Density functional theory investigation on thickness and load dependency of friction force between graphene and au interfaces

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Duygu Gizem Senturk.pdf

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2018

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Şentürk, Duygu Gizem

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As the investigation of materials at nano scale become possible with today's technology it is observed that some physical phenomenons have different characteristics at atomistic scale than macroscopic one because of the quantum mechanical effects. One of these physical processes that differs at nano scale is the friction force. While it is expected that the friction force to be independent of contact area and velocity according to Amontos-Coulomb laws, it was observed that it changes by the effect of some parameters such as contact area, velocity, load and temperature at smaller scales. This study will include nanotribological calculations which analyzes the friction force between objects at atomic level. The lateral friction force that arises from the relative sliding motion of materials can be investigated in experimental manner using the Friction Force Microscopy (FFM) which is modified version of the Atomic Force Microscopy (AFM). It is also possible to obtain a detailed understanding of friction in atomic scale by modelling the mechanism of FFM using computational methods. The ab initio Density Functional Theory (DFT) is one of these methods that one can perform accurate calculations for the relative sliding motion of FFM probe tip and the surface. The importance of these kind of numerical methods is the convenience of investigating the wide range of material interactions that are not achievable with experimental methods. As it was observed that the two dimensional materials such as graphene, hexagonal boron nitride(h-BN) , $MoS_2$ provides good performance as dry lubricants, the scope of the nanotribology studies shifted into the frictional behaviors of these systems and their effects on other type of materials. In this thesis, we focus on the lateral friction force between two dimensional graphene sheets and three high-symmetry surfaces of gold. Our aim is to understand the results of FFM experiments by modelling the friction mechanism between Au coated probe-tip and graphene surface by implementing static calculations based on Density Functional Theory. As the Au coated probe slides over graphene, Au surfaces with different orientations would interact with graphene surface and three of them namely Au(100), Au(110) and Au(111) are reviewed as the subjects of this study. The effects of physical variables such as an external load applied to structures and increasing the thickness of the surfaces were interpreted. Results of this thesis can provide useful informations about minimizing the friction between objects with the help of different parameters which would be beneficial in industrial manner about reducing the loss of energy arises due to friction.

Subject Keywords

Physics ., Density functionals., Friction., Graphene., Gold.

URI

http://etd.lib.metu.edu.tr/upload/12621774/index.pdf
https://hdl.handle.net/11511/27142

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Graduate School of Natural and Applied Sciences, Thesis

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Citation Formats

D. G. Şentürk, “Density functional theory investigation on thickness and load dependency of friction force between graphene and au interfaces,” M.S. - Master of Science, Middle East Technical University, 2018.