Vapor-phase Synthesis And Photoluminescence Properties Of GeO₂ And In₂Ge₂O₇ One-dimensional Nanostructures

Nanoscale one-dimendional (1D) materials have stimulated great interest due to their importance in basic scientific research and potential technology applications. Quasi-one-dimensional nanomaterials, include nanowires/rods, nanotubes, nanobelts, nanoneedles, coaxial nanocables, heterojunction and superlatice nanowires, etc. Among these materials, oxide one-dimensional nanomaterials have attracted more attention. Although the research of 1D oxide nanomaterials has already made considerable progress, it still remains a significant challenge to achieve controlled synthesis of desired morphologies, components, and structures. First part of this paper is that synthesis of GeO₂ nanowire arrays by a simple thermal evaporation method. The last two parts are synthesis, characterization and photoluminescence properties of ternary compound In₂Ge₂O₇ nanobelts and chainlike In₂Ge₂O₇/amorphous GeO₂ core/shell nanocables. The main contents and conclusions can be summarized as following:1. Self-catalytic VLS growth and optical properties of single-crystalline GeO₂ nanowire arrays.GeO₂ nanowire arrays were synthesized by a conventional thermal evaporation method with a Si (111) wafer used as substrate. The growth process of the GeO₂ nanowire arrays is based on self-catalytic vapor-liquid-solid(VLS) growth mechanism. Its morphology and microstructures were determined by scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and photoluminescence spectroscopy. The diameter and length of as-synthesized GeO₂ nanowire is about 100nm and several micrometers, respectively. The diameter of the spherical particles at the tip of the nanowires is about several hundreds of nanometers. The GeO₂ nanowire are found to be very sensitive to the irradiation of the electron beam. The nanowire will transform quickly from single crystal into amorphous in seconds under electron beam irradiation and, accordingly, the electron diffraction spots disappeared completely. The room temperature PL spectrum of GeO₂ nanowire arrays shows one violet emission peak centered at 411nm and two blue emission peak centered at 448nm and 471nm.2. Synthesis and photoluminescence properties of In₂Ge₂O₇ nanobeltsLarge-scale In₂Ge₂O₇ nanobelts were successfully synthesized by the simple thermal evaporation method without the presence of catalyst. The growth process of the ternary In₂Ge₂O₇ nanobelts is based on vapor-solid (VS) growth mechanism. Its morphology and microstructures were determined by scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and photoluminescence spectroscopy. The as-synthesized In₂Ge₂O₇ are single crystals with a monoclinic thortveitite-type structure growing along the [210] direction. The nanobelts have widths of 300-500 nm, thickness of 50-70 nm and lengths ranging from several tens to several hundreds of micrometers. A strong and broad violet emission peak at about 410 nm was observed in the room-temperature photoluminescence measurements.3. Synthesis of chainlike In₂Ge₂O₇/amorphous GeO₂ core/shell nanocables and their photoluminescence properties.Novel chainlike In₂Ge₂O₇/amorphous GeO₂ core/shell nanocables were successfully synthesized by the simple thermal evaporation method without the presence of catalyst. The growth process of the nanocables is based on vapor-solid (VS) growth mechanism. Its morphology and microstructures were determined by scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and photoluminescence spectroscopy. Studies indicate that typical chainlike nanocables consist of single crystalline In₂Ge₂O₇ nanowires (core) with diameter of about 30 nm and amorphous GeO₂ chainlike nanostructures (shell). Four emission peaks, namely 401 nm, 448.5 nm, 466.5 nm and 491 nm, were observed in the room-temperature photoluminescence measurements.