Enhanced terahertz conductivity in ultra-thin gold film deposited onto (3-mercaptopropyl) trimethoxysilane (MPTMS)-coated Si substrates

Various material properties change considerably when material is thinned down to nanometer thicknesses. Accordingly, researchers have been trying to obtain homogeneous thin films with nanometer thickness but depositing homogeneous few nanometers thick gold film is challenging as it tends to form islands rather than homogenous film. Recently, studies have revealed that treating the substrate with an organic buffer, (3-mercaptopropyl) trimethoxysilane (MPTMS) enables deposition of ultra-thin gold film having thickness as low as 5 nm. Different aspects of MPTMS treatment for ultrathin gold films like its effect on the structure and optical properties at visible wavelengths have been investigated. However, the effect of the MPTMS treatment on electrical conductivity of ultra-thin gold film at terahertz frequency remains unexplored. Here, we measure the complex conductivity of nanometer-thick gold films deposited onto an MPTMS-coated silicon substrate using terahertz time-domain spectroscopy. Following the MPTMS treatment of the substrate, the conductivity of the films was found to increase compared to those deposited onto uncoated substrate for gold films having the thickness less than 11 nm. We observed 5-fold enhancement in the conductivity for a 7 nm-thick gold film. We also demonstrate the fabrication of nanoslot-antenna arrays in 8.2-nm-thick gold films. The nanoslot-antenna with MPTMS coating has resonance at around 0.5 THz with an electric field enhancement of 44, whereas the nanoslot-antenna without MPTMS coating does not show resonant properties. Our results demonstrate that gold films deposited onto MPTMS-coated silicon substrates are promising advanced materials for fabricating ultra-thin terahertz plasmonic devices

Interplay between Strong Coupling and Radiative Damping of Excitons and Surface Plasmon Polaritons in Hybrid Nanostructures

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Topology-Changing Broadband Metamaterials Enabled by Closable Nanotrenches

One of the most straightforward methods to actively control optical functionalities of metamaterials is to apply mechanical strain deforming the geometries. These deformations, however, leave symmetries and topologies largely intact, limiting the multifunctional horizon. Here, we present topology manipulation of metamaterials fabricated on flexible substrates by mechanically closing/opening embedded nanotrenches of various geometries. When an inner bending is applied on the substrate, the nanotrench closes and the accompanying topological change results in abrupt switching of metamaterial functionalities such as resonance, chirality, and polarization selectivity. Closable nanotrenches can be embedded in metamaterials of broadband spectrum, ranging from visible to microwave. The 99.9% extinction performance is robust, enduring more than a thousand bending cycles. Our work provides a wafer-scale platform for active quantum plasmonics and photonic application of subnanometer phenomena

Real-time observation of ultrafast Rabi oscillations between excitons and plasmons in metal nanostructures with J-aggregates

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Erratum to Antiresonant ring interferometry as a sensitive technique for measuring nonlinear optical properties of thin films

There is a critical need for a simple technique for the accurate measurement of weak optical nonlinearities such as the nonlinear coefficients of thin films. We discuss the experimental set-up and provide a realistic analysis for a sensitive and single beam technique based on an antiresonant ring interferometer for measuring nonlinear optical coefficients in thin films. The technique was benchmarked using toluene and its superiority was demonstrated by measuring the effective nonlinear absorption coefficient of a 1.3 μm thick CdS film, which could not be detected using standard techniques such as z-scan. We show that this technique can, in principle, be used for films with thickness down to the nanometer.© Elsevie

Antiresonant ring interferometry as a sensitive technique for measuring nonlinear optical properties of thin films

There is a critical need for a simple technique for the accurate measurement of weak optical nonlinearities such as the nonlinear coefficients of thin films. We discuss the experimental set-up and provide a realistic analysis for a sensitive and single beam technique based on an antiresonant ring interferometer for measuring nonlinear optical coefficients in thin films. The technique was benchmarked using toluene and its superiority was demonstrated by measuring the effective nonlinear absorption coefficient of a 1.3 μm thick CdS film, which could not be detected using standard techniques such as z-scan. We show that this technique can, in principle, be used for films with thickness down to the nanometer regime.© Elsevie

Relaxation and Excitation Rate Modifications by Metal Nanostructures for Solar Energy Conversion Applications

Metal nanostructures supporting plasmonic resonances offer pronounced modifications of an electromagnetic environment for efficient light harvesting in solar energy conversion applications. Since these modifications may give rise to competing effects, boosting overall conversion efficiency needs optimization of structural and spectral parameters of emitter-metal nanostructure hybrid systems. Here, we employ finite-difference time-domain simulations to investigate modifications in relaxation and excitation rates of a dipole emitter in proximity to three representative gold nanostructures, namely nanospheres, nanorods, and slot antennas. We present detailed investigations of parameter space in terms of nanostructure type, emitter position, and spectral range to identify regions of optimum performance for solar energy conversion applications. Our results suggest that for selected parameter sets, hybrid systems yield substantial enhancement in the excitation rate as well as suppression of luminescence, which are primary considerations in photovoltaic and photocatalysis applications, whereas regions of enhanced luminescence are more favorable for luminescent solar concentrators. Nanostructures with a higher aspect ratio are found to be more efficient. Particularly, the gap modes of slot antennas exhibit pronounced suppression of luminescence yield and light confinement over a broad spectral range from 550 nm up to 2200 nm, besides offering a larger usable volume compared to singular nanoparticles investigated here