13th International Conference on Fracture June 16–21, 2013, Beijing, China -6- These diffused Si atoms mainly originate from the following chemical reaction, 4Al + 3SiO2 = 2Al2O3 + 3Si. When the temperature is above 300°C, there exists a chemical reaction between the Al and SiO2 [18]. The silicon dioxides come from the slightly oxidizing of silicon wafer on its exposed surface before the aluminum sputtering process of these silicon wafers. Table 2. Some fractal patterns were analyzed with the EDX and EBSD systems of INCA. The microanalyses show that the fractal patterns contain the crystalline grains of Aluminum and Silicon. These fractal patterns were formed in the process of anodic bonding due to the limited diffusion and aggregation of Si atoms in the Al film. These diffused Si atoms mainly originate from the following chemical reaction, 4Al + 3SiO2 = 2Al2O3 + 3Si. When the temperature is above 300°C, there exists a chemical reaction between the Al and SiO2 [18]. The silicon dioxides come from the slightly oxidizing of silicon wafer on its exposed surface before the aluminum sputtering process of these silicon wafers. Table 2. The typical fractal dimensions of the fractal patterns in the Al films[19] DB = 1.702 DB = 1.695 DB = 1.681 DB = 1.696 DB = 1.700 DB = 1.727 When the Al film is thin enough, the fractal patterns run through the span of the whole thickness of the film, and bond with the substrate and glass. The strength of chemical bond is 799.6±13.4 kcal/mol for Si-O, 511±3 kcal/mol for Al-O, and 325±7 kcal/mol for Si-Si [20]. Therefore, the fractal pattern improves the bonding strength between the Pyrex glass and the aluminum thin film coated on the silicon substrate. 3.2.2. Dendritic nanostructures In all anodically-bonded samples, dendritic nanostructures were found in the Pyrex glass near the Al/glass interface, as shown in Figure 7. The dendritic nanostructures, which are seen over the whole thin area, exhibit a similar maximum height of 600-650 nm in the specimens bonded at 350°C, 400 V. These three-dimensional treelike structures have a trunk of tens nanometers in diameter (less than 40 nm). TEM cannot show all the small branches of these 3-D dendritic nanostructures.
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