International Precision Incorporated

Akira Yonezawa

Kohei Shirota

An electron microscope comprises an objective lens, at least an intermediate lens and a projector lens arrayed in this order on an optical axis. A movable aperture element is disposed between the objective lens and the intermediate lens whose disposition and magnetic excitation are so selected that electron beam diverging from a crossover produced at a back focal plane of the objective lens is focused on a plane of the movable aperture element. In the case of an electron microscope comprising an objective lens, an objective aperture element, a selected area aperture element, at least an intermediate lens and a projector lens arrayed in this order along an optical axis, an additional lens is disposed between the objective aperture element and the selected area aperture element. Disposition and magnetic excitation of the additional lens are so selected that electron beam diverging from a crossover produced at a back focal plane of the objective lens is focused at a plane of the selected area aperture element. In both electron microscopes, divergence angle of the electron beam scattered by a specimen is restricted by the movable aperture element or the selected area aperture element.

Electron microscope

A transmission electron microscope comprises an objective lens and a condenser lens which are so arranged that excitation of the condenser lens can be varied in association with variation in excitation of the objective lens. A cross-over point which is produced by the condenser lens of the last stage in the non-excited state of the objective lens is caused to coincide with a preselected position on the optical axis of the microscope, which position is determined in accordance with magnitude of excitation of the objective lens. The position of a convergence point of the electron beam produced downstream of a specimen to be observed is maintained substantially constant independently from variations in excitation of the objective lens. The direction in which the electron beam impinges on specimen at a point to be observed is maintained substantially constant independently from variation in excitation of the objective lens. An image of improved quality is obtained without the field of view being narrowed, while observation can be made with constant magnification independently from different focus states. Aberrations are significantly decreased.

Transmission electron microscope

A symmetrical magnetic field type objective lens for an electron microscope comprises an upper magnetic pole piece and a lower magnetic pole piece disposed below the upper pole piece with a predetermined inter-pole distance S. Bores of a same diameter b are formed in the upper and the lower pole pieces, respectively. The distance S and the diameter are selected so that 1.ltoreq.S/b.ltoreq.5. Additionally, excitation J of the objective lens is so selected with respect to a predetermined magnetomotive force Jc.o. of a Riecke-Ruska's condenser objective lens that the condition that 1.4 Jc.o..ltoreq.J.ltoreq.1.7 Jc.o. is fulfilled. The objective lens assures a wide field of view without being accompanied with blurs or distortion of image.

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Fussa, Japan

Akira Yonezawa