Practical Electron Microscopy and Database

The typical energy resolution for EDS is of on the order of 150 eV. This is suffcient in most cases for resolving peaks of different elements, but is inadequate for detecting chemical shifts of the atoms which are of the order of a few electronvolts. EDS is thus mainly used for composition analysis.

For low-energy EDS measurements of heavy elements in bulk materials, the spatial resolution can be enhanced if the X-ray lines of a proper low-excitation energy are used. With an accelerating voltage of 5 kV, the K line is available only for atomic numbers below 20, above which L lines is needed, and M lines must be used for atomic numbers above 42. This application of low energy X-ray lines sacrifice the efficiency of X-ray generation and is subject to chemical bonding effects.

EDS is a more challenging task compared to other techniques like Electron Energy Loss Spectroscopy (EELS) or X-ray Photoelectron Spectroscopy (XPS). EDS is primarily used for elemental analysis by detecting characteristic X-rays emitted from a specimen when it is bombarded with an electron beam. These X-rays correspond to specific energy levels associated with different elements, allowing for qualitative and quantitative analysis of the material's composition.

However, detecting chemical shifts with EDS is not straightforward due to the relatively broad energy resolution of EDS detectors, typically in the range of 100-200 eV. This resolution is often insufficient to resolve the small shifts in X-ray energies that result from changes in the chemical environment of an atom, such as variations in oxidation states or bonding configurations. While these chemical shifts are present, they are usually too small to be distinguished from the main peak with standard EDS equipment.

In some advanced cases, EDS can detect slight shifts in the peak positions or changes in the shape of X-ray emission lines, which might indicate different chemical states or environments of the same element. For example, variations in the Lα or Kα line positions might be observed for elements like iron or titanium in different oxidation states, but these shifts are subtle and often require careful calibration and high-resolution detectors.

Overall, while EDS is highly effective for elemental identification and mapping, its capability to detect chemical shifts is limited. For detailed chemical state analysis, techniques with higher energy resolution, such as EELS, XPS, or Wavelength-Dispersive X-ray Spectroscopy (WDS), are generally preferred.