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Surface properties such as adhesion are influenced by the surface topography. This dependency complicates any quantitative investigation of the material constants. A simple and efficient model is used to calculate the influence of the topography on the pull of force determined by a scanning force microscope (SFM). In the model the SFM tip is represented by a sphere. The sample surface is modeled by two geometries: a step on a plane and a blister (spherical cap) on a plane. The atomic interaction between the tip and the surface is of the Lennard-Jones type. The theoretical results are compared with SFM-measurements on highly oriented pyrolytic graphite (HOPG) in electrolytic environment. The calculations are in good agreement with the measured images.The SFM has become an indispensable tool for surface investigations on the nanometer scale. With the SFM it is possible to image the sample topography and properties such as friction [1-3], local stiffness [4], the adhesive force [5-8], and magnetic [9] and electrical forces [9]. In order to investigate these properties, specialized measurement modes are used. One main interest in SFM investigations is to determine macroscopic material constants, such as the friction coefficient, on a microscopic scale. It has been shown that this is very difficult. To determine the influence of material parameters on the measured signals the interaction between the tip and the sample has to be examined. Because material properties are often not directly accessible and the measured signal depends nonlinearly on various parameters, it is necessary to compare simulations and measurements.When formulating a theory, one can have two sometimes contradicting aims: either one focuses on the behavior of the interaction between the tip and the sample or one is interested in explaining the results of a specific experimental setup. The first concept is represented by the theories of Hertz [10], Johnson et al. [11], Derjaguin et al. [12], and Maugis [13]. * Corresponding author These theories describe the interactions necessary to the understanding of the tip-sample system. The second concept is exemplified by the works of Burnham [14] and Rabe [15].Their goal is to compare computer simulations with a real experiment. The model for the SFM typically consists of a sphere or point mass representing the tip and a plane representing the sample. However, these simplifications often make a comparison between the theoretical and the measured results impossible. For example, the representation of the surface by a plane is not sufficient if the calculations should describe the dependence on topographical changes. Investigating surface properties, e.g. the adhesive force, on a corrugated sample, one notices that SFM images show a change in the properties correlated with topographical features. The adhesive force often decreases strongly at slopes even if the height differences at the surface are rather small (see SFM images in Fig. 1).It is interesting to explore whether these variations in the adhesive fo...

The tip-sample distance in near-field scanning optical microscopy is typically controlled by the shear-force interaction between the laterally vibrating tip and sample. In this article, a mode of shear-force feedback is described in which an additional vertical modulation is introduced. Similar to the tapping mode applied in atomic force microscopy, the modulated shear-force technique deals with problem due to the snap to contact and therefore improves the mapping of soft and ductile materials, such as biological samples and soft polymers. The imaging properties of the modulated shear-force mode is demonstrated on structures of a soft polymer blend. Additionally, the modulated shear-force technique allows a simple comparison between effects in the optical far field and in the optical near field.

Articles you may be interested inMorphological observation and adhesive property measurement on human ovary carcinoma cells by atomic force microscopy J.The combination of two well-established dynamic scanning force microscopy ͑SFM͒ modes is incorporated for SFM in combined dynamic X mode or CODY Mode® SFM. A vertical modulation of low frequency and large amplitude is superimposed with a second vertical modulation of high frequency and low amplitude leading to a combination of pulsed force mode SFM, force modulation, and phase sensitive SFM. SFM in the new mode allows the simultaneous mapping of a number of physical surface properties including adhesive force and elasticity over one scan. The new SFM technique is nondestructive and alteration or even destruction of the sample surface is reduced to a minimum. A polymer blend ͑two homopolymers spin coated on silicon from a tetrahydrofuorane solution of a mixture of poly-2-vinylpyridin and polytertbutylmethacrylate͒ was used as a sample for comparative measurements between pulsed force mode, force modulation mode and the new SFM mode.

Regardless of all the great progress in new scanning probe microscopy techniques, the concurrent measurement of adhesive and frictional forces with local resolution using scanning force microscopy (SFM) has not been possible until now. In this paper, we present a novel scanning probe microscopy mode, called combined dynamic x mode or CODYMode®. In CODYMode® SFM at least two oscillations with sufficiently different frequencies and amplitudes are superimposed and interact with the sample surface. This enables the concurrent measurement of the topography, adhesive and frictional forces beside further mechanical surface properties of the sample. By means of the characterization of plasma treated biaxially oriented polypropylene foils the benefits of the new modulation technique are pointed out where common SFM techniques are not adequate. As second application high-velocity friction experiments (in the range of several centimeters per second) on silicon under controlled environmental conditions are introduced and the role of the native water film on it is discussed under friction and viscoelastic aspects.

In this letter, we present a promising scanning probe microscopy mode, called combined dynamic X mode or short CODYMode®. In CODYMode® scanning force microscopy, at least two modulations with sufficiently different frequencies and amplitudes are superpositioned and interact with the sample surface. This enables the concurrent measurement of the topography, adhesive and frictional forces, and further mechanical surface properties of the sample. The general advantages of CODYMode® are discussed. This technique is predestined for investigation of delicate samples (polymers, biological samples, etc.) in which common scanning force microscope techniques are not adequate. An ABC-triblock copolymer system served as sample system.

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