The effect of mechanical vibration and drift on the reconstruction of exitwaves from a through focus series of HREM images

Experimental HREM images can show a limited resolution as a result of mecha nical vibration and drift. Tn this paper the effect of such mechanical vibr ations on the accuracy of the through focus exit wave reconstruction method is investigated for different thicknesses of a test structure of La3Ni2B2N 3. A through-focus series of HREM images for this structure is simulated fo r different kinds of mechanical vibration corresponding to an information l imit g of about 7 nm(-1): (1) no mechanical vibration, (2) isotropic mechan ical vibration, and (3) several anisotropic mechanical vibrations. From the se through-focus series the reconstructed exit wave is calculated (Ultramic roscopy 64 (1996) 109). The above isotropic and anisotropic mechanical vibr ations have a large effect on the reconstructed exit waves when compared wi th the reconstructed, exit wave without mechanical vibration, i.e. the rang e of amplitudes and phases in a reconstructed exit wave decreases and the b ackground intensity increases. The initial thickness and orientation can be obtained using a least-squares refinement procedure (Acta Crystallogr. A 5 4 (1998)91) when then is no mechanical vibration present. In the case of is otropic or anisotropic vibration, the refined thickness and orientation are likely to give wrong results depending on the size of the vibrations and o n the number of significant reflections (which is related to the size of th e unit cell, the thickness and the misorientation). (C) 1999 Elsevier Scien ce B.V. All rights reserved.