Lattice matched single crystal substrates result in the epitaxial growth of materials. This is due to the less strain in the crystal, thereby exhibiting the material in a low energy state. On the contrary, the polycrystalline substrates lead to the random growth of the material.
What are the main reasons behind the non-epitaxial growth of the material on a polycrystalline and no lattice-matched substrate? How the nucleation and growth proceed on such substrates. I am only considering the substrate effect (nucleating sites) and not the other deposition parameters.
Thanks.
Dear Chandan, first of all I agree with the answer given by Dr Nolze. However, I think that your ideas about the phenomenon we call "epitaxy" are not adequate to give a complete understanding of this complex geometrical-physical property arising whe two crystalline materials come in contact. To improve the quality of your knowledge on these topics, I would like to suggest the following papers: 1) I.V. Markov, Crystal Growth for beginners, Worrld Scientific, 1995 2) - R. Kern, G. Le Lay, J.J. Métois "Basic Mechanisms in the early stages of the Epitaxy" in : Current Topics in Materials Science, vol. 3 Ed. E, Kaldis, pg 131-419, North Holland 1979 All the best ! Dino
Epitaxy only happens if the translation symmetry along the surface is comparable for both phases. Therefore, epitaxy is the exception and not the rule since practically all phases have different lattice parameters and do not match at all. Thus, ideal epitaxy is nearly excluded. In semiconductor industry one uses doping to adjust lattice parameters in order to get a better or nearly perfect match. But this has very strong limitations. Epitaxy is also a 2D effect, i.e. the translation symmetry has to match only for this specific surface orientation. If a cubic phase grows on a hexagonal substrate it typically means: (111) paralle to (0001). the smmetry plays an important role. Theoretically, you could also selct another surface plane, e.g. the two-fold axis of the lattice, which might match to the cubic (110) or even (001) if the c/a ratio of the hexagonal phase is very special.
In 3D epitaxy is called topotaxy and practically means the same. The translation lattices have to match now in 3D. This does not mean a match of 1:1, but somtimes e.g. also 1:3 works (i.e. a huge cell with a lattice parameter 3-times bigger matches to the length of three unit cells of the other phase).
If such geometric relationships do not exist a crystal starts to grow and simply uses any surface position as nucleous. This also happens during epitaxy, but since all newly formed crystals have the same orientation you can somtimes only find small angle boundaries if they grow together. For perfect crystals even they disappear. However, if they don't have any correlation to the substrate grain they grow randomly and thus a polycrystalline material forms despite even an expensive single-crystalline substrate orientation.
Dear Chandan, first of all I agree with the answer given by Dr Nolze. However, I think that your ideas about the phenomenon we call "epitaxy" are not adequate to give a complete understanding of this complex geometrical-physical property arising whe two crystalline materials come in contact. To improve the quality of your knowledge on these topics, I would like to suggest the following papers: 1) I.V. Markov, Crystal Growth for beginners, Worrld Scientific, 1995 2) - R. Kern, G. Le Lay, J.J. Métois "Basic Mechanisms in the early stages of the Epitaxy" in : Current Topics in Materials Science, vol. 3 Ed. E, Kaldis, pg 131-419, North Holland 1979 All the best ! Dino
Thanks Prof. Dino for your answer. I have gone through Markov's article and several others. Still, the adequate reasons need to be explored.
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