Nano 'Sandwich' Could Enhance Optical Properties, Tunability of Graphene

Use of a “nanoscale sandwich,” made from two-atom-thick slices of graphene around nanoclusters of magnesium oxide (MgO), could expand the optoelectronic properties for graphene.

Researchers at Rice University, using previous experiments on hybrid materials as a reference point, applied high-level first-principle calculations to their exploration of the electronic and optical properties of mono- and double-layer graphene encapsulating MgO clusters.

The researchers correlated the stability of adsorption, geometry, charge transfer, band structures, the optical absorption spectrum and the van der Waals pressure for their “nano sandwich”. Results revealed various synergies in electro- and opto-mutable properties of the MgO/graphene material.

Nanoclusters of magnesium oxide sandwiched between layers of graphene make a compound with unique electronic and optical properties, according to researchers at Rice University who made computer simulations of the material. Courtesy of Lei Tao/Rice University.

Additionally, the researchers found that 2D-MgO flakes on graphene layers exhibited surface polarization effects, in contrast to isolated neutral flakes. The 2D-MgO flakes on graphene layers showed a significant charge transfer from graphene to n-doped flakes, breaking the symmetry of graphene layers.

The researchers observed that, while there was one quantum emission in the visible light region for a single MgO flake, a wide range of visible light was accessible for MgO on mono- and double-layer graphene.

“We saw that while this single flake of magnesium oxide absorbed one kind of light emission, when it was trapped between two layers of graphene, it absorbed a wide spectrum. That could be an important mechanism for sensors,” said materials scientist Rouzbeh Shahsavari.

The findings could support further insight and design strategies for modifying 2D materials for applications in optoelectronics, and could broaden the spectrum of strategies for fabricating novel hybrid 2D heterostructures by encapsulating external molecules. The graphene/MgO compound could be useful for molecular sensing, catalysis and bio-imaging.

Rouzbeh Shahsavari, Rice University. Courtesy of Jeff Fitlow/Rice University.

“There is no single material that can solve all the technical problems of the world,” Shahsavari said. “It always comes down to making hybrid materials to synergize the best features of multiple components to do a specific job. My group is working on these hybrid materials by tweaking their components and structures to meet new challenges.”

The research was published in Nanoscale (doi: 10.1039/C6NR08586E).