## 4 Patterning towards Devices: Conventional and Unconventional Methods
### Block copolymer lithography  
A very recent patterning technique is the block copolymer lithography, which differs from the conventional lithography approaches, since the pattern formation of NPs is not promoted by a masked radiation source, but is induced by the spatial confinement of periodic separated phases of block copolymers (BCPs). These polymers are known for their spontaneous assembling in well-defined morphologies (lamellar, cylindrical, spherical) and topographic nanometer scale contrast [1, 157, 158, 159]. Namely, the surface chemistry of BCP domain sidewalls has been found to direct, as well as to confine the organization of embedded NPs resulting in nanoscale patterns whose dimensions match those of the polymer chain lengths. As a matter of fact, the NP patterns exhibit final resolutions within 10-100 nm, lower than those achieved with conventional lithography. In addition, since the size, shape and surface chemistry of the self-assembled BCP domains can be predicted on the basis of macromolecular rules the final size and geometry of the NP patterns can be tuned. Due to these properties, BCPs are considered as a new generation of resists and block copolymer lithography results in a high resolution machining method, which allows for patterning areas larger than those processed with conventional lithography, avoiding the use of clean room conditions and expensive masks as well [1, 157, 158, 159]. A common approach typically employed in BCP lithography relies on the _in situ_ nucleation, growth and assembly of NPs directly in BCP domains. Here, the surface chemistry of pre-existing BCP domains is designed with specific chemical functionalities arranged in a periodic order for selectively templating the organization of the NPs on the BCP domain surfaces. This approach has been used to generate periodic patterns of carbon nanotubes [160, 161], gold [162] and semiconducting [163] NPs for large scale integrated circuits, energy storage and electronic devices and biomedical applications. Self assembled thin films of asymmetric BCPs, namely polystyrene-block-poly-(methyl methacrylate)s (PS-b-PMMAs) have been used for growing vertical single wall carbon nanotube (SWNT) arrays from nanopatterned arrays of iron catalyst. In this work, the hexagonally organized pores of PS were used as templates for the formation of iron catalyst particles deposited over the block copolymer template via tilted evaporation and the CNTs grow on the catalyst by plasma enhanced chemical vapor deposition [160]. The same approach has been used to generate vertical wall--number-selected N-doped CNT arrays 52 um in length by plasma enhanced chemical vapor deposition in NH\({}_{3}\) environment [161]. In both works, the nanometer design of the catalyst size achieved by the block copolymer confinement enables a control of both the CNT wall number and diameter. Au NPs 1.4 nm in diameter have been selectively generated in regular hexagonally packed cylinders of polystyrene-b-poly-4-vinylpyridine (PS-b-P4 VP) block copolymers by _in situ_ reduction of a gold precursor. After the generation and growth of the NPs, both the morphology and the periodicities of the block copolymers are preserved at the macroscopic level [162]. Block copolymers on poly-(styrene)-block-poly(acrylic acid) (PS-b-PAA) have been used to synthesized semiconducting metal sulfide NPs from aqueous solution at low temperature. When the PS-b-PAA spherical templates are exposed to an appropriate precursor for NPs favorable interactions between surface-COOH moieties of the PAA block and precursor metal ions promote a preferential heterogeneous nucleation and growth of the NPs at the PAA domain surface, resulting in the occurrence of NP arrays replicating the periodicities of the PS-b-PAA domains [163]. However, in this case also the _in situ_ approach provides a poor control of the size, surface chemistry and architecture of the generated embedded NPs, thus limiting the exploitation of their functionalities.