Resolution Improvement in Aberration-Corrected Low- Voltage TEM with Monochromator at 60 kV

Abstract

We have developed a low-voltage electron microscope equipped with a monochromator and Delta-type Cs correctors, which shows atomic resolution at accelerating voltages of 60, 30 and 15 kV. In theory, resolution of TEM images at 60 kV is severely affected by chromatic aberration, which is proven by our calculations of contrast transfer functions and multi-slice image simulation taking chromatic aberration into account with experimental conditions. Experimentally, TEM images of gold nano-particles were observed with non-monochromated and monochromated electron sources at 60 kV. Detectable spatial frequency in the image with the monochromated source was higher than that with non- monochromated source. We have demonstrated that the TEM image resolution at the low- voltage is improved by using a monochromated electron source, which reduce the energy spread of the electron source.