Magnetene: Graphene-like 2D material leverages quantum effects to achieve ultra-low friction

This schematic shows the lattice structure of magnetene, with red spheres depicting iron and red ones depicting oxygen. Credit: University of Toronto Engineering

A team of researchers from the University of Toronto Engineering and Rice University have measured the behavior of a material called magnetene. Strategies for designing low-friction materials for use in a variety of fields, including tiny, implantable devices, are shown in the results.

A 2D material is composed of a single layer of atoms. It is similar to Graphene, a material that has been studied for its unusual properties since 2004.

Peter Serles is the lead author of a new paper published today in Science Advances.

The theory was that the sheets of Graphene slide past each other easily because they are weakly bonding. It doesn't take much effort to spread the deck out because the cards are so easy to pick up.

The team, which includes Professors Filleter and Singh, and Post-Doc Yadav, wanted to compare the two materials to see if they were the same.

Magnetene is a form of iron oxide which is normally found in a 3D lattice. The Rice University team treated 3D magnetite using high-frequency sound waves to separate a few sheets of 2D magnetene.

The University of Toronto Engineering team put the sheets into the microscope. The probe is dragged over the top of the magnetene sheet to measure the force. The process is similar to how a record player's stylus is dragged across the surface of a record.

Peter Serles is a PhD candidate. The low-friction behavior of this material is due to quantum effects. Credit: University of Toronto Engineering.

The bonds between the layers of magnetene are stronger than those between a stack of Graphene sheets, says Serles. They don't move past each other. The tip of the probe and the uppermost slice of magnetene had the same amount of friction.

The theory that the sheets can slide because they are only bonded by weak Van der Waals forces is no longer valid. The low-friction behavior of magnetene, which doesn't exhibit these forces due to its structure, suggests something else is going on.

"When you change from a 3D material to a 2D material, there are a lot of strange things that happen," says Serles. It can be very smooth or very rough depending on the angle you cut it from. The atoms are able to vibrate in different ways because they are no longer restricted in the third dimensions. The electron structure changes as well. We found that all of these affect the situation.

The team compared their experimental results to those predicted by computer simulations. The probe tip sliding over the 2D material was simulation of the behavior of the mathematical models constructed by Yadav and Singh. The models that incorporated the quantum effects were the best predictors.

Serles says that the team's findings offer new information for scientists and engineers who want to design ultra-low-friction materials. Such substances could be useful in small-scale applications.

A tiny pump that delivers a controlled amount of a drug to a specific part of the body is a possible example. Other kinds of micro-electro-mechanical systems could harvest the energy of a beating heart to power a sensor, or power a tiny robotic manipulator capable of sorting one type of cell from another in a petri dish.

Filleter says that the ratio of surface area to mass is high when dealing with tiny moving parts. It means that things are more likely to get stuck. We've shown in this work that these 2D materials have low friction because of their tiny scale. The quantum effects wouldn't apply to larger materials.

Magnetene is very attractive for use in implantable mechanical devices because of the scale-dependence effects and the fact that iron oxide is non-toxic and inexpensive. There is more work to be done before the quantum behaviors are fully understood.

He says that they have tried this with other iron-based 2D materials, but they don't see the same quantum signatures. We need to know why these quantum effects are happening, so that we can design new kinds of low-friction materials.

Peter Serles and his team have a paper on Friction of magnetene, a non–van der Waals 2D material. has a DOI of/10.1126/sciadv.abk 2041.

Science Advances has journal information.

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