GB1025674A - Electrostatic immersion objective lens - Google Patents

Abstract

1,025,674. Emission microscopes. TRUB TAUBER & CO. A.G. Nov. 13, 1962 [Nov. 22, 1961], No. 42812/62. Heading H1D. An electrostatic immersion objective for an emission microscope comprises an emitter electrode K, an intermediate electrode Z, a control electrode S and an accelerating electrode A, the bore in the intermediate electrode Z having a diameter D z and an axial length z, each of which is at most one fifth of the distance a between emitter K and electrode Z. In a preferred arrangement, a is 3 mm., z is 0À25 mm. and D z is 0À3 mm., so that the field between cathode K and electrode Z stays homogeneous until near the bore, and the beam almost immediately afterwards enters the field of the Einzel lens Z-S-A, electrode Z being at the same potential as anode A, and the control electrode potential being variable and less than a tenth of the anode potential relative to the cathode. The bore in electrode Z is chosen to restrict the image at the smallest magnification used, and may be funnel-shaped with its narrow part adjacent the cathode and may have rounded edges. One or more of the electrodes may be adjustably mounted for transverse displacement or relative inclination to compensate astigmatism due to lack of rotational symmetry in the bore of electrode z. An apertured screen B may be provided beyond anode A. After passing the objective, beam electrons may be deflected by a magnetic field so that negative ions alone are used for image formation. Also the polarity of the electrode potentials may be reversed for image formation with positive ions.