Extremely confined gap surface-plasmon modes excited by electrons

Abstract

High-spatial and energy resolution electron energy-loss spectroscopy (EELS) can be used for detailed characterization of localized and propagating surface-plasmon excitations in metal nanostructures, giving insight into fundamental physical phenomena and various plasmonic effects. Here, applying EELS to ultra-sharp convex grooves in gold, we directly probe extremely confined gap surface-plasmon (GSP) modes excited by swift electrons in nanometre-wide gaps. We reveal the resonance behaviour associated with the excitation of the antisymmetric GSP mode for extremely small gap widths, down to B5 nm. We argue that excitation of this mode, featuring very strong absorption, has a crucial role in experimental realizations of non-resonant light absorption by ultra-sharp convex grooves with fabricationinduced asymmetry. The occurrence of the antisymmetric GSP mode along with the fundamental GSP mode exploited in plasmonic waveguides with extreme light confinement is a very important factor that should be taken into account in the design of nanoplasmonic circuits and devices.

The Substrate Effect in Electron Energy-Loss Spectroscopy of Localized Surface Plasmons in Gold and Silver Nanoparticles

“…3 accessible, allowing LSPs to be probed and studied with sub-nanometer spatial resolution 6,8,[22][23][24][25][26] . TEM requires specimens thin enough to be electron transparent (typically below 100 nm) and therefore, plasmonic nanoparticles studied by EELS are typically supported on thin membranes 6,8,27 or buried in a thin embedding material 28 .…”

On the origin of nonlocal damping in plasmonic monomers and dimers

“…22,23,24,25,26,27,28,29,30,31 In particular, we first explore the real-space formulation 21,32 and numerical implementations 33 of the long-existing nonlocal hydrodynamic theory. 34,35,36,37 We then address a recent extension of this theory which accounts for drift-diffusion dynamics, namely the generalized nonlocal optical response (GNOR) theory.…”

Electron energy-loss spectroscopy of branched gap plasmon resonators

“…Although there exists several approaches to calculating the EELS signal by solving the retarded Maxwell's equations in a particular geometry374051525354, we are primarily interested in the physical mechanism of the resonances and therefore adopt a simpler, yet accurate approach to determining the EELS signal. We model the resonator as a one-dimensional slit of length L surrounded by silver and with effective index n eff ( w ), which depends on the slit width w .…”

“…STEM EELS is a powerful characterization tool due to the combination of Angstrom spatial resolution with millielectronvolt spectral resolution over a broad energy range3031. In recent years, STEM EELS has proved to be an indispensable tool for optical characterization28 and has been utilized in many diverse plasmonic studies32333435363738394041424344.…”