Back Injection Molding of Sub-Micron Scale Structures on Roll-to-Roll Extrusion Coated Films.

Roll-to-roll extrusion coated films were bonded onto polymer parts by back injection molding (BIM). The polypropylene (PP) coated polyethylene terephthalate (PET) films were pre-patterned with microstructured V-shaped grooves with 3.2 µm and 53 µm width, and other geometries. Bonding on PET and poly(methyl methacrylate) (PMMA) parts was facilitated by either higher tool or melt temperatures but was particularly enhanced by applying a mild oxygen plasma to the backside of the PET film prior to injection of the polymer melt. Silver wires from conductive nanoparticle ink were embedded into the PP coating during the BIM process by controlled collapse of the V-grooves. Thus, the feasibility of combining standard carrier film materials for printed flexible electronics and packaging into a non-flat polymer part was demonstrated, which could be a helpful step towards the fabrication of polymer parts with surface functionality.

High-aspect-ratio nanoimprint process chains.

Different methods capable of developing complex structures and building elements with high-aspect-ratio nanostructures combined with microstructures, which are of interest in nanophotonics, are presented. As originals for subsequent replication steps, two families of masters were developed: (i) 3.2 µm deep, 180 nm wide trenches were fabricated by silicon cryo-etching and (ii) 9.8 µm high, 350 nm wide ridges were fabricated using 2-photon polymerization direct laser writing. Both emerging technologies enable the vertical smooth sidewalls needed for a successful imprint into thin layers of polymers with aspect ratios exceeding 15. Nanoridges with high aspect ratios of up to 28 and no residual layer were produced in Ormocers using the micromoulding into capillaries (MIMIC) process with subsequent ultraviolet-curing. This work presents and balances the different fabrication routes and the subsequent generation of working tools from masters with inverted tones and the combination of hard and soft materials. This provides these techniques with a proof of concept for their compatibility with high volume manufacturing of complex micro- and nanostructures.

Integrated Photonic Nanofences: Combining Subwavelength Waveguides with an Enhanced Evanescent Field for Sensing Applications.

Photonic nanofences consisting of high aspect ratio polymeric optical subwavelength waveguides have been developed for their application into photonic sensing devices. They are up to millimeter long arrays of 250 nm wide and 6 µm high ridges produced by an advanced lithography process on a silicon substrate enabling their straightforward integration into complex photonic circuits. Both simulations and experimental results show that the overlap of the evanescent fields propagating from each photonic nanofence allows for the formation of an effective waveguide that confines the overall evanescent field within its limits. This permits a high interaction with the surrounding medium which can be larger than 90% of the total guided light intensity (approximately 20000 times larger than the evanescent field of a standard waveguide with equivalent dimensions). In this work, we not only investigate the photonic properties of these structures but also demonstrate their successful integration into a photonic sensor. An absorbance-based sensor for the determination of lead in water samples is therefore achieved by the combination of the photonic nanofences with an ion-sensitive optical membrane. The experimental results for lead detection in water show a sensitivity of 0.102 AU/decade, and a linear range between 10(-6) M and 10(-2) M Pb(II). A detection limit as low as 7.3 nM has been calculated according to IUPAC for a signal-to-noise ratio of 3.

Organic-inorganic-hybrid-polymer microlens arrays with tailored optical characteristics and multi-focal properties.

Plano-convex microlens arrays of organic-inorganic polymers with tailored optical properties are presented. The fine-tuning of each microlens within an array is achieved by confining inkjet printed drops of the polymeric ink onto pre-patterned substrates. The lens optical properties are thus freely specified, and high numerical apertures from 0.45 to 0.9 and focal lengths between 10 µm and 100 µm are demonstrated, confirming theoretical predictions. Combining nanoimprint lithography approaches and inkjet printing enables using the same material for the microlenses and their substrates, improving the optical performances. Microlens arrays with desired specifications are printed reaching yields up to 100% and high lens reproducibility with standard deviations of the apparent contact angle under 1° and of the numerical apertures and focal lengths under 6%. Microlens arrays involving lenses with different characteristics, e.g. multi focal length, and thus focal planes separated by only few microns are printed with the same reproducibility.

Novel 3D micro- and nanofabrication method using thermally activated selective topography equilibration (TASTE) of polymers.

Micro- and nanostructures with three-dimensional (3D) shapes are needed for a variety of applications in optics and fluidics where structures with both smooth and sharp features enhance the performance and functionality. We present a novel method for the generation of true 3D surfaces based on thermally activated selective topography equilibration (TASTE). This technique allows generating almost arbitrary sloped, convex and concave profiles in the same polymer film with dimensions in micro- and nanometer scale. We describe its principal mechanism exemplified by pre-patterned poly (methyl methacrylate) resist which is exposed to high energy electrons prior to a thermal annealing step enabling the selective transformation of stepped contours into smooth surfaces. From this we conclude, that TASTE not only offers an enormous degree of freedom for future process variations, but also will advance the patterning capabilities of current standard 3D micro- and nanofabrication methods.

Nano-mechanical transduction of polymer micro-cantilevers to detect bio-molecular interactions.

Using variothermal polymer micro-injection molding, disposable arrays of eight polymer micro-cantilevers each 500 µm long, 100 µm wide and 25 µm thick were fabricated. The present study took advantage of an easy flow grade polypropylene. After gold coating for optical read-out and asymmetrical sensitization, the arrays were introduced into the Cantisens(®) Research system to perform mechanical and functional testing. We demonstrate that polypropylene cantilevers can be used as biosensors for medical purposes in the same manner as the established silicon ones to detect single-stranded DNA sequences and metal ions in real-time. A differential signal of 7 nm was detected for the hybridization of 1 µM complementary DNA sequences. For 100 nM copper ions the differential signal was found to be (36 ± 5) nm. Nano-mechanical sensing of medically relevant, nanometer-size species is essential for fast and efficient diagnosis.

3D visualization of mold filling stages in thermal nanoimprint by white light interferometry and atomic force microscopy.

A method for continuous 3D visualization of the mold filling at a microscopic level during a thermoplastic nanoimprint process was developed. It is based on superposition of micrographs of a series of different stages of imprint. It was applied to two common 3D microscopies with different resolution limitations. Due to advanced image processing, the animated movie sequence, available as supplementary multimedia information in the online version of this journal, gives an unprecedented insight into the complex polymer flow and shows how voids are forming and vanishing during the imprint process around micropillars. The method has advantages over current real-time methods and can be used as an analytical tool for optimization of processes and improvement of stamp design down to the sub-10 nm nanometer range.