"Unlike previous approaches to intercalating guest materials between graphene layers, our new technique allows us to encapsulate virtually any species, including tin, gold, lead, cobalt or lead sulphide," team leader Alex Zettl of the University of California at Berkeley told nanotechweb.org. "It also allows for layer-by-layer control of the guest."

For graphene veils, the guest species are widely separated from each other, he explained, and each guest particle is individually draped within a close-fitting yet atomically thin graphene net that protects the guest. In contrast, graphene sandwiches result when guest species are relatively closely spaced and form a nearly continuous inner layer – which makes up the sandwich "filling".

Since the encapsulated materials move and react differently depending on whether they are in the veil or sandwich arrangement, these novel graphene structures can be used as 2D platforms to control the movement and chemical interactions of the guest species, explained co-team leader Jeong Yong Lee of KAIST.

The researchers employed chemical vapour deposition to synthesize large areas of monolayer graphene and then transferred these onto a substrate. By repeated transfer, the graphene can be sequentially stacked, layer by layer. "However, before placing each new sheet, we deposit our guest species," said Zettl. "These species can be metallic, semiconducting or insulating nanocrystals and nanorods, for example."

No limit
In theory, there is no limit to the number of layers that can be stacked, he adds. And even though graphene was used as the host material in this work, other materials such as boron nitride and several dichalcogenides could potentially be substituted for the graphene.

According to the team, the veil and sandwich superstructures can be used as nanoscale reaction chambers for alloying diverse guest materials. "Moreover, the structures can be intermixed and electrically gated if desired and have potential applications in chemical sensors, solar cells, batteries and other optical, electrical, magnetic and mechanical applications," stated team member Jong Min Yuk, who is currently working at both KAIST and Berkeley.

The researchers are now busy trying to encapsulate organic or biomaterials between the graphene layers to make other novel superstructures.

The work was detailed in Nano Letters.