"Ultrasmall Quantum Dots via Electroporation of Vesicles"

Zoltan A. Schelly

Department of Chemistry and Biochemistry, UTA

Wednesday, February 23, 2005, 4:00 PM

 

     Abstract:

  The usually diffusion-controlled self-aggregation of nascent molecules of semiconductors (M+X-) or metals (M) in solution represent an experimental challenge for arresting the growth of the particles at a subnanometer size.  Unfortunately, the typical remedy of capping the clusters alters their electronic and optical properties.  We have discovered a novel method that resolves these problems.  The essence of the method is the initial encapsulation of the metal ion (M+) in synthetic vesicles (liposomes) and the placement of the anion (X-) in the bulk solution.  Exposure of the suspension to a rectangular pulse of a homogenous electric field E of suitable intensity and duration causes the formation of transient pores in the vesicle's bilayer (electroporation).  Some of the metal ions ejected through the pores react with the anions in the bulk, and the freshly created monomers (M+X-) adsorb on the exterior surface of the vesicle.  On the vesicle surface, the self-aggregation is slowed down to the hour and day timescales which allows for convenient optical monitoring of the growth of the clusters.  On the example of the creation of PbS quantum dots (QD) the net process may be illustrated as

The discussion will focus on the transient electro-optics of vesicles, the mechanism of electroporation, and our experimental and theoretical findings of the unusual optical properties of subnanometer size AgBr, CdS, PbS, ZnS, and gold quantum dots.


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