Influence of reaction parameters on the photoluminescence properties of free standing functionalized silicon nanocrystal
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1260-T06-05
Influence of reaction parameters on the photoluminescence properties of free standing functionalized silicon nanocrystals Anoop Gupta1 and Hartmut Wiggers1, 2 1
Institute for Combustion and Gasdynamics, University of Duisburg-Essen, 47057 Duisburg, Germany 2 Center for Nanointegration Duisburg-Essen (CeNIDE), University of Duisburg-Essen, 47057 Duisburg, Germany ABSTRACT While silicon nanostructures acquire novel optical properties due to miniaturization, the stability of light emission is severely limited because of exciton trapping due to surface oxidation coming along with the formation of defects. Grafting of organic molecules on a hydrogen-terminated silicon surface via hydrosilylation provides a promising route to stabilize their surface against oxidation. In this communication, we report on the effect of surface passivation on the optical properties of freestanding silicon nanocrystals (Si-NCs). The surface functionalization of hydrogen-terminated Si-NCs with organic molecules was achieved via liquid phase hydrosilylation. We demonstrate that surface functionalization does not preserve the original emission of hydrogen-terminated Si-NCs. It is observed that the emission spectrum of green emitting hydrogen-terminated Si-NCs is red shifted after surface functionalization. We find that the direction of shift does not depend on the type of organic ligands and the reaction conditions, however, the amount of shift can be altered. The factors influencing the shift in the emission spectra of functionalized Si-NCs with respect to hydrogen-terminated samples are discussed. INTRODUCTION The exciting discovery of visible red photoluminescence (PL) from porous silicon at room temperature by Canham in 1990 stimulated the great interest in luminescing silicon crystallites due to the possibility of manufacturing optoelectronic devices based on silicon. Size-reduction of Si-NCs below 5 nm generates enhanced PL in the visible regime, which is believed to be the result of quantum confinement effects [1, 2]. In spite of showing high PL efficiency, the surface oxidation of Si-NCs limits their long term stability even in ambient conditions. The continuous air exposure of Si-NCs results in rapid decay of PL intensity and blue shifted emission [3, 4]. One of the promising routes to stabilize the surface of Si-NCs against oxidation is grafting of organic molecules to the hydrogen-terminated surface via hydrosilylation. The hydrosilylation step involves an additive reaction between an unsaturated C-C bond and a silicon hydride (Si-H) group, which can be activated by several methods, such as radical initiation, photochemical activation with UV light, and thermal activation [5]. The introduction of functional group on the surface of Si-NCs tailors their interfacial property and can provide protection against oxidation and hydrolysis processes. While surface functionalization provides long term PL stability, it does not conserve the original emission and the PL intensity of hydrogen-terminated Si-NCs. For example, Buriak an
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