Nanotechnology Now

Our NanoNews Digest Sponsors

Heifer International

Wikipedia Affiliate Button

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

Chemists Cook up New Nanomaterial and Imaging Method: Nanomaterials can store all kinds of things, including energy, drugs and other cargo January 19th, 2017

National Space Society Congratulates SpaceX on the Falcon 9's Return to Flight January 19th, 2017

Eric Berger Wins the National Space Society's 2017 Space Pioneer Award for Mass Media January 19th, 2017

Nanometrics to Announce Fourth Quarter and Full Year Financial Results on February 7, 2017 January 19th, 2017

Display technology/LEDs/SS Lighting/OLEDs

Self-assembling particles brighten future of LED lighting January 18th, 2017

Dressing a metal in various colors: DGIST research developed a technology to coat metal with several nanometers of semiconducting materials January 17th, 2017

Miniscule amounts of impurities in vacuum greatly affecting OLED lifetime December 30th, 2016

Chemistry

Chemistry on the edge: Experiments at Berkeley Lab confirm that structural defects at the periphery are key in catalyst function January 13th, 2017

Researchers produced nitrogen doped bimodal cellular structure activated carbon December 29th, 2016

Safe and inexpensive hydrogen production as a future energy source: Osaka University researchers develop efficient 'green' hydrogen production system that operates at room temperature in air December 21st, 2016

Discoveries

Chemists Cook up New Nanomaterial and Imaging Method: Nanomaterials can store all kinds of things, including energy, drugs and other cargo January 19th, 2017

'5-D protein fingerprinting' could give insights into Alzheimer's, Parkinson's January 19th, 2017

Strength of hair inspires new materials for body armor January 18th, 2017

Self-assembling particles brighten future of LED lighting January 18th, 2017

Announcements

Chemists Cook up New Nanomaterial and Imaging Method: Nanomaterials can store all kinds of things, including energy, drugs and other cargo January 19th, 2017

National Space Society Congratulates SpaceX on the Falcon 9's Return to Flight January 19th, 2017

Eric Berger Wins the National Space Society's 2017 Space Pioneer Award for Mass Media January 19th, 2017

Nanometrics to Announce Fourth Quarter and Full Year Financial Results on February 7, 2017 January 19th, 2017

Energy

Chemists Cook up New Nanomaterial and Imaging Method: Nanomaterials can store all kinds of things, including energy, drugs and other cargo January 19th, 2017

Dressing a metal in various colors: DGIST research developed a technology to coat metal with several nanometers of semiconducting materials January 17th, 2017

Stability challenge in perovskite solar cell technology: New research reveals intrinsic instability issues of iodine-containing perovskite solar cells December 26th, 2016

Nanoscale 'conversations' create complex, multi-layered structures: New technique leverages controlled interactions across surfaces to create self-assembled materials with unprecedented complexity December 22nd, 2016

Quantum Dots/Rods

Carbon dots dash toward 'green' recycling role: Rice scientists, colleagues use doped graphene quantum dots to reduce carbon dioxide to fuel December 18th, 2016

Two electrons go on a quantum walk and end up in a qudit: Russian scientists find a way to reliably connect quantum elements December 13th, 2016

Trickling electrons: Close to absolute zero, the particles exhibit their quantum nature November 10th, 2016

Notre Dame researchers find transition point in semiconductor nanomaterials September 6th, 2016

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