You have to look closely, but the mountains are alive with the force of van van Waals.
Scientists at Rice University found that nature’s ubiquitous “weak” force is sufficient for rigid nanosets, expanding their potential for use in nanoscale optics or catalytic systems.
Changing the size of nanoscale particles changes their electromagnetic properties, said Matt Jones, Norman and Jean Hackerman assistant professor of chemistry and assistant professor of materials science and nanoengineering. This makes the event worth further study.
“People care about particle size, because shape changes its optical properties,” Jones said. “This is a completely novel way of changing the shape of a particle.”
Jones and graduate student Sarah Rehan led studies in the Nano Letters of the American Chemical Society.
Van der Waals is a weak force that allows neutral molecules to attract each other through randomly fluctuating dipoles based on distance. Although small, its effect can be seen in the macro world, such as when Jakaus walks on the walls.
“The van der Waals forces are everywhere and essentially, everything at the nanoscale is viscous,” Jones said. “When you place a large, flat particle on a large, flat surface, there’s a lot of contact, and that’s enough to permanently deform a particle that’s really thin and flexible.”
In the new study, the Rice team decided to see if the force could be used to manipulate an 8-nanometer thick sheet of ductile silver. After a mathematical model that he discovered was possible, he placed a 15-nanometer-wide iron oxide nanosphere on a surface and sprinkled prism-shaped nanosets on them.
Without applying any other force, he observed through a transmission electron microscope that the nanosheets acquired permanent bumps, where none was already present, right above the sphere. As measured, the deformations were approximately 10 times larger than the width of the sphere.
The hills were not very high, but simulations confirmed that the attraction between the van der Waals sheet and the substrate surrounding the shells was sufficient to affect the plasticity of the silver crystalline atomic lattice. They also showed that the same effect would occur in silicon dioxide and cadmium selenide nanosheets and perhaps other compounds.
“We were trying to make really thin, large silver nanoplates and when we started taking pictures, we saw these weird, six-fold stress patterns, like flowers,” said Jones, who advanced microscopy in 2018. Earned a Multi-Packard Fellowship to develop technology. .
“It made no sense, but we finally figured out that it was a little ball of gunk that was wrapped in a plate, causing tension,” he said. “We don’t think anyone had investigated, so we decided to have a look.
“What it comes down to is that when you make a particle really thin, it becomes really flexible, even if it’s a hard metal,” Jones said.
In further experiments, the researchers observed that nanospheres could be used to control the shape of the deformation, from single ridges when the two spheres are close, to the shape of the saddle to separate shapes or to separate bumps.
They determined that sheets with a ratio of about 10 nanometers thick and a ratio of about 100 are the most favorable for deformation.
The researchers said their technique creates “a new class of curvature structures based on substrate topography” that would be difficult to generate lithographically. ” This opens up new possibilities for electromagnetic devices that are particularly relevant to nanophotonic research.
Suppressing the silver lattice also replaces the inert metal by creating a defect in a potential catalyst where a chemical reaction can occur.
“It gets exciting because now, most people make this type of metametry through lithography,” Jones said. “It is a really powerful tool, but once you have used your metal to pattern it, you can never change it.
“Now we have the option, perhaps someday, to create a material that has a set of properties and then replace it by distorting it,” he said. “Because the forces required to do so are very small, we hope to find a way to toggle between the two.”