ELECTRON-SPECTROSCOPY OF LA1.85SR0.15CUO4(001) - LEED, AES, XPS AND EELS STUDIES

Experimental investigations of cleaned (0 0 1) surfaces of superconducting (SC) and nonsuperconducting (NSC) La1.85Sr0.15CuO4 single crystals are carried out in the range 20-300 K by LEED, AES, UPS, XPS, and EELS techniques. Different surface cleaning procedures are used. It is found that cleaned (0 0 1) surfaces are rather stable in ultra-high vacuum and possess very low sticking coefficients for all residual gases, except oxygen. It is established by LEED that these (0 0 1) surfaces are nonreconstructed in the whole range 20-300 K. The surfaces are sensitive to the electron beam: At the exposure to an electron beam (E = 100eV, J = 10-6 A) the sharpness of the LEED pattern increases in time. It is argued that this is due to the extra ordering of the surface stimulated by beam. The Auger and XPS peak amplitude dependencies on angle of incidence of the primary beam with respect to the surface are investigated. From the obtained results it is suggested that cleaned (and probably as grown) La1.85Sr0.15CuO4(0 0 1) surfaces are formed by Cu-O planes with saturated chemical bonds. It is found that UPS and EELS spectra are practically identical for both SC and NSC single crystals. The results of the EELS of La1.85Sr0.15CuO4(0 0 1) are summarized. It is suggested, that similar to La1.85Sr0.15CuO4 ceramics, the bulk plasmon energy is hWb = 13.2eV and the surface plasmon hWs = 8.9eV. On this basis it is argued that the one-electron approximation is not satisfactory to describe bulk and surface plasmon excitation for La1.85Sr0.15CuO4 single crystals. © 1990 IOP Publishing Ltd.