Three-dimensional ADF imaging of individual atoms by through-focal series scanning transmission electron microscopy.

Aberration correction in scanning transmission electron microscopy has more than doubled the lateral resolution, greatly improving the visibility of individual impurity or dopant atoms. Depth resolution is increased five-fold, to the nanometer level. We show how a through-focal series of images enables single Hf atoms to be located inside an advanced gate dielectric device structure to a precision of better than 0.1 x 0.1 x 0.5 nm. This depth sectioning method for three-dimensional characterization has potential applications to many other fields, including polycrystalline materials, catalysts and biological structures.