Passivation, Separation and Characterization of Plasma Synthesized Silicon Nanoparticles
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Passivation, Separation and Characterization of Plasma Synthesized Silicon Nanoparticles Jifang Cheng1, Catherine Jimenez1, Jacob P. Bell1, Ingrid E. Anderson2, Chito Kendrick2, Yongan Yang1, Reuben T. Collins2 and S. Kim R. Williams1 1 Chemistry and Geochemistry Department, Colorado School of Mines, 1500 Illinois St, Golden, CO 80401, U.S.A. 2 Physics Department, Colorado School of Mines, 1500 Illinois St, Golden, CO 80401, U.S.A. ABSTRACT Silicon nanoparticles (Si NPs) were synthesized by plasma enhanced chemical vapor deposition (PECVD) using silane as a silicon source. Allylamine was used as passivation ligands to form water-soluble Si NPs. Finally, aqueous asymmetric flow field-flow fractionation was used to successfully separate the polydisperse Si NPs into monodisperse Si NP fractions. INTRODUCTION Semiconductor nanoparticles with unique optical and electronic properties have shown potential application in many fields from sensor technology to optoelectronics[1-3]. With their tunable band-gap[4,5], low toxicity, and biocompatibility[6-8], silicon nanoparticles (Si NPs) have generated wide interest among scientists in various research areas. Important properties of these nanoparticles such as photoluminescence, absolute quantum yields, and exciton lifetime are sizedependent[4,9,10]. Significant research effort has been directed towards controlled synthesis of monodispersed Si NPs with desirable properties. However, most synthesis procedures yield polydispersed Si NPs with significant size inhomogeneity. Thus, the need for development of post-synthesis, purification and separation methods has become a necessity, albeit one that has not yet received a great deal of attention. Gradient density ultracentrifugation[10] and sizeselective precipitation[9] have been reported as successful approaches for post synthesis sizeseparation of Si NPs. In this work, aqueous asymmetric flow field-flow fractionation (AF4) was used to separate Si NPs into homogenous fractions with narrow size distributions. EXPERIMENT Si NPs with small diameters were synthesized by PECVD at a pressure of ~4x10-3 Torr with 13.56 MHz radio frequency at 40 Watt plasma. The feed gas was 1.4 sccm of SiH4 heavily diluted in 275 sccm of argon. The as-synthesized Si NPs were etched in 5% HF for about 5 minutes to remove dangling bonds and obtain hydrogen terminated Si NPs. These hydrogenterminated Si NPs were passivated by allylamine under hydrogen hexachloroplatinate (IV) (H2PtCl6) as the catalyst in isopropanol. The allylamine-terminated Si NPs were separated by aqueous AF4 using 0.001% FL-70 in distilled ion (DI) water as a carrier liquid with a ultraviolet (UV) detector to identify the sample elution information. The allylamine-terminated Si NPs and blue dye were focused on narrow bands at about 2 mm intervals, which were 3.4 cm from the inlet, and 24.6 cm from the outlet. Different fractions containing monodispersed Si NPs were
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collected at the AF4 channel outlet. Transmission electron microscopy (TEM) was used to characterize the size distri
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