Single crystals of benzil, benzil aniline, and salicylidene-aniline have been successfully grown using a modified Bridgman-Stockbarger technique for three different crystal-growth systems. The unique feature of the Bridgman- Stockbarger technique is that the crystal-melt surface can be viewed from any direction, and the temperature between the hot and cold zones can be adjusted at any time during the melt.

First, scientists at NASA's Marshall Space Flight Center in Huntsville, Alabama, and Alabama A & M University, Normal, Alabama, designed and fabricated the melt-growth system using two immiscible liquids. In this crystal-growth system, two zones were made up of immiscible liquids, water, and silicone oil. These two liquids were contained in a right circular glass cylinder. Each zone was individually heated and stirred for temperature uniformity within the zone, and the temperature of each zone was controlled by a PID controller to within ±0.1 °C.

The Bridgman-Stockbarger melt-growth system uses two immiscible liquids.

The organic material was placed in a clean glass ampoule and lowered slowly from the hotter zone to the cooler zone. Lowering speeds of less than 0.2 millimeters per hour were required to grow good-quality crystals. This system was limited to temperatures of 85 °C or less since one of the zones contained water. Crystals of nonlinear optical material salicylidene-aniline were grown using this system.

To extend the temperature range, a second system was constructed using aluminum end plates and glass walls to contain the heated fluids. Glass cylinders 4 in. (10 cm) in diameter were cut and polished at both ends. An O-ring groove was cut into each end plate and filled with a silicone two-part adhesive. Two separate zones were stacked, one on top of the other. The temperature of each zone was controlled separately by circulating constant-temperature silicone oil using Neslab high-temperature circulating baths.

Also, in this crystal-growth system, a glass conical-tip ampoule was used as a crucible. A conventional crystal-pulling- and-rotation system was used to lower the ampoule through the zones.

Over the last three years, a variety of organic nonlinear crystals have been grown using this melt-growth system.

Finally, an all-glass melt-growth system was used for larger diameter bulk single crystals. To alleviate the problem of clear visualization of the growth interface, an all-glass melt-growth system was designed and fabricated in Alabama A & M University's glass-blowing shop.

This system again uses a two-zone system, but was constructed to allow for the growth of larger diameter (25 mm) organic crystals. The temperature was controlled by Neslab constant-temperature baths by circulating silicone oil. A commercial crystal-pulling system was used to lower the ampoule through the zones.

This work was done by M.D. Aggarwal, W.S. Wang, J. Choi, and Robert Metzl of Alabama A & M University of Normal, Alabama, and Benjamin G. Penn and Donald O. Frazier of Marshall Space Flight Center. Inquiries concerning rights for the commercial use of this invention should be addressed to

the Patent Councel, Marshall Space Flight Center (256) 544-0258

Refer to MFS-26439.

Photonics Tech Briefs Magazine

This article first appeared in the October, 1998 issue of Photonics Tech Briefs Magazine.

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