Subangstrom resolution imaging using annular dark-field STEM

Annular dark-field STEM is shown to be extremely robust to the effects of chromatic aberration, allowing transfer to below 1 angstrom using underfocus to counteract the effects of spherical aberration. It is shown that the effect of chromatic focus spread is to impose an upper limit to the transfer function that is proportional to the reciprocal of spatial frequency, which is a much less severe truncation of information in reciprocal space than for conventional high-resolution TEM