The Weak Signal Detection System And Technology Research Of The Probe Oscillation Of Non-Contact Atomic Force Microscopy

Atomic Force Microscope(AFM)has become the most popular observation and operation tools in the field of modern surface science rely on its ultra-high resolution,it has application prospects in many fields of cutting-edge research.AFM not only can be applied to all sorts of new materials surface research such as semiconductors,insulators,but also can operate atoms/molecules on surface.These promote the development of atomic device.The weak signal detection of probe oscillation is a core technology in AFM,the sensitivity of cantilever deflection detection sensor is one of the important influence factors for evaluating the performance of AFM.At present,the most popular weak signal detection system is Optical Beam Deflection(OBD)detection system which is easy to operate,but its noise level is higher than Optical Interference detection method.Now many researches require the ultra-high resolution of AFM,but only a few institutions research how to reduce noise levels.Therefore,the optimization of OBD detection system was researched in this paper,details are as follows:Firstly,the principle of AFM was studied in detail,and the advantages and disadvantages of various kinds of cantilever deflection detection methods were analyzed.Through researching the design theory of traditional OBD detection methods,a new method was proposed for improving sensitivity and reducing noise.Then the new OBD detection system was designed which was equipped with the circuit for amplifying,filtering and calculating.Second,specifically testing the new OBD detection system.Comparing with the traditional OBD detection system,the new design had a better quality of laser,the optical beam path was easy to adjust in three directions,and it had an ability that the alignment of optical beam path can be confirmed intuitively.Third,the probe oscillation test and the system noise determination was experimented using the new OBD detection system.We got the resonance frequency of probe with higher quality factor,then through calculating thermal noise and testing the total noise,we determined the noise level of system.It is a certification that the new OBD detection system has a high sensitivity and low noise performance.Fourth,testing image resolution using our homemade Ultra-High Vacuum Room Temperature Non-Contact Atomic Force Microscope(UHV-RT-NC-AFM)with the new OBD detection system.We verified system functions of measuring Contact Potential Difference(CPD)and force spectroscopy between probe and sample,so that we could compensate the influence of electrostatic force between the probe and sample,and illustrated the relationship between interaction and distance of atoms.Through the experiment we got the step image of Si(111)surface and the topography image with atomic resolution.These are certifications that the new OBD detection system has a high sensitivity and low noise performance and AFM can get atomic resolution images.Above all,we improved the sensitivity of OBD detection system and reduce the system noise through researching and designing,finally improved the resolution of AFM.We developed a new path to independently research and develop instruments of precision measuring,had an important theory significance and practical application value.