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IRG-III Highlight

Big meets very small: Light from single nanocrystal quantum dots

Figure: The schematic illustrates a light emitting device (LED) where the emitters are individual nanocrystals. In the device, isolated nanocrystal quantum dots are sandwiched between layers of organic molecules that effectively serve as leads. The photographs at the bottom show electrical operation of the device (right) compared to when it is probed optically (left), using a microscope as illustrated. The bright spots in the circles and squares in the photographs correspond to light emitted from single nanocrystals. The spatial correlation of these spots in the two photographs shows that the same individual nanocrystals are being interrogated. The graph shows the signature peak expected from a single nanocrystal emitting light.

Bringing together in devices the macroscopic world (big) with the nanoscale world (very small) continues to be a major challenge, yet it must be addressed to fully harness some of the unique properties that can arise when dimensions are decreased to nanometer length scales. For example, individual nanostructures are intrinsically hard to “wire” with current carrying leads, yet many of their unique attributes only emerge when they are electrically addressed one at a time. The usual approach is to attempt to scale down the leads to be of the dimensions of the nanostructure. This is intrinsically difficult because the tools to reproducibly create metal leads that are <10 nm in size simply do not exist. This work, by members of IRG-III of the MIT MRSEC, demonstrates an alternative strategy by using very thin layers of evaporated semiconducting organic molecules as the leads, and placing nanocrystals of semiconductors that are <10 nm in size at the interface between these layers. This new approach solves the connection problem by effectively turning the traditional wiring scheme on its side and takes full advantage of the nanometer precision that is achievable in laying down thin films.

 

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