Biomolecular mechanism of silica synthesis opens novel routes to low-temperature nanofabrication of semiconductors and other advanced materials

Summary form only given. Biological systems fabricate multifunctional, high-performance materials at low temperatures and near-neutral pH with a precision of three-dimensional nanostructural control that exceeds the capabilities of present human engineering. We discovered the mechanism governing the nanofabrication of silica in a biological system, and translated this mechanism to develop a new low-temperature route for the synthesis of a wide range of nano structured metal oxide, -hydroxide and -phosphate semiconductor thin films without the use of organic templates. As a first proof of principle, we have used this process for the low-temperature synthesis of a strongly photo conductive cobalt hydroxide-based thin film material never before attainable through conventional or high-temperature methods. This new biologically inspired synthesis method yields exceptionally pure inorganic semiconductors, and thus is potentially integrable with conventional manufacturing methods. In research leading to these developments, we discovered that the silicateins, a family of enzyme proteins we found occluded within the silica needles made by a marine sponge, can catalyze and structurally direct the polymerization of silica, silsesquioxanes, organometallics and a wide range of metal oxide semiconductors from the corresponding molecular precursors at neutral pH and low temperature. These were the first reported examples of enzyme-catalyzed, nano structure-directed synthesis of semiconductors. Interaction with the template-like protein surface stabilizes polymorphs of these materials (e.g., the anatase form of titanium dioxide and the spinel polymorph of gallium oxide) otherwise not formed at low temperatures. This observation and the preferential alignment of the Ga2O3 nanocrystallites suggested a pseudo-epitaxial relationship between the mineral crystallites and specific functional groups on the templating protein surface. As described above, we have used this biologically inspi- - red process for the low-temperature synthesis of a large number of metal-oxides, -hydroxides and -phosphates, producing many in forms that could not be attained by conventional syntheses. The electronic properties of these novel materials suggest strong advantages for energy applications