Corona-poling

Following these early solid-state investigations, 1,907 nm EFISHG studies by Tam and co-workers on several complexes [W(CO)5L] (L = py or a 4-substituted py) quote (3 values similar to that of 4-nitroaniline (ca. 10 x 10-30 esu) and sensitive to the nature of the pyridyl substituent.67-69 These results were quickly followed by ZINDO/SCI-SOS calculations on the same series of complexes by Kanis et al.70 the first time that MO theory had been used to describe the quadratic NLO responses of metal complexes. The results of these calculations agree reasonably well with the EFISHG data, and indicate that the modest (3 responses can be traced to relatively small Ap12 values.70 Lacroix et al. obtained low 1,064 nm SHG activities by corona poling films of poly (4-vinylpyridine) and of two other related polymers functionalized with W(CO)5 centers.71... 

Hill, R. A. Knoesen, A. Mortazavi, M. A., Corona poling of nonlinear polymer thin films for electro optic modulators, Appl. Phys. Lett. 1994, 65, 1733 1735... 

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 4. Long-term decay parameters (r2, equation 1) for d33 of (PS)O-NPP films simultaneously corona poled and cross-linked with the indicated equivalents of 1,4-butanediol diglycidyl ether/equiv-alents available phenol OH groups.

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. 

Dopant orientation during and following electric field-induced poling can be studied continuously and in real time in order to examine the microenvironment surrounding the dopants in terms of the polymer relaxations and the applied corona field. In the results presented below, the SHG of 4-dimethylamino-4 -nitrostilbene (DANS) dispersed in polystyrene (PS) or poly(methyl methacrylate) (PMMA) matrices has been examined in corona poled films as a function of temperature in order to understand the effect of thermal conditions on the temporal stability of the dopant orientation. 

Surface voltage decay was measured with a Trek Model 341 high voltage electrostatic voltmeter (ESVM). The ESVM drives the potential of a probe body to the same potential as the film surface voltage. This device measures the voltage independent of distance within 5 mm of the film surface without causing current flow, which would modify the data. After poling, the corona needle was removed and the probe of the ESVM was placed 3 mm from the film surface. 

Figure 1. Effect of temperature on the temporal stability of X film (related to and the angle between the applied field and dopant optical axis) for corona poled PS and PMMA films doped with 4 wt.% DANS. X Vilm(0/x film(t=0) versus time after the field is removed, where t=0 denotes the time that the applied field is removed. The initial temperature is 110°C, and the final temperatures after the field is removed are 11 (PC [PS (0),PMMA ( )], 95°C [PS CD,PMMA ( )] or 60°C [PS (A), PMMA (A)].

Figure 2. Surface voltage decay as a function of time for corona poled PS (O) and PMMA ( ) films doped with 4 wt.% DANS. Films poled at -3000V (0.6 cm air gap) for 15 min at 25°C.

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