The properties of methylene- and amine-substituted zeolites from first principles

All-silica zeolite frameworks doped with methylene and amine groups are studied using density functional theory-based electron structure calculations. Strain energies are calculated in a novel way, by comparing zeolite energies with appropriate polymer reference systems. The modified zeolites are found to be mechanically stable structures with surprisingly little strain. Distortions due to impurities result in broadened Si-O-Si angle distributions in the lattice surrounding defects. Our results suggest that zeolites can accommodate both methylene and amine groups at high concentrations with minimal strain. The amine-doped zeolites are strong Lewis bases suggesting novel applications in base catalysis.     

Size-controlled aerosol synthesis of silver nanoparticles for plasmonic materials

Aerosol techniques were used to synthesize spherical and monodisperse silver nanoparticles for plasmonic materials. The particles were generated with an evaporation-condensation technique followed by size selection and sintering with a differential mobility analyzer and a tube furnace, respectively. Finally, the nanoparticles were collected on a glass substrate with an electrostatic precipitator. The particle size distributions were measured with a scanning mobility particle sizer and verified with a transmission electron microscope. A spectrophotometer was used to measure the optical extinction spectra of the prepared samples, which contained particles with diameters of approximately 50, 90 and 130?nm. By controlling the particle size, the dipolar peak of the localized surface plasmon resonance was tuned between wavelengths of 398 and 448?nm. In addition, quadrupolar resonances were observed at shorter wavelengths as predicted by the simplified theoretical model used to characterize the measured spectra.     

Spectral control in anisotropic resonance-domain metamaterials

We introduce a concept to control the spectral and dichroic properties of metamaterials. The approach is based on anisotropic metal nanoparticles and on varying their mutual orientation in a periodic lattice. Even seemingly inconsequential changes in particle ordering strongly modify the dichroic properties of the arrays and result in either very narrow resonances or ultrabroad extinction ranges. The results arise from long-range diffractive coupling between the particles, as determined by the dependence of the array unit cell size on particle ordering.