Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Mechanical and Materials Engineering

Supervisor

Sun, Xueliang

Abstract

Atomic layer deposition (ALD) is a thin film deposition technique that has a rich history of being an enabling technique. This vapor phase deposition process can produce a variety of thin films and nanostructures. ALD is based on sequential, self-limiting reactions and provides angstrom level control over film growth. Furthermore, ALD allows for conformal deposition on high-aspect ratio structures and can provide tunable film composition. As nanotechnology marches forward, the development of nanomaterials has significantly advanced. Additional functionality can be imparted to nanomaterials by using surface modification techniques. Given the advantages of ALD, this technique has become a powerful tool for modifying the surface of materials and increasing the functionality and application of nanomaterials. The toolkit of available materials for surface modification is further augmented by including molecular layer deposition (MLD), a technique used to grow organic polymer-like materials. By combining ALD and MLD together, novel inorganic-organic hybrid materials can be produced with specifically tailored properties.

The first part in the thesis investigates the effect of ozone on nitrogen doped carbon nanotubes (NCNTs) and pristine carbon nanotubes (PCNTs). The deleterious effects of ozone were found to occur only for NCNTs, while little to or no damage occurs for PCNTs. Furthermore, this work highlights the importance of understanding precursor-substrate interaction, especially when dealing with nanomaterials.

The second and third part of this thesis outline the synthesis of novel thin films made by ALD and MLD. First, an aluminum alkoxide film with tunable conductivity was made using trimethylaluminium (TMA), ethylene glycol (EG), and terephthaloyl chloride in various subcycle configurations to control the ratio of aluminum to carbon in the film. The films were then pyrolyzed in a reducing atmosphere to yield a conductive aluminum oxide/carbon composite. Depending on the ratio of aluminum to carbon in the grown film, post-pyrolyzed films displayed varying levels of electronic conductivity. Synchrotron based XPS was then used to elucidate the origin of conductivity within the film. The second novel film is a mixed inorganic-organic polyurea film. For the first time, polarization-dependent x-ray absorption spectroscopy was used to determine the difference in orientation and ordering between pure organic polyurea films and inorganic-organic polyurea films. In-depth analysis of this data revealed that the hybrid inorganic-organic films possessed a high degree of ordering compared to their organic counterpart. Both studies present the possibility of combining ALD and MLD in tuning various film properties such as electronic conductivity and oligomer packing density.

The fourth part of this thesis investigates the formation of single-atom and ultra-small clusters of platinum produced by ALD. The self-limiting characteristics of trimethyl(methylcyclopentadienyl)-platinum on NCNTs and PCNTs was investigated by varying precursor exposure time and determining the influence of reactor temperature. This study determined that a 1 minute exposure of the Pt precursor at 250°C yielded primarily single atoms and ultra-small clusters on NCNTs, but not PCNTs. Extended x-ray fine structure analysis was conducted to determine the bonding characteristics of Pt to NCNTs and PCNTs. This study outlines the necessary conditions to deposit single atom and ultra-small clusters of Pt on carbon nanotube substrates and the parameters that influence this process.

The final experimental investigation of this thesis is the protection of metallic lithium (Li) by ALD and MLD. Fifty cycles of either TMA-H2O, TMA-EG or TMA-glycerol (GLY) were used to coat the surface of Li metal. Galvanostatic cycling of Li symmetric cells was then conducted to determine the protective capabilities of these films. The results revealed that electrodes coated with TMA-GLY provided prolonged cyclability of metallic Li electrodes. For the first-time gravimetric intermission titration technique was then conducted on coated electrodes to unravel the effects of lithium electrodissolution and electroplating. This study demonstrated that the longevity of TMA-GLY coated electrodes originates from the relatively low overpotential required to plate and strip Li from the MLD film. Finally, scanning electron microscopy and Rutherford backscattering spectometry was used to determine composition and morphology of the formed solid electrolyte interphase on coated electrodes following electrochemical cycling.

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