Tip imaging

The main body of artifacts in STM and SFM arises from a phenomenon known as tip imaging Every data point in a scan represents a convolution of the shape of the tip and the shape of the feature imaged, but as long as the tip is much sharper than the feature, the true edge profile of the feature is represented. However, when the feature is sharper than the tip, the image will be dominated by the edges of the tip. Fortunately, this kind of artifact is usually easy to identify. 

Because many kinds of features have steep sides, tip imaging is a common plague of SFM imj es. One consolation is that the height of the feature will be reproduced accurately as long as the tip touches bottom between features. Thus the roughness statistics remain fairly accurate. The lateral dimensions, on the other hand, can provide the user with only an upper bound. 

The main difficulty with STM and SFM techniques is the problem of tip imaging. Neither technique is recommended for obtaining accurate measurements of edge profiles of vertical or undercut surfaces. In addition, SFM tips cannot accurately image the lateral dimensions of features with sides steeper than 55° at present. Obtaining SFM tips with more suitable aspect ratios is an area of active research. 

Carboxylic groups positioned at the open ends of SWCNTs were coupled to amines to form AFM probes with basic or hydrophobic functionalities by Wong et al. [117] (Scheme 1.8). Force titrations recorded between the ends of the SWCNT-AFM tips and hydroxy-terminated SAMs confirmed the chemical sensitivity and robustness of the AFM tips. Images recorded on patterned SAM allowed real molecular-resolution imaging [117]. 

Fig. 36. High-resolution in-situ AFM image of Ge( 11) in H2SO4 (a) and time sequence of images (b) showing the growth of a hydride layer. The regular rectangular shape of features, which should be dendrites, is due to tip imaging (after [21]).

FIGURE 6 Nozzle tip images, twin-fluid atomizer, showing impact of feed rheology. 

Fig. 2.27 SEM images of different specialized AFM probes (1) tips of widely different radii (a) 870 nm, (b) 150 nm and (c) 20 nm (d, e) thermal probe and tip (images courtesy Anasys Instrument Inc.)...

One central concern with routine AFM on polymers is the presence of shear forces that occur in CM. These forces are a result of friction between AFM probe tip and the polymer sample and may deform and plastically modify the polymer surface. This has been observed even for glassy materials, such as PS, when imaged at ambient conditions (see Sect. 3.2.3 in Chap. 3 Fig. 3.16). In addition to sample damage, the tip may be affected by adhering particulates or, even worse, by wear. These phenomena limit the resolution dramatically and may result in unwanted artefacts (excessive tip imaging). Thus, minimized imaging forces are essential, and this may require the operation under a suitable liquid to eliminate capillary forces. 

Figure 4.10 The JSPM-5200 scanning probe microscope can be configured as either an atomic force microscope (ATM) or scanning tunnelling microscope (STM) by changing the tip (Image courtesy of Jeol).

Figure 3. Transmission electron microscopy of enzyme-cleaved, tobacco mosaic virus particles on the apex of a tungsten field-emitter tip (imaged at 200kV). TMV sample kindly supplied by P. J. Butler, the MRC, Cambridge, England.

Lightning over Seattle, Washington. [Chuck Pefley/Tips Images)... 

Figure 3 Scanning electron micrograph of (A) mechanically sharpened platinum-iridium STM probe, (B) silicon nitride AFM cantilevers, and (C) carbon nanotube tip on silicon nitride AFM cantilever tip. (Images (A) and (B) are courtesy of Veeco Instruments Santa Barbara, CA, USA, with permission.)...

As expected for an electrochemical process, the i-V curves also depend upon the tip material. For a blunt W tip on mica treated with TE buffer solution (Figure 17.2.20B), the current is stable and increases almost linearly for positive tip bias, but tends to saturate and shows considerable hysteria on scan reversal in the negative tip bias region. Thus with a W tip, imaging at positive bias is appropriate. The observed electrochemical behavior also depends on the pretreatment of the insulating substrate like mica. For example, the voltam-metric behavior is very different when the mica is simply immersed in water (even for a... 

Study of Adhesion Properties of Polypropylene Surfaces by Atomic Force Microscopy Using Chemically Modified Tips Imaging of Functional Group Distribution... 

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