A High Resolution Electron Spectrometer for Use in Transmission Scanning Electron Microscopy

Abstract

The design and construction of a double focusing uniform field magnetic electron spectrometer are described. The pole pieces of the magnet are curved in an effort to correct all median plane aberrations and thereby increase the collecting power. The spectrometer has been installed on a scanning microscope which uses a field emission gun to produce a 100 Å probe. Energy analysis of the transmitted electrons as well as filtered diffraction patterns can be obtained from areas as small as 100 Å in diameter. In addition, the area under study can be observed directly in the scanning transmission mode, using electrons of any selected energy loss. A resolution of the spectrometer of 2 ppm at an electron energy of 20 keV is shown and the measured second order aberration coefficient is <5% of that of an equivalent straight edge sector magnet. Also, the solid angle for collection of electrons is about an order of magnitude greater than that of the equivalent straight edge magnet at any given resolution. Experimental results in all modes of operation are presented.