PhotoMetrics, Inc.
15801 Graham St.
Huntington Beach CA 92649
(714) 895-4465
Fax (714) 893-4682

e-mail: lab@photometrics.net

Wavelength Dispersive X-Ray Spectrometry (WDS)

WDS identifies the elemental composition of materials imaged in the SEM with an order of magnitude better spectral resolution, sensitivity and ability to determine concentratins 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

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.