[1] P.E. Batson, High Resolution
Electron Energy Loss Spectrometer for the Scanning Transmission Electron
Microscope, Rev. Sci. Inst. 57, 43-48 (1986). [2] P.E. Batson, Parallel
Detection for High Resolution Electron Energy Loss Studies in the Scanning
Transmission Electron Microscope, Rev. Sci. Inst. 59, 1132-1138 (1988). [3]
P.E. Batson, High
Resolution Spectrometer Coupling to the Sub-Angstrom IBM STEM, in Microscopy and Microanalysis, edited by
D. Piston, J. Bruley, I.M. Anderson, P. Kotula, G. Solorzano, A. Lockey, and S. McKernan
(Cambridge University Press, Cambridge, 2003), pp. 836 -837.
The EELS spectrometer is a Wien Filter type
mounted within a high voltage electrode.[1,2] The filter is designed for a center pass
energy of 100-200 eV, giving it a very high energy
dispersion -- of order mm/eV. This center pass
energy is defined by a very accurate 15-1200V scanning power supply which is in
turn connected to the microscope high voltage. This design is capable of about
60 meV energy resolution at a collection half angle
of 10 mR at the specimen, and a center pass energy
definition of better than 20 meV. In the figure below, I show a design intended to optimize the
spectrometer for operation with the aberration corrected probe.[3] The Wien Filter has
a first order focus in the energy dispersive direction, but does not modify the
electron paths in the perpendicular direction.
Therefore we use a combination of a cylindrical lens and a weak quadrupole to produce focusing in the energy dispersive
direction and to maintain a narrow beam in the spectrometer in the other
direction. This design suggests that a
15 meV resolution should be possible using 15 mR collection
half angle at the specimen.
