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Colloidal quantum dots (QDs) are promising candidates for single-photon sources with applications in photonic quantum information technologies. Developing practical photonic quantum devices with colloidal materials, however, requires scalable deterministic placement of stable single QD emitters. In this work, we describe a method to exploit QD size to facilitate deterministic positioning of single QDs into large arrays while maintaining their photostability and single-photon emission properties. CdSe/CdS core/shell QDs were encapsulated in silica to both increase their physical size without perturbing their quantum-confined emission and enhance their photostability. These giant QDs were then precisely positioned into ordered arrays using template-assisted self-assembly with a 75% yield for single QDs. We show that the QDs before and after assembly exhibit anti-bunching behavior at room temperature and their optical properties are retained after an extended period of time. Together, this bottom-up synthetic approach via silica shelling and the robust template-assisted self-assembly offer a unique approach to produce scalable quantum photonics platforms using colloidal QDs as single-photon emitters.

We propose a novel optimization framework for video object segmentation, given the initial annotations of objects in the keyframes of an input video sequence. In this work, video data is represented by a Markov Random Field model, and segmentation is achieved by finding the minimum graph cut label assignment. More specifically, we first create a bilateral representation of the input video sequence which reduces the size of the graph that the min-cut must operate on. We then introduce dynamic appearance models to learn the segmentation likelihoods, and the reliability of likelihoods is measured to identify false likelihoods that may cause segmentation errors. Thus, the model accurately describes changes in the object’s appearance that have evolved over time. Furthermore, we augment spatial and temporal connections using a soft higher-order potential, ensuring long-range label consistency in the segmentation. We provide extensive analysis and evaluation with respect to the influence of each component of the framework through the ablation study. Experiments on three benchmark datasets (DAVIS 2016, YouTube-Objects and SegTrack v2) show that our method achieves competitive performance compared to state-of-the-art while having the order of magnitude faster runtime.

Resolving the dynamics of photoexcited d-holes in metallic nanostructures is one step in the rational design of plasmonic photocatalysis. Here, we track the creation and relaxation of charge carrie...

Plasmonic metal nanoparticles exhibit large dipole moments upon photoexcitation and have the potential to induce electronic transitions in nearby materials, but fast internal relaxation has to date limited the spatial range and efficiency of plasmonic mediated processes. In this work, we use photo-electrochemistry to synthesize hybrid nanoantennas comprised of plasmonic nanoparticles with photoconductive polymer coatings. We demonstrate that the formation of the conductive polymer is selective to the nanoparticles and that polymerization is enhanced by photoexcitation. In situ spectroscopy and simulations support a mechanism in which up to 50% efficiency of nonradiative energy transfer is achieved. These hybrid nanoantennas combine the unmatched light-harvesting properties of a plasmonic antenna with the similarly unmatched device processability of a polymer shell.

Plasmon-mediated processes provide unique opportunities for selective photocatalysis, photovoltaics, and electrochemistry. Determining the influence of particle heterogeneity is an unsolved problem because often such processes introduce irreversible changes to the nanocatalysts and/or their surroundings. The challenge lies in monitoring heterogeneous nonequilibrium dynamics via the slow, serial methods that are intrinsic to almost all spectral acquisition methods with suitable spatial and/or spectral resolution. Here, we present a new metrology, snapshot hyperspectral imaging (SHI), that facilitates in situ readout of the tube lens image and first-order diffraction image of the dark-field scattering from many individual plasmonic nanoparticles to extract their respective spectra simultaneously. Evanescent wave excitation with a supercontinuum laser enabled signal-to-noise ratios greater than 100 with a time resolution of only 1 ms. Throughput of ∼100 simultaneous spectra was achieved with a highly ordered...

We report a study of the shape-dependent spectral response of the gold nanoparticle surface plasmon resonance at various electron densities to provide mechanistic insight into the role of capacitive charging, a topic of some debate. We demonstrate a morphology-dependent spectral response for gold nanoparticles due to capacitive charging using single-particle spectroscopy in an inert electrochemical environment. A decrease in plasmon energy and increase in spectral width for gold nanospheres and nanorods was observed as the electron density was tuned through a potential window of -0.3 to 0.1 V. The combined observations could not be explained by existing theories. A new quantum theory for charging based on the random phase approximation was developed. Additionally, the redox reaction of gold oxide formation was probed using single-particle plasmon voltammetry to reproduce the reduction peak from the bulk cyclic voltammetry. These results deepen our understanding of the relationship between optical and electronic properties in plasmonic nanoparticles and provide insight toward their potential applications in directed electrocatalysis.

Removing effects of sample heterogeneity through single-molecule and single-particle techniques has advanced many fields. While background free luminescence and scattering spectroscopy is widely used, recording the absorption spectrum only is rather difficult. Here we present an approach capable of recording pure absorption spectra of individual nanostructures. We demonstrate the implementation of single-particle absorption spectroscopy on strongly scattering plasmonic nanoparticles by combining photothermal microscopy with a supercontinuum laser and an innovative calibration procedure that accounts for chromatic aberrations and wavelength-dependent excitation powers. Comparison of the absorption spectra to the scattering spectra of the same individual gold nanoparticles reveals the blueshift of the absorption spectra, as predicted by Mie theory but previously not detectable in extinction measurements that measure the sum of absorption and scattering. By covering a wavelength range of 300 nm, we are furthermore able to record absorption spectra of single gold nanorods with different aspect ratios. We find that the spectral shift between absorption and scattering for the longitudinal plasmon resonance decreases as a function of nanorod aspect ratio, which is in agreement with simulations.

We introduce the concept of bio-inspired catalytic hydrogenation of nitroarenes by mimicking the catalytic behavior of enzymes with NiS2+x nanoparticles and polymeric melon (g-C3N4). The g-C3N4-supported NiS2+x nanoparticles functioned as ligand-free and noble metal-free catalysts and offered high efficiency, comparable to noble metal-based catalysts, but at a much better selectivity.

The incorporation of metal nanoparticles into bulk electrochemical systems has resulted in technological advances in electronics, electrocatalysis, and sensing. Metal “nanoelectrodes” are exposed to varied chemical environments that can cause dissolution under applied potentials, often below bulk oxidation values. Gold nanorods are being developed as superior light harvesting nanoantennas in photoelectrocatalysis, and light scatterers for nanoscopic spectroelectrochemical sensing. However, dissolution poses a critical problem for gold nanoelectrode functionalized devices as the electrochemical and optical properties of nanoparticles are highly dependent on size and shape, and the cost of replacement can be prohibitive. We employed an analytical, single particle approach to monitor the chloride-mediated dissolution pathway of gold nanorods in the presence of oxoanion electrodissolution inhibitors. Hyperspectral dark-field imaging revealed that the morphological stability of gold nanorods at anodic potentials improved with the addition of low relative concentrations of oxoanions to aqueous halide electrolyte solutions. Single particle measurements were necessary to address the inter-particle heterogeneity of chemically synthesized gold nanorods. Direct correlation imaging of single gold nanorods with scanning electron microscopy supported the reaction pathway heterogeneity statistics and electrodissolution potentials obtained spectroscopically. We determined that the electrodissolution inhibition capacity of oxoanions in the presence of chloride ions for gold nanoparticles was governed primarily by the electroadsorption potential and ionicity of the oxoanion. Determining the factors for inhibition will assist in the expansion of the electrochemical stability window, opening new avenues for gold nanoelectrodes in diverse and harsh catalytic and sensing environments.