Quantitative imaging of subsurface structures and mechanical properties at nanoscale using atomic force microscope

The atomic force microscope (AFM) is a powerful instrument to image topography, mechanical, electrical, and magnetic properties of surfaces at nanoscale. This dissertation focuses on quantitative subsurface and mechanical properties imaging potential of AFM probes. In this work, extensive modeling of AFM probes is presented for thorough understanding of capabilities and limitations of current techniques, these models are verified by various experiments, and different methods are developed by utilizing a force-sensing integrated read-out active tip (FIRAT), which is an active AFM probe with broad bandwidth. These recently introduced methods aim to provide more accurate topography imaging and more sensitive elasticity mapping by AFM on composite materials.;For quantitative subsurface imaging, a 3-D FEA model of AFM tip-sample contact is developed and this model can simulate AFM tip scan on nanoscale-sized buried structures. The 3-D FEA contact model is verified experimentally by employing ultrasonic AFM methods. The simulation results show that one can detect the presence of nanometer-sized subsurface structures by utilizing sensitive elasticity imaging at the nanoscale.;FIRAT, which is active and broadband, is utilized for interaction force imaging during intermittent contact mode and the mechanical characterization capability of this probe is investigated in this dissertation. Analytical and Simulink models are used to study several parameters such as dynamics and material properties. According to the simulation results; probe dynamics, stiffness, stiffness ambiguity, the assumed contact mechanics model, and noise are important parameters that determine the error rates on the measured mechanical properties.;In intermittent contact mode AFM, lowering contact force may result in instability in the imaging and users don't have direct control over the contact forces. To solve this issue, the active nature and high bandwidth of FIRAT probe are utilized and an active tip control (ATC) method is introduced. An experimental set-up for ATC is designed and experimental studies that verify the increased accuracy in topography imaging are performed.;Accuracy of elasticity measurement by AFM highly depends on the probe stiffness and it decreases when the surface stiffness does not match probe stiffness. This constitutes a challenge on the samples with different stiffness regions, such as nanobeads on polymers. A combined ultrasonic AFM and interaction force imaging method is introduced to solve the reduced elasticity measurement sensitivity on stiff materials. An experimental set-up is built to test this idea, the calibration steps for quantitative analysis are determined, and the increased elasticity sensitivity of the combined operation is verified.