Metastable ultrathin crystal in thermally grown SiO2 film on Si substrate

A silicon dioxide film on a silicon substrate is the most essential element in semiconductor devices and various advanced materials. We have elucidated the atomic structure of SiO2 films using low-dose scanning transmission electron microscopy (STEM). We have visualized a metastable crystalline SiO2 layer near a silicon substrate, which was not revealed in previous studies probably due to the vitrification caused by electron irradiation. Our experimental results also suggest a crystallographic nature of various surface oxides.