Time-resolved measurements show colloidal nanoplatelets act like quantum wells

Dec 07, 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: Toward making lithium-sulfur batteries a commercial reality for a bigger energy punch

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

Faster colloidal fluorescence emitters: Nanoplatelets

Dec 09, 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 ...

Nano discs pose potential health risk

Feb 21, 2012

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

Life Expectancy on the Rise -- Even for Quantum States

Apr 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 ...

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

Jun 09, 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 ...

Recommended for you

For electronics beyond silicon, a new contender emerges

Sep 16, 2014

Silicon has few serious competitors as the material of choice in the electronics industry. Yet transistors, the switchable valves that control the flow of electrons in a circuit, cannot simply keep shrinking ...

Making quantum dots glow brighter

Sep 16, 2014

Researchers from the University of Alabama in Huntsville and the University of Oklahoma have found a new way to control the properties of quantum dots, those tiny chunks of semiconductor material that glow ...

The future face of molecular electronics

Sep 16, 2014

The emerging field of molecular electronics could take our definition of portable to the next level, enabling the construction of tiny circuits from molecular components. In these highly efficient devices, ...

Study sheds new light on why batteries go bad

Sep 14, 2014

A comprehensive look at how tiny particles in a lithium ion battery electrode behave shows that rapid-charging the battery and using it to do high-power, rapidly draining work may not be as damaging as researchers ...

User comments : 0