Minimum detection limit and spatial resolution of thin-sample field-emission electron probe microanalysis

Nanoscale Phase-Separated Structure in Core-Shell Nanoparticles of SiO2-Si1-xGexO2 Glass Revealed by Electron Microscopy

SiO₂-based optical fibers are indispensable components of modern information communication technologies. It has recently become increasingly important to establish a technique for visualizing the nanoscale phase-separated structure inside SiO₂-GeO₂ glass nanoparticles during the manufacturing of SiO₂-GeO₂ fibers. This is because the rapidly increasing price of Ge has made it necessary to improve the Ge yield by clarifying the detailed mechanism of Ge diffusion into SiO₂. However, direct observation of the internal nanostructure of glass particles has been extremely difficult, mainly due to electrostatic charging and the damage induced by electron and X-ray irradiation. In the present study, we used state-of-the-art scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), and energy dispersive X-ray spectroscopy (EDX) to examine cross-sectional samples of SiO₂-GeO₂ particles embedded in an epoxy resin, which were fabricated using a broad Ar ion beam and a focused Ga ion beam. These advanced techniques enabled us to observe the internal phase-separated structure of the nanoparticles. We have for the first time clearly determined the SiO₂-Si_1-xGe_xO₂ core-shell structure of such particles, the element distribution, the degree of crystallinity, and the quantitative chemical composition of microscopic regions, and we discuss the formation mechanism for the observed structure. The proposed imaging protocol is highly promising for studying the internal structure of various core-shell nanoparticles, which affects their catalytic, optical, and electronic properties.

Observation of Fine Distribution of Minor Dopants in an Erbium-Doped Fiber Core using a Sample Thinning Technique for Field Emission Electron Probe Microanalysis

To observe the fine distribution of minor aluminum and germanium dopants in the erbium-doped fiber (EDF) core of an optical amplifier, a sample thinning technique was applied for field emission electron probe microanalysis (FE-EPMA) together with wavelength-dispersive X-ray spectrometry. This technique significantly improved the spatial resolution without much degradation of the minimum detection limit for FE-EPMA. As such, this enabled us to observe the distribution of minor dopants in EDF. Moreover, we propose a very simple sample preparation to prevent electron-beam radiation damage, a problem involved with FE-EPMA of low-conductivity materials such as SiO2 glass, which is the main component of EDF.

Electron Probe Microanalysis: A Review of the Past, Present, and Future

The 50th anniversary of the application of electron probe microanalysis (EPMA) to the Earth Sciences provides an opportunity for an assessment of the state-of-the-art of the technique. Stemming from the introduction of the first automated instruments, the latest developments of EPMA and some typical applications are reviewed with an eye to the future. The most noticeable recent technical achievements such as the field-emission electron gun, the latest generation of energy and wavelength dispersive spectrometers, and the development of analytical methods based on new sets of first principle data obtained by the use of sophisticated computer codes, allow for the extension of the method to the analysis of trace elements, ultra-light elements (down to Li), small particles, and thin films, with a high degree of accuracy and precision and within a considerably reduced volume of interaction. A number of working examples and a thorough list of references provide the reader with a working knowledge of the capabilities and limitations of EPMA today.

Combination of high spatial resolution and low minimum detection limit using thinned specimens in cutting-edge electron probe microanalysis

The effect of sample thickness on the spatial resolution and minimum detection limit (MDL) has been investigated for field-emission electron probe microanalysis with wavelength dispersive X-ray spectroscopy (FE-EPMA-WDX). Indium gallium phosphide samples thinned to thicknesses of about 100, 130, 210, 310, and 430 nm provided effective thin-sample FE-EPMA-WDX in the resolution range of 40-350 nm and MDL range of 13,000-600 ppm (mass). A comparison of the FE-EPMA results for thin and bulk samples demonstrated that thin-sample FE-EPMA can achieve both higher sensitivity and better spatial resolution than is possible using bulk samples. Most of the X-rays that determine the MDL are generated in a surface region of the sample with a depth of approximately 300 nm. The spatial resolution and MDL can be tuned by the sample thickness. Furthermore, analysis of small amounts of Cl in SiO2 indicated that thin-sample FE-EPMA can realize a spatial resolution and MDL of 41 nm and 446 ppm at Iprob=50 nA, respectively, whereas bulk-sample FE-EPMA offers a resolution of only 348 nm and MDL of 426 ppm.