Wavelength Dispersive Spectrometry (WDS)
WDS identifies the elemental composition of materials imaged in the
Electron
Microscope with an
order of magnitude better spectral resolution, sensitivity and ability to
determine concentrations of light elements than is achievable with
EDS. Most elements are
detected below 0.1% and some as low as a few ppm.
Applications include
 | Identification of spectrally overlapped elements, such as
| S in the presence of Pb or Mo |
| W or Ta in Si, or N in Ti |
| Br in Al, common in semiconductor device failure |
|
| Detection of low concentration species (down to 100 or even
10 ppm)
| P or S in metals |
| Contaminants in precious metal catalysts |
| Trace heavy metal contamination |
| Performance-degrading impurities in high temperature solder alloys |
|
| Analysis of low atomic number elements
| Composition of advanced ceramics and composites |
| B in BPSG films (sensitivity to 2000 ppm) |
| Oxidation and corrosion of metals |
| Characterization of biomedical and organically modified materials |
| Characterization of polymers with respect to fillers and
contaminants |
|
Principle of Operation
The characteristic X-ray photons excited by the electron beam are sorted
using a diffracting crystal, whose angular placement relative to the sample
and photodetector is a unique measure of their wavelengths. As with EDS, the
resulting spectral distribution is automatically compared with those from
actual standards or synthetic X-ray fluorescence spectra of material
formulations.
WDS vs. EDS
X-ray microanalysis in the scanning electron microscope is accomplished
using EDS and/or WDS. EDS is more commonly applied due to its simplicity and
speed, while WDS offers an important and often critical refinement
of EDS data by providing
| Analysis for light elements with at least an order of magnitude higher
sensitivity than available (ultrathin X-ray window) EDS instruments |
| Resolution of severely overlapped spectrum peaks for improved element
specificity |
| Lowered detection limits over the entire periodic table |
| More accurate quantitative analyses. |
|
