Abstract
The paper describes the construction and performance of an atom-probe field-ion microscope which uses a time-gated microchannel plate as a single-ion detector with spatial resolution. The instrument has a mass resolution Delta m/m in the range 1/15 to 1/25, and a spatial resolution of the order of 1 nm. It is particularly suitable for the detection of segregation at grain boundaries, and an example (oxygen in molybdenum) is given.