Navigation Links
In new quantum-dot LED design, researchers turn troublesome molecules to their advantage
Date:11/15/2011

Cambridge, Mass. November 15, 2011 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).

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


'/>"/>

Contact: Caroline Perry
cperry@seas.harvard.edu
617-496-1351
Harvard University
Source:Eurekalert

Related biology technology :

1. National Ergonomics Expo Sees 86% On-Site Exhibitor Renewal Rate for 2009; New Products from Contour Design, Equipois, Goldtouch and Herman Miller Win 2008 NECE Attendees Choice New Product Awards
2. Sanofi Pasteur to Acquire VaxDesign, a U.S. Biotechnology Company
3. Understanding the science of solar-based energy: more researchers are better than one
4. Researchers decode viral process that prepares cells for HIV infection
5. Dartmouth researchers advance cellulosic ethanol production
6. Researchers develop new model for cystic fibrosis
7. Use it or lose it? Researchers investigate the dispensability of our DNA
8. Sigma-Aldrich and the University of Illinois Offer New Boronic Acid Surrogates to Researchers Worldwide Through Licensing Agreement
9. Researchers write protein nanoarrays using a fountain pen and electric fields
10. Researchers show how to stamp nanodevices with rubber molds
11. The Lancets New Online Medical Journal Helps Clinicians and Medical Researchers Find Practice-Changing Evidence Quickly and Easily
Post Your Comments:
*Name:
*Comment:
*Email:
(Date:5/19/2016)... - I dati saranno presentati nel ... ° Congresso della Società Americana di ... Le conclusioni dello studio indicano un tasso di risposta del ... 90% presenta una d urata della risposta (Duration Of ... cento dei pazienti ha riscontrato un beneficio clinico.   ...
(Date:5/18/2016)... 2016 The Biotech industry continues to ... that there are no opportunities ahead. Today, ActiveWallSt.com has on ... THLD ), Seattle Genetics Inc. (NASDAQ: SGEN ... Corp. (NASDAQ: OPHT ). Sign up now to ... http://www.activewallst.com/ Threshold Pharmaceuticals Inc.,s shares gained ...
(Date:5/18/2016)... ... 2016 , ... The Academy of Model Aeronautics has been helping graduating seniors ... total of $1 million in awarded scholarships. , The AMA is happy to announce ... the nation has helped bring the total of AMA scholarships that have been given ...
(Date:5/17/2016)... ... May 17, 2016 , ... ... waste reduction applications, announced today it will be showcasing ManureMagicâ„¢ at booth V1061 ... was featured in the Wall Street Journal last year and more recently made ...
Breaking Biology Technology:
(Date:4/28/2016)... and BANGALORE, India , April 28, ... Systems, a product subsidiary of Infosys (NYSE: INFY ... announced a global partnership that will provide end ... use mobile banking and payment services.      (Logo: ... key innovation area for financial services, but it also plays ...
(Date:4/15/2016)... , April 15, 2016  A new ... make more accurate underwriting decisions in a fraction ... timely, competitively priced and high-value life insurance policies ... screenings. With Force Diagnostics, rapid testing ... lifestyle data readings (blood pressure, weight, pulse, BMI, ...
(Date:3/31/2016)... March 31, 2016  Genomics firm Nabsys has completed ... Barrett Bready , M.D., who returned to the ... original technical leadership team, including Chief Technology Officer, ... Development, Steve Nurnberg and Vice President of Software and ... company. Dr. Bready served as CEO of ...
Breaking Biology News(10 mins):