Position averaged convergent beam electron diffraction: Theory and applications

摘要: A finely focused angstrom-sized coherent electron probe produces a convergent beam diffraction pattern composed of overlapping orders diffracted disks that sensitively depends on the position within unit cell. By incoherently averaging these patterns over many positions, develops ceases to depend lens aberrations and effective source size, but remains highly sensitive specimen thickness, tilt, polarity. Through combination experiment simulation for wide variety materials, we demonstrate averaged can be used determine sample thicknesses (to better than 10%), tilts 1mrad) polarity same optical conditions as in atomic resolution scanning transmission microscopy imaging. These measurements carried out by visual comparison without need apply pattern-matching algorithms. The influence thermal diffuse scattering is investigated comparing frozen phonon absorptive model calculations. We appropriate measuring thickness other parameters even relatively thick samples (>50nm).