Seed Crystals and High Pressure

We would like to show you some examples of our work to give you an idea of the varied nature of our business.

Everything starts in our crystal growth hall:
Here we work with custom-built furnaces, mainly using the Bridgman-Stockbarger (named after Percy Williams Bridgman and Donald C. Stockbarger) is a technique used for the production of large single crystals, like fluorides, silicon or gallium arsenide. A crucible filled with raw material powder is inserted into a furnace with different temperature zones. The raw material melts in the hotter part of the furnace. Crystallisation begins when the molten raw material is transferred into a cooler section of the oven. The seed crystals which are oriented along the axis of the crucible grow the fastest. To accelerate this process we use specially shaped crucibles. and Nacken-Kyropoulos (named after Richard Nacken and Spyro Kyropoulos) is a technique for the production of single crystals, like alkali halides or sapphires. A cooled rod is inserted into the melt for the crystal to grow on. At the beginning a polycrystalline region is formed at the rod but by reduction of the diameter of the grown material during pulling, single crystalline growth is afforded. Nowadays single crystal seeds are used. techniques. Using the Stockbarger process a melting crucible filled with raw material powder is inserted into a custom built furnace with different temperature zones. The raw material melts in the hotter part of the furnace before being transferred into a cooler section, which begins the crystallisation process from the seed crystal outwards. Using the Kyropoulos process the crucible is not transferred between different temperatures zones, but remains at a constant temperature. A cooled rod is inserted into the melt for the crystal to grow on. The crystal is extracted from the crucible after crystallisation by lowering the smelting temperature.

A lot of experience is needed to grow crystal as the physical processes involved will only yield high quality results under optimum conditions: every part of the process from the temperature adjustments to the speed of development of the crystal has to be just right.

In addition, the crystallisation process takes place in a  vacuum over the course of several weeks – and must not be interrupted at any cost!

Thanks to 60 years’ of experience we rarely encounter any problems – but the quality of the raw crystal cannot be judged by the naked eye - which brings us to the next step in the process: Quality Control of the blanks.

> 2: MATERIAL QUALITY CONTROL