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Cobalt Co Notes


Cobalt (Co) General Information

Cobalt is one of the most widely recognized metals in the world. It has a density of 8.9 g/cc, a melting point of 1,495°C, and a vapor pressure of 10-4 Torr at 1,200°C It is a lustrous, hard metal that is gray in appearance and characteristically ferromagnetic. One of its most popular uses is as a blue pigment found in paint, jewelry, and glass. It is often alloyed with other metals to make engine parts and cutting tools. Its two main vacuum applications are as a ferromagnetic layer in the production of magnetic storage media and as a transitional layer in battery fabrication.

Cobalt Co Specifications

Material TypeCobalt †
SymbolCo
Atomic Weight58.933195
Atomic Number27
Color/AppearanceLustrous, Metallic, Grayish Tinge
Thermal Conductivity100 W/m.K
Melting Point (°C)1,495
Coefficient of Thermal Expansion13.0 x 10-6/K
Theoretical Density (g/cc)8.9
SputterDC
Max Power Density
(Watts/Square Inch)
80*
FerromagneticMagnetic Material
Z Ratio0.343
E-BeamExcellent
Thermal Evaporation Techniques Boat:  W, Nb
Basket:  W
Crucible:  Al2O3
E-Beam Crucible Liner MaterialDirect in Hearth
Temp. (°C) for Given Vap. Press. (Torr) 10-8:  850
10-6:  990
10-4:  1,200
CommentsAlloys with W/Ta/Mo.

† Magnetic material (requires special sputter source).

* This is a recommendation based on our experience running these materials in KJLC guns. The ratings are based on unbonded targets and are material specific. Bonded targets should be run at lower powers to prevent bonding failures. Bonded targets should be run at 20 Watts/Square Inch or lower, depending on the material.

Z-Factors

Empirical Determination of Z-Factor

Unfortunately, Z Factor and Shear Modulus are not readily available for many materials. In this case, the Z-Factor can also be determined empirically using the following method:

  • Deposit material until Crystal Life is near 50%, or near the end of life, whichever is sooner.
  • Place a new substrate adjacent to the used quartz sensor.
  • Set QCM Density to the calibrated value; Tooling to 100%
  • Zero thickness
  • Deposit approximately 1000 to 5000 A of material on the substrate.
  • Use a profilometer or interferometer to measure the actual substrate film thickness.
  • Adjust the Z Factor of the instrument until the correct thickness reading is shown.

Another alternative is to change crystals frequently and ignore the error. The graph below shows the % Error in Rate/Thickness from using the wrong Z Factor. For a crystal with 90% life, the error is negligible for even large errors in the programmed versus actual Z Factor.

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