Preparation, Characterization And Photoluminescence Properties Of Transparent Conducting Oxide Nanowires

Transparent conducting oxides(TCOs) have attracted considerable attention in recent years for their potential applications in the development of nanoscale electronic and optoelectronic devices. People put more researches on TCOs nanowires, nanorods, nanoparticles and films. In this paper, one-dimensional transparent conducting oxide nanomaterials Zn₂SnO₄, ITO(Sn:In₂O₃) and Sn-doped Ga₂O₃ have been synthesized by thermal evaporation. The morphology, structure, chemical composition and physical properties of these quasi-one-dimensional nanostructures are characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray spectroscopy (EDS) and photoluminescence (PL) spectroscopy. Some novel methods to synthesize quasi-one-dimensional nanostructures have been developed. The growth mechanisms of products of different morphologies are further investigated. The relationship between photoluminescence properties and the morphologies is discussed. The following are the main contents and conclusions:1. Study on ITO nanowires synthesized by thermal evaporation.Mass production of uniform ITO (Sn:In₂O₃) nanostructures has been achieved by a simple thermal evaporation technique. The XRD spectrum shows that as-synthesized products are mainly consist of In₂O₃ and SnO₂;The morphologies of the sample was characterized by field-emission scanning electron microscopy . We analyzed the formation mechanism of the ITO nanowires , VS mechanism is probably to be the right one for explaining nanowires growth. The room temperature PL spectrum of ITO nanowires shows two clear emission bands that one is centered at 418nm and the other is centered at 505nm. Compared with the RT PL of In₂O₃ nanowires, it induced red shift in our products PL. We tried inner stress and defects contribute the red shift.2. Synthesis and photoluminescence of Zn₂SnO₄ nanowires without any catalysts or substrates.Large-scale fabrication of single-crystalline Zn₂SnO₄ nanowires were synthesized by a simple thermal evaporation method without any catalysts or substrates. A mixed gas which was contained with Ar and H₂ was introduced alllong . The product consists of a large quantity of one-dimensional (1D) nanostructure with a typical length of about tens to several hundred micrometers and diameter normally in the range of 50 to 100nm. A formation mechanism based on a self-catalytic VLS growth is proposed for interpreting the growth of the Zn₂SnO₄ nanowires. Probable temperature and original materials, also the single atmosphere and appropriate pressure may presumably play a very important role in the process.The PL spectrum of Zn₂SnO₄ nanowires at room temperature shows a broad blue emission band centered at a wavelength of 580 nm. 3. Synthsis and photoluminescence properties of Sn:Ga₂O₃ nanostructures.The Sn-doped Ga₂O₃ nanostructures were synthesized by a direct thermal evaporation method of a mixture of SnO and Ga₂O₃ powders in Ar atmosphere at 1000℃ with Au as a catalyst, and a SnO₂:Ga₂O₃ heterogeneous nanocomb structure was observed in the samples. For the nanocomb structure growth, the analysis results of our experiments accord with the VS growth mechanism. As-synthesized products were characterized with FE-SEM, XRD, EDS, HR-TEM. The photoluminescence spectrum (PL) of the nanowires shows a blue-green emission around the 500-700 nm wavelengths with a maximum center at 585 nm under the room temperature. Large charge density of Sn will induce more defects such as oxygen vacancies which act as luminescent centers. Movever , the high aspect ration of the nanowires favored the existence of large quantities of oxygen vacancies.