Scanning Microscopy


A new type of photodiode array (PDA) which allows the individual access of single diodes is used to record energy loss electrons directly without electron photon conversion.

The detector is part of an electron energy loss parallel detection system which consists of a sector field spectrometer and a quadrupole lens system to magnify the spectra electron-optically.

The parallel detector is a new random access PDA (RAPDA) which allows the individual access of single diodes. Therefore, different parts of the spectrum with dramatically different electron rates (zero loss peak, plasmon loss, ionization edges) can be recorded, each with optimum acquisition time and number of read-outs. This method allows the use of all available information in one recording of a spectrum for an increased intensity range compared to self-scanning PD As (SSPDAs) where all the diodes have to be read out in a row.

Direct illumination of the diodes increases the sensitivity of the detector by two orders of magnitude for 40 keV electrons compared to detectors with electron photon conversion. No apparent radiation damage of the diodes was observed if the detector was cooled down to temperatures below -80°C.

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