The image shows a representation of a three-dimensional hybrid of graphene and boron nitride nanotubes, which would have pseudomagnetic properties. Image: Shahsavari Lab/Rice University.
The image shows a representation of a three-dimensional hybrid of graphene and boron nitride nanotubes, which would have pseudomagnetic properties. Image: Shahsavari Lab/Rice University.

Building up novel materials from individual atoms goes faster when some of the trial and error is eliminated. A new Rice University and Montreal Polytechnic study aims to do that for hybrid nanomaterials made from graphene and boron nitride.

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

Defining the properties of various different combinations would simplify the development process for manufacturers who want to use these exotic materials in next-generation electronics. The researchers discovered not only electronic properties but also magnetic properties that could be useful. Their results appear in the journal Carbon.

Shahsavari's lab studies materials to see how they can be made more efficient, functional and environmentally friendly. These include macroscale materials like cement and ceramics as well as nanoscale hybrids with unique properties.

"Whether it's on the macro- or microscale, if we can know specifically what a hybrid will do before anyone goes to the trouble of fabricating it, we can save cost and time and perhaps enable new properties not possible with any of the constituents," Shahsavari said.

His lab's computer models simulate how the intrinsic energies of atoms influence each other as they bond into molecules. For this new work, the researchers modeled hybrid structures that combine graphene with either carbon nanotubes or boron nitride nanotubes.

"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," he said. "Then we designed three different nanostructures with different junction geometry."

They modeled two hybrids with graphene sheets seamlessly joined to carbon nanotubes, and, for the first time, a hybrid comprising graphene sheets with boron nitride nanotubes. How the sheets and tubes merged determined the properties of these hybrids. They also built versions with nanotubes sandwiched between the graphene sheets.

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 rings 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, they discovered that pseudomagnetic fields form at the junctions of the hybrid systems.

"The pseudomagnetic 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," Shahsavari said. He noted that the effect may be useful in spintronic and nano-transistor applications.

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

All the effects serve as a road map for nanoengineering applications, Shahsavari said.

"We're laying the foundations for a range of tunable hybrid architectures, especially for boron nitride, which is as promising as graphene but much less explored," he said. "Scientists have been studying all-carbon structures for years, but the development of boron nitride and other two-dimensional materials and their various combinations with each other gives us a rich set of possibilities for the design of materials with never-seen-before properties."

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.