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Quantitative Analysis Using LaB6 as an Example

Lanthanum hexaboride (LaB6) provides a very illustrative example for quantitative EDS analysis in S/TEM, since it contains two extremes, a very light element (B) and a heavy element (La). LaB6 can be used to show the performance of Bruker's XFlash® detectors and the Cliff-Lorimer quantification routine.

The quantification test of an unknown sample part begins with element identification. Elements to be quantified can be defined by automated or interactive routines. Element lines in the spectrum originating from stray radiation (e.g. Cu from the sample holder) or contamination (e.g. carbon) can be assigned for deconvolution only. Thus the respective signal can be used for line deconvolution but is not taken into account for the determination of the element concentration in the specimen. The next step is background subtraction. A special physical bremsstrahlung model is provided for perfect fit of background. The third step is peak deconvolution. Several different fit models are available for optimum peak separation. Finally, quantification is completed using theoretical or calibrated Cliff-Lorimer (CL) factors.

A LaB6 standard (turquoise spectrum in the image gallery) can be used to calibrate the Cliff-Lorimer factors experimentally.

The results using theoretical CL factors already show the excellent performance of Bruker's Cliff-Lorimer quantification. They are very close to the expected composition of 14.29 at.% and 85.71 at.% for La and B, as the tables in the image gallery show. Also, the outcome using the La K series for quantification instead of the L-series shows that the QUANTAX system is well suited for spectra acquisition and also quantification beyond 20 keV line energy up to 80 keV as well.

Spectrum of the LaB6 standard used for Cliff-Lorimer factor calibration. The low energy region appears with high channel width since the measurement was carried out up to 80 keV.
The low energy range of the experimental LaB6 spectrum with smaller channel width. This way we can measure only up to 10keV, but with higher energy resolution.
The high energy region of the spectrum with the channel width as shown before for 80 keV measurement range.
Quantification result as expected, correct for both, using the La-K as well as the La-L-Line series.