LEED Observation of a 1 x 8 Superlattice in the Surface of Lanthanum Cuprate.

Basal-plane surfaces of single crystal samples of La sub 2 CuO sub 4 , parent compound of a class of high T sub c superconductors, are found to display, a 1x1 LEED pattern which converts to a 1x8 pattern after annealing. The superlattice is attributed to chains of ordered oxygen vacancies. Auger spectroscopy suggests that in the 1x8 configuration the crystal prefers to terminate with a Cu-O rather than a La-O plane.