Dislocation contrast in high-angle hollow-cone dark-field TEM

摘要: Abstract Dislocations and grain boundaries have been imaged by high-angle hollow-cone dark-field transmission electron microscopy (HADF-TEM). The characteristics of image contrast in HADF-TEM are similar to those annular scanning (HAADF-STEM, or Z-contrast STEM), but different mechanisms could be involved each case because differences the respective scattering geometries. In HADF-TEM, depends not only sensitively on local mass-thickness specimen (i.e., Z-contrast), also much more diffracting conditions that initially set up for corresponding on-axis bright-field TEM imaging, as well position dislocation foil. dislocations appearing images a one-to-one correspondence with present BF-TEM image. technique thus shares many properties conventional diffraction imaging. is generated two-step mechanism — creation diffuse due lattice distortion around cores subsequent channelling propagation diffusely scattered electrons parallel optic axis, governed dynamical effects. determined first step, final essentially second step. It last step makes imaging analogous respects bright HAADF-STEM at least part created atomic rearrangement relaxation. This Huang contrast, which usually does carry atomic-number-sensitive information. has demonstrated HADF- an easy method determining positions foil thickness direction.