*What Are Nanocrystals??? *How Are Nanocrystals Prepared??? *How To obtain Silicon Nanocrystals??? 1-Electrochemical Etching
Published on: Mar 3, 2016
Transcripts - Nanocrystal synthesis
*What Are Nanocrystals???
*How Are Nanocrystals Prepared???
*How To obtain Silicon
*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
e.g., multiply twinned
*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
*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
*The newer and simpler strategy:
Use of preformed nanocrystals as templates
and chemical transformation to change the
*Silicon nanocrystals are prepared using
electrochemical etching of silicon wafers.
*The procedure takes place under normal
atmosphere, in Teflon chambers with electrical
current flowing through the electrolyte.
*The final product are oxide-covered silicon
*Disadvantage of this method: The natural
tendency of oxide-covered silicon nanocrystals
to form strongly bound large agglomerates of
1: Electrochemical etching
*The electrochemical etching, is based on the use of
*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.
*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.
*Synthesis of Water-Soluble Blue Photoluminescent Silico
*Nanocrystalline Silicon for Nanophotonics
*Journal of the Korean Physical Society, Vol. 42, February 2003
Synthesis of Silicon Nanocrystals
By: Cho Joon Wo & Lee So Jin
By: Nathanael Smith