Nanopatterning by Swift Heavy Ions
Abstract: Today, the dominating way of patterning nanosystems is by irradiation-based lithography (e-beam, DUV, EUV, and ions). Compared to the other irradiations, ion tracks created by swift heavy ions in matter give the highest contrast, and its inelastic scattering facilitate minute widening and high aspect ratios (up to several thousands). Combining this with high resolution masks it may have potential as lithography technology for nanotechnology. Even if this ‘ion track lithography’ would not give a higher resolution than the others, it still can pattern otherwise irradiation insensitive materials, and enabling direct lithographic patterning of relevant material properties without further processing. In this thesis ion tracks in thin films of polyimide, amorphous SiO2 and crystalline TiO2 were made. Nanopores were used as templates for electrodeposition of nanowires.In lithography patterns are defined by masks. To write a nanopattern onto masks e-beam lithography is used. It is time-consuming since the pattern is written serially, point by point. An alternative approach is to use self-assembled patterns. In these first demonstrations of ion track lithography for micro and nanopatterning, self-assembly masks of silica microspheres and porous alumina membranes (PAM) have been used. For pattern transfer, different heavy ions were used with energies of several MeV at different fluences. The patterns were transferred to SiO2 and TiO2. From an ordered PAM with pores of 70 nm in diameter and 100 nm inter-pore distances, the transferred, ordered patterns had 355 nm deep pores of 77 nm diameter for SiO2 and 70 nm in diameter and 1,100 nm deep for TiO2. The TiO2 substrate was also irradiated through ordered silica microspheres, yielding different patterns depending on the configuration of the silica ball layers. Finally, swift heavy ion irradiation with high fluence (above 1015/cm2) was assisting carbon nanopillars deposition in a PAM used as template.
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