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Aluminum Al Notes


Aluminum (Al) General Information

Aluminum is one of the most common metals in the world. It can be found in kitchen utensils, cars, street lights, and the popular aluminum foil food packaging. Aluminum is a silvery-white, metallic material. It is light, malleable, ductile, and non-magnetic under normal conditions. It has a density of 2.7 g/cc, a melting point of 660°C, and a vapor pressure of 10-4 Torr at 1,010°C. Although it is not a strong material, it is a good conductor of heat and electricity and is able to form an oxide layer that is resistant to corrosion. Due to its high reactivity, it is rarely found in nature as a free element. When evaporated in a vacuum, aluminum layers form a reflective coating found on telescopes, automotive headlamps, mirrors, packages, and toys. It is widely used in the aerospace, automotive lighting, OLED, and optical industries.

Aluminum Al Specifications

Material TypeAluminum
SymbolAl
Atomic Weight26.9815386
Atomic Number13
Color/AppearanceSilvery, Metallic
Thermal Conductivity235 W/m.K
Melting Point (°C)660
Coefficient of Thermal Expansion23.1 x 10-6/K
Theoretical Density (g/cc)2.7
SputterDC
Max Power Density
(Watts/Square Inch)
150*
Type of BondIndium, Elastomer
Z Ratio1.08
E-BeamExcellent
Thermal Evaporation Techniques Basket:  W
Crucible:  TiB2-BN, BN
E-Beam Crucible Liner MaterialFABMATE®, Intermetallic
Temp. (°C) for Given Vap. Press. (Torr) 10-8:  677
10-6:  821
10-4:  1,010
CommentsAlloys W/Mo/Ta. Flash evap or use BN crucible.

* 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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