Silicon nanocolumns on nanosphere lithography templated substrates: effects of sphere size and substrate temperature.

Glancing angle ion beam sputter deposition was used to grow regular arrays of Si nanocolumns with a nominal height of 650 nm at room temperature on polystyrene nanospheres with sphere diameters between 260 nm and 3550 nm, and at elevated temperatures on SiO2 nanospheres with a sphere diameter of 360 nm. Top view and cross sectional scanning electron microscopy reveals that the Si nanocolumns resemble cylinder-like structures, terminated by a hemispherical cap. Diameter, height and inter-column-spacing are found to depend linearly on the nanosphere diameter, thus giving the possibility to grow arrays of vertical Si columns with distinct porosities. For the growth at elevated temperatures, it was found that while on non-patterned substrates diffusion effects lead to broadening and finally merging of initially separated nanocolumns, on nanosphere patterned substrates this broadening effect is only moderate. No merging of columns is observable in this case, but a decrease of the column height due to a temperature-driven inter-column densification.