Epitaxy metal substrate

Non-epitaxial electrodeposition occurs when the substrate is a semiconductor. The metallic deposit cannot form strong bonds with the substrate lattice, and the stability conferred by co-ordination across the interface would be much less than that lost by straining the lattices. The case is the converse of the metal-metal interface the stable arrangement is that in which each lattice maintains its equilibrium spacing, and there is consequently no epitaxy. The bonding between the met lic lattice of the electrodeposit and the ionic or covalent lattice of the substrate arises only from secondary or van der Waals forces. The force of adhesion is not more than a tenth of that to a metal substrate, and may be much less. 

Epitaxial effects are not limited to single-crystalline substrates. The possibility for substrate-induced epitaxial development in the difficult case of ZnSe (cf. conventional electrodeposition) has been established also by using strongly textured, albeit polycrystalline, zinc blende (111) CdSe electrolytic films to sustain monolithic growth of ZnSe in typical acidic selenite baths [16]. Investigation of the structural relations in this all-electrodeposited ZnSe/CdSe bilayer revealed that more than 30-fold intensification of the (111) ZnSe XRD orientation can be obtained on the textured (111) CdSe films, compared to polycrystalline metal substrates (Fig. 4.2). The inherent problems of deposition from the Se(IV) bath, i.e., formation of... 

Epitaxial metal deposition — In an epitaxial deposition the crystal lattice of the substrate is continued in the deposit. In homoepitaxy the substrate and the growing film... 

X-ray and electron diffraction techniques have been used to obtain the data on epitaxy. X-ray diffraction methods are particularly useful for thick oxide films and have the advantage of giving diffraction patterns from both the oxide film and the metal suhstrate. For oxide films less than several hundred Angstroms thick, electron diffraction techniques are necessary in most cases, hi general, an electron diffraction pattern is not obtained from the metal substrate unless the oxide film is extremely thin, the surface is only partially covered with oxide, or the metal surface is rough. Reflection type diffraction techniques have been used with bulk specimens and transmission techniques with thin specimens and stripped oxide films from bulk metal specimens. Bach technique has its special advantages and limitations, but these will not be discussed here. 

The adherence of the oxide to the metal substrate may be related to the epitaxial relationships of the oxide-metal system. Bardolle (53) showed that die adherence of the oxide diminished with the multiplication of the epitaxial possibilities. Thus on iron the oxide was less adherent on the Oil and 113 faces than on the 001 faces. The authors observed that when a copper single crystal sphere was heated in oxygen at a high temperature until a thick oxide scale formed on the high rate faces, the oxide cracked and flaked off easily on these faces but adhered tightly on the low rate faces. In this case the high rate faces show the greatest number of possible orientations, whereas the low rate faces show only one orientation. It should be noted that Bardolle s observations indicated that the faces with multiple orientations on iron were slow rate faces. 

It is of some interest to consider the situation where one of the ideahzed 2D systems that have been addressed can be followed in a layer-by-layer growth mode from a strictly 2D plane to one that is more 3D like. Such is the situation in the formation of multilayer molecular films adsorbed to uniform substrates or where epitaxial metal or soft matter growth is realized in chemical vapor deposition, molecular beam epitaxy or polymeric deposition systems. The hneshape discussion above has to be modified to account for the development of the third dimension of order in the system. Conceptually this is rather straightforward. Instead of considering, as Warren did, an ideal 2D reciprocal lattice composed of an ordered array of uniform rods, the reciprocal lattice for an idealized multilayer (e.g., two to five individual layers) system is characterized by... 

In general, clusters of atoms on a native metal substrate are formed with epitaxial orientation. For this case, the contact interface energy, cy in eq. (4.5) vanishes, and the surface of the substrate has the same composition and atomic structure as the deposited cluster, so that cTsub = ory. Hence,... 

For STM and many other surface-science techniques, conductive samples are needed. However, many oxides with perfect stoichiometry are insulators. This problem has been addressed by studying thin oxide films grown on metal singlecrystal substrates. Epitaxial, thin oxide films can be grown for the right choice of metal substrates, which exhibit surfaces with structures similar to those for bulk oxide samples. 

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