A spherical a berration-corrected 200 kV TEM

A spherical aberration (C-s)-corrected 200 kV TEM was newly developed. The column of the microscope was extended by 25 cm and the inner yoke of the objective lens was modified to insert some parts of the corrector elements. The corrector has two hexapole elements that play a main role in C-s correction and they are placed at a position equivalent to the coma-free point of the objective lens by using two transfer doublet lenses. The C-s correction was successfully carried out by means of the third-order aberration that was generated in the two extended hexapoles. The C-s can be corrected to the desired value and also can be overcompensated in order to produce a negative C-s, as with the corrected C-s of -23 mum shown in this work. The optical system of the corrector does not produce second- and fourth-order aberrations, and can correct residual aberrations up to the third order. All of the corrector elements are computer-controlled and the third-order aberrations are quite stable after they are properly corrected. The resolution of 0.135 nm was experimentally confirmed by the Young's fringe method. Image simulations of a silicon [110] single crystal were made with various C-s and defocus values to demonstrate the effectiveness of arbitral control of C-s.