Ag nanoparticles-functionalized rough silicon nanowires array and its unique response characteristics to ultrararefied NO2

A facile and cost-effective preparation process for Ag nanoparticles modified Si nanowires (Ag NPs@RNWs) was first developed based on the metal-assisted chemical etching (MACE)-produced Ag dendrites. Partial removal of the wrapped Ag dendrites and a crucial tetramethylammonium hydroxide (TMAH) post-etching treatment are sequentially involved in the process. The crucial step of TMAH-etching induces a loose array of needle-like SiNWs with highly rough surface (RNWs), and causes redistribution of the attached Ag NPs. HRTEM observations reveal that numerous tiny Ag NPs with size of 2-6 nm are firmly inlaid on the concave-convex surface of RNWs. Comparative investigations of NO2-sensing properties among the bare-SiNWs, RNWs and Ag NPs@RNWs were carried out at room temperature. The Ag NPs@RNWs sensor exhibits considerably enhanced response (about five times higher) compared with bare-SiNWs and can rapidly response ultrararefied NO2 with deep ppb level. Above results demonstrate the considerable effect of the Ag NPs modification process developed here; the resulted rough and loose array promotes the response speed of the SiNWs sensors and the formed tiny Ag NPs contributes dramatic enhancement in response sensitivity. The enhanced response of Ag NPs@RNWs is analyzed based on Ag modification-induced electronic sensitization and TMAH etching-induced structural modulation.