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All matter is composed of atoms, which are too small to see without powerful modern instruments including electron microscopes. The same electrons that form images of atomic structures can also be used to move atoms in materials. This technique of single-atom manipulation, pioneered by University of Vienna researchers, is now able to achieve nearly perfect control over the movement of individual silicon impurity atoms within the lattice of graphene, the two-dimensional sheet of carbon. The latest results are reported in the scientific journal Nano Letters.

As an epoch-making achievement in nanotechnology, the scanning tunneling microscope has since the late 1980s been able to move atoms over
surfaces, and has until very recently been the only technology capable of moving individual atoms in such a controlled manner. 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. Even with manual operation, the achieved movement rate is already comparable to the state-of-the-art in any atomically precise technique. "The control we are able to achieve by essentially directing the electron beam by hand is already remarkable, but we have further taken the first steps towards automation by detecting the jumps in real time," says Susi. The new results also improve theoretical models of the process by including simulations by collaborators in Belgium and Norway.

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Category: Science