. Introduction
The fabrication, characterization and manipulation of nanosystems—systems that have features or characteristic lengths between 1 and 100 nm—brings together physics, chemistry, materials science and biology in an unprecedented way [1]. Phenomena occurring in such systems are fundamental to the workings of semiconductor devices, but also to living organisms. The ability to fabricate nanostructures is essential in the further development of functional devices that incorporate nanoscale features. Even more essential is the ability to introduce a wide range of chemical and materials flexibility into these structures to build up more complex nanostructures that can ultimately rival biological nanosystems. In this respect, polymers are potentially ideal nanoscale building blocks because of their length scale, well-defined architecture, controlled synthesis, ease of processing and wide range of chemical functionality that can be incorporated. Fabricating nanostructures using conventional projection photolithographic techniques is not (yet) possible, but the use of ever decreasing exposure wavelengths does push their limits into the ∼120 nm size range. New polymer chemistry has led to chemically amplified resists [2] and the incorporation fluorine into polymers has lead to the development of new resists for 157 nm UV lithography [3]. There are also very encouraging results suggesting that the so-called 100-nm barrier may eventually be overcome using photolithography [4]. Substantially smaller features are routinely produced with e-beam and focused ion beam lithography. In e-beam lithography, a tightly focused beam of high-energy electrons is used to pattern a layer of electron-sensitive polymer, mostly poly(methyl methacrylate) (PMMA) [5]. The resolution limit of e-beam lithography is based on intermolecular forces between unexposed walls and exposed polymer resist molecules which prevents the exposed molecules from being dissolved in the developer solution [6]. Ultimately, the resolution limit is determined by the radius of gyration of the exposed polymers in the developer solvent, but linewidths smaller than 5 nm have been achieved [7] and [8]. E-beam lithography is not yet suitable as a tool for mass production of nanostructures as it is a slow and sequential process. Hence, non-photolithographic methods could provide technologically simpler and cheaper nanofabrication routes. In this review we will look at a number of promising polymer-based nanofabrication strategies that have been developed recently, with an emphasis on those techniques that incorporate nanostructured polymers into devices and that exploit intrinsic polymer properties.
. IntroductionThe fabrication, characterization and manipulation of nanosystems—systems that have features or characteristic lengths between 1 and 100 nm—brings together physics, chemistry, materials science and biology in an unprecedented way [1]. Phenomena occurring in such systems are fundamental to the workings of semiconductor devices, but also to living organisms. The ability to fabricate nanostructures is essential in the further development of functional devices that incorporate nanoscale features. Even more essential is the ability to introduce a wide range of chemical and materials flexibility into these structures to build up more complex nanostructures that can ultimately rival biological nanosystems. In this respect, polymers are potentially ideal nanoscale building blocks because of their length scale, well-defined architecture, controlled synthesis, ease of processing and wide range of chemical functionality that can be incorporated. Fabricating nanostructures using conventional projection photolithographic techniques is not (yet) possible, but the use of ever decreasing exposure wavelengths does push their limits into the ∼120 nm size range. New polymer chemistry has led to chemically amplified resists [2] and the incorporation fluorine into polymers has lead to the development of new resists for 157 nm UV lithography [3]. There are also very encouraging results suggesting that the so-called 100-nm barrier may eventually be overcome using photolithography [4]. Substantially smaller features are routinely produced with e-beam and focused ion beam lithography. In e-beam lithography, a tightly focused beam of high-energy electrons is used to pattern a layer of electron-sensitive polymer, mostly poly(methyl methacrylate) (PMMA) [5]. The resolution limit of e-beam lithography is based on intermolecular forces between unexposed walls and exposed polymer resist molecules which prevents the exposed molecules from being dissolved in the developer solution [6]. Ultimately, the resolution limit is determined by the radius of gyration of the exposed polymers in the developer solvent, but linewidths smaller than 5 nm have been achieved [7] and [8]. E-beam lithography is not yet suitable as a tool for mass production of nanostructures as it is a slow and sequential process. Hence, non-photolithographic methods could provide technologically simpler and cheaper nanofabrication routes. In this review we will look at a number of promising polymer-based nanofabrication strategies that have been developed recently, with an emphasis on those techniques that incorporate nanostructured polymers into devices and that exploit intrinsic polymer properties.
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