Epitaxial crystallization investigation

Thin polymer films may also be investigated by TEM and high resolution images are obtained for e.g. thin films of liquid crystalline polymers [64]. Usually thin microtome cuts from bulk samples are investigated, but also epitaxial growth of polyoxymethylene on NaCl [152], chain folding of polyethylene crystals [153], epitaxial crystallization of polypropylene on polystyrene [154] or monomolecular polystyrene particles [155] are observed. The resolution is, however, in most cases not comparable to STM. 

Epitaxial crystallization of polymers has been investigated for a wide variety of substrates minerals (alkali halides, talc, mica, and so on), low molecular weight organic materials (condensed and linear aromatics, benzoic acid and many of its substituted variants and their salts or hemiacids, other organic molecules of different types), and other crystalline polymers. 

All monomer epitaxial crystallization and polymerization is controlled by the substrate surface and results in new, highly oriented crystalline films with new structures and properties which are presently under investigation. 

Stocker, W. et al. (1998). Epitaxial Crystallization and AFM Investigation of a Frustrated Polymer Structure Isotactic Poly(propylene), p Phase. Macromolecules, Vol.31, Issue 3, pp. 807-814. 

Stocker, W., Lovinger, A.J., Schumacher, M. et al. Atomic Force Investigations of epitaxially crystallized tactic poly(propylenes). ACS Symposium Series, in press. 

Stocker, W., Schumacher, M., Graff, S. et al. (1998) Epitaxial crystallization and AFM investigation of a frustrated polymer structure isotactic jx)ly(propyl-ene), p phase. Macromolecules, 31, 807-14. 

Stocker W, Schumacher M, Graff S, Thierry A, Wittmann JC, Lotz B. Epitaxial crystallization and AFM investigation of a frustrated polymer structure, isotactic poly (propylene), P phase. Macromolecules 1998 31 807-814. 

Ion beam-induced epitaxial crystallization (IBIEC) has attractive features from the viewpoint of beam-solid interactions especially in semiconductors. Specific properties and phenomenological understandings of IBIEC in Si have been hitherto obtained on the basis of extensive investigations (41-45). The features of the process have provided not only a new field of investigation of beam-solid interactions but also a possibility of process application of Si because of its advantages, such as processing at low temperatures, local process capability, and metastable phase formation by impurity atom incorporation at a nonthermal equilibrium concentration. 

Epitaxial crystallization of materials has been known for a long time. The oriented crystallization of a given crystal (the deposit) on the surface of another crystal (the substrate) has been investigated in quite some detail by Royer in the late 1920s [1], His work dealt mostly with minerals, for which X-ray investigations had established either the unit-cell geometry and dimensions or even the detailed crystal structure. On the basis of this information and by analyzing the relative orientations of the substrate and deposit, Royer could estab-... 

Epitaxial crystallization is stUl the topic of numerous investigations in the field of materials science, especially in relation with the formation of nanostructured layers in devices. Epitaxial crystallization has comparatively... 

Similar investigations performed with polyamides are comparatively less telling. Indeed, the hydrogen-bonded sheets are a strong structural feature that does not leave much leeway for diverse epitaxial crystallizations. So far, the only contact plane observed in epitaxial crystallization of polyamides is indeed the hydrogen-bonded sheet [16]. This in turn implies that substrates with a periodicity close to 0.48 to 0.5 nm are most appropriate (provided of course that their compatibility with polyamides is sufficient). In this respect also, investigation of epitaxial crystallization of polyamides teaches us less than that of PE. However, further research is needed to investigate if some less standard crystal modifications of polyamides, such as the 7 form of polyamide 6, can be produced by epitaxial crystallization. 

The correct analysis of epitaxial crystallization of polymers cannot merely rely on global investigation techniques. Whereas the latter are suitable for screening, epitaxy takes place at a very different length scale, namely at the unit-cell level. It is therefore mandatory to use techniques that can read the molecular organization at a local scale. Moreover, in case a metastable crystal form is produced, the impact of epitaxy may be lost beyond only a few nanometers away from the interface. This contribution has developed some of... 

Recrystallization in the stretched state results in the formation of a crystalline network that prevents contraction of the oriented crystalline structure during strain recovery, and thereby freezes the orientation in the elastic film. The data suggests that recrystallization is possibly in the form of epitaxial crystallization of a -PP (daughter) lamellae on top of oriented a-PP (mother) fibrillar crystals. The origin and nature of the orientation of the y-PP needs explanation, and is currently under investigation. 

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