Study of laser-deposited Bi 2Sr 2CaCu 2O 8 + δ thin films by rutherford backscattering, X-ray photoemission and X-ray Auger spectroscopies

Abstract

Combining Rutherford backscattering spectroscopy (RBS), X-ray photoemission spectroscopy (XPS) and X-ray Auger spectroscopy, we have studied thin films of Bi 2Sr 2CaCu 2O 8 + δ deposited by laser ablation on oriented MgO(100) single crystals. RBS and XPS indicate the absence of interdiffusion into the substrate and continuity of the films. On heating the films in vacuum up to the fusion temperature (880°C), oxygen losses are observed and correlated with the disappearance of formal Cu 3+, with the strong decrease in oxidized (hole-doped) oxygen and with a metal- semiconductor phase transition. An appreciable percentage of formal Cu 3+ (about 24%) is estimated from the analysis of the Auger Cu L 3VV spectrum in contrast to the ceramic case where formal trivalent copper is not present. This is likely because the thin film (textured) structure allows the retention of more excess oxygen than the surface of the ceramic grains. We suggest that Cu 3+ appears under the form of 3d 9 L and 3d 10 L 2 configurations, instead of 3d 8, consistently with the formation of p holes ( L , L 2) in the valence band.