The Atomic Force Microscope AFM

Atomic force microscopy (AFM) or, as it is also called, scanning force microscopy (SFM) is based on the minute but detectable forces - of the order of nano Newtons -between a sharp tip and atoms on the surface. The tip is mounted on a flexible arm, called a cantilever, and is positioned at a subnanometre distance from the surface. If the sample is scanned under the tip in the x-y plane, it feels the attractive or repulsive force from the surface atoms and hence it is deflected in the z-direction. The deflection can be measured with a laser and photo detectors as indicated schematically in Fig. 4.29. Atomic force microscopy can be applied in two ways. 

In the contact mode, the tip is within a few angstroms of the surface, and the interaction between them is determined by the interactions between the individual atoms in the tip and on the surface. 

The second mode of operation is the non-contact mode, in which the distance between tip and sample is much larger, between 2 and 30 nm. In this case one describes the forces in terms of the macroscopic interaction between bodies. Magnetic force microscopy, in which the magnetic domain structure of a solid can be imaged, is an example of the non-contact mode operation. 

A third mode, which has recently become the standard for work on surfaces that are easily damaged, is in essence a hybrid between contact and non-contact modes, and is sometimes called the tapping mode. In this case the cantilever is brought into oscillation such that the tip just touches the surface at the maximum deflection towards the sample. When the oscillating cantilever approaches the maximum deflection, it starts to feel the surface and the oscillation becomes damped, which is 

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The development of a host of scanning probe devices such as the atomic force microscope (AFM) [13-17] and the surface forces apparatus (SFA) [18-22], on the other hand, enables experimentalists to study almost routinely the behavior of soft condensed matter confined by such substrates to spaces of molecular dimensions. However, under conditions of severe confinement a direct study of the relation between material properties and the microscopic structure of confined phases still remains an experimental challenge. 

Technologically, the most important member of the scanning probe family is perhaps the atomic force microscope (AFM), which has found applications in... 

In the past decade, much development has taken place in regard to measuring the forces involved in these colloidal systems. In one method, the procedure used is to measure the force present between two solid surfaces at very low distances (less than micrometer). The system can operate under water, and thus the effect of addictives has been investigated. These data have provided verification of many aspects of the DLVO theory. Recently, the atomic force microscope (AFM) has been used to measure these colloidal forces directly (Birdi, 2002). Two particles are brought closer, and the force (nanoNewton) is measured. In fact, commercially available apparatus are designed to perform such analyses. The measurements can be carried out in fluids and under various experimental conditions (such as added electrolytes, pH, etc.). 

The atomic force microscope (AFM) has been used to investigate LB film quality and other properties and to obtain sizes and distributions of MC produced within LB films. For example, in an image of a three-layer CuAr film on mica, large pits were evident (9). In a cross-section analysis a stepped drop of 7.5 nm to the substrate was consistent with three monolayers of an M-Ar film ( 2.5 nm per layer). The thickness of LB films can also be obtained in good-quality films by excavating down to the substrate by the AFM tip in contact mode (45,80). 

The field ion microscope is perhaps the simplest of all atomic resolution microscopes as far as mechanical and electrical designs are concerned. The atomic resolution microscopes, at the present time, include also different types of electron microscopes,1 the scanning tunneling microscope (STM)2 and the atomic force microscope (AFM)2 Before we discuss the general design features of the field ion microscope it is perhaps worthwhile to describe the first field ion microscope,3 and a very simple FIM4 which can be constructed in almost any laboratory. The first field ion microscope, shown in Fig. 3.1, is essentially a field emission microscope5 except that it is now equipped with a palladium tube with... 

There are of course many other similarities and differences, and some of them are listed in Table 5.1 without further explanations. In general, STM is very versatile and flexible. Especially with the development of the atomic force microscope (AFM), materials of poor electrical conductivity can also be imaged. There is the potential of many important applications. A critically important factor in STM and AFM is the characterization of the probing tip, which can of course be done with the FIM. FIM, with its ability to field evaporate surface atoms and surface layers one by one, and the capability of single atom chemical analysis with the atom-probe FIM (APFIM), also finds many applications, especially in chemical analysis of materials on a sub-nanometer scale. It should be possible to develop an STM-FIM-APFIM system where the sample to be scanned in STM is itself an FIM tip so that the sample can either be thermally treated or be field evaporated to reach into the bulk or to reach to an interface inside the sample. After the emitter surface is scanned for its atomic structure, it can be mass analyzed in the atom-probe for one atomic layer,... 

Gratza, A.J. and Hillnerb, P.E. (1993) Poisoning of calcite growth viewed in the atomic force microscope (AFM)./. Cryst. Growth, 129, 789-793. 

The atomic force microscope (AFM) and its closely allied device, the lateral... 

Recently, the DAE-0 and DAO-E lattices have been constructed (E. Winfree et al., 1998). With both it is possible to ligate the strands together to get very long reporter strands. The most effective characterization of these arrays has been achieved without ligating them, merely by visualizing them in the atomic force microscope (AFM). It is possible to include a DAO+J or DAE+J motif in these arrays where the J hairpin points up, sometimes DAO+2J or DAE+2J, with one hairpin pointing up and one down these hairpins have no effect on the topology of the array, just as... 

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. 

Since 1981, researchers have developed a number of modifications of the STM for uses in which the original instrument is not suitable. For example, the atomic force microscope (AFM) was invented in 1986 by Binnig and Christoph Gerber at IBM-ZRL and Calvin Quate at Stanford University. The AFM can be used on nonconductive surfaces, such as organic materials, on which the STM cannot he used. Today the STM, AFM, and related devices are collectively known as scanning probe microscopes (SPMs). 

The atomic force microscope (AFM), (Aktary et al., 2001 Binnig et al. 1986 Warren et al., 1998) and the lateral force microscope (LFM), (Mate et al., 1987) are valuable tools for characterizing the forces involved between surfaces in contact, both lubricated and unlubricated. A particular strength of AFM/LFM is... 

The next radical improvement in scanned probe microscopies was the invention of the atomic force microscope (AFM) in 1986 by Binnig, Quate,92 and Gerber93 [29]. The X- and Y-piezoelectric scanners were kept, but the atomically sharp conducting tip was replaced by a sharp (but not atomically sharp ) Si cantilever (Fig. 11.42), with a mirror glued to its back. 

A "direct" observation of individual atoms is achieved in atomic resolution transmission electron microscopes (AR-TEM), in the scanning tunneling microscope (STM), and in the atomic force microscope (AFM) (5, 4). While AR-TEM are large machines with very high voltage (6 x 105 to 106 volts) applied to an electron-transparent small object, STM and AFM are small devices with ultrasensitive tip positioning mechanics that is suited for flat or near-flat objects and will... 

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. 

Considering techniques that allow the imaging of lipid surfaces, scanning probe microscopes such as the atomic force microscope (AFM) (13, 23) have become very appealing. The AFM allows measurements of native lipid samples under physiologic-like conditions and while biological processes are at work. It is hence often used to determine lipid membrane stmctures, stmctural defects in membranes, domain formation, and even the behavior of lipid rafts with high nanometer-scale lateral resolution. 

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