There are a lot of similarities between real atoms and the quantum "dots" used to confine electrons in semiconductors. Now Uri Banin and colleagues from the Hebrew University in Israel have directly measured the atomic-like electronic states in a quantum dot for the first time (Nature 400 542).
Banin and co-workers used quantum dots made of indium arsenide, covered with a nonconducting barrier of hexane dithiol molecules and linked to a conducting gold film. The radius of the nearly spherical indium arsenide nanocrystals varied between 10 and 40 nm. Electrons tunnel from the gold through the insulating layer to the nanocrystal. The number of electrons in the dot can be controlled by adjusting the voltage on the gold film.
Quantum dots can only confine electrons at low temperatures, so the Israeli team had to adapt a scanning tunnelling microscope to operate at cryogenic temperatures. When Banin and co- workers examined the current-voltage curve of the tip as it moved over the nanocrystals, they noticed a number of discrete single-electron tunnelling peaks that matched the pattern of energy levels seen in real atoms.
