Fernando Gonzalez-Posada Flores
University of Montpellier / CNRS
Dr. Fernando González-Posada received his bachelor in Physics (2003) in the Autonomic University of Madrid and his PhD (2009) in the Polytechnic University of Madrid, working in the design, fabrication and characterisation of high electron mobility transistors based on III-nitrides. In 2011, he joined the Nanophysics and Semiconductors group at CEA-Grenoble. He worked in the design, fabrication and characterization of single GaN nanowires UV photodetectors. He researched one year in Chalmers Technological University focused in solar fuel development based in metallic nanoparticles photocatalysis. Since 2013, he is associate professor of the University of Montpellier and researches in semiconductor plasmonic sensors.
Introduction
Resonant surface enhanced infrared absorption (SEIRA) spectroscopy relies on advanced nanofabrication to tailor plasmonic antenna resonances at targeted wavelengths.[1] Strongest signal enhancement is obtained with plasmonic resonances tuned to molecular absorption features. This helps lower the IR spectroscopy detection limit and enables the minute detection of analyte quantities.
The tunability of the plasmonic antenna resonances is achieved by their geometry, size or interaction. Doped semiconductors go beyond, as the doping level is an additional parameter to tune the plasma frequency, contrariwise to noble metals where it is a material constant. In the IR, doped semiconductors are advantageous due to their lower carrier density, which engenders low Ohmic losses and resonances close to their plasma frequency.[2]
In this work, we investigate SEIRA performance of highly doped InAs0.91Sb0.09 plasmonic nanoantenna arrays with different models and molecular layers.
Methods
Plasmonic resonators were fabricated by large-area surface patterning (interferential or UV lithography) and selective chemical etching from epitaxial highly doped InAs0.91Sb0.09 films grown on GaSb substrates. Analyte layers were deposited by spin- or drop casting. SEIRA signals were evaluated using a normalization to the plasmonic background, to extract the vibrational signals from FTIR spectroscopy in reflectance mode. Additionally, finite-difference time-domain (FDTD) simulations were used to calculate far-field spectra and near-field profiles.
Results and discussion
Firstly, a higher doping level was correlated to a higher SEIRA signal using PDMS layers in line nanoantenna arrays. The highest doping induces in FDTD simulations an electric field less pinned inside the nanoantennas. Secondly, broadband resonant SEIRA of vanillin molecules is demonstrated using rectangular nanoantenna arrays with low aspect ratio. The Fano line vibrational shape features spectrally covered by the large LSPR evidences the coupling. Due to their anisotropy, the nanoantennas display polarization switchable mid-IR plasmonic resonances in two spectral bands. SEIRA signals were measured on characteristic benzene ring fingerprint vibrations, interesting for pharmaceutical applications or environmental monitoring. Finally, recent results using SiO2 layers deposited by e-beam are under study for industrial coating controls. In sum, we will present SEIRA for different materials using semiconductor nanoantennna arrays.
References
[1] F.Neubrech et al. Chem.Rev.2017,117,5110-5145.
[2] A.Boltassevva et al. Science,2011,331,290-291.
Optical properties of nanostructures , Strong light-matter interactions at the nanoscale , Enhanced spectroscopy and sensing
