Special offer - Delivery now £4.99 when ordered onlineVitreous carbon discs and graphite discs and plates
Standard SEM stubs are nearly all made from aluminium and sometimes brass which can be undesirable for X-ray analysis and other imaging methods. For small specimens, powders, fibres and particles in solution the finish of the stub and the material of the stub can also interfere with imaging and analysis. In such cases a carbon disc with a high quality surface finish can be used to mount the specimen being analysed.
Carbon (graphite) or vitreous carbon discs from Micro to Nano can be placed between the stub and the specimen to form a protective shield and prevent interference from the aluminium stub surface.
Vitreous carbon is superior in hardness, surface finish, mechanical and chemical stability. The table below shows which materials are best for which application. Generally speaking, vitreous carbon is the better choice, but for less demanding applications carbon (graphite) discs/plates can be used.
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Smooth surface |
V |
X |
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Hard surface |
V |
X |
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Easy to clean and re-use |
V |
O |
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SE imaging |
V |
X |
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BSE imaging |
V |
V |
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X-ray microanalysis |
V |
V |
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Spectral Analysis |
V |
O |
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Aqueous Solutions |
V |
X |
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Pricing |
O |
V |
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High purity |
V |
V |
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Conductivity |
V |
V |
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Packaging |
Each |
Packs of 10 / or 5 |
V= Best O= Medium X= Not Recommended
Please click here for specifications and physical properties
Vitreous carbon, glassy carbon or glass-like carbon has many applications in research, science, metallurgy and chemical analysis. For microscopy related techniques this material has a number of desirable properties which makes it an ideal substrate material:
- Vitreous carbon combines the glassy, ceramic properties of carbon with those of graphite
- It is a conductive material
- It is a high purity, hard, non-porous, corrosion resistant material
- It is impermeable to gasses and/or liquids
- Has good thermal stability and great resistance against thermal shock
- Smooth surface
- Less hydrophobic than graphite
For microscopy and analytical applications it is important to know that the smooth surface gives rise to low electron signals, both secondary electrons (SE) and backscattered electrons (BSE). The high purity carbon material contributes only C to the X-ray spectrum which makes vitreous carbon ideal for EDX and WDX investigations of small specimens, powders, particulates, and fibres. Vitreous carbon is less hydrophobic than graphite and is more suitable for preparing particles in aqueous solution where that solution will spread more evenly over the surface.
Surface finish of vitreous carbon discs
Micro to Nano vitreous carbon discs are lapped on one side to provide a smooth surface, typically 0.05-0.01μm. They can be used many times after cleaning and lapping. For lapping we suggest using either diamond lapping film with water or a SiC-in-water suspension.
Purity, handling and sizes of the vitreous carbon discs
High purity vitreous carbon material has less than 30ppm impurities in total. Typical impurities for vitreous carbon can be:
- Ca 10ppm
- Si 14ppm
- Al, Fe, K, Na, Ni and Sn all less than 1ppm
- Ba, Be, Bi, Cd, Co , Cr, Cu, Mg, Mo, Sr, Ti, V, W, Zn and Zr all less than 0.1ppm
The sizes available are: 10, 12.7, 19.0 25.0 and 32mm diameters which fit onto the most popular pin stubs and cylinder mounts. The discs have a thickness or either 2 or 3mm and can be easily handled. For SEM applications we suggest using a strong conductive carbon glue (preferable) or silver glue to mount the vitreous carbon discs onto SEM stubs.
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Physical properties of HG grade vitreous carbon |
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Maximum temperature (vacuum or inert gas),ºC |
3000 |
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Density, g/cm3 |
1.42 |
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Hardness, Vickers, HV |
230 |
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Permeability coefficient, cm2/s |
10-9 |
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Open porosity, % |
0 |
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Young's Modulus, GPa |
35 |
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Compressive strength, Gpa |
0.48 |
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Flexural strength, Gpa |
0.26 |
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Thermal conductivity (30ºC) W/km |
6.3 |
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Electrical Resistance (30ºC), Ωµm |
45 |
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Thermal Expansion Coefficient (20-200ºC), /K |
2.6x10-6 |
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 High Purity Vitreous Carbon disc 10.0 x 2.0mm (each) |
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High Purity Vitreous Carbon disc 12.7 x 2.0mm (each) |
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High Purity Vitreous Carbon Plancets / Disc 19.0 x 2.0mm (each) |
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High Purity Vitreous Carbon Planchet / Disc 25.0 x 3.0mm (each) |
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High Purity Vitreous Carbon Planchet / Disc 32.0 x 3.0mm (each) |
Carbon (Graphite) discs / plates
please click here for specifications and physical properties
Graphite planchettes or discs consists of high purity, graphitized, soft spectral grade carbon. This material is softer and less strong than vitreous carbon materials but when handled with care it is still an excellent substrate for SEM imaging and X-ray micro-analysis. 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 is not as smooth as with the vitreous carbon discs and is visible in SE imaging. Carbon discs are also more porous and more hydrophobic than vitreous carbon discs.
Surface finish of graphite discs
The standard ground finish 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 - 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 planchettes or discs 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.
Sizes available are 10, 12.7, 25.4 and 32mm diameters, all with a thickness of 1.6mm. These four sizes can be used on all popular SEM stubs and mounts. Since the material is relatively soft, we strongly suggest glueing the planchettes onto SEM stubs or mounts with a conductive carbon or silver glue. We would discourage the use of SEM stubs fully made of carbon - the material is soft and the pin can easily break off and during handling, plus soft carbon can easily shed material which can potentially cause contamination. Carbon discs glued onto SEM stubs combine the advantages of the low contributing carbon background, low costs, easy handling and storage with a sturdy aluminium base. When the top of the specimen stub is completely covered by the graphite discs there is no imaging or analytical contribution from the supporting SEM stub.
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Physical properties of spectral grade high purity carbon |
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Density, g/cm3 |
1.6 |
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Hardness, Shore |
33 |
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Porosity, % |
29 |
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Young's modulus, Mpa |
22 |
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Compressive strength, Mpa |
48 |
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Flexural strength, Mpa |
27 |
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Electrical resistance, Ωμm |
65 |
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Thermal expansion, /K |
1.9 x 10-6 |
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 High Purity Graphite disc, 10.0 x1.6mm (pack of 10) |
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High Purity Graphite discs 12.7 x1.6mm (pkg/10) |
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High Purity Graphite Planchet or Disc, 25.4 x1.6mm (pkg/10) |
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High Purity Graphite discs 32.0 x1.6mm (pack of 10) |
Carbon (graphite) plates
Graphite plates are useful as a larger specimen support or if the sample needs to be shielded against X-ray or backscattered electron signals originating from the SEM stage. The surface finish of graphite plates is less fine than graphite planchets - the plates are cut from thicker plates to reduce thickness and weight. Made from high purity graphite material, they are available in sizes 50 x 50 x 1mm,100 x 50 x 2mm and 100 x 100 x2mm. For increased mechanical stability graphite plates can be mounted metal substrates. Graphite plates are sold in packs of five.
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 High Purity Graphite Plate, 50 x 50 x 1mm (pkg/5) |
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 High Purity Graphite Plate, 100 x 50 x 2mm (pkg/5) |
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 High Purity Graphite Plate, 100 x 100 x 2mm (pkg/5) |