Contact AFM

The following model of the corrosion process can be proposed based on the wealth of data provided by the combined application of SPFM, contact AFM, and IRAS At low RFl, the principal corrosion prodnct, hydrated alnminnm snlfate, is solid. It acts as a diffn-sion barrier between the acid and the alnminnm snbstrate and prevents fnrther corrosion. The phase separation observed between the acid and the salt at low RH strongly snggests that the salt inhibits fnrther corrosion once it precipitates. At high RH, on the other hand, alnminnm snlfate forms a liqnid solntion. Snlfnric acid mixes with this solntion and reaches the nnderlying snbstrate, where fnrther reaction can occnr. The flnid snlfate solntion also wets the snrface better and thns spreads the snlfnric acid. The two processes assist each other, and the corrosion proceeds rapidly once the critical RH of 80-90% is reached. 

Figure 14. (a) A cyclic contact AFM and (b) a fluorescence micrograph measured simultaneously with SNOAM of a mixed monolayer of SA-PFECA-CD (1 1 1/100) polyion complexed with PVA deposited on a cover glass plate. 

AFM can be run under room conditions. It can be performed in either of the two forms— a contact mode and a noncontact mode. It does not require the use of electrically conductive material since (in the contact mode) the tip actually touches the surface rather than residing immediately above it, as is the case with STM. In both the contact and the noncontact mode, light is used as the sensing source rather than an applied voltage. In contact AFM, a cantilever... 

Figure 8.5 a) Schematic of the 7x 7 reconstruction of the Si(l 11) surface, b) Image of a Si 7x 7 surface obtained with a combination of STM and a special non-contact AFM mode [331] (see Section 8.6.3). Only the adatoms are visible under the chosen imaging conditions. Single defects of the surface structure are resolved (circles). The picture was kindly provided by E. Meyer. 

FIG. 2. Contact AFM images of y-Fe2Oj nanocrystal patterns drawn (a) on mica along with (b) its surface plot, (c) on silicon with the native SiOr layer (arrows point to closely-drawn patterns) and (d) on etched silicon. 

Contact AFM [241, 242] Topographic imaging of solid substrates Mechanical properties Local adhesive properties... 

Fig 7. Non-contact AFM image of a Ti02(l 10)(lxl) surface. Reprinted with permission from ref [54],... 

A model involving discrete bond breaking was proposed for the formation of the (1x3) surface [107,108]. Surfaces were prepared that exhibited both, the (1x1) termination and the ridges typical for the (1x3) surface. STM and non-contact AFM images showed an intermediate phase, which had a (1x3) symmetry, but did not possess the characteristics of the microfaceted structure. Raza et al. [107] suggested that the bonds labeled a in Fig. 15 are broken, which allows the Ti atoms to relax towards the other rows of bridging oxygen atoms. 

Zeolite beta has been widely studied as a Bronsted acid catalyst and has been shown to be highly active for reactions such as alkylation and acylation [8,9]. The effect of the crystallite size on the catalytic activity of beta has been investigated [10] but since betas often have very high external surface areas, it is possible that acid sites associated with framework aluminium close to the outer surface will contribute to the overall catalytic activity of the zeolite. This may adversely affect the shape-selectivity of the reaction. In this study a series of beta zeolites with differing Si/Al ratio and ESA were investigated by means of non-contact AFM and N2 absorption measurements and the catalytic activity was tested by an acylation reaction capable... 

Figure 2 Non-contact AFM of (a) calcined BET102B and (b) PBloxA2, top view presentation, scan area 1x1...

Fig. 4.23. Contact AFM scan of a 9/ area on mica substrate showing rectangles of various aspect ratios filled with Au nanocrystals. The patterns were obtained by translating an AFM cantilever dipped in a sol across the surface.

Fig. 5.10 Non-contact AFM image of a silica glass fracture prepared 1 x 10 11 mbar and imaged at 1 x 10-8 mbar [43],...

Fig. 3.44 Intermittent contact AFM of two virions in linear arrangement on graphite (reproduced with permission from [96]). The measured height of 18 nm corresponds to the true diameter, while the width (ca. 85 nm (fwhm)) is attributed to the AFM tip shape. Reproduced with permission from [96]. Copyright 2004. American Chemical Society...

The phase angle shift can be used to obtain contrast due to local differences in energy dissipation as a consequence of different surface characteristics related to materials properties. These different properties allow one to differentiate materials with different adhesion [110] or widely different Young s moduli, if these differences are related to differences in energy dissipation [111-115]. Hence the amorphous and crystalline phases in semicrystalline polymers can be clearly differentiated, as discussed in Sect. 3.2, as well as different phases in polymer blends or filled systems (see below). As an example, we show in Fig. 3.52 an intermittent contact AFM phase image of a block copolymer thin film on silicon [116]. 

Fig. 3.52 Left (a) Schematic of intermittent contact mode AFM and phase imaging right (b) intermittent contact AFM phase image of a 30 nm thin block copolymer films on silicon [(poly(isoprene)-b-poly(ferrocenyl dimethylsilane), 29 kg/mol/15 kg/mol], which displays a in-plane worm-like surface pattern of poly(ferrocenyl dimethylsilane) in a matrix of poly (isoprene). From the 2D FFT analysis (inset) an average repeat period of 33 nm was estimated. Reprinted with permission from [116]. Copyright 2000. American Chemical Society...

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