Crystal growth
Let us think about the natural formation of crystals. On the earth's surface there are all kinds of atoms – they are continually moved around, mixed by wind, water, volcanic actions etc. Yet somehow one Si atoms find another Si atoms and find oxygen atoms to form silica. Na atoms find Cl atoms and gradually build up NaCl crystal, adding one atom at a time.
How does it happen that once a crystal growth process begins it only allows a particular type of atom to join on it? It happens because the whole system is working towards the lowest possible energy. A growing crystal will allow a new atom to join if only it is going to make the total energy of the system as low as possible. But how does it know that it will be the minimum energy. Well in nature, it happens by trial and error method. Let's say Na and Cl atoms are forming crystal from its water solution. In liquid, all the atoms are in perpetual motion. Each atom bounces against its neighbors about times every second. So if a right atoms goes to a right place the probability of jumping off is somewhat lower. By continually testing over periods of years or millions of year at a frequency of tests per second, eventually they grow into a big crystal.
Depending on the constituent materials, and their melting behavior, there are several crystal growth methods employed in laboratories.
We will discuss about three different crystal growth methods.
- Flux method or high temperature solution growth method
- Bridgman method
- Czochralski method