RESUMO
Barium disilicate is one of the glass-ceramic systems where internal nucleation and crystallization can occur from quenched glass upon heat treatment without requiring nucleating agents. The structural origin of the nano-clusters formed during low temperature heat treatment is of great interest in gaining a fundamental understanding of nucleation kinetics in silicate glasses. Here, we present experimental investigations on the low temperature heat treatment of barium disilicate (BaO·2SiO2) glass. Several experimental techniques were used to characterize the structural nature of barium disilicate glasses that were heat treated between the glass transition temperature, Tg, and the peak temperature of crystal growth, Tcr. The data show that small amounts of crystallites including BaSi2O5 as well as other higher Ba/Si ratio phases are formed. Moreover, unlike that reported for lower BaO content (BaO<33mol%) barium silicate glass or the analogous Li2O-SiO2 glasses, no clear evidence is observed for liquid/liquid phase separation in barium disilicate glass.
RESUMO
Wide bandgap metal fluorides are the materials of choice for optical coating applications at 193 nm. Low loss and environmentally stable optics requires a mitigating fluoride film structure on a nanometer scale. To understand the growth mechanism of fluoride materials, GdF(3) films grown on CaF(2) (111) and SiO(2) substrates were investigated. Film inhomogeneity and surface roughness were modeled by fitting ellipsometric data with an effective medium approximation, indicating a correlation between film inhomogeneity and surface roughness. The modeled surface roughness was compared with the atomic force microscope measurement. Film inhomogeneity was correlated to the cone-shaped columnar structure revealed by cross-sectional images from a scanning electron microscope. The film crystalline structure was determined by x-ray diffraction measurement, suggesting a different growth mechanism of GdF(3) films on crystalline and amorphous substrates.