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Cerium-doped manganite thin films were grown epitaxially by pulsed laserdeposition at $720 ^\circ$C and oxygen pressure $p_{O_2}=1-25 $Pa and weresubjected to different annealing steps. According to x-ray diffraction (XRD)data, the formation of CeO$_2$ as a secondary phase could be avoided for$p_{O_2}\ge 8 $Pa. However, transmission electron microscopy shows the presenceof CeO$_2$ nanoclusters, even in those films which appear to be single phase inXRD. With O$_2$ annealing, the metal-to-insulator transition temperatureincreases, while the saturation magnetization decreases and stays well belowthe theoretical value for electron-doped La$_{0.7}$Ce$_{0.3}$MnO$_3$ with mixedMn$^{3+}$/Mn$^{2+}$ valences. The same trend is observed with decreasing filmthickness from 100 to 20 nm, indicating a higher oxygen content for thinnerfilms. Hall measurements on a film which shows a metal-to-insulator transitionclearly reveal holes as dominating charge carriers. Combining data from x-rayphotoemission spectroscopy, for determination of the oxygen content, and x-rayabsorption spectroscopy (XAS), for determination of the hole concentration andcation valences, we find that with increasing oxygen content the holeconcentration increases and Mn valences are shifted from 2+ to 4+. Thedominating Mn valences in the films are Mn$^{3+}$ and Mn$^{4+}$, and only asmall amount of Mn$^{2+}$ ions can be observed by XAS. Mn$^{2+}$ and Ce$^{4+}$XAS signals obtained in surface-sensitive total electron yield mode arestrongly reduced in the bulk-sensitive fluorescence mode, which indicateshole-doping in the bulk for those films which do show a metal-to-insulatortransition.

Transport, magnetic, and structural properties of La$_{0.7}$Ce$_{0.3}$MnO$_3$ thin films. Evidence for hole-doping