# Doped Zinc Oxide Nanoparticles: Synthesis, Characterization and Potential Use in Nanomedicine
## 3 Synthesis Methods and Characterization
### Other Techniques  
Despite their application being mostly limited to the synthesis of ZnO films, other synthesis techniques for doping ZnO are worthy of mention.  
An example is chemical vapor deposition (CVD), which is typically used to grow thin films. In the work of [PERSON] et al., Mn-doped ZnO flower-like structures were successfully grown in a CVD system and the corresponding optical properties were analyzed [206]. In this case, Zn and MnCl\({}_{2}\) in powder form were used as solid source materials for growing the flower-like structures. The SEM results reported highly oriented structures, but most of the dopant ions accumulated on the outermost surface of the nanostructures. A Fe/Co doping of ZnO nanowires was obtained by the CVD method as well and the resulting nanostructures were characterized by a high degree of crystallinity and an interesting ferromagnetic behavior [207].  
Sonochemical syntheses are recently acquiring a lot of interest as well, since the high energy which is freed due to air bubble cavitation can be exploited to locally overcome the limits of pressure and temperature which commonly affect other techniques [208]. A sonochemical wet impregnation method was instead exploited for the fabrication of Ce-doped ZnO nanoparticles for photocatalytic applications [209]. The doped ZnO nanoparticles were fabricated by keeping in sonication a solution of ZnO nanoparticles and ammonium ceric nitrate in distilled water, and then drying the precipitates.  
Other examples include the synthesis of ZnO-graphene nanohybrids, where different morphologies could be obtained according to the synthesis solution pH [210]. The sonochemical approach has been successfully exploited also to dope ZnO with both common and exotic doping elements like dysprosium [211], magnesium [212] and praseodymium [213], revealing the high versatility of this method.  
An alternative technique for doping is to mix pure ZnO powders with those of the dopant species, and then thermally anneal the mixed powders together at a high temperature. This method was exploited by [PERSON] et al. to obtain Mg-doped nanoparticles and to evaluate the increase of the corresponding photocatalytic activity with respect to pure ZnO [214]. Mechanical alloying--which does not use temperature, but simply mixes and ball mills ZnO and the dopant metal powders together--was able to include the metal into the ZnO particles. With this method, Fe was included in the ZnO matrix up to 7.08% without any clear evidence of the formation of iron clusters [174]. A ferromagnetic behavior was also found in this system.  
Finally, other techniques are based on the deposition of doped ZnO coatings and thin films such as magnetron sputtering [129], pulsed laser deposition [215] and many others.  
In summary, wet chemical methods are surely the most exploited and promising routes to obtain good quality doped ZnO nanoparticles, with a large variety of precursors and parameters that allow an extreme customizability of the resulting material. Other techniques, like combustion methods, revealed to be useful in terms of the rapidity of reaction but the dopant atom inclusion in the crystalline lattice of ZnO is poor with respect to chemical routes, limiting their applications to systems in which the quality of the material is not a key parameter.