Study of Ca 1 −xPr xF 2+ x solid solution thin films grown on silicon substrates

Abstract

Ca 1 −x Pr xF 2+ x thin films, x varying from 0.01 to 0.10, were grown on Si (100) substrates by sublimation under ultra-high vacuum of solid solution powders obtained from high purity CaF 2 and PrF 3 initial powders. First, the synthesis of the bulk solid solutions was controlled using X-ray diffraction and Raman spectroscopy. A complete transformation seems to be obtained by heating for 8 hours under vacuum the mixed initial powders at a temperature of 1400 K. However, for x=0.10, a Rutherford backscattering (RBS) of α particles study shows that to obtain homogeneous thin films a pre-evaporation of the product at 1500 K during approximately 30 min is necessary. After such a treatment, the films are of the desired composition and the Pr 3+ ions are uniformly distributed within the layers. On the other hand, for the lower praseodymium contents, the alloy produced by heating the initial powders at 1400 K sublimes congruently. Moreover, in this case a RBS study in channeling conditions shows that the films are of epitaxial quality and a photoluminescence study shows that the interstitial fluoride ions, which balance the rare earth trivalent ions in the matrix, are preferentially located in nn (nearest neighbor) sites, of C 4v symmetry (tetragonal).