چكيده به لاتين
Atomic force microscopy (AFM) is considered as a powerful and leading tool in the nanotechnology, which is capable of imaging from conductive and non-conductive surfaces with atomic local separation. This thesis investigates the AFM piezoelectric micro-cantilever vibrational behavior with rectangular cross-section in different environments. Vibrational behavior analysis of AFM in dynamic mode which is consisted of non-contact and tapping modes is done.
Timoshenko’s beam theory is used for modeling and Micro-cantilever has been modeled by using Hamilton’s principle with considering geometrical discontinuities and in order to discrete equations of motion, finite element method is used. The dynamic of this system is affected by internal forces between probe tip and sample surface, including Van der Waalse, Capillary and contact forces. Also in liquid environment, the simulation is done according to the changes caused by fluid presence around the micro-cantilever.
Simulation results showed that in air environment, the tip-sample forces caused the reduction in amplitude and in resonant frequency, too. The surface topography results showed that piezoelectric micro-cantilever behavior in the sample surface topography in higher modes and specially in the tapping mode than the non-contact mode is improved, time delay decreased and showed a more accurate figure of roughness.In fluid environment with the reduction of micro-cantilever gap, because of intensifying fluid squeeze force, the vibrational amplitude and micro-cantilever frequency decreased and also vibrational behavior Sensitivity of the angular micro-cantilever than the squeeze force is decreased because of the reduction of this force and increasing the probe length leads to decrease in the squeeze force; consequently, it has an effect on increasing the vibrational amplitude. In investigation of micro-cantilever vibrational behavior in liquid environment, also the shear force on micro-cantilever is studied and observed that amplitude and frequency are decreased with cosidring this force. Topography simulation results in liquid environment in amplitude mode, showed time delay reduction than the air environment.
In order to investigation of micro-cantilever vibrational behavior sensitivity than the geometrical parameters chenges, sensitivity analysis is done. Results of sensitivity analysis showed that the most effective parameter on amplitude and frequency is the length of micro-cantilever. In the first mode, micro-cantilever first section length has the most effect on amplitude, topography depth and time delay while in the second mode the greatest effect is related to the tip length. Also the result showed that the effect of equilibrium distance on the micro-cantilever amplitude is more than the other constant that its effect is greater with increasing moisture.
