Study On Steered Molecular Dynamics Simulation Of Adsorption Properties Of Carbon Nanotubes On A Silicon Substrate

As a very important method in computational approaches, the molecular dynamicssimulation plays a significant role in many fields. A lot of researches have been done tosimulate the system of carbon nanotube (CNT) and silicon (Si) substrate. The peeling andshearing of the system mentioned above are simulated here. The influences of tensile velocity,radius, the length and the defects on peeling forces of the peeling process are speciallydiscussed. The relationship between the peeling angle and the critical peel-off force is alsodiscussed. On the other hand, the influences of tensile velocity, radius and two kinds ofdefects on the shearing process are investigated.Firstly, we systemically introduce the molecular dynamics simulation techniqueincluding a detailed introduction of main concept and the process of programming. Therelevant details of the simulation technique used in this study are also summarized. Thechoice of potential function, the unity of the unit, and the choice of timestep are enumerated.Secondly, the steered molecular dynamics (SMD) simulation technique is used toinvestigate the peeling of a single-walled carbon nanotube (SWCNT) from a silicon substrateat different angles at room temperature. There is a regular relationship between the averageforce F probed by the ideal spring and the peeling distance X when the carbon nanotube (CNT)is peeled from the silicon substrate. A large positive and a large negative peak value can befound during the peeling process. The average forces F for varied peeling velocities areinvestigated and their peak values are fitted as a function of the peeling velocity. The criticalpeel-off force decreases with the increasing peeling angle, which agrees with the theoreticalprediction. The SMD simulated results show that there is a linear relationship between thepeak value and the peeling velocity, which agrees well with some experiments of biophysicspeeling. The influences of both radius and length of the CNT on the peeling process are alsoexamined. The numerical results indicate that the peak value of the peeling force isindependent on the length of the CNT but increases linearly with the radius of the CNT. Thepeak value of the peeling force is almost independent on the5-7-7-5defect in the CNT but iscritically weakened by the radius defect of the CNT.Finally, the steered molecular dynamics (SMD) simulation technique is used toinvestigate the shearing of a single-walled carbon nanotube (SWCNT) on silicon substrate atroom temperature. The average shearing forces at different shearing velocity are compared and then the relationship between the shearing force and velocity is discussed. According tothe modified Bell’s approach, we obtain the energy barrier and the distance between thetransition state and the equilibrated state. The SMD simulation results show that the shearingforce increases linearly with logarithm velocity, and agrees well with similar experimentalresults in the biophysics. However, compared with macromolecules, the CNT has a strongeradhesion on the silicon surface. The effect of both radius and5-7-7-5defect as well as radiusdefect of CNT on the shearing are also discussed. The present study shows that the peak valueof shearing force is almost independent on5-7-7-5defect but increases linearly with theradius of CNT and is critically weakened by the radius defect of the CNT.The suggested method provides a theoretical prediction for the future experiment atatomic scale, which is helpful for the potential application of the CNT in the silicon-basedmicroelectronics industry.