Mechanical Measurement And Subsurface Imaging Based On Contact Resonance Atomic Force Microscopy

With the invention of new nanomaterials,dimension reduction of devices,and technology development in the microscale and nanoscale,high-resolution,precise and convenient measurement are of necessity.As one of scanning probe microscopy with nano spatial resolution,atomic force microscopy is widely utilized due to the advantages of simple sample preparation,varied working environments and nondestructive measurement.Many modules based on atomic force microscopy are invented to extract local properties,which include electric conductivity,magnetic permeability and mechanical strength.And precise characterization of mechanical properties becomes an important demand for the applications of new materials and devices.As representative characterization technique,contact resonance atomic force microscopy has been developed and investigated widely.In the aspects of theoretical basis,practical application and imaging optimization,some works on this technique have been carried out.However,there remain many critical problems to solve,which include more precise measurement of mechanical parameters,potential applications of subsurface imaging,characterization capability improvement and so on.We carry out investigations on these aspects based on contact mechanism and cantilever vibration model.Firstly,we analyze the contact between the tip apex and sample surface,and induce the transfer function from contact stiffness to Young’s modulus by Hertz,DMT and JKR mechanical models.The relation between resonance frequency and contact stiffness is derived according to Euler-Bernoulli equation with the boundary conditions of tip side.The cantilever vibration model for harmonic atomic force microscopy is also analyzed.Through finite element analysis and theoretical simulation,we obtain contact resonance frequency and harmonic amplitude,respectively.These calculation mothods provide basic implements for further investigations.Then,we carry out quantitative mechanical measurement in the nanoscale.Contact resonance atomic force microscopy is utilized to measure Young’s modulus precisely through acquiring contact spectra on the sample,and transferring resonance frequencies to Young’s moduli with cantilever vibration model and contact mechanism.Then to investigate interfacial properties,we continuously image the topography of buckles,and observe the delamination evolution and interface deterioration.Through fitting elastic strain energy with buckle area,we obtain the adhesion strength of interfaces between thin film and elastic polymers.After that,we apply contact resonance atomic force microscopy for subsurface characterization based on pratical applications.Edge-clamped circular freestanding plate model is established to approximate embedded defects.Semi-analytical solution for axisymmetric indentation problem of a tip contacting with a multilayered sample is utilized to characterize flexible circuits.For lateral etching in fabrication proceduces,we quantatively analyze the etching speedwith defomation model of center-supported rectangular or circular thin plate under a concentrated force.We also investigate other interfacial detaching phenomena besides buckles between graphite and polymers.Lastly,we propose cantilever structure optimizations to improve the characterization capability.Facing the acute frequency sensitivity decrease with the increase of contact stiffness,we attach a mass on the tip side.And to enhance contact resonance atomic force microscopy and harmonic atomic force microscopy simultaneously,we design multifunctional cantilevers through removing or adding mass.For facilitating mechanical characterization using contact resonance atomic force microscopy,we tailor the cantilever structure to linearize the frequency-stiffness relation.