Time-resolved measurements show colloidal nanoplatelets act like quantum wells

December 7, 2012
Time-resolved measurements show colloidal nanoplatelets act like quantum wells
Schematic and transmission electron microscope (TEM) image of CdSe nanoplatelets with a thickness of 5 monolayers.

The relaxation of high-energy carriers (electrons and holes) in colloidal nanoplatelets have been measured by researchers in the Nanophotonics Group at the Center for Nanoscale Materials, working with colleagues at the University of Chicago. The measurements show that the carriers behave like carriers in quantum wells. Quantum wells have found widespread application in optoelectronics, and the new results suggest that colloidal nanoplatelets should find similar applications, with the added advantage that they can be produced at low cost and in large quantities.

Quantum wells are thin semiconductor layers in which charge carriers are confined in one dimension but are free to move in the other two dimensions. Such confinement means that these structures have tuneable optical bandgaps and can strongly absorb and emit light, which makes them good materials for optical modulators and . Until recently, could be produced only by using expensive crystal-growth techniques such as and metal-organic vapor-phase epitaxy. Recently, however, methods have been developed to chemically synthesize thin, flat, in solution. These "nanoplatelets" are only a few atomic layers thick but tens to hundreds of nanometers across. Charge carriers in these structures should therefore behave as they would in a quantum well. Measurements of and emission from nanoplatelets have indicated that this is indeed the case, but evidence has been indirect, and results from different groups have disagreed with one another quantitatively.

The new experiments use time- and frequency-resolved photoluminescence measurements to monitor how high-energy charge carriers relax in the nanoplatelets. The observed relaxation was consistent with quantum well behavior, and qualitatively different from what would be expected for a quantum dot, where carriers are confined in all three dimensions. Moreover, the relaxation is rapid, occurring in less than 50 picoseconds. This means that the nanoplatelets should serve well as the active material in optical modulators and in semiconductor lasers.

Explore further: Life Expectancy on the Rise -- Even for Quantum States

More information: M.Pelton, S. Ithurria, R.D. Schaller, D.S. Dolzhnikov, and D.V. Talapin, "Carrier cooling in colloidal quantum wells," Nano Lett. ASAP (2012). DOI: 10.1021/nl302986y

Related Stories

Life Expectancy on the Rise -- Even for Quantum States

April 14, 2009

(PhysOrg.com) -- For the first time, scientists have succeeded in measuring and controlling the lifetime of quantum states with potential use in optoelectronic chips. This achievement is highly significant for the ongoing ...

'Dark Pulse Laser' produces bursts of... almost nothing

June 9, 2010

In an advance that sounds almost Zen, researchers at the National Institute of Standards and Technology and JILA, a joint institute of NIST and the University of Colorado at Boulder, have demonstrated a new type of pulsed ...

Faster colloidal fluorescence emitters: Nanoplatelets

December 9, 2011

(PhysOrg.com) -- Significant advances in the application of colloidal structures as light emitters and lasers may soon be realized following the discovery of very fast fluorescence emission rates in colloidal nanoplatelets. ...

Nano discs pose potential health risk

February 21, 2012

(PhysOrg.com) -- A revolutionary material that is used in computer technology could pose health risks to those involved in its manufacture.

Recommended for you

Fast times and hot spots in plasmonic nanostructures

August 4, 2015

The ability to control the time-resolved optical responses of hybrid plasmonic nanostructures was demonstrated by a team led by scientists in the Nanophotonics Group at the Center for Nanoscale Materials including collaborators ...

Study explores nanoscale structure of thin films

August 4, 2015

The world's newest and brightest synchrotron light source—the National Synchrotron Light Source II (NSLS-II) at the U.S. Department of Energy's Brookhaven National Laboratory—has produced one of the first publications ...

Meet the high-performance single-molecule diode

July 29, 2015

A team of researchers from Berkeley Lab and Columbia University has passed a major milestone in molecular electronics with the creation of the world's highest-performance single-molecule diode. Working at Berkeley Lab's Molecular ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.