Nano-cantilever

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. 

Inouye, Y, Hayazawa, N., Hayashi, K., Sekkat, Z., and Kawata, S. 1999. Near-fleld scanning optical microscope using a metallized cantilever tip for nano spectroscopy. Proc. SPIE Int. Soc. Opt. Eng. 3791 40-48. 

Figure 2.20 Cantilever fabrication based on both top-down fabrication and bottom-up assembly.109 (Reprinted with permission from F. Hua et al., Nano Lett. 2004, 4, 823-825. Copyright 2004 American Chemical Society.)...

The field of nanolithography is intimately connected with nanomanipulation. In nanomanipulation generally a preformed nanoparticle, nanotube or a nanowire is manipulated to place it at a predetermined site. The most widely used tool for nanomanipulation is the cantilever of the AFM that provides a robotic arm to place the nano-objects in predetermined sites. A nanoparticle weakly adsorbed on a substrate can be moved by an AFM tip when it works in contact mode. This is not wanted but if the particle is selected and then moved by the AFM then it becomes a useful tool. The AFM-based manipulation turns the unwanted aspect to an advantage. For instance if one wants to place a nanowire between two electrodes an AFM cantilever can be used to image the wire and push it between the two electrodes. The advantage of the cantilever is that a predetermined force can be applied and also the same instrument can image it. The basic idea behind SPM-based nanomanipulation is shown in Figure 21.17. 

The STM tip can also be used for nanomanipulation. In fact the first atomic level nanomanipulation was done by STM only [91]. However, in more recent context, by nanomanipulation we generally imply use of an AFM cantilever to manipulate nano-objects. This field, however, is in its early stages and there is a need to understand the physics of the manipulation in terms of the basic forces that are involved in this process. It is realized that it is different from what one sees in micromanipulation. There are three main road blocks that need to be solved effectively before this field can mature. First, there is the need to understand the basic physical and chemical processes that take place at the scale of a few nanometers, including the mechanics. Second, one need to develop effective hardware as well as control that has resolution and reproducibility of manipulation at this level. Third, there is a need for effective automation and software. Interestingly, these road-... 

Nanoscale measurements have been performed by AFM in contact mode. For the nano-adhesion measurement, force-distance curves have been obtained (Fig. 5.3). The maximum cantilever deflection D during separation is directly proportional to the adhesion force. 

For PDMS 6, the deflection D was quite constant before and after extraction and was close to 70 nm (with AD=5 nm). The deflection value did not depend on the contact force for PDMS 6. Measurements were not possible with PDMS 17 before extraction because the AFM tip could not be separated from the PDMS surface within the measurable cantilever deflection range. Hence the adhesion value could not be determined, but it has to be considered as important. After extraction of free chains (PDMS 17 ), measurements were possible and the deflection value D obtained was close to 500 nm (with AD=30 nm). Hence, in correlation with the macro-adhesion results, the nano-adhesion of PDMS 17 was much greater than that of PDMS 6. 

However, the nano-adhesion of PDMS 17 decreased after extraction. This result is the opposite of that for macro-adhesion, where an increase in adherence was observed after extraction. Important adsorption phenomena of the numerous and long free chains of PDMS 17 on the AFM tip could explain the higher nano-adhesion observed before extraction. The mobility of these free chains (greater than of pendant chains) allows a better adsorption on the tip, avoiding the separation (with the same experimental device, i.e., cantilever stiffness). 

NR having a standard recipe with 10-phr CB (NR 10) was the specimen. The compound recipe is shown in Table 3.1. The surface sectioned by cryomicrotome (Reichert FCS, Leica Co. Ltd.) was examined by AFM, NanoScopelV (Veeco Instruments Inc., United States). The cantilever used in this study was made of Si3N4 (NP, Nano-probe, United States). Adhesion between the probe tip and the specimen surface makes the situation complicated, and it becomes impossible to apply mathematical analysis via Eq. 3.3 or 3.5 with the assumption of Hertzian contact. Thus, aU the experiments were performed in distilled water. The selection of cantilever is another important factor that influences the quantitative value of the Young s modulus. We used a spring constant of 0.12N/m (nominal), which is appropriate to deform the... 

Direct visualization of nano- and micrometer-sized objects is the most straightforward way for their analysis in surface and polymer science, biomaterial research, and biology. Rapid progress in engineering and microtechnology has led to numerous techniques that allow observation and mechanical manipulation of microscopic objects of various natures. AFM [52] is the most commonly used of these techniques. In AFM, a sample surface is mechanically scanned with a tiny probe—a sharpened stylus fixed at the end of a flexible cantilever. When the stylus interacts with the samples, the resulting force acts on the stylus and causes deflection of the cantilever. This deflection is detected via an optical lever system, that is, a laser beam reflected from the end of the... 

Further information about the possible range of mechanical effects that occur within thin synthetic gel substrates has been provided in a study that used gel indentation with the cantilever of an atomic force microscope (AFM). Gels of varying thickness, H, were made at the same time with the same polyacrylamide gel solutions to maintain a constant E of tissue-like ( kPa) elasticities, and the gels were all indented by l-2 pm at forces that bend the cantilever in the nano-Newton (nN) range. An apparent elasticity E pp was obtained in this AFM experiment by fitting the force/versus indentation depth d with a generalized Hertz model ... 

Mar r proposals for applying nanotechnology to CBD involve the use of proteins (i.e., enzymes, antibodies). Antibodies provide the specificity, and to some extent sensitivity, for many proposed nano CB sensors (e.g., nanowires (41,42), cantilevers (43), SPR (44), etc.), while others rely on amperometric detection of enzyme catalysis (45). In addition, enzymes that specifically attack CB targets show some promise for relatively benign decontamination. However, one of the major obstacles to the adoption of these promising protein-based nanotechnologies is the fragility of the proteins under normal environmental conditions. Even in solution, protein half-lives at room temperature can be as... 

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