High Speed Alumina Nanotemplate Fabrication on Silicon Substrate

Alumina nanotemplates integrated on silicon substrate with pore diameters of 12 nm to 100 nm were prepared by galvanostatic anodization. High current density (e.g. 100 mA.cm ^-2) promoted a highly ordered hexagonal pore structure with fast formation rate independent of anodizing solutions, where 2000 nm/min, 1000 nm/min were achieved at current densities of 100 mA.cm ^-2 and 50 mA.cm ^-2, respectively. These rates were approximately two orders of magnitude greater than other reports in the literature. Different electrolytes of sulfuric acid (1.8 to 7.2 M), oxalic acid (0.3 M) and mixed solutions of sulfuric and oxalic acid were evaluated as anodizing solutions. Sulfuric acid promoted smaller pore diameter with lower porosity than mixed acids and oxalic acid. The I-V characteristics strongly depend on solution composition, temperature, and bath agitation. In the case of sulfuric acid, the breakdown voltage (U _B) varied linearly with logarithmic of sulfuric acid concentration (U _B = 24.5-11 log [H ₂SO ₄]) and it decreased at higher temperature. The pore diameter of silicon-integrated alumina nanotemplate varied linearly with measured voltage with a slope of 2.1 nm/V, which is slightly smaller than reported data on bulk aluminum (2.2 nm/V and 2.77 nm/V). Thermoelectric Bi ₂Te ₃ nanowires with diameter of 43 nm were electrodeposited.