Decontamination in the Electron Probe Microanalysis with a Peltier-Cooled Cold Finger

Buse, Ben; Kearns, Stuart L.; Clapham, Charles; Hawley, D. W.

doi:10.1017/s1431927616011715

Cited by 13 publications

(9 citation statements)

References 16 publications

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“…The electrical conductivity of the uncoated oxidized Bi substrates was sufficient to allow for EPMA analysis without any charging being evident. To minimize carbon contamination, a 10 µ m defocused beam was used in conjunction with a Peltier cooled cold trap (Buse et al, 2016) for all analyses. For each accelerating voltage, a 4 × 3 array of 20 µ m spaced analysis points was acquired, using count times of 60 s on peak and 30 s on each of two background positions for each element line.…”

Section: Methodsmentioning

confidence: 99%

Electron Probe Microanalysis Through Coated Oxidized Surfaces

Matthews¹,

Buse

Kearns

2019

Microsc Microanal

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Low voltage electron probe microanalysis (EPMA) of metals can be complicated by the presence of a surface oxide. If a conductive coating is applied, analysis becomes one of a three-layer structure. A method is presented which allows for the coating and oxide thicknesses and the substrate intensities to be determined. By restricting the range of coating and oxide thicknesses, tc and to respectively, x-ray intensities can be parameterized using a combination of linear functions of tc and to. tc can be determined from the coating element k-ratio independently of the oxide thickness. to can then be derived from the O k-ratio and tc. From tc and to the intensity components of the k-ratios from the oxide layer and substrate can each be derived. Modeled results are presented for an Ag on Bi2O3 on Bi system, with tc and to each ranging from 5 to 20 nm, for voltages of 5–20 kV. The method is tested against experimental measurements of Ag- or C-coated samples of polished Bi samples which have been allowed to naturally oxidize. Oxide thicknesses determined both before and after coating with Ag or C are consistent. Predicted Bi Mα k-ratios also show good agreement with EPMA-measured values.

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Section: Methodsmentioning

confidence: 99%

Electron Probe Microanalysis Through Coated Oxidized Surfaces

Matthews¹,

Buse

Kearns

2019

Microsc Microanal

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“…To change FeLβ f /FeLα f by 1% relative (within measurement error) would require >100 nm of C contamination (calculated using CalcZAF) during the 150 s analysis. This is far more than has been measured in previous studies (e.g., 8 ± 2 nm over 180 s; Buse et al 2016), therefore the effect of contamination can be considered negligible.…”

Section: During Electron Beam Irradiationmentioning

confidence: 56%

High spatial resolution analysis of the iron oxidation state in silicate glasses using the electron probe

Hughes

Buse

Kearns

et al. 2018

American Mineralogist

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The iron oxidation state in silicate melts is important for understanding their physical properties, although it is most often used to estimate the oxygen fugacity of magmatic systems. Often high spatial resolution analyses are required, yet the available techniques, such as μXANES and μMössbauer, require synchrotron access. The flank method is an electron probe technique with the potential to measure Fe oxidation state at high spatial resolution but requires careful method development to reduce errors related to sample damage, especially for hydrous glasses. The intensity ratios derived from measurements on the flanks of FeLα and FeLβ X-rays (FeLβ f /FeLα f ) over a time interval (time-dependent ratio flank method) can be extrapolated to their initial values at the onset of analysis. We have developed and calibrated this new method using silicate glasses with a wide range of compositions (43-78 wt% SiO 2 , 0-10 wt% H 2 O, and 2-18 wt% FeO T , which is all Fe reported as FeO), including 68 glasses with known Fe oxidation state. The Fe oxidation state (Fe 2+ /Fe T ) of hydrous (0-4 wt% H 2 O) basaltic (43-56 wt% SiO 2 ) and peralkaline (70-76 wt% SiO 2 ) glasses with FeO T > 5 wt% can be quantified with a precision of ±0.03 (10 wt% FeO T and 0.5 Fe 2+ /Fe T ) and accuracy of ±0.1. We find basaltic and peralkaline glasses each require a different calibration curve and analysis at different spatial resolutions (~20 and ~60 μm diameter regions, respectively). A further 49 synthetic glasses were used to investigate the compositional controls on redox changes during electron beam irradiation, where we found that the direction of redox change is sensitive to glass composition. Anhydrous alkali-poor glasses become reduced during analysis, while hydrous and/or alkali-rich glasses become oxidized by the formation of magnetite nanolites identified using Raman spectroscopy. The rate of reduction is controlled by the initial oxidation state, whereas the rate of oxidation is controlled by SiO 2 , Fe, and H 2 O content.

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“…The rate in an SEM/EPMA then becomes a factor of the chamber vacuum level. The improvement seen in vacuum levels when liquid nitrogen traps are used in the analysis chamber (e.g., Buse et al, 2016) implies that at least the H 2 O is present in the chamber atmosphere and not just adsorbed on the sample surface. The rate of erosion is therefore significantly less limited than is the deposition, since diffusion rates of O 2 and H 2 O in the gas phase would be expected to be significantly higher than for the surface diffusing hydrocarbons.…”

Section: Discussionmentioning

confidence: 99%

Electron Beam-Induced Carbon Erosion and the Impact on Electron Probe Microanalysis

Matthews¹,

Kearns²,

Buse³

2018

Microsc Microanal

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Electron beam-induced carbon contamination is a balance between simultaneous deposition and erosion processes. Net erosion rates for a 25 nA 3 kV beam can reduce a 5 nm C coating by 20% in 60 s. Measurements were made on C-coated Bi substrates, with coating thicknesses of 5–20 nm, over a range of analysis conditions. Erosion showed a step-like increase with increasing electron flux density. Both the erosion rate and its rate of change increase with decreasing accelerating voltage. As the flux density decreases the rate of change increases more rapidly with decreasing voltage. Time-dependent intensity (TDI) measurements can be used to correct for errors, in both coating and substrate quantifications, resulting from carbon erosion. Uncorrected analyses showed increasing errors in coating thickness with decreasing accelerating voltage. Although the erosion rate was found to be independent of coating thickness this produces an increasing absolute error with decreasing starting thickness, ranging from 1.5% for a 20 nm C coating on Bi at 15 kV to 14% for a 5 nm coating at 3 kV. Errors in Bi Mα measurement are <1% at 5 kV or above but increase rapidly below this, both with decreasing voltage and increasing coating thickness to 20% for a 20 nm coated sample at 3 kV.

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Decontamination in the Electron Probe Microanalysis with a Peltier-Cooled Cold Finger

Cited by 13 publications

References 16 publications

Electron Probe Microanalysis Through Coated Oxidized Surfaces

Electron Probe Microanalysis Through Coated Oxidized Surfaces

High spatial resolution analysis of the iron oxidation state in silicate glasses using the electron probe

Electron Beam-Induced Carbon Erosion and the Impact on Electron Probe Microanalysis

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