Scanning force microscope

Li Y Q, Tao N J, Pan J, Garcia A A and Lindsay S M 1993 Direct measurement of interaction forces between colloidal particles using the scanning force microscope Langmuir 9 637... 

Scanning force microscopes use a sharp tip mounted on a flexible cantilever. When the tip comes within a few A of the sample s surface, repulsive van der Waals forces... 

Secondary Electron Microscopy with Polarization Analysis Scanning Force Microscopy Scanning Force Microscope... 

Sarid, D., lams, D., Weissenberger, V. and Bell, L.S., Compact scanning-force microscope using a laser diode. Opt. Lett., 13(12), 1057-1059 (1988). 

Whilman, L.J. and Colton, R.J., Design and calibration of a scanning force microscope for friction, adhesion, and contact potential studies. Rev. Sci. fnsirum., 66, I (1995). Ba.selt, D.R. and Baldeschwieler, J.D., Imaging spectro.scopy with the atomic-force microscope. J. AppL Pliys., 76(1), 33-38 (1994). 

Mazeran, P.E. and Loubet, J.L., Normal and lateral modulation with a scanning force microscope, an analysis implication in quantitative elastic and friction imaging. Tribal. Lett., 7(4), 199-212(1999). 

FIG. 13 Schematic drawing of writing with molecnles on S-layers. The tip of a scanning force microscope is nsed to drag-and-drop positively charged ferritin molecnles. 

The second device with which surface forces can be measured directly and relatively universally is the atomic force microscope (AFM) sometimes also called the scanning force microscope (Fig. 6.8) [143,144], In the atomic force microscope we measure the force between a sample surface and a microfabricated tip, placed at the end of an about 100 //,m long and 0.4-10 //,m thick cantilever. Alternatively, colloidal particles are fixed on the cantilever. This technique is called the colloidal probe technique . With the atomic force microscope the forces between surfaces and colloidal particles can be directly measured in a liquid [145,146], The practical advantage is that measurements are quick and simple. Even better, the interacting surfaces are substantially smaller than in the surface forces apparatus. Thus the problem of surface roughness, deformation, and contamination, is reduced. This again allows us to examine surfaces of different materials. 

Scanning Force Microscopes for Studying Material Properties. .. 81... 

Conceptually, predecessors of the scanning force microscope are the surface force apparatus (SFA) [73,74] and the stylus profilometer [75,76]. The SFA enables measurement of normal and friction forces between molecularly smooth surfaces as small as 1 nN as a function of distance with a resolution of 0.1 nm. In addition to the local force measurement, the profilometer provides a topographic map of the surface by scanning the surface with a sharp probe. However, the profilometer is not suitable for structure characterisation because of the large radius of the tip (about 1 pm) and the low sensitivity of the force sensor (in the range of 1(T2 to 1(T5 N). 

For a typical value of the Hamaker constant in vacuum, A=10 19 J, the attractive force emerging between a tip with an apex radius of 10 nm and a surface separated by 1 nm distance will be F=1 nN. This value sets an approximate scale of the forces which are sensed by the scanning force microscope. 

Scanning force microscopes can be operated in many ways measuring different interactions between the probe tip and sample and using different types of detection schemes. Development of new modes is driven by the wish of the experimentalist (i) to discriminate the different contributions to the net force, such as adhesion, elasticity and viscosity, (ii) to enhance the resolution and contrast of the microscope, and (iii) to diminish distortion of the tip and sample during scanning. 

Therefore, in most cases the scanning force microscope gives a lattice image similar to diffraction techniques. Visualisation of non-periodic structures or lattice defects, which means the true atomic resolution is exceptional and practically not attainable for polymers [58,236,246]. The smallest defects observed by conventional SFM are linear dislocations whose lengths exceed the contact diameter [247-249]. To approach the true atomic resolution, the aperture must be decreased as far as possible by using sharper tips and operating at lowest measurable forces to minimise the contact area. For example, to achieve the contact... 

Fig. 20. Different surface morphologies illustrate limitations in the nanoscopic resolution of the scanning force microscope. a - two rigid spheres, b - two rigid spikes, c - two soft spheres. While Az is the lower limit for the dimple to be resolved by the tip of radius R, d corresponds to the lateral resolution of the SFM tip...

Complementary to the SFA experiments, SFM techniques enabled direct, non-destructive and non-contact measurement of forces which can be as small as 1 pN. Compared to other probes such as optical tweezers, surface force balance and osmotic stress [378-380], the scanning force microscope has an advantage due to its ability in local force measurements on heterogeneous and rough surfaces with excellent spatial resolution [381]. Thus, a force-distance dependence measured from a small surface area provides a microscopic basis for understanding the macroscopic interfacial properties. Furthermore, lateral mapping... 

Shortly after the invention of STM, another scanning probe microscopy has been developed, which is based on the force between a bendable probe and the surface. The atomic or scanning force microscope (AFM or SFM) is now the most popular tool in nanoscience. Constant progress allows today lateral resolution which is comparable to STM. 

Fig. 2 Schematic representation of the basic detection elements of the scanning force microscope and of the piezoelectric transducers generating the displacement modulations for purposes of dynamic mechanical measurements. The dynamic components of the tip-sample forces resulting from the normal/lateral displacement modulations are detected via the torsion/bending of the microscopic cantilever and the deflection of the laser beam reflected off the rear side of the cantilever. The positional shift of the latter is registered by means of a segmented photo-diode...

The restriction to mica was overcome by a relatively recent technique the atomic force microscope (AFM). sometimes also called the scanning force microscope [69. AFMs are usually used to image solid surfaces. Therefore a sharp tip at the free end of a cantilever spring is scanned over a surface. Tip and cantilever are microfabricated. While scanning, surface features move the tip up and down and thus deflect the cantilever. By measuring the deflection of the cantilever, a topographic image of the surface can be obtained. 

SCANNING FORCE MICROSCOPE STUDIES OF DETACHMENT OF NANOMETER ADHERING PARTICULATES... 

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