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Development of an aerosol-CVD technique for the production of CNTs with integrated online controlMeysami, Seyyed Shayan January 2013 (has links)
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 cm<sup>2</sup>), 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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Reactivity of Pd single crystal, alloy and model catalyst surfacesPerkins, Neil January 2001 (has links)
No description available.
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Synthesis and characterisation of single-source CVD precursors for M-N-Si compositesCosham, Samuel January 2010 (has links)
No description available.
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Novel fabrication processes for thin film vapour deposited strain gauges on mild steelDjugum, Richard, n/a January 2006 (has links)
Pressure measurement using a strain gauge bonded with epoxy adhesive to a metallic
mechanical support has been, and still is, extensively employed, however, for some
applications the use of an epoxy is inadequate, especially when temperatures exceed
120C. There is therefore particular interest in the use of thin film techniques to
vacuum deposit strain gauges directly on metallic substrates. Such devices are highly
cost effective when produced in large quantities due to the manufacturing techniques
involved. This makes them ideally suited for use in large-volume products such as
electronic weighing scales and pressure transducers. In this thesis, new techniques for
fabricating thin film vapour deposited strain gauge transducers on metal substrates for
application as novel pressure sensors in the fastener industry are developed.
Clearly, for a vapour deposited strain gauge to function correctly, it is essential that it be
deposited on a defect free, high quality electrically insulating film. This was a
significant challenge in the present study since all available physical vapour deposition
(PVD) equipment was direct current (DC) and insulators of around 4 um thick were
needed to electrically isolate the strain gauges from metal. As a result, several methods
of depositing insulators using DC were developed. The first involved the use of DC
magnetron sputtering from an aluminium target to reactively deposit up to 4 um thick
AlN. DC magnetron discharges suffer arc instability as the AlN forms on the target and
this limits the maximum thickness that can be deposited. Consequently, the arc
instability was suppressed manually by increasing argon gas flow at the onset of arcing.
Although the deposited AlN showed a high insulating resistance, it was found that the
breakdown voltage could significantly increase by (a) utilising a metallic interlayer
between the thin film insulator and the metallic substrate and (b) annealing in air at
300C. A second deposition method involved the use of DC magnetron sputtering to
deposit modulated thin film insulators in which an aluminium target was used to
reactively deposit alternating layers of aluminium nitride and aluminium oxide. These
films showed significant increases in average breakdown voltage when the number of
layers within the composite film was increased. The third method involved the
deposition of AlN thin film insulators using partially filtered cathodic arc evaporation
with shielding. Initially, AlN was deposited under partially filtered conditions to obtain
a relatively thick (~ 4 um) coating then, while still depositing under partially filtered
conditions, a smooth top coating was deposited by using a shielding technique. The
deposition of metal macroparticles is an inherent problem with cathodic arc deposition
and shielding is one form of macroparticle filtering. Such particles are highly
undesirable in this study as they are electrically conductive. A fourth coating technique
for depositing insulators on steel was based on thermal spray technology. Insulating
films of Al2O3 were plasma sprayed and then polished to thereby fabricate viable
electrical insulators for vapour deposited strain gauges.
With respect to depositing strain gauges two methods were employed. The first
involved the sputter deposition of chromium through a shadow mask to form a strain
gauge with gauge factor sensitivity of around 2. The second used cathodic arc
evaporation to fabricate a multi-layered strain gauge composed of alternating CrN and
TiAlN layers that yielded a gauge factor of around 3.5. The technique achieves better
compatibility between gauge and insulator by allowing a wider selection of materials to
form the gauge composition. Finally, a novel pressure sensor in the form of a load cell
was developed that consisted of a chromium strain gauge on a steel washer electrically
insulated with AlN thin film. The load cell showed good performance when tested under
compressive load.
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Evolution of AlN buffer layers on Silicon and the effect on the property of the expitaxial GaN filmZang, Keyan, Wang, Lianshan, Chua, Soo-Jin, Thompson, Carl V. 01 1900 (has links)
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)
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Structural analysis of metalorganic chemical vapor deposited AlN nucleation layers on Si (111)Zang, Keyan, Wang, Lianshan, Chua, Soo-Jin, Thompson, Carl V. 01 1900 (has links)
AlN nucleation layers are being investigated for growth of GaN on Si. The microstructures of high-temperature AlN nucleation layers grown by MOCVD on Si (111) substrates with trimethylaluminium pre-treatments have been studied using atomic force microscopy (AFM) and transmission electron microscopy (TEM). The AFM results show that with TMA pre-treatments, AlN grows in a pseudo-2-dimensional mode because the lateral growth rate of AlN is increased, and the wetting property of the AlN on silicon is improved. Also, no amorphous SiNx layer was observed at the interface with TMA pre-treatments and AlN films with good epitaxial crystalline quality were obtained. Transmission electron diffraction patterns revealed that the AlN and Si have the crystallographic orientation relationship AlN [0001]âSi[111] and AlN[11 2 0] âSi[110]. High resolution transmission electron microscopy indicates a 5:4 lattice matching relationship for AlN and Si along the Si [110] direction. Based on this observation, a lattice matching model is proposed. / Singapore-MIT Alliance (SMA)
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The Effect of Periodic Silane Burst on the Properties of GaN on Si (111) SubstratesZang, Keyan, Chua, Soo-Jin, Thompson, Carl V. 01 1900 (has links)
The periodic silane burst technique was employed during metalorganic chemical vapor deposition of epitaxial GaN on AlN buffer layers grown on Si (111). Periodic silicon delta doping during growth of both the AlN and GaN layers led to growth of GaN films with decreased tensile stresses and decreased threading dislocation densities, as well as films with improved quality as indicated by x-ray diffraction, micro-Raman spectroscopy, atomic force microscopy, and transmission electron microscopy. The possible mechanism of the reduction of tensile stress and the dislocation density is discussed in the paper. / Singapore-MIT Alliance (SMA)
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Metal particle catalyst formation from thin films for the creation of vertically aligned carbon nanotube structuresOlsen, Brian Unknown Date
No description available.
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An investigation of various hydrocarbon sources in the production of carbon nanoparticles via a plasma enhanced chemical vapour deposition technique.Singh, Shivan Royith. January 2010 (has links)
A simple, low cost microwave plasma enhanced chemical vapour deposition (PECVD) technique for the production of carbon nanostructures has been developed in the School‟s Materials Science Laboratory. The technique utilises a conventional microwave oven as an energy source, various hydrocarbons as a carbon source, a metallic aerial as a catalyst and hydrogen to support the process. The input hydrocarbon and the hydrogen flow rate are
independently varied to investigate their effect on the resultant nanostructures. This technique allows for the production of carbon nanotubes (CNTs), onion-like nanostructures structures (ONSs) and amorphous carbon, which has been verified via transmission and scanning electron microscopy. A change in input parameters results in the controllable yield of CNTs versus
ONSs. The formation of amorphous carbon is reduced by controlling the hydrogen flow rate. In further experiments, the thermal conductivity of the ONSs is investigated using the "Lee‟s Disk" method. It was observed that bulk ONS specimens exhibit a thermal conductivity above that of amorphous carbon powder. Insufficient quantities of CNTs were grown using this method to facilitate a comparable thermal conductivity investigation. / Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2010.
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Surface reactions of zinc vapour with steel relevant to the Zn-55%Al-1.5%Si hot dip metal coating processWilliams, Joseph James. January 2005 (has links)
Thesis (Ph.D.)--University of Wollongong, 2005. / Typescript. Includes bibliographical references: leaf 191-198.
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