Post-deposition treatments mechanical

The properties of thin films are primarily determined by the type of chemical element or compound they comprise and by the film thickness. Their optical, electro-optical, electrical and mechanical behaviour is also determined by structure, microstructure, surface and interface morphology, chemical composition, purity and homogeneity. These are strongly influenced by the film preparation method, the chosen parameters, and by post-deposition treatments. 

Luo, Cui and Li (1999) addressed the problem of temperature sensitivity of IBAD of ACPs and their subsequent crystallisation forming hydroxyapatite. Post-depositional annealing temperatures were decreased to 400 °C. The crystallisation of calcium phosphate coating is a hydroxyl ion diffusion-controlled process, thought to be the mechanism responsible for the decrease of the crystallisation temperature. The detailed study of the crystallisation process of calcium phosphate coatings shows that the crystallinity of the hydroxyapatite coating can be well controlled by adjusting the post-heat-treatment time. 

The trees seem to be formed by stacking of the crystallites in size ranging Ifom 30 to 50 nm which is apparently much smaller than the particle size in the film deposited without DC bias. The mechanism to make the difference is not clear at present time. We assume that the application of the DC bias increased the concentration of species in the gas phase, i.e. the flux of the arriving atoms or clusters on the substrate, as well as the concentration of the ionized species, which results in more nuclei on the substrate. The increase of the concentration of species in the gas phase can also lead to less time for the adatoms to diffuse on the surface of the substrate or the deposited film, which can result in small particle in the deposited films. The similarity of the microstructures of the films deposited under DC bias and that deposited at high reagent concentration (see Fig. If) can support our assumption. The low density films in the forest-like microstructure can be densified by post thermal treatment. The images in Figure 7 indicate both the... 

The high-temperature requirement places restrictions on the type of substrate that can be used. For instance some steels will lose their mechanical properties at these temperature and will require a heat treatment after coating. They may also change dimensions sufficiently to require post-deposition machining. 

Finally, some post-fabrication treatments of the deposited meshes can be hardly compatible with living cells and biologically functional compounds, especially when these processes involve (chemical, thermal, UV, etc.) cross-linking to enhance the mechanical strength of the scaffold and its stability in aqueous environments. These procedures, besides complicating the overall fabrication process, may have in principle a detrimental effect on the level of biocompatibility and on the functionality of embedded molecular dopants. 

Generally, for the low temperature deposition of a compound film, one of the reacting species should be condensable and the other gaseous e.g. Ti -i- N. If both are condensable, e.g. Tl + C, the best deposition condition is to have a high substrate temperature to promote reaction, have concurrent bombardment, or use post-deposition heat treatment to react the mixture. The stoichiometry of a deposited compound can depend on the amount of reaction that occurs before the surface is buried. This depends on the amount of reactant available, the reaction probability, and the deposition rate. Reactively deposited films of oxides, carbides, nitrides, and carbonitrides are commonly used in optics, electronics, decorative, and mechanical applications. 

Excellent transport characteristics, solubilization power, and sensitivity to process variables all contribute to the success of the methodology. The generic scheme involves homogenization, impregnation, deposition, and optional post treatment steps such as curing reactions. The mechanism of transport in the porous matrix is permeation and diffusion while the primary mechanisms for deposition are pressure reduction, temperature swing, sorption, and reaction (i.e., polymerization). 

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