HIGH-RESOLUTION SCANNING-TRANSMISSION ELECTRON-MICROSCOPY

High-resolution imaging in scanning transmission electron microscopy (STEM) instruments is achieved with a variety of detector configurations including bright-field/dark-field (BF/DF) imaging by coherent phase contrast, high-angle annular dark-field (HAADF) imaging by incoherent atomic number contrast and many other imaging modes. With the use of post-specimen lenses to expand/compress the whole diffraction pattern, the collection angles of both the BF and the ADF detector can be varied continuously and different detector configurations may be realized. Image resolution is improved by increasing the collection angle of the BF detector. The phase and diffraction contrast in a large-angle bright-field (LABF) image is reduced and LABF images have less dependence on the change of beam defocus and the variations of sample thickness. Applications of these high-resolution STEM imaging modes to the study of interfaces are discussed.