Surface force microscopy

Surface force microscopy Surface topology, homogeneity local differences... 

Spectroscopic ellipsometry, flow cell ATR-FTIR, flow cell Quartz crystal microbalance, flow cell Surface plasmon resonance, flow cell Surface force microscopy... 

The problem of lamellar structures like 2H-M0S2 and 2H-WS2 is the easy oxidation at the edges of crystals. These structures easily adhere to surfaces, while fullerenes do not, as Rapoport et al. showed using surface force microscopy (SFM). IFs are swept by the tip in the contact image mode, which proves their weak adhesion on a surface [41]. In the case of porous matrices, platelets are perpendicular to the surface involving their rapid deterioration during friction, whereas the fullerenes enter into the asperities, which act as reservoirs [42]. The spherical structure of the IF avoids problems of orientation encountered with 2H platelets [43]. 

Figure 40 Surface force microscopy height images of polystyrene-WocAr-poly(o-butyl methacrylate) films on corrugated substrates with 170 and 80nm periods, respectively. The images are 5pm wide. The direction of ridge orientation is shown by the white arrows. Adapted and reprinted with permission from Fasolka, M. J. etal. Phys. Rev. Lett. 1997, 79(16), 3018.2 ...

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]. 

AFM Atomic force microscopy [9, 47, 99] Force measured by cantilever deflection as probe scans the surface Surface structure... 

SFM Scanning force microscopy Another name for AFM Surface structure... 

Protein adsorption has been studied with a variety of techniques such as ellipsome-try [107,108], ESCA [109], surface forces measurements [102], total internal reflection fluorescence (TIRE) [103,110], electron microscopy [111], and electrokinetic measurement of latex particles [112,113] and capillaries [114], The TIRE technique has recently been adapted to observe surface diffusion [106] and orientation [IIS] in adsorbed layers. These experiments point toward the significant influence of the protein-surface interaction on the adsorption characteristics [105,108,110]. A very important interaction is due to the hydrophobic interaction between parts of the protein and polymeric surfaces [18], although often electrostatic interactions are also influential [ 116]. Protein desorption can be affected by altering the pH [117] or by the introduction of a complexing agent [118]. 

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. 

These authors doubt that such interactions can be estimated other than empirically without fairly accurate knowledge of the structure in the interfacial region. Sophisticated scattering, surface force, and force microscopy measurements are contributing to this knowledge however, a complete understanding is still a long way off. Even submonolayer amounts of adsorbed species can affect adhesion as found in metals and oxides [74]. 

We have considered briefly the important macroscopic description of a solid adsorbent, namely, its speciflc surface area, its possible fractal nature, and if porous, its pore size distribution. In addition, it is important to know as much as possible about the microscopic structure of the surface, and contemporary surface spectroscopic and diffraction techniques, discussed in Chapter VIII, provide a good deal of such information (see also Refs. 55 and 56 for short general reviews, and the monograph by Somoijai [57]). Scanning tunneling microscopy (STM) and atomic force microscopy (AFT) are now widely used to obtain the structure of surfaces and of adsorbed layers on a molecular scale (see Chapter VIII, Section XVIII-2B, and Ref. 58). On a less informative and more statistical basis are site energy distributions (Section XVII-14) there is also the somewhat laige-scale type of structure due to surface imperfections and dislocations (Section VII-4D and Fig. XVIII-14). 

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. 

Lateral force microscopy (LFM) has provided a new tool for the investigation of tribological (friction and wear) phenomena on a nanometre scale [110]. Alternatively known as friction force microscopy (FFM), this variant of AFM focuses on the lateral forces experienced by the tip as it traverses the sample surface, which... 

GiessibI F J 1995 Atomic resolution of the silicon (111 )-(7 7) surface by atomic force microscopy Science 260 67... 

Perez R, Payne M C, Stich i and Terakura K 1997 Roie of covaient tip-surface interactions in noncontact atomic force microscopy on reactive surfaces Phys. Rev. Lett. 78 678... 

Zong Q, inniss D, K]oiier K and Eiings V B 1993 Fractured poiymer/siiica fiber surface studied by tapping mode atomic force microscopy Surf. Sc/. Lett. 290 L688... 

Miyatani T, Florii M, Rosa A, Fu]ihira M and Marti O 1997 Mapping of electric double-layer force between tip and sample surfaces in water with pulsed-force-mode atomic force microscopy Appl. Phys. Lett. 71 2632... 

Bammerlin M, Luthi R, Meyer E, Baratoff A, Lu J, Guggisberg M, Gerber Ch, Howald L and Gutherodt H-J 1997 True atomic resolution on the surface of an insulator via ultrahigh vacuum dynamic force microscopy Probe Microsc. 1 3... 

Fukui K, Onishi H and Iwasawa Y 1997 Atom-resolved image of the 7102(110) surface by noncontact atomic force microscopy Phys. Rev. Lett. 79 4202... 

Raza H, Pang C L, Haycock S A and Thornton G 1999 Non-contact atomic force microscopy imaging of 7102(100) surfaces Appl. Surf. Sc/. 140 271... 

Hegenbart G and Mussig Th 1992 Atomic force microscopy studies of atomic structures on AgBr(111) surfaces Surf. Sc/. Lett. 275 L655... 

Overney R, Howald L, Frommer J, Meyer E, Brodbeck D and Guntherodt H 1992 Molecular surface structure of organic crystals observed by atomic force microscopy Ultramicroscopy 42-A4 983... 

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