A parallel-detection electron spectrometer using quadrupole lenses

Abstract

Serial detection systems that are standardly employed in electron energy loss spectrometry (EELS) only examine one energy channel at a time and are therefore inherently inefficient. Parallel detection systems using either photodiode arrays or charge-coupled devices (CCDs) promise to remove this inefficiency. However, to completely replace the serial detection systems, they will need 1) a detective quantum efficiency (DQE) approaching 100%, 2) a dynamic range sufficient to cover the range of intensities encountered in the energy loss spectra (about 106), and 3) ability to operate without any loss in energy resolution.We have constructed and tested a parallel detection system which incorporates three quadrupole lenses placed after the magnetic sector prism of the Gatan 607 spectrometer, a single crystal YAG scintillator, and a fiber-optically coupled linear photodiode array. The quadrupoles magnify the small dispersion (1.8μm per eV at 100kV primary voltage) of the spectrum produced by the magnetic sector to as high as 1 mm per eV without producing any spectrum rotation and with small power requirements.