Manipulation of the Superhydrophobicity of Plasma-Etched Polymer Nanostructures.

The manipulation of droplet mobility on a nanotextured surface by oxygen plasma is demonstrated by modulating the modes of hydrophobic coatings and controlling the hierarchy of nanostructures. The spin-coating of polytetrafluoroethylene (PTFE) allows for heterogeneous hydrophobization of the high-aspect-ratio nanostructures and provides the nanostructured surface with "sticky hydrophobicity", whereas the self-assembled monolayer coating of perfluorodecyltrichlorosilane (FDTS) results in homogeneous hydrophobization and "slippery superhydrophobicity". While the high droplet adhesion (stickiness) on a nanostructured surface with the spin-coating of PTFE is maintained, the droplet contact angle is enhanced by creating hierarchical nanostructures via the combination of oxygen plasma etching with laser interference lithography to achieve "sticky superhydrophobicity". Similarly, the droplet mobility on a slippery nanostructured surface with the self-assembled monolayer coating of FDTS is also enhanced by employing the hierarchical nanostructures to achieve "slippery superhydrophobicity" with modulated slipperiness.

Selective hierarchical patterning of silicon nanostructures via soft nanostencil lithography.

It is challenging to hierarchically pattern high-aspect-ratio nanostructures on microstructures using conventional lithographic techniques, where photoresist (PR) film is not able to uniformly cover on the microstructures as the aspect ratio increases. Such non-uniformity causes poor definition of nanopatterns over the microstructures. Nanostencil lithography can provide an alternative means to hierarchically construct nanostructures on microstructures via direct deposition or plasma etching through a free-standing nanoporous membrane. In this work, we demonstrate the multiscale hierarchical fabrication of high-aspect-ratio nanostructures on microstructures of silicon using a free-standing nanostencil, which is a nanoporous membrane consisting of metal (Cr), PR, and anti-reflective coating. The nanostencil membrane is used as a deposition mask to define Cr nanodot patterns on the predefined silicon microstructures. Then, deep reactive ion etching is used to hierarchically create nanostructures on the microstructures using the Cr nanodots as an etch mask. With simple modification of the main fabrication processes, high-aspect-ratio nanopillars are selectively defined only on top of the microstructures, on bottom, or on both top and bottom.

The Rise of Scalable Micro/Nanopatterning.

This is the golden age of scalable micro/nanopatterning, as these methods emerge as an answer to produce industrial-scale nano-objects with a focus on economical sustainability and reliability.[...].

Fabrication of polymer nanowires via maskless O2 plasma etching.

In this paper, we introduce a simple fabrication technique which can pattern high-aspect-ratio polymer nanowire structures of photoresist films by using a maskless one-step oxygen plasma etching process. When carbon-based photoresist materials on silicon substrates are etched by oxygen plasma in a metallic etching chamber, nanoparticles such as antimony, aluminum, fluorine, silicon or their compound materials are self-generated and densely occupy the photoresist polymer surface. Such self-masking effects result in the formation of high-aspect-ratio vertical nanowire arrays of the polymer in the reactive ion etching mode without the necessity of any artificial etch mask. Nanowires fabricated by this technique have a diameter of less than 50 nm and an aspect ratio greater than 20. When such nanowires are fabricated on lithographically pre-patterned photoresist films, hierarchical and hybrid nanostructures of polymer are also conveniently attained. This simple and high-throughput fabrication technique for polymer nanostructures should pave the way to a wide range of applications such as in sensors, energy storage, optical devices and microfluidics systems.

Highly ordered hollow oxide nanostructures: the Kirkendall effect at the nanoscale.

Highly ordered ultra-long oxide nanotubes are fabricated by a simple two-step strategy involving the growth of copper nanowires on nanopatterned template substrates by magnetron sputtering, followed by thermal annealing in air. The formation of such tubular nanostructures is explained according to the nanoscale Kirkendall effect. The concept of this new fabrication route is also extendable to create periodic zero-dimensional hollow nanostructures.

Wafer-scale pattern transfer of metal nanostructures on polydimethylsiloxane (PDMS) substrates via holographic nanopatterns.

In this paper, we report on a cost-effective and simple, nondestructive pattern transfer method that allows the fabrication of metallic nanostructures on a polydimethylsiloxane (PDMS) substrate on a wafer scale. The key idea is to use holographic nanopatterns of a photoresist (PR) layer as template structures, where a metal film is directly deposited in order to replicate the nanopatterns of the PR template layer. Then, the PDMS elastomer is molded onto the metal film and the metal/PDMS composite layer is directly peeled off from the PR surface. Many metallic materials including Ti, Al, and Ag were successfully nanopatterned on PDMS substrates by the pattern transfer process with no use of any adhesion promoter layer or coating. In case of Au that has poor adhesion to PDMS material, a salinization of the metal surface with 3-(aminopropyl)-triethoxysilane (APTES) monolayer promoted the adhesion and led to successful pattern transfer. A series of adhesion tests confirmed the good adhesion of the transferred metal films onto the molded PDMS substrates, including scotch-tape and wet immersion tests. The inexpensive and robust pattern transfer approach of metallic nanostructures onto transparent and flexible PDMS substrates will open the new door for many scientific and engineering applications such as micro-/nanofluidics, optofluidics, nanophotonics, and nanoelectronics.

Tunable two-mirror interference lithography system for wafer-scale nanopatterning.

We have designed and analyzed a novel (to the best of our knowledge) two-beam interference lithography system for large-area (wafer-level) nanopatterning with enhanced tunability of pattern periodicities. The tunable feature has been achieved by placing two rotational mirrors in the expanded beam paths at regulated angles for a desired period. Theoretical analyses show that the effective pattern coverage area greater than a 4 in. (10 cm) wafer scale is attainable with a 325 nm (30 cm coherence length) HeCd laser and 4 in. (10 cm) mirrors, while the pattern coverage area is restrained by the overruling effects between the optical coherence and mirror size. The experimental results also demonstrate uniform nanopatterns at varying periods (250-750 nm) on 4 in. (10 cm) substrates, validating the theoretical analyses. The tunable two-mirror interferometer will offer a convenient and robust way to prepare large-area nanostructures on a wafer scale with superior tunability in their pattern periodicities.

Large-area pattern transfer of metallic nanostructures on glass substrates via interference lithography.

In this paper, we report a simple and effective nanofabrication method for the pattern transfer of metallic nanostructures over a large surface area on a glass substrate. Photoresist (PR) nano-patterns, defined by laser interference lithography, are used as template structures where a metal film of controlled thickness is directly deposited and then transferred onto a glass substrate by the sacrificial etching of the PR inter-layer. The laser interference lithography, capable of creating periodic nano-patterns with good control of their dimensions and shapes over a relatively large area, allows the wafer-scale pattern transfer of metallic nanostructures in a very convenient way. By using the approach, we have successfully fabricated on a glass substrate uniform arrays of hole, grating, and pillar patterns of Ti, Al, and Au in varying pattern periodicities (200 nm-1 µm) over a surface area of up to several cm(2) with little mechanical crack and delamination. Such robust metallic nanostructures defined well on a transparent glass substrate with large pattern coverage will lead to advanced scientific and engineering applications such as microfluidics and nanophotonics.

Two degrees-of-freedom Lloyd-mirror interferometer for superior pattern coverage area.

In this study, we have developed a tunable Lloyd-mirror interferometer with two degrees of freedom, in contrast to a traditional system with one degree of freedom. This new Lloyd-mirror interferometer allows an angular rotation of the mirror independently from that of a sample stage, resulting in an increased pattern coverage area with tunable pattern periodicity. Both theoretical and experimental results verify that the tunable characteristic of the modified configuration enhances the nanopatterning capabilities of the Lloyd-mirror interference lithography system especially in achieving greater pattern coverage area for larger pattern periodicities.