AFM Techniques

EFM is a related technique in which the electrical field of the sample surface is detected directly. The technique is dependent upon the tip charge, because changes in cantilever oscillation are dependent upon the specific electrostatic interaction between tip and sample. In both techniques, a specific voltage can be applied to the tip to impose specific electrical interactions with the sample for certain applications. 

In liquid ECAFM applications, the AFM tip and sample surface comprise the working and counter electrodes of an electrochemical cell. Additionally, a reference electrode can be incorporated into the liquid cell allowing the instrument to effectively perform as a three-electrode electrochemical cell. The technique has expanded into several applications where electrosynthesis and electrodeposition reactions can take place simultaneously with imaging [54]. Electrical connections can be made between the tip and enzymes on a surface to measure electron transfer and conductivity [44,52,55]. In addition, the tip can be functionalized with electroactive biomolecules to perform redox reactions and measure the amperometric and voltammetric response in situ [56]. 

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The structural state of dendritic macromolecules at air-water (Langmuir mono-layers) and air-solid (adsorbed monolayers, self-assembled films and cast films) interfaces have been reviewed by Tsukruk [17]. Although this work summarizes various characterization techniques for dendritic films by AFM techniques, in this chapter, we will present recent progress on the characterization of the dendritic film surface morphologies. 

It was found that dendrimer monolayers formed on a silicon surface by all amine-terminated generations are very smooth and homogeneous, with very light, grainy surface morphologies, Figure 12.7(a). The thickness of dendrimer monolayers was measured by the AFM technique from occasional holes in the... 

There are a few requirements that must be met if this AFM technique is to be used to measure molecular volumes. First, the molecules on the surface must be soft enough that the molecule flattens out completely on the surface, i.e. the... 

The brittleness reported can either be a function of chain scission and/or chain branching as the AFM technique cannot distinguish between those two processes, only that the sample has become brittle as opposed to initial ductility before exposure. 

McLean, R. S., Doyle, M. and Sauer, B. B. 2000. High-resolution imaging of ionic domains and crystal morphology in ionomers using AFM techniques. 

There are four chapters on selective processing. The first of these chapters, by Dalton, focuses on using XPS and AFM techniques for the direct study of selective reagent adsorption. Next, Breen presents recent developments in using... 

Electrodeposition on semiconductor surfaces is useful from the point of view of application in metal/semiconductor-Schottky and ohmic contacts. CycKc voltammetry, current transient methods, STM, and AFM techniques have been used to study Pb electrodeposition on n-Si(lll) surface [311, 313-315]. Lead deposition on the H-terminated Si(lll) is... 

The AFM technique is easy to apply, the specimen can be imaged in air or liquid, the resolution is very high, and the sample preparation is much simpler if compared to those required by traditional microscopy. 

AFM technique is able to provide information about the individual molecules of the material and the way in which size and shape of molecules affect their behavior in foods. 

Pantolactone, dihydro-3-hydroxy-4//-dimethyl-2(3//)-furanone (103) which is an important starting material of the synthesis of pantothenic acid, was also easily resolved by complexation with 10a. When a solution of 10a (5.5 g, 9.93 mmol) and rac-103 (2.6 g, 20 mmol) in 1 1 benzene-hexane (20 ml) was kept at room temperature for 1 h, a 1 1 complex of 10a and (.S)-(-)- 03 was obtained, after two recrystallizations from 1 1 benzene-hexane, as colorless needles (2.05 g), which upon heating in vacuo gave (S)-(-)-103 of 99% ee (0.39 g, 30%).40 In order to clarify the mechanism of the precise chiral recognition between 10a and (S)-(-)-103, their inclusion complex crystal was studied by X-ray analysis40 and by AFM technique.41... 

In Ref. [76] we showed that the necklace conformations can exist also in the presence of counterions and that they exhibit a variety of conformational transitions as a function of density. The end-to-end distance was found to be a non-monotonic function of concentration and showed a strong minimum in the semi-dilute regime. Here we have found for short chains a collapse of each chain into a globular stable state which repel each other due to their remaining net charge. The focus of a more recent work was to analyze, by extensive computer simulations in detail, three possible experimental observables, namely the form factor, the structure factor and the force-extension relation, which can be probed by scattering and AFM techniques [77]. The details of the simulation techniques can be found in Refs. [76, 77]. 

SECM instruments (77,78) will undoubtedly increase the scope and power of SECM. Further improvements in the power and scope of SECM has resulted from its coupling scanning probe or optical imaging techniques, such as AFM (57,79) or single-molecule fluorescence spectroscopy (80). The combined SECM-AFM technique offers simultaneous topographic and electrochemical imaging in connection to a probe containing a force sensor and an electrode component, respectively. 

Using suitable preparation techniques, reproducible AFM imaging of starch granules has been performed. While studies performed to date had different aims and resulted in images of the starch granules at different resolutions, they are complementary in nature and demonstrate both the versatility and applicability of the AFM technique to starch research. It is, nevertheless, important to recognize the primary sources of artifacts in AFM images.104,111... 

All polymer films were used as prepared, i.e. the samples were not mechanically rubbed. Samples that were contacted with other polymer sheets and afterwards separated, showed highly electrically charged surfaces which cannot be studied by the AFM techniques mentioned below. 

The development of novel methods that allow probing the mechanics of colloidal scale shells is a prerequisite for gaining understanding of the physico-chemical mechanisms that govern shell mechanics. This however requires also an in depth treatment of the shell deformation problem under the specific circumstances of the experiment. Both aims are subject of this paper for the particular case of polyelectrolyte multilayer shells investigated with the colloidal probe AFM technique. While the experimental... 

The more recent neutron reflectivity studies have established that flattened surface micelle or fragmented bilayer structure in more detail and with more certainty, using contrast variation in the surfactant and the solvent [24, 31]. However, the extent of the lateral dimension (in the plane of the surface) and the detailed structure in that direction is less certain. From those neutron reflectivity measurements [24, 31] and related SANS data on the adsorption of surfactants onto colloidal particles [5], it is known that the lateral dimension is small compared with the neutron coherence length, such that averaging in the plane is adequate to describe the data. The advent of the AFM technique and its application to surfactant adsorption [15] has provided data that suggest that there is more structure and ordering in the lateral direction than implied from other measurements. This will be discussed in more detail in a later section of the chapter. At the hydrophobic interface, although the thickness of the adsorbed layer is now consistent with a monolayer, the same uncertainties about lateral structure exist. 

Chen et al. [67,68] further extended the study of binary blends of ESI over the full range of copolymer styrene contents for both amorphous and semicrystalline blend components. The transition from miscible to immiscible blend behavior and the determination of upper critical solution temperature (UCST) for blends could be uniquely evaluated by atomic force microscopy (AFM) techniques via the small but significant modulus differences between the respective ESI used as blend components. The effects of molecular weight and molecular weight distribution on blend miscibility were also described. 

For the sake of completeness It is recalled that AFM techniques (see sec. 1.2) can also be used for adsorption from solution. For this method to work, the adsorbed molecules should be tightly adsorbed, in case the tip displaces them. This requires flat surfaces with molecules fitting in registry, Langmulr-Blodgett layers and similar adsorbates. 

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