Chemical reduction of three-dimensional silica micro-assemblies into microporous silicon replicas
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- Chemical reduction of three-dimensional silica micro-assemblies into microporous silicon replicas
- Bao, Zhihao; Weatherspoon, Michael R.; Shian, Samuel; Cai, Ye; Graham, Phillip D.; Allan, Shawn M.; Ahmad, Gul; Dickerson, Matthew B.; Church, Benjamin C.; Kang, Zhitao; Abernathy, Harry W., III; Summers, Christopher J.; Liu, Meilin; Sandhage, Kenneth H.
- POROUS SILICON; GAS SENSOR; VAPOR; EMISSION; DIOXIDE; WATER
- Issue Date
- NATURE PUBLISHING GROUP
- NATURE, v.446, no.7132, pp.172 - 175
- The carbothermal reduction of silica into silicon requires the use of temperatures well above the silicon melting point (≥2,000°C). Solid silicon has recently been generated directly from silica at much lower temperatures (≤850°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°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 m2 g-1), and contained a significant population of micropores (≤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.
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