Molecular Chirality Detection with Periodic Arrays of Three-Dimensional Twisted Metamaterials.

Rapid detection of the handiness of chiral molecules is an important topic for pharmaceutical industries because chiral drugs with opposing handiness sometimes exhibit unwanted side effects. In this research, a rapid optical method is proposed to determine the handiness of the chiral drug "Thalidomide". The platform is a large array of three-dimensional (3D) twisted metamaterials fabricated with a novel method by combining nanospherical-lens lithography (NLL) and hole-mask lithography (HML).

Polarization-Selecting III-Nitride Elliptical Nanorod Light-Emitting Diodes Fabricated with Nanospherical-Lens Lithography.

Current-injected elliptical nanorod light-emitting diodes (LEDs) are demonstrated to emit polarized light with a bottom-emitting configuration. The polarization ratio of the electroluminescence reaches 3.17 when the length of the minor axis for the elliptical nanorods is as small as 150 nm.

Avoided resonance crossing and non-reciprocal nearly perfect absorption in plasmonic nanodisks with near-field and far-field couplings.

Avoided resonance crossings (ARC) in plasmonic nanodisk structures due to near field or far field couplings were numerically demonstrated. Near field coupling in disk dimmer with both vertical or side-by-side arrangement leads to both energy and linewidth anti-crossing by varying one disk size across the other. Far field coupling in double layered disk arrays of extremely small gap size or gap size with Fabry Perot resonant condition close to the frequency selective surface (FSS) stopband center leads to non-reciprocal absorption spectrum as one disk size varying across the other.

Au nanorod design as light-absorber in the first and second biological near-infrared windows for in vivo photothermal therapy.

Photothermal cancer therapy using near-infrared (NIR) laser radiation is an emerging treatment. In the NIR region, two biological transparency windows are located in 650-950 nm (first NIR window) and 1000-1350 nm (second NIR window) with optimal tissue transmission obtained from low scattering and energy absorption, thus providing maximum radiation penetration through tissue and minimizing autofluorescence. To date, intensive effort has resulted in the generation of various methods that can be used to shift the absorbance of nanomaterials to the 650-950 nm NIR regions for studying photoinduced therapy.

Observation of absorption-dominated bonding dark plasmon mode from metal-insulator-metal nanodisk arrays fabricated by nanospherical-lens lithography.

Plasmon hybridization modes are observed in the extinction spectra of a metal-insulator-metal (MIM) nanodisk array fabricated using nanospherical-lens lithography. Two distinct hybridization modes are observed in this vertically aligned configuration. Theoretical simulation indicates that the bonding mode located at a lower energy level exhibits an antiphase charge distribution and corresponds to the dark plasmon mode.

Influence of surface plasmon resonance on the emission intermittency of photoluminescence from gold nano-sea-urchins.

The effect of surface plasmon resonance (SPR) on the blinking emission of photoluminescence from noble metal nanostructures still requires further investigation in quantum mechanics and limits their applications. We investigate one photon luminescent emission intermittency of noble metal nanostructures with differently sized sea-urchin-shaped nanoparticles, known as nano-sea-urchins (NSUs). The probability of the "on" process in one photon luminescent emission intermittency of NSUs increases due to the strong electric field of SPR.

Surface plasmon-enhanced and quenched two-photon excited fluorescence.

This study investigated theoretically and experimentally that two-photon excited fluorescence is enhanced and quenched via surface plasmons (SPs) excited by total internal reflection with a silver film. The fluorescence intensity is fundamentally affected by the local electromagnetic field enhancement and the quantum yield change according to the surrounding structure and materials. By utilizing the Fresnel equation and classical dipole radiation modeling, local electric field enhancement, fluorescence quantum yield, and fluorescence emission coupling yield via SPs were theoretically analyzed at different dielectric spacer thicknesses between the fluorescence dye and the metal film.

Gap structure effects on surface-enhanced Raman scattering intensities for gold gapped rods.

Gapped rods provide a unique platform for elucidating structure/function relationships, both for single-molecule electrochemical techniques and for surface-enhanced Raman scattering (SERS). This paper attempts to elucidate the dependence of SERS intensities on gap topography and gap distance for gold gapped rods with segment lengths varying over a wide range (40-2000 nm). Significantly, we have determined that rough gaps lead to a smaller SERS enhancement than smooth gaps for these structures even though the rough gaps have a larger total surface area.

Ellipsometric studies of optical properties of local surface plasmon resonance for Au nanoparticles on the substrate.

Few ellipsometric studies have been conducted on Au self-assembled monolayers (SAM), with large discrepancies obtained for refractive index values. Because the Au NPs layer is a kind of composite layer, Au NPs and void, the effective media approximate (EMA) model was employed to investigate the optical properties of Au NPs. The reflective coefficient (approximately 1.

Surfactants-aided syntheses of different sizes and triangular shape of gold nanoparticles using trisodium citrate in environmentally friendly and photoinduced methods.

We prepared gold nanoparticles (Au NPs) by only using trisodium citrate as the stabilizer. The detailed reaction mechanisms of S(N)1 and E1 reactions are examined and evidenced in this study by FTIR data. Citric acid is a kind of tertiary substrate.

Ellipsometric advances for local surface plasmon resonance to determine chitosan adsorption on layer-by-layer gold nanoparticles.

The ellipsometric measurement of local surface plasmon resonance (LSPR) caused by the adsorption of chitosan on layer-by-layer gold nanoparticles (Au NPs) was investigated. Six nanometer (6 nm) Au NPs were prepared and layer-by-layer Au NPs were fabricated to shift the LSPR to 520, 540, and 560 nm, respectively, due to the Mie theory. The thicknesses and the fractions of the layer-by-layer Au NPs were measured accurately using a combination of the Fresnel equation and the Maxwell-Garnett equations for ellipsometry.

Heterodyne apertureless near-field scanning optical microscopy on periodic gold nanowells.

Heterodyne detection for apertureless near-field scanning optical microscopy was used to study periodic gold nanowell arrays. Optical near-field amplitude and phase signals were obtained simultaneously with the topography of the gold nanowells and with different polarizations. Theoretical calculations of the near-fields were consistent with the experiments; in particular, the calculated amplitudes were in especially good agreement.

Localized surface plasmon resonance spectroscopy of single silver nanocubes.

In this work, we use dark-field microscopy to observe a new plasmon resonance effect for a single silver nanocube in which the plasmon line shape has two distinct peaks when the particles are located on a glass substrate. The dependence of the resonance on nanocube size and shape is characterized, and it is found that the bluer peak has a higher figure of merit for chemical sensing applications than that for other particle shapes that have been studied previously. Comparison of the measured results with finite difference time domain (FDTD) electrodynamics calculations enables us to confirm the accuracy of our spectral assignments.

Surface plasmon standing waves in large-area subwavelength hole arrays.

A flexible and parallel procedure to generate large-area, free-standing films of subwavelength hole arrays has been demonstrated. This method is materials-general, and multilayered films of different materials were constructed. The optical quality of these films was tested using a near-field scanning optical microscope, which revealed the formation of surface plasmon standing wave patterns that were consistent with numerical simulations.

Surface plasmon generation and light transmission by isolated nanoholes and arrays of nanoholes in thin metal films.

Extensive 3-D finite-difference time-domain simulations are carried out to elucidate the nature of surface plasmon polaritons (SPPs) and localized surface plasmon polaritons (LSPs) generated by nanoscale holes in thin metallic films interacting with light. Both isolated nanoholes and square arrays of nanoholes in gold films are considered. For isolated nanoholes, we expand on an earlier discussion of Yin et al.

Near-field photochemical imaging of noble metal nanostructures.

The sub-diffraction imaging of the optical near-field in nanostructures, based on a photochemical technique, is reported. A photosensitive azobenzene-dye polymer is spin coated onto lithographic structures and is subsequently irradiated with laser light. Photoinduced mass transport creates topographic modifications at the polymer film surface that are then measured with atomic force microscopy (AFM).

Finite-difference time-domain model of lasing action in a four-level two-electron atomic system.

We report a new finite-difference time-domain (FDTD) computational model of the lasing dynamics of a four-level two-electron atomic system. Transitions between the energy levels are governed by coupled rate equations and the Pauli Exclusion Principle. This approach is an advance relative to earlier FDTD models that did not include the pumping dynamics, or the Pauli Exclusion Principle.

Numerical study of light correlations in a random medium close to the Anderson localization threshold.

We applied a finite-difference time domain algorithm to the study of field and intensity correlations in random media. Close to the onset of Anderson localization, we observe deviations of the correlation functions, in both shape and magnitude, from those predicted by the diffusion theory. Physical implications of the observed phenomena are discussed.