Study On The Fabrication Of Germanium Dioxide Materials By Liquid Phase Deposition Method

In recent years, fabrication of GeO₂ materials including micro- and nano-sized particles, fibers and film materials has been widely studied. In this work, an acid induced liquid phase deposition method was developed for the preparation of GeO₂ particles, fibers and films at low temperature. The morphologies, structures and growth mechanisms of these materials were investigated.Stable germanate ion precursor solution with high solid content was synthesized based on the study of the reaction between hexagonal GeO₂ raw powders and aqueous ammonia. It was confirmed that the optimal GeO₂ content of the germanate ion precursor solution was 5%(wt) and the best acid induced reaction condition for the liquid phase deposition process was pH=3. Micro- and nano-sized hexagonal GeO₂ particles with morphologies quite different from the GeO₂ raw powders were obtained by using various sorts of acids as the induction agent at room temperature. Particles with spherical-like, truncated cube-like and perfect cubic-like shapes were synthesized when phosphoric acid, hydrochloric acid and ascorbic acid were used, respectively. It was found that the growth of GeO₂ particles in the liquid phase deposition process follows the BFDH and HP crystal growth models. According to these models, a GeO₂ nuclear with a shape consisting of two hexagonal pyramids at the ends and a hexagonal prism in the middle will gradually grow into a cubic-shaped particle due to the differences of growth rate of crystal planes. Different morphologies and particle sizes of the crystals obtained by using different acids after certain precipitation time were attributed to their acidic differences,causing different stages of crystal growth.Stable germanate ion precursor solution was synthesized by using hexagonal GeO₂ powders and NaOH aqueous solution as raw materials. Nano-sized fiber products were produced by using sulfuric acid as induction agent under hydrothermal conditions. It was shown that one-dimensional fibers with length of 0.5²5μm and width of 80nm¹Î¼m could be obtained when the temperature, pH value and concentration of precursor solution were controlled within the ranges of 150²00℃, 2⁵ and 1.5²%, respectively. The cross-section of the fiber is trigonal and the fiber has a single crystal structure. The fiber is composed of Ge and O and the Ge/O molar ratio is about 1:2. The fiber products show a melting point above 1100℃and probably belong to an isomer of hexagonal GeO₂. It was indicated that the formation of the fiber products was related to the atom distribution in the GeO₂ crystal plane and the pressure sensitivity of GeO₂ crystal lattice, and that the fiber growth process follows the screw dislocation crystal growth model. Compared with the hexagonal GeO₂ fibers reported elsewhere, the nano fiber products synthesized in this work also exhibit strong blue photoluminescence but the emission band is much more blue-shifted. This is considered to be related to the effects of the high pressure under hydrothermal condition on the GeO₂ crystal lattices.Hexagonal GeO₂ ceramic films were deposited onto plane- or irregular-shaped glass substrates at room temperature by using sulfuric acid as the induction agent for the liquid phase deposition process. It was determined that homogeneous GeO₂ ceramic films with high adhesion force were able to be obtained when the pH value of the precursor solution was controlled within the scope from 1 to 4. Furthermore, it was found that a large number of nano pores were formed in the GeO₂ ceramic films at pH=4. In this work, KNO3 catalyst was loaded onto this porous GeO₂ films and the catalytic activity of the film on the oxidation of diesel soot was found to be highly improved confirming that these films are good catalyst carrier materials. Compact GeO₂ films were fabricated by heat treated the as-deposited GeO₂ ceramic films at 1120℃. It was shown that the compact GeO₂ film has great potential to be used as the reflective film of hollow waveguide for CO₂ laser delivery based on the investigations of its reflective spectra according to Kramers-Kroning relations. Metallic Ge films with nano porous structures could be prepared by reduced the as-deposited GeO₂ ceramic films under hydrogen atmosphere at 600℃. The films show strong photoluminescence within 540⁵65nm under excitation at 450 nm. Therefore, the techniques for the preparation of these film materials may also have potential applications in fabrication of Ge based semiconductor and light emission devices.