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Magnesium Mg Notes


Magnesium (Mg) General Information

Magnesium is a grey-white, alkaline earth metal with a melting point of 649°C, a density of 1.74 g/cc, and a vapor pressure of 10-4 Torr at 327°C. It is extremely flammable, especially in powder form, and fires are difficult to extinguish. Magnesium is also an essential element to life. Magnesium is responsible for regulating nerve function, blood pressure, and the levels of nutrients in the human body. It is extensively used in the production of aircraft, engine casings, laptops, cell phones, and cameras. Magnesium and its alloys are evaporated under vacuum for the development of magnetic storage media, optical storage media, and semiconductors.

Magnesium Mg Specifications

Material TypeMagnesium
SymbolMg
Atomic Weight24.305
Atomic Number12
Color/AppearanceSilvery White, Metallic
Thermal Conductivity160 W/m.K
Melting Point (°C)649
Coefficient of Thermal Expansion8.2 x 10-6/K
Theoretical Density (g/cc)1.74
SputterDC
Max Power Density
(Watts/Square Inch)
35*
Type of BondIndium, Elastomer
Z Ratio1.61
E-BeamGood
Thermal Evaporation Techniques Boat:  W, Mo, Ta, Cb
Coil:  W
Basket:  W
Crucible:  Al2O3
E-Beam Crucible Liner MaterialFABMATE®, Graphite, Tungsten
Temp. (°C) for Given Vap. Press. (Torr) 10-8:  185
10-6:  247
10-4:  327
UN Number 1869
CommentsExtremely high rates possible.

* 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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