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      • Bilkent Theses
      • Theses - Graduate Program in Materials Science and Nanotechnology
      • Graduate Program in Materials Science and Nanotechnology - Master's degree
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      The mechanical characterization of two-dimensional materials (WS2, MoS2, and graphene) and the effect of defects on young`s modulus of CVD grown single-layer graphene

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      Author
      Adilbekova, Begimai
      Advisor
      Dana, Aykutlu
      Date
      2017-11
      Publisher
      Bilkent University
      Language
      English
      Type
      Thesis
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      Abstract
      With the first isolation of graphene two-dimensional (2D) materials attracted the enormous interest of many researchers. Owing to extraordinary properties and atomic thickness 2D materials have many applications in gas detection, electrodes, energy storage devices, field effect devices, sensors, photodetectors, solar cells, nanocomposites, actuators/ resonators, biological membranes,cancer detectors, piezoresistive pressure sensors, gas impermeable membranes, gas or liquid separation. Despite the atomic thickness, the gapless character of the graphene limits its applications in modern electronic devices. There are two strategies for solving the problem, first one is to open the band-gap in graphene and second is to explore new 2D materials. Generation of defects and applying an electrical field can increase the band-gap of graphene but defects can affect other properties of it. Therefore, there is a need for new analogs and transition metal dichalcogenides (TMDs) are the most promising ones. TMDs drew the attention of many researchers because of the remarkable electronic and optical properties. TMD materials exhibit a semiconducting nature owing to the presence of the band-gap, which is essential for the logical operations. Besides electronic properties, the mechanical properties( Young`s Modulus) play a significant role in applications of 2D materials. 2D materials are most promising candidates for flexible electronic devices, which received enormous interest in recent years. But the applied strain and other external forces can modify the structure of crystalline graphene and TMDs, consequently affect the performance and lifetime of devices. In this work, we aimed to measure the Young`s Modulus of graphene, MoS2 film, MoS2 and WS2 flakes with an Atomic Force Microscope (AFM). In addition, we sought the relation between the defect intensity and Young`s Modulus of graphene. The defects in graphene were generated by Ga+ with different doses in Focused Ion Beam (FIB). We found Young`s Moduli of graphene, MoS2 film, MoS2 and WS2 flakes to be 270 N/m, 330 N/m, 90 N/m and 140 N/m, respectively. These values are lower than those given in a literature, what might be caused by the pre-existence of unwanted defects. Also, it appeared that the introduction of defects leads to the fall in Young`s Modulus values of the graphene.
      Keywords
      2D materials
      Graphene
      MoS2 film
      MoS2 flakes
      WS2 flakes
      Young`s Modulus
      Defects
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      http://hdl.handle.net/11693/35683
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      • Graduate Program in Materials Science and Nanotechnology - Master's degree 142
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