Supported Ag-TiO2 core-shell nanofibres formed at low temperature by plasma deposition

Ag-TiO2 nanofibres ( about three mu m long and 30 - 150 nm thick) formed by a single-crystalline silver wire ( 20 - 30 nm thick) and an external layer of amorphous TiO2 of variable thickness are prepared at 403 K by oxygen plasma activation of a silver substrate followed by plasma deposition of TiO2. Thicker fibres of anatase crystallites surrounding the silver wire were prepared when plasma deposition was carried out at 523 K. The fibres have been analysed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and x-ray photoemission spectroscopy (XPS). The plasmon losses of the silver core wire have been characterized by electron energy loss spectroscopy in the TEM microscope. Based on the experimental evidence, a new volcano-type mechanism of formation of these core - shell fibres is proposed, whereby the effect of the plasma and the high mobility of the silver would be key factors determining their morphology and dimensions.