## 2 Nanocomposite Materials
### NC synthesis  
Among several strategies proposed for the preparation of NCs [19, 20], colloidal chemistry-based routes offer numerous advantages. In particular, the decomposition of defined precursors in presence of coordinating agents allows a good control over size, shape and size distribution of NCs by using relatively simple experimental conditions. NC dimensions and shape can be finely tuned by changing reaction parameters such as temperature, time, surfactants and ratio between the precursors, thus allowing to obtain high-quality materials with tailored properties at relatively low cost [21]. Colloidal chemistry routes have demonstrated their applicability to a broad range of nanostructured materials with predictable and/or unprecedent properties including metal NPs (Au [22], Ag [23], Pt [24], Pd [25], Ni, Fe [27], Cu [28], Co [29], Ru [30]) and their alloys (CoPt\({}_{3}\)[31], FePt [32]), magnetic NPs (Fe\({}_{2}\)O\({}_{3}\)[33], CoO [34]), semiconductor oxides (TiO\({}_{2}\)[35], ZnO [35], SnO\({}_{2}\)[36], SiO\({}_{2}\)[37]), II-VI semiconductors emitting in the UV-vis range (ZnS [38], ZnSe [18], CdS [39], CdSe [40], CdTe [41]), III-V (InAs [42], InP [43]) and IV-VI semiconductors (PbS [44], PbSe [45], PbTe [46]) emitting in the near infrared region and multicomponent nanostructured materials (TiO\({}_{2}\)/Ag [47], TiO\({}_{2}\)/Au [48], TiO\({}_{2}\)/Fe\({}_{2}\)O\({}_{3}\)[49], CdSe@ZnS [50], CdSe@ZnSe [51], CdSe@ZnS@SiO\({}_{2}\)[52], Au@SiO\({}_{2}\)[53], CdSe@CdS@ZnS [54], CdSe@CdTe@ZnSe [55]). Typically, colloidal nanomaterials are synthesized by reacting appropriate molecular precursors, that is, inorganic salts or organometallic compounds. The temporal separation of the nucleation event from the nuclei growth is the key point to synthesize NCs with controlled dispersion in size and shape. This goal can be achieved in presence of one or more surfactant molecules. Such amphiphilic organic compounds are composed of one hydrophilic moiety (a polar or a charged functional group) and a hydrophobic part (usually, one or more hydrocarbon chains) able to dynamically coordinate the surface of growing crystals. [56] Typical surfactants include long-chain (C\({}_{8}\)-C\({}_{18}\)) carboxylic and phosphonic acids, alkane thiols, alkyl phosphines, alkyl phosphine oxides, and alkylamines such as hexadecylmine. Such synthetic routes (typically termed \"hot-injection techniques\" being the precursors rapidly injected into a hot solvent with subsequent temperature drop) provide NCs presenting a surface coated with organic agents which can play a twofold role allowing the dispersion in organic solvent and at the same time improving the surface passivation. Noble metal NPs (Au [57], Ag [58], Pt [59], Pd [60]) and their alloys [61] can be synthesized in mild experimental conditions (_i.e._, room temperature, ambient atmosphere and using water as solvent) by reducing metal ions using chemical reducing agents [62] or photochemical processes [22] in the presence of coordinating agents (typically long-chain alkanethiols, amines, or fatty acids) or in micellar templates. The latter approach provides water soluble metal NPs. One of the great advances of colloidal chemistry routes relies on the possibility to finely tune the nanostructured material morphology by properly choosing the synthetic conditions. NPs are terminated by facets that expose different crystallographic planes showing different chemical reactivity. Selectiveadhesion of surfactant molecules [63], traces of metal ions [64], concentration of reactants [35], injection rate of precursors [18,41] and growth temperature [65], allow for tuning the growth kinetics of different crystal facets and tailoring the NC shape from nearly spherical to highly anisotropic nanostructures.