Atom Every atom is composed of a nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and typically a similar number of neutrons. Protons and neutrons are called nucleons. More than 99.94% of an atom's mass is in the nucleus. The protons have a positive electric charge, the electrons have a negative electric charge, and the neutrons have no electric charge. If the number of protons and electrons are equal, that atom is electrically neutral. If an atom has more or fewer electrons than protons, then it has an overall negative
Single-atom transistor Single-atom transistor A single-atom transistor is a device that can open and close an electrical circuit by the controlled and reversible repositioning of one single atom. The single-atom transistor was invented and first demonstrated in 2004 by Prof. Thomas Schimmel and his team of scientists at the Karlsruhe Institute of Technology (former University of Karlsruhe). By means of a small electrical voltage applied to a control electrode, the so-called "gate electrode", a single silver atom is reversibly moved in and out of a tiny junction, in this way closing and opening an electrical contact. Therefore, the single-atom transistor works as