## 2 Nanocomposite Materials  
The synthesis of nanocomposite materials allows access to the peculiar properties of inorganic nano-sized materials to fabricate high technologic impact patterned devices. For instance, the development of novel functional materials for microelectronic and photonic applications has represented during the last years a challenging task to improve the design and fabrication of MEMS and NEMS integrated devices [6]. Nanocomposites can be formed by blending inorganic nanoclusters, fullerenes, clays, metals, oxides or semiconductors with numerous organic polymers or organic and organometallic compounds, biological molecules, enzymes, and sol-gel derived polymers [7; 8; 9; 10; 11; 12; 13; 14; 15]. The resulting hybrid materials will be characterized by electrical, optical, magnetic and catalytic properties arising from the inorganic moiety, and enhanced thermal and mechanical stability originating from the polymeric matrix. In addition, new collective properties will depend from the arrangement or organization of the inorganic nanofillers in the organic moiety. Furthermore, polymers enable the processability and manipulation of inorganic NPs for obtaining technologically appealing and functional micro and nanostructures. Thanks to their physical and chemical stability, easy molding, tunable mechanical properties, the incorporation of NPs in such organic matrix is an ideal strategy to provide processability and structurability to inorganic nanomaterials. Interactions between NC surfaces and surrounding polymer matrix can result in reactions like surface reorganization and charge transfer which influence mechanical and surface electronic properties of the material, respectively. Several nanomaterials, differing in size and composition (semiconductor, magnetic, metal and oxide) (Figure 1), have been recently exploited for the fabrication of nanocomposite materials. In the following a non exhaustive summary will be given, in order to provide a panorama of the recent research efforts in this innovative field. In particular, a large interest has been recently devoted to nanocomposite based on embedding semiconductor and metal NPs in polymers. The interest in preparing semiconductor NC based nanocomposites is mainly due to the peculiar size-dependent optical properties exhibited in quantum  
Figure 1: TEM images of colloidal NCs with different composition which can be incorporated in a host polymer matrix. confinement regime, when NCs dimensions are comparable with the De Broglie wavelength associated to the charge carriers. Their narrow emission, high photoluminescence quantum yield, large absorption spectra as well as their spectral tunability (Figure 2, top panel) and fast relaxation dynamics make the NCs potential candidates for developing devices in several fields ranging from photonic to optoelectronic and sensing [16, 17]. Metal NPs are characterized by original absorption resonances, such as surface plasmons, due to the collective oscillations of electrons in the NPs, and their spectral position is related to NP shape (transverse and longitudinal plasmons for nanorods), chemical environment and interparticle distance (Figure 2 bottom panel). The accurate and precise control of size, shape, crystalline phase and surface chemistry of NCs is a _sine qua non_ condition to fully exploit their peculiar properties in different environments. Among the several strategies that can be followed for NC synthesis, colloidal chemistry routes, allow an excellent control on size, shape and crystalline phase, crucial parameters for defining the electronic, optical, magnetic and catalytic size and shape dependent properties of nanomaterials.