Light-Assisted Catalysis and the Dynamic Nature of Surface Species in the Reverse Water Gas Shift Reaction over Cu/γ-AlO.

The reverse water gas shift (RWGS) reaction converts CO and H into CO and water. We investigated Cu/γ-AlO catalysts in both thermally driven and light-assisted RWGS reactions using visible light. When driven by combined visible light and thermal energy, the CO conversion rates were lower than in the dark.

A coating design to rule them all: asymmetric Fabry-Perot resonators with diverse optical response based on Au films with high-temperature sensitivity.

Thermal annealing of thin metal films induces morphology changes that have a dramatic effect in the optical properties. Here we propose an asymmetric Fabry-Perot resonator consisting of a top metal film, a dielectric spacer, and a bottom metal mirror that can display a diverse infrared response. Thermally induced morphology changes result in large reflectivity variations within a limited temperature range following the top film transition between conductive, highly lossy, and transparent regimes.

Quantifying Shape Transition in Anisotropic Plasmonic Nanoparticles through Geometric Inversion. Application to Gold Bipyramids.

Unraveling the nuanced interplay between the morphology and the optical properties of plasmonic nanoparticles is crucial for targeted applications. Managing the relationship becomes significantly complex when dealing with anisotropic nanoparticles that defy a simple description using parameters like length, width, or aspect ratio. This complexity requires computationally intensive numerical modeling and advanced imaging techniques.

Reverse engineering of e-beam deposited optical filters based on multi-sample photometric and ellipsometric data.

A post-production characterization approach based on spectral photometric and ellipsometric data related to a specially prepared set of samples is proposed. Single-layer (SL) and multilayer (ML) sets of samples presenting building blocks of the final sample were measured ex-situ, and reliable thicknesses and refractive indices of the final ML were determined. Different characterization strategies based on ex-situ measurements of the final ML sample were tried, reliability of their results was compared, and the best characterization approach for practical use, when preparation of the mentioned set of samples would be a luxury, is proposed.

Green Nanocoatings Prepared by Crosslinking Self-Assembled Fatty Acids on Metals.

Self-assembled monolayers (SAMs) are an important element of modern nanotechnology and surface functionalization. However, their application is still limited because they are easily removed from the surface of the object in corrosive environments. Crosslinking would make SAMs more resistant to the corrosive environment they are exposed to.

Compact formulation of the transparent-absorbing isotropic interface electromagnetic problem.

A complete formulation of the electromagnetic problem corresponding to the light incidence from a transparent to an absorbing medium (isotropic materials) is developed. According to the standard separation in and polarization cases, we explicitly obtain all the relevant formulas that relate the polarization and Poynting vectors of the reflected and transmitted beams with the incident ones. Overall, the procedure is compact since it is short and complete.

Optical microstructures based on surface-selective growth of Ag nanoparticles on thermally poled soda-lime glass.

Glass is important as a substrate for coatings in a wide range of applications or as a substrate for the fabrication of optical micro/nano structures. Coating by wet chemistry methods often demands modifications of the glass surface properties involving several steps. In addition, the micro/nano structuring is usually a several-step process.

Optical absorption in array of Ge/Al-shell nanoparticles in an Alumina matrix.

The absorption spectra in array of Ge, Al and Ge/Al-shell nanoparticles immersed in alumina (AlO) matrix is calculated in framework of ab initio macroscopic dielectric model. It is demonstrated that absorption is strongly enhanced when germanium nanospheres are encapsulated by Al-shell. Two absorption peaks, appearing in the spectra, correspond to low energy ω and high energy ω plasmons which lie in visible and ultraviolet frequency range, respectively.

Preparation of non-oxidized Ge quantum dot lattices in amorphous AlO, SiN and SiC matrices.

The preparation of non-oxidized Ge quantum dot (QD) lattices embedded in AlO, SiN, SiC matrices by self-assembled growth was studied. The materials were produced by magnetron sputtering deposition, using different substrate temperatures. The deposition regimes leading to the self-assembled growth type and the formation of three-dimensionally ordered Ge QD lattices in different matrices were investigated and determined.

Relation between 2D/3D chirality and the appearance of chiroptical effects in real nanostructures.

The optical activity of fabricated metallic nanostructures is investigated by complete polarimetry. While lattices decorated with nanoscale gammadia etched in thin metallic films have been described as two dimensional, planar nanostructures, they are better described as quasi-planar structures with some three dimensional character. We find that the optical activity of these structures arises not only from the dissymmetric backing by a substrate but, more importantly, from the selective rounding of the nanostructure edges.

Boosting Fano resonances in single layered concentric core-shell particles.

Efficient excitation of Fano resonances in plasmonic systems usually requires complex nano-structure geometries and some degree of symmetry breaking. However, a single-layered concentric core-shell particle presents inherent Fano profiles in the scattering spectra when sphere and cavity modes spectrally overlap. Weak hybridization and suitable choice of core and shell materials gives rise to strong electric dipolar Fano resonances in these systems and retardation effects can result in resonances of higher multipolar order or of magnetic type.

Dark modes and Fano resonances in plasmonic clusters excited by cylindrical vector beams.

Control of the polarization distribution of light allows tailoring the electromagnetic response of plasmonic particles. By rigorously extending the generalized multiparticle Mie theory, we show that focused cylindrical vector beams (CVB) can be used to efficiently excite dark plasmon modes in nanoparticle clusters. In addition to the small radiative damping and large field enhancement associated to dark modes, excitation with CVB can give place to unusual phenomenology like the formation of electromagnetic cold spots and the generation of Fano resonances in highly symmetric clusters.

Oscillations in spectral behavior of total losses (1 - R - T) in thin dielectric films.

We explain reasons of oscillations frequently observed in total losses spectra (1 - R - T) calculated on the basis of measurement spectral photometric data of thin film samples. The first reason of oscillations is related to difference in angles of incidence at which spectral transmittance and reflectance are measured. The second reason is an absorption in a thin film.

Design and production of bicolour reflecting coatings with Au metal island films.

Optical properties of metal island films (MIFs) can be combined with interference of dielectric coatings. A set of multilayer designs containing metal clusters reflecting different colours from front and back side of the coating was obtained by numerical optimization. The chosen designs presenting the range of feasible colours were deposited by electron beam evaporation.

Comparison of two techniques for reliable characterization of thin metal-dielectric films.

In the present study we determine the optical parameters of thin metal-dielectric films using two different characterization techniques based on nonparametric and multiple oscillator models. We consider four series of thin metal-dielectric films produced under various deposition conditions with different optical properties. We compare characterization results obtained by nonparametric and multiple oscillator techniques and demonstrate that the results are consistent.

Near-field coupling of metal nanoparticles under tightly focused illumination.

The influence of strongly focused radiation on the electromagnetic interaction of metal particles is studied. The near-field distribution of silver dimers is calculated by combining a multiple scattering approach and the multipolar expansion of focused beams based on the Richards-Wolf description of diffracting systems. The results show that tight focusing can induce larger maximum field enhancement and stronger localization of the near field than can plane wave illumination.

Use of gold island films in design of reflectors with high luminosity.

We describe the optical properties of gold island films embedded between SiO2 and/or TiO2 layers. Plasmonic properties of gold films have been characterized using spectrometry and variable angle spectroscopic ellipsometry for various combinations of the embedding media. The obtained refractive indices of embedded gold island films have been used in the design of several types of multilayer reflectors.

Gradient silver nanoparticle layers in absorbing coatings--experimental study.

Metal island films show a characteristic absorption peak related to the surface plasmon resonance of free electrons. This kind of film can be used in absorbing coatings, together with dielectric layers. Such absorbing multilayer coatings, with and without the gradient of the silver mass thickness in metal island films throughout the coating, have been deposited by electron beam evaporation.

General approach to reliable characterization of thin metal films.

Optical constants of thin metal films are strongly dependent on deposition conditions, growth mode, and thickness. We propose a universal characterization approach that allows reliable determination of thin metal film optical constants as functions of wavelength and thickness. We apply this approach to determination of refractive index dispersion of silver island films embedded between silica layers.

On the dielectric function tuning of random metal-dielectric nanocomposites for metamaterial applications.

The potential of random metal-dielectric nanocomposites as constituent elements of metamaterial structures is explored. Classical effective medium theories indicate that these composites can provide a tunable negative dielectric function with small absorption losses. However, the tuning potential of real random composites is significantly lower than the one predicted by classical theories, due to the underestimation of the spectral range where topological resonances take place.

Optical characterization of hybrid antireflective coatings using spectrophotometric and ellipsometric measurements.

A hybrid antireflective coating combining homogeneous layers and linear gradient refractive index layers has been deposited using different techniques. The samples were analyzed optically based on spectrophotometric and spectroscopic ellipsometry measurements under different angles of incidence in order to precisely characterize the coatings. The Lorentz-Lorenz model has been used to calculate the refractive index of material mixtures in gradient and constant index layers of the coating.

Modeling of optical properties of silver-doped nanocomposite glasses modified by electric-field-assisted dissolution of nanoparticles.

It has been demonstrated recently that silver nanoparticles embedded in a glass matrix can be dissolved by the combination of an intense dc electric field and moderately elevated temperature. In an intermediate state of this process percolated silver layers inside the glass can also occur. These structural modifications significantly modify the optical behavior of the glass, suggesting an interesting perspective for the engineering of optical properties of this kind of metallodielectric materials.

Use of information on the manufacture of samples for the optical characterization of multilayers through a global optimization.

We present a procedure for the optical characterization of thin-film stacks from spectrophotometric data. The procedure overcomes the intrinsic limitations arising in the numerical determination of many parameters from reflectance or transmittance spectra measurements. The key point is to use all the information available from the manufacturing process in a single global optimization process.