Doctor of Philosophy
Mechanical and Materials Engineering
To measure force by AFM with high resolution requires accurate calibration of optic – lever detection sensitivity and spring constant. On biological AFM force mode, the coupling effects of the liquid environment, spot size of laser beam and laser spot location on AFM cantilever backside, must be considered to correlate the static sensitivities from force curves in air and in liquid for calibration. An effective model has been developed first and experimentally elucidated to calibrate the static sensitivity in liquid. The proposed model eliminates inconvenience of static sensitivity calibration in liquid with possible contamination sources.
The static sensitivity based on force curve can not be directly applied on dynamic modes. The second part of our work analyzed optimization of the dynamic sensitivity of an AFM vibrating at different flexural modes. We have proposed a calibration method to determine the dynamic sensitivity by the force curve, and further developed amplitude sensitivity as the dynamic sensitivity at tapping frequency to calibrate the spring constant of the cantilever by the thermal method.
In contrast to the calibration at normal direction, there are main difficulties for the lateral sensitivity and spring constant of a cantilever. A new friction mode is developed in the third part to bypass the difficulties and directly measure friction force or friction coefficient instead, by applying a special T–shape cantilever. An effective method has been proposed to minimize possible errors with this friction mode. We also demonstrate the validation of the mode to distinguish hydrophobic and hydrophilic groups at nanoscale.
Liu, Yu, "Atomic Force Microscopy for Better Probing Surface Properties at Nanoscale: Calibration, Design and Application" (2010). Electronic Thesis and Dissertation Repository. 21.