Nanotechnology Now







Heifer International

Wikipedia Affiliate Button


DHgate

Home > Press > Putting more science into the art of making nanocrystals

Abstract:
Preparing semiconductor quantum dots is sometimes more of a black art than a science. That presents an obstacle to further progress in, for example, creating better solar cells or lighting devices, where quantum dots offer unique advantages that would be particularly useful if they could be used as basic building blocks for constructing larger nanoscale architectures.

Putting more science into the art of making nanocrystals

Columbia, SC | Posted on July 11th, 2013

Andrew Greytak, a chemist in the College of Arts and Sciences at the University of South Carolina, is leading a research team that's making the process of synthesizing quantum dots much more systematic. His group just published a paper in Chemistry of Materials detailing an effective new method for purifying CdSe nanocrystals with well-defined surface properties.

Their process uses gel-permeation chromatography (GPC) to separate quantum dots from small-molecule impurities, and the team went further in characterizing the nanocrystals by a variety of analytical methods. A comparison of their purified quantum dots with those purified by the traditional method of multiple solvation and precipitation cycles underscored the utility of the new method in preparing uniform semiconductor nanocrystals highly amenable to further synthetic manipulation.

Quantum dots

Quantum dots, which are nanocrystals with diameters in the range of 5-10 nanometers, have optical and other physical properties different from those of larger crystals. The reduced size allows them to absorb and emit different colors than bulk quantities of the same compound because of quantum mechanical effects; they also have very large surface-to-volume ratios and can be sensitive to surface treatments.

Greytak's laboratory typically prepares quantum dots in hydrophobic solvents (such as 1-octadecene), so they come out "capped" with hydrophobic molecules and dissolve readily in nonpolar solvents. "The way the process works, you always have a significant amount of unreacted starting material, high-boiling solvents and extra surfactants in there that are important to the synthesis," said Greytak. "But once the synthesis is complete, they're impurities that need to be removed."

The historic method of quantum dot purification is cycles of solvation, precipitation (such as with alcohol), decanting of impurities and re-solvation. Although the method has been in use for some 20 years, it has a fundamental shortcoming.

"With the precipitation and redissolution process, it's not actually doing the separation on the basis of the size of the particle, it's doing it on the basis of the solubility," said Greytak. "So if you have impurities that have solubility qualities similar to those of the particle, they aren't removed."

Gel-permeation chromatography

Greytak directed his team, which included graduate students Yi Shen, Megan Gee and Rui Tan, in developing GPC as a highly effective alternative. A size-exclusion technique, GPC separates chemical species according to molecular weight and is commonly used with macromolecules.

Compared with materials prepared through the precipitation and re-solvation process, the GPC-purified quantum dots had better stability at high temperature. Moreover, a series of NMR measurements assisted by USC research associate professor Perry Pellechia indicated that the GPC method was much more effective in removing weakly adsorbed ligands from the quantum dot surface.

Carrying a synthetic process forward

The team further examined the suitability of the quantum dots for further synthetic manipulation. Again, the GPC-purified products were superior, both in CdS shell growth on CdSe quantum dots as well as ligand exchange of cysteine on CdSe/CdxZn1-xS quantum dots.

Greytak sees the method as a fundamental step forward in being able to further manipulate quantum dots, whether in constructing larger architectures or asserting control over how the nanocrystal colloids behave in solution.

"What we like to say is that we're developing a sequential, preparative chemistry for semiconductor nanocrystals," said Greytak. "In most synthetic chemistry, you have a starting material, you do a reaction, and you proceed through a series of intermediates with well-defined structures that can be isolated. For a nanomaterial, it's much more difficult, because we're not making molecules, we're making a population of particles that has, let's say, a radius of two nanometers. They aren't all identical, and achieving a consistent product has been challenging, both in terms of how to isolate it and characterize it.

"So we're really working toward being able to characterize a sample, with, say NMR and thermogravimetric analysis, and being able to really predict with confidence how it's going to react in a subsequent step."

####

For more information, please click here

Contacts:
Steven Powell

803-777-1923

Copyright © University of South Carolina

If you have a comment, please Contact us.

Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.

Bookmark:
Delicious Digg Newsvine Google Yahoo Reddit Magnoliacom Furl Facebook

Related News Press

News and information

Rutgers, NIST physicists report technology with potential for sub-micron optical switches March 31st, 2015

Prototype 'nanoneedles' generate new blood vessels in mice: Scientists have developed tiny 'nanoneedles' that have successfully prompted parts of the body to generate new blood vessels, in a trial in mice March 31st, 2015

Super sensitive measurement of magnetic fields March 31st, 2015

Nanomedicine pioneer Mauro Ferrari at ETH Zurich March 31st, 2015

Display technology/LEDs/SS Lighting/OLEDs

Roll up your screen and stow it away? Tel Aviv University researchers develop molecular backbone of super-slim, bendable digital displays March 30th, 2015

Solving molybdenum disulfide's 'thin' problem: Research team increases material's light emission by twelve times March 29th, 2015

Haydale Announce Dedicated Graphene Inks Manufacturing Capability March 25th, 2015

Chemistry

Tokyo Institute of Technology research: Catalyst redefines rate limitations in ammonia production March 30th, 2015

Chemists make new silicon-based nanomaterials March 27th, 2015

Discoveries

Rutgers, NIST physicists report technology with potential for sub-micron optical switches March 31st, 2015

Prototype 'nanoneedles' generate new blood vessels in mice: Scientists have developed tiny 'nanoneedles' that have successfully prompted parts of the body to generate new blood vessels, in a trial in mice March 31st, 2015

Super sensitive measurement of magnetic fields March 31st, 2015

From tobacco to cyberwood March 31st, 2015

Announcements

Rutgers, NIST physicists report technology with potential for sub-micron optical switches March 31st, 2015

Prototype 'nanoneedles' generate new blood vessels in mice: Scientists have developed tiny 'nanoneedles' that have successfully prompted parts of the body to generate new blood vessels, in a trial in mice March 31st, 2015

Super sensitive measurement of magnetic fields March 31st, 2015

Nanomedicine pioneer Mauro Ferrari at ETH Zurich March 31st, 2015

Energy

Wrapping carbon nanotubes in polymers enhances their performance: Scientists at Japan's Kyushu University say polymer-wrapped carbon nanotubes hold much promise in biotechnology and energy applications March 30th, 2015

Solving molybdenum disulfide's 'thin' problem: Research team increases material's light emission by twelve times March 29th, 2015

SUNY Poly & M+W Make Major Announcement: Major Expansion To Include M+W Owned Gehrlicher Solar America Corporation That Will Create up to 400 Jobs to Develop Solar Power Plants at SUNY Poly Sites Across New York State March 26th, 2015

Hong Kong Investors Bullish on Dais Analytic Invest $5.75M, Provide $60M Contract, and Create New Joint Venture Company March 26th, 2015

Quantum Dots/Rods

Next important step toward quantum computer: Scientists at the University of Bonn have succeeded in linking 2 different quantum systems March 30th, 2015

Tiny bio-robot is a germ suited-up with graphene quantum dots March 24th, 2015

Rice fine-tunes quantum dots from coal: Rice University scientists gain control of electronic, fluorescent properties of coal-based graphene March 18th, 2015

Ghent University leads large-scale European training project on quantum dots March 13th, 2015

NanoNews-Digest
The latest news from around the world, FREE




  Premium Products
NanoNews-Custom
Only the news you want to read!
 Learn More
NanoTech-Transfer
University Technology Transfer & Patents
 Learn More
NanoStrategies
Full-service, expert consulting
 Learn More










ASP
Nanotechnology Now Featured Books




NNN

The Hunger Project







© Copyright 1999-2015 7th Wave, Inc. All Rights Reserved PRIVACY POLICY :: CONTACT US :: STATS :: SITE MAP :: ADVERTISE