Force volume imaging

These include contact force imaging (CFI) mode, in which the tip is scanned across the sample surface at constant force, tapping mode in which the tip oscillates close to the surface enabling either the forces or phase relationships between load and displacement to be used to form the image, and local force spectroscopy or force/volume imaging in which the variation of force with tip/sample separation at a point can be used to study local interachons. 

Gaboriaud, E, Parcha, B. S., Gee, M. L., Holden, J. A., and StrugneU, R. A. 2008. SpatiaUy resolved force spectroscopy of bacterial surfaces using force-volume imaging. Colloids Surfaces B-Biointerfaces 62, 206-213. 

FIGURE 9.17 A 20 X 20 jun amplitude image of the PU sample after several 16 X 16 force—volume tests in the same area. (From Huson, M.G. and Maxwell, J.M., Polym. Test., 25, 2, 2006.)... 

FIGURE 21.15 The results of force-volume measurement on NRIO sample, (a) Apparent height image, (b) reconstmcted real height image, and (c) Young s modulus distribution image. The maximum load was set to 6.0 nN. 

Another recent example of the use of CFM for polymer surfaces is force-volume mapping of stabilized polypropylene films (process stabilizers, UV-stabilizers and antioxidants) [186,187]. The mapping was performed using methyl- or hydroxy- functionalized tips in water or in nitrogen atmosphere. Differences in the pull-off forces between the additives and polypropylene allowed imaging with sub-micrometer resolution of the lateral distribution of the additives present on the surface. By performing pull-off measurements on spin-coated films of pure additives, characteristic pull-off force values were obtained, which made it possible to discriminate between the antioxidant. 

A fundamental problem in force volume mode is the relatively long acquisition time that can easily amount to tens of minutes and can give rise to excessive drift. This and the memory usage for storing all data points limit the resolution of the force maps to typically 64 x 64 data points compared to the typical 512 x 512 pixels for standard AFM images. A critical point that has hindered the widespread use of force volume is automated data evaluation, which is currently not part of standard AFM software of the commercial suppliers. Since some thousand force curves have to be evaluated for each data set, sophisticated software routines have to be developed by the users for automated analysis to efficiently use force volume mode. 

The principal equipment for the ultrasonic examination is the P-scan system, PS-4, which is a computerised ultrasonic system, developed by FORCE Institute, for automatic, mechanical and manual ultrasonic examination of welds and materials. The system has documentation and storage facilities for all data related to each inspection operation, and includes visualisation of the inspection results in the form of images of the material volume examined. 

Every method, with the exception of imaging technologies, provides the measurement of an equivalent spherical diameter in one form or another. The spherical diameter information can be deduced indirectiy from the behavior of the particles passing through restricted volumes or channels under the influence of gravity or centrifugal force fields, and from interaction with many forms of radiation. 

---