Accession Number : ADP008042

Title :   Effects of Fresnel Fringes on TEM Images of Interfaces in X-Ray Multilayers,

Corporate Author : CALIFORNIA UNIV BERKELEY LAWRENCE BERKELEY LAB

Personal Author(s) : Nguyen, Tai D. ; O'Keefe, Michael A. ; Kilaas, Roar ; Gronsky, Ronald ; Kortright, Jeffrey B.

Report Date : 05 MAR 1992

Pagination or Media Count : 3

Abstract : Cross-sectional High-Resolution Transmission Electron Microscopy (HRTEM) has been widely used to examine the structure and morphology at multilayer interfaces at an atomic scale. Assessment of the interfacial structures quantitatively from these TEM images however is difficult due to the Fresnel fringe effects, which produce different apparent structures with defocus values in the images. These fringes result from the electrons experiencing an abrupt change in the scattering potential parallel to the electron beam path. Imaging of multilayers in cross-section, in which the electrons travel parallel to the interfaces between the two layer materials, always results in such fringes. X-ray multilayers having alternating layers of very different atomic numbers or scattering powers are more prone to these fringes than the heterostructures having less contrast layers. The visibility of the fringes increases with increasing defocus away from the minimum contrast, while optimum resolution in bright-field imaging is obtained at the Scherzer defocus, which is about 100 nm from the minimum contrast for most high resolution microscopes. Fresnel fringes are thus present when imaging at optimum defocus. The effects of these fringes have been commonly overlooked in efforts of making quantitative interpretation of interfacial profiles. They however have also been employed to characterize the structures and compositional roughness at interfaces.

Descriptors :   *ELECTRON BEAMS, *ELECTRON MICROSCOPY, *IMAGES, *INTERFACES, *LAYERS, *X RAYS, *OPTICS, *DIFFRACTION, *LIGHT SOURCES, *WAVE PROPAGATION, ATOMIC PROPERTIES, CONTRAST, CROSS SECTIONS, ELECTRONS, HIGH RESOLUTION, MATERIALS, MICROSCOPES, MICROSCOPY, MORPHOLOGY, NUMBERS, OBSERVATION, PATHS, PROFILES, RESOLUTION, ROUGHNESS, SCALE, SCATTERING, SILICON, STRUCTURES, TRAVEL, VALUE, VISIBILITY, MOLYBDENUM, TUNGSTEN, SILICON, CARBON, RUTHENIUM, CHARGE DENSITY.

Subject Categories : Optics
      Atomic and Molecular Physics and Spectroscopy
      Particle Accelerators

Distribution Statement : APPROVED FOR PUBLIC RELEASE