Atomic force microscope model

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. 

Simpson RT, Thoma F, Brubaker JM (1985) Chromatin reconstituted from tandemly repeated cloned DNA fragments and core histones a model system for study of higher order structure. Cell 42 799-808 Sugiyama S, Yoshino T, Kanahara H, Kobori T, Ohtani T (2003) Atomic force microscopic imaging of 30 nm chromatin fiber from partially relaxed plant chromosomes. Scanning 25 132-136 Sugiyama S, Yoshino T, Kanahara H, Shichiri M, Fukushi D, Ohtani T (2004) Effects of acetic acid treatment on plant chromosome structures analyzed by atomic force microscopy. Anal Biochem 324 39 4... 

There have now been attempts to determine rheological properties on the nanoscale. The nano-rheological properties (surface viscoelasticity) of emulsion droplets have been estimated through modelling based on data from atomic force microscope measurements [371]. 

To achieve high resolution with an atomic force microscope it is necessary to focus only on the short range forces. In Fig. 5 the distance dependence of the tunneling current and a short range force (modeled by a gradient of a Morse potential) is compared. 

Figure 18.1 Surface structure ofTi02(l 10) characterized by STM and non-contact atomic force microscope (NC-AFM). (a) An empty state STM image (7.3 x 7.3 nm2, Vs = 1.2 V, It = 0.15 nA) of a TiO2(110) surface at RT. (b) A structure model of a clean Ti02(l 10) surface. The fivefold coordinated Ti atoms are visualized, (c) A perspective view of a TiO2(110) surface with oxygen defect.

Atomic force microscope (AFM). Sample solutions at 100 ng/ml or less were cemented onto mica and imaged in a model Nanoscope Ilia scanning probe microscope with TESP cantilevers (Veeco/Digital Instruments, Santa Barbara, CA) operated in the intermittent contact mode on an atomic force microscope. 

The atomic force microscope (AFM) is a promising device for the investigation of materials surface properties at the nanoscale. Precise analysis of adhesive and mechanical properties, and particularly of model polymer surfaces, can be achieved with a nanometer probe. This study distinguishes the different contributions (chemical and mechanical) included in an AFM force-distance curve in order to estabhsh relationships between interfacial tip-polymer interactions and the surface viscoelastic properties of the polymer. 

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 ... 

Mechanical characterization. For the application of catalytic nanostructures, these nanorods may experience significant forces due to the flow of hquid and gas around them. The mechanical robustness of the nanorod structures as well as the connection to the substrate must be evaluated. Techniques such as manipulation via an atomic force microscope may be used to determine the strength of these structures. Theoretical modeling will also contribute to this effort. 

The Young s modulus of a cell can be measured using an atomic force microscope (AFM) by indenting the cell with the AFM tip. Based on Hertz model, the Young s modulus, E, can be calculated as [7]... 

The need for mechanical reinforcement has been the driving force for most of the reported work on polymer/CNT composites. In an attempt to investigate the mechanical properties of electrospun PAN/SWNT nanofibers, Ko et al. (75) have used an atomic force microscope (AFM) to measure the elastic modulus of the electrospun composite nanofibers. The obtained fiber modulus was 140 GPa, a value which is much higher than that of conventional PAN fibers (60 GPa) (75). In a somewhat related but independent study, Mathew et al. (92) also used AFM to measure the mechanical properties of electrospun polybutylene/MWNT terephthalate nanofibers. Elastic deformation of MWNTs in electrospun PEO/MWNT and PVA/MWNT nanofibers was studied by Zhou and co-workers (84), and was found to increase with an increase in the modulus of the polymer matrix. In the same study, a simplified model was also proposed to estimate the elastic modulus ratio of MWNT and polymers. To confirm the validity of their model, these authors compared the model predictions with experimental data obtained from AFM measurements. 

In the atomic force microscope, a fine pointed probe, typically lOOmn diameter, is brought into close proximity with a smooth sample, which is controlled in position by a piezotube. The overall scheme was described in Chapter 3. Here the objective is to describe adhesion experiments as the probe is brought into adheave cxmtact with dry surfaces. Figure 4.15 shows the probe as it nears the sample. On the right is an atontic model of the near-contact region showing how the tip is from 10-100 nm diameter under normal circumstances,... 

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