Nanoparticles under a few nanometres in size have structures and material functions that differ from the bulk because of their distinct geometrical shapes and strong quantum confinement. These qualities could lead to unique device applications. Our mass spectral analysis of CdSe nanoparticles reveals that (CdSe)(33) and (CdSe)(34) are extremely stable: with a simple solution method, they grow in preference to any other chemical compositions to produce macroscopic quantities. First-principles calculations predict that these are puckered (CdSe)(28)-cages, with four- and six-membered rings based on the highly symmetric octahedral analogues of fullerenes, accommodating either (CdSe)(5) or (CdSe)(6) inside to form a three-dimensional network with essentially heteropolar sp(3)-bonding. This is in accordance with our X-ray and optical analyses. We have found similar mass spectra and atomic structures in CdS, CdTe, ZnS and ZnSe, demonstrating that mass-specified and macroscopically produced nanoparticles, which have been practically limited so far to elemental carbon, can now be extended to a vast variety of compound systems.

The temperature dependences of the energy and the width of a surface plasmon resonance are studied for copper nanoparticles 17-59 nm in size in the silica host matrix in the temperature interval 293-460 K. An increase of the temperature leads to the red shift and the broadening of the surface plasmon resonance in Cu nanoparticles. The obtained dependences are analyzed within the framework of a theoretical model considering the thermal expansion of a nanoparticle, the electron-phonon scattering in a nanoparticle, and the temperature dependence of the dielectric permittivity of the host matrix. The thermal expansion is shown to be the main mechanism responsible for the temperature-induced red shift of the surface plasmon resonance in copper nanoparticles. The thermal volume expansion coefficient for Cu nanoparticles is found to be size-independent in the studied size range. Meanwhile, the increase of the electron-phonon scattering rate with the temperature is shown to be the dominant mechanism of the surface plasmon resonance broadening in copper nanoparticles.K e y w o r d s: surface plasmon resonance, copper nanoparticles, temperature-induced effects

We report aqueous phase synthesized semiconductor nanoparticles with well-defined numbers of constituent atoms. Aqueous phase synthesis provides many advantages over organic phase synthesis for producing such high-quality semiconductor nanoparticles. We synthesized CdSe nanoparticles with excellent colloidal and optical stabilities directly in aqueous solution at room temperature and then identified them as selectively grown (CdSe)33 and (CdSe)34 magic-sized clusters. These clusters displayed extremely sharp excitonic absorption and emission peaks because of their practically monodispersed size distribution. Their X-ray diffraction pattern and Raman spectral features were considerably different from the corresponding pattern and features for typical crystalline CdSe nanoparticles. Growth of our magic-sized clusters was very slow and proceeded via the formation of different sizes of progressively larger CdSe nanoparticle intermediates with time. Our results demonstrated that aqueous phase synthetic routes could be successfully adopted for producing high-quality semiconductor nanoparticles.