First 3-D imaging of excited quantum dots

February 08, 2018

WASHINGTON, D.C., February 8, 2018 -- Quantum dots are rapidly taking center stage in emerging applications and research developments, from enhanced LCD TVs and thin-film solar cells, to high-speed data transfer and fluorescent labeling in biomedical applications.

Researchers are still studying how to precisely control the growth of these nanoscale particles and their underlying quantum behavior. For instance, defects form during production of semiconductor materials, so identical dots can differ in composition from one another.

To learn more about these defects -- and whether they are a bane or an advantage -- a U.S. research team, from the University of Illinois and the University of Washington, has, for the first time, demonstrated imaging of an electronically excited quantum dot at multiple orientations. They report their findings this week in The Journal of Chemical Physics, from AIP Publishing.

"Understanding how the presence of defects localizes excited electronic states of quantum dots will help to advance the engineering of these nanoparticles," said Martin Gruebele from the University of Illinois at Urbana-Champaign and a co-author of the paper.

Defects are often considered a hassle, but in the case of quantum dot applications, they are purposely created by doping any number of materials to impart specific functions. "[M]issing atoms in a quantum dot or substituting a different kind of atom are defects that will alter the electronic structure and change the semiconductivity, catalysis or other nanoparticle properties," Gruebele said. "If we can learn to characterize them better and precisely control how they are produced, defects will become desirable dopants instead of a nuisance."

In 2005, Gruebele's team created a new imaging technique, called single molecule absorption scanning tunneling microscopy (SMA-STM), that combines the high spatial resolution of a scanning tunneling microscope with the spectral resolution of a laser. SMA-STM allows individual nanoparticles to be imaged in a laser beam, so their excited electronic structure can be visualized.

Using the thin, sharp metal wire tip of the scanning tunneling microscope, they roll the laser-excited quantum dot on the surface to image slices at different orientations. The slices can be combined to reconstruct a 3-D image of an electronically excited quantum dot.

While the research in this article was limited to lead sulfide and cadmium selenide/zinc sulfide quantum dots, the technique can potentially be expanded to other compositions. Furthermore, SMA-STM can also be used to explore other nanostructures, such as carbon nanotubes and photocatalytic metal clusters.

Researchers are now working to advance SMA-STM into a single-particle tomography technique. But, before SMA-STM becomes a "true single-particle tomography approach," they still have to ensure that the scanning and rolling does not damage the nanoparticle while it is being reoriented.

"We speculate that, in the future, it may be possible to do single-particle tomography if damage to quantum dots can be avoided during repeated manipulation," Gruebele said.

Single-particle tomography would provide a clearer picture than conventional tomography by singling out defects in individual nanoparticles rather than re-creating an averaged 3-D image that combines the measurements of many particles.
The article, "Orientation-dependent imaging of electronically excited quantum dots," is authored by Duc A. Nguyen, Joshua Goings, Huy A. Nguyen, Joseph Lyding, Xiaosong Li and Martin Gruebele. The article will appear in The Journal of Chemical Physics Feb. 8, 2018 (DOI: 10.1063/1.5012784). After that date, it can be accessed at


The Journal of Chemical Physics publishes concise and definitive reports of significant research in the methods and applications of chemical physics. See

American Institute of Physics

Related Nanoparticles Articles from Brightsurf:

An ionic forcefield for nanoparticles
Nanoparticles are promising drug delivery tools but they struggle to get past the immune system's first line of defense: proteins in the blood serum that tag potential invaders.

Phytoplankton disturbed by nanoparticles
Products derived from nanotechnology are efficient and highly sought-after, yet their effects on the environment are still poorly understood.

How to get more cancer-fighting nanoparticles to where they are needed
University of Toronto Engineering researchers have discovered a dose threshold that greatly increases the delivery of cancer-fighting drugs into a tumour.

Nanoparticles: Acidic alert
Researchers of Ludwig-Maximilians-Universitaet (LMU) in Munich have synthesized nanoparticles that can be induced by a change in pH to release a deadly dose of ionized iron within cells.

3D reconstructions of individual nanoparticles
Want to find out how to design and build materials atom by atom?

Directing nanoparticles straight to tumors
Modern anticancer therapies aim to attack tumor cells while sparing healthy tissue.

Sweet nanoparticles trick kidney
Researchers engineer tiny particles with sugar molecules to prevent side effect in cancer therapy.

A megalibrary of nanoparticles
Using straightforward chemistry and a mix-and-match, modular strategy, researchers have developed a simple approach that could produce over 65,000 different types of complex nanoparticles.

Dialing up the heat on nanoparticles
Rapid progress in the field of metallic nanotechnology is sparking a science revolution that is likely to impact all areas of society, according to professor of physics Ventsislav Valev and his team at the University of Bath in the UK.

Illuminating the world of nanoparticles
Scientists at the Okinawa Institute of Science and Technology Graduate University (OIST) have developed a light-based device that can act as a biosensor, detecting biological substances in materials; for example, harmful pathogens in food samples.

Read More: Nanoparticles News and Nanoparticles Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to