High-resolution imaging with an aberration-corrected transmission electron microscope

• Published in: Ultramicroscopy Vol. 92; no. 3; pp. 233 - 242
• Main Authors: Lentzen, M., Jahnen, B., Jia, C.L., Thust, A., Tillmann, K., Urban, K.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01-08-2002; Elsevier Science
• Subjects: Aberration correction; Delocalisation; Electron, positron and ion microscopes, electron diffractometers and related techniques; Exact sciences and technology; High-resolution imaging; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Physics; Spherical aberration; Transmission electron microscopy; Aberration correction; 001 031; Transmission electron microscopy; Delocalisation; High-resolution imaging; Spherical aberration; Optical aberration; Transmission microscope; Imaging; Experimental study; High-resolution methods
• ISSN: 0304-3991; 1879-2723
• DOI: 10.1016/S0304-3991(02)00139-0

Recently an electromagnetic hexapole system for the correction of the spherical aberration of the objective lens of a
200
kV
transmission electron microscope has been constructed by Haider and coworkers. By appropriately exciting the hexapole elements it is possible to adjust specific values of the spherical aberration coefficient ranging from the value of the original uncorrected instrument over zero even to negative values. In the first part of the paper the consequences of the tunable spherical aberration are investigated. New imaging modes are available: By adjustment of an optimum value for the spherical-aberration coefficient, the point resolution of phase-contrast imaging can be extended to the information limit. Phase-contrast imaging can be improved by a reduced level of contrast delocalisation. For zero aberration contrast delocalisation does not occur. In this case high-resolution investigations are carried out under amplitude-contrast conditions, where the local image intensity of crystalline objects is controlled by electron diffraction channelling. The defocus and spherical aberration values related to the new imaging modes are given. In the second part novel applications of the instrument to semiconductor heterostructures and ceramic grain boundaries are examined.