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Zinc Selenide ZnSe Evaporation Process Notes

Zinc selenide is a chemical compound with a chemical formula of ZnSe. It is yellow to red in appearance with a melting point of >1,100°C, a density of 5.42 g/cc, and a vapor pressure of 10-4 Torr at 660°C. Zinc selenide is heavily used as an infrared optical material. It is evaporated under vacuum for infrared optical coatings, more specifically, night vision optical coatings.

Zinc Selenide ZnSe Specifications

Material TypeZinc Selenide
Color/AppearanceYellow to Red, Crystalline Solid
Melting Point (°C)>1,100
Theoretical Density (g/cc)5.42
Type of BondIndium, Elastomer
Z Ratio0.722
Thermal Evaporation Techniques Boat:  Ta, W, Mo
Coil:  W, Mo
Basket:  W, Mo
Crucible:  Q
E-Beam Crucible Liner MaterialTantalum, Molybdenum
Temp. (°C) for Given Vap. Press. (Torr) 10-4:  660
UN Number 3283
CommentsPreheat gently to outgas. Evaporates well.


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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