Heteroatom quantum corrals and nanoplasmonics in graphene

The objective of the Heteroatom quantum corrals and nanoplasmonics in graphene (HeQuCoG) project is to create atomically precise structures made of silicon and phosphorus atoms embedded in the lattice of graphene. This will be achieved by combining proven modeling techniques with sample fabrication via carefully controlled ion implantation, and subsequent manipulation in an atomic resolution scanning transmission electron microscope (STEM). The structures will be computationally designed for interesting nanoplasmonic enhancement and quantum confinement properties, and characterized by electron energy loss spectroscopy mapping in the STEM. The expected outcome is a systematic demonstration of truly atomic-level material design and the creation of freestanding quantum corral structures for the first time. The controlled manipulation of matter on truly the atomic scale has been a long-standing dream of nanotechnology. Pioneering directions towards have already been explored, chiefly with the help of scanning tunneling microscopy. However, compared to the manipulation of surface atoms, graphene heteroatoms have the advantage of being stable at room temperature and even if the sample is taken out of the instrument. Furthermore, the coupling of light to nanostructures via plasmon resonances is an intensively pursued and promising research field, which is awaiting breakthroughs in material design before the field can live up to its expected potential.

Materials are defined by their chemical structure - which atoms are placed where. To control their properties, one can either exchange atoms, or change their arrangement. The only tool to directly manipulate individual atoms, the scanning probe microscope, has since the late 1980s been able to move weakly bound atoms over surfaces held far below room temperature. A fundamentally different tool, the scanning transmission electron microscope (STEM), has recently become able to reliably focus an electron beam with sub-atomic precision. This allows the scientists to directly see each atom in two-dimensional (2D) materials like graphene, and also to target individual atoms with the beam. In 2014, Dr. Toma Susi discovered that silicon impurities occasionally found in graphene jump during imaging. Computer simulations explained the mechanism - an electron "kicks" the carbon neighbor of a silicon atom - revealing the potential to use the electron beam to manipulate strongly bound materials with atomic precision. With the support of the Austrian Science Fund and working with his colleagues of the Faculty of Physics at the University of Vienna, Susi recorded the first controlled movement of a silicon atom in 2017. Building on this work, the project team was able to establish this technique as robust way to move single atoms in graphene with truly atomic precision. Even with manual operation, the achieved movement rate of silicon impurities is already comparable to the state-of-the-art in any atomically precise technique. In further experiments the researchers were also able to control phosphorus impurities, which has interesting electronic and magnetic properties that may find potential applications in fields such as quantum computing. The project was thus able to establish electron microscopy as a new kind of atom manipulation tool.