SEM EDX extends optical analysis

Correlative Microscopy Extended Analysis Filter and Particle Traps PSE Operation Modes Spectra and Databases

SEM EDX vs. Optical Analysis

Particles not (or nearly not) detectable in optical analysis can be found by SEM analysis and subsequent EDX spectra analysis.


NaCl (Salt) optical image: Particle is not detectable in VDA 19.1 - ISO 16232 frame	NaCl (Salt) SEM image

SEM image can look quite different than optical image and can reveal much information

Optical image	SEM image


Corundum optical image	Corundum SEM image

Critical components (glass, abrasive materials) cannot be detected with optical methods

Optical image (glass fiber)	SEM image (glass fiber)

One cannot compare particle counts of optical and SEM methods:
These two detection princples "see" particles different.

Material	Optical detection	SEM detection
Organic (fiber)	good	bad
Graphite	good	bad
Corundum	bad	very good
Glass	not at all	very good
Salts	bad	very good

SEM-EDX versus LIBS (Laser Induced Breakdown Spectroscopy)

Optical microscopes with LIBS option can analyze only particles found in optical analysis.

SEM EDX versus LIBS, Pros and Cons

	LIBS	SEM-EDX
Velocity	Fast	Slow (needs vacuum)
Material depth	100 µm	1-2 µm
Particles	Only particles visible in optical microscope	All particles with elements > Boron
Repeatabilty	No (particle is destroyed)	Yes (EDX analysis is non destructive)
Detection size	Only particles > 10 µm (laser spot size)	< 1µm

SEM EDX versus XRF (X Ray Flourescence Spectroscopy)

Originally XRF is used for bulk material analysis, because X-Rays cannot be focussed very good.
For cleanliness/contamination analysis sometimes the technology is called Hybrid XRF, because also image analysis will be used to identify contamination particles.

First step: detection of particles.

Current X-Ray resolution cannot go below 20µm/pixel. Detectable particle size is limited.

Light elements will generate only faint shadows, heavy elements will generate black spots.

Next step: spectrum analysis of particles

For application where heavy elements (Fe, Cu…) of sizes > 20µm have to be found in large bulk areas, Hybrid XRF is ideal.

Due to limited spacial resolution, smaller particles and particle structures are not detectable.