Due to the development of semiconductor detectors with high spatial resolution -- e.g. charge coupled devices (CCDs) or photodiode arrays (PDAs) -- the parallel detection of electron energy loss spectra (EELS) has become an important alternative to serial registration. Using parallel detection for recording of energy spectroscopic large angle convergent beam patterns (LACBPs) special selected scattering vectors and small detection apertures lead to very low intensities. Therefore the very sensitive direct irradiation of a cooled linear PDA instead of the common combination of scintillator, fibre optic, and semiconductor has been investigated. In order to obtain a sufficient energy resolution the spectra are optionally magnified by a quadrupole-lens system.The detector used is a Hamamatsu S2304-512Q linear PDA with 512 diodes and removed quartz-glas window. The sensor size is 13 μm ∗ 2.5 mm with an element spacing of 25 μm. Along with the dispersion of 3.5 μm/eV at 40 keV the maximum energy resolution is limited to about 7 eV, so that a magnification system should be attached for experiments requiring a better resolution.
In an earlier paper1 it was found that to a good
approximation, the efficiency of collection of electrons that had lost
energy due to an inner shell excitation could be written as
where σE was the total excitation cross-section and
σE(θ, Δ) was the integral cross-section for
scattering within an angle θ and with an energy loss up to an energy Δ from
the excitation edge, EE. We then obtained:
where , with P being the momentum
of the incident electron of velocity v. The parameter r was due to the
assumption that d2σ/dEdΩ∞E−r for
energy loss E. In reference 1 it was assumed that r was a constant.
Electron energy loss spectroscopy of core-electron excitation in anisotropic systems: Magic angle, magic orientation, and dichroism