Sn-Doped Starfish-like Nanostructures from TiO2-SiO2 Core-Shell Nanocables and SiO2 Nanowires;Processing,Properties,and Characterization

摘要

Starfish-like TiO2:Sn/SiO2:Sn core-shell nanocables with SiO2:Sn nanowires were synthesized on a silicon substrate by thermal evaporation with addition of hydrogen gas at 1000°C.In this synthesis,SnO2,silica,and Ti powder were used as source materials.The hydrogen gas served to reduce the SnO2 to SnO_x(i.e.,SnO)vapors and to reduce the silica to SiO_x(i.e.,SiO)vapors.These vapors,together with Ti vapor,were incorporated into Au liquid droplets(catalyst heads)and seeded the growth of nanostructures(nanocables and nanowires).FESEM images indicated that each catalyst head functioned as a growth site,such that the nanostructures grew in starfish-like forms via a vapor-liquid-solid(VLS)mechanism.HRTEM images revealed that each nanocable was composed of a single-crystalline rutile TiO2Sn core(about 10-15 nm in diameter)with an amorphous SiO2:Sn shell(about 50-60 nm in thickness).The amorphous SiO2:Sn nanowires also grew densely on the Si substrate from the catalyst heads because of the high concentration of SiO_x vapor.Cathodoluminescence spectra revealed four emission peaks at 373 nm(3.32 eV),455 nm(2.72 eV),534 nm(2.42 eV),and 604 nm(2.05 eV)in the as-synthesized products.The TiO2:Sn cores and nanocrystals exhibited a quantum confinement effect,as revealed by Raman spectroscopy.The field-emission properties of the as-synthesized products provided a low turn-on field,which was estimated at ~3.1 V/mu m.at a current density of 1 mu A/cm2.