One of the world’s leading theoretical physicists working on the interactions of light with nanomaterials, Dr Alexandre Govorov, teams up with collaborators in the house of the world’s first supercomputer to apply the world’s best specialized software to calculate complex nanostructures capable of concentrating light and energy.
As a distinguished MATH + visiting scholar at the Zuse Institute in Berlin, Govorov studies chiral nanostructures that interact with polarized light – a field of which he is one of the founding fathers – and associates it with his pioneering work on hot electrons.
Nanocrystals like the ones Govorov is studying have potential for use in light imaging devices, electronics, sensors, and even biological applications. But Govorov has his eye on energy applications to efficiently harvest sunlight and convert it into chemical fuels.
“It’s a dream, to make it efficient and inexpensive,” said Govorov, E. and R. Kennedy professor emeritus of physics at Ohio University.
In its laboratory in Athens, Govorov’s team has a powerful IT cluster and commercial software. In Berlin, Dr Sven Burger uses specialized software to perform numerical calculations in nanoscience and electromagnetics. The two groups have been working together for three years and, in this new venture, they will develop digital models with applications in energy research and photonics. Among other nanostructures, they will model self-assembled DNA-based nanocrystals with optical responses – also known as DNA origami technology.
“We will model the behavior of these complex nanostructures and nanodevices under different conditions and how they can function as devices. We can design and visualize these models, then we can pass our data to the experimenters, and we hope our theory will work well.” , said Govorov. noted.
Their planned collaborations include:
- Numerical models for photonics, optoelectronics and solar energy conversion, including the study of the excitation of the carrier charge (electronic charge) in metallic nanostructures as well as the generation of hot electrons (photochemistry) .
- Chiral reactions and chiral growth using bioplasmonic nanocrystals, with potential applications in chiral photochemistry and biodetection.
Chirality: don’t look at yourself in the mirror
Govorov said one of the most interesting things he has discovered so far in his career is “the new optical properties of this chiral bioassembly of nanostructures.” Chirality means that an image cannot be superimposed on its mirror image. Having discovered this phenomenon, Govorov now wants to control it and use it.
Govorov discovered that chiral nanocrystals interact with polarized light and that the resulting optical properties can be important for optical applications.
The chirality can be in the form of a left or right helix; DNA is an example of a right-handed chiral structure. In their models, Govorov and Burger use models based on DNA assembly technology as the “architecture” to build their nanocrystals. While Burger and Govorov do computational nanoscience, real-world DNA assemblies are being made in Munich by Professor Tim Liedl, one of the world leaders in this difficult field.
One of the projects of the Berlin study is “the origin of chirality. Chirality is three-dimensional, and chirality is important for everything, for all biomolecules … Molecular recognition is based on chiral entities nested within each other, “Govorov said.” And we can demonstrate how the Chirality is created by building superstructures – nanocrystal by nanocrystal – and showing when chirality arises through DNA control. The Munich lab is good at performing such DNA tasks. “
In other words, they will model the construction of meta-molecules made up of nanocrystals and observe how this fundamental chiral property is created and evolves.
Hot electrons: harnessing energy
Govorov is also known for his pioneering work on the generation of hot electrons in optical nanomaterials. In a traditional metal, a high energy hot election is short lived and produces parasitic heat. But Govorov wants to harness this energy using plasmonic nanostructures where hot electrons are created in special spaces (hot spots) and, therefore, can be extracted.
He has written more than two dozen articles on the dynamics of hot electrons that can induce chemical reactions important for photovoltaics. And he doesn’t stop developing the theory. He is working with leading experimental groups, including the Argonne National Laboratory, on the generation of hot electrons from plasmonic hot spots. A related article on this topic was published by them in Nature Nanotechnology. His longtime collaborator at Argonne is Dr Gary Wiederrecht, Deputy Director of the Center for Nanoscale Materials.
These hot spots are believed to occur in the spaces or crevices between nanocrystals that do not fit together.
Where the theories of chirality and hot electrons meet
These two components – chirality and hot electrons – come together in the Berlin study, where collaborators “will calculate complex nanostructures with complex shapes, devices that require high-precision calculations. The Berlin group is the one of the best in such calculations, “Govorov mentioned.
Then, they will model how these chiral plasmonic structures can reflect light or generate hot electrons.
This collaboration recently resulted in a new publication, Long and short distance chiral interactions in assembled plasmon chains of DNA in Nature Communication, where the authors identify and implement different coupling entities – chiral and achiral – to demonstrate chiral transfer over distances close to 100 nanometers. The coupling is performed by an achiral nanosphere located between a pair of gold nanorods which are arranged far apart but chirally using DNA origami.
Such transfer distances are unprecedented for molecules, but they become possible thanks to plasmonic nanocrystals combined with DNA assembly. The above post in Nature Communication is just one example of a successful collaboration between the University of Munich, Zuse Berlin and OHIO. Another piece of their joint work, Hot electrons generated in chiral plasmonic nanocrystals as a mechanism for surface photochemistry and chiral growth, was recently published in a leading chemistry journal, JACS.
An international collaborative group at OHIO
The Ohio University Theoretical Group is highly international and collaborative. The group is well funded, producing around 20 articles per year. Their research recently resulted in a new patent on optical metapists.
The MATH + Distinguished Visiting Scholar Award from the Zuse Institute in Berlin also includes a student exchange program. The first visit of Eva Yazmin Santiago Santos, a doctoral student in physics at OHIO, is scheduled for February 2022.
Oscar Avalos Ovando, a postdoctoral researcher who obtained a doctorate. in OHIO physics in 2019 with Dr Sergio Ulloa’s group, is funded by another collaboration, a grant from the BSF US-Israel Foundation. The Govorov group has also received several grants from national funding agencies.