Single crystal

A single crystal or mono-crystal is a macroscopic crystal whose components (atoms, ions or molecules) form a continuous uniform, homogeneous crystal lattice. This distinguishes single crystals of polycrystalline aggregates, twinned crystals or amorphous substances.

Chemical classification

We can separate single crystals according to their chemical structure into three groups:

Application to the analysis

The crystal structure analysis for the elucidation of molecular structures is now a standard method of chemistry and biochemistry. However, this is the crystallization of the molecules requirement, which can be very difficult especially in biological molecules. Ideally, the test is performed on a single crystal. Sometimes this is impossible because not enough large single crystals of a substance are available. Nowadays, it is possible even to evaluate the diffraction pattern of the crystal powder in a crystal structure, but this is lost due to the superposition of the diffraction maxima of information, so that the results are of lesser quality. But even consuming cultured crystals do not have lattice defects.

Mechanical Technical Application

In the technique, single crystals are used because of their reproducible properties. Since they have almost no grain boundaries or other structural defects, for example, increases the mechanical strength of the material. For example, turbine blades from a single-crystal nickel-based alloy can be manufactured. In this case, the single crystals have a uniform orientation of the lattice structure, although they can have multiple phases.

Single crystal surfaces and two-dimensional crystals

Also, the surfaces of inorganic single crystals are monocrystalline. They can be understood as a two-dimensional crystal, if one considers only the top layer, and are the subject of research in the field of surface chemistry and physics. Low-index single-crystal surfaces are eg Si (111 ), Ag (100) or Au ( 110). On these surfaces the atoms are arranged on a flat terraces and are interrupted by usually monoatomic steps. Putting a single layer of organic molecules on single crystal surfaces, one usually obtains self- assembled monolayers at low coverage. This only one molecular layer of highly organic layers can be described analogous to inorganic single crystal surfaces as two-dimensional crystals. As with single crystals composed of atoms, the molecules are highly ordered here. Graph, a detached layer of carbon atoms, is also a two-dimensional crystal.