Surface analysis of single crystals in the Bi-Sr-Ca-Cu-O system by low-energy electron diffraction and Auger electron spectroscopy

The cleaved surfaces of low-Tc-phase single crystals in the Bi-Sr-Ca-Cu-O system were investigated by means of the LEED (low-energy electron diffraction) and AES (Auger electron spectroscopy) techniques. The LEED patterns from the cleaved surfaces exhibited a modulated structure with a period of about 4.8a, as expected from the modulation in the bulk crystals. The incident angular dependence of the Auger signal intensity revealed that the crystals were exactly cleaved between the Bi double layers. Through detailed analysis of the dependence based on a model calculation, it was found that oxygen was absent or strongly deficient on the cleaved surfaces. It was also suggested that the weak bond of Bi-O is the principal reason for the cleavability between the Bi double layers. (author)