title: Squeezing terahertz light into nanovolumes: nanoantenna enhanced terahertz spectroscopy (NETS) of semiconductor quantum dots.
abstract: Terahertz spectroscopy has vast potentialities in sensing a broad range of elementary excitations (e.g., collective vibrations of molecules, phonons, excitons, etc.). However, the large wavelength associated with terahertz radiation (about 300 μm at 1 THz) severely hinders its interaction with nano-objects, such as nanoparticles, nanorods, nanotubes, and large molecules of biological relevance, practically limiting terahertz studies to macroscopic ensembles of these compounds, in the form of thick pellets of crystallized molecules or highly concentrated solutions of nanomaterials. Here we show that chains of terahertz dipole nanoantennas spaced by nanogaps of 20 nm allow retrieving the spectroscopic signature of a monolayer of cadmium selenide quantum dots, a significant portion of the signal arising from the dots located within the antenna nanocavities. A Fano-like interference between the fundamental antenna mode and the phonon resonance of the quantum dots is observed, accompanied by an absorption enhancement factor greater than one million. NETS can find immediate applications in terahertz spectroscopic studies of nanocrystals and molecules at extremely low concentrations. Furthermore, it shows a practicable route toward the characterization of individual nano-objects at these frequencies.
authors.affiliation: Istituto Italiano di Tecnologia , via Morego 30, 16163 Genova, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Toma
authors.forename: Salvatore
authors.initials: S
authors.lastname: Tuccio
authors.forename: Mirko
authors.initials: M
authors.lastname: Prato
authors.forename: Francesco
authors.initials: F
authors.lastname: De Donato
authors.forename: Andrea
authors.initials: A
authors.lastname: Perucchi
authors.forename: Paola
authors.initials: P
authors.lastname: Di Pietro
authors.forename: Sergio
authors.initials: S
authors.lastname: Marras
authors.forename: Carlo
authors.initials: C
authors.lastname: Liberale
authors.forename: Remo
authors.initials: R
authors.lastname: Proietti Zaccaria
authors.forename: Francesco
authors.initials: F
authors.lastname: De Angelis
authors.forename: Liberato
authors.initials: L
authors.lastname: Manna
authors.forename: Stefano
authors.initials: S
authors.lastname: Lupi
authors.forename: Enzo
authors.initials: E
authors.lastname: Di Fabrizio
authors.forename: Luca
authors.initials: L
authors.lastname: Razzari
keywords: Fano-like interference; Terahertz spectroscopy; nanoantenna; phonon resonance; quantum dot; surface enhancement