Low-dose 2D and 4D STEM imaging of beam-sensitive materials

Scanning transmission electron microscopy (STEM) has not been widely regarded as an instrument suitable for low-dose imaging work, yet there is mounting evidence that a focused probe scanning rapidly over a sample can lead to reduced damage compared to wide-field illumination for the same total electron fluence.  Many materials of current interest, including hybrid perovskites for photovoltaic applications, Li-ion battery materials and polymers, are highly beam sensitive.  Here we demonstrate the application of both 2D and 4D STEM methods for low-dose structure determination.  I will show how low-angle annular dark-field (LAADF) imaging reveals previously unobserved defect structures in the hybrid perovskite formamidinium lead iodide (FAPbI3) used in photovoltaic applications.  Electron ptychography can be used to measure the small phase shifts that arise during electron transmission through light elements.  I will described how we use the technique and show direct imaging of atomic structure of a crystalline domains in the polyester, polyethylene naphthalate (PEN), and polyvinyl alcohol (PVA) .  Discrepancies between the observed structures and those previously determined using X-ray diffraction are found.