Reconstructing the third dimension

Abstract

An approach to microscopy has been developed that can be used to determine, from a single imaging angle, both the position of a specimen's individual atoms in the plane of observation and the atoms' vertical position. See Letter p.243 State-of-the-art electron microscopy can readily resolve structures with subatomic resolution, but making three-dimensional images of similar resolution is a tougher challenge. Here, Dirk Van Dyck and Fu-Rong Chen describe an original image-reconstruction method that extracts information on the whereabouts of all atoms, in the plane as well as in the vertical direction, from just one projection. The concept is based on the assumption that each atom acts as a point source, scattering spherical waves that propagate to the detector, where they interfere with spherical waves from other atoms. The observed 'exit wave' contains information on all atoms in the sample, and can be retrieved using appropriate algorithms. The approach is demonstrated experimentally for a two-layered graphene sample. The authors note that their reconstruction technique resembles that used by cosmologists to construct a Hubble plot, hence the name 'Big Bang tomography'.