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Gold Au Notes


Gold (Au) General Information

Gold is one of the most valuable and sought-after metals in the world. Since its discovery during ancient times, it has been utilized as jewelry, coins, and tools. Still, in today's economy, its most popular use is as jewelry. Gold is one of the more beautiful precious metals with a lustrous, yellow sheen. It has a melting point of 1,064°C, a density of 19.3 g/cc, and a vapor pressure of 10-4 Torr at 1,132°C with its ideal evaporation temperature being around 1,400°C. It is soft, dense, malleable, ductile, and an excellent conductor of heat and electricity. Deposited films of gold are used as layers in the production of semiconductors, sensors, batteries, and data storage.

Gold Au Specifications

Material TypeGold
SymbolAu
Atomic Weight196.966569
Atomic Number79
Color/AppearanceGold, Metallic
Thermal Conductivity320 W/m.K
Melting Point (°C)1,064
Coefficient of Thermal Expansion14.2 x 10-6/K
Theoretical Density (g/cc)19.32
SputterDC
Max Power Density
(Watts/Square Inch)
100*
Type of BondIndium, Elastomer
Z Ratio0.381
E-BeamExcellent
Thermal Evaporation Techniques Boat:  W*** Mo*** W
Crucible:  Al2O3, BN
E-Beam Crucible Liner MaterialFABMATE®, Molybdenum
Temp. (°C) for Given Vap. Press. (Torr) 10-8:  807
10-6:  947
10-4:  1,132
CommentsFilms soft; not very adherent.

*** Alumina Coated.

* 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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