The importance of recognizing a 1 × 1 structure preceding a superstructure in a chemisorption experiment is demonstrated by the system N-Ti(0001). Low-energy-electron-diffraction analysis of the 1 × 1 structure reveals that the N atoms are located in the octahedral holes 1.22±0.05 Å below the first layer of Ti atoms. Interatomic distances are such as to justify the view of the surface structure as a single double-layer of TiN.

• Received 26 January 1976

DOI:https://doi.org/10.1103/PhysRevLett.36.798