Automated solvent vapor annealing with nanometer scale control of film swelling for block copolymer thin films.

Molecular self-assembly of block copolymers has been pursued as a next generation high-resolution, low-cost lithography technique. Solvent vapor annealing is a promising way of achieving self-assembled patterns from polymers with high interaction parameters, χ, or high molecular weights. Compared to thermal annealing, the assembly in a solvated state can be much faster, but the film swelling process is typically challenging to control and reproduce. We report the design and implementation of an automated solvent annealing system that addresses these issues. In this system the film swelling is controlled via local heating or cooling, which enables exceptionally fast and precise modulation of the swelling. The swelling of the polymer films follows preprogrammed annealing profiles with the help of a feedback loop that compares and tunes the film thickness with respect to the set point. The system therefore enables complex annealing profiles such as rapid cyclic swelling and deswelling. We show that the orientation of the pattern morphology and the amount of lattice defects are influenced by the used annealing profile. We demonstrate that optimized profiles significantly shorten the annealing time (<15 min) of high-χ and high-molecular weight poly(styrene-b-2-vinylpyridine).

Mechanical Analysis of Ultrasound-Activated Pins and Resorbable Screws: Two Different Techniques to Fixate Osteosynthesis in Craniosynostosis Surgery.

PURPOSE: Ultrasound activation of resorbable pins directly into drilled holes of the calvarium was introduced to overcome the time-consuming installation in the resorbable osteosynthesis fixation in craniosynostosis surgery. There is paucity in the data comparing the mechanical properties of resorbable screws and ultrasound-activated pins produced by different manufacturers. The aim of this experimental study was to compare the mechanical properties of ultrasound-activated pins and resorbable screws. METHODS: A mechanical testing machine was used to characterize the mechanical performance of screws and ultrasound pins. The screws and pins were tested individually in 2 directions with respect to the longitudinal axis: vertical, that is, axial pull-out strength and horizontal, that is, shear strength. The mean maximum strength of fixation was determined. Broken screws and pinheads were analyzed by a scanning electron microscope to determine the site of fracture. RESULTS: All of the resorbable screws and pins broke at the point where the device enters bone. In pull-out testing, the mean maximum strength of the ultrasound-activated pins was 30.5 ± 5.4 N and that of the resorbable screws was 54.0 ± 0.3 N. In shear testing, the mean maximum strength of ultrasound-activated pins was 57.1 ± 20.1 N and that of the resorbable screws was 53.9 ± 0.4 N. CONCLUSIONS: In their intended configuration, there is no clinically significant difference in fixation strength between ultrasound-activated pins and resorbable screws.

Formation and use of biogenic jarosite carrier for high-rate iron oxidising biofilms.

Jarosite precipitates formed in iron oxidising bioreactors have been shown to harbour iron-oxidisers. The aim of this study was to develop an iron oxidising bioprocess where microorganisms are retained solely on biogenic jarosite particles. Based on preliminary experiments using a fluidised-bed bioreactor (FBR), the formed jarosite particles started to disintegrate and wash out at upflow velocities of ≥0.21 cm/s. Therefore, the generation and use of biogenic jarosite carrier was studied in an expanded-bed bioreactor (J-EBR) with an upflow velocity of 0.19 cm/s. Inside J-EBR, the jarosite particles formed granules of 0.5-3 mm containing 200-460 mg/g of attached biomass. The performance of J-EBR was compared with an activated carbon biofilm FBR at 0.82 cm/s upflow velocity (AC-FBR). At 35 ± 2 °C with a feed ferrous iron concentration of 10 g/l, the highest obtained iron oxidation rate of J-EBR (6.8 g/l/h) was 33% lower than that of AC-FBR (10.1 g/l/h). This was likely due to the 80% lower recirculation rate and subsequently higher oxygen mass transfer limitation in J-EBR compared to AC-FBR. The present study demonstrates that biogenic jarosite can be used for retainment of iron oxidising biofilms in expanded-bed bioreactors that oxidise iron at high rates.

High molecular weight block copolymer lithography for nanofabrication of hard mask and photonic nanostructures.

An unusual dot pattern was realized via self-assembly of high molecular weight polystyrene-block-polydimethylsiloxane (PS-b-PDMS) copolymer by a simple one-step solvent annealing process, optimized based on Hansen solubility parameters. Annealing PS-b-PDMS under neutral solvent vapors at room temperature produces an ordered arrangement of dots with ∼112 nm spacing and ∼54 nm diameter. The template is highly resistant to dry etching with chlorine-based plasma, enabling its utilization on a variety of hard masks and substrates. The self-assembled PDMS dots were further exploited as a template for direct patterning of silicon, metal, and dielectric materials. This nanopatterning methodology circumvents expensive and time-consuming atomic layer deposition, wet processes, and sequential infiltration techniques. Application-wise, we show a process to fabricate nanostructured antireflection surfaces (nanocones) on a 2 in. silicon wafer, reducing the reflectance of planar silicon from 35% to below 0.5% over a broad wavelength range. Alternatively, nanocones made of TiO2 on silicon exhibit low reflectance (<3%) and improved transmittance into the substrate at the visible wavelength range. The measured optical properties concur with the simulation results. The versatility of the PS-b-PDMS templates was further utilized for nanopatterning materials such as silicon-on-insulator substrates, gallium arsenide, aluminum indium phosphide, and gallium nitride, which are important in electronics and photonics.

All-Metal Broadband Optical Absorbers Based on Block Copolymer Nanolithography.

The growing interest in solar energy during recent years has spurred on the development of high-efficiency optical absorbers using emerging concepts in plasmonics and metamaterials. Most absorber designs require patterning on a subwavelength scale, making large-scale fabrication expensive or impractical. This study presents an all-metal metasurface with tightly packed, sub-80 nm nanodomes fabricated by template-stripping thin gold films from reusable silicon templates. Subwavelength patterning was achieved via molecular self-assembly of block copolymers, which enables large-area, periodic patterning with nanometer precision. The proposed nanodome surface acts as an optical absorber capable of absorbing 97% of incident light in the visible range 320-650 nm, and still more than 90% at high incidence angles. We demonstrate both experimentally and theoretically that the absorption behavior of the thin film can be controlled by changing the size of the nanodomes, namely, the gap between the structures. The enhanced absorption of light is attributed to localized particle plasmon and gap plasmon resonances. This research provides a straightforward and cost-effective strategy to design and fabricate thin, large-area, light-absorbing coatings that can be transferred onto nearly any rigid or flexible substrate. The all-metal metasurfaces are a promising candidate for plasmon-induced hot electron generation for efficient solar energy conversion in photovoltaic and photocatalytic devices.

Block Copolymer Patterning for Creating Porous Silicon Thin Films with Tunable Refractive Indices.

We investigated the use of block copolymer (BCP) self-assembly for tuning the optical properties of silicon. We fabricated porous silicon by etching a hexagonally ordered pore pattern onto the surface of silicon wafers using poly(styrene-2-vinylpyridine) to prepare the etch mask. Contrary to typical BCP lithography, we did not need to use a range of different polymers to vary the pore size. We used the dry etching time as a way to increase the pore diameter and thus the porosity. The optical properties of the fabricated porous thin films were characterized by two effective medium approximations. Both the volume-averaging theory and the 2D Maxwell-Garnett theory gave similar effective refractive index values, although the latter was more accurate in predicting the film porosity. The refractive indices of the produced thin films could be varied by controlling the porosity. A maximum decrease of 30% in the refractive index was observed at 34% porosity compared to bulk silicon. We also demonstrated over a 60% decrease in the reflectance of silicon at 500 nm wavelength. The presented BCP method can be used to tailor semiconductor and dielectric layers for photonic applications without the size limitations of conventional lithography or the unpredictability of other pore-forming fabrication methods.