuracy of the x-ray analysis system. In addition, there is a growing popularity of quality systems through laboratory accreditation and ISO 9000 related programs that require set quality control procedures for analytical instrumentation. Having similar standard procedures amongst labs would allow direct intercomparison of results. This intercomparison would help labs and manufacturers determine what are normal versus abnormal results and lead to higher quality instruments and analyses. We have been developing a standard operating procedure for the characterization of EDS x-ray analysis systems on electron beam instruments.We are designing the procedure to maximize the efficiency of each quality control (QC) measurement so that we spend as little time monitoring the analysis system as is possible. We first chose useful QC specimens and then designed data collection methods.

Yttria-doped zirconia plasma-sprayed thermal barrier coatings (TBC’s) have been used successfully to improve the performance and extend the life of industrial equipment such as jet engines. For this reason, there is considerable interest in understanding and improving the plasma spray process and resulting TBC’s. A collaborative research program exists between Sandia National Laboratories and the National Institute of Science and Technology (NIST) to study the materials and processes used in preparing the coatings as well as the relationship between the physical properties of the coating and its microstructure.The purpose of this work was to determine the elemental compositions on a micrometer scale of an yttria-doped zirconia coating. The cubic and tetragonal crystal forms of the yttria-doped zirconia have the most favorable thermal expansion coefficient, therefore providing the most effective thermal barrier. The Y concentration in these crystal phases is known to be 6-7 wt%, while the less desirable monoclinic phase, having a less favorable thermal expansion coefficient, contains less that 3 wt% Y.

Recent developments of glass capillaries allow x-ray probes to be focused down to micrometer sizes. These probes show promise for microanalysis applications, if they can reliably deliver high intensity, well formed x-ray beams to a specimen. We have developed an optical bench for viewing and evaluating the focused x-rays emitted from these capillaries. The optical bench allows pulse counting, direct viewing of the x-ray probe spatial distributions, and energy pass band by using exchangeable detectors. Our results are used to determine the probe forming capabilities of the lenses and to indicate problems and directions for improving the manufacturing of the x-ray optics.The x-ray optical bench is shown in a schematic diagram in figure A. It consists of a conventional CuKα x-ray diffraction tube joined to an optical table. An optical rail extends across them. A shielded box with a hinged side covers the source and the optical rail. The x-ray optic and exchangeable detector system are located on computer controlled stages to allow fine adjustments in all necessary translation and tilt directions. This optical bench permits measurements to be devised, performed, and changed with a minimum of difficulty. The optical bench allows for maximum flexibility in sample positioning, detector positioning, source size, and source collimation. The quantities that we evaluate in each optical element include focal spot size, spot uniformity, total spot flux, spot aberrations, diffuse scattered radiation, and depth of field or convergence.