Polydimethylsiloxane (PDMS) is a widely used material for fabrication of microfluidic devices and for replication of micro- and nanotextured surfaces. Shrinkage of PDMS in the fabrication process can lead to leaking devices and poor alignment of layers. However, corrections to the mold master are seldom applied to counteract the shrinkage of PDMS. Also, to perform metrological measurements using replica techniques one has to take the shrinkage into account. Thus we report a study of the shrinkage of PDMS with several different mixing ratios and curing temperatures. The shrinkage factor, with its associated uncertainty, for PDMS in the range 40 to 120 °C is provided. By applying this correction factor, it is possible to replicate structures with a standard uncertainty of less than 0.2% in lateral dimensions using typical curing temperatures and PDMS mixing ratios in the range 1:6 to 1:20 (agent:base).

Fabrication of micro‐ and nanostructures at line‐speed of 60 m min−1 by large‐area roll‐to‐roll extrusion coating is demonstrated. Nanopillars with diameters 80 nm and heights 100 nm are replicated in polypropylene. The main limiting factor for replication on nanoscale is the retardation time for solidification of the melt.

Thiol-ene polymers possess physical, optical, and chemical characteristics that make them ideal substrates for the fabrication of optofluidic devices. In this work, thiol-ene polymers are used to simultaneously create microfluidic channels and optical waveguides in one simple moulding step. The reactive functional groups present at the surface of the thiol-ene polymer are subsequently used for the rapid, one step, site-specific functionalization of the waveguide with biological recognition molecules. It was found that while the bulk properties and chemical surface properties of thiol-ene materials vary considerably with variations in stoichiometric composition, their optical properties remain mostly unchanged with an average refractive index value of 1.566 ± 0.008 for thiol-ene substrates encompassing a range from 150% excess ene to 90% excess thiol. Microfluidic chips featuring thiol-ene waveguides were fabricated from 40% excess thiol thiol-ene to ensure the presence of thiol functional groups at the surface of the waveguide. Biotin alkyne was photografted at specific locations using a photomask, directly at the interface between the microfluidic channel and the thiol-ene waveguide prior to conjugation with fluorescently labeled streptavidin. Fluorescence excitation was achieved by launching light through the thiol-ene waveguide, revealing bright fluorescent patterns along the channel/waveguide interface.

Lab-scale plasmonic color printing using nano-structured and subsequently metallized surfaces have been demonstrated to provide vivid colors. However, upscaling these structures for large area manufacturing is extremely challenging due to the requirement of nanometer precision of metal thickness. In this study, we have investigated a plasmonic color meta-surface design that can be easily upscaled. We have demonstrated the feasibility of fabrication of these plasmonic color surfaces by a high-speed roll-to-roll method, comprising roll-to-roll extrusion coating at 10 m min creating a polymer foil having 100 nm deep pits of varying sub-wavelength diameter and pitch length. Subsequently this polymer foil was metallized and coated also by high-speed roll-to-roll methods. The perceived colors have high tolerance towards the thickness of the metal layer, when this thickness exceeds the depths of the pits, which enables the robust high-speed fabrication. This finding can pave the way for plasmonic meta-surfaces to be implemented in a broader range of applications such as printing, memory, surface enhanced Raman scattering (SERS), biosensors, flexible displays, photovoltaics, security, and product branding.

We report a study of the correlation between three optical methods for characterizing surface roughness: a laboratory scatterometer measuring the bi-directional reflection distribution function (BRDF instrument), a simple commercial scatterometer (rBRDF instrument), and a confocal optical profiler. For each instrument, the effective range of spatial surface wavelengths is determined, and the common bandwidth used when comparing the evaluated roughness parameters. The compared roughness parameters are: the root-mean-square (RMS) profile deviation (Rq), the RMS profile slope (Rdq), and the variance of the scattering angle distribution (Aq). The twenty-two investigated samples were manufactured with several methods in order to obtain a suitable diversity of roughness patterns. Our study shows a one-to-one correlation of both the Rq and the Rdq roughness values when obtained with the BRDF and the confocal instruments, if the common bandwidth is applied. Likewise, a correlation is observed when determining the Aq value with the BRDF and the rBRDF instruments. Furthermore, we show that it is possible to determine the Rq value from the Aq value, by applying a simple transfer function derived from the instrument comparisons. The presented method is validated for surfaces with predominantly 1D roughness, i.e. consisting of parallel grooves of various periods, and a reflectance similar to stainless steel. The Rq values are predicted with an accuracy of 38% at the 95% confidence interval.

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We report a simple one-step maskless fabrication of inverted pyramids on silicon wafers by reactive ion etching. The fabricated surface structures exhibit excellent anti-reflective properties: The total reflectance of the nano inverted pyramids fabricated by our method can be as low as 12% without any anti-reflective layers, and down to only 0.33% with a silicon nitride coating. The results from angle resolved scattering measurements indicate that the existence of triple reflections is responsible for the reduced reflectance. The surfaces with the nano inverted pyramids also exhibit a distinct milky white color.