STUDY OF THE PHOTODISSOCIATION OF A CDSE NANOCRYSTAL BEAM BY MEANS OFPHOTOLUMINESCENCE AND RAMAN-SCATTERING

We developed an apparatus that enables us to perform optical measureme nts of nanocrystals suspended in vacuum. CdSe nanocrystals were produc ed by agas evaporation method, and nanocrystal beams were then formed using an inert-gas flow with differential pumping. We measured photolu minescence spectra of the nanocrystal beams with excitations of variou s photon energies and powers. For a low excitation power, edge emissio n of the CdSe nanocrystal beam was observed. With increase of the lase r power, Raman lines of Se dimers emitted due to the photodissociation of CdSe nanocrystals were observed. It was found that the thresholds of the excitation laser fluence for the photodissociation of CdSe nano crystals were much smaller than the thresholds of laser fluence for th e laser-induced emission of Se atoms from bulk CdSe. The electronic pr ocess is dominant in the photodissociation of CdSe nanocrystals whose surfaces are completely free. We suggest that the effective supply of carriers confined in nanocrystals to the surface state, and the excita tions of the completely free surface state induce the photodissociatio n of nanocrystals by excitation with much weaker irradiation than is r equired for dissociation of the bulk surface.