In the optimization of multilayer stacks for various optical filtering purposes not only the thicknesses of the thin films are to be optimized, but also the sequence of materials. Materials with very different optical properties, such as metals and dielectrics, may be combined. A genetic algorithm is introduced to search for the optimal sequence of materials along with their optical thicknesses. This procedure is applied to a heat mirror in combination with a blackbody absorber for thermal solar energy applications at elevated temperatures (250 °C). The heat mirror is based on silver films with antireflective dielectric layers. Seven dielectrics have been considered. For a five-layer stack the sequence (TiO(2)/Ag/TiO(2)/Ag/Y(2)O(3)) is found to be optimal.

The key to engineering a material lies in exploiting its beneficial characteristics while minimizing its inherent weaknesses. Whether the weakness is, for example, poor corrosion resistance or low hardness, applying a relatively thin coating of another material that mitigates the shortcoming of the underlying material is a practical solution allowing the composite pieces to be used in demanding environments. This method has been utilized in a wide variety of cases ranging from paint on wooden fences and ceramic thermal barriers on single-crystal superalloy turbine blades to tungsten carbide hard-facing layers on drilling equipment. Some materials may suffer from high cost and therefore are used as a thin layer to impart their desired properties. For instance, gold leaf is applied to buildings for appearance while diamond films are deposited onto normal cutting tools to improve their performance. The specific application typically dictates both the material and the deposition method for the coating. The gold leaf does not need to offer much resistance to abrasion or mechanical stress in order to maintain its beautiful shine far into the future. In contrast the diamond film must be strongly adhered to the underlying cutting tool surface if it is to survive the punishing wear and thermal stresses of machining operations.

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