Buckyball sandwich anyone?

Scientists have created a new structure by encapsulating a single layer of fullerene molecules between two graphene sheets. PICOMAT’s input, supported by EU-funding, helped to demonstrate the first direct images of a suspended 0D/2D heterostructure. This incorporates C60 molecules between two graphene layers in a suspended buckyball sandwich, as they reveal in a paper published in ‘Science Advances’.

As they state, they found, ‘clean and ordered C60 islands with thicknesses down to one molecule, shielded by the graphene layers from the microscope vacuum.’ They add that the material was partially protected from radiation damage during scanning transmission electron microscopy imaging. The resulting structures contain large atomically clean areas, allowing the direct study of C60 islands through scanning transmission electron microscopy (STEM).

A new age of carbon research

As one of the most versatile elements, carbon has held a central place in materials sciences for many years. It has several allotropes of different dimensionality, and it exhibits many different bonding geometries and as such, has attracted researchers’ attention. In 1991, one-dimensional carbon nanotubes became of interest, and in 2004 researchers started to experiment on the two-dimensional carbon allotrope, graphene. Different combinations of carbon allotropes such as fullerene-filled carbon nanotubes (carbon peapods) and graphite intercalated by fullerenes have been made already.

What makes PICOMAT’s (Picometer scale insight and manipulation of novel materials) research interesting is that by creating the fullerene-graphene system, the scientists have formed a new material that fills a gap in the available combinations of hybrid carbon heterostructures. Since the graphene sandwich provides a nanoscale reaction chamber, and a clean interface to the microscope vacuum, the observation of molecular dynamics in the transmission electronic microscope is possible. Researchers based at the University of Vienna expect this will open up new avenues for those interested in studying how other molecules, encapsulated in the same way, are structured.

How do you make a sandwich?

The researchers fabricated the sandwiches by using heat to evaporate C60 onto commercially available graphene-coated TEM grids. They then placed a second graphene-coated grid onto this and brought the two films into contact by evaporating a droplet of solvent. Unlike on a single layer of graphene, the sandwiches also contain fullerene monolayers, whose edges exhibit nonlinear image contrast of the moiré pattern of the suspended graphene layers.

Practical applications

The researchers explain that buckyball sandwiches are expected to have hybridised properties that could be suited for applications ranging from nanoscale lasers to spin cubit arrays and nanoscale mechanical elements. Additionally, they point out that alkali metal co-intercalation may turn it into a high-temperature superconductor.

For more information, please see:
CORDIS project webpage