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The first direct valence-selective structure determination by X-ray fluorescence holography is reported. The method is applied to investigate an epitaxial thin film of the rare earth monoxide YO, which has recently been synthesized by pulsed laser deposition. The surface of the sample is easily oxidized to Y2O3. In order to separate the structural information connected with the two different valence states of Y, the X-ray fluorescence holography measurements were performed close to the Y K absorption edge. Using the shift of the absorption edge for the different valence states, very different relative contributions of YO and Y2O3 are obtained. Thus, it is possible to distinguish the crystal structures of YO and Y2O3 in the thin-film sample. [ABSTRACT FROM AUTHOR]

Recently, it has been shown that atomic structure determination with X-ray fluorescence holography (XFH) can be hindered by matrix effects, i.e. beam attenuation and indirect excitation. The analysis was limited to the monochromatic regime. In this work, the description of matrix effects is extended to the polychromatic case. It is shown that matrix effects affect the element sensitivity of white-beam XFH by introducing distortions in the holographic signal which may lead to spurious maxima in the reconstructed image. For high energies of the X-ray beam it is found that the effect of beam attenuation is very weak and indirect excitation mainly contributes to the distortions. A correction for matrix effects is proposed in the high-energy range, which allows one to remove the distortions and retrieve pure element-sensitive information. Numerical model calculations are performed to visualize the reduction of element sensitivity and its implications on local structure imaging. [ABSTRACT FROM AUTHOR]