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Ytterbium Fluoride YbF3 Evaporation Process Notes

Ytterbium fluoride is an inorganic chemical compound with a chemical composition of YbF3. It is white and crystalline in appearance with a melting point of 1,157°C and a vapor pressure of 10-4 Torr at ~800°C. Users of ytterbium fluoride will utilize it in place of thorium fluoride (ThF4) which is radioactive. It is evaporated under vacuum for the production of IR lasers and filters.

Ytterbium Fluoride YbF3 Specifications

Material TypeYtterbium Fluoride
Color/AppearanceWhite, Crystalline Solid
Melting Point (°C)1,157
Theoretical Density (g/cc)8.2
Thermal Evaporation Techniques Boat:  Mo
E-Beam Crucible Liner MaterialTantalum, Molybdenum
Temp. (°C) for Given Vap. Press. (Torr) 10-4:  ~800


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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