Portal de Periódicos da CAPES

Correction of Spherical Aberration using Defocus Modulation Technique

1990; Cambridge University Press; Volume: 48; Issue: 1 Linguagem: Inglês

10.1017/s042482010018104x

2690-1315

Yoshifumi Taniguchi, Ryuichi Shimizu, Michio Chaya, Takashi Ikuta,

Electron and X-Ray Spectroscopy Techniques

In the electron optical system of transmission electron microscopes, there essentially exists a spherical aberration in the objective lens. A novel method to correct the spherical aberration based on the defocus modulation technique by the image integration with bipolar weighting functions have been proposed by one of the authors (T. I.). Because a coherent optical system is assumed in this method, this technique can be extended to the transmission electron microscopy. This paper presents the experimental confirmation of the usefulness of this method for the electron microscopy by off-line image integration of the series of though-focus images recorded on a video tape. A thermal field emission type electron microscope (JEM-100CFEG) was used in this experiment. The accelerating voltage was 80 kV and the spherical aberration coefficient of the objective lens was 6.1 mm. The sample was amorphous carbon film of 2 nm thick. Small particles of gold were evaporated onto the film in a Bell-jar. The image filing consists of 125 images as a through-focus series by step of 13.64 nm. Because of the residual asymmetry of the objective pole piece, it was unable to coincide the current center with the voltage center which is true optical axis of the electron microscope. The misalignment of the current center was corrected by shifting the image data itself in a computer after making the image data filing of the through-focus series. The image integration to reconstruct the aberration free images was performed with the corrected image data under appropriate bipolar weighting functions for real and imaginary terms.