FourierRatio Method for EELS Deconvolution  Practical Electron Microscopy and Database   An Online Book  

Microanalysis  EM Book http://www.globalsino.com/EM/  


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In general, if the TEM specimen is too thick (t/λ > 0.4), a deconvolution process must be employed to remove the effect of plural scattering, since the increase of plural scattering intensity in the higher energy region of an ionization edge can cause some artifacts: In this case, in order to deconvolute the coreloss spectrum, the Fourierratio method is applied. In this method, simply speaking, a spectrum is first backgroundsubtracted by fitting the preedge backgrounds with the powerlaw function and then deconvoluted by the Fourierratio method. The deconvolution procedure is then: In the Fourierratio method, the coreloss intensity that has been redistributed to higher energyloss by plural inelastic scattering has been brought back into the signal integration window Δ by deconvolution, I_{c}(β, Δ), is equivalent to I_{t}I^{1}_{c}(β, Δ)/I_{0}. [2] Here, I^{1}_{c} is its single scattering component. Such had been done with a program in FORTRAN. [1] Different from Fourierlog method, Fourierratio method is normally used when only limited spectral data is available. However, in most cases, recording lowloss and coreloss spectra under the same conditions is extremely challenging, since the acquisiton time required for a good SNR (signal to noise ratio) in the coreloss spectrum is usually not short enough to avoid saturation of the signal from the ZLP (zeroloss peak). Therefore, in practice, it is necessary to sacrifice the SNR in the coreloss signal, or utilize a spectrometer system that has an ultrafast electrostatic shutter installed.
[1] Kaikee Wong and R.F. Egerton, Correction for the effects of elastic scattering in coreloss quantification, Journal of Microscopy, Vol. 178, Pt 3, June 1995, pp. 198207.


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