Polypyrrole shell (nanoparticles)-functionalized silicon nanowires array with enhanced NH3-sensing response

Conducting polymer of polypyrrole (PPy) was employed to functionalize the ordered silicon nanowire (SiNWs) with the aim to enhance gas-sensing response at room temperature (RT). A dual-MACE process was first developed to form loose SiNWs (LNWs) array facilitating uniform attachment of PPy on whole nanowire surface. The LNWs array functionalized with continuous PPy ultrathin film and discrete PPy nanoparticles, i.e., PPy-shell@LNWs and PPy-NPs@LNWs, were prepared respectively via vapor chemical polymerization (VCP) and liquid chemical polymerization (LCP) of pyrrole monomer (Py). Comparative investigations on the NH3-sensing properties of the pristine SiNWs before and after dual-MACE treatment, and PPy-functionalized SiNWs of PPy-shell@LNWs and PPy-NPs@LNWs were carried out at RT. It was found that PPy functionalization enhances the NH3-sensing response of SiNWs-based sensors effectively. Formation of continuous PPy shell film is further found to result in more pronounced response enhancement when compared to the modification by discrete PPy NPs. The PPy-shell@LNWs and PPy-NPs@LNWs respectively exhibit about 27 and 6 times response enhancement to 10 ppm NH3 gas compared to the pristine one. The underlying NH3-sensing mechanism for the PPy-functionalized SiNWs, especially for the remarkable response enhancement of PPy-shell@SiNWs was demonstrated.