Sputter Coating
Definition
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, biological, fibre, dried biological) so that the primary electron beam does not charge up the surface and destroy the image. The coating is what lets you image a paint chip, a human hair or a polyester fibre in a conventional SEM.
- Process type
- Vacuum-deposition technique
- Coating thickness
- 2 to 10 nanometers (gold-palladium); up to 15 nanometers depending on metal
- Common metals
- Gold, gold-palladium, carbon
- Primary purpose
- Prevents charge accumulation on non-conductive samples during electron microscopy
Common questions
Why do non-conductive samples need sputter coating in SEM?+
When a primary electron beam hits a non-conductive sample, electrons accumulate on the surface and create static charge that distorts or destroys the image. Sputter coating applies a thin conductive layer (gold, gold-palladium, or carbon) that allows charge to dissipate, so you get a clear image of materials like polymers, hair, or fibre without the static noise.
How thick is a sputter coating layer?+
The coating is very thin, in the range of a few nanometers. Gold-palladium coatings are typically 2 to 10 nm; gold coatings can run up to 15 nm. The exact thickness depends on the metal used and the level of detail required. Either way, the layer is conductive enough to prevent charge buildup without obscuring the fine surface features of the sample.
What metals are used for sputter coating?+
The most common coatings are gold, gold-palladium alloy, or carbon. Gold-palladium is popular because it provides good conductivity while keeping the coating very thin. The choice depends on the sample type and what level of detail the microscopy needs to reveal.
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...
- 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...
- 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...
- 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...
- 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...
- Environmental SEM (ESEM)
- Variant of conventional SEM that runs the sample chamber at higher pressure (up to several torr of water vapour) instead of the...
- 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;...
- 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...
- Ultramicrotome
- A precision instrument for cutting sections of resin-embedded specimens to 60-100 nm thickness using a diamond knife, enabling TEM examination of the...
Explained in these topics
- Electron Microscopy: SEM, TEM and EDSA thin-film deposition process that deposits a conductive metal layer (typically gold-palladium, 2-10 nm) on a non-conductive specimen surface to prevent charg...
- Scanning Electron Microscopy (SEM) with EDXRFVacuum-deposition technique that lays a thin (5 to 15 nm) conductive layer of gold, gold-palladium or carbon onto a non-conductive sample (polymer, biological,...