Crystal growth

Crystal growth, is the process where a pre-existing crystal becomes larger as more molecules or ions add in their positions in the crystal lattice or a solution is developed into a crystal and further growth is processed. A crystal is defined as being atoms, molecules, or ions arranged in an orderly repeating pattern, a crystal lattice, extending in all three spatial dimensions. So crystal growth differs from growth of a liquid droplet in that during growth the molecules or ions must fall into the correct lattice positions in order for a well-ordered crystal to grow. The schematic shows a very simple example of a crystal with a simple cubic lattice growing by the addition of one additional molecule. Crystal growth, is the process where a pre-existing crystal becomes larger as more molecules or ions add in their positions in the crystal lattice or a solution is developed into a crystal and further growth is processed. A crystal is defined as being atoms, molecules, or ions arranged in an orderly repeating pattern, a crystal lattice, extending in all three spatial dimensions. So crystal growth differs from growth of a liquid droplet in that during growth the molecules or ions must fall into the correct lattice positions in order for a well-ordered crystal to grow. The schematic shows a very simple example of a crystal with a simple cubic lattice growing by the addition of one additional molecule. When the molecules or ions fall into the positions different from those in a perfect crystal lattice, crystal defects are formed. Typically, the molecules or ions in a crystal lattice are trapped in the sense that they cannot move from their positions, and so crystal growth is often irreversible, as once the molecules or ions have fallen into place in the growing lattice, they are fixed in place. Crystallization is a common process, both in industry and in the natural world, and crystallization is typically understood as consisting of two processes. If there is no pre-existing crystal, then a new crystal must nucleate, and then this crystal must undergo crystal growth. The interface between a crystal and its vapor can be molecularly sharp at temperatures well below the melting point. An ideal crystalline surface grows by the spreading of single layers, or equivalently, by the lateral advance of the growth steps bounding the layers. For perceptible growth rates, this mechanism requires a finite driving force (or degree of supercooling) in order to lower the nucleation barrier sufficiently for nucleation to occur by means of thermal fluctuations. In the theory of crystal growth from the melt, Burton and Cabrera have distinguished between two major mechanisms: