Metal Chalcogenides Nitrides Pnictides

The changes in the fundamental properties of materials as a function of the size, evolving from the isolated atoms or molecular clusters to a bulk phase, are most remarkably manifested in the case of semiconductor nanoparticles. The observation of quantum-confinement effects has generated substantial interest in their applications in device technology based on their novel optical and transport properties [457, 458]. For example, the bandgap in CdS can be tuned between 4.5 and 2.5 eV as the size is varied from the molecular regime to the macroscopic crystal, and the radiative lifetime for the lowest allowed optical excitation ranges from tens of picoseconds to several nanoseconds [14, 459]. The colloidal processing methods, based on controlled nucleation and rapid termination of growth, are commonly used to prepare II-VI compound semiconductor nanoparticles. These methods allow easy access to large quantities of nanomate-rials, but with relatively large dispersities (~10%). In this context, the use of SSPs containing metal-chalcogen bonds templated in molecular compounds is a promising route for controlled growth of nanomaterials. These clusters exist as discrete molecular species and can be seen as a fragment of the bulk lattice [22, 110]. O'Brien et al. have studied the thermolysis of metal dithio- and diselenocarbamate complexes (M{E2CNMe(C6H13)}2) as single molecular precursors for a one-pot synthesis of CdS, ZnS, CdSe, and ZnSe nanoparticles [103, 105, 234]. The fabrication of semiconductor nanocrystals from these molecular precursors (Fig. 26) is a one-step process, typically performed in the temperature range of 200-250 0C. This approach has been extended to the synthesis of PbS and PbSe from lead(II) alkyldithio- or alkyldiselenocarbamates, respectively [22, 188, 460].

TiO2 films.

0 0

Post a comment