3-dimensional imaging of dislocation microstructures by electron beams
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3-dimensional imaging of dislocation microstructures by electron beams J. S. Barnard1, J. H. Sharp2, S. Hata3, M. Mitsuhara3, K. Kaneko4 and K. Higashida3 1
Department of Materials Science & Metallurgy, University of Cambridge, Pembroke Street, Cambridge CB3 2QZ, United Kingdom. 2 Department of Materials Science & Engineering, University of Sheffield, Sir Robert Hadfield Building, Mappin Street, Sheffield S1 3JD, United Kingdom. 3 Department of Electrical and Materials Science, Kyushu University, Kasuga, 6-1 Kasugakoen, Kasuga, Fukuoka 816-8580, Japan. 4 Department of Materials Science & Engineering, Kyushu University, Nishi-ku, Fukuoka 8190395, Japan. ABSTRACT We review the progress in the electron tomography of dislocation microstructures in the transmission electron microscope (TEM). Dislocation contrast is visible both in conventional TEM and scanning TEM (STEM) modes and, despite the complicated intensity variations, dislocation contrast can be isolated using computational filtering techniques prior to reconstruction. We find that STEM annular dark-field (STEM-ADF) imaging offers significant advantages in terms of dislocation contrast and background artifacts. We present several examples, both in semiconducting and metallic systems, illustrating the properties of 3D dislocations. We present the high-angle triple-axis (HATA) specimen holder where the diffraction condition can be chosen at will and dislocation tomograms of multiple reflections can be combined. 3D dislocations are analyzed in terms of dislocation density and dislocation nodal structures. Several avenues of study are suggested that may exploit the 3D dislocation data. INTRODUCTION Stereography of dislocations was extensively used in the twentieth century for analyzing the three-dimensional structure of dislocation networks by both X-rays [1] and electrons [2]. Stereography gives direct interpretable perspective from a single point of view. With the development of brighter sources, accurate specimen movement and control and the computational means to reconstruct large, useful volumes of material, it is now possible to recover the full 3-dimensional nature of dislocations in a virtual 3D space using both X-rays [3] and electrons [4]. It is also possible to view and analyze dislocation microstructures from any angle. We look at the recent development of dislocation tomography in the transmission electron microscope (TEM) since its inception five years ago [4,5]. We examine the diffraction conditions and electron beam geometries necessary to obtain good, high visibility dislocation images for tomographic reconstruction and have studied the fidelity and properties of the 3D dislocations structures that are recovered.
WEAK BEAM TOMOGRAPHY (TEM) The weak-beam dark-field (WBDF) technique was used in the first implementation of dislocation tomography because of the narrow, bright contrast associated with dislocations when imaged with a weakly excited diffracting beam in the TEM. Understanding of the dislocation contrast mechanism began with the kinematic
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