Crystalline films deposition

Another recently discovered form of epitaxy is graphoepitaxy (Geis et al. 1979). Here a non-crystalline substrate (often the heat-resistant polymer polyi-mide, with or without a very thin metallic coating) is scored with grooves or pyramidal depressions the crystalline film deposited on such a substrate can have a sharp texture induced by the geometrical patterns. More recently, this has been tried out as an inexpensive way (because there is no need for a monocrystalline substrate) of preparing oriented ZnS films for electroluminescent devices (Kanata et al. 1988). 

The epitaxy reactor is a specialized variant of the tubular reactor in which gas-phase precursors are produced and transported to a heated surface where thin crystalline films and gaseous by-products are produced by further reaction on the surface. Similar to this chemical vapor deposition (CVE)) are physical vapor depositions (PVE)) and molecular beam generated deposits. Reactor details are critical to assuring uniform, impurity-free deposits and numerous designs have evolved (Fig. 22) (89). 

The nature of the deposit and the rate of nucleation at the very beginning of the deposition are affected, among other factors, by the nature of the substrate. A specific case is that of epitaxy where the structure of the substrate essentially controls the structure of the deposit.Plb lP ] Epitaxy can be defined as the growth of a crystalline film on a crystalline substrate, with the substrate acting as a seed crystal. When both substrate and deposit are of the same material (for instance silicon on silicon) or when their crystalline structures (lattice parameters) are identical or close, the phenomena is known as homoepitaxy. When the lattice parameters are different, it is heteroepitaxy. Epitaxial growth cannot occur if these stmctural differences are too great. 

Crystalline films of TiB2 obtained by CVD are used at lower temperatures as protective coatings. The interaction of these films with various substrates is studied" and desirable properties of the substrate in cases when the coating is deposited according to Eq. (a) are formulated. Substances meeting the requirements in this respect are W, Ta, Mo, WC, TiC, graphite, Fe-Ni-Co-Mn alloy (Kovar) and some high-chrome steels. 

Crystalline films of NbBj and TaB2 are deposited on Ta and Nb substrates, respectively, according to the dissociation reaction (g) when the process is carried out at a reduced pressure, a temperature of 1100°C for NbB2 and 1150°C for TaB2 and with source gases containing MBr, and BBr, in a stoichiometric ratio " . At temperatures below 1000°C only a metal deposit is obtained, whereas at 1000-1100°C deposition of metals, lower borides and MB, occurs . ... 

Chemical solution deposition (CSD) procedures have been widely used for the production of both amorphous and crystalline thin films for more than 20 years.1 Both colloidal (particulate) and polymeric-based processes have been developed. Numerous advances have been demonstrated in understanding solution chemistry, film formation behavior, and for crystalline films, phase transformation mechanisms during thermal processing. Several excellent review articles regarding CSD have been published, and the reader is referred to Refs. 5-12 for additional information on the topic. Recently, modeling of phase transformation behavior for control of thin-film microstructure has also been considered, as manipulation of film orientation and microstructure for various applications has grown in interest.13-15... 

Reagent selection, solvent, and choice of solution reaction conditions serve to define the nature of the solution precursor species that are formed and that will be used for him deposition. The characteristics of these solution species serve to define him processing characteristics, including aspects such as cracking tendency,50 organic burn-out temperature,48 and for crystalline films, crystallization temperature.49,51... 

Puiso, J. 2004. Growth kinetics and properties of lead sulfide thin films deposited on crystalline silicon using successive ionic layer adsorption and reaction method. Ph.D. thesis. Kaunas University of Technology, Kaunas, Lithuania. 

From the frequency measurements of the LB-film-deposited QCM plate in water, the behavior of phospholipid LB films can be classified into three types (i) phospholipids having relatively hydrophilic head groups such as DPPC and DPPG are hydrated and then easily flaked from the substrate in the fluid liquid crystalline state above Tc (ii) DPPE and DPPS having the less hydrophilic head groups are hydrated only near their Tc (iii) cholesterol LB films show relatively large hydration behavior even at low temperatures due to the water penetration into the structure defects in the membrane. 

The primary difference in the operating conditions for growth of crystalline as compared with amorphous material is the deposition temperature. In the current design, 500 K is assumed for amorphous film deposition, while higher temperatures in the range 700-950 K are required for epitaxial growth. The low-temperature amorphous film deposition first is used to optimize the process, while the high-temperature epitaxial deposition subsequently is used as the basis for a detailed economic analysis. 

Although there is no consistent explanation of the relationship between organic polymer morphology and electrical properties,amorphous structures are generally preferred over a crystalline structure. An experiment was conducted to study the structure of the film deposited using an inert carrier gas. The PNT-N... 

The films are epitaxial in the sense that the lattice constant is intermediate between those of copper and nickel. As indicated above, that modulated strain is probably responsible for the increased hardness. Other authors (5) have tried to explain similar effects by stating that the layers were specifically oriented. Our example (6) demonstrates that these considerations must be reexamined since it was possible to achieve the effect in a crystalline multilayer deposited on an amorphous nickel-phosphorus underlayer. It appears that layer thickness is the important parameter here. 

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