AVS 61st International Symposium & Exhibition
    Plasma Science and Technology Thursday Sessions
       Session PS-ThA

Paper PS-ThA1
Raman Spectroscopy as Diagnostics for Size Distribution and Surface Chemistry of Remote Plasma Synthesized Silicon Nanocrystals

Thursday, November 13, 2014, 2:20 pm, Room 305

Session: Plasma Processing of Nanoparticles and Nanomaterials
Presenter: MauritiusC.M. van de Sanden, Dutch Institute for Fundamental Energy Research (DIFFER), Netherlands
Authors: I. Dogan, Eindhoven University of Technology, Netherlands
R. Gresback, Tokyo Institute of Technology, Japan
T. Nozaki, Tokyo Institute of Technology, Japan
M.C.M. van de Sanden, Dutch Institute for Fundamental Energy Research (DIFFER), Netherlands
Correspondent: Click to Email
The possibility to realize advanced photon management in solar cells and ultrahigh capacity charge storage in Li-ion batteries with silicon nanocrystals (Si-NCs) have boosted the interest on them, thanks to their size dependent optical properties and surface reactivity. To promote the use of these properties of Si-NCs in solar cells and batteries in an optimized manner, particle size control and surface engineering are the critical requirements. Therefore, accurate analysis of the size distribution is essential to optimize the process parameters to reach an ultimate control on nanocrystal size, which raises the requirement of a suitable diagnosis and post-analysis route. The analysis technique to be used is expected to provide quantitative data of size and morphology related features in a fast and non-destructive manner. Common techniques, such as X-ray diffraction (XRD), transmission electron microscopy (TEM) and photoluminescence spectroscopy (PL) are time consuming and only provide qualitative data of the size distribution especially when the Si-NC size distribution is not monodisperse, which is hardly achievable in most of the nanocrystal processing tools. Thus, these techniques are far from being considered as ideal tools for effective size analysis. Our aim in this work is to demonstrate that, Si-NCs with multimodal size distributions can be quantitatively analysed in a fast and non-destructive way by using Raman spectroscopy (RS). Free standing densely packed Si-NCs are synthesized in Ar/SiH4 and Ar/SiCl4 gas mixtures by using a remote expanding thermal plasma and a ultra-high frequency non-thermal plasma. Synthesized Si-NCs have a multimodal size distribution with peak sizes of 5 nm and 70 nm, respectively. Experimental Raman spectra are deconvoluted for separate analysis of the sub-distributions by using the size dependent phonon confinement model. Comparison of the extracted size distributions with the distributions obtained from TEM and PL show that RS provides highly reliable, quantitative information of size distribution and volume fraction. Analysis of the surface chemistry of Si-NCs is performed by depositing a monolayer of Si-NCs on a 10 nm thick Ag. Using a 514 nm laser enhances of the Raman signal by two orders of magnitude, which reveals the presence of Si-Hx, Si-Ox and Si-Clx bonds on Si-NC surface. In addition, disappearance of Si-Hx signal with oxidation is observed. With this observation, we show that, Raman spectroscopy can be used for probing the surface chemistry of Si-NCs. These results propose that Raman spectroscopy has the potential to become a standard diagnostic tool for the size and surface chemistry analysis of Si-NCs.