Single Crystalline 2D Material Nanoribbon Networks: Optical and Electrical Properties

Muhammad Awais Aslam

Research output: ThesisDoctoral Thesis

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Abstract

Two-dimensional (2D) material nanoribbons offer vast opportunities ranging from next generation quantum electronics to enhanced sensing. However, the existing fabrication routes are mostly restricted to graphene nanoribbons where the majority of methods rely on solution processed nanoribbons which hinders their integration into devices. Methods opted for the fabrication of other 2D material nanoribbons do not offer sufficient quality, yield, and control over the nanoribbons¿ edge terminations. This has been a bottleneck in the experimental studies of nanoribbons to explore their electrical and optical properties. This work aims to propose a universal approach to synthesize networks of nanoribbons from arbitrary 2D materials while maintaining high crystallinity, narrow size distribution, and straightforward device integrability. Moreover, the resulting devices do not suffer from junction resistance issues. This is supported by in-operando Kelvin Probe Force Microscopy of nanoribbon field effect transistors (FETs). The single crystalline nature of the nanoribbons is verified by Raman spectroscopy. By relying on self-aligning organic nanostructures as masks, the possibility of controlling the predominant crystallographic direction of the nanoribbon¿s edges is also demonstrated. Electrical characterization shows record charge carrier mobilities and very high ON-currents despite extreme width scaling. Particularly, for graphene nanoribbons a well-defined and highly controllable system of hexagonal boron nitride encapsulated graphene nanoribbon networks with water terminated edges is also presented. The system exhibits a robust hysteresis of the remnant dipolar fields, which affect and modulate the conductivity of graphene nanoribbon networks. So far, such ambipolar behaviour in graphene nanoribbons has been only predicted theoretically. The undertaken experimental approach sheds light on the mechanisms governing the ferroelectric behavior in graphene nanoribbons and supports it theoretically via molecular dynamic simulations. This offers insights for the design of ferroelectric heterostructures and neuromorphic circuits. Lastly, the thesis presents all van-der-Waals semiconducting PtSe2 field effect transistors with high-performance transport characteristics. PtSe2 is proposed as an alternative channel material below thicknesses of 4 nm, a critical thickness limit below which Si electronics performance start to deteriorate. The work is also inspired by the need to address the challenges faced for the co-integration of 2D materials into back end of line processes used in Silicon technology.
Translated title of the contributionEinkristalline 2D-Material-Nanoband-Netzwerke: Optische und elektrische Eigenschaften
Original languageEnglish
QualificationDr.mont.
Awarding Institution
  • Montanuniversität
Supervisors/Advisors
  • Griesser, Thomas, Assessor A (internal)
  • Rodriguez, Raul, Co-Supervisor (external), External person
  • Resel, Roland, Assessor B (external), External person
  • Teichert, Christian, Supervisor (internal)
DOIs
Publication statusPublished - 2024

Bibliographical note

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Keywords

  • Nanoribbons
  • Ferroelectricity
  • 2D Materials
  • KPFM
  • Field Effect transistors

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