Properties of Si Nanowires Synthesized by Galvanic Cell Reaction

Abstract

A galvanic cell reaction is used to synthesize Si nanowires (SiNWs) in AgNO3/HF solution at 30 °C for 60 min. The AgNO3 concentration ise varied from M=0.0001 to 0.6 mol/L in aqueous HF solution (5 mol/L). Vertically well-aligned SiNW arrays are found to be formed in the limited AgNO3 concentration range of M∼0.02–0.08 mol/L. The maximum nanowire length is ∼35 µm (M∼0.05 mol/L). The photoluminescence (PL) spectra of the SiNWs exhibit a broad peak centered at ∼1.8 eV. Below M∼0.02 or above ∼0.08 mol/L, the solutions produce only roughened surfaces. No PL emission is observed from such surfaces. Passive HF etching of the SiNWs leads to the removal of the surface oxide overlayer and changes the wettability from highly hydrophilic (∼5°) to superhydrophobic (∼135°). Optical absorption and Fourier-transform infrared spectroscopy show that the SiNWs have an extremely large optical absorbability not only in the interband-transition region but also in the far-infrared spectral region.