Eric B. Steel

The existence of young soot in the exhaust of inverse diffusion flames

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.

Two-dimensional top hat filter for extracting spots and spheres from digital images

The top hat filter is a computer algorithm that extracts small, compact or rounded objects from digital images. Examples show application of the filter to micrographs and electron diffraction patterns.

VISIBILITY OF OBJECTS IN COMPUTER SIMULATIONS OF NOISY MICROGRAPHS

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° 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.

Effects of detector dead-time on quantitative analyses involving boron and multi-hit detection events in atom probe tomography.

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.

GERMANIUM SEGREGATION IN THE CO/SIGE/SI(001) THIN FILM SYSTEM

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.

Analysis of implanted silicon dopant profiles

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.

Polycapillary X-Ray Optic Spectral Gain and Transmission

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

Accuracy of the double variation technique of refractive index measurement

Errors in the double variation teclinique of refractive index measurement are analyzed using a new approach. The ability to measure matching wavelength is characterized, along with the effect on the calculated refractive index. Refractive index accuracy and precision are very dependent on the specifics of each calibration set, particularly the difference in dispersion between the liquid and solid. Our best precision (±1 or 2×10−4) is attained only when the difference in dispersion between liquid and solid is small, and is dependent on an individual operator’s ability to perceive changes in relief. This precision is impossible to achieve for the other glass/liquid combinations, where we are limited by a precision of approximately 1 nm in the selection of matching wavelength. A bias in the measurement of matching wavelength exists that affects the accuracy of the calculated refractive indices. The magnitude of the bias appears to be controlled by the bandpass of the graded interference filter. The errors in refractive index using a graded interference filter with a bandpass of 30 nm FWHM (full width at half maximum intensity) are an order of magnitude larger than the errors using a filter with a bandpass of 15 nm FWHM.

The Role of Multi-Hit Detection Events on the Accurate Measurement of Boron in Atom Probe Tomography

In atom probe tomography (APT), some elements tend to field evaporate preferentially in multi-hit detection events [1], where more than one ion is detected between pulses. Boron is one such element, and it is thought that a large fraction of the boron signal may be lost during data acquisition and not reported in the mass spectrum or the 3-D APT reconstruction. Understanding the relationship between the field evaporation behavior of boron and the limitations for detecting multi-hit events should provide insight into the signal loss mechanism for boron and suggest ways to improve boron detection accuracy.

Characterization of SiGe Bulk Compositional Standards with Electron Probe Microanalysis

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.