The scanning tunneling microscope has been able to move atoms over surfaces since the late 1980s. Now, the scanning transmission electron microscope (STEM) is able to reliably focus an electron beam with sub-atomic precision, allowing scientists to directly see each atom in two-dimensional materials like graphene, and also to target single atoms with the beam. Each electron has a tiny chance of scattering back from a nucleus, giving it a kick in the opposite direction.
Building on work published over the past few years, a research team at the University of Vienna led by Toma Susi has now used the advanced electron microscope Nion UltraSTEM100 to move single silicon atoms in graphene with truly atomic precision.
The researchers recorded nearly 300 controlled jumps. Additional to extended paths or moving around a single hexagon made of carbon atoms in graphene, a silicon impurity could be moved back and forth between two neighboring lattice sites separated by one tenth-billionth of a meter, like flipping an atomic-sized switch. In principle, this could be used to store one bit of information at record-high density.
The direct manipulation of individual atoms in materials using scanning probe microscopy has been a seminal achievement of nanotechnology. Recent advances in imaging resolution and sample stability have made scanning transmission electron microscopy a promising alternative for single-atom manipulation of covalently bound materials. Pioneering experiments using an atomically focused electron beam have demonstrated the directed movement of silicon atoms over a handful of sites within the graphene lattice. Researchers have now achieved a much greater degree of control, allowing them to precisely move silicon impurities along an extended path, circulating a single hexagon, or back and forth between the two graphene sublattices. Even with manual operation, the manipulation rate is already comparable to the state-of-the-art in any atomically precise technique. They further explore the influence of electron energy on the manipulation rate, supported by improved theoretical modeling taking into account the vibrations of atoms near the impurities, and implement feedback to detect manipulation events in real time. In addition to atomic-level engineering of its structure and properties, graphene also provides an excellent platform for refining the accuracy of quantitative models and for the development of automated manipulation.