Study of Ca1-xPrxF2+x solid solution thin films grown on silicon substrates

Ca1-xPrxF2+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 powde rs obtained from high purity CaF2 and PrF3 initial powders. First, the synt hesis of the bulk solid solutions was controlled using X-ray diffraction an d Raman spectroscopy. A complete transformation seems to be obtained by hea ting 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 alpha pa rticles study shows that to obtain homogeneous thin films a pre-evaporation of the product at 1500 K during approximately 30 min is necessary. After s uch a treatment, the films are of the desired composition and the Pr3+ ions are uniformly distributed within the layers. On the other hand, for the lo wer praseodymium contents, the alloy produced by heating the initial powder s at 1400 K sublimes congruently. Moreover, in this case a RES study in cha nneling conditions shows that the films are of epitaxial quality and a phot oluminescence study shows that the interstitial fluoride ions, which balanc e the rare earth trivalent ions in the matrix, are preferentially located i n nn (nearest neighbor) sites, of C-4v symmetry (tetragonal). (C) 1999 Else vier Science S.A. All rights reserved.