Zinc selenide can be e-beam evaporated with a tantalum or molybdenum crucible liner. However, thermal evaporation is more commonly used for depositing optical films because stoichiometric films are easier to obtain with this method.
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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 the power. With an evaporation temperature of ~900°C, we anticipate a deposition rate of 10-15 angstroms per second. 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.
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Due to its high vapor pressure at low temperatures, zinc selenide is typically evaporated in a dedicated vacuum chamber.
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:1. An Edmund Optics Zinc Selenide (ZnSe) meniscus lens (NT63-265) is shown below. ZnSe has a high refractive index and can be used when a short focal length is needed. Also, ZnSe is transparent from visible to long-wave infrared (IR) wavelengths, so this material is often used for IR applications. This lens is listed as having a diameter of 1/2 inch (12.7 mm) and an effective focal length of 1/2 inches (12.7 mm). The lens parameters are: R1 = 10.79 mm R2 = 22.96 mm t=2.70 mm (center thickness) n=2. at 1 = 2.94 um LAYOUT SAT MAR 14 TOTAL AXIAL LENGTH: 13. MM ZMAX_C 1). ZMX CONFIGURATION 1 OF 1 a) Use the lens maker's equation to find an estimate of the focal length b) Use the paraxial ray tracing approach to trace a parallel ray through this lens. Assume the initial ray has a height of 5 mm. Find the distance behind the second surface where the ray crosses the axis. This distance is known as the back focal distance. c) Trace a ray from an object point on-axis that is 50 mm from the front surface of the lens. Find the distance behind the second surface where the image is formed.
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