Jordi Sancho-Parramon

A general-purpose software for optical characterization of thin films: specific features for microelectronic applications

Abstract We present a detailed description of the features and capabilities of a new software for the optical characterization of thin films from spectrophotometric and/or ellipsometric measurements. The program allows the analysis of a wide range of multi-layered structures, either with respect to the composition, microstructure or thickness of any of the layers. Several spectra corresponding to different measurement techniques of a single sample may be fitted simultaneously. A short description of the dispersion models actually implemented to represent the materials is given. Several examples of use are discussed. These have been selected to illustrate important aspects that may be relevant to microelectronic applications.

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. This result suggests that a random mixture consisting of a metal matrix with embedded isolated dielectric inclusions is a promising design guideline for the fabrication of tunable composites for metamaterial purposes.

Plasmonic layers based on Au-nanoparticle-doped TiO2 for optoelectronics: structural and optical properties

The anti-reflective effect of dielectric coatings used in silicon solar cells has traditionally been the subject of intensive studies and practical applications. In recent years the interest has permanently grown in plasmonic layers based on metal nanoparticles, which are shown to increase light trapping in the underlying silicon. In the present work we have combined these two concepts by means of in situ synthesis of Au nanoparticles in a dielectric matrix (TiO2), which is commonly used as an anti-reflective coating in silicon solar cells, and added the third element: a 10-20% porosity in the matrix. The porosity is formed by means of a controllable wet etching by low concentration HF. As a consequence, the experimentally measured reflectance of silicon coated by such a plasmonic layer decreases to practically zero in a broad wavelength region around the localized surface plasmon resonance. Furthermore, we demonstrate that extinction and reflectance spectra of silicon coated by the plasmonic films can be successfully accounted for by means of Fresnel formulae, in which a double refractive index of the metal-dielectric material is used. This double refractive index cannot be explained by effective medium theory (Maxwell-Garnett, for example) and appears when the contribution of Au nanoparticles located at the TiO2/Si interface is high enough to result in formation of interface surface plasmon modes.

Optical characterization and reverse engineering based on multiangle spectroscopy

We perform characterization of thin films and reverse engineering of multilayer coatings on the basis of multiangle spectral photometric data provided by a new advanced spectrophotometer accessory. Experimental samples of single thin films and multilayer coatings are produced by magnetron sputtering and electron-beam evaporation. Reflectance and transmittance data at two polarization states are measured at incidence angles from 7 to 40 deg. We demonstrate that multiangle reflectance and transmittance data provide reliable characterization and reverse-engineering results.

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.

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. The obtained refractive index profiles have been compared with the targeted ones to detect errors in processes of deposition.

Electric field assisted dissolution of metal clusters in metal island films for photonic heterostructures

The dissolution of metal clusters in metal island films by the simultaneous application of electric field and temperature is reported. The consequent fading of surface plasmon resonance greatly modifies the optical properties of the samples. The dissolution process is verified in island films of different metals, obtained under different conditions and covered by different dielectric materials, as well as on multilayer dielectric stacks showing interferential properties. The tailoring possibilities of the optical behavior of metal island films combined with the inexpensive technical requirements of this approach open up the possibility to produce low-cost photonic heterostructures.

Tuning the effective dielectric function of thin film metal-dielectric composites by controlling the deposition temperature

Abstract. The influence of the substrate temperature on the effective optical behavior ofAg-SiO 2 composites obtained by electron beam evaporation was studied. Optical characteriza-tion of the composites was performed by means of spectroscopic ellipsometry measurements.Theeffectivedielectricfunctionofthecomposites,modeledusingamultipleoscillatorapproach,could be widely tuned by controlling the deposition temperature. The spectral dependence ofthe composite absorption appeared to be better described with a Gaussian line shape than withthe classical Lorentz oscillator model. The description of the effective dielectric function usingstandard effective medium theories failed and the experimental results could be explained onlyin the general framework of the Bergman spectral density theory. C 2011 Society of Photo-OpticalInstrumentation Engineers (SPIE) . [DOI: 10.1117/1.3590238] Keywords: metal-dielectric composites; metal island films; surface plasmon resonance; opticalconstants; effective medium theory; spectroscopic ellipsometry.Paper 11015SSR received Jan. 28, 2011; revised manuscript received Apr. 15, 2011; acceptedfor publication Apr. 15, 2011; published online May 13, 2011.

Hollow metal nanostructures for enhanced plasmonics: synthesis, local plasmonic properties and applications

Abstract Metallic nanostructures have received great attention due to their ability to generate surface plasmon resonances, which are collective oscillations of conduction electrons of a material excited by an electromagnetic wave. Plasmonic metal nanostructures are able to localize and manipulate the light at the nanoscale and, therefore, are attractive building blocks for various emerging applications. In particular, hollow nanostructures are promising plasmonic materials as cavities are known to have better plasmonic properties than their solid counterparts thanks to the plasmon hybridization mechanism. The hybridization of the plasmons results in the enhancement of the plasmon fields along with more homogeneous distribution as well as the reduction of localized surface plasmon resonance (LSPR) quenching due to absorption. In this review, we summarize the efforts on the synthesis of hollow metal nanostructures with an emphasis on the galvanic replacement reaction. In the second part of this review, we discuss the advancements on the characterization of plasmonic properties of hollow nanostructures, covering the single nanoparticle experiments, nanoscale characterization via electron energy-loss spectroscopy and modeling and simulation studies. Examples of the applications, i.e. sensing, surface enhanced Raman spectroscopy, photothermal ablation therapy of cancer, drug delivery or catalysis among others, where hollow nanostructures perform better than their solid counterparts, are also evaluated.

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. A true chiroptical response in the far-field is only allowed when the gammadia contain these non-planar features. This is demonstrated by polarimetric measurements in conjunction with electrodynamical simulations based on the discrete dipole approximation that consider non-ideal gammadia. It is also shown that subtle planar dissymmetries in gammadia are sufficient to generate asymmetric transmission of circular polarized light.