Design AFM Probe For Ultra-low Coefficient Of Friction Measurement In Nanoscale And Single-asperity Contact

With the continuous development of science and technology,atomic force microscope(AFM)related technology is becoming increasingly advanced,greatly promoting the understanding and research in the field of micro-tribology.Nowadays,AFM has been widely used in nano-tribology,micro-and nano-fabrication,as well as the study of super-lubricity phenomena in micro-and nano-scale.With the continuous development of super-lubricity technology,ultra-low friction phenomena(coefficient of friction(CoF)is less than or equal to 0.001)have been successively observed,and the friction and its resultant wear are ultra-low.If the super-lubricity is intensively used in the near future,it will be a significant progress in the history of science and technology,and thereby,it is of extremely important theoretical and engineering application value to achieve super-lubricity and to study its mechanism.However,the CoF measurement resolution of most AFMs is quite limited,which makes it difficult to measure the ultra-low CoF accurately and reliably.To resolve the problem,it is urgent to study AFM's measurement principle of CoF,and subsequently put forward a solution to realize an accurate and reliable measurement of ultra-low CoF.Therefore,in this thesis,the method of achieving ultra-low CoF measurement based on the AFM probe design has been systematically studied.Through establishing a theoretical model pertaining to AFM probe,using finite element simulations and experiments to verify the correctness of the model,then fabricating the target size of the designed AFM probe with the focused ion beam technique,and then carrying out the ultra-low CoF measurement experiments,and ultimately providing a design method of the AFM probe,which is used to measure the ultra-low CoF in nanoscale single-asperity contact.The main results and innovations of this thesis are as follows:(1)The force measuring theory of AFM was summarized in this paper,as well as the formula of the optical lever sensitivity of AFM was deduced.What's more,the biggest positive pressure and the minimum friction on AFM were detailedly studied.Bsaed on which an AFM probe was designed to measure the ultra-low CoF,and a design method of the AFM probe,which is used to measure the ultra-low CoF in nanoscale single-asperity contact,was also proposed.(2)Through calibrating the normal optical lever sensitivity SN and the lateral optical lever sensitivity SL on SPI3800N,the theory of optical lever was verified.(3)Through the theoretical model pertaining to AFM probe,a commercial AFM probe achieving the biggest CoF resolution on MFP-3D was selected.(4)A commercial AFM probe was modified by FIB to do the ultra-low CoF measurement experiments.The results indicated that the goal about the CoF resolution raise 2 orders of magnitude was achieved on MFP-3D.The design method of the AFM probe,which is used to measure the ultra-low CoF in nanoscale single-asperity contact,can insure the authenticity and reliability of the CoF measurement in the super-lubricity experiment on AFM.Especially,it provides a kind of important auxiliary measures to reveal the process of friction energy dissipation ways and rules in the industries and scientific research fields,such as physics,chemistry,life science,aerospace,automotive,electronics,information etc.