A new method of X-ray emission spectroscopy called soft X-ray emission spectroscopy (SXES) has been developed for both SEM and EPMA[1]. Recently we found that SEM/EPMA-SXES using variable low voltage analysis provides the depth chemical state information and we report its application.
For example, in the case of beryllium metal, using the equation of X-ray diffusion by Anderson-Hasler range, we estimated the X-ray range of Be-K emission from 0.2 KeV to 7 KeV. Especially from 0.2 to 1 KeV, it is found that the diffusion range is very small from singles of nm to 33 nm. At the 7 KeV, that is approximately 900 nm.
In practice, the surface of beryllium metal is quickly oxidized. The spectra of Be-K emission of beryllium metal at 1, 2 and 5 kV are compared. The Be-K peak profile at 5kV is a very typical strong sharp peak. However, at 1 kV, it is very weak and the main peak loses the sharpness. Moreover, it has a sub-peak at the lower energy of 90 eV which is influenced by the molecular orbital produced by beryllium and oxygen. At 2kV, the intermediate mixture peak profile between those at 1kV and 5kV can be observed. From the estimation of calculation and the examned results, the surface of 33 nm at 1kV is oxidized beryllium, the surface of 100 nm at 2kV is a mixture of metallic and oxidized beryllium, and the surface of 500 nm at 5kV is dominant of metallic beryllium.
We are continuing the effort to accumulate the SXE spectra of different multilayer materials. Without cutting the cross-section, we can investigate the layer structures by SXES with variable lower accelerating voltages to observe the chemical state difference at different depths.