Defect-Driven Reactivity of Layered Materials Examined through Atomic Layer Deposition

Citation

Mazza, Michael Francis (2022) Defect-Driven Reactivity of Layered Materials Examined through Atomic Layer Deposition. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/nnwh-5355. https://resolver.caltech.edu/CaltechTHESIS:01042022-032834418

Abstract

Layered materials are a unique class of materials that are characterized by strong covalent bonds in single layers in the two-dimensional plane, but much weaker van der Waals interactions between layers. This unique bonding environment gives rise to remarkable chemical and physical properties. These materials can be easily exfoliated into single atomic layers, true two-dimensional materials, or few-layer stacks. As the number of layers changes, the physical and chemical properties can be modified. Similarly, as the relative position of one or more layers is changed, this change in the bonding environment has substantial impacts on the properties. Due to their unique bonding environment, layered materials are unusually inert to atomic layer deposition. Atomic layer deposition (ALD) is a surface-sensitive deposition technique that relies on a sequence of chemical reactions on the surface of a substrate to deposit the target material. Using this surface-sensitive deposition technique, the crystal structure and chemical bonding environment of the layered material can be interrogated.

Chapter 1 investigates the spontaneous formation of highly ordered triangular and linear pattern depositions on layered material substrates. These patterns form with two different layered material substrates and with two separate ALD reactions. The pattern depositions do not change with increasing deposition time or with different concentrations of reactants. These networks, while highly unusual to observe chemically, are discussed through a well-established dislocation theory, where defects in the crystal structure of layered materials can impact the surface reactivity.

Chapter 2 explores the stacking order characteristics of few-layer materials and discusses how changing the stacking order can change the crystal structure and the electronic properties of the materials. The chapter describes the field of few-layer materials and the process of modifying or transferring nanoflakes to new substrates. The chapter introduces a new transfer system that allows for patterned nanoflakes with stacking fault networks to be transferred to new substrates with micron-scale precision. The crystal structure of both the deposited triangular networks and the layered material beneath is discussed.

Chapter 3 describes a new approach to selectively targeting defect sites in monolayer graphene. A new, water-free atomic layer deposition chemistry is introduced to precisely react metal oxides with high-energy defect sites on graphene. The quality of the film is interrogated and the selectivity of the film is determined by measuring the thickness of the film deposited on the defect-rich regions. The results confirm that this ALD process creates a robust passivating film while keeping the unperturbed regions clean of any metal oxide.

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