Terahertz phononic crystal in plasmonic nanocavity

Interaction between photons and phonons in cavity optomechanical systems provides a new toolbox for quantum information technologies.A GaAs/AlAs pillar multi-optical mode microcavity optomechanical structure can obtain phonons with ultra-high frequency(~THz).However,the optical field cannot be effectively restricted when the diameter of the GaAs/AlAs pillar microcavity decreases below the diffraction limit of light.Here,we design a system that combines Ag nanocav-ity with GaAs/AlAs phononic superlattices,where phonons with the frequency of 4.2 THz can be confined in a pillar with~4 nm diameter.The Q_(c)/V reaches 0.22 nm^(-3),which is~80 times that of the photonic crystal(PhC)nanobeam and~100 times that of the hybrid point-defect PhC bowtie plasmonic nanocavity,where Q_(c) is optical quality factor and V is mode volume.The optome-chanical single-photon coupling strength can reach 12 MHz,which is an order of magnitude larger than that of the PhC nanobeam.In addition,the mechanical zero-point fluctuation amplitude is 85 fm and the efficient mass is 0.27 zg,which is much smaller than the PhC nanobeam.The phononic superlattice-Ag nanocavity optomechanical devices hold great potential for applications in the field of integrated quantum optomechanics,quantum information,and terahertz-light transducer.

A high-quality factor hybrid plasmonic nanocavity based on distributed Bragg reflectors

Herein,we propose a high-quality（Q） factor hybrid plasmonic nanocavity based on distributed Bragg reflectors（DBRs） with low propagation loss and extremely strong mode confinement.This hybrid plasmonic nanocavity is composed of a high-index cylindrical nanowire separated from a metal surface possessing shallow DBRs gratings by a sufficiently thin low-index dielectric layer.The hybrid plasmonic nanocavity possesses advantages such as a high Purcell factor（Fp） of up to nearly 20000 and a gain threshold approaching 266 cm^（-1）at 1550 nm,promising a greater potential in deep sub-wavelength lasing applications.

Near-field and photocatalytic properties of mono-and bimetallic nanostructures monitored by nanocavity surface-enhanced Raman scattering

Localized surface plasmon resonances(LSPR)generated in a particle-film nanocavity enhance electric fields within a nanoscale volume.LSPR can also decay into hot carriers,highly energetic species that catalyze photocatalytic reactions in molecular analytes located in close proximity to metal surfaces.In this study,we examined the intensity of the electric field(near-field)and photocatalytic properties of plasmonic nanocavities formed by single nanoparticles(SNP)on single nanoplates(SNL).Using 4-nitrobenzenethiol(4-NBT)as a molecular reporter,we determined the near-field responses,as well as measured rates of 4-NBT dimerization into 4,4-dimercaptoazobenzene(DMAB)in the gold(Au)SNP on AuSNL nanocavity(Au-Au),as well as in AuSNP on AgSNL(Au-Ag),AgSNP on AuSNL(Ag-Au),and AgSNP on AgSNL(Ag-Ag)nanocavities using 532,660,and 785 nm excitations.We observed the strongest near-field signals of 4-NBT at 660 nm in all examined plasmonic systems that is found to be substantially red-shifted relative to the LSPR of the corresponding nanoparticles.We also found that rates of DMAB formation were significantly greater in heterometal nanocavities(Au-Ag and Ag-Au)compared to their monometallic counterparts(Au-Au and Ag-Ag).These results point to drastic differences in plasmonic and photocatalytic properties of mono and bimetallic nanostructures.

Electron transition manipulation under graphene-mediated plasmonic engineering nanostructure

Monolayer graphene has attracted enormous attention owing to its unique electronic and optical properties.However,achieving an effective approach without applying electrical bias for manipulating the charge transfer based on graphene is elusive to date.Herein,we realized the manipulation of excitons’transition from emitter to the graphene surface with plasmonic engineering nanostructures and firstly obtained large enhancements for photon emission on the graphene surface.The localized plasmons generated from the plasmonic nanostructures of shell-isolated nanoparticle coupling to ultra-flat Au substrate would dictate a consistent junction geometry while enhancing the optical field and dominating the electron transition pathways,which may cause obvious perturbations for molecular radiation behaviors.Additionally,the three-dimensional finite-difference time-domain and time-dependent density functional theory were also carried out to simulate the distributions of electromagnetic field and energy levels of hybrid nanostructure respectively and the results agreed well with the experimental data.Therefore,this work paves a novel approach for tunning graphene charge/energy transfer processes,which may hold great potential for applications in photonic devices based on graphene.

Deterministic assembly of single optical cavity formed by gold dimensional DNA origami

Controllable strong interactions between a nanocavity and a single emitter is important to manipulating optical emission in a nanophotonic system but challenging to achieve.Herein a three-dimensional DNA origami,named as DNA rack(DR)is proposed and demonstrated to deterministically and precisely assemble single emitters within ultra-small plasmonic nanocavities formed by closely coupled gold nanorods(AuNRs).Uniquely,the DR is in a saddle shape,with two tubular grooves that geometrically allow a snug fit and linearly align two AuNRs with a bending angle <10°.It also includes a spacer at the saddle point to maintain the gap between AuNRs as small as 2-3 nm,forming a nanocavity estimated to be 20 nm^(3) and an experimentally measured O factor of 7.3.A DNA docking strand is designed at the spacer to position a single fluorescent emitter at nanometer accuracy within the cavity.Using Cy5 as a model emitter,a -30-fold fluorescence enhancement and a significantly reduced emission lifetime(from 1.6 ns to 670 ps)were experimentally verified,confirming significant emitter-cavity interactions.This DR-templated assembly method is capable of fitting AuNRs of variable length-to-width aspect ratios to form anisotropic nanocavities and deterministically incorporate different single emitters,thus enabling flexible design of both cavity resonance and emission wavelengths to tailor light-matter interactions at nanometer scale.