Parallel detection electron spectrometer using quadrupole lenses

• Published in: Ultramicroscopy Vol. 22; no. 1; pp. 103 - 115
• Main Authors: Krivanek, O.L., Ahn, C.C., Keeney, R.B.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 1987
• ISSN: 0304-3991; 1879-2723
• DOI: 10.1016/0304-3991(87)90054-4

The design and performance of a parallel detection electron energy loss spectrometer utilizing several new design elements are described. The system uses three electromagnetic quadrupole lenses to transform the electron energy spectrum produced by a single magnetic sector spectrometer into a magnified spectrum suitable for parallel detection, and detects the spectrum with a single-crystal YAG scintillator, which is fiber-optically coupled to either a 512-channel or a 1024-channel photodiode detector. The photodiode is interfaced to a computer via direct memory access, and it is possible to read out entire spectra in 6.1 ms. The photodiode is cooled to -30°C, and the noise due to the dark current only begins to limit the detector performance for integration times longer than 100 s. The system is capable of achieving detective quantum efficiencies higher than 0.25 over eight decades of electron intensities of interest to EELS carried out in a transmission electron microscope. The optimum operation of the system is described and the theoretical limits of the system performance are discussed. Examples of results from several standard EELS test specimens are given, and the most probable future uses for parallel detection are briefly described.