Electrostatic Force Microscope

Dielectric relaxation of supported polymer films was measured for dry as well as wet samples by using the LDS method. A Veeco Multimode AFM (Nanoscope Ilia with ADC5 extension) was adapted to a frequency-modulated electrostatic force microscope (FM-EFM) and operated in lift mode (details are reported in Refs. [41, 47]) FM-EFM with improved bandwidth was here implemented through a RHK Technology PLLProll phase-locked-loop (PLL) frequency detector, having a nominal response bandwidth of 4 kHz that could be extended to about 10 kHz by... 

Electrophoresis (qv), ie, the migration of small particles suspended in a polar Hquid in an electric field toward an electrode, is the best known effect. If a sample of the suspension is placed in a suitably designed ceU, with a d-c potential appHed across the ceU, and the particles are observed through a microscope, they can all be seen to move in one direction, toward one of the two electrodes. AH of the particles, regardless of their size, appear to move at the same velocity, as both the electrostatic force and resistance to particle motion depend on particle surface this velocity can be easily measured. 

All this being said, perhaps the most definitive study of the relative roles of electrostatic and van der Waals forces was performed by Gady et al. [86,101,102]. In their studies, they attached a spherical polystyrene particle, having a radius between 3 and 6 p.m, to the cantilever of an atomic force microscope. They then conducted three distinct measurements that allowed them to distinguish between electrostatic and van der Waals forces that attracted the particle to various conducting, smooth substrates. 

Butt, H.J., Measuring electrostatic. Van der waals, and hydration forces in electrolyte-solutions with an atomic force microscope. Biophys. J., 60(6), 1438-1444 (1991). 

A very similar technique is atomic force microscope (AFM) [38] where the force between the tip and the surface is measured. The interaction is usually much less localized and the lateral resolution with polymers is mostly of the order of 0.5 nm or worse. In some cases of polymer crystals atomic resolution is reported [39], The big advantage for polymers is, however, that non-conducting surfaces can be investigated. Chemical recognition by the use of specific tips is possible and by dynamic techniques a distinction between forces of different types (van der Waals, electrostatic, magnetic etc.) can be made. The resolution of AFM does not, at this moment, reach the atomic resolution of STM and, in particular, defects and localized structures on the atomic scale are difficult to see by AFM. The technique, however, will be developed further and one can expect a large potential for polymer applications. 

Another alternative prototype of memory array, consisting of data stored as electrostatic charge or molecular dipole in a two-dimensional network of streptavidin cross-linked by biotinylated porphyrin derivative, was also suggested. Information reading was expected to be carried out using the electric force mode of the atomic force microscope [70]. 

Other explanations of the nature of the polymer to metal bond include mechanical adhesion due to microscopic physical interlocking of the two faces, chemical bonding due to acid/base reactions occuring at the interface, hydrogen bonding at the interface, and electrostatic forces built up between the metal face and the dielectric polymer. It is reasonable to assume that all of these kinds of interactions, to one degree or another, are needed to explain the failure of adhesion in the cathodic delamination process. 

The force microscope, in general, has several modes of operation. In the repulsive-force or contact mode, the force is of the order of 1-10 eV/A, or 10 -10 newton, and individual atoms can be imaged. In the attractive-force or noncontact mode, the van der Waals force, the exchange force, the electrostatic force, or magnetic force is detected. The latter does not provide atomic resolution, but important information about the surface is obtained. Those modes comprise different fields in force microscopy, such as electric force microscopy and magnetic force microscopy (Sarid, 1991). Owing to the limited space, we will concentrate on atomic force microscopy, which is STM s next of kin. 

In atomic force microscopy (AFM), the sharp tip of a microscopic probe attached to a flexible cantilever is drawn across an uneven surface such as a membrane (Fig. 1). Electrostatic and van der Waals interactions between the tip and the sample produce a force that moves the probe up and down (in the z dimension) as it encounters hills and valleys in the sample. A laser beam reflected from the cantilever detects motions of as little as 1 A. In one type of atomic force microscope, the force on the probe is held constant (relative to a standard force, on the order of piconewtons) by a feedback circuit that causes the platform holding the sample to rise or fall to keep the force constant. A series of scans in the x and y dimensions (the plane of the membrane) yields a three-dimensional contour map of the surface with resolution near the atomic scale—0.1 nm in the vertical dimension, 0.5 to 1.0 nm in the lateral dimensions. The membrane rafts shown in Figure ll-20b were visualized by this technique. 

Rosscll, J.P. et al.. Electrostatic interactions observed when imaging proteins with the atomic force microscope, Ultramicmscopy, 96, 37, 2003. 

The first problem was to ensure that at the chosen frequency and amplitude the geometry remained constant as the field was varied. The electrostatic force across the condenser will act to pull the plate down on its mounting and raise the liquid surface below the plate in the center of the trough. The first effect was negligible, and microscopic movements of... 

M3. Muller, D. J., Fotiadis, D., Scheuring, S., Muller, S. A., and Engel, A., Electrostatically balanced subnanometer imaging of biological specimens by atomic force microscope. Biophys. J. 76, 1101-1111 (1999). 

C. Rotsch and M. Radmacher, Mapping local electrostatic forces with the atomic force microscope, Langmuir, 13(10), 2825-2832 (1997). 

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