Atomic Force Microscopy AFM

AFM has been utilized successfully to measure the film formation characteristics of emulsion polymers [116,117], including emulsion blends [118,119]. With emulsion blends comprised of a high Tg/lowTg immisdble emulsion blend, the individual high Tg particles are easily resolved for room temperature cast samples as shown in Fig. 5.20. With annealing, the high Tg particles coalesce with the structure shown in Fig. 5.21. 

Atomic force microscopy measures surface morphology and surface interaction forces at the nanoscale level. It belongs to a broad range of probe microscopy family which exploits a 

Atomic force microscopy (AFM), invented in 1985 by Binnig, Quate, and Gerber [5.4, 

The value of the pull-off force can he reduced significantly hy imaging under liquids, because of elimination of capillary condensation forces, which pull the tip towards the sample. 

From the general principles described in the previous section the following basic components of an AFM can be identified  

Usually, in AFM the position of the tip is fixed and the sample is raster-scanned. After manual course approach with fine-thread screws, motion of the sample is performed with a piezo translator made of piezo ceramics like e. g. lead zirconate tita-nate (PZT), which can be either a piezo tripod or a single tube scanner. Single tube scanners are more difficult to calibrate, but they can be built more rigid and are thus less sensitive towards vibrational perturbations. 

In contrast to many other surface analytical techniques, like e. g. scanning electron microscopy, AFM does not require vacuum. Therefore, it can be operated under ambient conditions which enables direct observation of processes at solid-gas and solid-liquid interfaces. The latter can be accomplished by means of a liquid cell which is schematically shown in Fig. 5.6. The cell is formed by the sample at the bottom, a glass cover - holding the cantilever - at the top, and a silicone o-ring seal between. Studies with such a liquid cell can also be performed under potential control which opens up valuable opportunities for electrochemistry [5.11, 5.12]. Moreover, imaging under liquids opens up the possibility to protect sensitive surfaces by in-situ preparation and imaging under an inert fluid [5.13]. 

Whereas XRD patterns of the thin crystalline films provide information on the orientation and lattice distances perpendicular to the substrate, AFM has proven to be a powerful technique for obtaining structural information of thin-film surfaces of conjugated materials [95]. AFM imaging of the surface of a thin (10 nm) annealed film of Ooct-OPV5 confirmed the domain structure of the an- 

For this compound, the diffraction pattern (see Fig. 16-34) indicates that the as-deposited film is considerably more crystalline than that of Ooct-OPV5-CN. Annealing carried out at 160 °C for 5 min results in a polycrystalline film with im- 

The terms SFM (scanning force microscopy) and AFM (atomic force microscopy) are used synonymously the former term is used less frequently. In the initial stages of development, the latter term was exclusively used for setups providing atomic (or better) resolution. 

Chemical sensitivity can be conferred to AFM by coating the tip with covalently linked monolayers which affect the tip-surface interaction the method is called chemical force microscopy [77]. Additional modulation of the piezo actuator operating in z-direction and evaluation of the force signal can be used to measure the adhesion force between a surface and a chemically modified AFM tip [78]. Metal coated AFM tips can be used in a scanning electrochemical microscopy (SECM, see p. 264) mode [79] in studies of crystal dissolution or growth where surface processes are associated with considerable fluxes of species. 

Instrumentation. A cantilever with a sharp tip interacting with the surface under investigation is used. The actual bending of the cantilever is measured with a laser beam deflected from a mirror-like surface spot on the back of the cantilever towards a position-sensitive photodetector. The measured signal is used to control the piezo actuators. A constant force mode in which the cantilever-surface distance is kept at a preset interaction force and a constant height mode of scanning operation are possible. The principle of operation is schematically outlined in Fig. 7.9. 

In actual operation in the contact mode, the tip touches the surface like the stylus of a record player. In the non-contact mode, the cantilever is oscillated at a frequency close to the resonance frequency with a large amplitude. In this mode, vertical long-range forces are probed, whereas lateral forces (friction-like forces in the plane of the sample surface) are almost non-effective. These forces have been employed in lateral force microscopy (LFM). 

With chemically modified AFM tips, adhesion forces between the tip and a two-component self-assembled monolayer on a gold electrode have been studied [87]. Utilizing the different strengths of interaction between the modified tip (methyl and carboxyl terminating group functionalized), SAM areas with methyl and carboxyl end groups could be distinguished. 

The AFM makes use of a sharp tip attached to a cantilever, acting as a spring. Unlike STM, where the tunneling current is a measure of the interaction, the force between tip and sample is detected via its mechanical influence on the cantilever deflection or resonance. The AFM can be used to study insulating, semiconducting and conducting samples. 

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The ability to control the position of a fine tip in order to scan surfaces with subatomic resolution has brought scanning probe microscopies to the forefront in surface imaging techniques. We discuss the two primary techniques, scanning tunneling microscopy (STM) and atomic force microscopy (AFM) the interested reader is referred to comprehensive reviews [9, 17, 18]. 

Friction can now be probed at the atomic scale by means of atomic force microscopy (AFM) (see Section VIII-2) and the surface forces apparatus (see Section VI-4) these approaches are leading to new interpretations of friction [1,1 a,lb]. The subject of friction and its related aspects are known as tribology, the study of surfaces in relative motion, from the Greek root tribos meaning mbbing. 

We confine ourselves here to scanning probe microscopies (see Section VIII-2B) scanning tunneling microscopy (STM) and atomic force microscopy (AFM), in which successive profiles of a surface (see Fig. VIII-1) are combined to provide a contour map of a surface. It is conventional to display a map in terms of dark to light areas, in order of increasing height above the surface ordinary contour maps would be confusing to the eye. 

The most popular of the scanning probe tecimiques are STM and atomic force microscopy (AFM). STM and AFM provide images of the outemiost layer of a surface with atomic resolution. STM measures the spatial distribution of the surface electronic density by monitoring the tiumelling of electrons either from the sample to the tip or from the tip to the sample. This provides a map of the density of filled or empty electronic states, respectively. The variations in surface electron density are generally correlated with the atomic positions. 

Annis B K, Noid D W, Sumpter B G, Reffner J R and Wunderlich B 1992 Application of atomic force microscopy (AFM) to a block copolymer and an extended chain polyethylene Makromol. Chem., Rapid. Commun. 13 169 Annis B K, Schwark D W, Reffner J R, Thomas E L and Wunderlich B 1992 Determination of surface morphology of diblock copolymers of styrene and butadiene by atomic force microscopy Makromol. Chem. 193 2589... 

Experimental techniques based on the application of mechanical forces to single molecules in small assemblies have been applied to study the binding properties of biomolecules and their response to external mechanical manipulations. Among such techniques are atomic force microscopy (AFM), optical tweezers, biomembrane force probe, and surface force apparatus experiments (Binning et al., 1986 Block and Svoboda, 1994 Evans et ah, 1995 Israelachvili, 1992). These techniques have inspired us and others (see also the chapters by Eichinger et al. and by Hermans et al. in this volume) to adopt a similar approach for the study of biomolecules by means of computer simulations. 

Several striking examples demonstrating the atomically precise control exercised by the STM have been reported. A "quantum corral" of Fe atoms has been fabricated by placing 48 atoms in a circle on a flat Cu(lll) surface at 4K (Fig. 4) (94). Both STM (under ultrahigh vacuum) and atomic force microscopy (AFM, under ambient conditions) have been employed to fabricate nanoscale magnetic mounds of Fe, Co, Ni, and CoCr on metal and insulator substrates (95). The AFM has also been used to deposit organic material, such as octadecanethiol onto the surface of mica (96). New appHcations of this type of nanofabrication ate being reported at an ever-faster rate (97—99). 

The very new techniques of scanning tunnelling microscopy (STM) and atomic force microscopy (AFM) have yet to establish themselves in the field of corrosion science. These techniques are capable of revealing surface structure to atomic resolution, and are totally undamaging to the surface. They can be used in principle in any environment in situ, even under polarization within an electrolyte. Their application to date has been chiefly to clean metal surfaces and surfaces carrying single monolayers of adsorbed material, rendering examination of the adsorption of inhibitors possible. They will indubitably find use in passive film analysis. 

The lithium morphology at the beginning of the deposition was measured by in-situ atomic force microscopy (AFM) [42], When lithium was deposited at 0.6 C cm2, small particles 200-1000 nm in size were deposited on the thin lines and grain boundaries in LiC104-PC. Lump-like growth was observed in LiAsF6-PC along the line. 

Film-forming chemical reactions and the chemical composition of the film formed on lithium in nonaqueous aprotic liquid electrolytes are reviewed by Dominey [7], SEI formation on carbon and graphite anodes in liquid electrolytes has been reviewed by Dahn et al. [8], In addition to the evolution of new systems, new techniques have recently been adapted to the study of the electrode surface and the chemical and physical properties of the SEI. The most important of these are X-ray photoelectron spectroscopy (XPS), SEM, X-ray diffraction (XRD), Raman spectroscopy, scanning tunneling microscopy (STM), energy-dispersive X-ray spectroscopy (EDS), FTIR, NMR, EPR, calorimetry, DSC, TGA, use of quartz-crystal microbalance (QCMB) and atomic force microscopy (AFM). 

Atomic force microscopy (AFM) has become a standard technique for high-resolution imaging of the topography of surfaces. It enables one to see nanoscopic... 

SAXS), IR spectroscopy, NMR, transmission electron microscopy (TEM), or atomic force microscopy (AFM) and the thermal transitions by DSC and DMA. 

Valette-Hamelin approach,67 and other similar methods 24,63,74,218,225 (2) mass transfer under diffusion control with an assumption of homogeneous current distribution73 226 (3) adsorption of radioactive organic compounds or of H, O, or metal monolayers73,142,227 231 (4) voltammetry232,233 and (5) microscopy [optical, electron, scanning tunneling microscopy (STM), and atomic force microscopy (AFM)]234"236 as well as a number of ex situ methods.237 246... 

Atomic force microscopy (AFM) has been used to characterize dendrimers that have been adsorbed onto a surface such as silica. AFM involves moving a finely tipped stylus across a surface and monitoring the tip movements as it traces the surface topography. In studying adsorbed dendrimers, samples can be scanned repeatedly and in a variety of directions. When this is done, it is found that all the images are the same. True dendrimers form objects of only one size. 

It is our experience that to the first question, the most common student response is something akin to Because my teacher told me so . One is tempted to say that it is a pity that the scientific belief of so mat r students is sourced from an authority, rather than from empirical evidence - except that when chemists are asked question (ii), they find it not at all easy to answer. There is, after all, no single defining experiment that conclusively proves the claim, even though it was the phenomenon of Brownian motion that finally seems to have clinched the day for the atomists 150 or so years ago. Of course, from atomic forced microscopy (AFM), we see pictures of gold atoms being manipulated one by one - but the output from AFM is itself the result of application of interpretive models. 

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