Alumina Coated Sources

The advantage of Alumina coated evaporation sources over uncoated sources is good heat transfer and the inertness of Aluminium Oxide (alumina) with most metals. The alumina coating is non-porous and withstands temperature cycles without chipping. Also, molten evaporant does not wet the alumina surface but coalesces into a sphere and forms a point source, resulting in no resistant change. Alumina coated evaporation sources have longer life compared to the uncoated sources. The power requirements of such sources are 30 to 50% above those of comparable uncoated sources since the contact between the resistance-heated metal and the evaporant is reduced by the alumina coating. The alumina is semiconductor grade and is applied to the boat or basket by plasma-spray processes. Maximum operating temperatures of 1850 to 1900^oC degrees C are possible but should be avoided, and when evaporation is effected the power should be reduced slightly to avoid over heating.

The S35B, S38B, S42B and S45B Series Tungsten and Molybdenum Boats with alumina barriers have the benefit of a refractory metal boat and a ceramic barrier. The exposed metal area in the bottom of the boat allows the evaporant to be in good thermal contact with the source. The alumina barrier will inhibit the evaporant from creeping toward the heat sink or from wetting the entire boat.

Please visit the individual material pages for evaporation source recommendations. Click here to go to the Materials Division Page.

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