Modeling uncovers an 'atomic waltz' for atom manipulation

Based on computer simulations, indirect exchange mechanism for electron-beam manipulations of bismuth and antimony dopants within silicon. The crimson circle is a bismuth-atom, and the yellow and green spheres its closest and nearest silicon neighbors. Credit: Toma Susi and Alexander Markevich, University of Vienna, Andrew R. LupiniIn collaboration with Oak Ridge National Laboratory colleagues in the U.S., researchers from the University of Vienna's Faculty of Physics discovered a non-destructive way to manipulate donor impurities in silicon by focused electron irradiation. This indirect exchange process involves not just one, but two silicon atoms in a coordinated "waltz", which could open the door to the fabrication of solid state qubits. These results were published in the Journal of Physical Chemistry.Nanotechnology is a way to engineer materials at the atomic level. Examples of atom manipulation using scanning tunneling microscopy include the creation of quantum corals and rewritableatomic memories. While scanning probe techniques can be used to manipulate surface atoms, these tools cannot reach the bulk of the material. They must contact the sample with a physical tip and are usually stored at cryogenic temperatures.Recent advancements in scanning transmission electron microscope (STEM), have sparked interest in the use of an electron beam to manipulate atoms. Vienna is one of the most important hubs for this research. This technique has the unique ability to reach not only surface atoms, but also small-sized impurities in bulk crystals. Toma Susi says that this is more than a theoretical possibility. Our US collaborators recently demonstrated the first proof of principle manipulation of bismuth-dopants in silicon.This new work is a systematic modeling study of the electron beam manipulation of group V dopant element within silicon. The Vienna team discovered a new type of mechanism called indirect exchange. This involves not one, but two neighboring silicon elements in an atomic "waltz," which helps explain how electron impacts can move these impurities throughout the silicon lattice. Alexander Markevich says that while this mechanism is only applicable to the two heavier elements of bismuth or antimony, it is crucial to note that it is not destructive, since no atoms must be removed from the silicon lattice.The team also demonstrated for the first-time that it was possible to manipulate silicon antimony impurities using STEM. This is an experimental breakthrough. New applications could be possible through the precise placement of dopant electrons in crystal lattices, including quantum computation and solid-state sensing. This could have some exciting implications. Susi states that antimony dopants found in silicon have been suggested recently as promising candidates to make solid-state nuclear spin qubits. Our work may help open the door for their deterministic fabrication.Continue reading Manipulating single Atoms with an Electron Beam