Nanoscale Phase-Separated Structure in Core–Shell Nanoparticles of SiO₂–Si_1–xGe_xO₂ Glass Revealed by Electron Microscopy

Abstract

SiO-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 SiO-GeO glass nanoparticles during the manufacturing of SiO-GeO 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 SiO. 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 SiO-GeO 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 SiO-SiGeO 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.

Non-destructive depth profile evaluation of multi-layer thin film stack using simultaneous analysis of data from multiple X-ray photoelectron spectroscopy instruments

“…Knowing the depth profiles of chemical species near the surface of a sample is extremely important for discussing the properties of various products. There are various methods to evaluate depth profiles, such as scanning transmission electron microscopy (STEM)/energy dispersive X-ray spectroscopy (EDX) 1,2) and X-ray photoelectron spectroscopy (XPS) depth measurements with ion sputtering. [3][4][5] Among them, non-destructive depth profile evaluation using angleresolved XPS (ARXPS) data analysis techniques has the advantage of being able to evaluate the chemical states of atoms in the samples, [6][7][8] which cannot be exactly determined with destructive methods.…”