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Date of Award
Doctor of Philosophy (PhD)
ABSTRACT OF THE DISSERTATION
Nucleation and Growth of Atomic Layer Deposition films: Effect of Substrate and Precursor Chemistry
Doctor of Philosophy in Material Sciences and Engineering
Washington University in St. Louis, 2018
Professor Parag Banerjee, Chair
Atomic layer deposition (ALD) is a sequential, layer-by-layer, pin-hole free vapor-phase thin film deposition technique. ALD shows advantages over other thin film deposition techniques by enabling deposition of conformal and films with atomic scale controllability over thickness and composition. For ALD process, controlling the nucleation and growth is important since it will affect whether a continuous, conformal, and pin-hole free film can be deposited or not. The type of substrate and its surface functionalization determines the initial nucleation of ALD films, its evolving structure and hence the film properties.
This thesis address these specific challenges in the ALD nucleation and growth (N&G) by, 1) understanding the substrate effect on N&G of ALD, 2) understanding the precursor ligands effect on N&G of ALD, 3) understanding effect of ALD N&G films coupled to optically active metal surfaces and nanostructures.
In the first part of this thesis, the substrate effect on N&G of ALD is studied by ALD ZnO and Al2O3 on hydroxylated Si substrate and Au substrate. These two ALD processes have similar surface reaction. On Si substrate, 71.6% OH groups are associated with sitting molecule. No observation of nucleation delay. In Au substrate, an initial hydrophobic surface, takes 37 cycle for ALD Al2O3 to finish nucleation and grows as a film. After UV Ozone treatment to tune the Au surface into “clean”-hydrophilic state, the ALD ZnO only takes 5 cycle to finish nucleation.
The second part of the thesis, the precursor ligands effect on N&G of ALD is investigated by an ALD Ru process with a zero valent Ru precursor – RuDMBD(CO)3, and H2O. It shows that the complementary effect between precursor ligands dominate the nucleation and growth of Ru film on hydroxylated surface.
The third part of the thesis, ALD N&G films coupled to optically active metal and nanostructures is studied by applying ALD Al-doped-ZnO on AuNRs in anodic aluminum oxide (AAO) template to fabricate a 3D nanostructure plasmonic hot carrier device. The uniform coating of ALD film enhance the possibility to make complex plasmonic hot carrier device with moderate quantum efficiency.
The study presented in this thesis opens up new direction of studying ALD N&G that focus on the substrate and precursor chemistry. While studying ALD N&G can enhance the understanding about the basic of ALD, the final goal for using ALD is for application. Conformal and pin-hole free coating is critical film deposition.
Srikanth Singamaneni, Li Yang, Bryce Sadtler, Rohan Mishra,
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