Solid silicon monoxide is an amorphous material which has been commercialized for many functional applications. However, the amorphous structure of silicon monoxide is a long-standing question because of the uncommon valence state of silicon in the oxide. It has been deduced that amorphous silicon monoxide undergoes an unusual disproportionation by forming silicon- and silicon-dioxide-like regions. Nevertheless, the direct experimental observation is still missing. Here we report the amorphous structure characterized by angstrom-beam electron diffraction, supplemented by synchrotron X-ray scattering and computer simulations. In addition to the theoretically predicted amorphous silicon and silicon-dioxide clusters, suboxide-type tetrahedral coordinates are detected by angstrom-beam electron diffraction at silicon/silicon-dioxide interfaces, which provides compelling experimental evidence on the atomic-scale disproportionation of amorphous silicon monoxide. Eventually we develop a heterostructure model of the disproportionated silicon monoxide which well explains the distinctive structure and properties of the amorphous material.

The local atomic structures of amorphous Ge-Sb-Te phase-change materials have yet to be clarified and the rapid crystal-amorphous phase change resulting in distinct optical contrast is not well understood. We report the direct observation of local atomic structures in amorphous ${\mathrm{Ge}}_2{\mathrm{Sb}}_2{\mathrm{Te}}_5$ using “local” reverse Monte Carlo modeling dedicated to an angstrom-beam electron diffraction analysis. The results corroborated the existence of local structures with rocksalt crystal-like topology that were greatly distorted compared to the crystal symmetry. This distortion resulted in the breaking of ideal octahedral atomic environments, thereby forming local disordered structures that basically satisfied the overall amorphous structure factor. The crystal-like distorted octahedral structures could be the main building blocks in the formation of the overall amorphous structure of Ge-Sb-Te.

We have found nanoscale quasicrystal-like structural states exhibiting pseudotenfold nanobeam electron-diffraction patterns in the course of nanocrystallization process of an ${\text{Fe}}_{23}{\text{B}}_6$ structure in an ${\left({\text{Fe}}_{0.5}{\text{Co}}_{0.5}\right)}_{72}{\text{B}}_{20}{\text{Si}}_4{\text{Nb}}_4$ metallic glass. An existence of the intermediate states between the quasicrystal-like and ${\text{Fe}}_{23}{\text{B}}_6$ structures indicates that the quasicrystal-like structure is approximate to the ${\text{Fe}}_{23}{\text{B}}_6$ structure including no icosahedral atomic arrangement. The pseudotenfold electron-diffraction patterns are understood from a combination of three types of tiles found in the ${\text{Fe}}_{23}{\text{B}}_6$ structure. The three types of tiles can produce decagonal units which do not have any icosahedral atomic arrangement.

Nanoscale structural information of amorphous structures has become obtainable by using nanobeam electron diffraction in combination with high resolution imaging. In addition, accurate radial distribution function analysis using energy filter has also become available to know averaged amorphous structures. In this paper, we introduce some applications of these techniques, especially to several Fe-based metallic glasses. On the basis of these results, we discuss a relationship between the glass structure and the glass stability in Fe-based metallic glasses

We have examined the local atomic configurations of amorphous Fe-Si-B alloys by means of electron diffraction pair-distribution-function analysis and compared them with those of a metastable sigma phase formed during the crystallization process. We found a great structural similarity, not only at short range but also at medium range up to 1.0 nm, between amorphous Fe-Si-B and sigma phase structures. The results imply that the sigma phase structure can be regarded as a good crystalline approximant for the glass structures in this alloy system. The connections of coordination polyhedra in the sigma phase structure were also discussed.