When analyzing samples for analytical work in the SEM or for surface analysis the stubs used are nearly all made from aluminum and sometimes brass. This is fine for many applications if the sample is large enough and can be mounted directly on the stub. However, for small samples, powders, particles in solutions and fibers the finish and the material of the stub can interfere with imaging or X-ray analysis. Our graphite discs consists of high purity, soft spectral grade carbon. This material is softer and is less strong than the vitreous carbon materials. When handled with care they are still an excellent substrate for SEM imaging and X-ray micro-analysis. The carbon discs exhibit a low contribution for BSE imaging and a pure background with only the contribution of carbon for EDX and/or WDX analysis. The standard finish of our graphite discs are not as smooth as the vitreous carbon discs. Carbon discs are also more porous and more hydrophobic than vitreous carbon discs.
Carbon-Graphite Discs prevent interference.
To prevent interference of the stub surface you can place a carbon-graphite disc between the stub and the specimen and mount the specimen directly on these discs. Both discs varieties (also called planchets) form a protective shield.
Differences between vitreous carbon discs and carbon (graphite) discs.
There are some differences between vitreous carbon and graphite discs. Vitreous carbon is superior in hardness, surface finish, mechanical and chemical stability but it is more expensive than carbon discs. The table below will give guidance to which material is best for the application at hand. Generally speaking, vitreous carbon is the better choice, but for less demanding applications carbon (graphite) discs will do just fine.
V= Best O= Medium X= Not Recommended
Surface finish of graphite discs
The standard ground finish of our graphite discs on one side is 0.80μm. The finish can be easily improved by lapping the discs on fine 10um grinding or lapping paper with water as lubricant. It should be noted that the surface roughness of the soft graphite material can be improved to 0.05μm or better.
Purity, handling and sizes of graphite discs
The high purity carbon used for the carbon planchets or discs only has impurities of less than 2ppm with 1ppm or less for each single element. The impurities can be B, Mg, Al, Si, Ca or Fe.The sizes available are 10, 12.7, 25.4 and 32mm diameters, all with a thickness of 1.6mm. These 4 sizes can be used on all popular SEM stubs and mounts. Since the material is relatively soft, we strongly suggest to glue the planchets on SEM stubs or mounts with a conductive carbon or silver glue. We would like to discourage the use of SEM stubs fully made of carbon; the material is soft so the pin can easily break off and during handling the soft carbon can easily shed material which can potentially cause contamination. Carbon discs glued on SEM stubs combine the advantages of the low contributing carbon background, low costs, easy handling and storage with the sturdy aluminum base. When the top of the specimen stub is completely covered by the graphite discs there is no imaging or analytical contribution of the supporting