A low-energy electron-diffraction intensity analysis of a clean Pd{001} surface finds the first interlayer spacing expanded by about 3% and the second interlayer spacing slightly contracted by about 1% with respect to the bulk value (1.945 Å). These results contradict the trend usually observed or theoretically predicted on fcc {001} surfaces, where the first relaxation is a compression and the second is an expansion. Possible origins of this behavior are suggested.

• Received 31 August 1990

DOI:https://doi.org/10.1103/PhysRevB.42.11348