Genetically-Engineered Microdevices

Gas/solid displacement reactions have been examined as a means of altering the chemistry of bioclastic silica structures (e.g., the self-assembled microshells of diatoms, a type of aquatic algae) into other ceramic compositions. Complex-shaped silica microshells with nanoscale features were exposed to Mg(g) at 9OO deg C. The silica microshells underwent the following net displacement reaction: 2Mg(g) + SiO2(s) yields 2MgO(s) + ?Si) (1) where ?Si! refers to silicon dissolved within a Mg-Si liquid. The Mg-Si liquid, which formed by the continued reaction of excess Mg(g) with reduced Si, was observed to sweat away from the solid MgO product of this reaction at 900 deg C to yield Si-free micro/nanostructures. The resulting MgO structures retained the 3-D shapes and fine features of the starting diatom microshells. This demonstration of shape-preserving chemical conversion opens the door to a wide variety of other chemical conversion reactions that we have begun to examine.