Characteristic analysis of broadband plasmonic emitting devices based on transformation optics.

The crescent nanostructure with gain medium inside is theoretically studied to analyze the characteristic of plasmonic emitting with wide bandwidth. An accurate analytical model is built based on the transformation optics. In this model, the poles of the electrostatic potential function are in the second and the fourth quadrant of the complex plane if the imaginary part of the relative permittivity of the gain medium is larger than the loss compensation threshold, and then the extinction cross section is to be negative by integrating the electrostatic potential over the half complex plane via an inverse Fourier transform. The positive extinction cross section corresponds to absorption, and the negative corresponds to emission. The proposed analytical model agrees well with the numerical simulation results based on the finite element method, to give a physical insight into the loss compensation property of the plasmonic nanostuctures. Results show that the negative extinction cross section is realizable by introducing the gain medium into a plasmonic crescent nanowire, which is equivalent to an emitting device with wide bandwidth.

Collision-attachment simulation of membrane fouling by oppositely and similarly charged colloids.

The fouling propensity of oppositely charged colloids (OCC) and similarly charged colloids (SCC) on reverse osmosis (RO) and nanofiltration (NF) membranes are systematically investigated using a developed collision-attachment approach. The probability of successful colloidal attachment (i.e., attachment efficiency) is modelled by Boltzmann energy distribution, which captures the critical roles of colloid-colloid/membrane interaction and permeate drag. Our simulations highlight the important effects of ionic strength Is, colloidal size dp and initial flux J0 on combined fouling. In a moderate condition (e.g., Is =10 mM, dp=50 nm and J0= 100 L/m2h), OCC mixtures shows more severe fouling compared to the respective single foulant owing to electrostatic neutralization. In contrast, the flux loss of SCC species falls between those of the two single foulants but more closely resembles that of the single low-charged colloids due to its weak electrostatic repulsion. Increased ionic strength Is leads to less severe fouling for OCC but more severe fouling for SCC, as a result of the suppressed electrostatic attraction/repulsion. At a high Is (e.g., 3-5 M), all the single and mixed systems show the identical pseudo-stable flux Js. Small colloidal size leads to the drag-controlled condition, where severe fouling occurs for both single and mixed foulants. On the contrary, better flux stability appears at greater dp for both individual and mixed species, thanks to the increasingly dominated role of energy barrier and thus lowered attachment efficiency. Furthermore, higher J0 above limiting flux exerts greater permeate drag, leading to elevated attachment efficiency, and thus more flux losses for both OCC and SCC. Our modelling gains deep insights into the role of energy barrier, permeate drag, and attachment efficiency in governing combined fouling, which provides crucial guidelines for fouling reduction in practical engineering.

Ultrasensitive refractive index sensor based on the resonant scattering effect between double air circular-holes on silicon waveguides.

Recently, we have proposed a sensitive refractive index sensor design by integrating a circular-hole defect with an etched diffraction grating (EDG) spectrometer based on amorphous silicon photonic platforms. In the present paper, we will show that a much better sensitivity (~17422 nm/RIU) can be obtained by using double circular-holes with an appropriate interval. The influence of the double-hole interval on the performance of sensing applications is also characterized. A sinusoidal pattern of the sensitivity can be found as the interval increases. However, the intensity of the resonant peak (i.e., the detectability for sensing applications) significantly oscillates as the interval varies.

Correction: Significant field enhancements in an individual silver nanoparticle near a substrate covered with a thin gain film.

Correction for 'Significant field enhancements in an individual silver nanoparticle near a substrate covered with a thin gain film' by Jinhong Xian et al., Nanoscale, 2014, 6, 13994-14001, DOI: 10.1039/C4NR03678F.

Photochemically grown silver nanodecahedra with precise tuning of plasmonic resonance.

The ability to control the local surface plasmonic resonance (LSPR) absorption peaks of silver nanoparticles will greatly broaden the scope of their practical application. Conventional methods tune the LSPR peaks by modifying the shape or size of the silver nanoparticles. Here, we present a novel method to tune the LSPR band by controlling the particle corner sharpness. A modified photochemical method was used to prepare silver nanoparticles. It was found that the nanoparticles irradiated using light-emitting diodes (LEDs) with a wavelength of 455 nm were decahedral, although the reaction temperature was different. However, the in-plane dipole LSPR peak of the as-prepared silver nanodecahedra exhibited an evident red shift from 460 nm to 500 nm during the synthesis process, and the wavelength of the LSPR peak increased linearly as the reaction time increased. A numerical simulation conducted to investigate the mechanism behind the shift revealed that the red shift of the LSPR peak was mainly induced by the evolution of the corner sharpness of the silver nanodecahedra. These results demonstrated the effectiveness of the method in precisely tuning the LSPR peak by controlling the reaction time. By turning off the irradiation light, the photochemical process could be immediately terminated, and the LSPR peak of the silver nanoparticles remained constant. Compared with conventional methods, the present tuning precision can reach 1 nm.

Significant field enhancements in an individual silver nanoparticle near a substrate covered with a thin gain film.

In this paper, we propose a method to significantly enhance the local-field of a gap plasmonic system by placing a metallic nanoparticle in close proximity to a substrate covered with a thin film using a gain material (∼100 nm thickness). Compared with a conventional dielectric substrate, the thin gain film can contribute to several, or dozens, of times more intense local electric fields in the gap between the particle and the substrate. We use the finite difference time domain method to numerically analyze the influences of the gain coefficient of the film and of the other parameters on the field enhancement. The numerical results show that there is an optimal refractive index of the gain film that enables us to achieve a maximal field enhancement for a given NP radius. Moreover, the optimal refractive index of the gain film can be incorporated into any available materials using metal nanoparticles with an appropriate radius.