Current Status of Sapphire Technology For Window And Dome Applications

The properties of sapphire make it an ideal choice for future high speed missile applications compared to other existing or emerging materials. High fabrication cost and low material utilization from a sapphire boule cause high costs for sapphire domes. Significant improvements have been made by growing sapphire boules with orientation and contour slicing. A more desirable approach is to produce near net-shaped sapphire blanks directly from the melt. The feasibility of producing crack-free near net-shaped blanks with controlled inside and outside curvature from the melt in orientation has been demonstrated using the Heat Exchanger Method (HEM).

Semiconducting β‐FeSi2 films grown on‐oriented Si and on(11¯02)‐sapphire substrates are investigated by x‐ray diffraction, Nomarski optical microscopy, stress, and surface roughness measurements. As a result of an exothermic, nucleation controlled reaction, we observe a characteristic ring‐shaped surface pattern of the silicide. Surface roughness and stress in β‐FeSi2 are less pronounced for films grown at lower temperatures and cooling rates. Sapphire substrates result in smoother surfaces than Si due to the match of the thermal expansion coefficient of sapphire to the silicides.


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