Researchers at AIST, in collaboration with Osaka University, Tokyo Polytechnic University, Kyushu University, and National Tsing Hua University, have developed a technique to insert alkali metals into the interlayers of graphene, which is a single layer of carbon atoms arranged in a hexagonal lattice. They have succeeded in directly observing the atomic arrangement of the inserted alkali metal atoms which is a hexagonal close packed bilayer structure.