OBSERVATION OF ANOMALOUS LEED PATTERNS FROM LI ADSORBED CU(001) - 2 X-1, 3 X-3 AND 4 X 4

Lithium adsorption on Cu(001) at 300 K has been studied with low-energy electron diffraction (LEED) and Auger electron spectroscopy. The LEED patterns show a sequential change with increasing Li coverage; 2 x 1, 3 x 3 and 4 x 4. The 2 x 1 LEED pattern has weak streaky spots denoted by a matrix of (-1/4THETA2/1THETA0) in the coverage range of 0.375 less-than-or-equal-to THETA less-than-or-equal-to 0.4. The 4 x 4 pattern disappears upon further Li deposition and the surface becomes disordered. The features and behavior of the streaky spots are very similar to those observed for K or Cs adsorption on Ni(110) or Cu(110) at room temperature, and this leads to a structure model for 2 x 1; the Cu(001) surface undergoes a missing row type restructuring induced by Li adsorption. Li adatoms are located in missing rows formed by themselves resulting in the streaky spots. Possible structure models for the 3 x 3 and 4 x 4 structures are proposed and they are assigned to ordered surface-alloys of LiCu on Cu(001).