Amorphous Nanowires and Crystalline Thin Films of SiO_2-Li_2O Compounds obtained by Combustion Chemical Vapor Deposition

摘要

Amorphous silica films deposited by Combustion Chemical Vapor Deposition (CCVD) were modified by lithium addition in the precursor solution. The modified films were characterized by X-ray diffraction and scanning and transmission electron microscopy. The addition of lithium promoted the crystallization of Li_2O-SiO_2 compounds, mainly crystalline phases like Li_2SiO_3, Li_2Si_2O_5, quartz and cristobalite. Besides that, the morphology of the film was modified, leading to the formation of acicular structures and nanowires. The acicular structures were identified through TEM associated with SAED as crystalline phases, mainly constituted by Li_2SiO_3 and Li_2SiO_5. TEM and SEM analysis indicated that the nanowire diameter is between 20 and 80nm. In addition to this, SAED and microprobe EDS analysis indicated that these nanowires are constituted by amorphous silica. The probable growth mechanism of these nanowires is the vapor-liquid-solid (VLS) catalyzed by a liquid particulate composed by Li_2O-SiO_2.