Papers by Keyword: GeO₂

Abstract: Thermal oxidation of Ge was performed in dry oxygen ambience at atmospheric pressure at temperature ranging between 375 and 575°C. From SE analysis, the slope of Ge oxide growth and extinction coefficient (k) increases while refractive index (n) does not change with oxidation temperature. The reduction of activation energy for Ge thermal oxidation was explained by the retardation of diffusion oxidant through GeO₂ film during Ge oxidation. The generation of an oxygen-defect region in the Ge oxide layer at 490°C oxidation was confirmed by XPS analysis and an O₂ anneal at 375°C was effective to reduce this oxygen deficiency.

Abstract: We fabricated mono-dispersed β-quartz GeO₂ by microemulsion synthesis at room temperature. The obtained particles were 300 nm sized GeO₂ walnut and hollow waxberry shaped GeO₂ which were consisted of nanosphere with average size of 20 nm. The evolution of high pressure studies were devoted in a diamond anvil (DAC) cell by Angle Dispersed X-ray Diffraction (ADXD) at room temperature. A phase transformation of β-GeO₂ to amorphous GeO₂ was detected in walnut GeO₂, while the waxberry GeO₂ was found to transform to monoclinic phase directly. It is strongly suggested that size effect played a key role in the high-pressure transformation from the amorphous and monoclinic phase. By fitting the compression data to the BirchMurnaghan equation of state, the bulk moduli of the walnut and waxberry shaped β-GeO₂ particles were determined to be 33±5, and 38±4 GPa with B₀ = 3, respectively.

Abstract: We fabricated mono-dispersed hollow waxberry shaped ß-quartz GeO₂ by a facile one-step synthesis in emulsion at room temperature. TEM images indicated that hollow waxberry shaped GeO₂ were consisted of nano-sphere whose average size were estimated to be 20 nm. The growth mechanism and optical properties of the products were also investigated. The possible formation mechanism of the hollow interior is proposed as the Ostwald ripening. The optical properties of the ß-GeO₂ nanoparticles with hollow shapes were also studied with photoluminescence spectrum, which reveals a broad emission, suggesting potential applications in electronic and optoelectronic nanodevices. These attractive results provide us a new simple method further used to fabricate other specific hollow structure and indicate hollow waxberry shaped GeO₂ may have potential applications in light-emitting nanodevices.

Abstract: A simple synthesis method for single crystal GeO2 nanocubes in a reverse micelle system was reported here. Hydrolysis of germanium tetrachloride (GeCl4) in a micelle system produces GeO₂ nanocubes in the presence of oleylamine and cetyltrimethylammonium (CTAB). We found that we could obtain GeO₂ nanocubes with monodisperse size distribution, bimodal size distribution and polydisperse size distribution by varying the reaction parameters. We put forward a feasible explain for this phenomenon with using Gibbs free energy theory, and this theory can give some meaningful guidance for preparing monodisperse nanomaterials.

Abstract: Nanostructured materials were synthesized by thermal evaporation process using silicon dioxide and carbon from coconut shell charcoal or graphite mixed with GeO2 by the ratio of 5:1:1 at temperature 1200 oC in one atmosphere of nitrogen for 3 hours. The nanostructured materials were characterized by the stereo microscope (image analyzer) and scanning electron microscope. The diameters of nanowires vary from 10 nm to 50 nm and length of several 10 micrometers. Length of nanorods was around 15 micrometers and diameters vary from 10 nm to 100 nm.

Abstract: Ge nanocrystals (NCs) in GeO2 films obtained with the use of two methods were studied. The first method is a film deposition from supersaturated GeO vapor with subsequent dissociation of metastable GeO on heterophase system Ge:GeO2. The second method is growth of anomalous thick native germanium oxide layers with chemical composition GeOx(H2O) during catalytically enhanced Ge oxidation. The obtained films were studied with the use of photoluminescence (PL), Raman scattering spectroscopy, high-resolution electron microscopy (HREM). Strong PL signals were detected in GeO2 films with Ge-NCs at room temperature. “Blue-shift” of PL maximum was observed with reducing of Ge excess in anomalous thick native germanium oxide films. Also a correlation between reducing of the NC sizes (estimated from position of Raman peaks) and PL “blue-shift” was observed. The Ge NCs presence was confirmed by HREM data. The optical gap in Ge-NCs was calculated with taking into account quantum size effects and compared with the position of the experimental PL peaks. It can be concluded that a Ge-NC in GeO2 matrix is a quantum dot of type I.