Electron microscope
An electron microscope includes a monochromator, an image acquiring portion for obtaining an electron microscope image containing interference fringes of the electron beam formed by an aperture located behind the monochromator, a line profile acquiring portion for obtaining a plurality of line profiles passing through the center of the aperture on the EM image, an energy dispersion direction identifying portion for identifying the direction of energy dispersion of the monochromator on the basis of the line profiles obtained by the line profile acquiring portion, and an optics controller for controlling an optical system on the basis of a line profile in the direction of energy dispersion to bring the focal plane for the electron beam exiting from the monochromator into coincidence with the achromatic plane.
1. An electron microscope equipped with a monochromator that has a first energy filter for dispersing an electron beam according to kinetic energy, an energy-selecting slit disposed on an energy dispersive plane, and a second energy filter for canceling energy dispersion of the electron beam passed through the energy-selecting slit, said electron microscope comprising:
an image acquiring portion for obtaining an electron microscope image containing interference fringes of the electron beam formed by an aperture located behind the monochromator;
a line profile acquiring portion for obtaining a plurality of line profiles passing through a center of the aperture on the electron microscope image;
an energy dispersion direction identifying portion for identifying a direction of energy dispersion of the monochromator based on the plurality of line profiles obtained by the line profile acquiring portion; and
an optics controller for controlling an optical system based on a line profile in the direction of energy dispersion to bring a focal plane for the electron beam exiting from the monochromator into coincidence with an achromatic plane.
2. The electron microscope as set forth in claim 1 , wherein said energy dispersion direction identifying portion finds a ratio of a local maximum value to a local minimum value for each of the plurality of line profiles and identifies said direction of energy dispersion based on the found ratios.
3. The electron microscope as set forth in claim 1 , wherein said optics controller controls said optical system based on a ratio of a local maximum value to a local minimum value of the line profile in said direction of energy dispersion.
4. The electron microscope as set forth in claim 1 , wherein said optics controller controls a strength of an electromagnetic field of at least one of said first energy filter and said second energy filter based on the line profile in said direction of energy dispersion to bring said achromatic plane into coincidence with said focal plane.
5. The electron microscope as set forth in claim 1 , wherein said optics controller controls an electrostatic lens mounted ahead of said monochromator based on the line profile in said direction of energy dispersion to bring said focal plane into coincidence with said achromatic plane.
6. The electron microscope as set forth in claim 1 , wherein said optics controller controls a magnetic lens mounted ahead of said monochromator based on the line profile in said direction of energy dispersion to bring said focal plane into coincidence with said achromatic plane.
7. The electron microscope as set forth in claim 1 , wherein said optics controller controls astigmatism produced by said monochromator based on the line profile in said direction of energy dispersion to bring said focal plane into coincidence with said achromatic plane.