Yan Fang

The Study of Surface Plasmon in Au/Ag Core/Shell Compound Nanoparticles

Au/Ag core/shell nanoparticles are fabricated by laser-ablating Ag plates in Au colloid solution. The absorption band is found to blue shift with increasing ablation time. Mie theory calculations show that the shift is caused by the increase of the Ag shell thickness. The average Ag shell thickness can be determined from the measured absorption peak. Using the plasmon hybridization approach, we show that the absorption band around 510xa0nm originates from an anti-bonding mode ω−+ caused by the interaction between a bonding Ag shell mode ω−− and Au sphere mode ωS-Au. The blue shift of the ω−+ mode with the increase of Ag shell thickness is also well predicted by the hybridization theory.

Reversible Defect in Graphene Investigated by Tip-Enhanced Raman Spectroscopy

In this paper, a single defect in graphene was created by an Au nanoparticle attached to atomic force tip working in tapping mode. Then it was investigated by tip-enhanced Raman spectroscopy (TERS). The TERS tip interacted with the graphene are able to induce an atomic deformation of carbonic structure which then can be recovered after retracting the tip. The reversible defect was confirmed by the iterative observation of D-band Raman signal of graphene as the tip force on and off. Further more, the Au particles as a nano-antenna can enhance the weak D-band signal from the single graphene defect significantly. These finds will give us better understanding of the origination of graphene defects and the interaction between nanoparticles and graphene.

From gold nanorods to nanodumbbells: a different way to tailor surface plasmon resonances by a chemical route

Spherical ended and arrow ended gold nanodumbbells were synthesized by a simple approach of introducing gold nanorods to solutions of sodium hydroxide and ascorbic acid, respectively. From UV-visible absorption spectroscopy, the transverse and longitudinal surface plasmon resonance that corresponds to electron oscillations perpendicular and parallel to the gold nanorods showed either blue or red shift, depending on the concentration of the acid or alkali solution. The morphological change from gold nanorods to spherical ended and arrow ended dumbbells was assessed by transmission electron microscopic (TEM) analysis. A theoretical model using the volume integral equation method was used to simulate the surface plasmon resonance of the gold nanodumbbells, which was in good agreement with the experimental observations. From the experimental observations and numerical calculations, a new growth mechanism for gold nanodumbbells is proposed.

Photo-assisted control of gold and silver nanostructures on silicon and its SERRS effect

A facile approach to control the growth of gold nanostructures on n-type silicon by galvanic displacement was demonstrated previously. It was observed that in the presence of light and red laser, at initial stages, gold nano-needles were formed, which then grew perpendicular to the substrate with time. However, the growth process has not yet been understood completely. Here, we have attempted to understand the galvanic displacement phenomena in the presence and absence of light by characterizing the growth process using transmission electron microscopy, atomic force microscopy and x-ray diffraction. Furthermore, we also evaluated the effect of laser on the deposition of silver on silicon wherein the use of green laser resulted in the formation of dendrites, whereas spherical nanoparticles were formed in dark. To further evaluate the benefits of the metal–semiconductor hybrid structure, we also evaluated the surface enhanced resonance Raman spectroscopy (SERRS) of the hybrid substrates and give evidence of the importance of the semiconductor substrate/metal–semiconductor interface in enhancing the SERRS activity.

The Preparation of Silver Nanowires and the Study of SERS Activity of Single Nanowire

In this report, the polyol process was used for preparing silver nanowires. In this improved method, the silver nanowires with high purity, high yield and high sensitive surface enhanced Raman scattering (SERS) activity were synthesized mainly by sealed heating. Then the samples were characterized by scanning electron microscopy (SEM). Its optical absorption properties were measured by UV-Vis spectrophotometer; furthermore, SERS spectra of R6G molecule on the single nanowire was obtained and systematically studied by excitation wavelength 532nm. Our experimental results showed that the length of nanowires by our improved method is uniform and has high yield, high purity and higher SERS enhancement effect. The UV-Vis absorption spectrum of the samples displayed the transverse and longitudinal plasma resonance (SPR) absorption bands of silver nanowires which are located at 358nm and 416nm, respectively. Also single nanowire SERS activities which are dependent on the different substrates were researched.

The Surface-Enhanced Raman Spectroscopy of Graphene Deposited by Silver Nanoparticle Islands

The deposition of silver nanoparticles on graphene, induced additional corrugations of graphene, a new type of artificial defects. It is very notable that new significant Raman modes were achieved and rationally assigned, indicating that SERS effect is a powerful technique not only for identifying the number of graphene layers but for investigating the interaction mechanism of graphene and nanoparticles. This is of crucial importance for developing the graphene–based electronic devices modified by atomic–clusters or nanoparticles.

Synthesis of Highly Ordered Silver Nanowire Arrays with SERS Activity

The highly ordered silver nanowire arrays were fabricated successfully by an easily produced and handled approach with the assistance of nanoporous anodized aluminum oxide(AAO) template. The silver nanowires with uniform diameters are highly ordered and parallel to each other. A broad UV-visible absorption band with a center at 401nm of silver nanowire arrays were detected. Optimized surface enhanced Raman scattering(SERS) signals of crystal violet molecules(CV) were recorded. It was found that the substrate exhibits strong enhancement properties due to the surface plasma resonance(SPR) of highly ordered silver nanowire arrays. The enhancement factor was calculated as 3.5×106. In addition, the results offered a simple technique in preparing highly ordered nanowire arrays which can be used as negative-refractive-index material as well as excellent SERS substrate.

The Fabrication of La0.9Sr0.1CoO3 Thin Films and its LITV Effect Applications

High quality La0.9Sr0.1CoO3 (LSCO) thin films grown on 5° vicinal cut LaAlO3 (LAO) (100) substrates were deposited by pulse laser deposition (PLD). Laser induced thermoelectric voltage (LITV) was detected instantly with fast response time and extremely narrow full width at half maximum (FWHM) when 248 nm pulse laser radiated on the surface of LSCO thin films. These merits of LSCO thin films make it one ideal material to fabricate light detectors and photosensitive device. With the increase of pulse laser energy, the peak voltages increase linearly, so LSCO thin films can be used to make high precision laser energy/power meter.

Preparation of Au@Ag Core-Shell Nanorods and Investigation of its Surface Plasmon

Different aspect ratio (length/width) gold nanorods were prepared in aqueous solution by seeding growth method. Aspect ratio of the nanorods was controlled accurately by changing the silver ions concentration. Ultraviolet-visible (UV-vis) spectra demonstrate the regularation that longitudinal plasmon resonance absorption wavelength of gold nanorods reveal red shift with the increase of aspect ratio. Gold nanorods were wrapped with Ag shells by chemical reduction silver ions on its surface. Different from gold nanorods, the transverse modes of the Au@Ag core-shell nanorods have two bands which contributed from the Ag and Au, respectively. On the other hand, centers of longitudinal surface plasmon of the core-shell nanorods exhibit blue shift with the Ag shell thickness increasing.