Bálint Fodor

Optical Models for the Characterization of Silica Nanosphere Monolayers Prepared by the Langmuir−Blodgett Method Using Ellipsometry in the Quasistatic Regime

We investigated different optical models (one-layer, multilayer, parametric multilayer, and statistical parametric) for the ellipsometric characterization of thin films made of silica spheres in the diameter (D) range of 90-450 nm prepared by the Langmuir-Blodgett (LB) technique. As a continuation of a previous work (Nagy, N., et al. Langmuir 2006, 22, 8416) in terms of threshold wavelength determination and optical models, we investigated the wavelength range of the quasistatic limit (requirement for the effective medium approximation) depending onD.We compared the above models in the aspect of fit quality, stability, uncertainty of parameters, and the amount of information that can be obtained from the evaluation. Besides fundamental properties like diameter, coverage, or packing density, using sophisticated models we can also determine the size distribution of the particles. The ellipsometric results were compared with the results of dynamic light scattering and of scanning electron microscopy.

Effective medium approximation of ellipsometric response from random surface roughness simulated by finite-element method

Abstract We used numerical simulations based on the finite-element method (FEM) to calculate both the amplitude and phase information of the scattered electric field from random rough surfaces, which can be directly compared to ellipsometric measurements and effective medium approximation (EMA) calculations. FEM can serve as an exploration tool for the relationship between the thickness of the surface roughness evaluated by Bruggeman EMA and the morphological parameters of the surface, such as the root mean square height, the lateral auto-correlation length, and the typical average slope. These investigations are of high interest in case of poly-crystalline and amorphous materials. The paper focuses on the simulations of rough Si surfaces. The ellipsometric calculations from FEM and EMA simulations match for wavelengths of illumination much shorter than the typical feature size of the surface. Furthermore, for these cases, the correlation between the EMA thickness and the root mean square height of the roughness for a given auto-correlation length is quadratic, rather than linear, which is in good agreement with experimental measurements and analytical calculations presented in recent reports.

Optical characterization of macro-, micro- and nanostructures using polarized light

Reflection of light measured in a polarimetric, scatterometric and spectroscopic way allows the measurement of structures in a broad size range from large (meter) scales like photovoltaic panels down to small (nanometer) scales like nanocrystals. Optical metrology continues to be improved to measure those materials with increasing sensitivity and accuracy, typically in a form of thin films on high quality substrates. This review provides an overview of some recently developed or improved methods, e.g. divergent light source ellipsometry for the mapping of large surfaces for photovoltaic applications, Fourier scatterometry for the measurement of periodic structures with sizes comparable to the wavelength of illumination, as well as spectroscopy around the band gap photon energies to characterize nanostructures - without attempting completeness.

Optimized plasma-polymerized fluoropolymer mask for local porous silicon formation

Mass production of hybrid silicon/porous silicon substrates requires a simple, low-cost, and reliable patterning process to locally form porous regions on silicon wafers. An innovative masking technology based on plasma-polymerized fluoropolymer (PPFP) has been proposed as a promising candidate. However, the use of PPFP film on silicon substrate requires an adhesion promoter which may cause several side effects, including film peeling-off and pinhole formation. This work aims to improve the adhesion strength without using the adhesion promoter. The present study shows that, by adopting a hydrogen-terminated surface and an optimized gas precursor composition of 25/25 sccm CHF3/C2H4, good adhesion of PPFP to silicon is obtained before and during porous silicon formation. PPFP mask deposited at high pressure shows well-defined borders after anodization. Finally, an optimized PPFP-based patterning process is proposed.

Multiple angle of incidence, spectroscopic, plasmon-enhanced, internal reflection ellipsometry for the characterization of solid-liquid interface processes

A semi-cylindrical lens in Kretschmann geometry combined with a flow cell was designed for a commercial rotating compensator ellipsometer to perform internal reflection spectroscopic ellipsometry measurements, while allowing the use of multiple angles of incidence. A thin glass slide covered with a gold film was mounted between the half-cylindrical lens and a small-volume flow cell ensuring an improved sensitivity for protein adsorption experiments. The performance of the system was investigated depending on the angle of incidence, wavelength range and thickness of the gold films for surface plasmon resonance enhanced ellipsometric measurements, and a sensitivity increase was revealed compared to ellipsometric measurements with standard flow cells, depending on the measurement parameters and configuration. The sensitivity increase was demonstrated for fibrinogen adsorption.

Composite polymeric-inorganic waveguide fabricated by injection molding for biosensing applications

Inorganic based optical transducers have demonstrated their suitability for labelled and label-free sensing of biomolecules but suffer from their relatively high cost. Photonic structures fabricated in polymer by molding techniques could drastically reduce the cost per test and pave the way for label-free screening in point-of care environment where the cost per test is an essential concern. In this paper we present the advances in the fabrication of waveguides with cyclo olefin copolymer (COC) cladding and TiO2 core with mass-production compatible injection molding and evaporation. We demonstrate the optical propagation in a slab waveguide supporting both transverse electric and magnetic modes and monitor the response of the phase difference between the two modes when a droplet of water is deposited on the chip.