Atomic force microscopy cantilever

M. Reinstaedtler, U. Rabe, V. Scherer, J.A. Turner, and W. Arnold, Imaging of flexural and torsional resonance modes of atomic force microscopy cantilevers using optical interferometry. Surface Science, (2003) in print... 

Neumeister, J. M. and Ducker, W. A., Lateral, normal, and longitudinal spring constants of atomic force microscopy cantilevers. Rev. Sci. Instrum., 65, 2527-2531 (1994). 

Lugstein, A., E. Bertagnolli, C. Kranz, A. Kueng, and B. Mizaikoff, Integrating micro-and nanoelectrodes into atomic force microscopy cantilevers using focused ion beam techniques, Appl. Phys. Lett., Vol. 81, 2002 pp. 349-351. 

The mechanical moduli and dependency on the content of the hydroxyapatite nanoparticles could be analyzed using three point bending with a tipless atomic force microscopy cantilever (12). An increase of the hydroxyapatite content up to 20% increased the mechanical properties of the composite scaffolds. But a further increase above 20% disrupted the polymer chain networks within silk fibroin nanofibers and weakened the mechanical strength (10). 

Kageshima, M., Ogiso, H., Nakano, S., et al. (1999) Atomic force microscopy cantilevers for sensitive lateral force detection. Jpn J AppI Phys 1 38 3958-3961. 

AFM Atomic force microscopy [9, 47, 99] Force measured by cantilever deflection as probe scans the surface Surface structure... 

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. 

Figure 4.29. Experimental set-up for atomic force microscopy. The sample is mounted on a piezo electric scanner and can be positioned with a precision better than 0.01 nm in thex, y, and z directions. The tip is mounted on a flexible arm, the cantilever. When the tip is attracted or repelled by the sample, the deflection of the cantilever/tip assembly is...

Atomic force microscopy (AFM) is a variant of STM and was introduced in 1986 by Binnig et al. (11). AFM belongs to a family of near-field microscopies and is capable of imaging a wide variety of specimens surface down to an atomic scale. The technique employs a probe (pyramidal tip) mounted at the end of a sensitive but rigid cantilever (see Fig. 2). The probe is drawn across the specimen under very light mechanical loading (1). Measurements of the probe s interaction with the sample s surface are accomplished with a laser beam reflected from the cantilever. 

Figure 7.14 Experimental set-up for atomic force microscopy. The sample is mounted on a piezoelectric scanner and can be positioned with a precision better than 0.01 nm in the x, y, and z direction. The tip is mounted on a flexible arm the cantilever. When the tip is attracted or repelled by the sample, the deflection of the cantilever/tip assembly is measured as follows. A laser beam is focussed at the end of the cantilever and reflected to two photodiodes, numbered 1 and 2. If the tip bends towards the surface, photodiode 2 receives more light than 1, and the difference in intensity between 1 and 2 is a measure of the deflection of the cantilever and thus of the force between the sample and the tip. With four photodiodes, one can also measure the sideways deflection of the tip, for example at an edge on the sample surface.

Chen et al. (2007) have developed a nanoinjector that injects compounds immobilized on MWNT-atomic force microscopy (AFM) tips into the cells. First, a MWNT-AFM tip was fabricated from a normal AFM tip with an MWNT on one end. Next, a compound of interest was immobilized on the MWNT-AFM tip through a disulfide bond linkage. After MWNT-AFM tip was tapped on the cell, the cantilever was further lowered and the MWNT nanoneedle then penetrated the membrane. Once inside the cell, the disulfide linkage was broken under the cells reducing environment and the compound of interest was released inside the cell. The MWNT-AFM tip was then removed from the cell. In this study, protein was... 

Fig. 15.3. Microcantilever for atomic-force microscopy, (a) A glass substrate with four cantilevers, (b) One of the cantilevers, (c) Close-up view of the tip. (After Albrecht et al. 1990.)...

Another device that yields results of the same kind as STM is atomic force microscopy (AFM) (Binning, 1986). This avoids dependence on an electron stream (which cannot be obtained from insulators)58 and relies on the actual interatomic forces between a microtip and nearby surface atoms. The forces experienced at a given point by the tip are sensed by a cantilever spring. The movements of this are slight, but they can be measured by means of interf erometry and in this way the movement of the tip can be quantified. The sensitivity of the atomic force microscope is less than that of STM, but its action is independent of the electrical conductivity of the surface and it is therefore to be preferred over STM, particularly for studies in bioelectrochemistiy. 

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. 

In experiments with friction force microscopy, the tip forms a contact of a few nanometers in diameter with the substrate, a so-called nanocontact. In reality, friction of macroscopic bodies is determined by the interaction via m/crocontacts. One possibility of extending the method of friction force microscopy to larger contact areas is the use of the colloidal probe technique, where a small sphere is attached to the end of an atomic force microscope cantilever (see Section 6.4). Even for microcontacts, the proportionality between the true area of contact and the friction force was observed (see example 11.1). 

Although the resolution of atomic force microscopy (AFM) is basically inferior to that of STM, the technique has the advantage that insulating materials can also be used as substrates. In AFM the forces acting between the tip and the sample surface are detected. The probe tip mounted on a flexible cantilever scans over the sample. AFM can be operated in contact mode, exploiting repulsive forces, as well as in non-contact mode, exploiting attractive forces. In the contact mode the probe tip is in direct contact with the sample surface (Fig. 7.8). Either the tip is passed over the sample surface at constant height (CHM,... 

Using the FM mode in vacuum improved the resolution dramatically and atomic resolution was obtained even on chemically reactive samples. In this article we focus on FM mode atomic force microscopy. In FM-AFM, a cantilever with eigenfrequency /o and spring constant k is subject to controlled feedback such that it oscillates with a constant amplitude A as illustrated in Fig. 9. 

---