Formation and characterization of nanoporous structures on surface of LPD-derived GeO₂ ceramic film

This work represents an idea of forming nanoporous structures on surface of a LPD (liquid phase deposition)-derived GeO₂ ceramic film by thermal reduction of GeO₂ under hydrogen atmosphere. SEM, XRD and Raman analyses show that well-defined nanopores with size in range of 10-100 nm have been formed on surface of GeO₂ film by annealing at 600 C for 5-10 min. The pore formation process is furthered by structural defects which serve as active sites for the thermal reduction reaction. Fast phase transformation from hexagonal GeO₂ to tetragonal GeO₂ has occurred within the first 5 min of annealing. Green-yellow (2.32 eV) and violet (2.9 eV) photoluminescences originating from O-Ge-O and ≡Ge-Ge≡ defects are observed in the film samples. The photoluminescence peak intensity decreases with increase of annealing time due to diminution of O/Ge ratio. The film annealed for 5 min exhibits a maximum green-yellow to violet PL peak ratio, which is related to generation of some new O-Ge-O defects at the phase interface.