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.