Cantilevers, microscopic

Detection of cantilever displacement is another important issue in force microscope design. The first AFM instrument used an STM to monitor the movement of the cantilever—an extremely sensitive method. STM detection suffers from the disadvantage, however, that tip or cantilever contamination can affect the instrument s sensitivity, and that the topography of the cantilever may be incorporated into the data. The most coimnon methods in use today are optical, and are based either on the deflection of a laser beam [80], which has been bounced off the rear of the cantilever onto a position-sensitive detector (figme B 1.19.18), or on an interferometric principle [81]. 

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

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... 

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). 

Fig. 10. Scanning electron microscope (SEM) image of the probe with an MWCNT attached to a silicon cantilever [35]. Protruding of one individual MWCNT has been confirmed by transmission electron microscope (TEM) measurement (not shown here).

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. 

K., Sekkat, Z. and Kawata, S. (1999) Near-field scanning optical microscope using a metallized cantilever tip for nanospectroscopy. Proc. SPIE, 3791,40-48. 

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.

All the STM results from our group presented in this chapter employed the variable temperature STM, with tips made by electrochemical etching of tungsten wire. For noncontact AFM (NC-AFM), we employ commercial conducting silicon cantilevers with force constants of approximately 2-14 rn 1 and resonant frequencies of approximately 60-350kHz (Nanosensors and Mikromasch). The NC-AFM images we present here were recorded in collaboration with Professor Onishi at Kobe University and employed a UHV JEOL (JSPM-4500A) microscope. 

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]... 

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