Researchers have shown how the motion of individual atoms on surfaces of graphene—a one atom thick layer of carbon—can be controlled. The adatom diffusion rate and hopping direction can be tuned by lowering the diffusion barrier using an effective electric field. This was shown using in situ scanning tunneling microscopy at low temperatures and the mechanism was elucidated using first-principles calculations. The electric field is locally tuned by inserting metal atoms below graphene. The metal atoms can be added to form regions of higher charge compared to areas without intercalated metal atoms. The potential difference between the intercalated and clean graphene regions generates an electric field directing adatoms deposited on top to hop in the direction controlled by the field. This biased diffusion leads to selective mass transport and spatially constrained nucleation of islands made from adatoms. Depending on the charge state of the adatoms, mass transfer can be biased to either the intercalated or pristine areas. Controlling the spatial distribution of the intercalant areas has promising implications for the design of novel electronic and spintronic devices made from graphene.
Schematic representation of how the adatoms (small spheres) are guided by the electric field. The non-intercalated domain shown in the middle of the figure has higher electrostatic potential. An electric field is generated at the boundary and, in this case, the middle region attracts the adatoms.
Metal Intercalation-induced Selective Adatom Mass Transport on Graphene