Jonghoon Choi, Chemical and Biomolecular Engineering, University of Maryland and NIST, 100 bureau drive, stop 8312, Gaithersburg, MD 20899, Vytas Reipa, Biochemical Science, National Institute of Standards and Technology, 100 Bureau Drive, BLDG 227, Gaithersburg, MD 20899, and Nam Sun Wang, Chemical Engineering, University of Maryland, 9000 Rockville Pike, 5766 Bldg 13/3N07, Bethesda, MD 20892.
In this study, we investigate optical characteristics of alkene passivated Silicon nanocrystals. We explore the effect of the alkene chain length on the optical properties of Si nanocrystals. Si nanocrystals are first synthesized from the anodic etching of Si wafers and mechanical stripping of the porous surface layer from the etched wafers. Following photo reaction with 250 nm UV light promotes a surface modification of hydrogen terminated Si nanocrystals with selected alkenes through hydrosilylation. Turbid and brownish particle suspension turns to clear solution after 30 min photo reaction when observed under visible light. Also, red emitting Si nanocrystals turn bright blue under 360 nm UV light excitation. The resulting fluorescent Si nanocrystals with alkene modified surface were characterized with photoluminescence spectroscopy, high resolution transmission electron microscope, absorption spectroscopy, and time resolved fluorescence spectroscopy. Surface alkylation shows photoluminescence shifts to higher energies and intensity enhancement while photoluminescence peaks of different alkene modified Si NCs reflect variation in exciton lifetime. The quantum efficiency of Si nanocrystals decreases with increasing alkene carbon chain length. Photoluminescence decay lifetime of alkene passivated Si NCs are all in the nano second range, indicating direct inter band transitions. Further research on photoluminescence efficiency and particle stability dependence on passivating shell composition of our Si nanocrystals would facilitate biomedical applications of Silicon nanoparticle.