Quantitative Optical Characterization of Temperature Effects in Plasmonic Metamaterials: A Synergetic Spectroscopic-Ellipsometry and Finite-Difference-Time-Domain Approach

The science and engineering of the optical response of micro- to nano- scale structures can benefit tremendously from far field optical characterization techniques capable to provide quantitative information on the sample’s actual properties: composition, structure, and morphology with sub-wavelength resolution. Among the myriad of applications, ranging from fundamental to technological, where such quantitative characterization capabilities are desirable, the renewed interest in the characterization and control of sub-wavelength temperature distributions presents unique challenges and vast opportunities. The opportunities arise because the control and measure of temperature distributions at the micro- to nano- scale will have profound impact in biology, chemistry, and physics. A major struggle, however, is the difficulty to provide quantitative, contactless, and marker-free experimental measurements of such temperature distributions. Optical techniques can satisfy the requirements for this task and among them, spectroscopic ellipsometry (SE) is a leading candidate because of its phase sensitivity and self-referenced characteristics. On multilayered samples SE is routinely used to provide quantitative information on each layers characteristics based on detailed analysis of the spectrally- and depth- resolved sample’s optical functions (n, k) using the well-known Fresnel coefficients and matrix transfer formalism. However, structured non-layered samples require numerical fully vectorial data analysis. The rigorous coupled-wave analysis (RCWA) has been highly successful to study the optical critical dimension (OCD) analysis of 1D gratings in the semiconductor industry but so far it faces unresolved difficulties to provide quantitative results for modern nanotechnology applications. For such complex cases, our group recently provided the first systematic validation of an alternative to RCWA: we demonstrated that quantitative SE data analysis can be based on the far-field propagation of the near-field response of the sample calculated using the Finite-Difference Time-Domain (FDTD) method. In this project we will use the SE-FDTD strategy developed by our group to enable realistic, quantitative optical characterization of the complete temperature effects in plasmonic metamaterials including changes in refractive index and thermal expansion effects. This project will thus enable the systematic study of sub-micron temperature distributions that will include important characteristics of relevance for the optimization and engineering of thermal fields in plasmonic metamaterials. To this end we will continue the development of advanced polarimetric strategies that are expected to provide much needed optical characterization capabilities of subwavelength - sized structures capable to quantitatively correlate highly sensitive SE measurements with the morphology and optical properties of complex structured materials with applications in nano-optics and nano-photonics.