1 Å-resolution chemical imaging by phase contrast technique

Atomic-resolution high-voltage electron microscopy (ARHVEM) was applied to map chemical compositions of GaNAlNAlGaN layers. Image simulation showed that image variation of the GaN was faster than that of the AlN with an increase in the sample thickness. However, at less than approximately 3 nm thickness, images of the GaN and AlN closely resembled their atomic structures simultaneously at an adequate defocus condition. Under this experimental condition, the GaN and AlN layers, both having the same wurtzite structure, were discriminated by contrasts of the cations. Contrasts of the N enabled us to determine thickness variation between the GaN and AlN. ARHVEM observation showed that, although the morphology of the interface between the GaN and AlN seems to be rough, the interface is locally sharp on an atomic scale.