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Modeling of Force Interactions between Tip of Atomic Force Microscopy in Trolling Mode and Environment

Falsafi, Ali | 2015

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 47978 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Nejat Pishkenari, Hossein
  7. Abstract:
  8. Submerging of the Micro-beam of the AFM is indispensible in case of imaging bio-samples. (Bio-samples are unstable in non-aquos environment.), so hydrodynamical interaction of liquid and beam (viscous and meniscus forces) will result into quality factor decrease. This will cause image resolution decrement as well as damage to the sample because of large tip-sample forces during imaging of the bio-samples. The proposed method “Trolling mode AFM” keeps the micro-beam of the AFM out of the liquid, by adding a nano-needle to the end of the AFM tip. This would lead to resolve the aforementioned problems. Modeling of a part of the operation of this mechanism was done in this thesis, in order to understand the operation in a better fashion is the goal of the project. In this thesis one of the most important and effective aspects of the interaction of the mechanism and its envorinment has been studied. The proper model to carry out the simulation is recognized to be coarse-grained model. (The reason is declared into details in section 2.3). Among the coarse-grained methods, MARTINI coarse-graining and Many-body Dissipative Particle Dynamics has been employed. The simulation results are the geometrical charactristics of the meniscus layer like its height, the contact angle, and the evanescent length, besides, in addition the interaction forces of the nano-needle and the liquid is studied as well. Generally speaking results depicts increase of the interaction forces and the meniscus layer height and decrease of the contact angle by increasing the needle’s diameter as well as the surace hydrophilicity. The proposed suggestions for the Trolling Mode AFM regarding to the results are to use thinner (more slender) and more hydrophobic needles to be added to the end of the tip, In addtion the uppermost meniscus layer height can help designers to choose the shortest possible needle length for the Trolling mode AFM in order to prevent the tip to touch the liquid surface on its own
  9. Keywords:
  10. Molecular Dynamics ; Coarse Grained Model ; Trolling Mode Atomic Force Microscopy (AFM) ; Atomic Force Microscopy (AFM) ; Capillary Effect

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