Solid capping layers

The pressure acting on the fluid layer, from the solid capping layers, consists of four parts [5]. The first pressure contribution comes from the van der Waals interactions across the film [34],... 

We introduce a pressure due to the contact mechanics between the upper and lower solid capping layers because we wish to simulate the local contact between top and bottom layers and the ejection of fluid from this region. We adopt an exponential repulsive term of the form [36]... 

In summary, the different pressures are shown schematically in Fig. 2. The attractive van der Waals forces act across the film and favor thinner film thicknesses, the bending elastic forces depend on the fourth-order derivatives of the height variations and essentially penalizes curvature in the height, the contact pressure is included for numerical stability and ensures that the solid capping layers do not overlap, and finally the stretching elastic forces describe the pressure on the fluid due to in-plane displacements in the solid capping layers. The behavior of the model depends upon the interactions of all these pressures, as well as the kinetics of fluid transport, in response to these pressures. 

Figure 2. Schematic of various pressures accounted for in the model. We include the pressures due to the bending and stretching of the solid capping layers, the van der Waals forces across the film, and a pressure term that accounts for contact mechanics between the top and bottom solid layers.

Initially the van der Waals forces across the film drive undulation growth in these systems and cause the surface instability to occur. The growth is resisted by the elastic deformation of the solid capping layers, which also maintains the films structural integrity. Eventually, the solid capping layers locally meet and the fluid is ejected from these regions of the film to form isolated pockets of fluid. 

Figure 1.9 SEM images [34] of (a) original porous SiC surface after PECE, (b) early stage formation of columnar pore in cross-section, (c) porous surface structure 20 pm below the original surface after 90 min of RIE (the inset shows the Fourier transform of a larger area of this picture), and (d) the self-ordered columnar porous structure below the cap layer in cross-section. Reproduced from Y. Ke, R.P. Devaty and W.J. Choyke, Self-ordered nanocolumnar pore formation in the photoelectro-chemical etching of 6H SiC, Electrochem. Solid-State Lett., 10(7), K24-K27 (2007). Copyright 2007, with permission from The Electrochemical Society...

We now return our attention to the evolution of ultrathin solid-fluid-solid films, which are the focus of this study. Using a computer model, which couples the fluid flow of the polymer with the elastic deformation of the capping layers, we can simulate the evolution of the these films. In particular, we evolve the ultrathin... 

Below 0.7 J/cm, the Si cap suffers strong deformations caused by the melting of the subjacent layer, which is manifested by the cracks seen by SEM and disordered seen in AFM. The recrystallization at these relatively low energy densities starts from both interfaces Si cap/melt and melt/solid SL (or buffer or substrate), so that the existence of a solid surface layer with the thickness varying... 

A solid region capped with a uniform layer of different uniform concentfation. The initial concentration in the capped layer of thickness y i is Ci, and the underneath layer is at concentration C2. The concentration at the fluid-capped layer interface is maintained at Co to start the process diffusion-advective process. The concentration profile is... 

In order to prepare an extended-lattice monolayer, the organization of the surface template layer is the crucial step. For zirconium phosphonate layers, it is found that the LB method produces an organized phosphonic acid surface layer that in turn can be used to produce monolayer or multilayer zirconium phosphonate films. Once the template layer is in place, self-assembling the capping layer generates a zirconium phosphonate bilayer that more closely resembles the solid-state structure than does a bilayer formed by capping the template with another LB film. If the LB template is used to prepare multilayer films, the well-characterized and ordered template layer... 

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