Thin films crystallization

Main use Nondestructive depth profiling of thin films, crystal... 

We have already mentioned that depending on composition, semicrystalline triblock copolymers can show some conflict between microphase separation and superstructure formation. In fact, one of the controversial aspects is the question whether block copolymers can or cannot exhibit spherulites. This is a relevant question because spherulitic structures greatly affect the ultimate mechanical properties, and the boundaries between adjacent spherulites are often weak points in mechanical performance. Kim et al. [125] studied the competition between crystallization within microphase-separated regions and reorganization into supermolecu-lar spherulites in semicrystalline PS-b-PB-b-PCL triblock copolymers. These authors found that the formation of spherulites is strongly affected by the thickness of the specimen in such a way that thin films crystallize into... 

In this paper we report functional waveguides exhibiting SHG in tapered thickness 2-methy1-4-nitroani1ine(MNA) thin film crystal waveguide, and all optical bistabi1ity,in tensity dependent optical modulation in vacuum evaporated polydiacetylene(PDA) thin film waveguides. 

Another technique we used to observe these distributions is scanning electron microscopy with energy dispersive x-ray analysis (EDAX). Concentrations of Cyasorb UV 1084, [2-2 -thiobis(4-ter -octylphenolato)-n-butylamine nickel], a nickel-containing UV absorber, were point counted to obtain nickel concentrations along a spherulite diameter. Figure 3 shows results for 1 and 4 wt % additive. This shows a uniform melt concentration, a boundary peak, a lower concentration within the spherulite, and a central dip. The resolution and sensitivity with this technique are poorer than with the optical microscopy. With every method, thin film crystallized samples and microtomed sections of bulk samples gave similar results. 

Some optical density studies have been done by Suryanarayanan (1977), Suryanarayanan and Brun (1976) and Suryanarayanan et al. (1977). They have shown that for Tm and Yb as substituted elements the thin films crystallized in the fee NaCl structure. The optical density of a Smo.6Ybo.4S film (a = 5.84 A) shows three broad absorption bands due to the transition (Sm ) 4f - 4f 4d (t2g, Cg), and a maximum which can be attributed to the transition (Yb ) 4f4f( Fs/2) 5d t2g or 4f4f ( F / ) 5d Cg. They conclude that Yb and Sm are both stable divalent ions, and that the S.C. - M. transition cannot be observed. Some other results have been described for samples such as Smo.7Tmo.3S, Smo.4Tmo.6S [for a Tm content <0.3 the optical density spectra are identical to (M. SmS)], and Smi- Yb S. For the last one the lattice parameter of the fee cell decreases from 5.97 to 5.68 A with x increasing from 0 to 1. The optical spectra show the first three peaks of Sm and another one corresponding to a transition relative to Yb, as noted above. 

In-situ Observation of Polyethylene Thin-film Crystallization... 

Thakur and Meyler [22] have reported the growth of thin-film single crystals of poly(diacetylenes) by a shear process that produces aligned areas of about 1 cm-from melts and about 50 mm- from solution. These thin-film crystals were reported to be four orders of magnitude larger than those previously prepared by Isoda [23]. 

FIGURE 22.11 AFM amplitude images of PLLA thin films (crystallized at 160°C) prepared from chloroform solutions with the concentrations of 0.25 (a), 0.5 (b), and 2.0% (w/v). The film thicknesses measured by AFM were 20 (a), 50 (b), and 200 nm (c), respectively, (a) Dendritic crystal, (b) hexagonal crystal, and (c) early stage of spherulitic morphology with edge-on and flat-on lamellae. Reprinted with permission from Ref. 65. Copyright 2001, American Chemical Society. 

C. W. Teplin, D. S. Ginley, and H. M. Branz, A new approach to thin film crystal silicon on glass Biaxial-textured silicon oh foreign template layers, J. of Non-Crystalline Solids 352, 984 (2006). 

Figure 2.62. Melting curves of low-density polyethylene thin film crystallized in a stepwise manner (sample 0.0%). Then the film was drawn at room temperature to various draw ratios. The elongation is indicated at each curve. It is remarkable that the crystallites responsible for the multiple melting behavior are mechanically stable up to -200% elongation, and almost 500% elongation is needed to erase the thermal history mechanically. Perkin-Elmer DSC2, heating rate 10°C/min. [From Varga et al. (1979) reprinted with permission of Springer-Verlag.]...

As a result, the sol-gel-derived SBT thin films crystallized, by rapid thermal annealing in an oxygen atmosphere below 550°C, and they exhibited preferred (115) orientation (Kato et al., 1998). The crystallinity improved and the crystallite size increased with increasing temperature up to 700°C. In the case of SBN thin films, a low heating rate (2°C/min)... 

P-E hysteresis loops of alkoxy-derivedSrBi2Ta20 thin films crystallized at 650, 700,... 

The crystallinity and crystallographic orientation of the SBT thin films crystallized at 650°C were improved by the UV irradiation under appropriate conditions at the stage of the as-deposited and noncrystalline thin films (Nishizawa et al., 2003). By the spectroscopic analyses, it was found that the chemical structure of the noncrystalline Sr-Bi-Ta-O thin films on Pt layer on Si changed by UV irradiation under the appropriate conditions. Additionally, the UV irradiation was considered to accelerate the polymerization and to change the interaction between the noncrystalline Sr-Bi-Ta thin films and Pt layer on Si (Nishizawa et al., 2003). 

Kato and co-workers have developed thin-film composites of CaCOs and organic macromolecules.When CaC03 crystals are grown on poly-(vinyl alcohol) matrices with the addition of poly(acrylic acid), relief structures are obtained on the thin film. They prepared calcite thin-film crystals with the periodic changes of crystallographic orientations in the first step (Fig. 17). In the second step, the relief structures consisting of needlelike... 

Figure 9.8 Transmission electron micrograph of lamellae in an initially amorphous thin film crystallized by heating at 5 °C/min from room temperature to 155 °C. Reprinted from [70], with kind permission from Springer Science+Business Media.

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