Backscattered Electron (BSE) Imaging
Definition
An SEM imaging mode sensitive to atomic number and crystallographic texture; can reveal grain-boundary elongation patterns in the sub-surface cold-worked zone after surface obliteration.
- Primary use in forensics
- Restoring obliterated serial numbers and examining multilayer materials like paint cross-sections
- Sensitivity metric
- Z-contrast: signal intensity is proportional to mean atomic number of the material
- Reveals subsurface structures
- Can detect cold-worked grain-boundary patterns beneath surface damage
Common questions
What does BSE imaging show that regular electron microscopy doesn't?+
BSE imaging is sensitive to atomic number (Z-contrast). Elements with heavier atoms appear brighter, which lets you see differences in composition that secondary electron microscopy can't reveal. This makes it especially useful for spotting paint layers with different element-rich compositions or detecting surface alterations on metal.
How can BSE imaging help restore erased serial numbers?+
When a serial number is ground or filed away, the surface metal gets cold-worked and the grain boundaries become elongated in the subsurface zone. BSE imaging detects these grain-boundary patterns in the cold-worked layer beneath the obliteration, revealing the original number even though the surface is gone.
What's the relationship between brightness and composition in BSE images?+
Signal intensity is proportional to mean atomic number. Heavy-element-rich layers appear bright, while light-element layers appear dark. This Z-contrast property is what makes BSE so powerful for examining layered samples like paint chips, where different pigments contain different elements.
Related terms
- ASTM E2885-13
- ASTM International standard practice for restoration of obliterated vehicle identification numbers; the reference protocol for VIN casework in US and internationally aligned...
- ASTM E2937
- ASTM International standard guide for identification of paint binders by pyrolysis-GC-MS; specifies pyrolysis conditions, GC column, oven program, and diagnostic ion reporting.
- ATR (Attenuated Total Reflectance)
- An FTIR sampling mode in which the sample is pressed against a diamond or ZnSe crystal and the evanescent wave probes the...
- Cold-Working Stress Field
- Residual plastic deformation and elevated dislocation density in a metal lattice created by stamping; persists below the visible surface even after surface...
- Davis Reagent
- Variant etchant for steel using cupric ammonium chloride (Cu(NH4)2Cl4) in dilute HCl. Slower acting than Fry's, sometimes preferred when contrast on Fry's...
- Electrolytic Etching
- Electrochemical alternative to chemical etchants. The part is the anode in an electrolyte bath; controlled current selectively dissolves the strained metal at...
- ENFSI EPG Protocol
- European Network of Forensic Science Institutes Expert Working Group on Paint protocol; the European standard for paint comparison examination sequence and reporting.
- Fry's Reagent
- Classical etchant for plain carbon and low-alloy steel: 40 g cupric chloride (CuCl2) + 90 mL concentrated HCl + 100 mL water....
- FTIR Microspectroscopy
- Fourier-transform infrared spectroscopy collected from a microscope-focused spot of 10-20 µm diameter; the primary technique for paint binder characterisation.
- INTERPOL iARMS
- INTERPOL's Illicit Arms Records and tracing Management System. Multilateral database enabling law enforcement in INTERPOL member countries to trace recovered or seized...
- IRUG Database
- Infrared and Raman Users Group spectral database; covers historic pigments, artists' materials, and museum-object coatings. Primary reference for art-investigation paint analysis.
- Likelihood Ratio Reporting
- A Bayesian framework for reporting paint-comparison conclusions, expressing the probability of the observed data given the hypothesis of common source versus the...
Explained in these topics
- Paint Layer Examination: Cross-Section, FTIR and Py-GC-MSSEM imaging mode where signal intensity is proportional to mean atomic number (Z-contrast); heavy-element-rich layers appear bright.
- Restoration of Erased Serial NumbersAn SEM imaging mode sensitive to atomic number and crystallographic texture; can reveal grain-boundary elongation patterns in the sub-surface cold-worked zone...