Processing and Devices for Chemically Reactive Two-Dimensional Materials

Wells, Spencer Allan

doi:https://doi.org/10.21985/n2-a59j-th38

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Processing and Devices for Chemically Reactive Two-Dimensional Materials

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Two-dimensional (2D) materials are a promising class of electronic materials that have generated great interest to improve and create new and existing technologies. The promise of this family of materials relies on their high surface-to-volume ratio and atomic thickness in addition to their unique (opto)electric properties. However, these morphological properties that drive interest also raise concerns for long-term stability and reliability of these materials. Understanding ambient reactivity in 2D materials and developing broadly applicable passivation strategies is essential for the further adoption of this class of materials. Ambient exposure can have a deleterious impact on material properties, altering dopant concentration, introducing scattering centers and traps, and more. Developing universalizable approaches to characterize these changes is needed to generate a fundamental understanding 2D material reactivity and to mitigate degradation. Indeed, engineering broadly applicable passivation and functionalization procedures to encapsulate and protect 2D materials can dramatically improve stability and offer opportunities to tailor material properties, enabling new applications, measurement techniques, and synthesis routes. This dissertation describes progress in characterizing, passivating, modifying, and fabricating devices from chemically reactive 2D materials. Black phosphorus (BP) is introduced as a prototypical chemically reactive 2D nanomaterial that reacts and degrades after exposure to water and oxygen in ambient. Initially a liability for device fabrication, this reactivity is exploited, allowing the creation of highly sensitive and selective gas and ion sensors and intentional covalent functionalization and doping with aryl diazonium molecules. Ambient degradation can be arrested by well-engineered atomic layer deposition (ALD) of an alumina film, stabilizing BP properties and allowing the creation of new devices including polarization-sensitive photodetectors and the measurement of new properties including quantitative conductivity anisotropy and electronic trap states. Furthermore, understanding the degradation of BP can allow for scalable production through liquid phase exfoliation (LPE). Transistors made from LPE BP can be fabricated into field effect transistors (FETs) with device performance commensurate with state-of-the-art micromechanically exfoliated material, a first for LPE material. Finally, understanding developed for BP are shown to be broadly applicable across other 2D materials, universalizing high quality LPE device performance and long-term stabilizing FET encapsulation to ambient reactive InSe.

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