INCREASE OF CURRENT-DENSITY OF THE ELECTRON-PROBE BY CORRECTION OF THE SPHERICAL-ABERRATION WITH A SIDE-ENTRY TYPE FOIL LENS

A side-entry type foil lens for insertion into the gap of the polepieces of a probe-forming lens was developed, The new design allows an accurate alignment of the foil lens and therefore better correction performance compared with the top-entry type foil lens previously used, The scanning transmission electron microscope (STEM) image taken with the foil lens at a large beam convergence semi-angle of 26 mrad showed the sharpness of the image to be similar to that taken without the foil lens at the optimum angle of 14 mrad, confirming correction of the spherical aberration, The optimum foil lens voltage giving the best image quality was in good agreement with the calculations of the probe current density profiles, The signal-to-noise ratio of the image was improved because of the higher probe current due to the increased beam convergence angle, This shows the effectiveness of the spherical aberration correction with the foil lens.