This shows a conventional scanning tunneling microscope image of a quantum dot (top), compared with an image produced using the new excited-state SMA-STM technique (bottom). Image: Martin Gruebele.
This shows a conventional scanning tunneling microscope image of a quantum dot (top), compared with an image produced using the new excited-state SMA-STM technique (bottom). Image: Martin Gruebele.

Researchers have developed an imaging technique that uses a tiny, super-sharp needle to nudge a single nanoparticle into different orientations and capture 2D images to help reconstruct a 3D picture. This method is able to image individual nanoparticles at different orientations while in a laser-induced excited state.

The findings, published in a paper in The Journal of Chemical Physics, brought together researchers from the University of Illinois and the University of Washington, Seattle, in a collaborative project through the Beckman Institute for Advanced Science and Technology at the University of Illinois.

Nanostructures like microchip semiconductors, carbon nanotubes and large protein molecules contain defects that form during synthesis, causing them to differ in composition from one another. However, these defects are not always a bad thing, said Martin Gruebele, the lead author of the paper and an Illinois chemistry professor and chair.

"The term 'defect' is a bit of a misnomer," Gruebele said. "For example, semiconductors are manufactured with intentional defects that form the 'holes' that electrons jump into to produce electrical conductivity. Having the ability to image those defects could let us better characterize them and control their production."

As advances in technology allow for smaller and smaller nanoparticles, it is critical for engineers to know the precise number and location of these defects to assure quality and functionality. This study focused on a class of nanoparticles called quantum dots. These are tiny, near-spherical semiconductors used in technology like solar panels, live cell imaging and molecular electronics – the basis for quantum computing.

The team observed the quantum dots using a single-molecule absorption scanning tunneling microscope (SMA-STM) fitted with a needle sharpened to a thickness of only one atom at its tip. The needle nudges the individual quantum dots around on a surface and scans them to get a view from different orientations to produce a 3D image.

The researchers said there are two distinct advantages of the new SMA-STM method when compared with the current main method for studying quantum dots, a Nobel Prize-winning technique called cryogenic electron tomography (CryoET).

"Instead of an image produced using an average of thousands of different particles, as is done with CryoET, SMA-STM can produce an image from a single particle in about 20 different orientations," Gruebele said. "And because we are not required to chill the particles to near-absolute zero temperatures, we can capture the particles at room temperature, not frozen and motionless."

The researchers looked at semiconductor quantum dots for this study, but they say SMA-STM can also be used to explore other nanostructures such as carbon nanotubes, metal nanoparticles or synthetic macromolecules. The group believes the technique could even be refined for use with soft materials like protein molecules, Gruebele said.

The researchers are working to advance SMA-STM into a single-particle tomography technique, which means they will need to prove the method is non-invasive. "For SMA-STM to become a true single-particle tomography technique, we will need to prove that our nudges do not damage or score the nanoparticle in any way while rolled around," Gruebele said. "Knocking off just one atom can fundamentally alter the defect structure of the nanoparticle."

This story is adapted from material from the University of Illinois at Urbana-Champaign, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.