Surface plasmons (SPs) are coherent oscillations of conduction electrons on a metal surface excited by electromagnetic radiation at a metal -dielectric interface. The growing field of research on such light -metal interactions is known as ‘plasmonics’. 1-3 This branch of research has attracted much attention due to its potential applications in miniaturized optical devices, sensors, and photonic circuits as well as in medical diagnostics and therapeutics. 4-8

Nanostructured plasmonic sensors.

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New approaches to nanofabrication: molding, printing, and other techniques.

The ability to pattern functional polymers at different length scales is important for research fields including cell biology, tissue engineering and medicinal science and the development of optics and electronics. The interest and capabilities of polymer patterning have originated from the abundance of functionalities of polymers and a wide range of applications of the patterns. This paper reviews recent advances in top-down and bottom-up patterning of polymers using photolithography, printing techniques, self-assembly of block copolymers and instability-induced patterning. Finally, challenges and future directions are discussed from the point of view of both applicability and strategies for the surface patterning of polymers.

Patterning surfaces with functional polymers

Nanoimprint lithography (NIL) is a high throughput, high-resolution parallel patterning method in which a surface pattern of a stamp is replicated into a material by mechanical contact and three dimensional material displacement. This can be done by shaping a liquid followed by a curing process for hardening, by variation of the thermomechanical properties of a film by heating and cooling, or by any other kind of shaping process using the difference in hardness of a mold and a moldable material. The local thickness contrast of the resulting thin molded film can be used as a means to pattern an underlying substrate on wafer level by standard pattern transfer methods, but also directly in applications where a bulk modified functional layer is needed. Therefore it is mainly aimed toward fields in which electron beam and high-end photolithography are costly and do not provide sufficient resolution at reasonable throughput. The aim of this review is to play between two poles: the need to establish standard processes and tools for research and industry, and the issues that make NIL a scientific endeavor. It is not the author’s intention to duplicate the content of the reviews already published, but to look on the NIL process as a whole. The author will also address some issues, which are not covered by the other reviews, e.g., the origin of NIL and the misconceptions, which sometimes dominate the debate about problems of NIL, and guide the reader to issues, which are often forgotten or overlooked.

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Nanoimprint lithography: An old story in modern times? A review

Nanoimprinting promises low-cost fabrication of micro- and nano-devices by embossing features from a hard mould onto thermoplastic materials, typically polymers with low glass transition temperature. The success and proliferation of such methods critically rely on the manufacturing of robust and durable master moulds. Silicon-based moulds are brittle and have limited longevity. Metal moulds are stronger than semiconductors, but patterning of metals on the nanometre scale is limited by their finite grain size. Amorphous metals (metallic glasses) exhibit superior mechanical properties and are intrinsically free from grain size limitations. Here we demonstrate direct nanopatterning of metallic glasses by hot embossing, generating feature sizes as small as 13 nm. After subsequently crystallizing the as-formed metallic glass mould, we show that another amorphous sample of the same alloy can be formed on the crystallized mould. In addition, metallic glass replicas can also be used as moulds for polymers or other metallic glasses with lower softening temperatures. Using this 'spawning' process, we can massively replicate patterned surfaces through direct moulding without using conventional lithography. We anticipate that our findings will catalyse the development of micro- and nanoscale metallic glass applications that capitalize on the outstanding mechanical properties, microstructural homogeneity and isotropy, and ease of thermoplastic forming exhibited by these materials.

Nanomoulding with amorphous metals

We show that small diameter, single-walled carbon nanotubes can serve as templates for performing polymer imprint lithography with feature sizes as small as 2 nm − comparable to the size of an individual molecule. The angstrom level uniformity in the critical dimensions of the features provided by this unusual type of template provides a unique ability to investigate systematically the resolution of imprint lithography at this molecular scale. Collective results of experiments with several polymer formulations for the molds and the molded materials suggest that the density of cross-links is an important molecular parameter that influences the ultimate resolution in this process. Optimized materials enable reliable, repetitive patterning in this single nanometer range.

Jingfeng Wang

Papers

Polymer Imprint Lithography with Molecular-Scale Resolution