Bryan C. Sih

Metal nanoparticle—conjugated polymer nanocomposites

Recent literature describing nanocomposites of metal nanoparticles and conjugated polymers and oligomers are reviewed. Preparation of these nanocomposites by chemical and electrochemical methods are described, and the electronic and optical properties of these materials are discussed. Some initial applications that have been investigated for such nanocomposites are covered.

Metal-containing conjugated materials : oligomers, polymers, and nanomaterials

We describe new developments in hybrid conjugated materials containing metal complexes or nanoparticles. Phosphino-oligothiophenes are useful building blocks for metal-containing polymers and oligomers, and as cross-linkable surface passivating groups for metal nanoparticles. These materials may find application as new chemical sensors, switches, or transistors in molecular electronics.

Effects of silver doping on ferroelectric SrBi2Ta2O9

Silver-doped SrBi2Ta2O9 (Ag:SBT) ceramics were synthesized by solid state reactions. The reaction mechanism has been deduced based on the crystal defect chemistry. It involves the diffusion of Ag+ and O2− ions into the (Bi2O2)2+ layers between the perovskite-like units to recover the bismuth and oxygen vacancies, respectively, which were inherently present in SBT ceramics due to the volatilization of Bi2O3 at high temperatures. The Ag:SBT samples have been characterized by a variety of techniques: x-ray diffraction, dielectric and ferroelectric measurements, and impedance spectroscopy. Ag doping is found to significantly affect the structural and physical properties of SBT, including lattice parameters, Curie temperature, bulk conductivity, activation energy, and ferroelectricity. These effects have been interpreted based on the model of the recovery of oxygen and bismuth vacancies upon Ag doping. The effects of Ag diffusion should be taken into account when using Ag as electrode materials for the charact...

Surface-plasmon resonance sensing of alcohol with electrodeposited polythiophene and gold nanoparticle-oligothiophene films

Electrodeposited films of polythiophene or gold nanoparticles (NPs) capped with conjugated oligothiophenes prepared on thin gold films are employed in a Kretschmann-type surface-plasmon resonance detector. The polythiophene films selectively respond to alcohol (ethanol or methanol) and toluene vapors but not to hexanes or water vapors, while the nanoparticle/oligothiophene films respond only to alcohol vapors of the solvents tested. For both films, the response to vapors consisted of the minimum in the reflectance curve (θ0) shifting to a higher angle as the thickness of the film increased. Slight increases in dielectric constant were also observed. The NPs do not result in an enhancement in sensitivity, contrary to theoretical predictions that suggest greater sensitivity may be achieved due to localized surface-plasmon effects associated with the presence of the Au NPs in the dielectric.

Acoustic anomalies and central peak in SrBi2Ta2O9 single crystals studied by micro-Brillouin scattering

Acoustic properties of layered perovskite SrBi2Ta2O9 (SBT) single crystals were investigated by micro-Brillouin scattering. Two elastic stiffness coefficients, c33 and c44, defined within the pseudotetragonal crystallographic axes, and the corresponding sound velocities were determined in the temperature range between 290 and 773 K. The longitudinal sound velocity propagating along the pseudotetragonal c axis was found to be very small, which can be related to the weak interlayer bonding of SBT. The corresponding c33 shows marked softening on approaching the ferroelectric phase transition temperature Tc around 600 K from both high- and low-temperature sides. The hypersonic attenuation increases markedly around Tc, which seems to reflect not only the bilinear coupling between the order parameter and the strain in the ferroelectric phase, but also the electrostrictive coupling in the paraelectric phase. Furthermore, a quasielastic central component was observed near Tc, which is believed to be partly respon...