![]() ![]() The crystal orientation can be determined at each pixel in real space by comparison with previously simulated patterns residing in an on-line library 12. PED is primarily used for solving unknown structures 11 but by rastering the beam across a 2D field of view, acquiring 2D PED patterns pixel by pixel, a four-dimensional (4D) data set can be acquired (a ‘diffraction-image’). In PED, a focused probe is rocked in a hollow cone about the optic axis above the specimen and de-rocked below, to produce a diffraction pattern of the same geometry as a conventional pattern but one which contains a larger number of reflections and where the diffracted intensities, by virtue of the rocking action of the Ewald sphere during the precession, are integrated across the Bragg condition. Here though, we use a direct method for determining local orientation and crystallography, one that is amenable to being coupled with a STEM approach, namely precession electron diffraction (PED) 10. ![]() The local crystallography of materials may be studied using a number of techniques, including electron holography 8 and lensless imaging/coherent diffraction 9, which rely on a coherent source of electrons and phase retrieval algorithms, as well as more conventional dark-field approaches. By combining scanning transmission electron microscope (STEM) imaging 1 with spectroscopy using X-rays 2 or energy loss 3 and with tomographic acquisition 4, 5, multi-dimensional data sets 6 provide unique spatially resolved physico-chemical information not achievable by any other method 7. The morphological, composition and crystallographic complexity of modern materials and devices has driven the development of sophisticated microscopy tools to enable imaging and analysis across many length-scales. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |