Crystals from ultrathin films

Maillard D, Prud homme RE (2008) Crystallization of ultrathin films of polylactides from chain chirality to lamella curvature and twisting. Macromolecnles 41 1705-1712 Mano JF, Wang Y, Viana JC, Denchev Z, Oliveira MJ (2004) Cold crystallization of PLLA studied by simultaneous SAXS and WAXS. Macromol Mater Eng 289 910-915... 

Zhang, F., Baralia, G.G., Nysten, B., Jonas, A.M. Melting and van der Waals stabilization of PE single crystals grown from ultrathin films. Mactomolecules 44(19), 7752—7757 (2011)... 

Studying the temperature evolution of UV Raman spectra was demonstrated to be an effective approach to determine the ferroelectric phase transition temperature in ferroelectric ultrathin films and superlattices, which is a critical but challenging step for understanding ferroelectricity in nanoscale systems. The T. determination from Raman data is based on the above mentioned fact that perovskite-type crystals have no first order Raman active modes in paraelectric phase. Therefore, Raman intensities of the ferroelectric superlattice or thin film phonons decrease as the temperature approaches Tc from below and disappear upon ti ansition into paraelectric phase. Above Tc, the spectra contain only the second-order features, as expected from the symmetry selection rules. This method was applied to study phase transitions in BaTiOs/SrTiOs superlattices. Figure 21.3 shows the temperature evolution of Raman spectra for two BaTiOs/SrTiOa superlattices. From the shapes and positions of the BaTiOs lines it follows that the BaTiOs layers remain in ferroelectric tetragonal... 

These surface excitons become important for very thin crystals, which consist to a large extent of surfaces. Here, the somewhat different excitons in the second and third layers from the surface can be more readily identified. Experimental results for ultrathin films are not yet available. 

As shown in Chapter 2, to optimize the contrast in the IR spectrum of an ultrathin film, it is necessary in many cases to use nonnormal angles of incidence and p-polarized radiation, which creates specific difficulties in the interpretation of the spectrum. The problems stem from the appearance of additional bands in the spectra of samples that are small relative to the wavelength these bands are due to the surface charges resulting from the polarization of the samples. The dependence of the transverse vibrational frequency of a polar crystal on the crystal size, called the size effect, was discovered by Frohlich [2]. A convincing explanation of this effect in the IR spectra of thin films was presented in 1963 by Berreman [3] while studying the transmission of 325-348-nm LiF layers. Consequently, this size effect in the IR spectra of ultrathin films became known as the Berreman effect by Harbecke et al. [4]. 

Fig. 7. Grazing incidence reflection FTIR spectra (p-polarized) of PEO (pyrene end-labeled) ultrathin films on oxidized silicon with different thicknesses (crystallized isother-mally at 40°C). The negative bands are typical of grazing incidence reflection spectra on nonmetallic surfaces. From Ref. 42.

Figure VLAl (a) Bright-field transmission electron micrograph of an iPP/CNT composite thin film nonisothermaUy crystallized from the melt during cooling at 5 °C/min scale bar 500 nm. Miltner et al. [221]. Reproduced courtesy of American Chemical Society, (b) Representative select-area electron diffraction pattern of the transcrystaUine-giown iPP crystals around the CNTs in an ultrathin film. Lu et al. [222]. Reproduced with permission of American Chemical Society.

Detavernier, C., Van Bael, M.K., Van den Rul, H and Mullens, J. (2009) Crystallization resistance of barium titanate zirconate ultrathin films from aqueous CSD a study of cause and effect. 

Figure 33 Fractal seaweed aggregate from an ultrathin molten film of poly(trifiuoroethylene) crystallized at 140°C. The insert is an electron diffraction pattern demonstrating that the selected area of ca. 10 gm diameter is a single crystal. From Lovinger and Cais [4] with permission from the American Chemical Society.

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