Hidden Chirality in Superficially Racemic Patchy Silver Films

Chiral patchy particle films where morphological enantiomers exist in equal proportion are found to have significant circular dichroism. It is determined that the rotation direction during glancing angle deposition breaks the racemic symmetry, resulting in a distribution of material which enhances the chirality of one set of enantiomers relative to the other. Microscopic analysis and geometric chirality calculations reveal that the chirality of the bulk film results from incomplete cancellations of even stronger local chiralities

Tunable Three-Dimensional Helically Stacked Plasmonic Layers on Nanosphere Monolayers

We report a simple and scalable method to fabricate helical chiral plasmonic nanostructures using glancing angle deposition on self-assembled nanosphere monolayers. By controlling the azimuthal rotation of substrates, Ag and SiO₂ layers can be helically stacked in left-handed and right-handed fashions to form continuous helices. Finite-difference time-domain simulations confirm the experimental results that show that these plasmonic helices exhibit strong chiroptical responses in the visible to near-IR region, which can be tuned by changing the diameter of nanospheres. With such flexibility in the design, helically stacked plasmonic layers may act as tunable chiral metamaterials, as well as serve as different building blocks for chiral assemblies

Ag Nanoparticle Embedded TiO₂ Composite Nanorod Arrays Fabricated by Oblique Angle Deposition: Toward Plasmonic Photocatalysis

Using a unique oblique angle co-deposition technique, well-aligned arrays of Ag nanoparticle embedded TiO₂ composite nanorods have been fabricated with different concentrations of Ag. The structural, optical, and photocatalytic properties of the composite nanostructures are investigated using a variety of experimental techniques and compared with those of pure TiO₂ nanorods fabricated similarly. Ag nanoparticles are formed in the composite nanorods, which increase the visible light absorbance due to localized surface plasmon resonance. The Ag concentrations and the annealing conditions are found to affect the size and the density of Ag nanoparticles and their optical properties. The Ag nanoparticle embedded TiO₂ nanostructures exhibit enhanced photocatalytic activity compared to pure TiO₂ under visible- or UV-light illumination. Ag plays different roles in assisting the photocatalysis with different light sources. Ag can be excited and can inject electrons to TiO₂, working as an electron donor under visible light. While under UV illumination, Ag acts as an electron acceptor to trap the photogenerated electrons in TiO₂. Due to the opposite electron transfer direction under UV and visible light, the presence of Ag may not result in a greater enhancement in the photocatalytic performance

Experimental and Numerical Study of the Effect of High Steam Concentration on the Oxidation of Methane and Ammonia during Oxy-Steam Combustion

The effect of high H₂O concentration during oxy-steam combustion on the oxidation of methane and ammonia was investigated both experimentally and numerically. Comparison experiments between O₂/N₂ and O₂/H₂O atmosphere were performed in a flow reactor at atmospheric pressure covering fuel-rich to fuel-lean equivalence ratios and temperatures from 973 to 1773 K. Experimental results showed that the presence of high H₂O concentration dramatically suppressed CO formation at temperatures above 1300 K. High H₂O concentrations inhibited NO formation under stoichiometric and fuel-lean conditions but enhanced NO formation under fuel-rich conditions. The chemical kinetic mechanism, which was hierarchically structured and updated, satisfactorily reproduced the main characteristics of CO and NO formation. High H₂O concentrations significantly alter the structure of radical pool and subsequently the formation of CO and NO. Ultralow CO concentrations above 1300 K are attributed to the enhancement of CO + OH ⇄ CO₂ + H by high OH radical concentrations. NO suppressions under stoichiometric and fuel-lean conditions are caused by strong suppression of NH₂ + O ⇄ H + HNO in the pathway NH₂ → HNO → NO. This suppression is due to the lack of O radicals. By contrast, NO enhancement under fuel-rich conditions is caused by the significant enhancement of NH₂ + OH ⇄ NH + H₂O in the pathway NH₂ → NH → HNO → NO. This enhancement is due to the fairly high OH concentration in the O₂/H₂O atmosphere