Degenerately doped semiconductor nanocrystals (NCs) exhibit a localized surface plasmon resonance (LSPR) in the infrared range of the electromagnetic spectrum. Unlike metals, semiconductor NCs offer tunable LSPR characteristics enabled by doping, or via electrochemical or photochemical charging. Tuning plasmonic properties through carrier density modulation suggests potential applications in smart optoelectronics, catalysis, and sensing. Here, we elucidate fundamental aspects of LSPR modulation through dynamic carrier density tuning in Sn-doped Indium Oxide NCs. Monodisperse Sn-doped Indium Oxide NCs with various doping level and sizes were synthesized and assembled in uniform films. NC films were then charged in an in situ electrochemical cell and the LSPR modulation spectra were monitored. Based on spectral shifts and intensity modulation of the LSPR, combined with optical modeling, it was found that often-neglected semiconductor properties, specifically band structure modification due to doping and surface states, strongly affect LSPR modulation. Fermi level pinning by surface defect states creates a surface depletion layer that alters the LSPR properties; it determines the extent of LSPR frequency modulation, diminishes the expected near field enhancement, and strongly reduces sensitivity of the LSPR to the surroundings.
Using nanometer spatial resolution electron-energy loss spectroscopy (EELS), energy dispersive X-ray spectroscopy (EDS), and cathodoluminescence (CL) mapping, we demonstrate that Au alloys containing a poor plasmonic metal (Pd) can nevertheless sustain multiple size-dependent localized surface plasmon resonances and observe strong field enhancement at Pd-rich tips, where the composition is in fact least favorable for plasmons. These Au/Pd stellated nanocrystals are also involved in substrate and interparticle coupling, as unraveled by EELS tilt series.
Nanostars (NSTs) are spiky nanocrystals with plasmonic hot spots. In this study, we show that strong electromagnetic fields localized in the nanostar tips are able to generate large numbers of energetic (hot) electrons, which can be used for photochemistry. To compute plasmonic nanocrystals with complex shapes, we develop a quantum approach based on the effect of surface generation of hot electrons. We then apply this approach to nanostars, nanorods and nanospheres. We found that that the plasmonic nanostars with multiple hot spots have the best characteristics for optical generation of hot el…
We show that the positioning of a nanometer length scale dielectric object, such as a diamond nanocrystal, in the vicinity of a gold bowtie nanoantenna can be used to tune the plasmonic mode spectrum on the order of a linewidth. We further show that the intrinsic luminescence of gold enhanced in the presence of nanometer-scale roughness couples efficiently to the plasmon mode and carries the same polarization anisotropy. Our findings have direct implications for cavity quantum electrodynamics related applications of hybrid antenna-emitter complexes.
We present two applications of a single nitrogen vacancy center in a nanodiamond as quantum probe for plasmonic nanostructures. Coupling to the nanostructures is achieved in a highly controlled manner by picking up a pre-characterized nanocrystal with an atomic force microscope and placing it at the desired position. Local launching of single excitations into a nanowire with a spatial control of few nanometers is demonstrated. Further, a two dimensional map of the electromagnetic environment of a plasmonic bowtie antenna was derived, resembling an ultimate limit of fluorescence lifetime nanosc…
The optical extinction spectra arising from localized surface plasmon resonance in doped semiconductor nanocrystals (NCs) have intensities and lineshapes determined by free charge carrier concentrations and the various mechanisms for damping the oscillation of those free carriers. However, these intrinsic properties are convoluted by heterogeneous broadening when measuring spectra of ensembles. We reveal that the traditional Drude approximation is not equipped to fit spectra from a heterogeneous ensemble of doped semiconductor NCs and produces fit results that violate Mie scattering theory. Th…
Magnetoplasmonics is highly promising to devise active optical elements: modulating the plasmon resonance condition with magnetic field can boost the performance of refractometric sensors and nanophotonic optical devices. Nevertheless, real life applications are hampered by the magnetoplasmonic trilemma: 1) a good plasmonic metal has sharp optical resonances but low magneto-optical response; 2) a magnetic metal has strong magneto-optical response but a very broad plasmonic resonance; 3) mixing the two components degrades the quality of both features. To overcome the trilemma, we use a differen…
We report the results of theoretical and experimental studies of photoluminescence of silicon nanocrystals in the proximity of plasmonic modes of different types. In our samples, the type of plasmonic mode is determined by the filling ratio of a one-dimensional gold grating which covers the thin film with silicon nanocrystals on a quartz substrate. We analyze the extinction and photoluminesce spectra of silicon nanocrystals and show that the emitted light is coupled to the corresponding plasmonic mode. We also demonstrate the modification of the extinction and photoluminesce spectra under the …
We demonstrate that an array of optical antennas may render a thin layer of randomly oriented semiconductor nanocrystals into an enhanced and highly directional source of polarized light. The array sustains collective plasmonic lattice resonances which are in spectral overlap with the emission of the nanocrystals over narrow angular regions. Consequently, different photon energies of visible light are enhanced and beamed into definite directions.
We experimentally measure and analytically describe the fluorescence enhancement obtained by depositing CdSe/CdS nanocrystals onto a gold plasmonic crystal, a two-dimensional grating of macroscopic size obtained by gold deposition on a self-assembled opal. We show evidences of nanocrystals near-field coupling to the gold Surface Plasmons Polaritons (SPP) followed by grating-induced SPP re-emission to far-field. We develop a theoretical framework and an original method in order to evaluate, from photoluminescence experiments, the SPP extraction efficiency of a grating.
Engineering Photon Avalanche Thresholds in Single Nanocrystals with Plasmonic Nanostructures
Nicolaus Copernicus University in Toruń（托伦哥白尼大学）；Institute of Advanced Studies, Nicolaus Copernicus University in Toruń（托伦哥白尼大学高级研究所）；Institute of Low Temperature and Structure Research, Polish Academy of Sciences（波兰科学院低温结构研究所）
Plasmonic nanoparticles influence the absorption and emission processes of nearby emitters due to local enhancements of the illuminating radiation and the photonic density of states. Here, we use the plasmon resonance of metal nanoparticles in order to enhance the stimulated depletion of excited molecules for super-resolved microscopy. We demonstrate stimulated emission depletion (STED) microscopy with gold nanorods with a long axis of only 26 nm and a width of 8 nm that provide an enhancement of the resolution compared to fluorescent-only probes without plasmonic components irradiated with th…
Tunable light filters are critical components for many optical applications in which light in-coupling, out-coupling or rejection is crucial, such as lasing, sensing, photovoltaics and information and communication technology. For this purpose, Bragg mirrors, band-pass filters with high reflectivity represent good candidates. However, their optical characteristics are determined at the stage of fabrication. Heavily doped semiconductor nanocrystals (NCs) on the other hand deliver a high degree of optical tunability through the active modulation of their carrier density ultimately influencing th…
The arrangement of plasmonic nanoparticles in a non-symmetrical environment can feature the far-field and/or near-field interactions depending on the distance between the objects. In this work, we study the hybridization of three intrinsic plasmonic modes (dipolar, quadrupolar and hexapolar modes) sustained by one elliptical aluminium nanocylinder, as well as behavior of the hybridized modes when the nanoparticles are organized in array or when the refractive index of the surrounding medium is changed. The position and the intensity of these hybridized modes were shown to be affected by the ne…
The detailed understanding of the physical parameters that determine Localized Surface Plasmon Resonances (LSPRs) is essential to develop new applications for plasmonics. A relatively new area of research has been opened by the identification of LSPRs in low carrier density systems obtained by doping semiconductor quantum dots. We investigate theoretically how diffuse surface scattering of electrons in combination with the effect of quantization due to size (QSE) impact the evolution of the LSPRs with the size of these nanosystems. Two key parameters are the length $R_0$ giving the strength of…
The field effect in metal-oxide-semiconductor (MOS) capacitors plays a key role in field-effect transistors (FETs), which are the fundamental building blocks of modern digital integrated circuits. Recent works show that the field effect can also be used to make optical/plasmonic modulators. In this paper, we report field effect electro-absorption modulators (FEOMs) each made of an ultrathin epsilon-near-zero (ENZ) film, as the active material, sandwiched in a silicon or plasmonic waveguide. Without a bias, the ENZ film maximizes the attenuation of the waveguides and the modulators work at the …
Localized surface plasmon resonances (LSPRs) have recently been identified in extremely diluted electron systems obtained by doping semiconductor quantum dots. Here we investigate the role that different surface effects, namely electronic spill-out and diffuse surface scattering, play in the optical properties of these ultra-low electron density nanosystems. Diffuse scattering originates from imperfections or roughness at a microscopic scale on the surface. Using an electromagnetic theory that describes this mechanism in conjunction with a dielectric function including the quantum size effect,…
We analyze an inherent nonlinearity of Surface Plasmon Polaritons at the interface of Fermi-Dirac metal plasma, stemming from the depletion of electron density in high-field intensity regions. The derived optical nonlinear coefficients are comparable to the experimental values for metals. We calculate the dispersion relations for the nonlinear propagation of high-intensity Surface Plasmon Polaritons, predicting a nonlinear induced cutoff and vanishing group velocity.
Anisotropic Dopant and Strain Architectures in WS$_2$ Nanocrystals Driven by Growth Kinetics
Universidade Federal de São Carlos（圣卡洛斯联邦大学）；Brazilian Synchrotron Light Laboratory (LNLS), Brazilian Center for Research in Energy and Materials (CNPEM)（巴西同步辐射光实验室（LNLS），巴西能源与材料研究中心（CNPEM））；Universidade Federal de Ouro Preto（欧鲁普雷图联邦大学）；The Pennsylvania State University（宾夕法尼亚州立大学）
