Adsorption Mechanisms And Functionalization Of Single-walled Carbon Nanotubes

Advanced molecular electronics and mechanics play a crucial role in nanoelectromechanical systems?NEMS?,nanobiotechnologies,and information technologies.Because of the one-dimensional tubular geometry along with the unique mechanical,optical and electronic properties,single-walled carbon nanotubes?SWNTs?become one of the ideal components for constructing functional nanodevices.It has reported that SWNTs have achieved the molecular gears,biosensors and integrated logic circuits.Despite SWNTs have the promising prospects in nanotechnology,the fundamental understandings of adsorption and friction are still missing for SWNTs,although they are essential for discriminating between metallic?M-?and semiconducting?S-?SWNTs as well as SWNTs functionalization.Adsorption is determined by the interactions between SWNTs and adsorbates.Therefore,the key to understanding the adsorption mechanisms of SWNTs is to reveal the role of SWNTs characteristics such as geometry,size and dielectric properties on adsorption,and to explore the effects of adsorbates'geometry,adsorption configuration,site and coverage on the behavior.Moreover,relative movements of the adsorbed SWNTs on substrate induce friction further,in which the dynamic transition of adsorption mainly depends on the motion modes.In this regard,studying the dynamic response of interactions between SWNTs and the substrate and unraveling the competition mechanisms between different motion modes are of significant importance for understanding the fundamental nature of friction.In this context,we adopted density functional theory methods augmented with nonlocal many-body dispersion interactions?DFT+MBD?to systematically study the adsorption and friction mechanisms of SWNTs.To explore the role of SWNTs characteristics on adsorption,We systematically study the adsorption of the isotropic noble-gas atoms Xe,Kr,and a highly anisotropic organic molecule n-heptane on both M-and S-SWNTs.It finds that the distinct polarizabilities of M-and S-SWNTs give rise to significantly distinct physisorption properties,which are also strongly depended on the SWNTs diameter,the adsorbate's anisotropy,adsorption site,and coverage.In essence,these phenomena stem from the wavelike charge-density fluctuations in SWNTs.Motivated by these results,n-heptane is suggested to be an effective sensor for the experimental discrimination of M-from S-SWNTs based on distinct physisorption behaviors.Furthermore,we take a systematic investigation on the adsorption behaviors of the planar Au₆cluster on SWNTs to study the dependence of adsorption on adsorbate characteristics.In this study,Au₆ cluster is found to take both lying and standing optimal configurations on SWNTs,in which the delicate balance between chemical binding,Pauli repulsion,MBD forces,and electrostatic interactions play a critical role.Moreover,these findings identify that the many-body effects of dispersion in low-dimensional adsorption systems can be tuned by chemical binding and Pauli repulsion from destabilization to stabilization effectively,which also depend on the adsorbates'anisotropy and atomic volume as well as the adsorption configuration strongly.Herein,a promising functional switch at a solely molecular scale is proposed based on the Au₆ cluster/N-doped SWNT?14,0?adsorption system,in which switching is realized by converting the bistable lying and standing configurations.Based on the above investigations on adsorption mechanisms,we study the rolling and sliding friction mechanisms of armchair?A-?and zigzag?Z-?SWNTs on graphene.It finds that rolling and sliding friction strongly rely on the stacking modes involved in the motions.In essence,it stems from the decay and fluctuations of the charge density with respect to the distance between SWNTs and graphene.As a result,Pauli repulsion dominates rolling,while MBD interactions dictate sliding.Moreover,there is a novel size-dependent sliding-rolling motion transition with SWNTs size increasing due to the opposite dependence of rolling and sliding friction on SWNTs size.Differing from the macroscopic picture,these phenomena indicate that the friction behaviors at the nanoscale exhibit the prominent size effect.With Prandtl-Tomlinson model,we further demonstrate the viscous frictional behaviors in both rolling and sliding.In particular,we extend a model based on potential corrugation to capture the energy dissipations during rolling and sliding with experimental accuracy.In summary,this study uncovers the mechanisms behind the adsorption and friction behaviors of SWNTs.These findings not only open the routines to discriminate between M-and S-SWNTs by using physisorbed adsorbates,but also provide new clues for the rational design of SWNTs-based functional nanodevices.