X-Ray Spectral Artifacts Encountered in the Sem and Stem

Bolon, R. B.

doi:10.1016/b978-0-12-440340-6.50008-x

Cited by 6 publications

(7 citation statements)

References 2 publications

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“…A combination of modeling and experimental measurements of known systems will benefit ESEM and LVSEM operators by raising awareness of the potential for spectral contamination. Bolon (1991) reported that at 3 Torr (399 Pa), 45% of the primary beam was scattered more than 25 µm and at 5 Torr (665 Pa) it was 66% at a working distance of 15 mm. This work finds that those percentages can be reduced by a factor of two or greater by decreasing the BGPL to 2 mm.…”

Section: Resultsmentioning

confidence: 97%

“…A chemical characterization problem arises when those x-rays reach the detector and are attributed to the material under the primary electron beam. Several researchers (Bache et al 1997;Bolon 1991;Danilatos 1988;Doehne and Bower 1993;Gilpin and Sigee 1995;Griffin 1992;Griffin and Nockolds 1996;Griffin et al 1993Griffin et al , 1994Griffin et al , 1995Wight et al 1997) have studied and reported on the experimental measurements of electron scattering in the gaseous environment of the ESEM. The early work was either done at much longer working distances, because of the design of the early ESEM, or the working distance was not reported.…”

Section: Introductionmentioning

confidence: 97%

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Experimental data and model simulations of beam spread in the environmental scanning electron microscope

Wight

2001

Scanning

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Summary: 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.

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Section: Resultsmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 97%

Experimental data and model simulations of beam spread in the environmental scanning electron microscope

Wight

2001

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“…It is clear that choosing a working distance by maximum x-ray count rate is not a good practice in the ESEM. Bolon (1991) used a Faraday cage made of a platinum aperture disk on a nickel block to establish that 45% of the beam will be scattered beyond 25 µm and 1.5% beyond 1.5 mm at an accelerating voltage of 30 kV, working distance of 15 mm, and chamber pressure of 400 Pa (3 torr). If the chamber pres- sure is increased to 5 torr, 66% of the beam is scattered beyond 25 µm and 8% beyond 1.5 mm.…”

Section: Introductionmentioning

confidence: 99%

The effect of some instrument operating conditions on the x‐ray microanalysis of particles in the environmental scanning electron microscope

Carlton¹

1997

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Summary:The objective of this investigation was to evaluate the practical effects of electron beam broadening in the environmental scanning electron microscope (ESEM) on particle x-ray microanalysis and to determine some of the optimum operating conditions for this type of analysis. Four sets of experiments were conducted using a Faraday cage and particles of copper, glass, cassiterite, and rutile. The accelerating voltage and chamber pressure varied from 20 to 10 kV and from 665-66 Pa (5.0 to 0.5 torr), respectively. The standard gaseous secondary electron detectors (GSED) and the long environmental secondary dectectors (ESD) for the ESEM were evaluated at different working distances. The effect of these parameters on the presence of artifact peaks was evaluated. The particles were mounted on carbon tape on an aluminum specimen mount and were analyzed individually and as a mixture. Substrate peaks were present in almost all of the spectra. The presence of neighboring particle peaks and the number of counts in these depended upon the operating conditions. In general, few of these peaks were observed with the long ESD detector at 19 mm working distance and at low chamber pressures. More peaks and counts were observed with a deviation from these conditions. The most neighboring peaks and counts were obtained with the GSED detector at 21.5 mm working distance, 10 kV accelerating voltage, and 665 Pa (5.0 torr) chamber pressure. The results of these experiments support the idea that the optimum instrumental operating conditions for EDS analysis in the ESEM occur by minimizing the gas path length and the chamber water vapor pressure, and by maximizing the accelerating voltage. The results suggest that the analyst can expect x-ray counts from the mounting materials. These tests strongly support the recommendation of the manufacturer to use the long ESD detector and a 19 mm working distance for EDS analysis. The results of these experiments indicate that neighboring particles millimeters from the target may contribute x-ray counts to the spectrum.

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“…The diversity and uniqueness of samples and experiments conducted in the following research efforts highlight the advantageous features of ESEM that we utilize in stone conservation. Researchers have observed insulators undergoing dynamic fracture (Bolon et al 1989), concrete hydration (Lange et al 1990), ancient ivory fragments (Koestler et al 1990), and materials undergoing phase changes (Bolon and Robertson 1990). The ESEM has been used for wool fiber research, determining the shape of dry and wet Bacillus apiarius spores and watching the growth of live specimens (Danilatos 1988).…”

Section: Microscope/microreactor Environment In the Environmental Scamentioning

confidence: 99%

Environmental microscopy in stone conservation

1996

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Summary:The natural weathering of stone is accelerated by the combined effects of acid rain, salt crystallization, and the freeze-thaw cycles of water. Since weathering will take place until the system reaches chemical equilibrium, we can mitigate the loss to historic stone monuments and structures by treatments of the stone that retard hydrolysis and impart mechanical strength. While macroscopic studies of stone weathering have been performed addressing the causes, the reactions, and the kinetics involved, the mechanisms of weathering, and the chemical remediation of stone need to be better understood at a microscopic level. Our approach uses environmental scanning electron microscopy where samples can be imaged in their wet, natural state, thus facilitating the in situ study of the weathering processes. The environment in the microscope is set up to simulate the conditions of degradation by introducing corrosive liquids and gases and varying the temperature, pressure, and water content in the environmental chamber of the microscope. In this study, we observed specimens of limestone, treated calcite, and sandstone. We have characterized the morphology, structure, and chemical constituents of the samples for comparison at a later stage when protective coatings will be applied. In situ leaching tests were performed on limestone samples to study the mechanisms of degradation. Granular disintegration due to leaching of the binding material between the grains was seen. We have also observed, in situ, the changes in the structure of sodium sulfate, used in salt crystallization tests, during hydration and dehydration cycles; it changed from that of dense grains to hydrated mesoporous granules with the generation of new surface area.

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X-Ray Spectral Artifacts Encountered in the Sem and Stem

Cited by 6 publications

References 2 publications

Experimental data and model simulations of beam spread in the environmental scanning electron microscope

Experimental data and model simulations of beam spread in the environmental scanning electron microscope

The effect of some instrument operating conditions on the x‐ray microanalysis of particles in the environmental scanning electron microscope

Environmental microscopy in stone conservation

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