Scott Wight - Academia.edu (original) (raw)
Papers by Scott Wight
Scanning, 2006
This work describes the comparison of experimental measurements of electron beam spread in the en... more This work describes the comparison of experimental measurements of electron beam spread in the environmental scanning electron microscope with model predictions. Beam spreading is the result of primary electrons being scattered out of the focused beam by interaction with gas molecules in the low-vacuum specimen chamber. The scattered electrons form a skirt of electrons around the central probe. The intensity of the skirt depends on gas pressure in the chamber, beam-gas path length, beam energy, and gas composition. A model has been independently developed that, under a given set of conditions, predicts the radial intensity distribution of the scattered electrons. Experimental measurements of the intensity of the beam skirt were made under controlled conditions for comparison with model predictions of beam skirting. The model predicts the trends observed in the experimentally determined scattering intensities; however, there does appear to be a systematic deviation from the experimental measurements.
Scanning, 2006
A device has been developed and used successfully on two models of the environmental scanning ele... more A device has been developed and used successfully on two models of the environmental scanning electron microscope that allows low-magnification imaging of about 30×, significantly better than the original 200× low-magnification imaging limit. This was achieved by using an additional aperture to limit the pressure at a point where it will not block the electron beam, and a larger aperture plate for the combination final aperture/secondary electron signal collection surface that also does not block the electron beam significantly.
Scanning, 2006
A device has been developed and used successfully on two models of the environmental scanning ele... more A device has been developed and used successfully on two models of the environmental scanning electron microscope that allows low-magnification imaging of about 30×, significantly better than the original 200× low-magnification imaging limit. This was achieved by using an additional aperture to limit the pressure at a point where it will not block the electron beam, and a larger aperture plate for the combination final aperture/secondary electron signal collection surface that also does not block the electron beam significantly.
Scanning, 2006
This work describes the comparison of experimental measurements of electron beam spread in the en... more This work describes the comparison of experimental measurements of electron beam spread in the environmental scanning electron microscope with model predictions. Beam spreading is the result of primary electrons being scattered out of the focused beam by interaction with gas molecules in the low-vacuum specimen chamber. The scattered electrons form a skirt of electrons around the central probe. The intensity of the skirt depends on gas pressure in the chamber, beam-gas path length, beam energy, and gas composition. A model has been independently developed that, under a given set of conditions, predicts the radial intensity distribution of the scattered electrons. Experimental measurements of the intensity of the beam skirt were made under controlled conditions for comparison with model predictions of beam skirting. The model predicts the trends observed in the experimentally determined scattering intensities; however, there does appear to be a systematic deviation from the experimental measurements.
Scanning, 2006
Phosphor imaging plate technology has made it possible to directly image the distribution of prim... more Phosphor imaging plate technology has made it possible to directly image the distribution of primary beam electrons and scattered electrons in the environmental scanning electron microscope. The phosphor plate is exposed under electron scattering conditions in the microscope chamber. When processed, the electron intensity distribution is displayed as a digital image. The image is a visual representation of the electron probe and skirt and may provide the basis for a more accurate model.
Microscopy Research and Technique, 1993
This work provides examples of some of the imaging capabilities of environmental scanning electro... more This work provides examples of some of the imaging capabilities of environmental scanning electron microscopy applied to easily charged samples relevant to particle analysis. Environmental SEM (also referred to as high pressure or low vacuum SEMI can address uncoated samples that are known to be difficult to image. Most of these specimens are difficult to image by conventional SEM even when coated with a conductive layer. Another area where environmental SEM is particularly applicable is for specimens not compatible with high vacuum, such as volatile specimens. Samples from which images were obtained that otherwise may not have been possible by conventional methods included fly ash particles on an oiled plastic membrane impactor substrate, a one micrometer diameter fiber mounted on the end of a wire, uranium oxide particles embedded in oil-bearing cellulose nitrate, teflon and polycarbonate filter materials with collected air particulate matter, polystryene latex spheres on cellulosic filter paper, polystyrene latex spheres ''loosely'' sitting on a glass slide, and subsurface tracks in an etched nuclear track-etch detector. Surface charging problems experienced in high vacuum SEMs are virtually eliminated in the low vacuum SEM, extending imaging capabilities to samples previously difficult to use or incompatible with conventional methods. o 1993 Wiley-Liss, Inc.*
Microscopy and Microanalysis, 2006
A new technique is described for the detection of x rays in electron column instruments used in m... more A new technique is described for the detection of x rays in electron column instruments used in microanalysis. In electron column instruments, the point source of x rays is produced by the interaction of a focused electron beam with the sample. Neither of the conventional methods, wavelength dispersive (WDS) nor energy dispersive (EDS) based spectrometry, is optimized for low Z element quantitative analysis. In WDS applications, where the analyte elements are Be through P, chemical effects complicate the x ray measurement process. Peak positions and shapes are altered, sometimes very strongly, by the electron configurations of the analyte atoms and neighboring atoms. In these cases, the ideal spectrometer would profile the peak and some small amount of continuum on either side of the peak such that an accurate peak area could be calculated. Present WDS spectrometers are serial in nature and cannot directly measure peak areas, often causing errors in the determination of light element concentrations. Bastin and co-workers have developed an elegant method to provide accurate area determinations, using the serial spectrometer, by a three point procedure. The parallel wavelength dispersive spectrometer (PWDS) proposed here is ideally suited for those applications.
Agu Fall Meeting Abstracts, Dec 1, 2002
Atmospheric Black Carbon (BC) is a ubiquitous and persistent component of atmospheric particulate... more Atmospheric Black Carbon (BC) is a ubiquitous and persistent component of atmospheric particulate matter, found at measurable levels in even the most remote locations. BC derives from combustion processes, the sources of which are highly variable spatially and temporally. Consequently, atmospheric BC has no fundamental chemical identity and therefore cannot be accurately measured using absolute methods. Because of its chemically ambiguous character, measurement of BC has long been problematic. Optical properties alone cannot, in principal, quantify both BC mass and the varying aerosol absorptivity upon which mass measurement relies. To overcome this problem, thermal optical analysis (TOA) utilizes the PM's thermal as well as optical properties. A different problem, however, confronts TOA: varying thermal desorption procedures result in different BC results for the same material. Our focus therefore, was to optimize the key TOA parameters that bias BC measurement: production of char (pyrolysis carbon) from organic carbon by the instrument, and separation of the char analytically from the BC that is native to the sample. In this work, we used response-surface methods to optimize a thermal desorption procedure for BC accuracy. To cover a range of samples, we modeled responses for two types of ambient samples (indoor laboratory air and outdoor urban air) and one carbonaceous aerosol source (forest fires). We identified four factors, associated with the temperature, duration and atmosphere (inert or oxidizing), of desorption steps that potentially contribute most to BC measurement variability. The four factors comprised a central composite factorial design for measuring BC concentration and laser response during the course of the TOA analysis. Scanning electron microscope images of particles on the TOA filters were also used to assess char optimization. The response surfaces for the BC to total carbon ratio and laser attenuation response were modeled using full second-order polynomials containing 15 terms that accounted for main effects from the factors, non-linear behavior within factors, and cross-factor interactions. Optimal conditions for BC accuracy were determined by the intersection between the laser response surfaces.
Http Dx Doi Org 10 1080 02786829108959526, Jun 8, 2007
Fibers and Polymers, 2015
Microscopy and Microanalysis, 2014
We performed cathodoluminescence spectroscopy of presolar and solar Al_2O_3 grains separated from... more We performed cathodoluminescence spectroscopy of presolar and solar Al_2O_3 grains separated from unequilibrated ordinary chondrites. While the CL spectra displayed significant diversity, they are useful to probe crystallinity of presolar Al_2_O3 grains.
Water environment research : a research publication of the Water Environment Federation, 2006
Environmental scanning electron microscopy (ESEM) with an energy-dispersive X-ray spectrometer (E... more Environmental scanning electron microscopy (ESEM) with an energy-dispersive X-ray spectrometer (EDS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) were demonstrated to be useful analytical tools for investigating surface and bulk components of individual floc particles from both full- and bench-scale activated sludge systems. Detailed surface imaging of various hydrated biological floc particles by ESEM revealed substantial differences in surface features between treatment systems, while EDS identified spatial differences in the iron and the aluminum distributions. The ToF-SIMS spectra had signature fragments of protein and polysaccharide material from the floc surface, suggesting that this technique is capable of surface profiling extracellular polymeric substances. Principal-component analysis of the positive ion ToF-SIMS spectra from the mixed-liquor-suspended solid (MLSS) samples and reference aquatic organic materials found slight differences between the full- a...
Water Environment Research, 2006
Environmental scanning electron microscopy (ESEM) with an energy-dispersive X-ray spectrometer (E... more Environmental scanning electron microscopy (ESEM) with an energy-dispersive X-ray spectrometer (EDS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) were demonstrated to be useful analytical tools for investigating surface and bulk components of individual floc particles from both full- and bench-scale activated sludge systems. Detailed surface imaging of various hydrated biological floc particles by ESEM revealed substantial differences in surface features between treatment systems, while EDS identified spatial differences in the iron and the aluminum distributions. The ToF-SIMS spectra had signature fragments of protein and polysaccharide material from the floc surface, suggesting that this technique is capable of surface profiling extracellular polymeric substances. Principal-component analysis of the positive ion ToF-SIMS spectra from the mixed-liquor-suspended solid (MLSS) samples and reference aquatic organic materials found slight differences between the full- and bench-scale MLSS surface properties but substantial differences among MLSS and treated effluent from the same facility.
Microscopy and Microanalysis, 2010
ABSTRACT Instrumentation and Techniques SymposiaAn X-Ray and Cathodoluminescence Study of Cassite... more ABSTRACT Instrumentation and Techniques SymposiaAn X-Ray and Cathodoluminescence Study of Cassiterite (SnO2)Article author querywight s [PubMed] [Google Scholar]vicenzi e [PubMed] [Google Scholar]meier d [PubMed] [Google Scholar]benkstein k [PubMed] [Google Scholar]S Wighta1, E Vicenzia2, D Meiera1 and K Benksteina1a1 National Institute for Standards and Technology
Microscopy and Microanalysis, 2011
Microscopy and Microanalysis, 2011
Microscopy and Microanalysis, 2006
Abstract Advances in Instrumentation and Techniques-Present and future limits of variable pressur... more Abstract Advances in Instrumentation and Techniques-Present and future limits of variable pressure and environmental SEM: Enabling nanoscale metrology, improved x-ray microanalysis and the understanding of novel contrasts in images of modern and novel ...
Scanning, 2006
This work describes the comparison of experimental measurements of electron beam spread in the en... more This work describes the comparison of experimental measurements of electron beam spread in the environmental scanning electron microscope with model predictions. Beam spreading is the result of primary electrons being scattered out of the focused beam by interaction with gas molecules in the low-vacuum specimen chamber. The scattered electrons form a skirt of electrons around the central probe. The intensity of the skirt depends on gas pressure in the chamber, beam-gas path length, beam energy, and gas composition. A model has been independently developed that, under a given set of conditions, predicts the radial intensity distribution of the scattered electrons. Experimental measurements of the intensity of the beam skirt were made under controlled conditions for comparison with model predictions of beam skirting. The model predicts the trends observed in the experimentally determined scattering intensities; however, there does appear to be a systematic deviation from the experimental measurements.
Scanning, 2006
A device has been developed and used successfully on two models of the environmental scanning ele... more A device has been developed and used successfully on two models of the environmental scanning electron microscope that allows low-magnification imaging of about 30×, significantly better than the original 200× low-magnification imaging limit. This was achieved by using an additional aperture to limit the pressure at a point where it will not block the electron beam, and a larger aperture plate for the combination final aperture/secondary electron signal collection surface that also does not block the electron beam significantly.
Scanning, 2006
A device has been developed and used successfully on two models of the environmental scanning ele... more A device has been developed and used successfully on two models of the environmental scanning electron microscope that allows low-magnification imaging of about 30×, significantly better than the original 200× low-magnification imaging limit. This was achieved by using an additional aperture to limit the pressure at a point where it will not block the electron beam, and a larger aperture plate for the combination final aperture/secondary electron signal collection surface that also does not block the electron beam significantly.
Scanning, 2006
This work describes the comparison of experimental measurements of electron beam spread in the en... more This work describes the comparison of experimental measurements of electron beam spread in the environmental scanning electron microscope with model predictions. Beam spreading is the result of primary electrons being scattered out of the focused beam by interaction with gas molecules in the low-vacuum specimen chamber. The scattered electrons form a skirt of electrons around the central probe. The intensity of the skirt depends on gas pressure in the chamber, beam-gas path length, beam energy, and gas composition. A model has been independently developed that, under a given set of conditions, predicts the radial intensity distribution of the scattered electrons. Experimental measurements of the intensity of the beam skirt were made under controlled conditions for comparison with model predictions of beam skirting. The model predicts the trends observed in the experimentally determined scattering intensities; however, there does appear to be a systematic deviation from the experimental measurements.
Scanning, 2006
Phosphor imaging plate technology has made it possible to directly image the distribution of prim... more Phosphor imaging plate technology has made it possible to directly image the distribution of primary beam electrons and scattered electrons in the environmental scanning electron microscope. The phosphor plate is exposed under electron scattering conditions in the microscope chamber. When processed, the electron intensity distribution is displayed as a digital image. The image is a visual representation of the electron probe and skirt and may provide the basis for a more accurate model.
Microscopy Research and Technique, 1993
This work provides examples of some of the imaging capabilities of environmental scanning electro... more This work provides examples of some of the imaging capabilities of environmental scanning electron microscopy applied to easily charged samples relevant to particle analysis. Environmental SEM (also referred to as high pressure or low vacuum SEMI can address uncoated samples that are known to be difficult to image. Most of these specimens are difficult to image by conventional SEM even when coated with a conductive layer. Another area where environmental SEM is particularly applicable is for specimens not compatible with high vacuum, such as volatile specimens. Samples from which images were obtained that otherwise may not have been possible by conventional methods included fly ash particles on an oiled plastic membrane impactor substrate, a one micrometer diameter fiber mounted on the end of a wire, uranium oxide particles embedded in oil-bearing cellulose nitrate, teflon and polycarbonate filter materials with collected air particulate matter, polystryene latex spheres on cellulosic filter paper, polystyrene latex spheres ''loosely'' sitting on a glass slide, and subsurface tracks in an etched nuclear track-etch detector. Surface charging problems experienced in high vacuum SEMs are virtually eliminated in the low vacuum SEM, extending imaging capabilities to samples previously difficult to use or incompatible with conventional methods. o 1993 Wiley-Liss, Inc.*
Microscopy and Microanalysis, 2006
A new technique is described for the detection of x rays in electron column instruments used in m... more A new technique is described for the detection of x rays in electron column instruments used in microanalysis. In electron column instruments, the point source of x rays is produced by the interaction of a focused electron beam with the sample. Neither of the conventional methods, wavelength dispersive (WDS) nor energy dispersive (EDS) based spectrometry, is optimized for low Z element quantitative analysis. In WDS applications, where the analyte elements are Be through P, chemical effects complicate the x ray measurement process. Peak positions and shapes are altered, sometimes very strongly, by the electron configurations of the analyte atoms and neighboring atoms. In these cases, the ideal spectrometer would profile the peak and some small amount of continuum on either side of the peak such that an accurate peak area could be calculated. Present WDS spectrometers are serial in nature and cannot directly measure peak areas, often causing errors in the determination of light element concentrations. Bastin and co-workers have developed an elegant method to provide accurate area determinations, using the serial spectrometer, by a three point procedure. The parallel wavelength dispersive spectrometer (PWDS) proposed here is ideally suited for those applications.
Agu Fall Meeting Abstracts, Dec 1, 2002
Atmospheric Black Carbon (BC) is a ubiquitous and persistent component of atmospheric particulate... more Atmospheric Black Carbon (BC) is a ubiquitous and persistent component of atmospheric particulate matter, found at measurable levels in even the most remote locations. BC derives from combustion processes, the sources of which are highly variable spatially and temporally. Consequently, atmospheric BC has no fundamental chemical identity and therefore cannot be accurately measured using absolute methods. Because of its chemically ambiguous character, measurement of BC has long been problematic. Optical properties alone cannot, in principal, quantify both BC mass and the varying aerosol absorptivity upon which mass measurement relies. To overcome this problem, thermal optical analysis (TOA) utilizes the PM's thermal as well as optical properties. A different problem, however, confronts TOA: varying thermal desorption procedures result in different BC results for the same material. Our focus therefore, was to optimize the key TOA parameters that bias BC measurement: production of char (pyrolysis carbon) from organic carbon by the instrument, and separation of the char analytically from the BC that is native to the sample. In this work, we used response-surface methods to optimize a thermal desorption procedure for BC accuracy. To cover a range of samples, we modeled responses for two types of ambient samples (indoor laboratory air and outdoor urban air) and one carbonaceous aerosol source (forest fires). We identified four factors, associated with the temperature, duration and atmosphere (inert or oxidizing), of desorption steps that potentially contribute most to BC measurement variability. The four factors comprised a central composite factorial design for measuring BC concentration and laser response during the course of the TOA analysis. Scanning electron microscope images of particles on the TOA filters were also used to assess char optimization. The response surfaces for the BC to total carbon ratio and laser attenuation response were modeled using full second-order polynomials containing 15 terms that accounted for main effects from the factors, non-linear behavior within factors, and cross-factor interactions. Optimal conditions for BC accuracy were determined by the intersection between the laser response surfaces.
Http Dx Doi Org 10 1080 02786829108959526, Jun 8, 2007
Fibers and Polymers, 2015
Microscopy and Microanalysis, 2014
We performed cathodoluminescence spectroscopy of presolar and solar Al_2O_3 grains separated from... more We performed cathodoluminescence spectroscopy of presolar and solar Al_2O_3 grains separated from unequilibrated ordinary chondrites. While the CL spectra displayed significant diversity, they are useful to probe crystallinity of presolar Al_2_O3 grains.
Water environment research : a research publication of the Water Environment Federation, 2006
Environmental scanning electron microscopy (ESEM) with an energy-dispersive X-ray spectrometer (E... more Environmental scanning electron microscopy (ESEM) with an energy-dispersive X-ray spectrometer (EDS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) were demonstrated to be useful analytical tools for investigating surface and bulk components of individual floc particles from both full- and bench-scale activated sludge systems. Detailed surface imaging of various hydrated biological floc particles by ESEM revealed substantial differences in surface features between treatment systems, while EDS identified spatial differences in the iron and the aluminum distributions. The ToF-SIMS spectra had signature fragments of protein and polysaccharide material from the floc surface, suggesting that this technique is capable of surface profiling extracellular polymeric substances. Principal-component analysis of the positive ion ToF-SIMS spectra from the mixed-liquor-suspended solid (MLSS) samples and reference aquatic organic materials found slight differences between the full- a...
Water Environment Research, 2006
Environmental scanning electron microscopy (ESEM) with an energy-dispersive X-ray spectrometer (E... more Environmental scanning electron microscopy (ESEM) with an energy-dispersive X-ray spectrometer (EDS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) were demonstrated to be useful analytical tools for investigating surface and bulk components of individual floc particles from both full- and bench-scale activated sludge systems. Detailed surface imaging of various hydrated biological floc particles by ESEM revealed substantial differences in surface features between treatment systems, while EDS identified spatial differences in the iron and the aluminum distributions. The ToF-SIMS spectra had signature fragments of protein and polysaccharide material from the floc surface, suggesting that this technique is capable of surface profiling extracellular polymeric substances. Principal-component analysis of the positive ion ToF-SIMS spectra from the mixed-liquor-suspended solid (MLSS) samples and reference aquatic organic materials found slight differences between the full- and bench-scale MLSS surface properties but substantial differences among MLSS and treated effluent from the same facility.
Microscopy and Microanalysis, 2010
ABSTRACT Instrumentation and Techniques SymposiaAn X-Ray and Cathodoluminescence Study of Cassite... more ABSTRACT Instrumentation and Techniques SymposiaAn X-Ray and Cathodoluminescence Study of Cassiterite (SnO2)Article author querywight s [PubMed] [Google Scholar]vicenzi e [PubMed] [Google Scholar]meier d [PubMed] [Google Scholar]benkstein k [PubMed] [Google Scholar]S Wighta1, E Vicenzia2, D Meiera1 and K Benksteina1a1 National Institute for Standards and Technology
Microscopy and Microanalysis, 2011
Microscopy and Microanalysis, 2011
Microscopy and Microanalysis, 2006
Abstract Advances in Instrumentation and Techniques-Present and future limits of variable pressur... more Abstract Advances in Instrumentation and Techniques-Present and future limits of variable pressure and environmental SEM: Enabling nanoscale metrology, improved x-ray microanalysis and the understanding of novel contrasts in images of modern and novel ...