A high performance electron energy loss spectrometer for use with a dedicated STEM

A uniform magnetic field spectrometer corrected for some second order aberrations has been designed and constructed. We demonstrate practical elimination of the focal plane tilt and two of the second order aperture aberrations. The spectrometer is capable of accepting absolute entrance semiangles of up to 7.8 mrad with a resolution better than 1/2 eV at 100 keV incident electron energies. With the addition of a weak octupole coil at the magnet entrance, a reduction in the limiting third order aberrations has been displayed.