A variable selection procedure for X-ray diffraction phase analysis.

The X-ray diffraction method has been widely used for qualitative and quantitative phase abundance analysis of crystalline materials. We propose the use of partial least squares when building the calibration model for a quantitative phase analysis based on X-ray diffraction spectra. We also propose a variable selection procedure to reduce the measurement points in terms of angles as an alternative to using the whole pattern. The proposed method is based on the variable importance in projection derived from the partial least squares and it considers some practical issues regarding the angle measurement. The method was particularly applied to the simultaneous determination of weight fractions of some iron oxides. It was found that the number of measurement points can be reduced to 30 percent of the total number of points with a small sacrifice in prediction error.

Electronic structure of P-doped ZnO films with p-type conductivity.

The electronic structure of laser-deposited P-doped ZnO films was investigated by X-ray absorption near-edge structure spectroscopy (XANES) at the O K-, Zn K-, and Zn L3-edges. While the O K-edge XANES spectrum of the n-type P-doped ZnO demonstrates that the density of unoccupied states, primarily O 2p-P 3sp hybridized states, is significantly high, the O K-edge XANES spectrum of the p-type P-doped ZnO shows a sharp decrease in intensity of the corresponding feature indicating that P replaces O sites in the ZnO lattice, and thereby generating P(O). This produces holes to maintain charge neutrality that are responsible for the p-type behavior of P-doped ZnO. Both the Zn K-, and Zn L3-edge XANES spectra of the P-doped ZnO reveal that Zn plays no significant role in the p-type behavior of ZnO:P.