AVS 60th International Symposium and Exhibition
    Advanced Surface Engineering Thursday Sessions
       Session SE+NS+TF-ThA

Invited Paper SE+NS+TF-ThA10
Ordered Arrays of Solid and Nanoporous Nanostructures: Particles, Alloy Particles, Pillars, Composites - From Design to Applications

Thursday, October 31, 2013, 5:00 pm, Room 203 C

Session: Nanostructured Thin Films and Coatings
Presenter: P. Schaaf, TU Ilmenau, Germany
Authors: P. Schaaf, TU Ilmenau, Germany
D. Wang, TU Ilmenau, Germany
Y. Yan, TU Ilmenau, Germany
A. Herz, TU Ilmenau, Germany
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Nanostructured materials gained attention for many applications due to their size effects on both physical and chemical properties and the effects of increased surface area. Modern nanotechnologies can fabricate nanostructured materials in different forms and with different structures, compositions and phases. Furthermore, a combination of different methods in nanotechnologies provides even more possibilities to design nanostructured materials with more diversity and complexity. Here, some examples will be presented. Metallic nanostructures are very interesting in catalysis and plasmonics. Ordered arrays of pyramidal pits were structured into the Si substrate by using nanoimprint lithography. After deposition of a thin Au film on a pre-patterned substrate, a dewetting process leads to the formation of ordered arrays of nanoparticles. Dewetting is a simple method to form metallic nanoparticles by reducing the surface energy. Structured substrates can modulate the chemical potential during dewetting, so that the ordered arrays of nanoparticles can result from the dewetting on pre-patterned substrates. By dewetting of bi-layers with two different types of metals, alloy nanoparticles can be formed. By tuning the layer thickness ratio and the total layer thickness, the particle size and composition of the particles can be well controlled. For example, the ordered arrays of Au-Ag alloy nanoparticles are fabricated by a combination of nanoimprint lithography and dewetting of Au/Ag bi-layers. By that, ordered arrays of nanoporous gold nanoparticles can be realized by combining a further process step of dealloying. Dealloying is a selective removing process, and nanoporous gold particles are formed by removing the Ag out of the Au-Ag alloy particles via submerging the sample in a HNO3 solution. The plasmonic property of the porous gold nanoparticles is clearly different from the solid gold nanoparticles with similar particle size.

Ordered arrays of single crystalline nanoporous Si nanopillars are fabricated by a combination of nanoimprint lithography and metal-assisted chemical etching. The pillar structure is first defined on the Si wafer via nanoimprint lithography, and then a thin Au film is deposited on the wafer. The metal-assisted chemical etching is performed in a solution consisting of HF and H2O2, and the Au film acts as catalyst for the etching process. The etching process with highly doped p-type Si leads to the formation of porous pillars. By combining a further process step of biomimetic synthesis, porous Si/TiO2 core/shell nanocomposite pillars are successfully produced. Besides, the TiO2 is N-doped and also partially filled in the porous Si core.