Atomic force microscopy experiments on atomically thin materials

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Bilkent University
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In 2004, successful isolation of graphene attracted immense attention of scientists because of atomic scale thickness and exotic functionalities. Regardless of graphene’s thickness and extraordinary properties only reason that limits the usage of graphene in electronics is no band gap. But there is a way to open band gap of graphene by introducing defects or applying electric field but defects introduction can affect its functionality. So, world moved towards transition metal dichalcogenides (TMDCs), new analogs of graphene with thickness dependent band gap option are promising nominee for potential applications in modern physics and electronics. Besides electronic properties, TMDCs depict excellent mechanical characteristics (in plane elastic modulus, breaking strength/strain and pretension) compared to conventional volumetric counterparts. The objective of this study is to investigate work function and mechanical properties of atomically thin materials using Kelvin probe force microscopy (KPFM) and Nanoindentation modes of Asylum Atomic Force Microscopy (AFM) respectively. Firstly, KPFM experiments were performed on CVD grown Vanadium Sesquioxide V2O3 to map surface potential variation and calculated work function value 4.91 eV. This will help in understanding band alignment, contact resistance and appropriate Schottky barrier height (SBH) by choosing metal contacts with closer work function to V2O3. Secondly by using AFM based nanoindentation we first time reported elastic features of metallic TMDCs: 2H-TaS2, 3R-NbS2, 1T-TaTe2 and 1T-NbTe2 with various thickness values suspended over circular holes. Comprehensive measurement was done on 2H-TaS2 and found thickness independent Young’s modulus for 2H-TaS2 is 114 ± 14 GPa, breaking strength 12.6 ± 2.6 GPa corresponds to nominal strain of 11% and ultimate strain of 0.22. Same mechanical features were investigated for other three materials and they also manifested extreme elasticity and high strain values compare to other 2D materials reported so far except graphene. This mechanical analysis of metallic materials will contribute in future flexible nano technological devices (for instance piezo electronics), wearable electronics, resistive coatings in electronic devices, nanoelectromechanical systems (NEMS) and strain sensors.

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Vanadium sesquioxide, Transition metal dichalcogenides, Kelvin probe force microscopy, Nanoindentation
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