AN IMAGING FILTER FOR HIGH-VOLTAGE ELECTRON-MICROSCOPY

An imaging filter suitable for energy-filtered electron microscopy at up to 1.25 MeV has been designed and built. The filter uses a single m agnetic sector with curved faces and 25 cm bending radius, 6 strong qu adrupole and 5 strong sextupole lenses. It corrects all important aber rations and distortions in both the spectrum and image planes to secon d order. The filter's primary detector is a lens-coupled, 1024 x 1024 pixel slow-scan CCD camera designed for operation above 400 keV. The p erformance of the filter mounted on three different JEOL ARM microscop es is illustrated with examples including spectra of energy resolution better than 1 eV recorded at 1.25 MeV, zero-loss-filtered images with spatial resolution of 1.1 Angstrom recorded at 1.25 MeV, inner shell loss spectra and elemental maps. The future applications of the filter are discussed briefly.