Tecnique

4D-STEM is combining scanning in STEM mode with the acquisition of full nanobeam diffraction patterns at every scan position, creating a 2D array of 2D diffraction patterns. The diffraction patterns contain both structural [1,2,3,4] and functional [5] information, which can be analyzed to retrieve both simultaneously from the same data set. This enables the most direct correlation of structural and functional properties and can further be readily combined with in-situ approaches to evaluate their dynamic evolution [1,6,7].

For crystalline materials, ACOM-STEM is well established yielding phase and orientation maps of materials with nanometer resolution [1,6,7]. This can be extended by Cepstral analysis for high quality strain mapping. The counterpart for amorphous materials is STEM-PDF [2,4,5], where the local pair distribution function provides information on short and medium ranger order in metallic glasses, disordered ceramics and organic materials. Analysis of the ellipticity of the diffraction halos further enables local strain analysis in these glassy materials [4,5]. 

The displacement of the diffraction patterns provides information on local electric and magnetic fields inside the sample. Using a singular valued decomposition approach [4] provides extreme sensitivity for measuring these displacements and thus access to small electric or magnetic fields [5]. Moreover, this approach suppresses most of the crystallographic artifacts enabling a precise measurement of the local fields. Because of the high sensitivity, it can be used to analyze typical ACOM-STEM and STEM-PDF data sets, thus giving access to simultaneous and correlated structural and functional information.