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Nano-hybrid materials creates 'pseudo-magnetic' effect

14 January 2016

Rice University and Montreal Polytechnic researchers are hoping to develop new hybrid materials from graphene and boron nitride that have novel properties.

The calculated properties of a three-dimensional hybrid of graphene and boron nitride nanotubes would have pseudo-magnetic properties, according to researchers (image: Shahsavari Lab/Rice University)

Rice materials scientist Rouzbeh Shahsavari and Farzaneh Shayeganfar, a postdoctoral researcher at Montreal Polytechnic, have designed computer simulations that combine graphene with either carbon or boron nitride nanotubes. Their hope is that such hybrids can take advantage of the best aspects of their constituent materials.

Defining the properties of various combinations would simplify development for manufacturers who want to use these exotic materials in next-generation electronics. However, the researchers found not only electronic, but also magnetic properties that could be useful.

"We wanted to investigate and compare the electronic and potentially magnetic properties of different junction configurations, including their stability, electronic band gaps and charge transfer," says Shahsavari. "Then we designed three different nanostructures with different junction geometry."

Two were hybrids with graphene layers seamlessly joined to carbon nanotubes. The other was similar but, for the first time, they modelled a hybrid with boron nitride nanotubes. How the sheets and tubes merged determined the hybrid's properties. They also built versions with nanotubes sandwiched between graphene layers.

Graphene is a perfect conductor when its atoms align as hexagonal rings, but the material becomes strained when it deforms to accommodate nanotubes in hybrids. The atoms balance their energies at these junctions by forming five-, seven- or eight-member rings. These all induce changes in the way electricity flows across the junctions, turning the hybrid material into a valuable semiconductor.

The researchers' calculations allowed them to map out a number of effects. For example, it turned out the junctions of the hybrid system create pseudo-magnetic fields.

"The pseudo-magnetic field due to strain was reported earlier for graphene, but not these hybrid boron nitride and carbon nanostructures where strain is inherent to the system," says Shahsavari. He notes the effect may be useful in spintronic and nano-transistor applications.

"The pseudo-magnetic field causes charge carriers in the hybrid to circulate as if under the influence of an applied external magnetic field," he adds. "Thus, in view of the exceptional flexibility, strength and thermal conductivity of hybrid carbon and boron nitride systems, we propose the pseudo-magnetic field may be a viable way to control the electronic structure of new materials."

The researchers say they are laying the foundations for a range of tunable hybrid architectures, especially for boron nitride, which is as promising as graphene though much less explored.

An article describing this work appears in the journal, Carbon.

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