Enhanced long-term stability of functionalized silicon nanoparticles using esters
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1207-N02-03
Enhanced long-term stability of functionalized silicon nanoparticles using esters Anoop Gupta1, Sebastian Kluge1, Christof Schulz1,2, Hartmut Wiggers1, 2 1
Institute for Combustion and Gasdynamics (IVG), University of Duisburg-Essen, Duisburg, Germany. 2 Center for Nanointegration Duisburg-Essen (CeNIDE), University of Duisburg-Essen, Duisburg, Germany. ABSTRACT The surface of freshly etched silicon nanoparticles (Si-NPs) was covalently bonded with alkyl groups and esters via thermally induced hydrosilylation. The surface chemistry of functionalized Si-NPs was analyzed at different air exposure time by means of Fourier transform infrared spectroscopy (FTIR). We observed that the stability of functionalized SiNPs significantly depends on the type of organic ligands attached to their surface. Esterterminated Si-NPs exhibit higher stability compared to that are bonded with alkyl groups. We show that the use of esters with large spatial configuration causes a lower surface coverage of Si-NPs but at the same time offers better protection against surface oxidation. INTRODUCTION The discovery of efficient light emission from silicon nanoparticles (Si-NPs) has stimulated intense research because of its potential applications in optoelectronic devices [1], light-emitting devices [2], and photo-pumped tunable lasers [3]. In addition, biocompatibility of Si-NPs makes them ideal candidates for fluorescent labeling in biological systems [4]. So far, the applicability of luminescent Si-NPs was hampered by their susceptibility towards oxidation. The slow oxidation of the particle surface leads to the formation of surface defects at the Si/SiOx interface, which are responsible for photoluminescence (PL) quenching and degradation of electronic properties. In order to prevent surface oxidation, the surface of SiNPs must be adequately passivated. Grafting of organic molecules on H-terminated silicon surface via hydrosilylation provides a promising route to stabilize their surface [5, 6]. Various researchers have successfully modified the surface of Si-NPs with organic molecules using insitu gas-phase surface functionalization [7, 8] and ex-situ liquid-phase surface functionalization [6, 9]. However, the steric hindrance of attached organic ligands limits the range of molecules that could be grafted to the surface. It has been observed that the functionalized Si-NPs show higher stability compared to hydrogen-terminated Si-NPs but their long term stability is limited because of incomplete surface coverage [10]. In this study, we show that the surface functionalization of Si-NPs using alkenes with an ester group provide much better passivation against surface oxidation compared to n-alkenes. Moreover, we show that the stability of ester terminated Si-NPs can be further enhance by choice of esters with large spatial configuration. EXPERIMENTAL Si-NPs were synthesized in a low-pressure microwave plasma reactor via pyrolysis of silane (SiH4). The details of the particle synthesis were discussed in detail in ref. [11]. Briefly
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