Zinc Sulfide (ZnS) Pieces Evaporation Materials

Zinc Sulfide (ZnS) Pieces Overview

We sell these pellets and pieces by unit weight for evaporation use in deposition processes. These approximate materials prices are published to provide budgetary guidelines. Actual prices can vary and may be higher or lower, as determined by availability and market fluctuations. To speak to someone directly about current pricing, please click here .

Zinc Sulfide (ZnS) General Information

Zinc sulfide is an inorganic chemical compound with a chemical formula of ZnS. It is white in appearance with a melting point of 1,700°C, a density of 3.98 g/cc, and a vapor pressure of 10^-4 Torr at ~800°C. It is often used as a phosphor and can emit various colors depending on the element introduced as an activator. It is evaporated under vacuum for infrared optical coatings, more specifically, night vision optical coatings.

Zinc Sulfide (ZnS) Specifications

**** Suggestion based on previous experience but could vary by process. Contact local KJLC Sales Manager for further information

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.

Thermal Evaporation of Zinc Sulfide (ZnS)

We recommend thermally evaporating zinc sulfide from a tantalum boat such as our EVS8B005TA. A tantalum baffle box like our EVSSO22 may also be used. Thermal evaporation is more commonly used for depositing optical films because stoichiometric films are easier to obtain using this method.

Pressure should be monitored to ensure outgassing is at an acceptable level before increasing power. With an evaporation temperature of ~800°C and a base pressure of 10^-6 Torr, we anticipate a deposition rate of 10-15 angstroms per second. It is important to note that zinc sulfide decomposes at the source and recombines at the substrate only if the substrate temperature is adequate and nucleation occurs.

Due to the high vapor pressures of both zinc and sulfur at low temperatures, zinc sulfide is usually deposited in a dedicated vacuum chamber.

E-beam Evaporation of Zinc Sulfide (ZnS)

Zinc sulfide can be e-beam evaporated from a tantalum or molybdenum crucible liner. However, thermal evaporation is more commonly used for depositing optical films because stoichiometric films are easier to obtain using this method.

We recommend to sweep the e-beam at low power to uniformly melt the material and avoid hole drilling. Evaporating at a low e-beam power will also help to avoid material dissociation. Pressure should be monitored to ensure outgassing is at an acceptable level before increasing power. With an evaporation temperature of ~800°C, we anticipate a deposition rate of 10-15 angstroms per second. It is important to note that zinc sulfide decomposes at the source and recombines at the substrate only if the substrate temperature is adequate and nucleation occurs. Substrate surface cleaning is required for good adhesion. Yttrium oxide (Y₂O₃), hafnium oxide (HfO₂), or fluorides can be used as a thin adhesion layer if necessary.

Another key process note is to consider the fill volume in the e-beam application because we find that the melt level of a material in the crucible directly affects the success of the crucible liner. Overfilling the crucible will cause the material to spill over and create an electrical short between the liner and the hearth. The outcome is cracking in the crucible. This is the most common cause of crucible liner failure. Placing too little material in the crucible or evaporating too much material before refilling can be detrimental to the process as well. When the melt level is below 30%, the e-beam is likely to strike the bottom or walls of the crucible which immediately results in breakage. Our recommendation is to fill the crucible between 2/3 and 3/4 full to prevent these difficulties.

Crucible liners should be stored in a cool, dry place and always handled with gloves or forceps.

Due to the high vapor pressures of both zinc and sulfur at low temperatures, zinc sulfide is usually deposited in a dedicated vacuum chamber.