high-contrast polepiece

When the high-resolution polepiece or the multiuse polepiece is used, the lens excitation is strong. As a result, the focal length of the objective lens is shortened and a diffraction pattern is formed above the objective aperture. The aperture cannot often select one diffraction spot but contain the effect of neighboring diffraction spots. The bright-field and dark-field images are influenced by other diffraction spots. To improve this failure, a polepiece that enables acquisition of one diffraction spot is available, which is called the "high-contrast polepiece." In this polepiece, the magnetic field produced is weakened a little by broadening the polepiece gap so that the diffraction pattern is formed on the objective aperture. For this polepiece, a Cs of 3.3 mm, a Cc of 3.0 mm and a spatial resolution for TEM image of 0.31 nm at an accelerating voltage of 200 kV have been attained. Also, the high-contrast polepiece allows the specimen holder to be tilted to ±(30° to 35°). It is used for bright and dark field microscopy of texture analysis of materials and for the studies of biological specimens.

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