Research On The Mass Sensitivity Of Graphene Resonators Based On Molecular Dynamics

The development of nanoelectromechanical resonators has had a tremendous impact on contemporary human technology and life.Related research and applications have been spread throughout the environmental,energy,and medical fields.Among them,the mass sensitivity of nanoelectromechanical resonators has been a hot issue in this field.Graphene is a perfect candidate for nanoelectromechanical resonators because of its excellent force-electric properties.Unlike macroscopic materials,graphene exhibits many novel properties due to surface effects,small size,and other effects.In this context,this thesis investigates the vibrational properties and mass-sensitivity of intrinsic graphene and defective graphene using molecular dynamics simulations,based on which two methods to improve the mass sensitivity are proposed.This thesis mainly contains the following four parts.In the first part,the tensile and vibrational properties of intrinsic graphene are investigated.Based on the atomic structure of graphene,a graphene drum resonator model is constructed.Graphene exhibits anisotropic characteristics,and the fracture mode and fracture strength of the two chiralities are not consistent.In addition,the simulation results of graphene resonators with different sizes show that the resonant frequency of intrinsic graphene decreases nonlinearly with increasing size,and the smaller size of graphene resonators have higher mass sensitivity but weaker stability to the adsorbed mass.Graphene subjected to stretching exhibited higher resonance performance and mass sensitivity.In addition,it was observed that the change in temperature affects the resonant frequency of the resonator and the trend is related to the tension in the initial conditions.Finally,the relationship between excitation velocity and resonant frequency was analyzed.An increase in the initial excitation velocity can increase the resonant frequency of graphene,but a higher excitation velocity decreases the mass sensitivity of graphene,which is related to the diffusion of adsorbed mass.This part provides a comprehensive analysis of the resonance and mass sensitivity of intrinsic graphene,and lays the foundation for the construction of nanoelectromechanical resonators.In the second part,the vibrational and mass sensitivity of defect-containing graphene is investigated.Based on the simulation results,it is found that defects play a very critical role in the vibration of graphene.A single single atomic defect has almost no effect on the resonant frequency of graphene,and when the number of defects increases,the resonant frequency decreases subsequently.In addition,nanopore defects weaken the vibrational ability of graphene more.Then,two models of graphene resonators with Stone-Wales defects were developed.It is found that Stone-Wales defects cause local stress concentration and out-ofplane displacement and change the vibration mode of graphene.In addition,both single-atom defects and SW defects located in graphene reduce the quality factor of graphene by an order of magnitude.Applying tension can improve the quality factor of single-atom defect graphene,and finally,the effect of defects on the quality sensitivity of graphene is explored.Graphene resonators containing single-atom defects or Stone-Wales defects exhibit higher mass sensitivity and higher stability of the adsorbed mass compared to the defect-free intrinsic graphene.This part of the study implies that defective graphene can be applied to the further design and use of resonators.The third part proposes a method to improve the graphene mass sensitivity using defect design.The defect design of graphene is performed using a kkirigami method,and the larger the size of the defect,the higher the mass sensitivity of graphene when the kirigami defect is close to the center of graphene.Under this condition,the mass sensitivity of the kirigami graphene resonator is up to 2.2 times that of the intrinsic graphene.In addition,the applied tension can effectively improve the sensitivity and resonant frequency of both intrinsic graphene and kirigami graphene.However,too high initial velocity or tension can cause the diffusion of gold atoms on graphene.This part of the study shows that kirigami graphene can be used to develop ultra-sensitive mass sensors.In the last part,a method is provided to improve mass sensitivity using graphene heterojunctions.The resonant frequency of the heterojunction resonator is intermediate between the two monolayer resonators and increases with increasing excitation velocity,which is related to the Young’s modulus and in-plane bending stiffness of the heterojunction material.However,the high temperature environment significantly decreases the stability and quality factor of the heterojunction resonator,and,the slap vibration phenomenon is observed at high temperature,which is related to the higher order vibration modes and the slip between the layers.Finally,the mass sensitivity of the heterojunction resonators was investigated,and the unstretched heterojunctions exhibited a lower mass sensitivity than monolayer graphene.However,when a 2% tensile strain is applied,the mass sensitivity of the heterojunction resonator can be significantly increased,comparable to that of monolayer graphene.