Atomic Force Microscope cantilevers

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). 

Sun, Z., Juriani, A., Meininger, G. A., and Meissner, K. E. 2009. Rrobing cell surface interactions using atomic force microscope cantilevers functionahzed for quantum dot-enabled Forster resonance energy transfer, /Biomed Opt 14(4), 040502. 

Hwang K Y, Kim S D, Kim Y W and Yu W R (2010) Mechanical characterization of nanofibers using a nanomanipulator and atomic force microscope cantilever in a scanning electron microscope, Polym Test 29 375-380. 

M. Reinstadtler, U. Rabe, V. Scherer, U. Hartmann, A. Goldade, B. Bhushan, and W. Arnold, On the nanoscale measurement of friction using atomic force microscope cantilever torsional resonances, Appl. Phys. Lett. 82, 2604 2606 (2003). 

Vinogradova, H. J. Butt, G. E. Yakubov, and E Feuillebois, Dynamic effects on force measurements. 1. Viscous drag on the atomic force microscope cantilever. Rev. Set Instrum., 5, 2330-2339 (2001). 

A. Maali, C. Hurth, T. Cohen-Bouhacina, G. Couturier, and J. P. Aime, Improved acoustic excitation of atomic force microscope cantilevers in liquids, App/. Phys. Lett., 88,163504 [2006). 

In the particular case of a nanoneedle at the end of a t3q>ical oscillating atomic force microscope cantilever (/ = 260 kHz), this evanescent length is of about 8 10 " m that can be larger than the... 

F. L. Degertekin, B. Hadimioglu, T. Sulchek, and C. F. Quate, Actuation and characterization of atomic force microscope cantilevers in fluids by acoustic radiation pressure, App7. Phys. Lett. 78,1628 (2001]. 

Sader JE, Chon JWM, Mulvaney P. Cahbration of rectangular atomic force microscope cantilevers. Rev Sci Instrum 1999 70 3967-3969. 

Figure 10 Force versus displacement curves recorded between functionalized atomic force microscope cantilever probes and surfeces. The adhesive interactions are strong for like-like interactions (COOH-COOH and CH3-CH3) but weak for interaction between unlike functional groups (COOH-CH3). Noy A, Frisbie CD and Lieber CM, unpublished results.

U. Rabe, K. Janser, W. Arnold, Vibrations of free and surface-coupled atomic force microscope cantilevers Theory and experiment. Rev. Sci. Insttum. 67(9), 3281-3293 (1996)... 

Liibbe, J., Temmen, M., Schnieder, H., and Reichling, M. (2011) Measurement and modelling of non-contact atomic force microscope cantilever properties from ultra-high vacuum to normal pressure conditions. Meas. Sci. Technel., 22, 055501. 

Equation (6.39) has been verified by a number of experiments. In classical experiments, a sphere falling in gravity toward a planar surface has been observed [633-635] see also Exercise 6.1. A typical experimental force versus distance curve, which is dominated by hydrodynamic drag, is shown in Figure6.5. In this experiment a borosilicate glass sphere of 18 pm diameter was moved toward a silicon wafer in aqueous electrolyte with 0.2 M KCl at 25 °C. Both surfaces are hydrophilic. The sphere is attached to an atomic force microscope cantilever of spring constant 0.26 N m . The cantilever was moved with a constant velocity of 40pm s toward... 

Fig. 5. Block diagram of contact atomic force microscope system in which cantilever deflection monitored optically with position-sensitive photodiode...

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. 

Chui, B.W., Stowe, T.D., Kenny, T.W., Mamin, H.J., Terris, B.D. and Rugar, D., Lowstiffness silicon cantilevers for thermal writing and piezoresistive readback with the atomic force microscope. Appl. Phys. Leu., 69(18), 2767-2769 (1996). 

Binnig et al. [48] invented the atomic force microscope in 1985. Their original model of the AFM consisted of a diamond shard attached to a strip of gold foil. The diamond tip contacted the surface directly, with the inter-atomic van der Waals forces providing the interaction mechanism. Detection of the cantilever s vertical movement was done with a second tip—an STM placed above the cantilever. Today, most AFMs use a laser beam deflection system, introduced by Meyer and Amer [49], where a laser is reflected from the back of the reflective AFM lever and onto a position-sensitive detector. 

Figure 3.2 The essential elements of an atomic force microscope. The sample is moved beneath a tip mounted on a cantilever a laser beam reflected off the back of the tip and on to a photodiode amplifies deflections of the cantilever.

Fig. 13.2. Addition of piezoelectric transducers to an atomic force microscope for acoustically excited probe microscopy. The forces acting between the tip and the sample are measured by the vertical and lateral deflections of the cantilever...

Hirsekorn, S., Rabe, U., and Arnold, W. (1997). Theoretical description of the transfer of vibrations from a sample to the cantilever of an atomic force microscope. Nanotechnology 8, 57-66. [295,298, 302]... 

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. 

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. 

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