Novel single-molecule precursor routes for the direct synthesis of InS and InSe quantum dots

Nanoparticles of InS and InSe capped with TOPO (tri-n-octylphosphine oxide) or nanoparticles of InSe capped with 4-ethylpyridine, which are close to mono-dispersed, have been prepared by a single-source route using tris(diethyldithiocarbamato)indium(III) or tris(diethyldiselenocarbamato)indium(III), respectively. The nanoparticles of InS and InSe both show quantum size effects in their optical spectra and the photoluminescence (PL) spectra show broad emissions due to the surface traps. Substantial blue shifts in the onset of absorption have been observed; 0.44 eV for InS and 1.60 eV for InSe. The X-ray diffraction (XRD) pattern of InS showed co-precipitation with TOPO and the crystalline particles turned powdery when studied by transmission electron microscopy (TEM). Selected area electron diffraction (SAED), X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies of the InSe nanoparticles show the hexagonal phase in the size range 5.8-7.0 nm. The crystallinity of the InSe nanoparticles was also evident from high resolution transmission electron microscopy (HRTEM), which gave well defined images of nanosize particles with clear lattice fringes.