Chiral nanosurfaces for enhancement of local electromagnetic field

The ability of plasmonic nanosurfaces to produce strong electromagnetic fields in their vicinity upon illumination can be used to enhance effects, such as those originating from chirality (lack of mirror symmetry) of molecules. We numerically investigate chiral nanosurfaces composed of plasmonic nanobars with varying packing densities. We identify the optimum illumination conditions for maximal field enhancement. Under these illumination conditions, the optical chirality near the surface exceeds the optical chirality of the incident light by almost an order of magnitude in a large area (200 nm × 200 nm) near the surface. Our simulations prove the nanosurfaces to be promising candidates for enhancement of chiral-optical effects.</p

Temperature-dependent Faraday rotation and magnetization reorientation in cerium-substituted yttrium iron garnet thin films

We report on the temperature dependence of the magnetic and magneto-optical properties in cerium-substituted yttrium iron garnet (Ce: YIG) thin films. Measurements of the Faraday rotation as a function of temperature show that the magnetic easy axis of thin Ce: YIG films reorients from in-plane to out-of-plane on cooling below -100 degrees C. We argue that the temperature-dependence of the magnetostriction and magnetocrystalline anisotropy of Ce: YIG is the dominant factor contributing to the change in easy axis direction, and we describe the changes in the magneto-optical spectra with temperature.National Science Foundation (U.S.) (Award ECCS-1607865)United States. Defense Advanced Research Projects Agency (Award FA8650-16-1-7641

Cu/Ag Sphere Segment Void Array as Efficient Surface Enhanced Raman Spectroscopy Substrate for Detecting Individual Atmospheric Aerosol

Surface enhanced Raman spectroscopy (SERS) shows great promise in studying individual atmospheric aerosol. However, the lack of efficient, stable, uniform, large-array, and low-cost SERS substrates constitutes a major roadblock. Herein, a new SERS substrate is proposed for detecting individual atmospheric aerosol particles. It is based on the sphere segment void (SSV) structure of copper and silver (Cu/Ag) alloy. The SSV structure is prepared by an electrodeposition method and presents a uniform distribution, over large 2 cm 2 arrays and at low cost. The substrate offers a high SERS enhancement factor (due to Ag) combined with lasting stability (due to Cu). The SSV structure of the arrays generates a high density of SERS hotspots (1.3 × 10 14/cm 2), making it an excellent substrate for atmospheric aerosol detection. For stimulated sulfate aerosols, the Raman signal is greatly enhanced (&gt;50 times), an order of magnitude more than previously reported substrates for the same purpose. For ambient particles, collected and studied on a heavy haze day, the enhanced Raman signal allows ready observation of morphology and identification of chemical components, such as nitrates and sulfates. This work provides an efficient strategy for developing SERS substrate for detecting individual atmospheric aerosol. </p

“Hot Edges” in Inverse Opal Structure Enable Efficient CO2 Electrochemical Reduction and Sensitive in-situ Raman Characterization

Conversion of CO 2 into fuels and chemicals via electroreduction has attracted significant interest. Via mesostructure design to tune the electric field distribution in the electrode, it is demonstrated that the Cu-In alloy with an inverse opal (CI-1-IO) structure provides efficient electrochemical CO 2 reduction and allows for sensitive detection of the CO 2 reduction intermediates via surface-enhanced Raman scattering. The significant enhancement of Raman signals of the intermediates on the CI-1-IO surface can be attributed to electric field enhancement on the "hot edges" of the inverse opal structure. Additionally, a highest CO 2 reduction faradaic efficiency (FE) of 92% (sum of formate and CO) is achieved at-0.6 V vs. RHE on the CI-1-IO electrode. The diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) results show that the Cu-In alloy with an inverse opal structure has faster adsorption kinetics and higher adsorption capacity for CO 2. The "hot edges" of the bowl-like structure concentrate electric fields, due to the high curvature, and also concentrate K + on the active sites, which can lower the energy barrier of the CO 2 reduction reaction. This research provides new insight into the design of materials for efficient CO 2 conversion and the detection of intermediates during the CO 2 reduction process. </p

Optical activity in third-harmonic Rayleigh scattering: A new route for measuring chirality

In 3D isotropic liquids, optical third-harmonic generation is forbidden, with circularly polarized light (CPL). Yet the associated nonlinear susceptibility directly influences the optical properties at the fundamental frequency by intensity dependence (Kerr effect). Here, the hidden third-harmonic optical properties upon CPL illumination are revealed by demonstrating a new effect, in hyper-Rayleigh scattering. This effect is succinctly enunciated: the intensity of light scattered at the third-harmonic frequency of the CPL incident light depends on the chirality of the scatterers. It is referred to as third-harmonic (hyper) Rayleigh scattering optical activity (THRS OA) and was observed from Ag nanohelices randomly dispersed in water. The first analytical theory model for the new effect in nanohelices is also provided, highlighting the role of localized transition dipoles along the helical length. THRS OA is remarkably user-friendly. It offers access to intricate optical properties (hyperpolarizabilities) that have so far been more easily accessible by computation and that are essential for the understanding of light−matter interactions. The new effect could find applications in hyper-sensitive characterization of the chirality in molecules and in nanostructures; this chirality plays a fundamental role in the function of bio/nano-machinery, with promising applications in next generation technologies

Dataset for ‘“Hot Edges” in Inverse Opal Structure Enable Efficient CO2 Electrochemical Reduction and Sensitive in-situ Raman Characterization’

This dataset contains the results of finite difference time domain (FDTD) calculations of electromagnetic fields and charge density near/on a surface with an inverse opal structure, and the results of COMSOL Multiphysics simulations of the same structure. The calculations were performed in Lumerical FDTD and COMSOL Multiphysics software. The results support the publication "“Hot Edges” in Inverse Opal Structure Enable Efficient CO2 Electrochemical Reduction and Sensitive in-situ Raman Characterization".The data were obtained by simulating a surface with inverse opal structure in Lumerical Finite Difference Time Domain (FDTD) software and COMSOL Multiphysics software. Details of the simulations are described in the related publication

Dataset for "Chiral nanosurfaces for enhancement of local electromagnetic field"

This dataset contains the results of calculations of electric fields and optical chirality 1 nm above the surface of an array of gold nanobars with varying length. The data support the publication "Chiral nanosurfaces for enhancement of local electromagnetic field".The data collection method is described in the related publication

Dataset for "Cu/Ag Sphere Segment Void Array as Efficient Surface Enhanced Raman Spectroscopy Substrate for Detecting Individual Atmospheric Aerosol".

This dataset contains the results of simulations of electromagnetic fields near the surface of a Cu/Ag sphere segment void array obtained using Lumerical FDTD software. The results support the publication "Cu/Ag Sphere Segment Void Array as Efficient Surface Enhanced Raman Spectroscopy Substrate for Detecting Individual Atmospheric Aerosol".The data were obtained by simulating various surface geometries in Lumerical Finite Difference Time Domain (FDTD) software. The exact geometries of the simulated structures and the simulation parameters are described in the related publication