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Silicon wafers with 100nm of silver coating

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Carbon 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.

Looking for sputtering targets? Please see metal sputtering targets

 

Vitreous carbon discs

Carbon (graphite) discs/plates

Smooth surface

V

X

Hard surface

V

X

Easy to clean and re-use

V

O

SE imaging

V

X

BSE imaging

V

V

X-ray microanalysis

V

V

Spectral Analysis

V

O

Aqueous Solutions

V

X

Pricing

O

V

High purity

V

V

Conductivity

V

V

Packaging

Each

Packs of 10 / or 5

V= Best         O= Medium       X= Not Recommended

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 gases 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.

Physical properties of HG grade vitreous carbon

Maximum temperature (vacuum or inert gas),ºC

3000

Density, g/cm3

1.42

Hardness, Vickers, HV

230

Permeability coefficient, cm2/s

10-9

Open porosity, %

0

Young’s Modulus, GPa

35

Compressive strength, Gpa

0.48

Flexural strength, Gpa

0.26

Thermal conductivity (30ºC) W/km

6.3

Electrical Resistance (30ºC), Ωµm

45

Thermal Expansion Coefficient (20-200ºC), /K

2.6×10-6
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