Regular nanostructures are of great interest due to their potential application in e.g. photonic crystals, data storage, displays, and biological sensors. A common way of fabricating nanostructures is by irradiation-based lithography. Fast heavy ion irradiation induces localized material transformation in matter, which, compared to e.g. e-beam or photo-lithography, gives a very high contrast between irradiated and non-irradiated regions. In addition, fast heavy ions can transform materials that are otherwise insensitive to electron or photon irradiation, they can induce high aspect ratio structures, and they are only minutely scattered.
In projection lithography the pattern is defined by a mask. Combining fast heavy ions with high resolution absorbing masks may thus have potential as a lithography technique for nanotechnology. The advantage with this technique is that it directly result in, without further processing, patterned material modifications. As a lithographic mask with large high-density nanopatterns, self-assembled materials with nano-scale features are an interesting option enabling parallel patterning.
In this work, we have used masks of porous anodic alumina membranes (PAM) and of self-assembled colloidal particles, to control the energetic heavy ions and transfer well defined patterns to different materials. Results on fabricating regular nanostructures on rutile TiO2 single crystals and amorphous SiO2 after ion irradiation through either PAM or self-assembled colloidal masks of silica spheres will be presented.
From an ordered PAM we obtained transferred patterns consisting of pores with the same hexagonal ordering, having a diameter of 77 nm, 100 nm inter-pore distances, and depths up to 1100 nm. Using self-assembled silica spheres as a mask the resulting patterns could be tuned by varying the geometric configuration of the silica sphere layers. Direct modification of the optical properties in a well-defined pattern will also be shown. Finally, fast heavy ion irradiation at high doses caused carbon deposition in a PAM template leading to ordered carbon nanopillar arrays. |