Morphology and Structural Change in Ammonia Annealed Core Shell Silicon Nanowires

Oxide shielded core shell silicon nanowires (Si NWs) of diameters ranging from 60 to 80 nm were grown on the p-type Si substrate by an atmospheric pressure chemical vapor deposition. These Si NWs were annealed for 60 min at 900 °C in ammonia atmosphere, and the microstructure evolution was studied by field emission scanning electron microscopy. Annealing caused the formation of silicon oxynitride (SiON) within the outer matrix of the amorphous silicon dioxide. The surface chemistry and chemical bonding of Si NWs have been characterized by X-ray photoelectron spectroscopy (XPS) and Fourier transformation infrared spectroscopy. The transverse optic vibration of Si–O shifted to lower frequency while longitudinal acoustic vibration of Si–O shifted to higher frequency. The total reflectance of ammonia annealed SiO 2 /SiNWs decreased from 8% to 2% over the UV–vis range as a result of SiON formation. The composition of the resulting SiON was converted from Si 35 O 61 to Si 41 O 36 N 17 with the silicon to oxygen ratio ranging from 0.57 to 1.13 at the ammonia flow rate of 400 standard cubic centimeters per minute. Moreover, the XPS results confirmed that the SiON networks were quite random with inhomogeneous compositions, and the valence band structure was tuned from a dumbbell to spherical shape by varying the ammonia flow rate.