have shown that this method yields negligible contact resistance and highly accurate conductivity values.5 Registry No. PP, 30604-81-0; PMT, 84928-92-7.(5) Conductivity values for homogeneous PP films were obtained by using this method and the more conventional four-point method; identical values were obtained. The four-point method cannot be used on these ultranarrow fibers.(6) The surface layers are less than 200 nm thick and cover 100% of the surface area; the fibers are 10 µ long and occupy 1% (or less) of the surface area.Furthermore, for several membranes, we measured the resistance, scraped off the surface layers, and then remeasured the resistance; Rm values with and without the surface layers were identical.

Polyaniline can be inserted in V2O5·nH2O xerogel by in situ oxidative polymerization/intercalation of aniline or anilinium in air. The reaction is facile and topotactic, forming polyaniline as the emeraldine salt. The interlayer separation (5.6 Å) is consistent with a monolayer of polymer chains in the V2O5 framework. Evidence is presented that oxygen acts as an electron acceptor both during the in situ reaction and long after intercalation is complete. The crucial role of oxygen in this reaction is probed and discussed. In an alternative route, anilinium is first intercalated and then, in a second step, is oxidatively polymerized in the xerogel upon exposure of the intercalate sample to air. Upon standing in air (aging), two processes occur independently in these materials:  (a) the partial reoxidation of the reduced V2O5 framework and (b) further oxidative coupling of anilinium and aniline oligomers inside the V2O5 layers, leading to longer chain molecules. These observations are supported by several physicochemical data. The magnetic moment of (PANI) x V2O5·nH2O decreases gradually upon exposure to air, but it does not change when the sample is stored in vacuum. Gel permeation chromatography (GPC) analysis results show that the molecular weight of polyaniline extracted from aged (PANI) x V2O5·nH2O is larger than that extracted from the fresh samples. The thermal stability of polyaniline extracted from aged (PANI) x V2O5·nH2O is better than that extracted from fresh samples. All (PANI) x V2O5·nH2O samples are paramagnetic with a Curie−Weiss and a temperature-independent van Vleck contribution. Variable-temperature 2H-wide-line NMR of (PANI) x V2O5·nH2O shows that the polymer chains are sterically confined with respect to phenyl ring rotation. The room-temperature conductivity of the freshly prepared (PANI) x V2O5·nH2O samples is in the range 10-4−10-1 S/cm depending on the degree of polymerization inside the layers, but the conductivity of aged samples is always greater. Room temperature thermoelectric power is negative and varies (−30 to 200 μV/K) depending on the polymer content and the degree of polymerization.

The linear and second-order nonlinear optical properties of single-crystal zinc tris(thiourea) sulfate, or ZTS, are determined. The deduced nonlinear coefficients are |d(31)| = 0.31, |d(32)| = 0.35, and |d(33)| = 0.23 pm/V compared with a |d(14)| value of 0.39 pm/V for potassium dihydrogen phosphate. Because it exhibits a low angular sensitivity (deltaDeltak/deltatheta), ZTS may prove useful for type-II second-harmonic generation from 1.06 to 1.027 microm. We present the phase-matching measurement data for ZTS and compare the calculated frequency conversion efficiency for ZTS with that of several other well-characterized materials.

The crystal structure, refractive indices, and phase-matching conditions for a new nonlinear optical material, L-histidine tetrafluoroborate (HFB), are reported. HFB grows readily, displays favorable mechanical characteristics, and has adequate birefringence to permit phase-matched parametric processes over much of its transparency range (250 nm to 1300 nm). The phase-matching loci and angular sensitivity for second-harmonic generation of 1064-nm light in single crystals of HFB were measured. The effective nonlinearity for HFB is comparable with that of beta-barium borate (~2 pm/V), and its angular sensitivity [delta(Deltak)/deltatheta] is somewhat smaller.

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