ChaoLing Du

Resonant Raman spectroscopy of (Mn,Co)-codoped ZnO films

Resonant Raman spectroscopy studies of (Mn, Co)-codoped ZnO films were carried out using the 325 nm laser as the excitation source. The mixed mode character of the longitudinal optical (LO) phonon reveals that the resonant Raman spectra of the films can be used to test the c-axis orientation degree of their crystallite grains. The ratio of integrated Raman intensities between the 2LO to LO changes as a function of annealing temperatures, which reaches maximum at about 800 °C and demonstrates the variation of electron-LO phonon coupling in the films. These can provide helpful information for the fabrication of ZnO based functional films and for the development of their future applications.

Surface-Enhanced Raman Scattering from Individual Au Nanoparticles on Au Films

We investigated the effect of optical thick metal films on the surface-enhanced Raman scattering (SERS) activity of individual Au nanoparticle (NP) monomers and dimers. The film presence is revealed to be positive for the SERS activity of individual NP monomers, while it is not always positive for the electromagnetic enhancement at hot spots for SERS of the dimer, which is explained well by our numerical simulations. The polarized SERS signals from the NP dimer are elucidated well in terms of the plasmon hybridization of the dimer. SERS contributions both from individual NP surfaces and the junction between the NP and its supporting substrate were discussed as well.

Numerically investigating the enhanced Raman scattering performance of individual Ag nanowire tips

The enhanced Raman scattering (ERS) performance of individual Ag nanowire (NW) tips with the shape of a bulb, a crown, a pencil, and a nanoparticle randomly decorated crown was numerically investigated by the finite element method. Their polarized surface ERS is revealed to be either anisotropic or isotropic, which is affected by the incident light wavelength and polarization and the shape of the tips. In our results, the pencil tip presents strong ERS effects with optimized ERS enhancement and lateral spatial resolution of about 0.3×109 and 1.3 nm, respectively. Effects of the pencil tip geometry (including the shape, angle, length, and size) on its tip ERS behavior are discussed as well. The present work also holds promise for individual Ag NW tip applications in microscope and spectroscope imaging and improvement, etc.

Raman mapping probing of tip-induced anomalous polarization behavior in V2O5 waveguiding nanoribbons

Spatially resolved and polarized micro-Raman spectroscopy has been performed on individual V2O5 waveguiding nanoribbons. The experimental results establish that the Raman-antenna patterns are strongly correlated with the local positions of the sample, which gives rise to a pronounced intensity contrast in the polarized mapping for certain phonon modes. The suppressed phonon signals at the body of a ribbon can be enhanced at the end facets, resulting from the effective waveguiding propagation along the nanoribbon and strong local electric field intensity at the ends. The phenomena reported here, in addition to providing insight into the tip effects on optoelectronic nanodevices, will facilitate the rational design of Raman detection in nanostructures.

Effect of near-field coupling on far-field inelastic scattering imaging of gold nanoparticles.

The optical near-field enhancement induced by coupling between noble nanoparticles and the substrate has been studied by a far-field imaging method. The longitudinal mode of the incident laser is revealed to contribute to the coupling. The far-field images of individual gold nanoparticles exhibit a peanut-shaped pattern; these were constructed by the intensity of inelastically scattered light. The coupling between gold nanoparticles and the silicon substrate leads to the patterned image. By tuning the separation between the gold nanoparticles and substrate using SiO(2) layers of different thickness, the coupling efficiency decreases with the thickness of the SiO(2) layer.

Plasmon Peak Sensitivity Investigation of Individual Cu and Cu@Cu2O Core–Shell Nanoparticle Sensors

It is crucial to reveal the plasmon peak sensitivity responses of individual Cu nanoparticles, which provide another kind of plasmon sensors besides Au/Ag ones. In this paper, such responses to both the bulk and local refractive index (RI) of individual Cu nanosphere sensors are theoretically investigated by Mie theory. Both of them are revealed to be quadratic. The underlying mechanisms are elucidated well in terms of Rayleigh approximation. The corresponding sensitivity factors are demonstrated to increase with the RI of the nanospheres’ bulk and local surrounding mediums linearly. The plasmon peak sensitivities and sensitivity factors of experimentally encountered Cu@Cu2O core–shell nanoparticles are calculated as well, which reveals that appropriate dielectric encapsulations to Cu nanospheres are favored for their potential plasmonic sensing and detection applications.

Dielectric Nanocup Coating Effect on the Resonant Optical Properties of Individual Au Nanosphere

By finite element method (FEM), dielectric nanocup coating effect on the resonant optical properties of individual Au nanosphere was investigated. It is demonstrated not deleterious to the sensing signals of the nanosphere. The proposed nanocomposite provides an interesting localized surface plasmon resonance (LSPR) sensor with quadratic response, which refractive index (RI) sensitivity is revealed to increase with the RI both of its surrounding and local environment. The differences between the LSPR peak positions of the nanocomposite measured from far-field and near-field spectra are discussed, too. It is believed to shed light on the future applications in surface enhanced Raman spectroscopy, biochemical sensing, and detections.

Plasmonic Coupling Effects on the Refractive Index Sensitivities of Plane Au-Nanosphere-Cluster Sensors

Plasmonic coupling effects (between neighboring components) are able to red shift the peak wavelengths of dipolar-localized surface plasmon resonances (LSPRs) and increase the corresponding refractive index sensitivity of nanoparticle sensors. The coupling effects on plane Au-nanosphere-cluster (including nanosphere dimer, trimer, pentamer, and heptamer) sensors are numerically investigated by finite element method (FEM). We found that the coupling does not violate the quadratic response characteristics of LSPR peak wavelengths, hence the linear responses of the sensitivities to the bulk refractive index of Au cluster sensors. Yet, for nanosphere dimer sensors, they contribute to the exponential decrease of sensitivities with their gap distances, which follow the universal plasmon ruler behavior. The amplitude of their fractional sensitivity shift is revealed to be bulk refractive index independent, which is different from that of their fractional LSPR peak wavelength shift. These are analytically explained well in terms of an effective nanoparticle model. The present work also gives an upper sensitivity limit for Au nanosphere dimer systems and provides a method to estimate the interparticle separation between the two component nanospheres of the dimer.

Raman mapping probing of V 2 O 5 waveguiding nanoribbons

Considering the smooth surface and high refractive index which give rise to the tight optical confinement, it is the first demonstration of efficient light propagation in V2O5 nanoribbons. The results provide useful information for the construction of future nanoscaled waveguide structures. Moreover, regular V2O5 waveguides were found to exhibit Raman signals with near-resonance excitation and guide these modes through the nanoribbon cavity. The results shown here provide experimental support for the development of novel nanophotonic elements. Furthermore, we discovered that the waveguiding property of the nanoribbon can modulate the polarized Raman scattering signal depending on the local field of the sample.