Needles and Haystacks: Influence of Catalytic Metal Nanoparticles on Structural and Vibrational Properties and Morpholog
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Needles and Haystacks: Influence of Catalytic Metal Nanoparticles on Structural and Vibrational Properties and Morphology of Silicon Nanowires Synthesized by MetalAssisted Chemical Etching M. K. Dawood1, S. Tripathy2, S. B. Dolmanan2, T. H. Ng1, T. Hao1 and J. Lam1 1 GLOBALFOUNDRIES Singapore Pte. Ltd, Singapore 738406. 2 Institute of Materials Research and Engineering (IMRE), Agency of Science Technology and Research (A*STAR), Singapore 117602. ABSTRACT Metal-assisted chemical etching (MACE) of silicon (Si) is a simple and low-cost process to fabricate Si nanostructures with varying aspect ratio and properties. In this work, we report on the structural and vibrational properties of Si nanostructures synthesized with varying metal catalyst. The morphology of the synthesized nanowires was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The optical and vibrational properties of the Si nanostructures were studied by photoluminescence and Raman spectroscopy using three different excitation sources (UV, visible and near-infrared) and are correlated to their microstructures. We propose that the excessive injection of holes into Si at the metal-Si interface and its diffusion to the nanowire surfaces facilitate the etching of Si on these surfaces, leading to a mesoporous network of Si nanocrystallites. When etched with catalytic Au nanoparticles, “haystacked” mesoporous Si nanowires were obtained. The straighter nanowires etched with Ag nanoparticles, consisted of a single crystalline core with a thin porous layer that decreased in thickness towards the base of the nanowire. This difference is due to the higher catalytic activity of Au compared to Ag for H2O2 decomposition. The SERRS observed during UV and visible Raman with Ag-etched Si nanowires and near-infrared Raman with Au-etched Si nanowires is due to the presence of the sunken metal nanoparticles. In addition, we explored the influence of varying H2O2 and HF concentration as well as the influence of increased etching temperature on the resultant nanostructured Si morphology. Such Si nanostructures may be useful for a wide range of applications such as photovoltaic and biological and chemical sensing. INTRODUCTION Metal-assisted chemical etching (MACE) of silicon (Si) is a simple and low-cost process to fabricate Si nanostructures with varying aspect ratio and properties [1]. MACE has therefore attracted substantial attention for a wide range of applications from electronics, optoelectronics to biomimicry and lab-on-a-chip devices [1-5]. In this work, we report on the structural and vibrational properties of Si nanostructures synthesized with varying metal catalyst (Au and Ag) and etched under different conditions. In order to address the size effect and surface vibrational properties in such complex nanowire structures, we have performed micro-Raman measurement with various laser excitation lines (325, 488 and 785 nm). The observations are correlated to the PL spectra when different etching parameters are used.
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