| Summary: | 碩士 === 國立中央大學 === 化學工程與材料工程學系 === 104 === In this study, we demonstrated that large-area arrays of vertically-aligned single crystalline silicon nanowire were successfully fabricated on (100)Si substrates by using the polystyrene nanosphere lithography combined with the Au-assisted chemical etching process. The diameter and length of these silicon nanowires are adjustable through oxygen plasma treatment and wet etching time. SEM, TEM, SEAD, and contact angle analysis reveal that silicon nanowires that produce on (001)Si substrate have flat ends and their axial orientation is along the [001] direction. The morphology of the silicon nanowires can be converted from flat top to sharp top by metal-catalyzed electroless deposition etching method through the oxidation-reduction of silver. After the process, the silicon nanowires still remain vertically aligned and exhibit a very remarkable tapered geometry. For the Co thin film coated needle-like silicon nanowires samples after annealing at 450℃~850℃ for 2-4hr in N_2/H_2 ambient, needle-like epitaxial CoSi_2/Si heterostructured nanowires were formed. The field emission measurement revealed that the vertical-aligned, needle-like silicon nanowire arrays process excellent field emission properties with low turn-on field, and high β values. The high field enhancement factor can be attributed to high aspect ratio, nanoscale tip and well-controlled spacing between wet etching silicon nanowires. It was also find that the field emission properties of needle-like silicon nanowires were greatly enhanced after the formation of CoSi_2 phase. The turn-on field was reduced 1.30 Vum^(-1) for the needle-like silicon nanowires to around 0.88 Vum^(-1) for the needle-like CoSi_2/Si heterostructured nanowires.
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