Michael K Kundmann

US Patent:

61845248, Feb 6, 2001

Filed:

Aug 24, 1998

Appl. No.:

9/138416

Inventors:

Henri Adriaan Brink - Berkeley CA
John Andrew Hunt - Freemont CA
Michael Karl Kundmann - Downers Grove IL

Assignee:

Gatan, Inc. - Pleasanton CA

International Classification:

H01J 4700

US Classification:

250305

Abstract:

Electron optical aberrations of an energy filtering system of an energy filtering transmission electron microscope (EFTEM) are automatically corrected under computer control to set up the EFTEM for use. Optics of the electron microscope preceding an energy filter are used to scan the beam at the entrance to the filter in a pattern corresponding to a defined geometry. The beam can either be finely focused to yield a spot at each position visited during the pattern scan, or the beam can be spread out and imprinted with a well-defined intensity distribution, such as normally occurs due to passage of the beam through a specimen, so that its relative scanned displacements can be assessed using cross-correlation techniques. In the case of the finely focused beam, electron images of the scanned pattern directly yield a spot pattern image. Deviations of the recorded spot pattern image from the defined scan geometry reflect the imaging aberrations introduced by the energy filter.

US Patent:

57985243, Aug 25, 1998

Filed:

Aug 7, 1996

Appl. No.:

8/684973

Inventors:

Michael Karl Kundmann - Downers Grove IL
Alexander Jozef Gubbens - Walnut Creek CA
Stuart Lawrence Friedman - Palo Alto CA
Ondrej L. Krivanek - Herts, GB2

Assignee:

Gatan, Inc. - Pleasanton CA

International Classification:

H01J 4700

US Classification:

250305

Abstract:

An energy filtering system of an EFTEM is automatically adjusted using a computer. The computer inserts an energy-selecting slit into the beam path and begins monitoring the position of the electron beam through a combination of the current sensors integral to the slit and the readout of an electron camera. The beam is centered within the slit by adjusting an energy dispersing element while monitoring beam sensors. After initial alignment, the slit is retracted and a reference aperture is inserted at the entrance to the energy filter. The electron camera captures an image of the reference aperture and the computer analyzes the deviations of the aperture image from its known physical dimensions in order to evaluate the electron optical distortions and aberrations of the filter. The computer uses the determined optical parameters to adjust the distortion and aberration correcting optical elements of the filter, whose effects are known due to previous calibration. After correcting the imaging aberrations, the reference aperture is withdrawn, the slit reinserted, and an isochromatic surface of the filter at the plane of the slit is measured by scanning the beam across a slit edge while integrating the transmitted beam intensity on the electron camera.