Quantitative Analysis and High-Resolution X-ray Mapping with a Field Emission Electron Microprobe

Hombourger, Chrystel; Outrequin, Michel

doi:10.1017/s1551929513000515

Cited by 17 publications

(7 citation statements)

References 7 publications

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“…WISC-Resolution output for hemispherical Cu-Mg-Pd precipitates in Mg-Pd. The scaled PENEPMA simulation, performed at 6 kV, matches well the experimental data of Hombourger and Outrequin[4].…”

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confidence: 68%

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Analytical Spatial Resolution in EPMA: What is it and How can it be Estimated?

Moy

Fournelle

2017

Microsc Microanal

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The imaging benefits of field emission SEM are clear: edge resolution down to ten or so nanometers, particularly for secondary electron images. Edge resolution is defined as the ability to distinguish two adjacent features, based upon difference in signal intensity (e.g. 88% -12%). However, improving EPMA analytical spatial resolution is complex. Changing the electron source on an electron microprobe from tungsten to a field emission one, and assuming an immediate improvement in analytical resolution with the typical accelerating voltage (15 kV), is problematic. Landing beam diameter is one factor, but most critical is the immediate electron scattering once electrons enter the target. Analytical resolution, then, is critically related to the energy of the incident electrons. Monte Carlo electron-target modeling demonstrates the necessity of decreasing beam energy (Figure 1).Reducing the accelerating voltage, with its benefit of constraining the incident electrons to a tighter interaction volume, however, leads to further complications in many cases -the necessity to alter the characteristic X-rays lines being used if the 'normal' ones are not being excited. This is particularly the case for the transition metals (e.g. Fe) and is discussed in an associated presentation at this conference [1]. And operation at lower keV (5-10 keV) accentuates the significance of the upper region of the sample and issues of carbon contamination and oxide coats on metals, which can impact the quality of the EPMA results. Additionally, the combination of tight FE beam diameter and reduced interaction volume may lead to alteration/damage of the target material.Working with EPMA of sub-micron phases, one inevitably asks "How small an object can you analyze?" Traditionally, equations for "X-ray range" and more recently, Monte Carlo simulations, have been used for estimates. However, it is useful to quote Barkshire et al [2]: "… instead of simply being able to resolve the feature in an image, the entire X-ray information volume must be contained within the feature. Thus, for this purpose a more reasonable definition of spatial resolution is the diameter of a feature such that it will include some fraction of the total X-ray intensity, e.g. 99 %." This definition for lateral analytical spatial resolution is the one we believe should be used in EPMA.We found NBS/NIST "failed standard" K409 to be useful for evaluating the various equations and Monte Carlo simulations; this material is a silicate glass with Na, Al and Fe present [3]. Rather than being a homogenous material, it has abundant ~800 nm magnetite (Fe3O4) crystals. There are different spacings of glass between the crystals, so FE-EPMA measurements of the glass at 5 and 7 keV were performed, and the results compared with the traditional X-ray range and Monte Carlo simulation results. The results suggested there was little if any improvement in decreasing the accelerating voltage from 7 to 5 kV.However, the geometry of this sample is not optimal for the usual situation of evaluating ...

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confidence: 68%

“…We have tested the program on one published example [4], small Cu-Mg-Pd precipitates in a Mg-Pd matrix at 6 keV. For this sample, the calculated analytical resolution, in radius, for the element Mg (Kα line; 1.254 keV), Pd (Lα line; 2.838 keV) and Cu (Lα line; 0.928 keV) are ~0.35-.4 µm, ~0.35-.4 µm and ~0.35-.4 µm, respectively.…”

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confidence: 99%

Analytical Spatial Resolution in EPMA: What is it and How can it be Estimated?

Moy

Fournelle

2017

Microsc Microanal

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“…In the present study, this analytical method was adopted for the fine-scale structures and tiny minerals in the Hiawatha melt grains. We reduced the acceleration voltage of the primary electron beam to 12 kV to reduce the interaction volume (Hombourger and Outrequin, 2013;McSwiggen, 2014;Fournelle et. al., 2016) and thus minimize the amount of mixed pixel data, and we used a 60 µm aperture with a low beam current.…”

Section: Discussionmentioning

confidence: 99%

Microporphyritic and microspherulitic melt grains, Hiawatha crater, Northwest Greenland: Implications for post-impact cooling rates, hydration, and the cratering environment

2022

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Sand-sized impactite melt grains hand-picked from a glaciofluvial sample proximal to the Hiawatha impact crater in Northwest Greenland contain new information about the crystallization and cooling history of this impact structure, which is concealed by the Greenland Ice Sheet. Of course, the original locations of the individual sand grains are unknown, but this is offset by the substantial number and wide variety of impactite grains available for study. A detailed investigation of 16 melt grains shows that post-cratering crystallization took place under very variable conditions of strong undercooling with temperatures that dropped rapidly from high above their solidus to far below. A distinct event of near-isochemical hydration at above or ∼250 °C is recorded by intense perlitic fracturing and the growth of closely packed mordenite spherulites only 1−3 μm across in felsic melt grains, which was followed by lower temperature hydrothermal alteration along the pre-existing perlitic fractures. The formation of abundant mordenite microspherulites appears to be very rare or not previously recorded in impactite melts and suggests the rapid infilling of the Hiawatha crater by a hydrous source. The infilling did not occur immediately after the impact as in submarine impacts, but soon thereafter, and before the establishment of a low-temperature hydrothermal alteration system common to the waning stage of cooling in many impact structures. These observations and previous documentation of terrestrial organic matter in the impactites are consistent with an impact into a water-rich terrestrial environment, such as through the Greenland Ice Sheet or into a forested, lacustrine−fluvial region.

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“…The mineral classifications could be used on particles down to 200 nm, even though the interaction volume of the beam was larger than 200 nm. Therefore, the obtained resolution of the To analyze the fine-grained fault gouge, we reduced the acceleration voltage of the primary electron beam to 10 kV to reduce the interaction volume [15][16][17], and therefore to minimize the amount of mixed pixel data, and used the 60-µm aperture providing a 1.8-nA beam current. Despite this reduction of primary electron energy to 10 kV, the interaction volume still has a diameter of up to approximately 1 µm for minerals with the lowest average atomic number (Z) and down to 400 nm for a high Z phase on top of a low Z phase (Figure 3).…”

Section: Methodsmentioning

confidence: 99%

Nanoscale Automated Quantitative Mineralogy: A 200-nm Quantitative Mineralogy Assessment of Fault Gouge Using Mineralogic

Graham¹,

Keulen

2019

Minerals

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Effective energy-dispersive X-ray spectroscopy analysis (EDX) with a scanning electron microscope of fine-grained materials (submicrometer scale) is hampered by the interaction volume of the primary electron beam, whose diameter usually is larger than the size of the grains to be analyzed. Therefore, mixed signals of the chemistry of individual grains are expected, and EDX is commonly not applied to such fine-grained material. However, by applying a low primary beam acceleration voltage, combined with a large aperture, and a dedicated mineral classification in the mineral library employed by the Zeiss Mineralogic software platform, mixed signals could be deconvoluted down to a size of 200 nm. In this way, EDX and automated quantitative mineralogy can be applied to investigations of submicrometer-sized grains. It is shown here that reliable quantitative mineralogy and grain size distribution assessment can be made based on an example of fault gouge with a heterogenous mineralogy collected from Ikkattup nunaa Island, southern West Greenland.

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Quantitative Analysis and High-Resolution X-ray Mapping with a Field Emission Electron Microprobe

Cited by 17 publications

References 7 publications

Analytical Spatial Resolution in EPMA: What is it and How can it be Estimated?

Analytical Spatial Resolution in EPMA: What is it and How can it be Estimated?

Microporphyritic and microspherulitic melt grains, Hiawatha crater, Northwest Greenland: Implications for post-impact cooling rates, hydration, and the cratering environment

Nanoscale Automated Quantitative Mineralogy: A 200-nm Quantitative Mineralogy Assessment of Fault Gouge Using Mineralogic

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