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We report on the use of silicon nanocrystals (Si-ncs) to activate nucleation and growth of carbon nanotubes (CNTs) without using any metal catalyst. Si-ncs with different surface characteristics have been exposed to the same CH4 low-pressure plasma treatment producing quite different results. Specifically, Si-ncs prepared by laser ablation in water have contributed to the formation of micrometre-sized silicon spherical particles. On the other hand, Si-ncs prepared by electrochemical etching did not induce any specific growth while the third type of Si-ncs, prepared by electrochemical etching and treated by a laser fragmentation process, induced the growth of multi-walled CNTs. The different outcomes of the same plasma process are attributed to the diverse surface features presented by the Si-ncs. [ABSTRACT FROM AUTHOR]

Abstract: We report on the role of selected silicon nanocrystal (Si-nc) synthesis techniques on the photoelectric properties of Si-ncs and conjugated poly(hexylthiophene) (P3HT)-based blends. Nanosecond laser processing – both ablation and fragmentation – in liquids and electrochemical etching are employed to fabricate surfactant-free Si-ncs. We demonstrate that the transport properties of the blend can be tuned by the processing conditions. The blends containing Si-ncs produced by laser ablation clearly show superior photovoltaic properties due to the enhanced bulk heterojunction surface area and improved charge transport. Finally, we argue that the nanosecond laser processing in liquid medium could be a flexible and efficient tool to tailor the photoelectric properties of the Si-ncs/P3HT nanocomposites. [ABSTRACT FROM AUTHOR]

Blue luminescent colloidal silicon nanocrystals (Si-ncs) were synthesized at room temperature by nanosecond pulsed laser ablation of a single-crystal silicon target in de-ionized water. Irregular Si-nc fragments obtained by laser ablation are stabilized into regularly shaped, spherical, and well-separated aggregates during the aging process in water. Aging in de-ionized water for several weeks improved the photoluminescence (PL) intensity. At least two weeks of aging are necessary for observation of broad blue room temperature PL with a maximum centered at 420 nm. Detailed structural analysis revealed that agglomerates after aging for several months contain Si-ncs with irregular shape smaller than the quantum confinement limit (<5 nm). These blue luminescent Si-ncs dispersed in de-ionized water exhibited a PL decay time of 6 ns, which is much faster than that of Si-ncs prepared in traditional ways (usually on the order of microseconds). The oxidized Si-ncs with quantum confinement effects are responsible for a PL band around 400 nm visible to the naked eye at room temperature. [ABSTRACT FROM AUTHOR]