XPS study of the effects of 30 MeV 32S-ion irradiation at T = 20 K on Ln 2− xCe xCuO 4−δ-cuprates

Abstract

We present in situ measured X-ray photoelectron spectra (XPS) of polycrystalline Ln 2− x Ce x CuO 4−δ (Ln  Nd, Sm; x = 0.0, 0.15) cuprates, which were irradiated with 30 MeV 32S ions at T = 20 K (LT). The fluences were chosen between 2.0 × 10 12 cm −2 and 5.0 × 10 14 cm −2. A comparable experiment was already performed by [1] at T = 295 K (RT). In this work we repeated the experiment at LT in order to suppress heating of the samples and healing effects. In both experiments we observed no change of the Ln valence, but a considerable reduction of the Cu valence, which was less pronounced in the LT-experiment. Furthermore the LT-irradiation caused an increase of the resistivity of the doped samples, which leads to an insulating shift of the Cu 2p and Ln 3d core level spectra. There was no oxygen O(2)-depletion in the LT-experiment, which we attribute to the higher binding energy of the O(2) at 20 K. These facts suggest that in the RT-experiment the heating of the sample overcompensated the influence of the healing effects.