Poled film coefficient

Second harmonic coefficients of the poled films were measured at... 

In many microelectromechanical systems (mems) based on piezoelectric thin films, flexure is deliberately used to amplify the available displacements (or alternatively to increase the sensitivity of a sensor). For simplicity (and to keep poling and actuation voltages low), films are often poled and driven by electrodes at the top and bottom surfaces. As a result, the critical piezoelectric coefficient is often e31 j, rather than d33j [24], For the direct effect, the effective film coefficient, e3ij can be defined by... 

The hb-PAEs of hb-P13 and hb-P15 contain NLO-active azo-functionalities, which are soluble, film-forming, and morphologically stable (Tg > 180 °C). Their poled films exhibited high SHG coefficients ( 33 up to 177pm/V), thanks to the chromophore-separation and site-isolation effects of the hyperbranched structures of the polymers in the three-dimensional space (Table 5) [28]. The optical nonlinearities of the poled films of the polymers are thermally stable with no drop in d33 observable when heated to 152 °C (Fig. 8), due to the facile cross-linking of the multiple acetylenic triple bonds in the hb-PAEs at moderate temperatures (e.g., 88 °C). 

The linear and nonlinear optical behaviors of poly-(1,6-heptadiyne)s containing NLO chromophores was summarized in Table 22. It was found that n of the copolymers gave higher values than that of poly-76 not bearing any chromophore while the values of Amax were similar to each other. This result clearly shows the effects of incorporation of chromophore into the polymer backbone. The values of electrooptic coefficients, r33, for poled film samples of poly-77 to poly-81 by using a simple reflection technique reported by Teng et al. was measured. Table 22 shows the measured electrooptic coefficients of polymer films at... 

Electrostatic layer-by-layer (LBL) self-assembly techniques based on oppositely charged poipelectrolytes can be useful to create stable noncentrosymmetric order in thin films. Using this interesting technique, thermodynamically stable noncentrosymmetric multilayer films can be prepared without any need for poling. Tripathy et al. reported the fabrication stable multilayer films of epoxy-based side chain azo polymers for second-order nonlinear optics.The second-order NLO coefficients of the five-bilayer LBL films of these polymers were found to be comparable to those of spin-coated poled films. A schematic view of the procedure to fabricate polyelectrolyte-based LBL films is shown in Fig. 7. 

Two triphenylamino-substituted chromophores with and without hydroxyl end, named TIOH and Tl (Figure 6.7), respectively, were synthesized and incorporated into hybrid organic-inorganic materials derived from 3-glydoxypropyltrimethoxysi-lane, tetraethoxysilane, and 3-aminopropyltriethoxysilane [54]. These stilbene-type chromophores were characterized by elemental analysis by NMR, FT-IR, UV-vis spectra, and TGA. The hyperpolarizabilities were characterized through solvato-chromic method. Both chromophores possessed higher thermal stability and competitive hyperpolarizabilities. Second harmonic generation was observed on poled films. The nonlinear coefficient of the samples was established at 41.2 pm/V for TIOFJ doped film and at 24.8 pm/V for Tl doped film. 

In molecularly doped polymers and polymers with nlo-active pendant groups the main polymer chain has a saturated chemical structure, which does not contribute significantly to the overall nlo properties. As noted earlier, it is necessary to induce polar order in such systems to obtain finite values of This is usually achieved by the application of an electric field while the polymer is heated above its glass transition temperature (Tg). This produces a partial ordering of the polar additive or pendent group. This order is then frozen in by cooling the polymer below Tg. For such poled films there are a limited number of finite, unequal components of the tensor The symmetry of such films is 00 mm, i.e. an infinite-fold rotation symmetry about the poling direction. The non-zero coefficients of the tensor are... 

The same effect of densilication on stability has also been observed by Wu et al. in another NLO chromophore, erythrosin-doped polyimide (Pyralin 2611) system. This polymer becomes highly anisotropic on densihcation. An initial decay of 35% of the electrooptic signal is observed for these films when the poled film is heated to 300°C, but there was no further decay after 1 h. At 200°C, there is an initial decay of 30%, but no further decay in 60 h. The electro-optic coefficient of this system was not reported. 

NPP-functionalized poly(2,6-dimethyl-l,4-phenylene oxide) (PPO) was prepared [101]. The analysis indicated 1.43-1.63 NNPO groups per PPO-repeat unit. These solution-processible PPO-NPP films had excellent transparency. The Tg for this polymer was reported to be 173 C. Despite the relatively low molecular hyperpolarizability of the chromophore, the corona-poled films exhibit coefficients as high as 27 pm V at 1.064 xm. 

Azo chromophores have been attached to polyimide as side chains [118]. The structure is shown in Scheme 7. With different spacer lengths and substituents, the polymers with between 140 and 190°C were obtained. Corona-poled films of these polymers have large nonlinear optical susceptibilities of = 23 pm V and EO coefficients of = 6.5 pm V at a wavelength of 1.3 xm. From the accelerated time-temperature measure-... 

The birefringent (BR) modulator makes use of polarized light and tensorial nature of the electrooptic coefficient. For example, poled organic polymer films are characterized by two nonzero components for the electrooptic tensor and parallel and orthogonal to the poling direction,... 

Figure 1. (A) Time dependence of the second harmonic coefficient of a PPO-NPP film (1.4 NPP moieties per polymer repeat unit) contact-poled at 1.2 MV/cm. Decay data taken at 25°C. The data points are shown as filled triangles. The two curves describing the biexponential fit to equation 1 are shown separately, with the open triangles representing data points dominating the short-term decay. (B) Time dependence of the second harmonic coefficient of a corona-poled PPO-NPP film (1.4 NPP moieties per repeat unit). Decay data taken at 25°C. The data points are shown as filled triangles. The two curves describing the biexponential fit to equation 1 are shown separately, with the open triangles representing data points dominating the short-term decay.

Table II. Second-Harmonic Coefficients ( 33) and Temporal Decay Parameters for Corona-Poled, NPP-Functionalized Poly(p-hydroxystyrene) Films as a Function of Thermal Cross-Linking a...

Figure 3. Time dependence of the second harmonic coefficient, d33, for corona-poled (PS)O-NPP films. A. Simultaneously poled (180°C) and cross-linked with 0.50 equiv. 1,2,7,8-diepoxyoctane/phenol OH B. Poled at 180°C C. Poled at 150°C. The solid lines are least-squares fits to equation 1, yielding the decay parameters in Table II.

Figure 5. Time dependence at room temperature of the second harmonic coefficient, d33 of epoxy films containing Disperse Orange 1 (4) after simultaneously poling and curing at 150°C.

Tg = 125-140°C, and was stable in a N2 atmosphere to 220°C. The 13C NMR spectrum revealed the presence of 7t-interaction between those chromophoric groups that are in isotactic relationship to each other ( 30-35% of total). The orientation of the chromophores in a PPNA sample (Tg = 125°C) was achieved in a thin film by the corona poling technique at temperatures above Tg. The subsequent freezing process resulted in a polymeric film that exhibited an initial high second-order nonlinear coefficient, d33=31 pm/V, as measured by Maker-fringe technique with 1.06 im fundamental. 

The electro-optic coefficient in a poled polymer film can be related to the second-order susceptibility as shown in Equation 5. 

As with the measurement of p, it is important to compare electro-optic coefficients determined by different methods. It is particularly important to establish consistency between electro-optic coefficients obtained from initially poled thin films and those existing in functional prototype devices. Such consistency not only adds credibility to reported material electro-optic activity, but also as-... 

A similar but more active chromophore 3 (RT-9800) was also incorporated as guest in a rigid-rod, high-temperature polyquinoline (PQ-100) (Scheme 1) [32]. Poling results from the guest-host polyquinoline thin films showed both exceptionally large electro-optic activity and long-term stability at 85 °C. After an initial drop from 45 to 26 pm in the first 100 hours, the electron-optic coefficient remained at 26 pm for more than 2000 hours (Fig. 3). 

Dumont and coworkers [136, 155, 156] have observed that shining doped (or functionalized) polymer thin hlms with noncentrosymmetric dipolar chromo-phores, induces a significant increase of electro-optic coefficient in the chromo-phore absorption band, corresponding to a better, polar orientation of chromo-phores. The measurements have been done by using the attenuated total reflection technique, and the optical field polarization was perpendicular to the applied low-frequency external electric field to the thin film (Fig. 33). A better stability of induced orientation was observed in the case of functionalized polymers than in guest-host system, as is usually the case with the static field poled polymers. The chromophores orient with dipolar moments perpendicular to the optical field (and parallel to the applied static (or low frequency) field. As will be discussed later, the chromophore orientation undergoes a trans-cis isomerization process (Fig. 34). 

What is also very interesting from the practical point of view is that such an alternate illumination of the zwitterionic chromophore during the corona poling leads to a significant increase of x susceptibility. The observed increase of 12 intensity by a factor of three (Fig. 42) corresponds to an improvement of x susceptibility (and correspondingly of the E-O coefficient r) by 70%. Also, the temporal stability of the induced noncentrosymmetric order in alternately illuminated thin films is significantly better than in untreated films (an increase of the decay time constant by a factor of 5 [174]). 

Poling induces a polar axis in the polymer film. The z-axis is essentially an infinite-fold rotational axis with an infinite number of mirror planes. This type of symmetry is denominated oomm or In this case the molecules are distributed cyllndrically about the z-axis and the angle a, defined as the angle between the z-axis and the dipole moment of the molecule, varies from molecule to molecule. In the weak poling limit the distribution of a is broad, but with a tendency to orient in the direction of z compared to the unpoled state. The non-vanishing nonlinear coefficients for C, . symmetry are = T = T . xSc = and x . 

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