Research On Multi-functional Scanning Kelvin Probe Force Microscopy

Scanning Kelvin probe force microscopy(S-KPFM)can realize nano-scale resolution imaging of the surface potential,which is one of the important methods for studying the electrical properties of materials.The more sophisticated and more complex development trend of micro-nano interface and structure puts forward higher requirements on S-KPFM.At present,S-KPFM has a single measurement parameter,limited resolution,and is difficult to measure the surface potential of a three-dimensional(3D)structure.In view of the above deficiencies,this dissertation starts with the model and theoretical simulation analysis of S-KPFM,and deeply researches on the open-loop measurement method,the design and preparation of a new Kelvin probe,the multiparametric simultaneous measurement method,and the 3D measurement method for the deep trench and the rotary body to make up for the shortcomings of the existing S-KPFM,and expand its application in surface/interface research.The open-loop KPFM based on dual-frequency excitation modulation(DFOL-KPFM)method is studied.In this method,the amplitude of the probe in the second-order mode is modulated by a superimposed low-frequency sinusoidal electrical excitation,and then the surface potential of the sample is calculated from the established solution model.The experimental results of in-situ characterization show that the proposed DFOL-KPFM is equivalent to the performance of the traditional closed-loop KPFM.In addition,it was verified that the proposed method can achieve high-precision measurement of the surface potential of conductors,semiconductors and insulator materials.The influencing factors of the cantilever homogenization effect in the surface potential measurement are analyzed.The KPFM based on the T-shaped probe for suppressing the homogenization effect is studied,and the T-shaped probe is prepared.The simulation results show that due to the structural symmetry of the T-shaped probe,when the torsion signal is used as the feedback signal of the surface potential measurement,the cantilever homogenization effect can be effectively suppressed in the amplitude modulation(AM)mode.At the same time,the orthogonality of the normal bending and torsional deformation of the T-shaped probe reduces the crosstalk of the measured signal,which effectively improves the energy resolution of the AM-KPFM.The experimental results compared with the traditional methods verify the ability of the proposed method to suppress thecantilever homogenization effect.A multiparametric KPFM(MP-KPFM)with peak force modulation is developed.The probe is periodically in contact with and separated from the sample during measurement: when the probe is in contact with the sample,the topography and nanomechanical properties are measured;when the probe is lifted,the adhesion and surface potential are measured.The experimental results show that the surface potential measurement performance of MP-KPFM is comparable to that of the traditional AM-KPFM.In addition,a composite probe consisting of a highly damped polymer cantilever and a silicon tip is designed and prepared to meet the requirements of high mechanical bandwidth and multiparametric measurements.Compared with traditional silicon probes,the mechanical bandwidth of the composite probe is increased by 4 times.Study on the 3D KPFM is carried out.The optic fiber probe with a large aspect ratio is used to solve the problem of measuring the surface potential of the trench bottom with a large aspect ratio in 3D structures/devices,and the cantilever homogenization effect is effectively reduced.This method has been successfully applied to the measurement of the deep-hole structure of the microbial fuel cell.Aiming at the measurement problem of the 3D surface potential of the rotary body,a multi-functional Kelvin probe test platform integrating the sample installation,position adjustment and rotation measurement is constructed,and the 360°rotation measurement for the surface potential of the micro-scale rotary body is realized.The measurement results of the zinc oxide microwire verify the feasibility of the proposed method.In summary,the DFOL-KPFM,the KPFM based on the torsion signal of the Tshaped probe,the MP-KPFM based on the force-displacement curve,and the 3D KPFM for specific 3D structures measurement are studied in this dissertation,which provide new methods and systems for the surface potential characterization,and have significant application potential in the surface science field.