Synthesis and characterization of Si/SiOx nanoparticles as building blocks for electronic and photonic applications

Date of Completion

January 2001

Keywords

Chemistry, Polymer

Degree

Ph.D.

Abstract

This dissertation thesis presents the syntheses and characterization of new Si/SiOx nanoparticles, suitable for various applications in electronic and photonic research. In the first part of the dissertation, we characterized the chemical structure of these Si/SiOx nanoparticles using X-ray Photoelectron Spectroscopy. X-ray photoelectron spectroscopy concurs with a core/shell (Si/SiOx) nanoparticle structure, with an average Si-atom ratio of 45/55 and x in the order of 1.5. The synthesis consists of a high-energy nano-milling process followed by a chemical modification of their surface using benzoyl peroxide, and a sonication/centrifugation process. The oxidation process that leads to the formation of a passivated outer shell of SiOx on top of the Si core allows the nanoparticles to suspend in the ethanolic solution. The sonication-assisted oxidation of these Si nanoparticles enables them to spontaneously self-assemble in thin films. Their rapid initial adsorption at a pH of 5.5 (which slows down significantly after three hours) appears to cover uniformly the different surfaces with individual nanosilicon particles as well as agglomerates. The mechanism of this self-assembly has been studied by Fourier Transform Infrared Spectroscopy (FTIR), atomic force microscopy (AFM) and spectroscopic techniques. ^ The coverage achieved by this method exhibits strong potential in suppressing light scattering, enabling the use of such elevated refractive index films as light outcoupling layers, along with numerous applications in the photonic industry. The crystallinity modification done by high-energy nano-milling of the surface modified Si nanoparticles has a great impact on their optical behavior. Raman investigation suggests that the Si core is composed of a crystalline and amorphous part with a respective ratio of 34 and 11 out of 45% of total number of Si atoms. ^ In the second part of the thesis, we show the preferential self-assembly of these surface modified Si/SiOx nanoparticles on polydimethylsiloxane (PDMS) spin-casted films versus UV-O3 converted SiOx network. Furthermore, the self-assembly of these nanoparticles on silica spheres is demonstrated. ^ For the past two decades, photonic crystals have generated great attention. We demonstrated the fabrication of a transparent, conductive, polyurethane elastomeric opal replica by vacuum/mechanical pressure assisted infiltration. By applying a stress on the structure, the periodicity is disturbed. For a given angle of incident white light excitation, from the uncompressed to the compressed sample, the emission is blue shifted (from red to green). ^

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