X Faculty Of Pharmacy

ASUOrganic

Chemistry“Nanocrystal Synthesis”By: Marina

Adel

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Index:* ???What Are Nanocrystals

* How Are Nanocrystals Prepar???ed

* How To obtain Silicon???Nanocrystals

1- Electrochemical Etching2-Pulverization

*References

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What Are Nanocrystals??? *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.

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*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!

Notes

How Are Nanocrystals

Prepared???*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.

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*The newer and simpler strategy: Use of preformed nanocrystals as

templates and chemical transformation to change the composition.

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Silicon Nanocrystals:How To Obtain Silicon Nanocrystals???

*Silicon nanocrystals are prepared using electrochemical etching of silicon wafers .

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*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.

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Notes

*Disadvantage of this method: The natural tendency of oxide-covered silicon nanocrystals to form strongly bound large agglomerates of tiny nanocrystals !

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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.

*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.

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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.

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References:*Synthesis of Water-Soluble Blue Photoluminescent

Silico:// . . . / ../ / /20091113/http research ncku edu tw re articles e

2.html

*Nanocrystal:// . . / /http en wikipedia org wiki Nanocrystal

*Nanocrystalline Silicon for Nanophotonics:// . . /26/ . ? =1http nanotech fzu cz index php file

*Journal of the Korean Physical Society, Vol. 42, February 2003Synthesis of Silicon Nanocrystals By: Cho Joon Wo & Lee So Jin

*Nanocrystal Synthesis By: Nathanael Smith

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