Twinning of Iridium in a Field Ion Microscope

Multiple twinning of [111]-oriented iridium crystals caused by the field stress is observed in a field ion microscope. The twin plane is pure (111) and the direction of shear [112̄]. The twins are formed only at small tip radii. The twins are stable enough to survive annealing to 1000°C and controlled field evaporation of many atomic layers.