Alumina nanotemplate fabrication on silicon substrate

Alumina nanotemplates integrated on silicon substrate with pore diameters of 12?100?nm were prepared by galvanostatic (constant current) anodization. High current density (e.g.?100?mA?cm?2) promoted a highly ordered hexagonal pore structure with fast formation rate independent of anodizing solution. Alumina formation rates of 2000 and 1000?nm?min?1 were achieved at current densities of 100 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?7.2?M), oxalic acid (0.3?M) and mixed solutions of sulfuric and oxalic acids were evaluated as anodizing solutions. At fixed current density, sulfuric acid promoted smaller pore diameter with lower porosity than mixed acids and oxalic acid. The I?V characteristics of aluminium anodization show the measured voltages at given current densities strongly depend on solution composition, operating temperature, and bath agitation. The pore diameter of the silicon-integrated alumina nanotemplate varied linearly with measured voltage with a slope of 2.1?nm?V?1, which is slightly smaller than reported data.