Nanogap optical antennas enable enhancement of light-matter interactions owing to their great field enhancement. Interesting properties have been studied over recent years, such as high-order harmonics generation, electrically driven absorption, optical rectification and nonlinear tunnelling effect. However, as the gap size is shrunk down to the nanometer scale, losses dramatically increase and coupling efficiency of antenna with free-space decreases. This work reports conditions of perfect coupling, also called critical coupling, between a periodic array of nanogap metal-insulator-metal (MIM) antennas and free-space. We demonstrate that critical coupling is still achievable, even for the thinnest gaps.
We investigate the optical properties of nanogap MIM nanoantennas with a 2.1 nm thick gap. These plasmonic nanoantennas consist of a gold film, an insulating layer deposited by Atomic Layer Deposition, and a periodically structured gold layer. MIM nanoantennas are characterized by a tunable spectral response and a high field confinement within the nanogap. Nanometric gaps enable high coupling between the plasmons of the top and bottom metal surfaces. We demonstrated an excellent agreement between optical measurements and classical electromagnetic simulations. In particular, we observed a fluctuation in the gap thickness of 0.2 nm.
Invited speaker: Sources for optical and infrared radiation are traditionally based on transitions between discrete electronic states and are therefore limited by the intrinsic emission properties of the semi-conductor or organic gain medium. Electron tunneling across narrow gaps may induce broadband photon emission due to inelastic transport through a tunneling junction; however, this process suffers from a very low efficiency, typically one photon per 10^5 electrons. Electrically-driven optical antennas could boost this quantum efficiency owing to concentrating photons and electrons within an ultrasmall volume. In my talk, I propose a new class of nanoscopic light sources that are not limited by quantum states, but rather depend on the antenna architecture and the applied bias. These compact light sources, based on electrically-driven nanogap optical antennas, feature a tunable emission wavelength, a high quantum efficiency, and operate at room temperature. As the fluctuations in the tunneling current constitute a broadband source, the electroluminescence can be tuned from the blue to the infrared spectral regions, by changing the antenna dimensions and the applied bias voltage. This implies that differently tuned devices can be integrated on-chip in close proximity on top of a wide variety of substrates or within microfluidic channels. Such multi-spectral sources have the potential to impact today’s Si-based electronic chips by employing fast light pulses as the communication path for higher data flux.
This letter provides a brief summary on early work and developments on both controlling and studying the optical
properties of resonant metal nanoparticles and reports on all progress achieved since two years. Our approach is based on
controlled nanoscale photopolymerization triggered by local enhanced electromagnetic fields of silver nanoparticles
excited close to their dipolar plasmon resonance. By anisotropic polymerization, symmetry of the refractive index of the
surrounding medium was broken: C1v symmetry turned to C2v symmetry. This approach has overcome all the
difficulties faced by scanning probe methodologies to reproduce the form of the near field of the localized surface
plasmons and provides a new way to quantify its magnitude. Furthermore, this approach leads to the production of
polymer/metal hybrid nano-systems of new optical properties.