ABSTRACT
Nanoparticles have been extremely interesting objects in modern materials science and nanophysics over the past decades due to their enormous technological importance. Although for various substances there is a possibility to change the nanoparticles into either a crystalline or an amorphous state by using reasonable synthesis methods, much attention has been paid to the former rather than the latter (Günter 2004). ere is no comprehensive work related to amorphous nanoparticles and this motivates us to write this chapter on the Handbook of Nanophysics. It is well known that crystalline nanoparticles have a well-de ned crystal structure with a large fraction of their atoms located on the surface, including a structural disorder in the vicinity of the surface when compared to that of a perfect crystal, which provide them with unique properties that are di erent from their crystalline bulk counterparts (Changsheng et al. 1999). In contrast, amorphous nanoparticles have a disordered structure, which may be divided into two parts, i.e., the core with structural characteristics close to that of the corresponding amorphous bulkcounterparts and a surface exhibiting a more porous structure due to the presence of large amounts of structural defects (Hoang and Khanh 2009). Due to their disordered structure, amorphous nanoparticles can have more advanced applications than a crystal structure with well-de ned properties. Indeed, it was found that catalytic amorphous Fe2O3 nanoparticles are more active than the nanocrystalline polymorphs of the same diameter thanks to the “dangling bonds” and a higher surface-bulk ratio (Srivastava et al. 2002). Due to surface e ects, the structure and the properties of amorphous nanoparticles are also di erent from those of their corresponding amorphous bulk-counterparts. erefore,
amorphous nanoparticles have attracted a great interest and have been under intensive investigation in the recent years (Libor et al. 2007, Wu et al. 2007). Much attention has been paid to the synthesis and the characterization of amorphous nanoparticles; therefore, important methods for the synthesis of amorphous nanoparticles have been listed in a subsequent section of the chapter. On the other hand, in order to get structural information about amorphous nanoparticles, one can use several diffraction techniques. However, more detailed information of the microstructure of amorphous nanoparticles at the atomic level can be provided by a computer simulation. erefore, we also discuss the results obtained by a computer simulation of amorphous nanoparticles. Moreover, the physicochemical properties of amorphous nanoparticles have been under intensive investigation by both experiments and computer simulations (Hoang 2007a, Libor et al. 2007, Wu et al. 2007, Hoang and Odagaki 2008, Hoang and Khanh 2009). In particular, amorphous nanoparticles can have advanced catalytic properties compared with traditional crystalline catalysts or good magnetic materials, etc., leading to their potential applications in various areas of technology (Srivastava et al. 2002, Libor et al. 2007, Wu et al. 2007). erefore, applications of amorphous nanoparticles have also been given considerable attention in the chapter.
