Zong-Suo Zhang

Fano resonances in dipole-quadrupole plasmon coupling nanorod dimers

We theoretically investigate the plasmon coupling in metallic nanorod dimers. A pronounced dip is found in the extinction spectrum due to plasmonic Fano resonance, which is induced by destructive interference between the bright dipole plasmon of a short nanorod and the dark quadrupole plasmon of a long nanorod. This Fano interference can also be explained as the coupling between the bright and dark modes both supported by the whole dimer. The Fano resonance can be tuned by adjusting the spatial or spectral separation between two nanorods in the dimer.

Plasmon-mediated radiative energy transfer across a silver nanowire array via resonant transmission and subwavelength imaging.

Efficient plasmon-mediated excitation energy transfer between the CdSe/ZnS semiconductor quantum dots (QDs) across the silver nanowire array up to 560 nm in length is observed. The subwavelength imaging and spectral response of the silver nanowire arrays with near-field point-source excitations are revealed by theoretical simulations. Our studies demonstrate three advantages of the nanosystem: efficient exciton-plasmon conversion at the input side of the array through near-field strong coupling, directional waveguidance and resonant transmission via half-wave plasmon modes of the nanowire array, and subwavelength imaging at the output side of the array. These advantages allow a long-range radiative excitation energy transfer with a high efficiency and a good directionality.

Twinned Fano interferences induced by hybridized plasmons in Au–Ag nanorod heterodimers

We theoretically investigated the plasmon interferences and hybridization in the Au–Ag nanorod heterodimers. Twinned Fanolike profiles are observed in the absorption cross sections of the gold and silver nanorods in the heterodimers, the Fano factors of which have the opposite signs near the antibonding resonances, which are found to be induced by the destructive interferences of two hybridized local surface plasmons. Both the value and sign of the Fano factors could be tuned by adjusting rod-lengths, which could find the applications in the design of plasmonic nanodevices.

Improved photoluminescence of silicon nanocrystals in silicon nitride prepared by ammonia sputtering

In the present work we investigated the photoluminescence property of silicon nanocrystals in silicon nitride prepared by ammonia sputtering. Silicon nanocrystals were demonstrated to form even after thermal annealing at 700 °C. Compared with the control sample using N(2) as the reactive gas, the luminescence intensity of silicon nanocrystals in silicon nitride prepared by NH(3) sputtering was greatly increased. The improvement in photoluminescence was attributed to the introduction of hydrogen-related bonds, which could well passivate the nonradiative defects existing at the interface between silicon nanocrystals and the silicon nitride matrix.

Plasmonic interferences and optical modulations in dark-bright-dark plasmon resonators

We fabricated dark-bright-dark plasmon resonators, investigated enhanced-transmission induced by plasmon transfer from the bright mode to the dark modes. Furthermore, we demonstrated interferences between dark plasmons excited by the near-field bright plasmons and directly excited by slantwise incident light, which leads to selective storage of excited energy in one of the two dark plasmon cells in the resonators by adjusting the phase between signal and control sources. This could find the applications in all-optical modulations.

Fano resonances in active plasmonic resonators consisting of a nanorod dimer and a nano-emitter

The optical emission response of a single nano-emitter coupled with a plasmonic nanorod dimer is investigated, where the short and long nanorods in the dimer support dipolar and quadrupolar plasmon resonance, repsectively. Fano resonances are observed with a nano-emitter being placed at either apex of the dimer. However, no Fano resonance is seen when the nano-emitter is placed in the gap of the dimer. Bonding and antibonding dipolar-quadrupolar plasmon couplings are closely related to the Fano resonances in this dimer system.

Role of interface in ion mixing induced amorphization in the Ag–Mo system with very positive heat of formation

A free energy diagram of the Ag–Mo system with a very positive heat of formation of +57 kJ/mol was constructed, with special consideration to the interfacial free energy in the multilayered films for ion mixing. It was found that amorphization was possible to achieve within two separate composition ranges toward Ag and Mo ends, respectively, if 12 layers, or about 13% of the interfacial atoms were included in the films. Accordingly, ion mixing of the Ag–Mo multilayered films was conducted at liquid nitrogen temperature by 190 keV xenon ions and the formation of amorphous phases was in good agreement with the calculation. Besides, a new metastable fcc phase was formed and, more interestingly, it transformed into an amorphous state upon aging, which can also be interpreted by a related free energy calculation.

Plasmonic interferences in two-dimensional stacked double-disk array

We numerically investigate the resonant spectral features of the two-dimensional stacked double-disk array. Narrow plasmon line shapes are observed on resonance spectra which are similar to the case of single-disk array. The electric field shows that the narrow plasmon modes are produced by the dark plasmon mode coupling to the diffraction which may be due to the retardation effect. The narrow mode and the dark mode overlap on resonance spectra, resulting in a Fano-like spectrum. The intensities of the electric fields for these narrow modes arising from the dark mode coupling are much stronger than that of the bright modes.

A comparative study of metastable alloy formation by ion mixing and thermal annealing of multilayers in the immiscible Y-Zr system

Abstract Amorphous alloys were formed in an immiscible Y–Zr system by ion mixing and thermal annealing of multilayered films consisting of nine alternate metal layers. In addition, two metastable crystalline phases, i.e. a fcc Zr-rich and a fcc Y-rich phase, were also obtained. A compatible thermodynamic interpretation was proposed and illustrated by a Gibbs free energy diagram, which was constructed based on Miedemas model and included the free energy curve of the multilayered films possessing excess interfacial energy. The formation mechanism of the metastable crystalline phase is also discussed in terms of the electronic structure as well as the growth kinetics.

Strong bonding magnetic plasmon hybridizations in double split-ring resonators.

The complex magnetic dipole plasmon couplings in double split-ring resonators are investigated. Two split peaks in the absorption spectrum of these coupled systems are observed, but even the shorter-wavelength resonance peak can be redshifted compared to the peaks of individual rings. The magnetic plasmon fields outside rings are found to play an important role in these strong couplings. Because of them, both bonding and antibonding plasmon hybridizations occur at each split peak. When bonding coupling effects are stronger than those of antibonding ones, this abnormal splitting behavior appears. When the coupling between rings becomes weaker, the splitting phenomenon tends to be normal.