quantitative analysis

Quantitative analysis means to measure the concentrations of each constituent elements of a specimen from the energy or wavelength of characteristic X-rays emitted from the specimen. The method to measure the energy is termed EDS (Energy Dispersive X-ray Spectroscopy) and the method to measure the wavelength is termed WDS (Wavelength Dispersive X-ray Spectroscopy).

Normally, when performing quantitative analysis of a certain element (element A) using EDS or WDS, a standard specimen is used, in which the concentration of element A is known.

First, the relative intensity (ratio) of the characteristic X-ray intensity of element A in an unknown specimen to that of the standard specimen is obtained. Next, the obtained relative intensity is multiplied by the concentration of element A in the standard specimen. Then, the concentration of element A in the unknown specimen is determined by multiplying by a correction factor that corrects the difference in the characteristic X-ray intensities from the standard specimen and the unknown specimen. Here, methods that obtain the correction factor are called quantitative correction, including ZAF correction and Phi-Rho-Z method (φ(ρz) method).

EDS has a function that can perform quantitative analysis without using a standard specimen, and is called standard-less quantitative (simple quantitative or semi-quantitative) analysis. In this method, the same quantitative analysis procedure as mentioned above is automatically performed using the X-ray intensity data acquired in advance from many standard specimens. Since the method requires no measurement of the standard specimens for analysis of each element, the quantitative analysis is performed easily and rapidly. However, the accuracy of quantitative correction may deteriorate if the elemental composition of an unknown specimen is not close to the composition of a standard specimen. For better quantitative analysis, the analysis that uses the standard specimens is needed.

It is noted that the quantitative analysis assumes that the element distribution is uniform in the X-ray generation region, the specimen surface is flat, and the incident electron beam is normal to the specimen surface.

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