Mapping Non-Crystalline Nanostructure in Beam Sensitive Systems With Low-dose Scanning Electron Pair Distribution Function Analysis

Abstract

Macroscopic properties of modern materials are increasingly determined by the nanoscale arrangement of different structural phases in complex multi-phase nanostructures. To develop nanostructure-property relationships, detailed local characterization methods are required, with most structural insight typically obtained via diffraction techniques [1]. Furthermore, many important non-crystalline or semi-crystalline systems, including metal-organic frameworks (MOFs) and inorganic glasses, are readily damaged when probed by ionizing radiation. Scanning electron diffraction (SED) microscopy has recently emerged as a powerful local diffraction technique capable of providing the necessary characterization and applicable to radiation sensitive materials. In SED, a 2D diffraction pattern is acquired at every pixel as a focused near-parallel electron beam is scanned across the specimen, However, most SED microscopy has been based on analysis of Bragg diffraction and is thus only applicable to crystalline components of nanostructure. Here, we generalize low-dose SED microscopy to address non-crystalline components of nanostructure using pair distribution function (PDF) analysis and demonstrate this approach by application to a beam-sensitive nanocomposite of amorphous ZIF-62 and amorphous 60NaPO3-40AlF3.