Sn-loss effect in a Sn-implanted a-SiO2 host-matrix after thermal   annealing: A combined XPS, PL, and DFT study
  Amorphous a-SiO2 host-matrices were implanted with Sn-ions with and without posterior thermal tempering at 900 {\deg}C for 1 hour in ambient air. X-ray photoelectron spectroscopy analysis (XPS core-levels, XPS valence band mapping), photoluminescence (PL) probing, and density functional calculations (DFT) were employed to enable a detailed electronic structure characterization of these samples. It was experimentally established that the process of Sn-embedding into the a-SiO2 host occurs following two dissimilar trends: the Sn4+ -> Si4+ substitution in a-SiO2:Sn (without tempering), and Sn-metal clustering as interstitials in a-SiO2:Sn (900 {\deg}C, 1 hour). Both trends were modeled using calculated formation energies and partial densities of states (PDOS) as well as valence band (VB) simulations, which yielded evidence that substitutional defect generation occurs with the help of ion-implantation stimulated translocation of the host-atoms from their stoichiometric positions to the interstitial void. Experimental and theoretical data obtained coincide in terms of the reported Sn-loss effect in a-SiO2:Sn (900 {\deg}C, 1 hour) due to thermally-induced electronic host-structure re-arraignment, which manifests as backward host-atoms translocation into stoichiometric positions and the posterior formation of Sn-metal clusters. 
D.A. Zatsepin, A.F. Zatsepin, D.W. Boukhvalov, E.Z. Kurmaev, N.V.   Gavrilov
cond-mat.mtrl-sci