-
[show abstract]
[hide abstract]
ABSTRACT: We have investigated experimentally the role of cantilever instabilities in determination of the static mode force-distance curves in presence of a dc electric field. The electric field has been applied between the tip and the sample in an atomic force microscope working in ultra-high vacuum. We have shown how an electric field modifies the observed force (or cantilever deflection)-vs-distance curves, commonly referred to as the static mode force spectroscopy curves, taken using an atomic force microscope. The electric field induced instabilities shift the jump-into-contact and jump-off-contact points and also the deflection at these instability points. We explained the experimental results using a model of the tip-sample interaction and quantitatively established a relation between the observed static mode force spectroscopy curves and the applied electric field which modifies the effective tip-sample interaction in a controlled manner. The investigation establishes a way to quantitatively evaluate the electrostatic force in an atomic force microscope using the static mode force spectroscopy curves.
Ultramicroscopy 08/2012; 122C:19-25. · 2.47 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We show that the static force spectroscopy curve taken in an atomic force microscope is significantly modified due to presence of intrinsic cantilever instability which occurs as a result of its movement in a nonlinear force field. This instability acts in tandem with such instabilities as water bridge or molecular bond rupture and makes the static force spectroscopy curve (including 'jump-off-contact') dependent on the step size of data collection. A theoretical model has been proposed to explain the data. We emphasize the necessity of taking care of this fundamental instability of the microcantilever in calculating the adhesive force and also in the interpretation of data taken using an atomic force microscope.
Nanotechnology 12/2009; 21(4):045706. · 3.98 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We show that the static force spectroscopy curve is significantly modified due to presence of intrinsic cantilever instability. This instability acts in tandem with such instabilities like water bridge or molecular bond rupture and makes the static force spectroscopy curve (including "jump-off-contact") dependent on the step-size of the movement of sample stage. A model has been proposed to explain the data. This has been further validated by applying an electric field between tip and substrate which modifies the tip-substrate interaction.
11/2008;
-
[show abstract]
[hide abstract]
ABSTRACT: In this paper, we describe the effects of nonlinear tip-sample forces on dynamic mode atomic force microscopy and spectroscopy. The jumps and hysteresis observed in the vibration amplitude (A) versus tip-sample distance (h) curves have been traced to bistability in the resonance curve. A numerical analysis of the basic dynamic equation was used to explain the hysteresis in the experimental curve. It has been found that the location of the hysteresis in the A-h curve depends on the frequency of the forced oscillation relative to the natural frequency of the cantilever.
Journal of Nanoscience and Nanotechnology 07/2007; 7(6):2167-71. · 1.56 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We find that the 'jump-into-contact' of the cantilever in the atomic force microscope (AFM) is caused by an inherent instability in the motion of the AFM cantilever. The analysis is based on a simple model of the cantilever moving in a nonlinear force field. We show that the 'jump-into-contact' distance can be used to find the interaction of the cantilever tip with the surface. In the specific context of the attractive van der Waals interaction, this method can be realized as a new method of measuring the Hamaker constant for materials. The Hamaker constant is determined from the deflection of the cantilever at the 'jump-into-contact' using the force constant of the cantilever and the tip radius of curvature, all of which can be obtained by measurements. The results have been verified experimentally on a sample of cleaved mica, a sample of Si wafer with natural oxide and a silver film, using a number of cantilevers with different spring constants. We emphasize that the method described here is applicable only to surfaces that have van der Waals interaction as the tip-sample interaction. We also find that the tip to sample separation at the 'jump-into-contact' is simply related to the cantilever deflection at this point, and this provides a method to exactly locate the surface.
Nanotechnology 02/2007; 18(3):035501. · 3.98 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We present an experimental investigation of the variation of the amplitude of vibrating microcantilever, as a function of distance (h) between the microcantilever and the sample in a Dynamic Force Microscopy (DFM) and explain the observations with a theoretical model. In DFM, as the cantilever tip approaches the sample, neither the force nor the response of the cantilever is in the linear regime. We present an exact numerical solution to the equation of motion of the oscillations of the microcantilever and present a quantitative explanation to the observed force versus distance curves, in terms of the resonance curves. We show that the change in the resonance frequency of the cantilever due to the atomic forces is highly nonlinear.
Emerging Technologies - Nanoelectronics, 2006 IEEE Conference on; 02/2006
