N. Ebrahimi

Nonlinear dynamics of tapping-mode atomic force microscopy in liquid

One problem in imaging is due to coexistence of double stable responses which can reduce the precision of the images. Our target is comparing coexistence of double responses in liquid with responses obtained in air. Contact forces have some differences in liquid in comparison to air in magnitude and in the formulation. Hydrodynamic forces are also applied on the cantilever. This may change the nonlinear dynamics of tapping-mode Atomic Force Microscopy (AFM) in liquid in comparison to air. In this paper, we have simulated a tapping-mode AFM (TMAFM) cantilever in liquid environment and explored the existence of multi responses in amplitude and phase diagrams. For modeling we have used a continuous beam model with its first mode and forward-time simulation method for the solution of its hybrid dynamics. Frequency response results of the simulation show a good agreement with experiments. The results for studying the nonlinear dynamics of an AFM microcantilever show that while there are two stable responses in...

Exploring the tip-sample interaction regimes in the presence of hysteretic forces in the tapping mode atomic force microscopy

In this article, the tip-sample interaction regimes in the presence of hysteretic forces are investigated using atomic force microscopy in the tapping mode. For this purpose, two samples that cause the formation of hysteretic forces, namely, silicon (stiff sample) with an adsorbed water film and polyethylene (compliant sample), are used. Also, for deriving the equation of motion of the microcantilever, the continuous beam model is used, and for determining the contact forces, depending on the sample under investigation, the Derjaguin–Muller–Toporov and Johnson–Kendall–Roberts contact mechanics models are used. The results indicate that the hysteretic interaction forces generate high-periodic and irregular responses at certain tip-sample separation distances. In fact, at these distances, a family of steady-state attractors is found that can be observed in one branch on the minimum tip-sample separation curves and in two separate branches on the average force curves. The reason for this occurrence might be ...

Dynamics of carbon nanotube tipped atomic force microscopy in liquid.

Carbon nanotubes (CNT) are proper tips for atomic force microscopes (AFMs) as a result of their small tip diameter, high aspect ratio, and high flexibility. For nanoscale imaging of soft biological specimens, a CNT tipped AFM is an ideal tool. In this article we review the application of CNTs as AFM tips and present related research about the forces applied from liquids on nanotubes. Then a dynamic mode CNT tipped AFM in liquid is modeled and simulated. The simulation results are compared with experimental results. For modeling and simulation, a continuous beam model and a forward-time simulation method are used. The simulation results show that when a CNT tip vibrates in liquid, the oscillation amplitude and resonance frequency are changed compared to the state of oscillation in air. The small structure of CNTs reduces the hydrodynamic forces, and the liquid environment reduces the adhesive forces between the CNT tip and the sample. These two factors make CNTs a good choice as an AFM tip.

Dynamics of TMAFM in liquid: Application to molecular metrology and biological sciences

Application of atomic force microscopy (AFM) in liquid is necessary for imaging and manipulation of biological specimens. The atomic force microscope (AFM) has become an indispensable tool in biology because it permits the imaging and probing of nanomechanical properties of biological samples such as biopolymers and viruses under physiological (liquid environments) conditions. In this paper, we have simulated a tapping-mode AFM (TMAFM) cantilever in liquid environment near a surface. Contact forces have some differences in liquid in comparison to air or vacuum in magnitude or formulation. Hydrodynamic forces are also applied on the cantilever due to the motion in liquid. For modeling we have used a continuous beam model with its first mode and forward-time simulation method for simulation of its hybrid dynamics. The results show a good agreement with experiments. They also show that the effect of separation on free vibration amplitude is great. Its effect on resonance frequency is considerable too. The resonance frequency in liquid is so small in comparison to air due to additional mass and also additional damping created by the viscosity of the liquid around.