Kavli Affiliate: David A. Muller
| First 5 Authors: Desheng Ma, Desheng Ma, , ,
| Summary:
Contrast transfer mechanisms for electron scattering have been extensively
studied in transmission electron microscopy. Here we revisit H. Rose’s
generalized contrast formalism from scattering theory to understand where
information is encoded in four-dimensional scanning transmission electron
microscopy (4D-STEM) data, and consequently identify new imaging modes that can
also serve as crude but fast approximations to ptychography. We show that tilt
correction and summation of the symmetric and antisymmetric scattering
components within the bright-field disk — corresponding to tilt-corrected
bright field (tcBF) and tilt-corrected differential phase contrast (tcDPC)
respectively — enables aberration-corrected, bright-field phase contrast
imaging (acBF) that makes maximal use of the 4D-STEM information under the weak
phase object approximation (WPOA). Beyond the WPOA, we identify the contrast
transfer from the interference between inelastic/plural scattering electrons,
which show up as quadratic terms, and show that under overfocus conditions,
contrast can be further enhanced at selected frequencies, similar to
phase-contrast TEM imaging. There is also usable information encoded in the
dark field region which we demonstrate by constructing a tilt-corrected
dark-field image (tcDF) that sums up the incoherent scattering components and
holds promise for depth sectioning of strong scatterers. This framework
generalizes phase contrast theory in conventional/scanning transmission
electron microscopy to 4D-STEM and provides analytical models and insights into
full-field iterative ptychography, which blindly exploits all above contrast
mechanisms.
| Search Query: ArXiv Query: search_query=au:”David A. Muller”&id_list=&start=0&max_results=3