An emitter in the vicinity of a metal nanostructure is quenched by its decay through non-radiative channels, leading to the belief in a zone of inactivity for emitters placed within <10nm of a plasmonic nanostructure. Here we demonstrate that in tightly-coupled plasmonic resonators forming nanocavities "quenching is quenched" due to plasmon mixing. Unlike isolated nanoparticles, plasmonic nanocavities show mode hybridization which massively enhances emitter excitation and decay via radiative channels. This creates ideal conditions for realizing single-molecule strong-coupling with plasmons, evident in dynamic Rabi-oscillations and experimentally confirmed by laterally dependent emitter placement through DNA-origami.The lifetime of an excited atomic state is determined by the inherent properties of the atom and its environment, first theoretically suggested by Purcell [1] followed by experimental demonstration [2]. Subsequent experiments further verified this by placing atomic emitters within various optical-field-enhancing geometries [3][4][5]. Plasmonic structures have the ability to massively enhance electromagnetic fields, and therefore dramatically alter the excitation rate of an emitter [6]. However, it is well known that placing an emitter close to a plasmonic structure (< 10nm), quenches its fluorescence [7][8][9]. Analysis by Anger et al. [6] showed this is due to the coupling of the emitter to non-radiative higher-order plasmonic modes that dissipate its energy. This 'zone of inactivity' was previously believed to quench all quantum emitters. However, recent advancements have shown that an emitter's emission rate can be enhanced with plasmonic nano-antennas [10][11][12][13][14][15][16][17].Generally a single emitter placed into near-contact with an optical antenna gives larger fluorescence since the antenna efficiently converts far-field radiation into a localized field and vice versa [10,12,13,18]. This was recently demonstrated by Hoang et al. [17] who showed that a quantum dot in a 12nm nano-gap exhibits ultrafast spontaneous emission. What however remains unclear is if this enhanced emission is strong enough to allow for single emitter strong coupling.In this Letter, we demonstrate and explain why quenching is substantially suppressed in plasmonic nanocavities, to such a degree that facilitates lightmatter strong-coupling of single-molecules, even at roomtemperature, as we recently demonstrated experimentally [19]. This is due to: (i) the dramatic increase in the emitter excitation (similar to plasmonic antennas), and (ii) the changed nature of higher-order modes that acquire a radiative component, and therefore increase the quantum yield of the emitter. Modes in plasmonic nanocavities are not a simple superposition of modes from the isolated structures, but instead are hybridplasmonic states [20][21][22][23][24]. Hence, higher-order modes that are dark for an isolated spherical nanoparticle, radiate efficiently for tightly-coupled plasmonic structures [25], significantly reducing the non-radiative...

By systematically studying the proton selectivity of free-standing graphene membranes in aqueous solutions we demonstrate that protons are transported by passing through defects. We study the current-voltage characteristics of single-layer graphene grown by chemical vapour deposition (CVD) when a concentration gradient of HCl exists across it. Our measurements can unambiguously determine that H + ions are responsible for the selective part of the ionic current. By comparing the observed reversal potentials with positive and negative controls we demonstrate that the as-grown graphene is only weakly selective for protons. We use atomic layer deposition to block most of the defects in our CVD graphene. Our results show that a reduction in defect size decreases the ionic current but increases proton selectivity.

Nanomachines capable of controlled programmable work at the nanoscale promise to revolutionize a vast range of research and eventually should impact on daily lives. Due to the ease of design and modification, DNA origami is emerging as a natural platform to build such machines. However, one essential challenge is the controlled and rapid actuation of DNA origami using an external biocompatible stimulus. Here, actuation based on temperature‐induced phase transitions of the thermo‐responsive polymer poly(N‐isopropylacrylamide) (PNIPAM) is reported. By incorporating this polymer into DNA origami structures on either side of a flexible region, a “DNA origami flexor” is created that uses the tunable PNIPAM hydrophobicity to reversibly open and close the DNA structures. Such a mechanism has the advantage of being versatile and biocompatible, and possessing strong response to temperature changes of a few degrees Kelvin.

We fabricate hetero-component 'dimers' built from a single 40 nm gold and a single 40 nm silver nanoparticle separated by sub-5 nm gaps. Successful assembly mediated by a specialized DNA origami platform is verified by scanning electron microscopy and energy-dispersive X-ray characterization. Dark-field optical scattering on individual dimers is consistent with computational simulations. Direct plasmonic coupling between each nanoparticle is observed in both experiment and theory only for these small gap sizes, as it requires the silver dipolar mode energy to drop below the energy of the gold interband transitions. A new interparticle-spacing-dependent coupling model for heterodimers is thus required. Such Janus-like nanoparticle constructs available from DNA-mediated assembly provide an effective tool for controlling symmetry breaking in collective plasmon modes.

Nonlinear field dependence of electrophoresis in high fields has been investigated theoretically, yet experimental studies have failed to reach consensus on the effect. In this work, we present a systematic study on the nonlinear electrophoresis of highly charged submicron particles in applied electric fields of up to several kV/cm. First, the particles are characterized in the low-field regime at different salt concentrations and the surface charge density is estimated. Subsequently, we use microfluidic channels and video tracking to systematically characterize the nonlinear response over a range of field strengths. Using velocity measurements on the single particle level, we prove that nonlinear effects are present at electric fields and surface charge densities that are accessible in practical conditions. Finally, we show that nonlinear behavior leads to unexpected particle trapping in channels. :1907.04278v1 [cond-mat.soft] arXiv