The shell matters: one step synthesis of core-shell silicon nanoparticles with room temperature ultra-narrow emission linewidth
Here we present a one-step synthesis that provides silicon nanocrystals with a thin shell composed of a ceramic-like carbonyl based compound, embedded in a porous organosilicon film. The silicon nanocrystals were synthesised from hydrogen silsesquioxane molecules, modified by organic molecule containing carbonyl group, which were annealed at 1000°C in a slightly reducing 5% H2 : 95% Ar atmosphere. The organic character of the shell is preserved after annealing due to trapping of organic molecules inside HSQ-derived oxide matrix that forms during the annealing. The individual silicon nanocrystals, studied by single dot spectroscopy, exhibited significantly narrower emission peak at room temperature (lowest linewidth ~ 17 meV) compared to silicon nanocrystals embedded in a silicon oxide shell (150 meV). Their emission linewidths are even significantly narrower than those of single CdSe quantum dots (>50 meV). It is hypothesized that the Si-core - thin shell structure of the nanoparticle is responsible for unique optical properties. Its formation within one synthesis step opens new opportunities for silicon-based quantum dots. The luminescence from produced nanocrystals covers a broad spectral range from 530-720 nm (1.7-2.3 eV) suggesting strong application potential for solar cells and LEDs, following the development of a suitable mass-fabrication protocol.