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.

Both Fe2O3 thin films and nanorod arrays are deposited using electron beam evaporation through normal thin film deposition and oblique angle deposition (OAD) and are characterized structurally, optically, and photocatalytically. The morphologies of the thin films are found to be arrays of very thin and closely packed columnar structures, while the OAD films are well-aligned nanorod arrays. All films were determined to be in the hematite phase (α-Fe2O3), as confirmed by both structural and optical characterization. Texture measurements indicate that films have similar growth modes where the [110] direction aligns with the direction of material growth. Under visible light illumination, the thin film samples were more efficient at photocatalytically degrading methylene blue, while the nanorod arrays were more efficient at inactivating E. coli O157:H7. The size of the targeted agent and the different film morphologies result in different reactant/surface interactions, which is the main factor that determines photoactivity. Furthermore, an analytic mathematical model of bacterial inactivation based on chemotactic bacterial diffusion and surface deactivation is developed to quantify and compare the inactivation rate of the samples. These results indicate that α-Fe2O3 nanorods are promising candidates for antimicrobial applications and are expected to provide insight into the development of better visible-light antimicrobial materials for food products and processing environments, as well as other related applications.

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.

We investigate Au-decorated Fe2O3 nanoparticle catalysts, Fe2O3–Au, where the supporting Fe2O3 nanoparticles are of different shapes: spheres, rings, and tubes. The decoration procedure for the Fe2O3–Au nanoparticles is identical for each shape, and is analogous to the synthesis of pure Au nanoparticles (AuNPs). These similarities allows for direct comparison between the different shapes and the pure AuNPs. The morphological, optical, and magnetic characterizations reveal that the Fe2O3–Au nanoparticles are hybrid structures exhibiting both plasmonic and magnetic properties. The different shape Fe2O3–Au nanoparticles and the AuNPs are evaluated for their ability to catalytically reduce 4-nitrophenol. Remarkably, it is found that Fe2O3–Au nanoparticles are more efficient catalysts than AuNPs because they can achieve the same, or better, catalytic reaction rates using significantly smaller quantities of Au, which is the catalytically active material. Taking into account the Au-loadings, the Fe2O3 rings and tubes are superior to the Fe2O3 spheres as catalytic supports due to their γ-Fe2O3 crystal phase. It is also shown that the Fe2O3–Au nanoparticles have the additional benefit for catalysis in that they can be recovered and reused via magnetic collection. Furthermore, the Fe2O3–Au nanoparticles and AuNPs are found to efficiently transduce heat from light through plasmonic absorbance, and this phenomenon is exploited to demonstrate the photothermal catalytic reduction of 4-nitrophenol.

In this work, hydrogen isotopes in the form of protium and deuterium were rapidly desorbed from magnetic-hydride iron oxide-palladium (Fe2O3-Pd) hybrid nanomaterials using an alternating magnetic field (AMF). Palladium, a hydride material with a well-known hydrogen isotope effect, was deposited on Fe2O3 magnetic nanoparticle support by solution chemistries and used as a hydrogen isotope storage component. The morphological, structural, optical, and magnetic studies reveal that the Fe2O3-Pd nanoparticles (NPs) are hybrid structures exhibiting both hydrogen isotope storage (Pd) and magnetic (Fe2O3) properties. The hydrogen isotope sorption/desorption behavior of metal hydride-magnetic nanomaterials was assessed by isothermal pressure-composition response curves (isotherms). The amount and rate of hydrogen isotope gas release was tuned by simply adjusting the strength of the magnetic field strength applied. Protium and deuterium displayed a similar loading capacity, namely H/M 0.55 and H/M=0.45, but different plateau pressures. Significant differences in the kinetics of release for protium and deuterium during magnetic heating were observed. A series of magnetically induced charge-discharge cycling experiments were conducted showing that this is a highly reproducible and robust process.

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...

Ultrafast exciton dynamics of aligned polycrystalline nanorod arrays composed of CdSe or CdSe/TiO 2 grown on conductive glass substrates using oblique angle deposition/codeposition have been studied using femtosecond transient absorption (TA) spectroscopy. Scanning electron microscopy images show that the morphology of the two samples are comparable in height, width, and tilt angle. X-ray diffraction and Raman spectroscopy indicate that the as-deposited CdSe nanorod arrays are in the hexagonal phase, while the TiO 2 is amorphous. In the TA studies, a pump wavelength of 580 nm was used to determine the exciton lifetimes of CdSe in the two samples. Transient bleach dynamics probed at 695 nm can be fit with triple exponential functions with lifetimes of 7 ps, 84 ps, and ∼1.0 ns for CdSe nanorods versus 0.5 ps, 3 ps, and 24 ps for the CdSe/TiO 2 composite-nanorods. These lifetimes are independent of the pump power, indicating that nonlinear processes are not involved. For CdSe nanorods, the two fast decays are mainly due to nonradiative electron−hole recombination or exciton relaxation mediated by trap states. The overall much faster decay in CdSe/TiO 2 nanorods is due to electron transfer from the conduction band of CdSe to the conduction band of TiO 2 . The electron injection rate from CdSe into TiO 2 was calculated to be 1.7 × 10 11 s −1 based on the average lifetime measured for CdSe with and without TiO 2 . This very high rate of electron injection is attributed to the large interfacial area and strong coupling between the two materials in CdSe/TiO 2 composite-nanorods. Such strongly coupled semiconductor−metal oxide heterostructures are desired for applications in solar energy conversion.

The use of hydrogen as a clean and renewable alternative to fossil fuels requires a suite of flammability mitigating technologies, particularly robust sensors for hydrogen leak detection and concentration monitoring. To this end, we have developed a class of lightweight optical hydrogen sensors based on a metasurface of Pd nano-patchy particle arrays, which fulfills the increasing requirements of a safe hydrogen fuel sensing system with no risk of sparking. The structure of the optical sensor is readily nano-engineered to yield extraordinarily rapid response to hydrogen gas (<3 s at 1 mbar H2) with a high degree of accuracy (<5%). By incorporating 20% Ag, Au or Co, the sensing performances of the Pd-alloy sensor are significantly enhanced, especially for the Pd80Co20 sensor whose optical response time at 1 mbar of H2 is just ~0.85 s, while preserving the excellent accuracy (<2.5%), limit of detection (2.5 ppm), and robustness against aging, temperature, and interfering gases. The superior performance of our sensor places it among the fastest and most sensitive optical hydrogen sensors.