Fresnel fringe effects at interfaces of thin multilayer structures

Abstract

Recent developments in the TEM Fresnel-fringe technique have provided an alternative method to the determination of structures and morphology of interfaces in multilayer thin film structures. This method has been employed in the investigation of structures and defects in grain boundaries, dislocations, precipitate platelets, twin boundaries, metal interfaces, and multilayer structures. It has been demonstrated that the fringe spacing primarily relates to the layer thickness, while the fringe contrast as a function of defocus relates to the magnitude of the localized change in the scattering potential and thus to the interfacial composition. The profile of the fringes is more closely related to the abruptness of the composition change at the interface. Other factors affecting the Fresnel fringe intensity are the specimen thickness, aperture size, beam convergence, and degree of tilt of the interface from the incident electron beam.Fresnel fringes result from the electrons experiencing an abrupt change in the inner scattering potential parallel to the electron beam path. Most previous calculations of the Fresnel contrast with defocus have simulated models based on one square or symmetrical trapezoid-shaped potential well, which are applicable only to a single interface or grain boundary, or to a few layer pairs of the multilayer.