- 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.
- 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.