Research On The Nonlinear Behaviors Of Graphene NEMS Resonator

Along with the rapid development of technology, people pay more and more attention to the nano electromechanical system in the basic research and application. Due to the advantages of small size and high resonant frequency, NEMS resonator has ability to act as typical nano-electromechanical devices. Because of the unique two-dimensional single atomic layer crystal structure, excellent mechanical, electrical, thermal and optical properties of grapheme, the grapheme can be used for the material of resonator which obtains the widespread application in the respects of sensor and communication for its good chararistics of low-power, high sensitive, very small quality and super high quality factors.When the size of resonator is in the nanoscale, under the action from the external drive, the resonator will quickly enter into a nonlinear regime and has obvious nonlinear effect. Using analysis, in this case, based on liner theory will lead to errors, so this thesis will carry out vibration performance of resonator of graphene nano-beam using nonlinear governing equations and simulates it by using molecular dynamics simulations. The specific contents of research are introduced as follows.Firstly, a briefly introduction of graphene properties and research status were introduced in this thesis. And the research progress of nanomechanical resonator at domestic and abroad at present were summarized.Secondly, based on the continuum model theory, the nonlinear governing equations of the nano-beam was build under the electrostatic drive mode, and considering the vander waals force introduced by very small gap. Then the nonlinear vibration of the graphene nano-beam resonator was analyzed by means of finite difference method and fast fourier transform. It is shown that graphene nano-electromechanical devices frequency have a phenomenon of migration from the natural frequency and shift to the right under the condition of unchanged AC amplitude and the smaller DC voltage. When DC voltage is larger, the frequency of the resonator shift to the right. The frequency offset is less effected by AC amplitude, and mainly influenced by DC bias voltage.Thirdly, the molecular dynamics simulation was used in this thesis to study the natural frequency of the graphene resonator, and the electrostatic force equivalent method was adopted to simulate graphene nano beam resonator under different external force, comparing the result with the theory of the continuum model. Results obtained by molecular dynamics simulation of frequency values are higher than the value using the continuum model theory. Through theoretical formula on the continuum model to add items to eliminate residual stress the frequency difference, According to the simulation result, it is shown that with the increasing of applied voltage the corresponding residual stress raises.In this thesis, the studying of the nonlinear characteristics of nano-electromechanical devices by the theory of continuum model method and molecular dynamics method will provide the theoretical foundation for subsequent experimental and data support, and for the application of graphene resonators in the quality of sensors and the mechanical sensors.