Ultramicrotome
Definition
A precision instrument for cutting sections of resin-embedded specimens to 60-100 nm thickness using a diamond knife, enabling TEM examination of the cross-sectional ultrastructure of fibres, paint layers, and biological samples.
- Cutting thickness
- 60-100 nm
- Blade
- Diamond knife
- Sample prep
- Resin-embedded specimens
- Downstream use
- TEM cross-sectional examination
Common questions
Why must sections be cut so thin before TEM examination?+
A transmission electron microscope forms its image from electrons passing through the specimen, so sections thicker than roughly 100 nm scatter or absorb too many electrons to produce a usable image, making ultrathin sectioning a prerequisite rather than a refinement.
What forensic materials commonly go through ultramicrotome sectioning?+
Paint chip cross-sections, textile fibres, and some biological tissue samples are embedded in resin and ultrathin-sectioned so their internal layer structure or ultrastructure can be examined under TEM, revealing detail not visible by light microscopy or SEM surface imaging alone.
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...
- Characteristic X-Ray
- An X-ray photon emitted when an outer-shell electron drops into an inner-shell vacancy created by ionisation. Energy is set by the difference...
- Energy-Dispersive X-Ray Spectroscopy (EDS)
- An X-ray detection method that simultaneously measures the energies of all characteristic X-ray photons emitted from the interaction volume, identifying all elements...
- FIB (Focused Ion Beam)
- A technique using a focused gallium ion beam to mill a specimen at a specific site-selected location, producing a TEM-quality cross-section with...
- Interaction Volume
- The pear-shaped region of specimen material within which the primary electron beam deposits energy and generates signals. At 20 kV in a...
- Lead-Free GSR
- Gunshot residue produced by ammunition using non-lead primer formulations (SINTOX, Diazol, or other variants). Does not contain the conventional Pb-Sb-Ba three-element combination;...
- 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...
- Silicon Drift Detector (SDD)
- The current standard EDS detector type, using a reverse-biased silicon chip cooled by a Peltier element to achieve high count-rate capability (up...
- 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,...
- ZAF Correction
- A software correction applied to raw EDS X-ray intensities to account for atomic number (Z), absorption (A), and fluorescence (F) effects within...