2021 Volume 56 Issue 2 Pages 87-90
Nano-diffraction imaging (NDI) is a novel imaging technique based on scanning transmission electron microscopy (STEM). It uses a nanometer-size electron beam to scan across a specimen, and the electron diffraction (ED) pattern at each position is recorded onto a two-dimensional (2D) pixelated detector. Here, we used NDI to image the nanoscale spatial distribution and orientation of lamellar crystals of polyethylene (PE) without any pretreatment (e.g., RuO4 staining). 2D ED patterns were obtained for two PE samples featuring significantly different crystal orientations, i.e., non-oriented and oriented samples. Spot-like diffractions, corresponding to orthorhombic PE 110 and 200 peaks, were observed. The detailed analysis of the diffractions provides the spatial distribution and orientation of lamellar crystals at nanometer resolutions. Though no distinct morphologies were observed under conventional STEM, we identified a substantial difference in lamellar orientation between non-oriented and oriented samples. Such local structural information is key to understanding higher-level hierarchical elements, e.g., spherulite, but cannot be obtained by conventional diffraction/scattering methods.
