Films, three-dimensional

In our recent work, we have used Pd deposited on t hkl) in order to characterize thin metal films [Arenz et al., 2002] and to test their catalytic activity (Fig. 8.16). We have employed both methodologies thermal evaporation in UHV and electrochemical deposition. For the Pd/Pt(l 11) system, in situ SXS measurements have been used to show that after the formation of 1 ML of pseudomorphic Pd film, three-dimensional pseudomorphic crystalline islands of pure Pd begin to aggregate. 

The limiting compression (or maximum v value) is, theoretically, the one that places the film in equilibrium with the bulk material. Compression beyond this point should force film material into patches of bulk solid or liquid, but in practice one may sometimes compress past this point. Thus in the case of stearic acid, with slow compression collapse occurred at about 15 dyn/cm [81] that is, film material began to go over to a three-dimensional state. With faster rates of compression, the v-a isotherm could be followed up to 50 dyn/cm, or well into a metastable region. The mechanism of collapse may involve folding of the film into a bilayer (note Fig. IV-18). 

On compression, a gaseous phase may condense to a liquid-expanded, L phase via a first-order transition. This transition is difficult to study experimentally because of the small film pressures involved and the need to avoid any impurities [76,193]. There is ample evidence that the transition is clearly first-order there are discontinuities in v-a plots, a latent heat of vaporization associated with the transition and two coexisting phases can be seen. Also, fluctuations in the surface potential [194] in the two phase region indicate two-phase coexistence. The general situation is reminiscent of three-dimensional vapor-liquid condensation and can be treated by the two-dimensional van der Waals equation (Eq. Ill-104) [195] or statistical mechanical models [191]. 

Figure Bl.22.11. Near-field scanning optical microscopy fluorescence image of oxazine molecules dispersed on a PMMA film surface. Each protuberance in this three-dimensional plot corresponds to the detection of a single molecule, the different intensities of those features being due to different orientations of the molecules. Sub-diffraction resolution, in this case on the order of a fraction of a micron, can be achieved by the near-field scaiming arrangement. Spectroscopic characterization of each molecule is also possible. (Reprinted with pennission from [82]. Copyright 1996 American Chemical Society.)...

Monitoring surface structures, especially during thin-film epitaxial growth can distinguish two- and three-dimensional defects... 

Figure 10.5. The three modes of growth of films (a) Frank and van der Merwe s monolayer (two-dimensional) mode (b) the Volmer-Weber three-dimensional mode (c) the Stranski-Krastanov mode involving two-dimensional growth followed by three-dimensional growth.

Film formation proceeds through condensation of hydroxyls to create a three-dimensional oxide network ... 

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