Surface science of diamond: Familiar and amazing

The crystal structure of diamond is identical with that of its more common semiconductor relatives silicon and germanium. Consequently, a number of surface properties in terms of reconstructions, surface states and surface band diagrams are similar as in the case of Si or Ge. But diamond also exhibits a number of unusual and potentially very useful surface properties. Particularly when the surface dangling bonds are saturated by monovalent hydrogen atoms (donor-like), surface states are removed from the gap, the electron affinity changes sign and becomes negative, and the material becomes susceptible to an unusual type of transfer doping where holes are injected by acceptors located at the surface instead of inside the host lattice. These surface acceptors can in the simplest case be adsorbed molecules conveniently chosen by their electron affinity, but they can also be solvated ions within atmospheric water layers or electrolytes in contact with the hydrogenated diamond surface. In this article the surface properties of diamond will be reviewed with special emphasis on this new kind of doping mechanism.