Comparison of open volumes in silica based thin films produced by different precursors

Silica thin films were deposited by spin coating on p-type (100) Si substrate and depth profiled with Positron Annihilation Spectroscopy (DP-PAS). A first series of samples were produced from precursor gel with molar ratio HSi(C2H5O)3 [=TES]: (CH3)HSi(C 2H5O)2 [=MDES] : H2O: EtOH 1 : 1 : 5 : 5. Samples were thermally treated in air at temperatures up to 600 °C. The structure and the chemical environment of the open volumes of these samples were compared with the ones of a previous studied second series of films obtained by hydrolysis and condensation reaction of Tetraethylorthosilicate (TEOS). The effects of sol precursors and thermal treatment temperature on open volumes were studied by Doppler broadening spectroscopy and detection of 3γ-annihilation of ortho-positronium. The introduction of CH3 groups by MDES produces an open disordered structure whose decoration of H atoms gives rise to a very high S parameter (1.076) but with very low positronium 3γ-annihilations. © Published under licence by IOP Publishing Ltd.