CCD-Based Parallel Detection System for Electron Energy-Loss Spectrometry and Imaging

摘要

A generic, 2-dimensional integrating detector based on a charge-coupled device (CCD) is being developed for applications in physical and biomedical research. A detector system, operating in a 1-dimensional mode, is currently being designed for electron energy-loss spectroscopy (EELS); when operated in a 2-dimensional mode it is suitable for electron imaging studies. An energy-loss spectrometer (Gatan 607) is being equipped with a magnifying quadrupole electron lens to produce an electron dispersion of approx.15 mm on a YAG:Ce scintillator. The scintillation light is coupled via an optical lens system to a 512 pixel x 512 pixel CCD. Energy-loss spectra are recorded successively in 5 pixel x 512 pixel frames. With a microscope beam current of 0.5 nAmp and electron energy of 120 keV, the integration (exposure) time for 100 frames is 40 msec and the readout and digitization time for 100 frames, using a 14-bit ADC, is 0.5 sec. The statistical precision expected by summing the 100 frames in the computer is 10 sup -4 for the zero-loss peak (DQE = 0.4). For a peak of 1/1000 the intensity of the zero-loss peak, the precision is 10 sup -2 (DQE = 0.2). To obtain the same precision (10 sup -2 ) with a 512-pixel linear photodiode array would require data from at least 280 frames and an acquisition time 35 to 70 times longer than the 40 msec required for the exposure of 100 frames in the CCD. (ERA citation 11:048440)