B. N. Chichkov

Development of functional sub-100 nm structures with 3D two-photon polymerization technique and optical methods for characterization

Investigations of two-photon polymerization (TPP) with sub-100 nm in the structuring resolution are presented by using photosensitive sol-gel material. The high photosensitivity of this material allows for TPP using a large variety in laser pulse durations covering a range between sub-10 fs and ≈140 fs. In this study, the authors demonstrate TPP structuring to obtain sub-100 nm in resolution by different approaches, namely, by adding a cross-linker to the material and polymerization with sub-10 fs short pulses. Additionally, a simulation and model based characterization method for periodic sub-100 nm structures was implemented and applied in an experimental white light interference Fourier-Scatterometry setup.

Closely packed hexagonal conical microlens array fabricated by direct laser photopolymerization

We apply femtosecond laser direct writing in photopolymers for manufacturing of conical microlenses and closely packed arrays thereof. We demonstrate the fabrication of high optical quality axicons of 15 µm in radius, having 150°, 160°, and 170° cone angles. Their optical properties and performance are modeled using the finite-difference time-domain method and compared with experimentally measured data. Additionally, optimization of the laser direct writing parameters regarding these types of micro-objects is presented. Possible applications of closely packed arrays of axicon microlenses are discussed, having potential attractivity in the fields of modern microscopy, light-based material processing, particle manipulation in microfluidic, and optofluidic applications.

Depth sensitive Fourier-Scatterometry for the characterization of sub-100 nm periodic structures

Recently Fourier-Scatterometry has become of increasing interest for quantitative wafer metrology. But also in other fields the fast and precise optical characterization of periodical gratings of sub 100 nm size is of great interest. We present the application of Fourier-Scatterometry, extended by the use of the coherent properties of white light for the characterization of sub-wavelength periodic gratings of photosensitive material structured by two-photon polymerization. First a simulation-based sensitivity comparison of Fourier-Scatterometry at one fixed wavelength, Fourier-Scatterometry using a white light light source and also additionally using a reference-branch for white-light-interference has been carried out. The investigated structures include gratings produced by two-photon polymerization of photosensitive material and typical semiconductor test gratings. The simulations were performed using the rigorous-coupled-waveanalysis included in our software package MicroSim. A sensitivity comparison between both methods is presented for the mentioned structure types. We also show our experimental implementation of the measurement setup using a whitelight- laser and a modified microscope with a high-NA (NA: 0.95) objective as well as a Linnik-type reference branch for the phase sensitive measurements. First measurements for the investigation of the performance of this measurement setup are presented for comparison with the simulation results.

3D biomedical implants fabricated using direct laser writing

We present our investigations into the design and fabrication of a complex shape, readily assembled micro check-valve using the two-photon polymerization technique and a hybrid material. A computational fluid dynamics study has been carried out in order to evaluate the flow performance of the valve under blood pressures exhibited in healthy human veins. The fabricated micro-valves exhibit good dimensional accuracy when compared to the CAD-created valve design and the capability of an internal moving component to perform its intended function.

Fourier Scatterometry for Characterization of Sub‐wavelength Periodic Two Photon Polymerization Structures

In the present paper we extend Fourier‐Scatterometry by the use of the coherent properties of white light for the characterization of sub‐wavelength periodic gratings of photosensitive material structured by two‐photon polymerization. Our goal is a fast and precise optical characterization of periodical gratings of sub 100 nm size. The investigated structures include gratings produced by two‐photon polymerization of photosensitive material and typical semiconductor test gratings. A Fourier‐Scatterometer has been set up using a white light source and also additionally a reference‐branch for white‐light‐interference (WLI). A sensitivity comparison between Fourier‐Scatterometry and WLI‐Scatterometry is presented.

Three‐dimensional Polycaprolactone Structures Fabricated by Two‐Photon Polymerization

Two‐photon polymerization has been employed to fabricate three‐dimensional structures using the biodegradable triblock copolymer poly(e‐caprolactone‐co‐trimethylenecarbonate)‐b‐poly(ethylene glycol)‐b‐poly(e‐caprolactone‐co‐trimethylenecarbonate) with 4,4’‐bis(diethylamino)benzophenone as the photoinitiator. The fabricated structures were of good quality and had four micron resolution. Initial cytotoxicity tests show that the material does not affect cell proliferation. These studies demonstrate the potential of two‐photon polymerization as a technology for the fabrication of biodegradable scaffolds for tissue engineering.