Design Principles for Optoelectronic Applications of Extraordinary Light Transmission Effect in Plasmonics Nanoapertures

The extraordinary light transmission effect (EOT) through sub-wavelength nanoapertures in opaque metal films has lead to observation of a wide variety of exciting new optical phenomena. This remarkable effect is generally related to the interaction of the light with the extended plasmonic resonances on the surface of the metal film and localized surface plasmons in the apertures. On the other hand, there is little conceptual understanding for controlling the localized surface plasmonic behavior of the individual apertures and their coupling to the extended surface plasmons. In this letter, we present an intuitive and straightforward picture of the extra-ordinary light transmission phenomena based on basic antenna principles for plasmonic excitations and coupling of these plasmonic excitations in complex nano-apertures. Our quasi-static model remarkably well explains our experimental measurements in shape anisotropic structures with unique properties controlled by adjusting the size and the geometry of the apertures. Our approach puts forward new design principles for potential applications ranging from subwavelength optoelectronics and data storage to bio/chemical sensing.

Core-Shell GaAs Nanowire p-n Junctions from Growth to Photovoltaic and Optoelectronic Applications

Carlo Colombo

Semiconductor nanowires (NWs) are filamentary crystals with the diameter ranging from few tens up to few hundreds of nanometers. In the last 15 years, they have been intensively studied for the prospectives that their unique quasi-one dimensional shape offers to both fundamental and applied physics. More recently particular attention has been dedicated to the advantages that their geometry exhibits in the separation and extraction of photo-generated carriers with respect to standard thin film or bulk technologies. The aim of this thesis is the realization and characterization of single GaAs NW photovoltaic and optoelectronic devices. The work starts with the synthesis of radial NWp-n junctions. The core growth has been realized using the Vapor-Liquid-Solid (V LS) mechanism by Molecular Beam Epitaxy (MBE). Differently from the commonly used V LS method, which requires Au particles as a catalyst, we use a self-catalyzed process which avoids potential contaminations. The shell is then overgrown around, switching the growth parameters toward standard thin film conditions. The doping mechanism of such a structure has been deeply investigated, with the purpose of discriminating in which way the dopants get incorporated in the crystal structure. A reproducible technique has been developed to electrically contact the NWs and test their photovoltaic properties. They have been measured under different illumination conditions. Conversion efficiency of about 4.5% have been measured under diffuse illumination at 1.5AM and more information about the uniformity of the junction have been deduced by scanning photo-current measurements. Due to the size comparable with the wavelength of the visible light, NWs exhibit characteristic absorption peaks as a function of the photon energy, often referred as Mie resonances. In order to engineer these resonances we have deposited metal nanoparticles on their facets and studied how the plasmonic excitation of the latter could couple with the NW leaky modes. The results have been analyzed with Finite Difference Frequency Domain (FDFD) simulations. Since GaAs is a direct band-gap material, the same devices have also been tested in a reverse way as light emitting diodes and plasmon generators. Finally some preliminary studies about the effect of axial wurtzite/zincblende polytypism on the electronic properties have been performed.

EPFL2012

Membrane activity detection in cultured cells using phase-sensitive plasmonics

Liliane Glauser, Johannes Gräff, Yasaman Jahani, Xiaokang Li, Ershad Mohammadi, Jose Vicente Sanchez Mut, Foziyeh Sohrabi

Despite the existence of various neural recording and mapping techniques, there is an open territory for the emergence of novel techniques. The current neural imaging and recording techniques suffer from invasiveness, a time-consuming labeling process, poor spatial/ temporal resolution, and noisy signals. Among others, neuroplasmonics is a label-free and nontoxic recording technique with no issue of photo-bleaching or signal-averaging. We introduced an integrated plasmonic-ellipsometry platform for membrane activity detection with cost-effective and high-quality grating extracted from commercial DVDs. With ellipsometry technique, one can measure both amplitude (intensity) and phase difference of reflected light simultaneously with high signal to noise ratio close to surface plasmon resonances, which leads to the enhancement of sensitivity in plasmonic techniques. We cultured three different types of cells (primary hippocampal neurons, neuroblastoma SH-SY5Y cells, and human embryonic kidney 293 (HEK293) cells) on the grating surface. By introducing KCl solution as a chemical stimulus, we can differentiate the neural activity of distinct cell types and observe the signaling event in a label-free, optical recording platform. This method has potential applications in recording neural signal activity without labeling and stimulation artifacts. (C) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

OPTICAL SOC AMER2020

Core-Shell GaAs Nanowire p-n Junctions from Growth to Photovoltaic and Optoelectronic Applications

Carlo Colombo

EPFL2012