Tingyin Ning

3D silver nanoparticles with multilayer graphene oxide as a spacer for surface enhanced Raman spectroscopy analysis

We report a three-dimensional (3D) SERS substrate with different numbers of silver nanoparticle (Ag NP) layers using multilayer graphene oxide (GO) as a spacer. The SERS performance of the 3D nanostructure was investigated and it was found that the SERS effect increased as the number of Ag NP layers increased, and showed almost no change for more than four layers. We found that the SERS performance of the 3D nanostructures can be mainly attributed to the topmost hot spots which are closely related to the Ag NP layers in the 3D nanostructure. Furthermore, we explored 3D nanostructures with different Ag NP layers using the finite difference time domain method (FDTD). The 3D SERS substrates also exhibit excellent detection capability. The limit of detection (LOD) was calculated down to 10-15 M for R6G and 10-12 M for CV. In addition, the reproducibility of the 3D SERS substrate was attributed obviously to the increasing number of Ag NP layers. Based on these promising results, the highly sensitive detection of molecules such as malachite green was demonstrated for food safety inspection.

Third-harmonic generation from gold nanowires of rough surface considering classical nonlocal effect

We demonstrate that the nonlocal dielectric response of metal, comparing with the traditional local model, will significantly boost the third-order harmonic generation (THG) from gold nanowires of rough surface by a factor of several orders of magnitude. The enhancement is probably due to the penetrated field into the fine nanostructures on the metal surface in nonlocal model. The anisotropy THG efficiency versus the angle of incidence is also demonstrated due to the inhomogeneous surface morphology. The possible ways to verify the nonlocal effect to the THG are demonstrated. The results have a general significance in explaining the experimental observations.

Theoretical design of a surface plasmon resonance sensor with high sensitivity and high resolution based on graphene–WS2 hybrid nanostructures and Au–Ag bimetallic film

We proposed a high sensitivity and a high resolution surface plasmon resonance sensor composed of graphene–WS2 hybrid nanostructure and Au–Ag bimetallic-layers film. The bimetallic-layer configuration uses the high sensitivity of gold and the narrow full width at half maximum (FWHM) of silver to improve the sensors sensitivity and resolution respectively. Graphene and WS2 serve as an effective light absorption medium. Once they cover the bimetallic-layer, the sensitivity can be further improved significantly. Graphene–WS2–Au–Ag model shows a higher sensitivity and higher resolution than that of the conventional sensing scheme where pure Au thin film is used. In our paper, we mainly use Fresnel equations and the transfer matrix method (TMM) to study the reflectivity and sensitivity as well as the full width at half maximum (FWHM) of the SPR sensor.

A sensitive 2D plasmon ruler based on Fano resonance

In this paper, we designed a 2D distance and rotation angle plasmon ruler based on Fano resonance of a trimer nanostructure, which consists of a concentric square nanoring–disk and an outside nanorod (CSRDR). The Fano dip energy and depth are fairly sensitive to the nanometer-scale displacements and rotations, when the nanodisk moves in all direction and rotates around its center. When the symmetry of the nanoring is broken, we can identify the moving and rotating direction of the nanodisk more accurately. We use the CSRDR nanostructure which supports a narrow line-width as a 2D plasmon ruler, which can enhance the sensitivity of a plasmon ruler significantly.

Second Harmonic Generation from Ultrathin Gold Nanotubes

We numerically study second harmonic generation from plasmonic nanotubes of air-core and ultrathin gold shell using classical nonlocal hydrodynamic model of free electron. We demonstrate that the nonlocal effect of gold significantly affects the linear optical response and second harmonic generation in such ultrathin nanotubes with shell down to a few nanometers or subnanometer scale, comparing with the conventional local Drude model of gold. We specially emphasize second harmonic generation from the nanotube structures of dipole plasmon resonance at fundamental wavelength and dipole/quadrupole resonance at second harmonic wavelength. Our results indicate that, the output of second harmonic generation is dominantly enhanced by the dipole plasmon resonance at fundamental wavelength via the strong local electric field and also can be significantly enhanced by dipole- and quadrupole-resonant scattering at second harmonic wavelength. The nonlinear sources of second harmonic generation in ultrathin gold nanotubes, including nonlinear Coulomb interaction, convective term, Lorentz force, and nonlinear pressure are studied separately, and the dominant contributions from convective term and nonlinear Coulomb term are reported.

A low lasing threshold and widely tunable spaser based on two dark surface plasmons

We theoretically demonstrate a low threshold and widely tunable spaser based on a plasmonic nanostructure consisting of two sets of disk-rings (TSDR). The TSDR nanostructure supports two dark surface plasmons (SPs), which are excited simultaneously by two bright SPs at Fano dips. The two dark SPs support lower effective mode volume, higher quality factor and higher Purcell factors. When the dark SPs serve as the pumping and lasing mode of a spaser, the spaser has a lower lasing threshold, a higher pump absorption efficiency and a lower threshold absorbed pump power than the spaser based on a bright SP. In addition, the lasing and pumping wavelengths of the spaser proposed in this article can each be tuned over a very wide wavelength range. Our results should be significant for the development of spasers.