Nanotechnology Now

Our NanoNews Digest Sponsors





Heifer International

Wikipedia Affiliate Button


android tablet pc

Home > Press > In new quantum-dot LED design, researchers turn troublesome molecules to their advantage : A robust new architecture enables optimization for quantum-dot displays

In an early design (left), the path of least resistance was between the quantum dots, so the current bypassed the dots and produced no light. Using the atomic layer deposition (ALD) technique (right), researchers were able to funnel current directly through the dots, creating a fully functional, single-layered QD-LED. Image courtesy of Edward Likovich.
In an early design (left), the path of least resistance was between the quantum dots, so the current bypassed the dots and produced no light. Using the atomic layer deposition (ALD) technique (right), researchers were able to funnel current directly through the dots, creating a fully functional, single-layered QD-LED.

Image courtesy of Edward Likovich.

Abstract:
By nestling quantum dots in an insulating egg-crate structure, researchers at the Harvard School of Engineering and Applied Sciences (SEAS) have demonstrated a robust new architecture for quantum-dot light-emitting devices (QD-LEDs).

In new quantum-dot LED design, researchers turn troublesome molecules to their advantage : A robust new architecture enables optimization for quantum-dot displays

Cambridge, MA | Posted on November 15th, 2011

Quantum dots are very tiny crystals that glow with bright, rich colors when stimulated by an electric current. QD-LEDs are expected to find applications in television and computer screens, general light sources, and lasers.

Previous work in the field had been complicated by organic molecules called ligands that dangle from the surface of the quantum dots. The ligands play an essential role in quantum dot formation, but they can cause functional problems later on.

Thanks to an inventive change in technique devised by the Harvard team, the once-troublesome ligands can now be used to build a more versatile QD-LED structure. The new single-layer design, described in the journal Advanced Materials, can withstand the use of chemical treatments to optimize the device's performance for diverse applications.

"With quantum dots, the chemical environment that's optimal for growth is usually not the environment that's optimal for function," says co-principal investigator Venkatesh Narayanamurti, Benjamin Peirce Professor of Technology and Public Policy at SEAS.

The quantum dots, each only 6 nanometers in diameter, are grown in a solution that glows strikingly under a black light.

The solution of quantum dots can be deposited onto the surface of the electrodes using a range of techniques, but according to lead author Edward Likovich (A.B. '06, S.M. '08, Ph.D. '11), who conducted the research as a doctoral candidate in applied physics at SEAS, "That's when it gets complicated."

"The core of the dots is a perfect lattice of semiconductor material, but on the exterior it's a lot messier," he says. "The dots are coated with ligands, long organic chains that are necessary for precise synthesis of the dots in solution. But once you deposit the quantum dots onto the electrode surface, these same ligands make many of the typical device processing steps very difficult."

The ligands can interfere with current conduction, and attempts to modify them can cause the quantum dots to fuse together, destroying the properties that make them useful. Organic molecules can also degrade over time when exposed to UV rays.

Researchers would like to be able to use those ligands to produce the quantum dots in solution, while minimizing the negative impact of the ligands on current conduction.

"The QD technologies that have been developed so far are these big, thick, multilayer devices," says co-author Rafael Jaramillo, a Ziff Environmental Fellow at the Harvard University Center for the Environment. Jaramillo works in the lab of Shriram Ramanathan, Associate Professor of Materials Science at SEAS.

"Until now, those multiple layers have been essential for producing enough light, but they don't allow much control over current conduction or flexibility in terms of chemical treatments. A thin, monolayer film of quantum dots is of tremendous interest in this field, because it enables so many new applications."

The new QD-LED resembles a sandwich, with a single active layer of quantum dots nestled in insulation and trapped between two ceramic electrodes. To create light, current must be funneled through the quantum dots, but the dots also have to be kept apart from one another in order to function.

In an early design, the path of least resistance was between the quantum dots, so the electric current bypassed the dots and produced no light.

Abandoning the traditional evaporation technique they had been using to apply insulation to the device, the researchers instead used atomic layer deposition (ALD)—a technique that involves jets of water. ALD takes advantage of the water-resistant ligands on the quantum dots, so when the aluminum oxide insulation is applied to the surface, it selectively fills the gaps between the dots, producing a flat surface on the top.

The new structure allows more effective control over the flow of electrical current.

"Exploiting these hydrophobic ligands allowed us to insulate the interstices between the quantum dots, essentially creating a structure that acts as an egg crate for quantum dots," says co-author Kasey Russell (A.B. '02, Ph.D. '09), a postdoctoral fellow at SEAS. "The benefit is that we can funnel current directly through the quantum dots despite having only a single layer of them, and because we have that single layer, we can apply new chemical treatments to it, moving forward."

Through Harvard's Office of Technology Development, Likovich and his colleagues have applied for a provisional patent on the device. Beyond the possible applications in computer and TV displays, lights, and lasers, the technology could one day be used in field-effect transistors or solar cells.

The research was supported by the Harvard University Center for the Environment; the Nanoscale Science and Engineering Center at Harvard, which is funded by the National Science Foundation (NSF); and the use of facilities at the Harvard University Center for Nanoscale Systems, a member of the NSF-supported National Nanotechnology Infrastructure Network.

####

For more information, please click here

Contacts:
29 Oxford Street
Cambridge, MA 02138, USA
Caroline Perry

617-496-1351

Copyright © Harvard's School of Engineering and Applied Sciences (SEAS)

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

Newly-Developed Nanobiosensor Quickly Diagnoses Cancer August 20th, 2014

Ultrasonic Waves Applied in Production of Graphene Nanosheets August 20th, 2014

The channel that relaxes DNA: Relaxing DNA strands by using nano-channels: Instructions for use August 20th, 2014

Success in Intracellular Imaging of Cesium Distribution in Plants Used for Cesium Absorption August 19th, 2014

Display technology/LEDs/SS Lighting/OLEDs

LEDs made from ‘wonder material’ perovskite: Colourful LEDs made from a material known as perovskite could lead to LED displays which are both cheaper and easier to manufacture in future August 5th, 2014

Martini Tech Inc. becomes the exclusive distributor for Yoshioka Seiko Co. porous chucks for Europe and North America July 20th, 2014

Carbodeon enables 20 percent increase in polymer thermal filler conductivity with 0.03 wt.% nanodiamond additive at a lower cost than with traditional fillers: Improved materials and processes enable nanodiamond cost reductions of up to 70 percent for electronics and LED app July 9th, 2014

'Nano-pixels' promise thin, flexible, high resolution displays July 9th, 2014

Govt.-Legislation/Regulation/Funding/Policy

Success in Intracellular Imaging of Cesium Distribution in Plants Used for Cesium Absorption August 19th, 2014

Electrical engineers take major step toward photonic circuits: Team invents non-metallic metamaterial that enables them to 'compress' and contain light August 19th, 2014

Promising Ferroelectric Materials Suffer From Unexpected Electric Polarizations: Brookhaven Lab scientists find surprising locked charge polarizations that impede performance in next-gen materials that could otherwise revolutionize data-driven devices August 18th, 2014

Novel chip-based platform could simplify measurements of single molecules: A nanopore-gated optofluidic chip combines electrical and optical measurements of single molecules onto a single platform August 14th, 2014

Discoveries

Newly-Developed Nanobiosensor Quickly Diagnoses Cancer August 20th, 2014

Ultrasonic Waves Applied in Production of Graphene Nanosheets August 20th, 2014

The channel that relaxes DNA: Relaxing DNA strands by using nano-channels: Instructions for use August 20th, 2014

Electrical engineers take major step toward photonic circuits: Team invents non-metallic metamaterial that enables them to 'compress' and contain light August 19th, 2014

Announcements

Newly-Developed Nanobiosensor Quickly Diagnoses Cancer August 20th, 2014

Ultrasonic Waves Applied in Production of Graphene Nanosheets August 20th, 2014

The channel that relaxes DNA: Relaxing DNA strands by using nano-channels: Instructions for use August 20th, 2014

Electrical engineers take major step toward photonic circuits: Team invents non-metallic metamaterial that enables them to 'compress' and contain light August 19th, 2014

Quantum Dots/Rods

Interaction between Drug, DNA for Designing Anticancer Drugs Studied in Iran August 17th, 2014

NANOPARTICLES INDIA August 8th, 2014

Researchers create quantum dots with single-atom precision June 30th, 2014

New Los Alamos Approach May Be Key to Quantum Dot Solar Cells With Real Gains in Efficiency: Nanoengineering Boosts Carrier Multiplication in Quantum Dots June 19th, 2014

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 1999-2014 7th Wave, Inc. All Rights Reserved PRIVACY POLICY :: CONTACT US :: STATS :: SITE MAP :: ADVERTISE