Using the time-of-flight atom-probe field-ion microscope, we have obtained an absolute composition depth profile of a Ni-Cu(5%) alloy, with single-atomic-layer resolution. The first-layer Cu composition is found to be (54.1±4.7)% on the (111) plane at 550°C. The Cu concentration of the near-surface layers is slightly lower as compared to the bulk. The composition returns to bulk value in about 5 atomic layers. Comparison of our result with those from other macroscopic techniques and existing theoretical models is also presented.

• Received 23 October 1978

DOI:https://doi.org/10.1103/PhysRevLett.42.588