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roelectrics/dielectrics, or liquid crystals, or polymeric materials are among the most relevant targets. The possibilities offered by the combination of stable elements are almost infinite, in that tens of elements can be combined in almost any relative proportion. Each resulting material is by definition different and is characterized by properties that can be exploited and optimized for a specific application.

Unfortunately, the ability to rationally predict the properties of a specific material composition is currently poor, and thus the rational design of enhanced materials is, at best, extremely difficult and long. Moreover, the synthesis and the characterization of such materials using classical inorganic SP chemistry methods is complex and time consuming. Full exploitation of material composites thus requires significantly higher throughput synthetic and screening methods, both to prepare large numbers of materials and to construct better predictive models to help drive the rational selection of elements and relative abundances in a composite. In this context combinatorial technologies appear ideally suited to boost the discovery of new materials via their synthesis, characterization, and screening.

Organic synthesis of a target molecule requires the design of a synthetic route, the selection of suitable, commercially available precursors, and the optimization of reaction conditions. It requires reaction monitoring and product characterization with various analytical techniques as well as work-up procedures to purify and isolate the target. The large amount of available knowledge, in terms of organic reaction mechanisms and the reactivity and stability of organic molecules, allows chemists to plan and carry out the above-mentioned steps, often even optimizing reported protocols according to target-specific needs. The transfer of classical protocols to solutionor solid-phase combinatorial protocols is also becoming an assessed field, as reported in previous chapters.

Inorganic solid-state chemistry is much simpler, in that only a few general synthetic methods exist to prepare a material of virtually any composition. The main issue is the preparation of a homogeneous material where all the components have completely diffused in the mixture to obtain the desired composition. Commonly encountered diffusion barriers could produce nonhomogeneous mixtures with varying compositions and thus prevent the synthesis of the desired material. Classical solid-state synthetic methods are based on intimate mixing and heating of finely powdered inorganic solids to create homogeneous new composites. They are hampered by the macroscopic size of the particles and often do not provide high-quality materials. A more promising technique is based on the sequential deposition of thin films of each component of the desired composite (16–18). The reduced thickness of the resulting film, typically in the range of several atomic layers, allows the total diffusion of each component in the film with no resistance. As of today, all the reported efforts in combinatorial materials science involving solid reagents have used thin-film deposition techniques, which are described in more detail in the next section. Liquid-phase techniques have also been used with success for combinatorial applications in a few reports and are thus also reported.