Progress in parallel-detection electron energy loss spectroscopy

Abstract

Parallel-detection electron energy loss spectrometers improve the detection efficiency by several hundred times compared to the traditional serial-detection spectrometers, but they have their own set of difficulties, such as the limited dynamic range of solid state detectors, the possibility of stray reflections of the intense zero loss beam giving rise to spurious background, and channel-to-channel gain variation. Fortunately, none of these difficulties is turning out to be insoluble. Here we report on improvements of the Gatan 666 parallel detection electron spectrometer in the areas of increasing the dynamic range of the detector, and in eliminating stray reflections.The increase in the dynamic range of the detector was needed especially for low energy losses (high spectral intensities), which usually saturated the detector even at the minimum acquisition time of 12 msecs. Accordingly, we have developed an electron attenuator which uses a magnetic dipole to sweep the spectrum across the detector perpendicular to the dispersion direction (Fig. 1).