Synthesis of Si Nanowire Arrays in AgO/HF Solution and Their Optical and Wettability Properties

Abstract

Silicon nanowire (SiNW) arrays are formed by Ag-assisted electroless etching at 25°C in 25% HF solution with AgO having concentration ranging from M = 0.003 to 0.2 mol/l. The maximum length of the SiNWs is ∼65 μm at an M of ∼0.045 mol/l. Optical absorption spectroscopy and Fourier-transform infrared spectroscopy show that the SiNWs have extremely large optical absorbability not only in the UV region but also in the far-infrared region. No photoluminescence is observed from the AgO/HF-formed SiNWs that are in direct contrast with the conventional AgNO3/HF-formed nanowires that generally emit orange light. Post-stain etching in the HF/HNO3 solution of the AgO/HF-formed nanowires enables light emission in the orange region. Passive HF etching of the SiNWs changes their wettability from highly hydrophilic (∼0°) to superhydrophobic (∼147°). This Ag-assisted electroless etching mechanism can be explained on the basis of an energy-band diagram of the Ag/p-Si interface in the AgO/HF solution.