Substrates smoothing layer

Relaxation phenomena arise already during the moment of a film drawing on a substrate when a shift pressure appears and possibilities for the cohesion break of an interface between the film and the substrate are created. During the drying, the coating should relax, forming a thin and smooth layer, thus the module of elasticity increases. Thus, the mechanical relaxation promotes decrease of the probability of fragile destruction and exfoliation of the film from the substrate [7],... 

Fig. 2 Example of an optimized OLED structure. (1) (2) cathode, Ag and LiE (3) electron transporting layer Alq3 (=Alqol3). (4) hole blocking layer, BCP. (5) electron-hole recombination zone/emitter layer, PVK doped, for example, with Ir(ppy)3. (6) and (7) anode, PEDOT doped with PSS (6) for improvement of hole injection and substrate smoothness and ITO (7) (=indium tin oxide). (8) glass support. For further details and explanations see text...

Spin casting is the technique used to produce ultra thin, smooth layers of polymers on top of flat substrates. A drop of a solution with concentrations of the order of a few mg per ml PAT in chloroform, say, is applied on top of the substrate surface as the substrate is spun around its surface normal at a speed of about 3000 rpm. The solvent evaporates immediately, i.e. in a fraction of a second. The technique is used for preparation of polymer samples for absorption studies. 

The experimental results presented here impressively demonstrate that a simple dewetting process of a thin polymer film on a chemically patterned substrate allows to transform a smooth layer of material into various stmctures. For increasing thickness of the layer the chemical pattern produces the following sequence (see Fig. 2.14) Cylindrical holes—droplets with the shape of a spherical cap—toroids. 

It is a challenge to prepare periodic metal-silicon multilayers with a period thickness of just a few nanometers, because the layers have to be extremely smooth (the roughness parameter o should be smaller than 0.5 nm). The best deposition temperature for molybdenum-silicon multilayers prepared by electron beam evaporation is about I70°C at lower temperatures the deposited atoms do not have enough mobility to form smooth layers, while at higher temperatures interdifftision increases and silicide interlayers are formed [1,7]. In conventional CVD the necessary substrate temperatures are much higher, which makes the use of a non-thermal energy supply, such as plasma or hot-filament, for the fiagmentation of the precursors, inevitable. 

For a reconstmcted surface, the effect of an adsorbate can be to provide a more bulk-like enviromnent for the outemiost layer of substrate atoms, thereby lifting the reconstmction. An example of this is As adsorbed onto Si(l 11)-(7 X 7) [37]. Arsenic atoms have one less valence electron than Si. Thus, if an As atom were to replace each outemiost Si atom in the bulk-temiinated stmcture, a smooth surface with no impaired electrons would be produced, with a second layer consisting of Si atoms in their bulk positions. Arsenic adsorption has, in fact, been found to remove the reconstmction and fomi a Si(l 11)-(1 x l)-As stmcture. This surface has a particularly high stability due to the absence of dangling bonds. 

Figure Bl.21.1 shows a number of other clean umeconstnicted low-Miller-index surfaces. Most surfaces studied in surface science have low Miller indices, like (111), (110) and (100). These planes correspond to relatively close-packed surfaces that are atomically rather smooth. With fee materials, the (111) surface is the densest and smoothest, followed by the (100) surface the (110) surface is somewhat more open , in the sense that an additional atom with the same or smaller diameter can bond directly to an atom in the second substrate layer. For the hexagonal close-packed (licp) materials, the (0001) surface is very similar to the fee (111) surface the difference only occurs deeper into the surface, namely in the fashion of stacking of the hexagonal close-packed monolayers onto each other (ABABAB.. . versus ABCABC.. ., in the convenient layerstacking notation). The hep (1010) surface resembles the fee (110) surface to some extent, in that it also...

The surface forces apparatus (SEA) can measure the interaction forces between two surfaces through a liquid [10,11]. The SEA consists of two curved, molecularly smooth mica surfaces made from sheets with a thickness of a few micrometers. These sheets are glued to quartz cylindrical lenses ( 10-mm radius of curvature) and mounted with then-axes perpendicular to each other. The distance is measured by a Fabry-Perot optical technique using multiple beam interference fringes. The distance resolution is 1-2 A and the force sensitivity is about 10 nN. With the SEA many fundamental interactions between surfaces in aqueous solutions and nonaqueous liquids have been identified and quantified. These include the van der Waals and electrostatic double-layer forces, oscillatory forces, repulsive hydration forces, attractive hydrophobic forces, steric interactions involving polymeric systems, and capillary and adhesion forces. Although cleaved mica is the most commonly used substrate material in the SEA, it can also be coated with thin films of materials with different chemical and physical properties [12]. 

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