Nanotech 2010

Electrical Properties of Functionalized Silicon Nanoparticles

S. Hartner, A. Gupta, H. Wiggers
University Duisburg-Essen, DE

Keywords: silicon, functionalization, electrical properties, impedance, conductivity organic molecules, alkenes


Phosphorous-doped as well as undoped Si-NPs with a mean particle diameter of about 50 nm were synthesized in a microwave plasma. The natural oxide was removed by etching the particles with hydrofluoric acid. In order to prevent the particles from re-oxidation, the surface of freshly etched particles was functionalized with different alkenes (C6, C10, C12, C1, C18) via thermal alkylation. The electrical conductivity of as-prepared, freshly etched, and functionalized Si-NPs was measured using impedance spectroscopy. For all samples, the freshly etched Si-NPs showed a large increase in conductivity compared to the respective as-prepared samples. Surprisingly, it is found that doping with phosphorus shows almost no difference in conductivity compared to undoped samples. After surface functionalization, conductivity decreases depending on length of the alkene used for stabilization. Freshly etched as well as functionalized samples with alkenes from C6 to C12 show semiconducting behavior (see fig 1) with high conductivity compared to the as-prepared materials. In contrast, samples functionalized with C14 and C18 show very poor conductivity. While FTIR-spectroscopy indicated that surface functionalization with C6-C10 is not very stable due to a creeping re-oxidation, dodecene (C12)-terminated nanoparticles showed the highest conductivity, even after storage in ambient conditions for half a year.
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