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>Magister Scientiae - MSc / In this thesis we report on the deposition of silicon nanostructures using a 3-zone thermal chemical vapour deposition process at atmospheric pressure. Nickel and gold thin films, deposited by DC sputtering on crystalline silicon substrates, were used as the catalyst material required for vapour-solid-liquid growth mechanism of the Si nanostructures. The core of this work is centred around the effect of catalyst type, substrate temperature and the source-to-substrate distance on the structural and optical properties of the resultant Si nanostructures, using argon as the carrier gas and Si powder as the source. The morphology and internal structure of the Si nanostructures was probed by using high resolution scanning and transmission electron microscopy, respectively. The crystallinity was measured by x-ray diffraction and the high resolution transmission electron microscopy. For composition and elemental analysis, Fourier transform infrared spectroscopy was used to quantify the bonding configuration, while electron energy-loss spectroscopy in conjunction with electron dispersion spectroscopy reveals the composition. Photoluminescence and UV-visible spectroscopy was used to extract the emission and reflection properties of the synthesized nanostructures.

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<p> High-density plasma technology is becoming increasingly attractive for the deposition of dielectric films such as silicon dioxide, silicon nitride and silicon oxynitride. In particular, inductively coupled plasma chemical vapor deposition (ICP-CVD) offers several technological advantages for low temperature processing over other plasma-enhanced chemical vapor deposition (PECVD), such as higher plasma density, lower hydrogen content films, and lower cost. A new ICP-CVD system has been set up at McMaster University. </p> <p> The project focused on the calibration of this system and the establishment of its performance characteristics. A combination of 0 2/ Ar/SiH4 gases was used to deposit Si02 thin films on single-crystal Si wafers under various conditions. Substrate temperatures were calibrated from 200 to 400°C, and were found to linearly relate to heater temperatures. Calibration of the minimum reflected power showed that the ICP source is efficient to generate a stable plasma for 02, N2 and Ar gases within a wide range of flow rates from 3 to 1 OOsccm, while the reflected power remains below 10 Watts. Uniformity was found to be sensitive to many factors. Under optimal conditions, uniformity could be controlled better than 1% with a good shape of thickness distribution. The refractive indexes of the deposited films were measured with ellipsometry and showed an inverse relation with the ratio of oxygen to silane flow rate. </p> / Thesis / Master of Applied Science (MASc)

This dissertation summarises the study of different aspects of the aerosol-assisted chemical vapour deposition (AACVD) technique for the production of multi-wall carbon nanotubes (MWCNTs). Upscaling the synthesis while retaining the quality of MWCNTs has been a prime objective throughout the work. A key aspect of this work was the study of different growth parameters and their influence on the homogeneity of the products across the reactor. The effect of the precursor composition on the yield and quality of MWCNTs were also investigated. It was shown that the synthesis rate can be significantly (60 – 80 %) increased by tuning the composition of the precursor. Moreover, by optimising the synthesis recipe and using a larger reactor, the synthesis rate and efficiency of the precursor were increased fivefold (up to 14 g/hr) and twice (up to 88 %) respectively. Large area (up to 90 cm²), mm-thick carpets of MWCNTs which were both free-standing and on substrate were produced. The carpets could withstand normal handlings without tearing apart, making them suitable for macroscopic characterisations and applications. By in-situ qualitative and quantitative gas analysis of the atmosphere of the reactor, the thermocatalytic cracking behaviour of 25 precursors was investigated and a mechanism for successive formation of different hydrocarbon fragments inside the reactor was proposed. A number of dedicated gas analysis methods and apparatuses such as a probe for zone-by-zone gas analysis of reactor and a heated chamber for preparation of standard gas analysis samples were developed to explore some of the least investigated aspects of the thermocatalytic cracking of precursors. Mapping the reactor revealed that some single-wall and double-wall carbon nanotubes (SWCNTs and DWCNTs) were also produced near the exhaust of the reactor. The SWCNTs were partly covered by fullerene-like species and resembled different forms of carbon nanobuds. In addition, the effect of the electron beam on the interaction of the SWCNTs and the fullerene-like species was studied in situ using high-resolution transmission electron microscopy (HRTEM).

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The morphology evolution of high-temperature grown AlN nucleation layers on (111) silicon has been studied using atomic force microscopy (AFM). The structure and morphology of subsequently grown GaN film were characterized by optical microscopy, scanning electron microscopy, x-ray diffraction, and photoluminescence measurement. It was found that a thicker AlN buffer layer resulted in a higher crystalline quality of subsequently grown GaN films. The GaN with a thicker buffer layer has a narrower PL peak. Cracks were found in the GaN film which might be due to the formation of amorphous SiNx at the AlN and Si interface. / Singapore-MIT Alliance (SMA)