Dry adhesion observed in small creatures, such as spiders, insects, and geckos, has many great advantages such as repeatability and strong adhesiveness. In order to mimic these unique performances, fibrillar surface with a mushroom shaped end has drawn lots of attentions because of its advantage in efficiently enhancing adhesion compared with other sphere or simple flat ends. Here, in order to study the effects of contact cap dimension on adhesion strength, patterned surfaces of mushroom-shaped micropillars with differing cap diameters are fabricated based on the conventional photolithography and molding. The normal adhesion strength of these dry adhesives with varying cap diameters is measured with home-built equipment. The strength increases with the rise of cap diameter, and interestingly it becomes strongest when the mushroom caps join together.
In this paper, microlens array with varying focal lengths were fabricated on a single microbowl-array textured substrate. The solid microbowl-arrayed NOA61 (kind of polyurethane-based polymer with UV curablity) surface was resulted from nanoimprinting by polydimethylsiloxane (PDMS) mold. The PDMS mold was replicated from an SU-8 master which was generated by electron beam lithography. Such microbowl-arrayed surfaces demonstrate petal-mimetic highly adhesive hydrophobic wetting properties, which can promote an irreversible electrowetting (EW) effect and a dereased contact angle of water droplets as well as other liquid droplets by applying direct current (DC) voltage. To fabricate a microlens array with varying focal-lengths, liquid NOA61 was supplied from a syringe on the solid NOA61 microtextured film and DC voltage was applied succesively. After removing the DC voltage, these liquid NOA61 microdrops deposited on the solid microtextured NOA61 surface on tin-indium-oxide coated substrate could be solidified via UV irradiation, thus leading to microlens array with uneven numerical apertures on a single substrate. Numerical simulation was also done to verify the EW effect. Finally, optical imaging characterization was performed to confirm the varied focus of the NOA61 microdrops.
A simple and high-accuracy alignment measurement method based on a moiré fringe pattern is proposed. It involves relative rotation positioning and relative linear displacement measurement. Taking full advantage of the magnification effect of moiré fringe in angular and linear displacement, the relative rotation between the template and the wafer is determined first by measuring the inclination of the moiré fringe, and then the relative linear displacement between them is acquired by evaluating the spatial phase shift of two matched moiré fringes. The frequency components in the orthogonal directions of the fringe image obtained by a fast Fourier transform (FFT) and zooming process are used to measure the inclination of the moiré fringe. By selecting different orthogonal directions, a moiré fringe with any inclination can be measured accurately. When gratings are adjusted to parallel, a frequency-domain analysis is also used to extract the spatial phase of fringes at a given frequency. According to the relationship between spatial phase and linear displacement, the misalignment is detected. In experiments, the repeatability for the misalignment measurement has reached 4.8 nm (3).