Interface crystal-amorphous

Fig. 2.17. Schematic illustration of the various quantities used to describe the growth of an amorphous interlayer. The composition profiles, chemical potential profile, etc., are shown. The quantity xA is the concentration of element A in the diffusion couple (in the text xA = 1 — x), while X, and X2 are the positions of the amorphous/crystal interfaces...

Channeling measurements have been used to study the epitaxial regrowth of Ge and Si crystals amorphized by ion implantation for a variety of crystal orientations (Csepregi et al. 1977). These studies have shown that, with the exception of (111) orientated Si crystals and samples cut within 16° of the (111) direction, the amorphous/crystal interface moves with a constant velocity toward the surface (at a fixed annealing temperature) and maintains a laterally uniform front. 

The first term in Eq. (5.11) reflects the gain in the bulk energy while the second term accounts for the variation in the total free energy associated with the replacement of the substrate/amorphous and vapour/amorphous interfaces (dAi) by the substrate/crystal and vapour/crystal interfaces. The last term represents the increase in the total free energy due to the increase in the crystal/amorphous interface (dA2). Taking into account Eq. (5.11) and the expressions for dV, dAi and dA2 given above, dG/dN can be expressed as ... 

Because experimental study of the structure of crystal/liquid interfaces has been difficult due to the buried nature of the interface and rapid structural fluctuations in the liquid, it has been investigated by computer simulation and theory. Figure B.3 provides several views of crystal/liquid (or amorphous phase) interfaces, which must be classified as diffuse interfaces because the phases adjoining the interface are perturbed significantly over distances of several atomic layers. 

On the other hand, a diffuse interface possesses a significantly wider core that extends over a number of atomic distances. A diffuse crystalline/amorphous phase interface is shown in Fig. B.3. Similar structures exist in crystal/liquid interfaces [5]. 

The effects of damage by ion implantation on the low-temperature diffusion of dopant can also be studied by implanting Si+ or Ge+ ions into predeposited layers in Si. Recently, Servidori et al. (58) studied the influence of lattice defects induced by Si+ implantation. Using triple crystal X-ray diffraction and TEM, they confirmed (1) that below the original amorphous surface-crystal interface, interstitial dislocation loops and interstitial clusters exist and (2) that epitaxial regrowth leaves a vacancy-rich region in the surface. 

For simulating the heterogeneous crystallization process, a test specimen witii a dimension of 3a 3a l2a including two amorphous-crystalline interfaces is prepared by attaching 12 layers of c-Si (216 atoms), as a crystalline seed, to a bulk fl-Si (648 atoms). The bulk a-Si is obtained by the above cooling process and pre-annealed at 500 K for 200 ps. The constant NVT MD simulations are carried out using the Newton equation with a time step for the integration set at 2fs. 

Figure Bl.24.11. The backscattering yield from an Si sample that has been implanted with Si atoms to form an amorphous layer. Upon annealing this amorphous layer recrystallizes epitaxially leading to a shift in the amorphous/single-crystal interface towards the surface. The aligned spectra have a step between the amorphous and crystal substrate which shifts towards the surface as the amorphous layer epitaxially recrystallizes on the Si. 

Finally, the degree of nucleation at the amorphous/ semicrystalline interfaces was found to be temperature dependent. When the crystallization temperature was raised, the nucleating efficiency of the interface was found to decrease [Bartezak et al., 1987]. 

So, if the interfacial regions have to be considered, we must differentiate the amorphous/crystal polymer interface from the amorphous polymer/mineral interface (29). By DMA measurements, a decrease in Tg matrix from 7°C for the PP/talc composites and also for the neat PP processed under similar conditions while a decrease upto 13°C was found for PP/mica composites. A higher fraction of free amorphous phase on the PP/mica system than on the PP/talc composites was evidenced. This free amorphous phase appeared to participate in the cooperative segmental free-rotation motion, well accepted (30) to be responsible for glass transition for the polymer matrix as fully discussed in Reference 29. 

Figure 4.55 shows a plot of various heat capacity data of PTT as shown in Figure 4.54 [65]. The fully amorphous point was calculated from the heat capacity of the glass and the melt, both extrapolated to the glass transition temperature. The heat of fusion of the 100% crystalline sample agrees also with a discussion of the entropies expected from similar polymers. The data points with somewhat lower ACp are most likely due to a small amount of RAF [64], frozen at the crystal interface, as indicated by the thin line.

Material with a higher degree of crystalline nature tends to be brittle because of the weak crystal-crystal interface. Amorphous material will have rubbery or glassy material behavior depending upon its glass transition temperature. 

Fig. 6.19 Crystal-Uke atoms in the layer left) and the fin right) after 60 ns annealing. The amorphous/crystaUine interface is visutilised by the line...

Lamellar morphology variables in semicrystalline polymers can be estimated from the correlation and interface distribution fiinctions using a two-phase model. The analysis of a correlation function by the two-phase model has been demonstrated in detail before [30,11] The thicknesses of the two constituent phases (crystal and amorphous) can be extracted by several approaches described by Strobl and Schneider [32]. For example, one approach is based on the following relationship ... 

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