Morphology evolution

To address the incorporation of non-cryslalline phases in polycrystalline diamond films and the morphological instabilities at high growth rates, Ravil conducted an experimental investigation of the combustion synthesis of diamond and proposed a model for the development of morphological instabilities in diamond films, as schematically depicted 

In addition to the statistical nature of the interface instabilities active in diamond CVD, the orientation effect and anisotropic growth of crystals (i.e., evolutionary selection) play an important role in the observed instability phenomenon. Surface chemical reactions that occur preferentially between the growing diamond surface and oxidizing species in the combustion synthesis ambient also influence the development of the microstructure and morphology of crystals in diamond films. For example, in combustion CVD, 

The morphological instabilities not only cause extreme variations in the sizes of individual crystallites in polycrystalline films, but also lead to the 

When diamond films are deposited chi non-diamond substrates, stresses may be generated in the films due to lattice mismatch and/or differences in thermal expansion coefiBcients between diamond and the substrate materials.In addition, lateral variations in the grain size, density, or impurities incorporated during growth may also lead to stresses, which may be either tensile or compressive. The stresses are known to generally build up with increasing film thickness, and will influence diamond-substrate adhesion and properties of diamond films.  

The primary difiBculty in diamond epitaxy is the small number of materials (Ni, Cu, Fe, Co, Si, and cBN) with suitable ciystal structure and lattiee constants. The extremely high surface energies of diamond and the existence of interfacial misfit and strain energies between diamond films and non-diamond substrates constitute the primary obstacles in forming oriented 

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D. Y. Li, L. Q. Chen. Morphological evolution of coherent multivariant TiNi precipitates in Ti-Ni alloys under an applied stress-a computer simulation study. Acta Mater 46 639, 1998. 

Various silver salts can be reduced to silver metal readily at temperatures well below 200 °C through different pathways [32]. We therefore used silver salt as nucleation inducing agent. Ag(acac) was used because of its good solubility in diphenyl ether. The morphology evolution of Pt multipods and nanoparticles was followed by TEM. 

Liu, Q., Mao, D., Chang, C. and Huang, F. (2007) Phase conversion and morphology evolution during hydrothermal preparation of orthorhombic I iMiiO, nanorods for lithium ion battery application, journui of Power Sources, 173, 538-544. 

Nadler, S.A. and Hudspeth, D.S.S. (1998) Ribosomal DNA and phylogeny of the Ascaridoidea (Nemata Secernentea) implications for morphological evolution and classification. Molecular Phylogenetics and Evolution 10, 221-236. 

Fig. 6 Schematic representation of the morphology evolution and the formation process of sodium and hydrogen-titanate nanostructures during hydrothermal synthesis in the presence of alkali medium. Elaborated from the picture and schemes reported by Wu et al.219...

Figure 1. Morphological evolution of unstressed thin-film regions, made ofinitially fourmonolayers, through thermal fluctuations. The early stages of islanding are examined on the left side, while the final equilibrium shapes are shown on the right for three different cases of substrate-vapor surface energy, y ...

Figure 2. Morphological evolution of unstressed thin-films under the zero-torque condition, in which all the interfaces are allowed to pucker freely. The corresponding Wulff constructions are also pictured for comparison.

Figure 7. Morphological evolution of a soft-hard-soft lamellar structure. A hard phase is sandwiched between two softphases withe = 0.01. Each layer has 50 ML, and the periodic length is equal to 200 a... 

A profile imprinted on a crystal surface will undergo morphological changes when relaxing towards equilibrium. This morphological evolution has been foiind, in experiments and theoretically, to be significant different above and below the roughening transition of the relevant surface. - ... 

Morphology evolution is thus found to be dependent on the processing technique applied to disperse the nanoparticles. The latex-blended and prevulcanized nanocomposites show predominant exfoliation with some intercalation, especially in uncured and prevulcanized samples. In conventionally cured but latex-blended nanocomposites, realignment of NA particles is visible, with a greater tendency of NA platelets towards agglomeration. In solid state mixing, the dispersion is still poorer. XRD studies also corroborate the above observations. 

Recently, a new concept in the preparation of TPVs has been introduced, based on the reaction-induced phase separation (RIPS) of miscible blends of a semicrystalline thermoplastic in combination with an elastomer, with the potential for obtaining submicrometer rubber dispersions. This RIPS can be applied to a variety of miscible blends, in which the elastomer precursor phase was selectively crosslinked to induce phase separation. Plausible schematic representation of the morphological evolution of dynamic vulcanization of immiscible and miscible blends is shown in Fig. 9. For immiscible blends, dynamic vulcanization leads to a decrease in the size... 

Fig. 9 Plausible representation of morphology evolution of reactive blending of immiscible and miscible blends...

All three approaches have been worked out. It has been demonstrated [R.F, Sekerka (1967)] that they lead to the same conclusions concerning the initial morphological stability. However, they must differ with respect to the morphological evolution and the selection of growth modes at later times. 

In the context of the morphological evolution of non-equilibrium systems, let us then ask whether the reaction path, when constructed for a system with stable interfaces, can tell us something about the instability of moving boundaries. For this we... 

The mechanisms above allow rapid diffusional transport of atoms along the surface. We discuss the role of surface diffusion in the morphological evolution of surfaces and pores during sintering in Chapters 14 and 16, respectively. 

MORPHOLOGICAL EVOLUTION DUE TO CAPILLARY AND APPLIED MECHANICAL FORCES... 

Analysis is simplified if 7 is isotropic—i.e., independent of geometrical attributes such as interfacial inclination n and, for internal interfaces in crystalline materials, the crystallographic misorientation across the interface. All interfacial energy reduction then results from a reduction of interfacial area through interface motion. The rate of interfacial area reduction per volume transferred across the interface is the local geometric mean curvature. Thus, local driving forces derived from variations in mean curvature allow tractable models for the capillarity-induced morphological evolution of isotropic interfaces. 

The particular characteristics of morphological evolution are determined by the dominant transport mechanism their analyses derive from the diffusion potential, which depends on the local curvature. For a surface of revolution about the z-axis, the curvature is given by Eq. C.16 that is,... 

Evolution by Surface Diffusion and by Vapor Transport. Although calculation of the morphological evolution for particular cases can become tedious, the kinetic equations are straightforward extensions of the isotropic case [11], For the movement of an anisotropic surface by surface diffusion, the normal interface velocity is an extension of Eq. 14.6 which holds for the isotropic case for the anisotropic case,... 

For morphological evolution during dissolution of a crystal (or disappearance of voids in a crystalline matrix), the same characteristic construction applies, but the sense of the surface normal is switched compared to Fig. 14.11. An example of dissolution is illustrated in Fig. 14.12. 

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