Lattice constants are fundamental parameters of a given crystal structure. The structure consists of the net and the basis. The net defines the geometric relationship amoung the lattice contants. Example nets are simple cubic, face centered cubic, hexagonal, and tetragonal. The basis is the set of constituent units that are placed at equivalent points in the net. The basis may be atoms, as in BCC Fe, or it may be entire molecules, as in protein crystal structures. The basis sets the dimensions of the lattice constants. By example, both Ni and Pt have an FCC net but their lattice constants a have different sizes.

We can strain the lattice and change the dimensions of the constants. Stretch or compress a single crystal rod along one of its directions to do this. Alternatively we can induce a change in basis. Heat BCC Fe from room temperature and it will eventually transform to FCC Fe in an allotropic phase transformation.

Thin films are just bulk materials with a macroscopic constraint on their physical size and shape. Sometimes, that constraint causes strain in the lattice, so the parameters are not the same as the bulk even though the net is the same. Sometimes the macroscopic constraint induces a change in crystal structure. The net is therefore entirely different than in the bulk. Finally, sometimes the macroscopic constraint on shape in a thin film causes the microstructure to change. The thin film may have more or differently-sized grains or voids.

We cause or induce the changes in crystal structure by how we prepare or process the film. Temperature, mechanical stress, and electric field are examples of system parameters that we can control during the preparation and processing.

Dear Hiba,

the crystal phase and thus the lattice constants a, b, c ( as well and the appropriate angles) depends on

i) the atoms involved in the formation process,

ii) the kind of manufacturing process and

iii) on the manufacturing conditions ( e.g.  temperature, partial pressure(s), etc.)

This holds for bulk material as well as for films/ thin films and  multilayer film.

Crystallinity of the material (bulk, film or stack of films) also depends on points  i) to  iii) as well as on the treatment after finishing the manufacturing.

But there  no relation between the magnitude of the lattice constants themselves and the degree of crystallinity.

Lattice constants are fundamental parameters of a given crystal structure. The structure consists of the net and the basis. The net defines the geometric relationship amoung the lattice contants. Example nets are simple cubic, face centered cubic, hexagonal, and tetragonal. The basis is the set of constituent units that are placed at equivalent points in the net. The basis may be atoms, as in BCC Fe, or it may be entire molecules, as in protein crystal structures. The basis sets the dimensions of the lattice constants. By example, both Ni and Pt have an FCC net but their lattice constants a have different sizes.

We can strain the lattice and change the dimensions of the constants. Stretch or compress a single crystal rod along one of its directions to do this. Alternatively we can induce a change in basis. Heat BCC Fe from room temperature and it will eventually transform to FCC Fe in an allotropic phase transformation.

Thin films are just bulk materials with a macroscopic constraint on their physical size and shape. Sometimes, that constraint causes strain in the lattice, so the parameters are not the same as the bulk even though the net is the same. Sometimes the macroscopic constraint induces a change in crystal structure. The net is therefore entirely different than in the bulk. Finally, sometimes the macroscopic constraint on shape in a thin film causes the microstructure to change. The thin film may have more or differently-sized grains or voids.

We cause or induce the changes in crystal structure by how we prepare or process the film. Temperature, mechanical stress, and electric field are examples of system parameters that we can control during the preparation and processing.