Semiconductor nanoparticle (NP) surface chemistry has long been recognized as central to the development and optimization of opto-electronic devices (based on NPs photoluminescence properties). Much attention has been directed to group II-VI quantum dots (QDs) for a variety of targeted applications, although their toxicity renders them incompatible with biological systems. Consequently, there is a renewed interest in nanostructured silicon that is more compatible with existing technology and biologically friendly.  Silicon NPs are capable of exhibiting high quantum yield emission and are considered environmentally adventitious compared to current Cd or Pb alternatives, but the origin of Si NP photoluminescence remains elusive. A significant advantage of using Si NPs is the ability to covalently modify their surface rather than employing datively bound ligands that can over time lead to aggregation, i.e. loss of opto-electronic properties. Though covalent surface modification of Si NPs has been realized, the mechanism of hydrosilylation at defect sites (steps) remains unknown, suggesting that work on model step surfaces could bring much needed insight.  Herein we report the functionalization of vicinal silicon (111) surfaces with both monohydride and dihydride step edges using a 9o off orientation in the (-1-12 &11-2) directions, respectively. Two reactions are studied as a function of immersion time on both model surfaces: i) thermal hydrosilylation with a terminal alkene (known to be concerted on flat surfaces) and ii) nucleophilic addition using small molecule (methanol). It is found that the nucleophilic system reacts preferentially at the step edge forming a bridge complex between the bridge and lower terrace hydrogen atoms, while the alkene reacts with all terrace and step (mono- and di-hydride) sites. Such selectivity opens the door for nanopatterning and provides important insight into the behavior of Si NPs.

Functionalization of vicinal silicon surfaces: Insight into Si nanoparticle reactivity

247th National Meeting (2014)

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