title: Chemical reduction of three-dimensional silica micro-assemblies into microporous silicon replicas.
abstract: The carbothermal reduction of silica into silicon requires the use of temperatures well above the silicon melting point (> or =2,000 degrees C). Solid silicon has recently been generated directly from silica at much lower temperatures (< or =850 degrees C) via electrochemical reduction in molten salts. However, the silicon products of such electrochemical reduction did not retain the microscale morphology of the starting silica reactants. Here we demonstrate a low-temperature (650 degrees C) magnesiothermic reduction process for converting three-dimensional nanostructured silica micro-assemblies into microporous nanocrystalline silicon replicas. The intricate nanostructured silica microshells (frustules) of diatoms (unicellular algae) were converted into co-continuous, nanocrystalline mixtures of silicon and magnesia by reaction with magnesium gas. Selective magnesia dissolution then yielded an interconnected network of silicon nanocrystals that retained the starting three-dimensional frustule morphology. The silicon replicas possessed a high specific surface area (>500 m(2) g(-1)), and contained a significant population of micropores (< or =20 A). The silicon replicas were photoluminescent, and exhibited rapid changes in impedance upon exposure to gaseous nitric oxide (suggesting a possible application in microscale gas sensing). This process enables the syntheses of microporous nanocrystalline silicon micro-assemblies with multifarious three-dimensional shapes inherited from biological or synthetic silica templates for sensor, electronic, optical or biomedical applications.
authors.affiliation: School of Materials Science & Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, USA.
authors.forename: Zhihao
authors.initials: Z
authors.lastname: Bao
authors.forename: Michael R
authors.initials: MR
authors.lastname: Weatherspoon
authors.forename: Samuel
authors.initials: S
authors.lastname: Shian
authors.forename: Ye
authors.initials: Y
authors.lastname: Cai
authors.forename: Phillip D
authors.initials: PD
authors.lastname: Graham
authors.forename: Shawn M
authors.initials: SM
authors.lastname: Allan
authors.forename: Gul
authors.initials: G
authors.lastname: Ahmad
authors.forename: Matthew B
authors.initials: MB
authors.lastname: Dickerson
authors.forename: Benjamin C
authors.initials: BC
authors.lastname: Church
authors.forename: Zhitao
authors.initials: Z
authors.lastname: Kang
authors.forename: Harry W
authors.initials: HW
authors.lastname: Abernathy
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Summers
authors.forename: Meilin
authors.initials: M
authors.lastname: Liu
authors.forename: Kenneth H
authors.initials: KH
authors.lastname: Sandhage
mesh_terms: D032701:Biomimetics / Q000379:methods*; D017377:Diatoms / Q000737:chemistry*; D008274:Magnesium / Q000737:chemistry; D008277:Magnesium Oxide / Q000737:chemistry; D008956:Models, Chemical; D049329:Nanostructures / Q000737:chemistry; D010084:Oxidation-Reduction; D016062:Porosity; D012825:Silicon / Q000737:chemistry*; D013696:Temperature
chemical_list: D008277:Magnesium Oxide; D008274:Magnesium; D012825:Silicon