Atomic force microscope structure

Overney R, Howald L, Frommer J, Meyer E and Guntherodt H 1991 Molecular surface structure of tetracene mapped by the atomic force microscope J. Chem. Phys. 94 8441... 

Chen C-FI, Washburn N and Gewirth A A 1993 In situ atomic force microscope study of Pb underpotential deposition on Au(111) Structural properties of the catalytically active phase J.Phys. Chem. 97 9754-60... 

The development of a host of scanning probe devices such as the atomic force microscope (AFM) [13-17] and the surface forces apparatus (SFA) [18-22], on the other hand, enables experimentalists to study almost routinely the behavior of soft condensed matter confined by such substrates to spaces of molecular dimensions. However, under conditions of severe confinement a direct study of the relation between material properties and the microscopic structure of confined phases still remains an experimental challenge. 

The thud step gives a polymer-rich phase forming the membrane, and a polymer-depleted phase forming the pores. The ultimate membrane structure results as a combination of phase separation and mass transfer, variation of the production conditions giving membranes with different separation characteristics. Most MF membranes have a systematic pore structure, and they can have porosity as high as 80%.11,12Figure 16.6 shows an atomic force microscope... 

A very similar technique is atomic force microscope (AFM) [38] where the force between the tip and the surface is measured. The interaction is usually much less localized and the lateral resolution with polymers is mostly of the order of 0.5 nm or worse. In some cases of polymer crystals atomic resolution is reported [39], The big advantage for polymers is, however, that non-conducting surfaces can be investigated. Chemical recognition by the use of specific tips is possible and by dynamic techniques a distinction between forces of different types (van der Waals, electrostatic, magnetic etc.) can be made. The resolution of AFM does not, at this moment, reach the atomic resolution of STM and, in particular, defects and localized structures on the atomic scale are difficult to see by AFM. The technique, however, will be developed further and one can expect a large potential for polymer applications. 

Recent developments have allowed atomic force microscopic (AFM) studies to follow the course of spherulite development and the internal lamellar structures as the spherulite evolves [206-209]. The major steps in spherulite formation were followed by AFM for poly(bisphenol) A octane ether [210,211] and more recently, as seen in the example of Figure 12 for a propylene 1-hexene copolymer [212] with 20 mol% comonomer. Accommodation of significant content of 1-hexene in the lattice allows formation and propagation of sheaf-like lamellar structure in this copolymer. The onset of sheave formation is clearly discerned in the micrographs of Figure 12 after crystallization for 10 h. Branching and development of the sheave are shown at later times. The direct observation of sheave and spherulitic formation by AFM supports the major features that have been deduced from transmission electron and optical microscopy. The fibrous internal spherulite structure could be directly observed by AFM. 

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... 

The possible structural involvement of linker histones in the methylation-mediated chromatin condensation has been recently addressed by using the Atomic Force Microscope [175]. This extensive study combined in vivo and in vitro approaches to demonstrate that DNA methylation could cause chromatin compaction only in co-operation with linker histone binding. Finally, it may be... 

Chemical and Genetic Probes—Nanotube-tipped atomic force microscopes can trace a strand of DNA and identify chemical markers that reveal DNA fine structure. A miniaturized sensor has been constructed based on coupling the electronic properties of nanotubes with the specific recognition properties of immobilized biomolecules by attaching organic molecules handles to these tubular nanostructures. In one study, the pi-electron network on the CNT is used to anchor a molecule that irreversibly adsorbs to the surface of the SWNT. The anchored molecules have a tail to which proteins, or a variety of other... 

This value of Aco corresponds to the cholesterol molecule oriented with the hydroxyl group pointing toward the water phase. Atomic force microscope (AFM) studies of cholesterol in Langmuir-Blodgett (LB) films has shown that there exist domain structures (see Chapter X). This has been found for different collapse lipid monolayers (Birdi, 2003). Different data have provided much information about the orientation of lipid on water (Table 4.1). 

Johnsson, P.A. Eggleston, C.M. Hochella, M.E. (1991) Imaging molecular scale structure and microtopography of hematite with the atomic force microscope. Am. Min. 76 1442-1445... 

Fig. 7 (a) Catechol derivatized tetracenes self-assemble on metal oxide surfaces such as aluminum oxide, (b) Schematic and (c) scanning electron micrographs of FET structures fabricated with a 5-nm aluminum oxide layer on top of a 5-nm thermally oxidized Si wafer to allow self-assembly of the derivatized tetracene between sub-100 nm Au source and drain electrodes, (d) /d-Eds characteristics of the assembled tetracene monolayer FET for a 40 nm channel length showing hole modulation and (inset) an atomic force microscope image of the FET channel... 

There are of course many other similarities and differences, and some of them are listed in Table 5.1 without further explanations. In general, STM is very versatile and flexible. Especially with the development of the atomic force microscope (AFM), materials of poor electrical conductivity can also be imaged. There is the potential of many important applications. A critically important factor in STM and AFM is the characterization of the probing tip, which can of course be done with the FIM. FIM, with its ability to field evaporate surface atoms and surface layers one by one, and the capability of single atom chemical analysis with the atom-probe FIM (APFIM), also finds many applications, especially in chemical analysis of materials on a sub-nanometer scale. It should be possible to develop an STM-FIM-APFIM system where the sample to be scanned in STM is itself an FIM tip so that the sample can either be thermally treated or be field evaporated to reach into the bulk or to reach to an interface inside the sample. After the emitter surface is scanned for its atomic structure, it can be mass analyzed in the atom-probe for one atomic layer,... 

Getting Physical with Your Chemistry Mechanically Investigating Local Structure and Properties of Surfaces with the Atomic Force Microscope 76... 

With the atomic force microscope surfaces can be scanned in UHV, air, and most favorably in liquids. Liquids have the advantage that the force between tip and sample, which might lead to a possible deformation of fragile sample structures, is smaller than in air or UHV. 

The most recent developments in determining the surface structure are the scanning tunneling microscope (STM) and the scanning or atomic force microscope (SFM or AFM) [36, 37]. These techniques are capable of imaging the local surface... 

The nature of structural orders in the PQT-12 thin films can be further characterized by atomic-force microscopic (AFM) analysis. Figure 4.10 shows the AFM phase images of a 20-nm PQT-12 film on an OTS-8-modified wafer surface before... 

Figure 3.1. Levels of structural analysis of tissues. The levels of structural hierarchy of tissues include levels viewed by eye, light microscope, electron microscope, and atomic force microscope.

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