| Summary: | 碩士 === 國立中央大學 === 化學工程與材料工程學系 === 104 === We report here the first study on the interfacial reactions of two-dimensional (2D) periodic arrays of Ni nanodots on nitrogen ion-implanted amorphous silicon (N2+-a-Si) substrates at different heat treatments. It was found from SEM observations that the size of the nanodots increased gradually by increasing annealing temperature up to 500 ℃ . Furthermore, for the higher temperature annealed samples, many of the nanodots were found to transit from the original triangular shape to become ring-like in shape. From TEM and SAED analyses, low resistivity NiSi was identified to be the only silicide phase form in N2+-a-Si samples annealed at 300-450 ℃ . As the annealing temperature was increased to 500 ℃ or above, the phase of silicide nanorings was converted into NiSi2 and the structure of the NiSi2 nanorings was polycrystalline. The results of planview HRTEM and cross-section TEM analyses further reveal that the inner region of the NiSi2 nanoring on N2+-a-Si substrate has become crystallized while the outer region of the NiSi2 nanoring is still amorphous. Complete recrystallization of the a-Si layer of the Ni metal nanodots N2+-a-Si sample can be achieved at a temperature as low as 550 ℃, which is about 200 ℃ lower than the annealing temperature required for complete solid-phase recrystallization of the blank N2+-a-Si sample. In addition, the presence of NiSi2 nanodots was found to significantly enhance the recrystallization of N2+-a-Si layer. The observed result can be explained by the Ni-silicide induced crystallization process.
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