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Performing elemental microanalysis with high accuracy and high precision by scanning electron microscopy/silicon drift detector energy-dispersive X-ray spectrometry (SEM/SDD-EDS).

Newbury DE, Ritchie NW - J Mater Sci (2014)

Bottom Line: SDD-EDS throughput, resolution, and stability provide practical operating conditions for measurement of high-count spectra that form the basis for peak fitting procedures that recover the characteristic peak intensities even for elemental combination where severe peak overlaps occur, such PbS, MoS2, BaTiO3, SrWO4, and WSi2.Accurate analyses are also demonstrated for interferences involving large concentration ratios: a major constituent on a minor constituent (Ba at 0.4299 mass fraction on Ti at 0.0180) and a major constituent on a trace constituent (Ba at 0.2194 on Ce at 0.00407; Si at 0.1145 on Ta at 0.0041).Measurement of trace constituents with limits of detection below 0.001 mass fraction (1000 ppm) is possible within a practical measurement time of 500 s.

View Article: PubMed Central - PubMed

Affiliation: Materials Measurement Science Division, National Institute of Standards and Technology, Gaithersburg, MD 20899 USA.

ABSTRACT

Electron-excited X-ray microanalysis performed in the scanning electron microscope with energy-dispersive X-ray spectrometry (EDS) is a core technique for characterization of the microstructure of materials. The recent advances in EDS performance with the silicon drift detector (SDD) enable accuracy and precision equivalent to that of the high spectral resolution wavelength-dispersive spectrometer employed on the electron probe microanalyzer platform. SDD-EDS throughput, resolution, and stability provide practical operating conditions for measurement of high-count spectra that form the basis for peak fitting procedures that recover the characteristic peak intensities even for elemental combination where severe peak overlaps occur, such PbS, MoS2, BaTiO3, SrWO4, and WSi2. Accurate analyses are also demonstrated for interferences involving large concentration ratios: a major constituent on a minor constituent (Ba at 0.4299 mass fraction on Ti at 0.0180) and a major constituent on a trace constituent (Ba at 0.2194 on Ce at 0.00407; Si at 0.1145 on Ta at 0.0041). Accurate analyses of low atomic number elements, C, N, O, and F, are demonstrated. Measurement of trace constituents with limits of detection below 0.001 mass fraction (1000 ppm) is possible within a practical measurement time of 500 s.

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a Analysis of NIST SRM 470 (K411 glass) as a flat, highly polished bulk sample (final polish with 100 nm alumina) using the k-ratio protocol with SDD-EDS measurements and NIST DTSA-II. Plot of Fe (normalized weight percent) vs. Mg (normalized weight percent) for 20 randomly selected analyses. Note the outlier (circled). b Analysis of NIST SRM 470 (K411 glass) as a flat, but slightly scratched bulk sample (scratches remaining after 1 µm diamond polish) using the k-ratio protocol with SDD-EDS measurements and NIST DTSA-II. Plot of Fe (normalized weight percent) vs. Mg (normalized weight percent) for 20 randomly selected analyses
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Fig3: a Analysis of NIST SRM 470 (K411 glass) as a flat, highly polished bulk sample (final polish with 100 nm alumina) using the k-ratio protocol with SDD-EDS measurements and NIST DTSA-II. Plot of Fe (normalized weight percent) vs. Mg (normalized weight percent) for 20 randomly selected analyses. Note the outlier (circled). b Analysis of NIST SRM 470 (K411 glass) as a flat, but slightly scratched bulk sample (scratches remaining after 1 µm diamond polish) using the k-ratio protocol with SDD-EDS measurements and NIST DTSA-II. Plot of Fe (normalized weight percent) vs. Mg (normalized weight percent) for 20 randomly selected analyses

Mentions: An example of how serious the impact of specimen geometry can be upon analytical accuracy is illustrated in Figs. 3 and 4 for the analysis of a microscopically homogeneous glass, NIST SRM 470 (K411), the complete composition of which is listed in Table 3. Table 3 also contains the results of a standards-based k-ratio protocol analysis of NIST SRM 470 (K411 glass) prepared in the ideal specimen geometry of a flat, highly polished surface (0.1 µm alumina final polish) with a thin (<10 nm) carbon conductive coating for charge dissipation. The relative errors as compared to the SRM certificate values for the average of 20 analyses range from −1.1 to 1.8 %. Figure 3a shows a plot of the distribution from 20 analyzed locations for the concentrations of magnesium and iron, elements which were chosen because the large difference in their photon energies, 1.254 keV for MgKα, β and 6.400 keV for FeKα, make them differentially sensitive to geometric effects since the low-energy photons of Mg suffer much higher absorption compared to the high-energy photons of FeKα [19]. The cluster of the analyses is seen to be very narrow, with one exception. A reasonable question the analyst might ask is whether this outlier represents an actual deviation in the local composition or arises from some other factor. Upon review of the analyzed locations, the outlier in Fig. 3 was in fact determined to be the consequence of an analysis that was performed in a scratch that remained after final polishing, thus representing a geometric effect rather than a true compositional variation. This surface roughness effect is illustrated for a more severe situation in Fig. 3b, which shows the results from 20 analyses at randomly selected locations on the scratched, irregular surface that remained after polishing with 1 µm diamond particles. The results show both a systematic shift in the apparent concentrations and a broadening in the distribution.Fig. 3


Performing elemental microanalysis with high accuracy and high precision by scanning electron microscopy/silicon drift detector energy-dispersive X-ray spectrometry (SEM/SDD-EDS).

Newbury DE, Ritchie NW - J Mater Sci (2014)

a Analysis of NIST SRM 470 (K411 glass) as a flat, highly polished bulk sample (final polish with 100 nm alumina) using the k-ratio protocol with SDD-EDS measurements and NIST DTSA-II. Plot of Fe (normalized weight percent) vs. Mg (normalized weight percent) for 20 randomly selected analyses. Note the outlier (circled). b Analysis of NIST SRM 470 (K411 glass) as a flat, but slightly scratched bulk sample (scratches remaining after 1 µm diamond polish) using the k-ratio protocol with SDD-EDS measurements and NIST DTSA-II. Plot of Fe (normalized weight percent) vs. Mg (normalized weight percent) for 20 randomly selected analyses
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Related In: Results  -  Collection

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Fig3: a Analysis of NIST SRM 470 (K411 glass) as a flat, highly polished bulk sample (final polish with 100 nm alumina) using the k-ratio protocol with SDD-EDS measurements and NIST DTSA-II. Plot of Fe (normalized weight percent) vs. Mg (normalized weight percent) for 20 randomly selected analyses. Note the outlier (circled). b Analysis of NIST SRM 470 (K411 glass) as a flat, but slightly scratched bulk sample (scratches remaining after 1 µm diamond polish) using the k-ratio protocol with SDD-EDS measurements and NIST DTSA-II. Plot of Fe (normalized weight percent) vs. Mg (normalized weight percent) for 20 randomly selected analyses
Mentions: An example of how serious the impact of specimen geometry can be upon analytical accuracy is illustrated in Figs. 3 and 4 for the analysis of a microscopically homogeneous glass, NIST SRM 470 (K411), the complete composition of which is listed in Table 3. Table 3 also contains the results of a standards-based k-ratio protocol analysis of NIST SRM 470 (K411 glass) prepared in the ideal specimen geometry of a flat, highly polished surface (0.1 µm alumina final polish) with a thin (<10 nm) carbon conductive coating for charge dissipation. The relative errors as compared to the SRM certificate values for the average of 20 analyses range from −1.1 to 1.8 %. Figure 3a shows a plot of the distribution from 20 analyzed locations for the concentrations of magnesium and iron, elements which were chosen because the large difference in their photon energies, 1.254 keV for MgKα, β and 6.400 keV for FeKα, make them differentially sensitive to geometric effects since the low-energy photons of Mg suffer much higher absorption compared to the high-energy photons of FeKα [19]. The cluster of the analyses is seen to be very narrow, with one exception. A reasonable question the analyst might ask is whether this outlier represents an actual deviation in the local composition or arises from some other factor. Upon review of the analyzed locations, the outlier in Fig. 3 was in fact determined to be the consequence of an analysis that was performed in a scratch that remained after final polishing, thus representing a geometric effect rather than a true compositional variation. This surface roughness effect is illustrated for a more severe situation in Fig. 3b, which shows the results from 20 analyses at randomly selected locations on the scratched, irregular surface that remained after polishing with 1 µm diamond particles. The results show both a systematic shift in the apparent concentrations and a broadening in the distribution.Fig. 3

Bottom Line: SDD-EDS throughput, resolution, and stability provide practical operating conditions for measurement of high-count spectra that form the basis for peak fitting procedures that recover the characteristic peak intensities even for elemental combination where severe peak overlaps occur, such PbS, MoS2, BaTiO3, SrWO4, and WSi2.Accurate analyses are also demonstrated for interferences involving large concentration ratios: a major constituent on a minor constituent (Ba at 0.4299 mass fraction on Ti at 0.0180) and a major constituent on a trace constituent (Ba at 0.2194 on Ce at 0.00407; Si at 0.1145 on Ta at 0.0041).Measurement of trace constituents with limits of detection below 0.001 mass fraction (1000 ppm) is possible within a practical measurement time of 500 s.

View Article: PubMed Central - PubMed

Affiliation: Materials Measurement Science Division, National Institute of Standards and Technology, Gaithersburg, MD 20899 USA.

ABSTRACT

Electron-excited X-ray microanalysis performed in the scanning electron microscope with energy-dispersive X-ray spectrometry (EDS) is a core technique for characterization of the microstructure of materials. The recent advances in EDS performance with the silicon drift detector (SDD) enable accuracy and precision equivalent to that of the high spectral resolution wavelength-dispersive spectrometer employed on the electron probe microanalyzer platform. SDD-EDS throughput, resolution, and stability provide practical operating conditions for measurement of high-count spectra that form the basis for peak fitting procedures that recover the characteristic peak intensities even for elemental combination where severe peak overlaps occur, such PbS, MoS2, BaTiO3, SrWO4, and WSi2. Accurate analyses are also demonstrated for interferences involving large concentration ratios: a major constituent on a minor constituent (Ba at 0.4299 mass fraction on Ti at 0.0180) and a major constituent on a trace constituent (Ba at 0.2194 on Ce at 0.00407; Si at 0.1145 on Ta at 0.0041). Accurate analyses of low atomic number elements, C, N, O, and F, are demonstrated. Measurement of trace constituents with limits of detection below 0.001 mass fraction (1000 ppm) is possible within a practical measurement time of 500 s.

No MeSH data available.


Related in: MedlinePlus