Thin film self-polarization

An alternative to avoid self-quenching is to use the electrostatic layer-by-layer assembly (ELBL) technique. It eliminates this effect because the indicator is distributed in consecutive (nanometer-thick) polymer layers, each of them having opposite polarity to the previous one. In fact, this technique can be utilized to adsorb the optimum dye concentration with adequate separation in thin film optical sensors [14,15]. 

A tool to visualize the domains in thin films is the 3-D piezoresponse force microscope (pfm, see also Chapter 12). Figure 1.22 shows an epitaxial pzt thin films grown on a (001) single crystalline SrTiC>3 substrate coated with La0.5Sr0.5CoO3 oxide layer. A detailed analysis point out that a self-polarized polarization mechanism is observed because the out-of-plane polarization in c-domains are preferentially orientated towards the bottom electrode, i. e. a remanent polarization exists without applying an external field. The domain configuration is always of the head-to-tail type. 

Another photochemically based gating system is the one by Brinker and coworkers in which the cis-trans isomerization of azobenzene was applied.69 (Triethoxysilylpropylureido)azobenzene was co-condensed with TEOS by evaporation-induced self-assembly to yield a functionalized mesoporous silica thin film. The propylureidoazobenzene groups inside of the mesopores could then be iso-merized from their stable elongated trans structure to the more compact cis geometry upon UV irradiation. The trans geometry could be recovered by thermal treatment. The authors suggested that the results of the transitions from trans to cis could lead to an increase in pore size of approximately 0.7 nm and an increase of the polarity from 0 to 3 D. This could be applied to regulation of ion transport however, they did not confirm such expectations.69... 

The analysis of thin films is often performed by infrared spectroscopy. Compared to reflection absorption measurements on metal surfaces using p-polarized fight at grazing incidence, investigation of self-supported thin films or of thin films on transparent substrates shows weaker infrared absorption bands. Weaker absorption bands are caused by the absence of the surface enhancement mechanism and the poorer reflectivity. On the other hand, due to the absence of the metal selection rule, spectra of p- and s-polarization can be recorded in the case of freestanding films or of transparent substrates. Complex spectral features may arise... 

Since 1990, self-assembly techniques involving covalent linkages and layer-by-layer fabrication were reported to yield robust noncentric super lattices highly suited for applications such as SHG and electro-optic effects. " Spontaneous and sequential adsorption of appropriately derivatized adsorbates onto substrates in a self-limiting fashion can yield thin films with uniform polar orders in individual layers. This represents an attractive approach to the construction of intrinsically acentric chromophoric super lattices. Li et reported synthetic routes to the... 

The choice of the particular monomers is based on the fact that PI is a nonpolar low Tg polymer, P2VP is a relatively more polar material with a coordinating ability, due to the presence of nitrogen in the side phenyl ring, with high Tg and the potential to be transformed into a water-soluble polyelectrolyte by postpolymerization reaction. On the other hand, PEO is a semicrystalline polymer, water-soluble (polar), and biocompatible. The incorporation of all these diverse properties in the same molecule makes these materials very interesting in terms of their self-organization in solution, bulk, and thin films. 

---