Preparation And Properties Of Ordered NiO-Si Composite Nanowire Arrays

Si-based nanoscale composite materials combine unique properties of Si nanomaterials and composite properties of a variety of other materials. Therefore its overall performance is particularly outstanding. Althoug silicon based nano-composite systems of ordered arrays of silicon nanowires and metal oxide compound have received considerable attention, the reports are rare. The nickel oxide is a p-type semiconductor, which has good chemical stability, high physical performance, environmentally friendliness, low price, ease of industrialization, and peculiar properties in gas sensor and super-capacitors, and thus has broad application prospects. This thesis studies morphologies of silicon nanowire - nickel oxide composite nanomaterials prepared by the oxidation of Ni-Si composite nanowire arrays, and examines their applications for gas sensors and super capacitors. The summary of the thesis is listed as follows:1. Using four different types of n-type silicon as raw materials and the method of silver ion catalyzed corrosion to fabricate the silicon nanowire arrays. The as prepared structures are then annealed under 350℃and 450℃for 1 hour for morphology characterization. The results show that: (1) the direction of silicon nanowires is the same as silicon crystal wafer and the diameter of silicon nanowires depens on the resistivity of silicon. (2) The best NiO-Si composite nanowire array is obtained using the template n(100) of the resistivity of 1 to 10Ω·cm with the length about 45μm and diameters between 30 300 nm. (3) The grain sizes of NiO nanoparticles depend on the annealing temperature, which are 13nm and 16nm under the annealing temperature 350℃and 450℃, respectively.2. Testing the electrochemical properties of NiO-Si composite nanowire arrays annealed under 350℃and 450℃. The electrochemical tests reveal that the constructed electrode has superior electrical conductibility and more active sites per unit area for chemical reaction processes, thereby possessing good cycle stability, high specific capacity and low internal resistance. The specific capacitance is up to 787.5 F·g^-1 at discharge current 2.5 mA and decreases slightly with 4.0 % loss after 500 circles, while the equivalent internal resistance is ³.1Ω. Owing to its favorable electrochemical performance, this ordered hybrid array nanostructure is a promising electrode material in future commercial ES.3. Testing the gas sensing perfomance of NiO-Si composite nanowire arrays obtained under annealing temperatures 350℃and 450℃, and comparing it to the conventional gas sensors prepared by NiO particals. The rusults show that NiO-Si composite nanowire arrays have much better performance and the samples annealed under 350℃has the best perfomance.