May 8, 2012
Optically trapped microspheres write nanofeatures on bumpy surfaces
While many lithography techniques can create nanofeatures on flat surfaces, few techniques are able to pattern rough or uneven surfaces, or surfaces with existing structures. To address this challenge, researchers from Princeton University, in the US, in collaboration with scientists from the University of Erlangen-Nuremberg, in Germany, have combined the idea of optical trapping with microsphere near-field focusing to develop a laser-direct write nanopatterning method for rough surfaces.
The technique uses a Bessel beam optical trap to position a sub-micron polystyrene sphere in water on a polyimide substrate in the x-y plane. In the z direction, the Bessel beam scattering force and the surface repulsion force compensate each other to self-position the bead relative to the target surface.
Parallel nanopatterns over a 1.5 µm model polyimide step were generated using a pair of trapped microspheres, which focus a processing laser beam in the near-field, and locally modify the surface right below the spheres. A feature size variation of less than 4% and a laterally positional accuracy of 25 nm across a step can be achieved using the set-up. The team employed a Brownian motion model to describe and predict the positional accuracy of the system.
The technique presented here explores the use of a pure optical method to fabricate user-defined nanofeatures on the fly in the absence of complex cleanroom procedures. Potential applications include the generation of nanopatterns for tissue engineering or plasmonic devices, and photonic structures for metamaterials.
Full details can be found in the journal Nanotechnology.
About the author
Yu-Cheng Tsai is a senior PhD student in the Craig B Arnold group, which is based in the mechanical and aerospace engineering department at Princeton University, New Jersey, US. His research focuses on two areas of optical science and engineering: using optical trap assisted nanopatterning (OTAN) technique for the generation of user-defined nanopatterns on rough or uneven substrates, and inventing and characterizing an innovative technique, which combines OTAN and multi-photon absorption, for the creation of 3D addictive nanostructures. Karl-Heinz Leitz is working on his doctoral thesis in the Department of Photonic Technologies with Prof. M Schmidt at the University of Erlangen-Nuremberg (Germany). His research in the field of laser-based micro- and nanostructuring is focused on ultrafast laser material processing, near-field nanostructuring and the numerical modeling of laser-beam-matter interaction phenomena.