Mathematical Problem Solving and Teacher Professional Learning: The Case of a Modified PISA Mathematics Task

Abstract

We present a method to prepare monolayer and multilayer suspended sheets of hexagonal boron nitride (h-BN), using a combination of mechanical exfoliation and reactive ion etching. Ultrahigh-resolution trans- mission electron microscope imaging is employed to resolve the atoms, and intensity profiles for reconstructed phase images are used to identify the chemical nature (boron or nitrogen) of every atom throughout the sample. Reconstructed phase images are distinctly different for h-BN multilayers of even or odd number. Unusual triangular defects and zigzag and armchair edge reconstructions are uniquely identified and characterized.