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.

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.

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.

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245 wileyonlinelibrary.com COMMUNICATION www.MaterialsViews.com www.advopticalmat.deThe interest in the interaction of metal helices with electromagnetic radiation has a long history. Traditionally, these interactions have been primarily applied in antenna engineering in the design of end fi re and polarization-insensitive receivers. [ 1 ] More recently, metal helices have been investigated for applications as chiral metamaterials, and have demonstrated some unique effects such as broadband circular polarization and negative refraction. [2][3][4][5] In particular, chiral metamaterial applications of metal helices in the visible wavelength region rely on effects associated with the strong resonances of localized surface plasmons of noble metals, especially gold and silver. However, due to the three-dimensional shape and requisite small feature sizes, the fabrication of plasmonic helices that are active in the visible wavelength region remains challenging. Most fabrication methods to date have relied on the use of rather complicated, expensive, and multi-step techniques to generate small-sized passive templates or scaffolds that are metalized to achieve plasmonic activity. For example, direct laser writing of helical cavities in positive tone photoresist, followed by development and electrochemical deposition of gold, has been used to produce square-lattice arrays of plasmonic helices that show a broadband response in the infrared region. [ 4 ] Additionally, selfassembled helical superstructures of noble metal nanoparticles and biological macromolecules (e.g., DNA, peptides, and proteins) have shown plasmonic chiral optical properties. [ 6 ] While these methods are certainly novel, one is consistently forced to choose between the simplicity of the method and the strength of optical activity in the production of plasmonic helices. In order to fulfi ll the promise of metal helices as chiral metamaterials, a scalable fabrication method capable of producing plasmonic helices with signifi cant optical activity will need to be developed.Glancing angle deposition (GLAD), a simple and scalable physical vapor deposition method based on geometric shadowing effect, [ 7 ] is a potential method to achieve this goal, and has already been used to design dielectric helices for circular polarizers based on the Bragg phenomenon. [ 8 ] Clearly, the incorporation of Ag and Au within the GLAD technique is a very appealing method of fabricating plasmonic helices for chiral metamaterial applications, especially given the recent demonstrated potential for GLAD roll-to-roll processing. [ 9 ] However, the high surface mobility of Ag or Au adatoms results in kinetic growth processes that overwhelm the shadowing effect, and precludes the production of non-equilibrium helical structures using conventional GLAD. [ 10 ] Large diameter, squareshaped Ag helices have been fabricated using oblique angle deposition (OAD), [ 11 ] a variation of GLAD, but the assimilation of Ag or Au within the full spectrum of GLAD structures has previously eluded...