Christoph Morhard

Nanopatterning by block copolymer micelle nanolithography and bioinspired applications

This comprehensive overview of block copolymer micelle nanolithography (BCMN) will discuss the synthesis of inorganic nanoparticle arrays by means of micellar diblock copolymer approach and the resulting experimental control of individual structural parameters of the nanopattern, e.g., particle density and particle size. Furthermore, the authors will present a combinational approach of BCMN with conventional fabrication methods, namely, photolithography and electron beam lithography, which combines the advantages of high-resolution micronanopatterning with fast sample processing rates. In addition, the authors will demonstrate how these nanoparticle assemblies can be transferred to polymer substrates with a wide range of elasticity. In the second part of this report the authors will introduce some of the most intriguing applications of BCMN in biology and materials science: The authors will demonstrate how nanoparticle arrays may be used as anchor points to pattern functional proteins with single molecule resolution for studying cellular adhesion and present a technological roadmap to high-performance nanomaterials by highlighting recent applications for biomimetic optics and nanowires.

Simulating different manufactured antireflective sub-wavelength structures considering the influence of local topographic variations

Laterally structured antireflective sub-wavelength structures show unique properties with respect to broadband performance, damage threshold and thermal stability. Thus they are superior to classical layer based antireflective coatings for a number of applications. Dependent on the selected fabrication technology the local topography of the periodic structure may deviate from the perfect repetition of a sub-wavelength unit cell. We used rigorous coupled-wave analysis (RCWA) to simulate the efficiency losses due to scattering effects based on height and displacement variations between the individual protuberances. In these simulations we chose conical and Super-Gaussian shapes to approximate the real profile of fabricated structures. The simulation results are in accordance with the experimentally determined optical properties of sub-wavelength structures over a broad wavelength range. Especially the transmittance reduction in the deep-UV could be ascribed to these variations in the sub-wavelength structures.

Antireflective subwavelength structures on microlens arrays—comparison of various manufacturing techniques

Antireflective subwavelength structures (ARS) resembling nanostructures found on the cornea of night-active insects reduce the reflection of light by providing a gradual change in the refractive index at the interface. These artificial ARS have mainly been fabricated by a combination of conventional lithography and reactive ion etching, which constrains their application to planar substrates. We report on the fabrication of ARS using three different techniques including bottom-up and top-down methods as well as their combination on microlens arrays (MLAs) made of fused silica. The optical performance of the resulting ARS on the MLAs is as good as ARS fabricated on planar substrates with increased transmission of up to 96% at certain wavelengths.

Antireflective ‘moth-eye’ structures fabricated by a cheap and versatile process on various optical elements

We present a cheap and versatile method to fabricate antireflective moth-eye structures on various substrates. This method consists of a mask created by a self-assembly technique (block copoplymer micelle nanolithography - BCML) and a subsequent reactive ion etching step. Contrary to most other methods this technique also allows for the creation of moth-eye structures on non-flat substrates. We demonstrate the superiority of this technique on a diffraction grating and on different lenses. Electron micrographs show that almost the whole surface area is homogenously covered with these antireflective nanostructures. Transmittance and reflectance measurements support these findings.