New research has revealed that the hills are alive with the force of van der Walls. Researchers at Rice University have found that nature’s ubiquitous ‘weak’ force is sufficient to indent rigid nanosheets, extending their potential for use in nanoscale optics or catalytic systems.

Changing the shape of nanoscale particles changes their electromagnetic properties, said Matt Jones, an assistant professor of chemistry and an assistant professor of materials science and nanoengineering at Rice University. That makes the phenomenon worth further study.

“People care about particle shape, because the shape changes its optical properties,” Jones said. “This is a totally novel way of changing the shape of a particle.” He and his colleagues report their work in a paper in Nano Letters.

Van der Waals is a weak force that allows neutral molecules to attract one another through randomly fluctuating dipoles, or separated opposite charges, depending on distance. Though small, its effects can be seen in the macro world, like when geckos walk up walls.

“Van der Waals forces are everywhere and, essentially, at the nanoscale everything is sticky,” Jones said. “When you put a large, flat particle on a large, flat surface, there’s a lot of contact, and it’s enough to permanently deform a particle that’s really thin and flexible.”

In the new study, the Rice team decided to see if this force could be used to manipulate 8nm-thick sheets of ductile silver. After a mathematical model suggested it was possible, the researchers placed 15nm-wide iron oxide nanospheres on a surface and then sprinkled prism-shaped nanosheets over them.

Without applying any other force, they saw through a transmission electron microscope that the nanosheets acquired permanent bumps where none existed before, right on top of the spheres. As measured, the distortions were about 10 times larger than the width of the spheres.

These hills weren’t very high, but simulations confirmed that van der Waals attraction between the sheet and the substrate surrounding the spheres was sufficient to influence the plasticity of the silver sheet’s crystalline atomic lattice. The researchers 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 images, we saw these strange, six-fold strain patterns, like flowers,” said Jones, who earned a multiyear Packard Fellowship in 2018 to develop advanced microscopy techniques.

“It didn’t make any sense, but we eventually figured out that it was a little ball of gunk that the plate was draped over, creating the strain,” he said. “We didn’t think anyone had investigated that, 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 rigid metal.”

In further experiments, the researchers discovered that the nanospheres could be used to control the shape of the deformation, ranging from single ridges when two spheres are close together to saddle shapes or isolated bumps when the spheres are farther apart. They determined that sheets less than about 10nm thick and with aspect ratios of about 100 are most amenable to deformation.

In the paper, the researchers noted their technique creates “a new class of curvilinear structures based on substrate topography” that “would be difficult to generate lithographically”. That opens up new possibilities for electromagnetic devices that are especially relevant to nanophotonic research. Straining the silver lattice could also turn the inert metal into a possible catalyst, by creating defects where chemical reactions can happen.

“This gets exciting because now most people make these kinds of metamaterials through lithography,” Jones said. “That’s a really powerful tool, but once you’ve used that to pattern your metal, you can never change it.

“Now we have the option, perhaps someday, to build a material that has one set of properties and then change it by deforming it. Because the forces required to do so are so small, we hope to find a way to toggle between the two.”

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

Source: https://www.materialstoday.com/nanomaterials/news/weak-force-impact-metal-nanosheets/

Researchers from the Institute of Industrial Science at the University of Tokyo in Japan have used molecular dynamics calculations to simulate the glass-forming ability of metallic mixtures. They show that even small changes in composition can strongly influence the likelihood that a material will assume a crystalline versus a glassy state upon cooling. This work, reported in a paper in Science Advances, may lead to a universal theory of glass formation and cheaper, more resilient, electroconductive glasses.

Although a table might be set with expensive ‘crystal’ glasses, crystal and glass are actually two very different states that liquids, including liquid metals, can assume as they cool. A crystal has a defined three-dimensional lattice structure that repeats indefinitely, while glass is an amorphous solid that lacks long-range ordering.

Current theories of glass formation cannot accurately predict which metallic mixtures will ‘vitrify’ to form a glass and which will crystallize. A better, more comprehensive understanding of glass formation would be a great help when designing new recipes for mechanically tough, electrically conductive materials.

Now, researchers at the University of Tokyo have used computer simulations of three prototypical metallic systems to study the process of glass formation. “We found that the ability for a multi-component system to form a crystal, as opposed to a glass, can be disrupted by slight modifications to the composition,” says first author Yuan-Chao Hu.

Stated simply, glass formation is the consequence of a material avoiding crystallization as it cools. This locks the atoms into a ‘frozen’ state before they can organize themselves into their energy-minimizing pattern. The researchers’ simulations showed that a critical factor determining the rate of crystallization was the liquid-crystal interface energy.

The researchers also found that changes in elemental composition can lead to local atomic orderings that frustrate the process of crystallization, because these orderings are incompatible with the crystal’s usual form. Specifically, these structures can prevent tiny crystals from acting as ‘seeds’ that nucleate the growth of ordered regions in the sample. In contrast with previous explanations, the scientists determined that the chemical potential difference between the liquid and crystal phases has only a small effect on glass formation.

“This work represents a significant advancement in our understanding of the fundamental physical mechanism of vitrification,” says senior author Hajime Tanaka. “The results of this project may also help glass manufacturers design new multi-component systems that have certain desired properties, such as resilience, toughness and electroconductivity.”

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

Source: https://www.materialstoday.com/amorphous/news/glass-forming-by-metallic-mixtures-becomes-clearer/

Scintacor: An Overview of Its Products and Capabilities

Ed Bullard and Martin Lewis

In this interview, AZoM talks to Ed Bullard and Martin Lewis, CEO and Principal Engineer at Scintacor respectively, about Scintacor, the companies products, capabilities, and vision for the future.

Source: https://www.azom.com/materials-news-index.aspx