CuSiGe-catalyzed growth of Si 1-x Ge x O y nanowire assemblies with various morphologies
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Si1−xGexOy nanowire (SiGeONW) assemblies with cord-, chain-, and tubelike morphologies were grown on a Si substrate via the carbothermal reduction of GeO2/CuO powders at 1100 °C in Ar. The growth of various SiGeONWs assemblies follows the vapor-liquid-solid process. The CuSiGe droplets formed during the growth of SiGeONWs simultaneously play the roles of catalyst and reactant. The morphology of SiGeONWs assemblies is not temperature controlled but dependent on the Cu concentration and the size of CuSiGe catalysts. This phenomenon is unlike the Geand Ga-catalyzed growth of SiOx nanowire assemblies. In addition, the processing parameters and the mechanisms for the growth of SiGeONWs assemblies with various morphologies are discussed.
I. INTRODUCTION
SiO2 nanowires (SiONWs) and GeO2 nanowires (GeONWs) have attracted significant research attention due to their promising properties such as intense blue light emission at room temperature and high refractive index.1,2 The optical properties of SiONWs may be improved by Ge doping because GeO2 is more refractive than SiO 2 . Ge + -doped SiO 2 films,and Si 1−x Ge x O 2 nanowires (SiGeONWs) have shown a blue shift of their photoluminescence peaks. 3,4 As yet, only the Aucatalyzed growth of SiGeONWs from a Si1−xGex film has been reported.4 On the basis of the vapor-liquid-solid (VLS) growth mechanism, SiONWs and GeONWs have been grown by various techniques, including laser ablation,1 thermal evaporation,5–13 laser ablation associated with thermal evaporation,14 and chemical vapor deposition.15,16 A common feature of the conventionally VLS-grown nanowires is that each nanowire terminates at its top end in a catalyst droplet. Recently, Ga,5,6,16 Sn,7,12 and Ge14 were proved to be effective catalysts for the growth of highly aligned SiONWs, which show many amazing morphologies and growth phenomena, unlike those observed in the conventional VLS growth process. In addition, for the Ga- and Ge-catalyzed growth of SiONWs, the morphology of the nanowire assemblies is temperature dependent.14,16 Furthermore, for the Ga-catalyzed
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0194 1618 J. Mater. Res., Vol. 22, No. 6, Jun 2007 http://journals.cambridge.org Downloaded: 31 Mar 2015
growth of SiONWs, an interesting sandwichlike growth process was observed, where the SiONWs nucleate and grow on the Si crystals instead of the Ga droplet surface.6 These results reveal that the growth route of nanowires still remains to be explored to enrich the current VLS growth mechanism. In the present study, we report the simultaneous growth of SiGeONW assemblies with various morphologies on a Si substrate at 1100 °C via the VLS mechanism. The morphology of SiGeONW assemblies is determined by the Cu concentration and the size of the CuSiGe catalysts formed during reactions. This result is different from the temperature-controlled growth of various SiONW assemblies catalyzed by Ge and Ga, respectively.14,16 Meanwhile, the processing parameters and mecha
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