Inverse Nanostructures Research Articles

Resist nanokirigami for multipurpose patterning.

Resist-based patterning solutions play essential roles in modern micro- and nanoscale science and technology. The commonly used 'resist' patterning strategy depends on selective-area scission or cross-linking of resist molecules under the action of an energy beam. In this work, we propose and demonstrate a different resist-patterning strategy, termed 'resist nanokirigami', in which the resist structures are defined by their outlines and revealed by selective mechanical peeling of the unwanted resist film. Unlike conventional resist-based patterning processes, the final resist-nanokirigami structures do not undergo exposure and the exposure area is dramatically reduced. With these two advantages, a variety of functional structures that are difficult or impossible to fabricate by conventional processes, such as inverse nanostructures and their oligomers, multi-scale electrodes and freestanding plasmonic nanogaps, can be easily achieved with much higher efficiency. Thus, with its unique and complementary capabilities, the resist-nanokirigami process provides a new patterning solution that expands the family of lithography techniques and will play a significant role in fabricating multi-scale functional structures.

Fabrication of biomimetic dry-adhesion structures through nanosphere lithography

Components with surface nanostructures suitable for biomimetic dry adhesion have a great potential in applications such as gecko tape, climbing robots, and skin patches. In this study, a nanosphere lithography technique with self-assembly nanospheres was developed to achieve effective and efficient fabrication of dry-adhesion structures. Self-assembled monolayer nanospheres with high regularity were obtained through tilted dip-coating. Reactive-ion etching of the self-assembled nanospheres was used to fabricate nanostructures of different shapes and aspect ratios by varying the etching time. Thereafter, nickel molds with inverse nanostructures were replicated using the electroforming process. Polydimethylsiloxane (PDMS) nanostructures were fabricated through a gas-assisted hot-embossing method. The pulling test was performed to measure the shear adhesion on the glass substrate of a sample, and the static contact angle was measured to verify the hydrophobic property of the structure. The enhancement of the structure indicates that the adhesion force increased from 1.2 to 4.05 N/cm2 and the contact angle increased from 118.6° to 135.2°. This columnar structure can effectively enhance the adhesion ability of PDMS, demonstrating the potential of using nanosphere lithography for the fabrication of adhesive structures.

Inverse Moth Eye Nanostructures with Enhanced Antireflection and Contamination Resistance.

Moth-eye-inspired nanostructures are highly useful for antireflection applications. However, block copolymer micelle lithography, an effective method to prepare moth eye nanopillars, can only be used on a limited choice of substrates. Another drawback of nanopillar substrates is that contamination is easily absorbed, thereby reducing transmittance. The production of antireflective surfaces that are contamination-resistant or that can be cleaned easily without the loss of optical properties remains challenging. Here, we describe an approach for creating inverse moth eye nanostructures on other optical substrates than the most commonly used fused silica. We demonstrate its feasibility by fabricating a borosilicate substrate with inverse nanostructures on both sides. The etching of nanoholes on both sides of the substrate improves its transmittance by 8%, thereby surpassing the highest increase of transmittance yet to be obtained with nanopillars on fused silica. More importantly, the substrate with inverse moth eye nanostructures is more robust against contaminations than the substrates with nanopillars. No significant decrease in performance is observed after five cycles of repeated contamination and cleaning. Our approach is transferable to a variety of optical materials, rendering our antireflection nanostructures ideal for applications in touch devices such as touch screens and display panels.