Nanocrystal synthesis
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This document discusses silicon nanocrystals. It defines a nanocrystal as a crystalline nanoparticle with at least one dimension less than or equal to 100 nm. It explains that silicon nanocrystals can emit light even though bulk silicon cannot. The document discusses two methods for preparing silicon nanocrystals: electrochemical etching of silicon wafers and pulverization. Electrochemical etching uses hydrofluoric acid to dissolve silicon and form a porous structure containing silicon nanocrystals. Pulverization produces silicon nanocrystal agglomerates in powder form.
Nanocrystal synthesis
- 2. X *What Are Nanocrystals??? *How Are Nanocrystals Prepared??? *How To obtain Silicon Nanocrystals??? 1-Electrochemical Etching 2-Pulverization *References
- 3. X *A nanocrystal is a crystalline nanoparticle. *Some sources define it as any single crystalline nanomaterial with at least one dimension ≤ 100 nm. *others define it as a nanoparticle with any kind of crystalline structure. e.g., multiply twinned configurations.
- 4. X *Silicon nanocrystals can provide efficient light emission even while bulk Silicon can't! *Nanocrystals embedded in solids can exhibit much more complex melting behavior than conventional solids!
- 5. *The traditional way : Prepare nanocrystals of a new material involved choosing molecular precursors, surfactants, and solvents using optimized reaction conditions causing the atoms to self-assemble into monodisperse nanocrystals. X *The newer and simpler strategy: Use of preformed nanocrystals as templates and chemical transformation to change the composition.
- 6. X *Silicon nanocrystals are prepared using electrochemical etching of silicon wafers.
- 7. X *The procedure takes place under normal atmosphere, in Teflon chambers with electrical current flowing through the electrolyte. *The final product are oxide-covered silicon nanocrystals.
- 8. X *Disadvantage of this method: The natural tendency of oxide-covered silicon nanocrystals to form strongly bound large agglomerates of tiny nanocrystals!
- 9. X 1: Electrochemical etching *The electrochemical etching, is based on the use of hydrofluoric acid. *Fluorine ions attack silicon surface, causing its dissolution into hexafluorosilicate ions.
- 10. *This dissolution forms voids in the silicon wafers, resulting in a porous structure with small chunks of silicon consisting of nanocrystals between the pores. *Ethanol, which is added in order to increase wettability and facilitate the penetration of the etching solution into the tiny pores. *The etching procedure yields a layer of interconnected silicon nanocrystals. X
- 11. X 2: Pulverization *Obtaining the sample in the powder-like form, consisting of larger agglomerates of small silicon nanocrystals. The powder can be stored for a long time in air without any detrimental effect on its properties.
- 12. X *Synthesis of Water-Soluble Blue Photoluminescent Silico http://research.ncku.edu.tw/re../articles/e/20091113/2.html *Nanocrystal http://en.wikipedia.org/wiki/Nanocrystal *Nanocrystalline Silicon for Nanophotonics http://nanotech.fzu.cz/26/index.php?file=1 *Journal of the Korean Physical Society, Vol. 42, February 2003 Synthesis of Silicon Nanocrystals By: Cho Joon Wo & Lee So Jin *Nanocrystal Synthesis By: Nathanael Smith
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