Nanomechanics and nanotribological characterization of self-assembled monolayers for nanosystems

Cheng Da Wu, Te Hua Fang, Jen Fin Lin

Research output: Chapter in Book/Report/Conference proceedingChapter


In recent decades, self-assembled monolayers (SAMs) have been applied intensively in nano/microelectromechanical systems (N/MEMS) to avoid failure during operation of these devices. The fundamental frictional and adhesion mechanisms of a self-assembled monolayer (SAM) during nano-scale sliding are studied using molecular dynamics (MD) simulation. The trajectory, tilt angles, normal forces, frictional forces, friction coefficients and potential energies per molecular chain of the SAM molecules are evaluated during the frictional process for various parameters including as sliding height, sliding direction (i.e. pro- or anti- the SAM tilt angle), sliding velocity and system temperature. The various parameters are discussed with regard to frictional forces, mechanisms and SAM structural transition. Results show that stickslip occurs and is related to the sliding period and tilt angle of the SAM molecules. Amplitude of the stick-slip cycle increases with decreasing sliding height until reaching a critical sliding height, which is characterized such that sliding below the critical height causes irreversible changes in the SAM molecular organization and cumulative loss of SAM lubricating efficiency. To more explore SAM's characteristics in nanosystem, the friction and adhesion mechanisms with and without a self-assembled monolayer (SAM) in nanotribology were studied. The MD model consisted of two gold planes with and without n-hexadecanethiol SAM chemisorbed to the substrate, respectively. The molecular trajectories, tilt angles, normal forces, and frictional forces of the SAM and gold molecules were evaluated during the frictional and relaxation processes for various parameters, including the number of CH2 molecules, the interference magnitude, and whether or not the SAM lubricant was used. When the number of CH2 molecules was increased, the SAM chains appeared to have bigger tilt angles at deformation. The magnitude of the strain energy that was saved and relaxed is proportional to the elastic deformable extent of the SAM molecules. The frictional force was higher for long chain molecules. With shorter SAM molecules, the adhesion force behavior was more stable during the compression and relaxation processes. Finally, SAM molecules were applied to a special case simulation such as an antistiction layers in nanoimprinting process to discuss the related behaviors of interface action.

Original languageEnglish
Title of host publicationAdvances in Nanotechnology
PublisherNova Science Publishers, Inc.
Number of pages35
ISBN (Electronic)9781617614873
ISBN (Print)9781607417316
Publication statusPublished - 2010 Jan 1

All Science Journal Classification (ASJC) codes

  • Engineering(all)

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