Nanostructured metal oxide semiconductor materials possess novel optical and electronic properties that can be tuned by manipulating the dimensions of the composite nanophases in the 1-100 nm size range. These materials have a host of potential applications, particularly for the fabrication of optoelectronic devices. However, it is difficult to fabricate nanostructured semiconductor materials and at the same time integrate these materials into patterned device features that possess the nanoscale and microscale elements needed for the next generation of optoelectronic devices.

We harnessed the mineralization capacity of single-celled algae called diatoms (the Bacillariophyceae) to biologically fabricate nanostructured materials composed of amorphous silicon and germanium oxides. The nanostructured metal oxide materials are self-assembled into submicron scale (100-500 nm) features such as periodic aperture arrays which resemble photonic crystals. Bioreactor cultivation technology was used to metabolically insert foreign dopant metals (for example germanium) into the silica matrix of the living diatom cell. The diatom cells were treated with aqueous hydrogen peroxide to remove organic materials. The resulting amorphous metal oxide microshells were imaged by SEM/TEM and characterized for optoelectronic properties by photoluminescence and electroluminescence. STEM-EDS analysis revealed that the germanium was uniformly distributed into the silica microstructure, but also possessed regions where germanium-rich nanoparticles were imbedded into the silica matrix.

Metabolic insertion of germanium described above imparted photoluminescent properties to the biologic silcon-germanium oxide nanomaterials. The material possessed strong blue photoluminescence centered at around 460 nm at 25 ^oC from a 337 nm laser excitation source. The intensity of photoluminescence depended upon the germanium content in the silica. Thermal annealing quenched the photoluminescent properties of the biogenic silicon-germanium nanocomposite frustules. The biologic silicon-germanium oxide nanomaterials also possessed strong blue electroluminescence. Interestingly, three distinct peaks were observed in the 300-400 nm range of the electroluminescence spectrum.

This work suggests that the biological fabrication of amorphous silicon-germanium oxide materials ordered at both the submicron and nanoscales may produce optoelectronic materials with interesting properties. Furthermore the biological fabrication route described in this paper is simple, environmentally friendly, and occurs at ambient conditions.