Atomic-scale structures in complex solids by Z-contrast STEM and first-principles theory
- Oak Ridge National Lab., TN (United States). Solid State Div.
Modern high-resolution scanning transmission electron microscopes are capable of forming electron probes below 2{angstrom}, sufficiently small to allow an atomic resolution Z-contrast image to be formed from many materials. Such images, formed with a high angle annular detector, are incoherent in nature, and can be described as a convolution of the probe intensity profile with an object function peaked sharply at the atomic sites. Unlike phase contrast microscopy, there is no phase problem associated with an incoherent image, and direct inversion to the projected atomic structure is possible. A quantitative method for structure retrieval is maximum entropy analysis, although under Scherzer incoherent conditions the probe tails are small, and peaks in the image intensity correspond closely to atomic positions. In such cases, an intuitive structure determination may be possible. Electron energy loss spectroscopy (EELS) may also be performed simultaneously, using the Z-contrast image to position the probe over selected atomic columns, providing complementary information on composition and electronic structure. On the theoretical side, present-day computers are now capable of electronic structure calculations that can be used to determine the preferred atomic arrangements in complex systems. Both first-principles and semiempirical approaches have been developed with complementary capabilities. Here the authors present several examples where a synergistic approach combining Z-contrast STEM, spatially resolved EELS and theoretical results have led to the elucidation of complex atomic structures. The ability to determine atomic structures experimentally to high accuracy provides both a perfect starting point for theoretical calculations and an ideal test of theoretical predictions. Theoretical studies can explore the new dimensions of time and energy. This combined approach leads to a detailed and comprehensive picture of complex atomistic mechanisms.
- Research Organization:
- Oak Ridge National Lab., Solid State Div., TN (United States)
- Sponsoring Organization:
- USDOE Office of Energy Research, Washington, DC (United States)
- DOE Contract Number:
- AC05-96OR22464
- OSTI ID:
- 672117
- Report Number(s):
- ORNL/CP-97024; CONF-980808-; ON: DE98005720; BR: KC0202040; TRN: AHC2DT07%%277
- Resource Relation:
- Conference: 14. international congress on electron microscopy, Cancun (Mexico), 31 Aug - 4 Sep 1998; Other Information: PBD: Feb 1998
- Country of Publication:
- United States
- Language:
- English
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