Quantum Dots With Single-Atom Precision

Aiming to make ever-faster and smaller computers that run on less power than today’s electronics, scientists have been studying ways of building circuits from nanosized semiconductor nanocrystals known as quantum dots. These bits of matter are often referred to as artificial atoms because of their atomlike electronic properties. Yet unlike atoms, quantum dots vary in size and shape. That diversity leads to electronic property differences that undermine their usefulness as nanocircuit building blocks. To bypass these uncontrolled variations, Stefan Fölsch of Paul Drude Institute for Solid-State Electronics, in Berlin; Steven C. Erwin of the Naval Research Laboratory, in Washington, D.C.; and coworkers devised a scanning tunneling microscopy method to make quantum dots with single-atom precision (Nat. Nanotechnol. 2014, DOI: 10.1038/nnano.2014.129). They used regularly spaced atomic vacancies that naturally form on the surface of an indium arsenide crystal—which resemble the voids of an egg carton—to hold a select number of indium atoms at fixed lattice locations. They then formed sets of geometrically and electronically identical indium quantum dots with up to 25 atoms and showed that the dots could be used to make identical artificial molecules.