Crystalline-amorphous interface

This equation can be used to determine ae using the experimentally determined Tm if the other parameters are known. In the Flory-Vrij model, oe is the sum of the free energy of formation from the melt of the amorphous/crystalline interface, (x0, and the free energy of formation from the melt of the amorphous layer, ad (Ashman and Booth 1975 Cooper et al. 1978)... 

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. 

Caturla, M.J., Diaz de la Rubia, T., and Gilmor, G.H. (1995) Recrystallization of a Planar Amorphous-Crystalline Interface in Silicon by Low Energy Recoils A Molecular Dynamics Study, / Appl. Phys., Vol. 77, pp.3121-3125. 

Figure 12. An amorphous-crystalline interface in Ge implanted (100) Si (10 cm 2, 300 keV, RT implant, no anneal). (a) Bright-field cross-sectional TEM micrograph. The dark band represents an amorphous layer. (b) Atomic resolution TEM micrograph showing atomic details of the interface. Note a stacking fault nucleus at the interface. (Adapted from Ref. 22.)...

The amorphous/crystalline interface is afterwards equilibrated at the target temperature during 4ps using a 2fs time step and the velocity scaling algorithm, prior to the use of a Nos6-Hoover thermostat to maintain the desired temperature during... 

The solid phase epitaxy of amorphous on crystalline silicon systems has been studied by molecular dynamics simulations. First a simulation scheme is consolidated in the case of an amorphous layer recrystallization where the a/c velocity is well known from experiments. An atomic model of the a/c interface is constmcted and annealed by MD using one suitable interatomic potential for Si-Si interactions. The motion of the amorphous/crystalline interface is extracted and compared to the experimental law by Olson and Roth. Although none of the potentials is in agreement with the experiments, two stand out Tersoff for SPE but accounting for a shift to higher temperatures compared to the real ones, and StiUinger-Weber, for LPE. 

Amorphous layers have been obtained using either picosecond pulses of 0.53ym[15] or nanosecond pulses of 0.347um [11]. The thickness of the layers depends on the substrate orientation, it is much higher for (111) than for (100) orientation. The amorphous-crystalline interface, as shown by transmission electron microscopy, is undulating with an amplitude of about 30% of the average thickness. The measured liquid-solid velocity for the amorphous formation is 15 m/sec. 

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]. 

Most polymers fall in the class of translucent resins. These include acetal, polyamide, polybutylene terephthalate (PBT), polyethylene, and polypropylene as examples. There are very few neat polymers that are truly opaque (this depends on thickness as well). Liquid crystal polymer (LCP) is an example of a typically opaque polymer. It is theorized that these semicrystalline and crystalline resins will scatter some portion of incident light due to spherulitic crystal structure and the amorphous-crystalline region interfaces themselves. 

Motooka, T. (1997) Molecular Dj nics Simulations for Amorphous/Crystalline Si Interface Amorphization and Crystallization Induced by Simple Defects, Nuclear Instruments and Methods in Physics Research B, Vol. 127/128, pp.244-247. 

Figure 7. A computer-generated picture of the crystalline/amorphous silicon interface.

In the semi-crystaUine polymer solid, most of polymers trespass the crystalline interfaces, and a restriction occurs to the mobility of non-crystalline part of polymers near the crystalline-amorphous interfaces. The restricted portion of polymers displays glass transition at the temperature higher than those noncrystalline free polymers. Wunderlich named this non-crystalline part of polymer near the crystalline surfaces as the rigid amorphous polymer (Wunderlich 2(X)3). Treating semi-crystalline polymers as formed by three parts (flexible amorphous far... 

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