## 4 Patterning towards Devices: Conventional and Unconventional Methods
### Direct-write techniques
#### 4.3.3 Nano imprint lithography  
Nano Imprint Lithography (NIL) is an innovative and low cost lithographic technique based on the mechanical embossing principle, which allows high throughput, high-resolution and parallel patterning for applications ranging from magnetic media to optical devices. The technique consists on the replication of a stamp into a soft material, forming complex three dimensional nanostructures. More in detail, a hard mould obtained by electron beam or UV lithography with micro and nanoscale features is embossed into a polymer film spun on a substrate, under controlled pressure and temperature above the glass transition temperature of the polymer. Sometimes also UV radiation is used for resist curing. Figure 6: UV–Vis absorption and PL spectra of CdS and CdSe(r)ZnS NCs of different diameters in CHCl\({}_{3}\), (top panel); fluorescence microscope images of single- and multi-colour microarrays of NC functionalized PS ink-jet printed by a single and a multi nozzle system, respectively (bottom panel) [175]. Then, after reduction of temperature and pressure release, the demolding occurs, creating a thickness contrast in the polymer material. Residual polymer layers can be removed by a subsequent plasma based anisotropic etching treatment. By the nanoimprinting approach, patterning of nanostructures with excellent resolution (below 10 nm) can be obtained, overcoming the limitations set by light diffractions or scattering occurring in other conventional techniques. NIL allows to fabricate resist patterns as in lithography, but can also directly imprint functional device structures directly in polymers. In recent literature only few examples are reported for the use of this promising technique to pattern nanocomposite materials. A UV-curable monomer, hydroxyethyl methacrylate mixed with a highly concentrated nanosilver colloid has been used for direct imprinting metal pattern for electronic device structures. The imprinted patterns were heat-treated to cause sintering of the nanosilver particles and shrink the cured polymer matrix. Then silver etchant was applied to remove the residual layer before a thorough rinsing [176]. Silicaol particles have been used as inorganic components in the fabrication of organic-inorganic hybrid materials for UV-nanoimprint lithography (UV-NIL) and their surface has been modified with photofunctional crosslinkers to promote the dispersion into photofunctional monomers with non-solvent systems. The monomers have been mixed with other monomers and a photoinitiator to prepare various imprint materials. As a result, 200 nm line and space patterns have been successfully imprinted with no shrinkage and these materials have showed greatly improved UV hardening properties and physical properties such as refractivity, thermal stability compared to organic (non-hybrid) materials [177]  
The NIL has been successfully applied to luminescent CdSe(r)ZnS NC based composites in presence of PMMA co-polymers [107], but also in commercial thermoplastic and UV curable resist [178, 179] nanocomposites that have been easily patterned with micro and nano resolution. In the first example, the homogeneous NP distribution in the polymer matrix, induced by the presence of functional groups on polymer chains allows to obtain highly luminescent nanocomposite materials. It is worth to note that no significant alterations in the optical properties of the composites have been observed after the patterning process. Indeed, the composite materials after the NIL still retain the original luminescence, in spite of the hard conditions used during the imprinting process (temperature up to 170 \({}^{\circ}\)C and pressure up to 60 bars). By this emerging technique, luminescent CdSe(r)ZnS NC-PMMA co-polymer based composites have been directly patterned by using an electron beam written stamp to fabricate both at the micro and nano scale emitting devices [107, 178].