Design of a 400KV Ultrahigh-Resolution Analytical TEM

Abstract

The condenser-objective (C/O) lens proposed by Riecke, which has a very short gap length and small spherical aberration, was utilized for a commercial 200 kV ultrahigh resolution analytical TEM by Yanaka and Kaneyama. Fig. 1 shows the relation between theoretical resolution and objective lens (OL) spherical aberration coefficient (Cs) at accelerating voltages 200-1250 kV. It was reported that the Cs of a 400kV high resolution TEM is 1.0 mm and its resolution is 0.167 nm. The Cs of 400kV analytical TEM is 1.8 mm and the pre-field spherical aberration coefficient (Csp) is 1.8 mm. Fig. 2 (A), (B) show beam broading in specimens against the thickness when a 200kV and a 400kV electron beam transmit the specimen (C-Au), respectively. The broading of 400kV electron beam is about half of 200kV one. Then it is expected that spacial resolution of x-ray analysis improve. The above-captioned 400kV ultrahigh resolution analytical TEM is designed by applying a new technology which is adopted for a 200kV ultrahigh resolution analytical electron microscope, JEM-2010.Its fundamental construction is the same as the 400kV analytical electron microscope JEM-4000FX, except the 0L. The goniometer is a modified JEM-2010 goniometer, because it is too small for 400kV EM. Although it was expected that the focus ampere turn increases because of its short gap length, the objective lens coil used by JEM-4000EX/FX is adopted, because it has enough capacity. The shapes of the upper yoke and objective polepiece were calculated by the finite element method (55×110 Meshes) under the following condition: (1) maximum tilting-angle 10° (2) x-ray take-off angle 17.5° and solid angle 0.068 strad (3) minimized Cs.