GeO2 nanotubes and nanorods synthesized by vapor phase reactions
Introduction
Nanoscale one-dimensional (1D) materials (such as nanowires, nanotubes, nanobelts, etc.) have attracted much attention due to their remarkable physical, chemical and mechanical properties [1], [2], [3], [4]. Germanium oxide (GeO2) is an important material for optical fibers, which has a blue luminescence [5] with peak energies around 3.1 eV (400 nm) and 2.2 eV (563.6 nm). GeO2-based glass is thought to be more refractive and has higher linear coefficient of thermal expansion than the corresponding of SiO2 [6]. Another important application of GeO2 is in the vacuum technology [7]. Several synthesis methods of 1D structures of GeO2 have been reported, such as GeO2 hiskers synthesized by laser ablation [8], GeO2 nanowires prepared via physical evaporation [9] and carbothermal reaction [6], dot-patterned nanowires of α-GeO2 prepared by the oxide-assisted growth method [10] and GeO2 nanorods grown by carbon nanotube confined reaction [11]. As the nanotubes are superior to other morphologies as both inner and outer surfaces can be modified, and up to now, there are rarely reports about GeO2 nanotubes. So in this communication, we report the reparation of GeO2 nanotubes and nanorods by a simple chemical evaporation method. The as-synthesized nanostructures of GeO2 may have potential applications in nanodevice with diverse functions.
Section snippets
Experimental procedure
The synthesis of GeO2 nanotubes and nanorods was carried out in a simple CVD system composed of a high-temperature horizontal tube furnace and a digital gas flow controller. The raw materials used in this work were Ge powders (mass purity: 99.999%). A boat containing 2 g metallic Ge powders was placed in the center of furnace. The cleaned polished Al2O3 (0001) wafers were placed in another alumina boat which was transferred into the alumina tube at the downstream side. The system was flushed
Results and discussion
After ultrasonic dispersion in alcohol, the sample was put onto a transmission electron microscopy (TEM) grid for structural analysis. It was found that the products have a rod-like morphology with diameter distribution from 100 to 150 nm and length ranging from 550 to 1000 nm (Fig. 1a). The selected area electron diffraction (SAED) (top inset in Fig. 1a) pattern shows the products' single crystal properties. The energy-disperse spectroscopy (EDS) which is detected from several rod-like
Conclusions
In summary, we have obtained α-GeO2 nanorods and nanotubes by using a thermal evaporation method. The nanorods have diameter distribution from 100 to 150 nm and length ranging from 550 to 1000 nm. The nanotubes were first synthesized with outer diameter of 100 nm and length of about 1000 nm. The nanotubes have a serrated outer wall which is formed by twin crystals. These twin boundaries can strengthen the mechanical property and increase the electrical resistance of GeO2. Some of the nanotubes
Acknowledgements
We thank professor S.Y. Zhang and G.P. Li of the University of Science and Technology of China (USTC) for their assistance in TEM and HRTEM study. This work was supported by the Ministry of Science and Technology of China (Grant No. 1999064501).
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