Formation of hook-shaped and straight silica wires by a thermal vapor method

Hook-shaped and straight silica wires have been successfully synthesized on silicon wafer through a simple thermal vapor method with or without assistance of Al, respectively. The hook-shaped silica wires have amorphous structures with nearly 100 μm long and about 4 μm in average diameters, while the straight silica wires are hundreds of micrometers long and approximately 50–300 nm in diameters. The composition analysis revealed that larger Al/SiO_x islands can form on the silicon substrate with Al catalysts, whereas tiny silica clusters form without Al catalysts. They could act as the nucleation centers for the growth of silica wires with different shapes. The formation process of hook-shaped silica microwire results from a thermal gradient on the silicon substrate. The thermal gradient may be caused by the cold gas flowing during the process or other factors that lead to uneven temperature. On the contrary, straight growth of silica submicrowire is unacted on the thermal gradient factor due to the tiny silica clusters as nucleation centers. The present simple and low-cost process of producing hook-shaped and straight silica wires in bulk may lead to potential applications in catalysts, electrode materials, biosensing, etc.