U.S. Philips Corporation

Alan F De Jong

Harald Rose

Karel D Van Der Mast

Johan G Bakker

Bernardus J Bormans

Dirk E Van Dijck

Raymond Wagner

Peter E Asselbergs

In an electron microscope it is sometimes important that specimens can be studied at a very low temperature (for example, that of liquid helium). In the case of known specimen holders the specimen is cooled by supplying the cooling medium via a bore in the specimen holder; this causes thermal drift of the removed specimen holder each time when a specimen is exchanged, and also an acoustic coupling (i.e. transfer of vibrations) exists with the dewar vessel connected to the specimen holder. In accordance with the invention, the specimen is arranged on the end 20 of the specimen holder 7 by means of a separate transport unit 13, 36 so that it is not necessary to remove the specimen holder 7 in order to exchange a specimen, with the result that the specimen holder is not heated. Moreover, the coupling to the cold source 22, 28 can take place via a flexible cooling conduit 30 which extends directly to the end 20 to be cooled and may be permanently connected thereto, thus avoiding the transfer of vibrations.

Particle-optical apparatus including a low-temperature specimen holder

An imaging symmetrical energy filter (of the .OMEGA.-type) comprising two pairs of sector magnets (1), (2), (3), (4) for an electron microscope. The second-order chromatic aberration is corrected by arranging the two pairs of sector magnets {(1),(4) and (2),(3)} further apart. This enables suitable arrangement of the coils to generate correction hexapole fields, so that the chromatic error is even completely eliminated. Moreover, correction of the third-order aperture aberration is also possible by constructing the hexapole coil (9) in the symmetry plane also as an octupole coil. Further correction of this third-order aberration is achieved by applying an octupole field (5) directly at the entrance of the first sector magnet (1) and an octupole field (13) directly at the exit of the fourth sector magnet (4).

Energy filter with correction of a second-order chromatic aberration

A method of autotuning an electron microscope by producing a series of images of the object to be examined, using a defined tilt of the electron beam in a different direction for each respective image. The images are thereby displaced relative to one another. Each image is then decomposed into a linear and a non-linear component thereof, and the linear image components are separated by Fourier filtering. The relative displacements of a number of the linear image components relative to each other are measured, and the measured displacement values are combined to derive autotuning parameters for the electron microscope.

Method for autotuning of an electron microscope, and an electron

In an electron microscope correction of spherical and chromatic aberration can be achieved in a number of freely adjustable directions by using a multipole correction element whereby a magnetic or electrostatic octupole field, rotatable about the optical axis, or a combined rotatable magnetic and electrostatic quadrupole field is generated. A corrected overall image can be obtained by combination of images successively corrected in different directions. In the case of holographic images, correction in the direction perpendicular to the line direction in the hologram enhances the accuracy of phase determination. A correction element of this kind, having comparatively small dimensions of from 1 to 2 cm, can be simply mounted, notably in a transmission electron microscope, in a space provided for the stigmator.

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Eindhoven, Netherlands

Alan F De Jong