Abstract
A detailed analysis is presented of a particular iridium-0.3 a/o zirconium field-ion specimen in which twin lamellae were observed. The orientation relationship between the twinned and matrix structures is demonstrated and, further, it is shown that these lamellae are parallel-sided and fully coherent. The resolution of the field-ion microscope allows the detailed (111) stacking sequence across the twins to be investigated. The origin of the dim/bright contrast found to be characteristic of the presence of the individual (111) composition planes when observed in the (111) imaging region is discussed in terms of the energy of such a coherent interface, the local (111) stacking sequence and the tip geometry.