Oriented films of polyvinylidene fluoride [(CH2CF2)n], a polar polymer possessing symmetry mm2, can be made significantly pyroelectric and optically nonlinear by poling in an electric field. A pyroelectric coefficient (dP/dT = 2.4 ± 0.7 nC/cm2°C) comparable to that of single-crystal LiNbO3 is observed. The nonlinear optical coefficients d33, d32, and d31 of polyvinylidene fluoride (PVF2) are measured relative to d11 of crystalline quartz [d33 (PVF2)≃2d31 (PVF2) ≃d11(SiO2); d32(PVF2)≃0]. The poled films have specific advantages for pyroelectric detection of electromagnetic radiation and for optical parametric devices.

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A simple, portable electrochemical surface-enhanced Raman spectroscopy (SERS) system is reported, consisting of a small benchtop Raman spectrometer, a laptop computer, and a portable USB potentiostat. Screen printed electrodes modified with silver colloidal nanoparticles are used as the SERS-active electrode, which exhibit long-term stability once prepared. Spectroelectrochemical analyses of para-aminothiophenol and melamine as model systems was conducted. In both cases, an increase in SERS signal is observed upon modulation of the applied voltage, indicating an inherent benefit of such a system wherein the surface charge can be easily tuned. Given the low cost, rapid analysis time, and good sensitivity of this system, this simple setup could be implemented for many on-site sensing applications, ranging from food and drug analysis to environmental monitoring and to chemical and biological warfare agent detection.

Molecules or ions of the form BOx−n lack a center of symmetry whenever the B atom has a nonbonded pair of electrons. The problem of generating an acentric crystal can be approached by using these acentric oxygen polyhedrons as building blocks. A very high incidence of acentricity is found in compounds based on distorted BO3−n octahedra, such as XeO3, AIO3 (A=H, Li, Na, K, Rb, Cs, NH4, and Tl), and MTeO3 (M=Ca, Sr, Ba, Zn, Cd, Hg, Pb, Ni). Since these materials also have large indices of refraction, the concept of acentricity via nonbonded electrons provides a new and important guideline in the search for nonlinear optical materials.

By using an evaporated silver film that has a continuously varying thickness, we have demonstrated the dependence of surface-enhanced Raman scattering (SERS) on the dielectric properties of the film. These results support local field models that are based on metal-particle resonances for SERS.

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