| dc.description.abstract | In this study, p-type and n-type (001) Si wafers were used as the starting materials. To fabricate large-area, vertically aligned silicon nanowires (SiNWs) and porous SiNWs on (001) Si substrate, a low-cost and high-throughput method which is based on metal-assisted electroless chemical etching process was adopted. Some of the blank-Si and SiNWs samples were oxidized by oxygen plasma treatments or thermal oxidation to grow a thin oxide layer on the surfaces. The surface morphologies, crystal structures and crystallographic orientations of the different types of SiNWs samples produced here have been systematically investigated by the SEM, TEM images and SAED analyses. For gas sensing experiments, the blank-Si and SiNW samples were exposed to various concentrations of ammonia and oxygen gases at room temperature. The observed results clearly reveal that compared with blank-Si sample, the vertical Si nanowires sample possesses good gas sensing characteristics at room temperature and their sensitivity increasing with increasing gas concentrations. The enhanced gas-sensing properties can be attributed to the high specific surface of the SiNWs samples. It was also found that the Si-based samples with different oxide shells have almost the same gas-sensing performances. However, if the surface oxide shells were removed, the Si-based samples would lose their gas-sensing ability. Furthermore, contrary to expectation, it was surprising to find that both n-type and p-type Si-based samples exhibited the same characteristics gas-sensing as the conventional p-type metal oxide semiconductors. The abnormal results suggest that the gas-sensing behaviors of Si-based samples may not directly relate to the type of Si substrates. The oxide shells of Si-based samples may play crucial role in the gas-sensing mechanism. | en_US |