Thin and Ultrathin Films

Nevertheless, situahons exist where the spreading of thin hlms is important on its own. Better resolution than ophcal microscopy, with about +14 error in linear measurement shows that a thin precursor him exists ahead of this region, a him sufhciently thin (below 100 run) that disjoining pressiue plays a role (Bascom et al., 1964). Lopez et al. (1976) used Hamaker-type disjoirung pressiue as a driving force and showed that such contact lines spread as 1 instead of the slower in the bulk liquid. 

Even fiuther ahead lies the region of ultrathin hlms. In general, they appear to be thick adsorbed hlms, the rate of movement of which is governed by an effective surface diffusion (Heslot et al., 1989 O Connor et al., 1996). If a very small soiuce is layered on a solid surface inihally and it spreads under surface diffusion, then the governing equahon (from Equarion 6.2) is 

A very peculiar kind of spreading has also been observed, in that the liquid prohle is strahhed, going up in steps of one molecular layer thickness (Fraysee et al., 1993). Quantitative models exist (de Games and Cazabat, 1990). 

It appears that for answers to the questions of what the stincture of the actual contact line is under dynamic conditions and what causes it to spread, we will have to move from phenomenology to molecular physics. Early work goes back to Thompson and Robbins (1989). Recent works by van Remoortere et al. (1999) 

Equations of motion of individual molecules are governed by Newton s laws. For the /th particle 

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Another area of development is in lower-cost thin- and ultrathin-film designs. One such product is made by Nanosolar of copper indium gallium selenide (CIGS), which is claimed to achieve up to 19.5% efficiency and is as thin as a newspaper. This claim is yet to be proved. The collector cost is also reduced, because the substrate material on which the ink is printed is much less expensive than the stainless steel substrates that are often used in thin-film solar panels. The manufacturer claims a five- to tenfold reduction in the collector cost (about 1/W) compared to conventional PV cells. 

A large number of solution-based processing methods have been used for manufacturing films and fibers from a wide variety of commercial polymers [94-96]. These methods are in fact ideal for the processing of nonmelting but soluble polymers or for the processing of thermally sensitive polymers. Also, they are often the most appropriate methods for the fabrication of very thin films and fibers that cannot be produced by melt extrusion, and they are particularly useful to deposit functional thin and ultrathin films over a wide variety of substrates. 

Fig. 21 Temperature dependence of the loss modulus E" for PS1.46M thin and ultrathin films coated on PI substrates. The data for a control PI are also shown...

Finally, dynamic mechanical analysis (DMA) for PS in thin and ultrathin films is discussed. Studies over the past 15 years have shown that the Tg of nanometer thick polymer films can vary significantly with the film thickness K) when h falls below 50 nm [61-65]. Although the Tg has been found to both increase [5, 66, 67] and decrease [4, 10, 63, 68, 69] with decreasing h, the latter has drawn vastly more attention because of the significantly bigger size of the effect. 

Fig. 24 Temperature depaidence of " for PS 1.46M thin and ultrathin films sandwiched between SiO c layers...

Interfacial stability and dynamics of thin and ultrathin films, thin liquid films, and foams... 

Brennecka, G.L., Parish, C.M., Tuttle, B.A., Brewer, L.N., and Rodriguez, M.A. (2008) Reversibility of the perovskite-to-fluorite phase transformation in lead-based thin and ultrathin films. Adv. Mater., 20, 1407-1411. 

Mareau and Prud homme. Multilayer structures grown at room temperature in films with d > 100 nm, best described as poorly faceted hedrites, exhibit single crystal texture by ED [70]. The inescapable conclusion is that, at least in thin and ultrathin films, the growth direction of, or within, a single crystal can occur in a manner that bears no relation to crystal symmetry. 

In the case of a composite membrane consisting of a skinless porous substrate and a dense film, permeability and permselectivity may be determined solely by the resistance of the denser film. Different membrane polymers may therefore be employed for the thin barrier layer and the thick support structure. This permits a combination of properties which are not available in a single material. Such membranes were initially developed for desalination by reverse osmosis where they are known as thin- or ultrathin-film composites or nonlntegrally-skinned membranes. A second type of composite membrane is utilized for gas separations. It is a composite consisting of an integrally-skinned or asymmetric membrane coated by a second, more permeable skin which is used to fill skin defects. The inventors of the latter have entitled their device a resfstanee model membrane, but the present author prefers the term coated integrally-skinned composites. 

A Rheovibron DDV-OIFP (A D, Tokyo, Japan) tester has been used for DMA. In general, DMA has been accepted as a powerful method for studying the relaxation behavior of bulk samples. However, previous to these experiments, no one knew whether the technique was sensitive enough to be used with thin and ultrathin polymer films. To answer this question, a d3mamic viscoelastic measurement for thin PS films supported on substrates was conducted. 

B. SURFACE HYPERFINE FIELD. The demagnetizing field and the Lorentz field are not defined for the atoms at the surface. Calculations of the magnetic dipole fields at atoms near the surface in fine particles and thin films of a-Fe show that only the first surface layer is perturbed, with variations of the order of lOkOe depending on the position at the surface. Studies of thin and ultrathin metal films by Mossbauer spectroscopy (see, e.g.. Refs. 31, 224, 238, and 239) show that one or two atomic layers are perturbed, as for the magnetization (see Section B.3). The surface hyperfine field may be larger or smaller than in the bulk at... 

Thin Films and Ultrathin Films of Polymer Blends 581 89 84... 

The Kelvin Probe Technique as Reference Electrode for Application on Thin and Ultrathin Electrolyte Films... 

Despite the enormous practical importance, little is known about the fundamentals of what actually determines the surface properties of the thin and ultrathin organic/polymeric films used as functional coatings. Many physical and chemical factors have been identified but the overall picture is very complex and hence we are far from a coherent understanding. 

Frank CW, Rao V, Despotopoulou MM, Rease RFW, Hins-berg WD, Miller RD, Rabolt JF. Structure in thin and ultrathin spin-cast polymer films. Science 1996 273 912-915. 

At the end of this article, one should be able to briefly describe the anomalous transitions in near-surface layers, nanocomposites, and ultrathin films. Glass Transition on the Polymer Surface and in the Polymer Thin... 

Hall DB, Undeihill P, Torkelson JM (1998) Spin coating of thin and ultrathin polymer films. Polym Eng Sci 38(12) 2039-2045... 

As discussed in Section 2.23.1.2, one of the advantages of AFM over electron miaoscopy is that it enables 3D imaging of untreated samples in a physically relevant environment. Given the surface nature of the technique, initial AFM studies of phase separation processes in polymer mixtures have been primarily focused on thin or ultrathin films. " " The confinement in a film and component segregation to the interfaces have been shown to have a profound effect in both spinodal decomposition, and nucleation and growth processes of the phase separation. The spectrum of AFM applications has been extended to bulk phase separation of polymer mixtures using conventional and oblique microtoming of polymer blend films. 

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