A HIGH-SENSITIVITY CCD SYSTEM FOR PARALLEL ELECTRON-ENERGY-LOSS SPECTROSCOPY (CCD FOR EELS)

A cooled frame transfer CCD camera system was developed and tested as a parallel detector in an electron energy-loss spectrometer mounted on a transmission electron microscope. The use of a shutterless camera w ith a frame transfer CCD collected virtually 100% of the photon signal with a reasonably fast acquisition time. The system detective quantum efficiency was over 90% under normal experimental conditions. Because of the low channel to channel gain variations in the CCD, the signal- to-noise ratio and the detection limit were substantially better than that obtained with a silicon intensified target (SIT) camera, and dire ct fitting to the standard data was feasible. Quantitation at the phos phorus L edge generated from a phosphoprotein, phosvitin, showed that, under identical experimental conditions, direct fitting of spectra ob tained with this CCD system gave better sensitivity than that given by the SIT camera system. Because of its larger pixel charge well, the C CD system can also operate at a much higher beam current, resulting in a significant reduction in the time required for elemental mapping at a given sensitivity.