| Anodic aluminum oxide (AAO) template has a lot of properties, such as uniform parallel pores, high pore density and pore size distribution uniformity. Furthermore, the pore diameter is controllable according to practical needs. These characteristics make the AAO as one of the ideal nano template. In this paper, the AAO templates were prepared by anodizing highly pure aluminum foils in 0.3M oxalic acid solution through a two-step preparation technology. Besides, the basic theory of AAO template and the preparation method of ultra thin alumina mask were studied.(1) The aluminum foil annealed before anodization can create higher pore distribution after two-step anodization. Nanodot array ranked by hexagon were found in the head of AAO template. Formation of Nanodot array is related to the drop-well formed by first anodization on aluminum foil. Self-organized formation of hexagonal pore is caused by the mechanical stress, which is associated with the expansion of the aluminum during oxide formation which is the cause of repulsive forces between neighboring pores during the oxidation process.(2) The etching mechanism of the pore-opening process of AAO template with PMMA protective layer has been studied. Firstly, due to the reaction of the acid solution with the alumina on the surface of barrier layer, the barrier layer begins to thin. After some time of etching, the center point of the hemispherical barrier layer starts to open, while the other parts of the barrier layer keep closed. With further etching, the pore opening becomes larger. The pore-opening size increases with the etching time. Meanwhile, the acid solution goes into the pores via the pore openings and etches the pore walls, that is, there is a pore-widening process accompanying the pore-opening process. After analysis and calculation, the rate of etching in 5wt% H3PO4 solution at 30℃is about 0.755nm/min; the pores start to open at about 47 mins etching time; the thickness of barrier layer is about 36nm. (3) The relations between the thickness of AAO template and oxidation time at different temperature were analyzed quantitatively: 17℃:Y = -0.72 + 0.208 X,the growth rate at 17℃is about 0.208μm/min; 10℃:Y = -0.356 + 0.08 X,the growth rate at 10℃is about 0. 08μm /min; 0℃: Y = -0.94 + 0.044 X,the growth rate at 0℃is about 0.044μm/min; where Y is the thickness of AAO template, and X is the oxidation time. The relationship between thickness of AAO template (x) and oxidation time (t) was deduced theoretically: x(t) = D + k - t k =σi_ m exp( - B_ 2 E_ m) D is the constant, it represents the initial condition, and k is the growth rate of AAO template. D and k are constant at given temperature.(4) The empirical relationship between the growth rate of AAO template (k,μm/min) and the temperature (T,K) was established: k = A1 exp( - Q / T) + y0 A1=1.842E-18,Q=7.41,y0=0.018(5) Attached ultra thin alumina mask (attached-UTAM) on substrate with different thickness and aspect ratio of the apertures was fabricated using a general preparation method. There is no gap between the UTAM and substrate, no residual material on the substrate and the pore is perpendicularity to the substrate. Key Words: AAO; PAA; UTAM; growth kinetics;... |
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