Synthesis Of Silicon-Based Nanostructures By Chemical Vapour Growth On Silicon Wafer And From Pyrolysis Of Oil Palm Fibres
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Date
2012-05
Authors
Chiew, Yi Ling
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Publisher
Universiti Sains Malaysia
Abstract
Silicon-based nanostructures were successfully synthesized from two different routes of chemical vapour growth (CVG) on silicon wafers and pyrolysis of oil palm fibres. In CVG, SiC nanorods, SiC nanocolumns as well as SiC/SiO2 core-shell nanowires, nanocables and nanowebs were produced by heating only Si wafers and activated carbon powder (ACP) under vacuum/argon at 1300°C. The oxidation time, soaking time and amount of ACP influenced the morphologies of nanostructures. SiC nanorods and nanocolumns were formed at soaking time of 1 hour, with increasing diameter and yield when oxidation time was raised from 1 to 12 minutes. The structure then changed to SiC/SiO2 core-shell clusters, nanowires, nanocables and nanowebs along with some SiOx nanowires when soaking time was 2 hours, at different locations on silicon wafers that decreased in diameter with increasing amount of ACP. The different nanostructures were a result of aerodynamic effects in the crucible due to pressure difference inside and outside the crucible. The growth of these nanostructures was under vapour-solid mechanism. In pyrolysis of oil palm fibres, SiC nanowires and nanocones were produced by heating oil palm empty fruit bunch fibres and rice husk ash (RHA) or tetraethyl orthosilicate (TEOS) as carbon and silicon sources, respectively, under argon atmosphere, though TEOS-impregnated samples showed higher yield of nanowires. The amount of Si sources and pyrolysis temperature influenced the products formed. When RHA was used and the amount was increased to 80%, structure changed from SiC nanowires to nanocones but overall, 40% RHA was the ideal amount in growing nanowires with maximum yield and least impurities.
When pyrolysis temperature was raised, there was an increase in the yield. When TEOS was used, only SiC nanowires were formed and an increase in TEOS concentration led to an increase in the yield but only to a certain extent due to lower fluidity of TEOS at higher concentrations. Thus, 10% TEOS was the ideal concentration. When pyrolysis temperature was raised, a decrease in diameter was observed in TEOS samples. The diameter drop was an effect of higher atom desorption rate at higher temperatures.
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Keywords
Synthesis of silicon-based nanostructures by chemical vapour growth , on silicon wafer and from pyrolysis of oil palm fibres