The Dynamics Of Quartz Tuning Fork And Its Application On Conduction Mechanism Of RGO/AuNPs

Scanning probe microscope(SPM)is the most effective method of nanoscale performance characterization,its choice of sensors determines accuracy,stability,measurement range and applied range of the nanoscale performance characterization.Quartz tuning forks have high quality factor,high elasticity coefficient and self-excitation detection,and other advantages,thus they can be adapted to various extremely environment.They have been widely used in SPM by replacing micromechanical cantilever sensors.However,the asymmetrys and nonlinear vibration of quartz tuning forks will cause system errors of calibration,and severely impact the accuracy of nanomechanical measurement.This problem needs to be efficiently addressed.In this paper,the amplitude ratio and the phase difference of two prongs were introduced as asymmetry vibration parameters,two coupled harmonic oscillators model of the quartz tuning forks was re-studied,and the impact of asymmetry force gradient,damping and mass difference between two prongs on calibration constant was discussed.The asymmetry vibration of the quartz tuning forks caused by force gradient and damping to be due to elastic coupling on the base,the quartz tuning forks generated frequency shift and amplitude ratio change by force gradient,and meanwhile force gradient was positively correlated and negative correlated with frequency shift and amplitude ratio change,respectively;the quartz tuning forks generated excitation voltage change and phase difference by damping,and meanwhile damping was positively correlated and negative correlated with excitation voltage change and phase difference,respectively.Although force gradient and damping would generate asymmetry vibration of quartz tuning forks,they do not affect the calibration constant relation.mass difference has a linear relation with calibration constant,and severely impact the calibration constant.We have designed an in-situ calibration method of quartz tuning forks.This method based on a self designed dual-output phase locked loop(PLL)and a laser illumination system implementation.We controlled quartz tuning fork stable oscillation by one output of the dual-output PLL,the other output of the dual-output PLL load to laser,and load alternating force to a prong quartz tuning fork by photothermal excitation theory,to achieve quantitative simulation of force gradient and damping of the tip-sample interaction.We acquired quantitative relation between measurement informations and detection signal by this calibration method,decoupled the conservative and dissipative forces between tip and sample.The S4 quartz tuning fork based on this calibration method was used to measure interactive force between carbon fiber tip and highly oriented pyrolytic graphite surface.The results showed that frequency shift caused by damping to the total frequency shift reached 36.15 % in maximum,and excitation voltage change caused by force gradient to the total excitation voltage change reached 8.15 % in maximum.These results embodied that the calibration method developed in this paper can significantly increase nanomechanical measurement accuracy of the quartz tuning forks.We researched batch quartz tuning forks of the different mass difference by this calibration method and the results showed that the calibration constant do not show any regular variations verifying this relates to deep structural factors of quartz tuning forks.From the view of current research,quartz tuning forks as nanomechanical sensor must be calibrated before use.We developed electrostatic force microscope(EFM)and kelvin probe force microscopy(KPFM)based on the quartz tuning forks,and the measurement of nanoscale surface topography,electrostatic force and contact potential difference was realized.Research methods of EFM,KPFM and measurement of the conductivity of different temperature were combined to study the electrical properties the typical nano devices composed of reduced graphene oxide(rGO)/gold nanoparticles(AuNPs).The results showed that the conductivity of rGO was enhanced for 3 orders of magnitude due to the introduction of AuNPs,and its maximum value reached 88.54 S/m.AuNPs as nano electrodes disperse the micron-scale rGO nanosheets into a great number of nanoscale rGO devices,result in the short circuit of rGO,narrowing the gap distance,thus improving the conductivity of rGO.