Environmental SEM (ESEM)
Definition
Variant of conventional SEM that runs the sample chamber at higher pressure (up to several torr of water vapour) instead of the standard 10^-5 torr vacuum. Allows imaging of hydrated, oily or volatile samples without dehydration, including some biological tissues and uncoated polymer surfaces. The trade-off is reduced resolution and reduced EDS performance because of beam scattering in the gas.
- Chamber pressure
- Up to several torr, versus 10^-5 torr in conventional SEM
- Advantage
- Images hydrated, oily, or volatile samples uncoated
- Trade-off
- Reduced resolution and weaker EDS performance
Common questions
Why would an examiner choose ESEM over conventional SEM despite the resolution loss?+
Conventional SEM requires a high vacuum and often a conductive coating, which can dehydrate or alter delicate biological tissue or volatile trace material. ESEM avoids that by running at higher chamber pressure, preserving the sample's native state for imaging.
Does ESEM avoid the need for elemental analysis trade-offs entirely?+
No. Gas molecules in the chamber scatter the electron beam, which degrades the X-ray signal used for EDS elemental mapping, so an examiner accepts a real trade-off between preserving the sample and getting the sharpest elemental data.
Related terms
- ASTM E1588
- ASTM International standard practice for gunshot residue analysis by scanning electron microscopy with energy-dispersive spectrometry. Defines particle classification (characteristic, consistent-with, indicative), morphology...
- Back-Scattered Electron (BSE)
- High-energy electron from the primary beam that has bounced elastically off a nucleus and exited the sample. BSE yield increases with atomic...
- EDS / EDXRF Detector
- Silicon-drift detector mounted at a fixed take-off angle to the sample that reads characteristic X-rays emitted as the primary beam ionises atoms...
- Secondary Electron (SE)
- Low-energy electron (below 50 eV) ejected from the top few nanometres of the sample when the primary beam knocks a loosely bound...
- Sputter Coating
- Vacuum-deposition technique that lays a thin (5 to 15 nm) conductive layer of gold, gold-palladium or carbon onto a non-conductive sample (polymer,...