STM of the cleaved superconductor IrTe2. IrTe2, a layered compound with a triangular iridium lattice, exhibits a structural phase transition at approximately 250 K. Superconductivity is a phenomenon of exactly zero electrical resistance and expulsion of magnetic fields occurring in certain materials when cooled below a characteristic critical temperature. A scanning tunneling microscope (STM) is an instrument for imaging surfaces at the atomic level. The STM is based on the concept of quantum tunneling. When a conducting tip is brought very near to the surface to be examined, a bias (voltage difference) applied between the two can allow electrons to tunnel through the vacuum between them.