Bioinspired ceramic thin film processing: Present status and future perspectives

Nature has ingeniously succeeded in producing an impressive variety of inorganic functional structures with a designed shape and size on specific sites through a biologically controlled biomineralization process, usually at near room temperature and in aqueous solutions. The most important principle understood from biomineralization processes is that nucleation and growth of the biomineral phase are almost always carefully and exquisitely controlled by complex organic matrix biopolymers-preorganized supramolecular templates, which are associated to regulate a single, precise step in either the nucleation or the growth portion of the production of the mineral phase. The interaction at a molecular-level solid-liquid interface between a specific surface chemistry and a solution supersaturated with respect to the inorganic material is one key feature of natural biomineralization. The study of biomineralization offers valuable insights into the scope and nature of materials chemistry at the inorganic-organic interface, which represents an inspiration toward future innovations in seeking highly efficient and/or unique materials synthesis strategies. So-called bioinspired ceramics processing has been developed to produce ceramic thin films, to create specific microstructures, or to control crystallization. In the present review, attention is drawn toward the recent increase in research activities involving the preparation of functional ceramic thin films induced by a specific chemical surface modification. This review provides a brief description of the bioinspired process for in situ patterning of ceramic oxides using a template derived from a self-assembled monolayer (SAM) for site-selective nucleation and growth from solutions under normal conditions in terms of pressure and temperature, emphasizing the fundamental knowledge of the chemistry of solutions and interfaces. Our discussion is limited to methods that grow films in a liquid phase by control of the supersaturation of the solution. Sol-gel and methods equipped with additional energy sources, such as hydrothermal synthesis and electrochemical deposition, are excluded. The following issues are addressed: preparation, photocleavage (for structural/lateral modification) and characterization of SAMs, surface-interface chemistry and solution chemistry for the deposition of ceramic oxides from solutions, and patterning of ceramic oxides on the template of SAMs from aqueous solution under mild conditions. We start with a brief overview of the present status of the fundamental methodology for the synthesis of ceramic thin films from solutions and patterning techniques. Then we discuss the biomineralization process and its inspiration to create novel approaches for the production of engineering materials, focusing on ceramic films. Then we discuss chemical aspects of the deposition of films from solutions, including solution chemistry, modification of surfaces, and the physics and chemistry of interfaces. Next, several experimental examples are given to explain how these aspects influence the formation of films and their properties. Finally, we summarize and discuss future techniques for this field.