Chemical composition of hybrid silicon nanoparticles and ultrafast dynamics of charge carriers

Resumo

The qualitative and quantitative composition of hybrid Si/SiO_x/SiO₂/OH(D) nanoparticles synthesized from silicon monoxide has been determined by X-ray photoelectron spectroscopy. The nanoparticles are composed of a Si crystalline core and a SiO_x/SiO₂/OH(D) shell, where SiO_x is the interface of intermediate oxides corresponding to the Si¹⁺, Si²⁺, and Si³⁺ valence states of silicon and SiO₂/OH(D) is the external shell of the nanoparticle. The chemical composition and average stoichiometry of deuterated and nondeuterated nanoparticles have been determined; the identified compositions have been compared. The dependence of photoluminescent properties on the composition of the samples has been discussed. Two forms of hydrophilic silicon nanoparticles with identical crystalline cores—photoluminescent deuteriumpassivated particles oxidized in completely deuterated dimethylsulfoxide and nonphotoluminescent hydrogen- passivated reference samples oxidized in dimethylsulfoxide—have been studied by broadband femtosecond spectroscopy. It has been found that there are significant differences in the ultrafast spectral–temporal induced absorption dynamics of these two forms in the energy range corresponding to the calculated bandgap of the nanoparticles. The observed difference has been attributed to the specific features of the relaxation of excited charge carriers in the energy states responsible for photoluminescence in the red spectral region.