Effect of a dielectric coating on quenching in a molecule-nanosphere system

We investigate the effect a dielectric coating has on the energy transfer between a molecule and a silver nanosphere. For a fixed wavelength excitation resonant with the bare nanoparticle, increasing the shell thickness increases the non-radiative decay rate and decreases the radiative decay rate, which decreases the total efficiency of the emission process. The excitation wavelength can be tuned to improve the efficiency for coated nanoparticles, leading to values that are comparable to bare nanoparticles. As such, dielectric coatings are able to effectively limit quenching without sacrificing efficiency

Distance dependent quenching effect in nanoparticle dimers

In this paper, we investigate the emission characteristics of a molecule placed in the gap of a nanoparticle dimer configuration. The emission process is described in terms of a local field enhancement factor and the overall quantum yield of the system. The molecule is represented as a dipolar source, with fixed length and fed by a constant current. We first describe the coupled dimer-molecule system and compare these results to a single sphere-molecule system. Next, the effect of dimer size is investigated by changing the radius of the nanoparticles. We find that when the radius increases, a saturation effect occurs that trends towards the case of a radiating dipole between two flat interfaces, which we refer to as a parallel plate waveguide geometry. An analytical solution for the parallel plate waveguide geometry is presented and compared to the results for the spherical dimer configuration. We use this approximation as a reference solution, and also, it provides useful guidelines to understand the physical mechanism behind the energy transfer between the molecule and the dimer. We find that the emission intensity undergoes a quenching effect only when the inter-nanoparticle gap distance of the dimer is very small, meaning that strong coupling prevails over energy engaged in the heating process unless the molecule is extremely close to the metal surface

Exceptional Optical Response of Archimedean Boron and Group‑V Ultrathin Nanosheets

The ascendancy of ultrathin films has emerged as a boon for 21st century nanotechnologies that rely on flexibility, tunable properties, and active surface area. We explore uncharted configurations with Archimedean (4,8)-tessellations that exhibit exceptional light–matter interactions captured with time-dependent density functional theory. We find that planar monolayers of haeckelite boron-pnictogen binary materials possess strong interband absorbance and absorption coefficients that rival existing ultrathin films. These observables were found to occur in the ultraviolet for the boron-nitride nanosheet and in the infrared region of the electromagnetic spectrum for heavier pnictogens, suggesting a route for photocapture of high density solar photons. Moreover, we find the buckled haeckelite boron arsenide supports a similar, yet slightly decreased, optical response that is blue-shifted from its planar configuration. The strong optical response of these ultrathin films emerges from their unique bandstructures, localization of π-electrons in the ground state, Van Hove singularities at band extrema, and complementary elemental properties. Consequently, the (4,8) haeckelite motif demonstrates that many 2D films with distinctly different lattice tessellations from that of established ultrathin materials could have a significant impact on the field

Electronic Properties of Halogen-Adsorbed Graphene

We have investigated the electronic properties of 1-, 2-, and 3-layer graphene upon surface adsorption of halogen molecules by means of density functional calculations. The most stable adsorption site is parallel to the graphene surface with the diatomic atoms centered over adjacent carbon rings. Bader analysis shows a large charge transfer between F₂ and graphene, which significantly extends the fluorine bond length, while only small amounts of charge are transferred to Cl₂, Br₂, and I₂. Adsorbed halogens alter the electronic properties of graphene by pushing the Fermi level down and bringing forth an accessible impurity band that can be utilized to alter the material properties. Moreover, molecule–surface interactions introduce a bandgap at the K-point between 3 and 330 meV, depending upon the particular graphene-halogen system. When adsorbed on 1-layer graphene, halogen molecules typically open a small bandgap; however, they induce a notably larger bandgap on the 2-layer AB-stacked and 3-layer ABC-stacked graphene. This work suggests an effective way to tune the electronic properties of two-dimensional graphene by adsorption of halogen molecules

Surface Plasmon Coupling on Linked Au–Pt Nanorods

This work demonstrates that surface plasmon coupling in linked Au–Pt NRs (NRs) can be controlled by adjusting the relative ratio of material segment lengths. The NRs were synthesized through an anodic aluminum oxide template assisted sequential electrochemical deposition route. Optical spectra of the NRs in solution were acquired in the UV–vis–NIR region to examine surface plasmon coupling. Analysis of the spectra indicated that effective surface plasmon coupling could occur in Au-dominated NRs but not in Pt-dominated ones. The optical properties of Au–Pt–Au three-segment NRs were also examined, and the results provided further clarification regarding the conditions that yield effective coupling of NR segments in these structures. Electrodynamics calculations on two- and three-segment NRs were performed and found to be in good agreement with experiment. These findings regarding surface plasmon coupling of linked, hybrid NRs extend the fundamental knowledge of surface plasmon coupling from single component to hybrid systems and are useful for a variety of applications that necessitate fine controllability of the plasmonic properties