The chemical composition of a sample can be determined using x-ray analysis.
This is done by collecting and analysing the characteristic x-rays that are emitted by the sample during electron bombardment.
X-rays can be detected using either Energy Dispersive Spectroscopy (EDS) or Wavelength Dispersive Spectroscopy (WDS) techniques.
X-ray Generation
When an electron from a K-shell is replaced by one from the next closest shell (L), the energy released is designated as a Kα x-ray.
When an electron from a K-shell is replaced by one from the second closest shell (M), the energy released is designated as a Kβ x-ray.
Each shell has a different energy level and as an electron drops shells the excess energy is released as a photon (γ) which is the x-ray.
These events cause a unique energy release and can be detected in the SEM using an energy-dispersive spectroscopy (EDS) detector.
Varying Accelerating Potential
Decreasing the accelerating potential of the electron beam will reduce the interaction volume
This decrease will increase the resolution of chemical analysis
However, some x-rays may not be detected by standard EDS detectors and specialist EDS detectors may be needed, like a windowless detector
Increasing the accelerating potential of the electron beam will increase the interaction volume
This increase will decrease the resolution, however, it will enable analysis of structures deeper into the sample, i.e. printed circuit board below a protective polymeric coating.
