On-chip focusing of light by metallic nanotip

We present a numerical simulations, fabrication and experimental results for on-chip focusing of surface plasmon polaritons (SPPs) in metal nanotip coupled to the silicon waveguide. © 2011 Optical Society of America.

On-chip focusing of light by Metallic Nanotip

We investigate numerically and experimentally the on-chip nanoscale focusing of surface plasmon polaritons (SPPs) in metallic nanotip coupled to the silicon waveguide. Strong field enhancement is observed at the apex of the tip. © 2010 Optical Society of America.

Enhancement of the far-field output power and the beam properties of plasmonic very small aperture lasers

The properties of plasmonic very small aperture lasers are shown: these integrate surface plasmon structures with very small aperture lasers. The transmission field can be confined to a spot of subwavelength width in the far field, and according to the finite difference time domain simulation results the focal length of the spot can be modulated using different ring periods. Scanning of the subwavelength gating in the far field has been realized numerically. Such a device can be used with a high-resolution far-field scanning optical microscope.

Mid-infrared heavily n-doped GaAs extraordinary transmission through subwavelength grooves

Transmission of an electromagnetic wave from a heavily doped n-type GaAs film is studied theoretically. The calculations are performed using the two-dimensional finite-different time-domain method. From the calculations, we find the extraordinary transmission of p-polarized waves through the film with subwavelength grooves on both surfaces at mid-infrared frequencies. By determining a set of groove parameters, we optimize the transmission to as high as 55.2%. We ascribe this extraordinary transmission to the coupling of the surface-plasmon polariton modes and waveguide modes. Such an enhanced transmission device can be useful for mid-infrared wave filters, emitters, and monitors.

Design of plasmonic back structures for efficiency enhancement of thin-film amorphous Si solar cells

Metallic back structures with one-dimensional periodic nanoridges attached to a thin-film amorphous Si (a-Si) solar cell are numerically studied. At the interfaces between a-Si and metal materials, the excitation of surface-plasmon polaritons leads to obvious absorption enhancements in a wide near-IR range for different ridge shapes and periods. The highest enhancement factor of the cell external quantum efficiency is estimated to be 3.32. The optimized structure can achieve an increase of 17.12% in the cell efficiency. (C) 2009 Optical Society of America

Simulation of light coupling enhancement and localization of transmission field via subwavelength metallic gratings

Surface plasmons(SPs) generated in nano metallic gratings on medium layer can greatly enhance the transmission field through the metallic gratings. The enhancement effect is achieved from lambda = 500 nm to near-infrared domain. The enhancement rate is about 110 % at the wavelength of about 6 10 nm and about 180 % at lambda = 700 nm and 740 nm where most kinds of thin film solar cells have a high spectral response. These structures should provide a promising way to increase the coupling efficiency of thin film solar cells and optical detectors of different wavelength response.

Plasmonic very-small-aperture lasers

The fabrication of plasmonic very-small-aperture lasers is demonstrated in this letter. It is an integration of the surface plasmon structures and very-small-aperture lasers (VSAL). The experimental and numerical results demonstrate that the transmission field can be confined to a spot with subwavelength width in the far field, and the power output can be enhanced 140% of the normal VSAL. Such a device can be useful in the application of a high resolution far-field scanning optical microscope. (C) 2007 American Institute of Physics.

SERS的基底、机理及在分子组装和生物分析中的应用研究

自表面增强Raman散射（SERS）在粗糙化的银电极上被首次发现以来，对于SERS的研究取得了很大的进展。主要集中在对SERS基底的构筑、SERS机理的解释以及SERS的应用方面，包括在表面科学及生物分析中的应用。本论文主要通过纳米合成及组装技术构筑了具有高活性、稳定性及重现性好的SERS基底，研究了SERS的电磁增强机理以及SERS在分子组装体与生物分析中的应用。关于SERS基底的构筑，我们主要合成了中空的银金纳米结构，在玻碳表面构筑了高SERS活性的银纳米簇、在水汽界面构筑了二维金纳米阵列及金纳米棒的聚集体膜作为SERS基底。我们还研究了处于金属纳米粒子-耦联分子-金属纳米粒子以及银纳米片-耦联分子-宏观金银两种三明治结构中耦联分子的SERS谱，得出存在于这两种三明治结构中的局域电磁耦合效应LSP-LSP (Localized Surface Plasmon)及LSP与宏观金银表面的表面等离子极化SPP (Surface Plamon Polartion)之间的电磁耦合效应，即LSP-SPP耦合。对于SERS的应用，我们首先研究了SERS在分子组装体方面的应用，得出分子在金属表面的吸附行为；同时利用SERS所具有的独特特征，分别研究了SERS在活体细胞以及构建适配子传感器方面的应用。具体工作如下： 1. SERS基底的构筑 采用种子调控的置换反应制备了中空的银金双金属纳米结构，研究了探针分子在其上的SERS效应; 采用静电组装的方法在玻碳表面构筑了具有SERS活性的银纳米簇；在水汽界面构筑了具有高SERS活性的二维金纳米阵列及金纳米棒的聚集体膜，同时研究了这些纳米结构作为SERS基底的特征。 2. SERS的电磁耦合增强机理 通过构筑金/银纳米粒子-耦联分子-银纳米粒子的三明治结构，研究了处于该结构中的耦联分子的SERS谱，得出存在于金银纳米粒子间的局域的表面等离子之间的耦合效应，即LSP-LSP电磁耦合；研究了处于宏观金/银-耦联分子-银纳米片的三明治结构中耦联分子的SERS谱，得出存在于这种三明治结构中的银纳米片的局域表面等离子共振与宏观金、银表面的表面等离子极化之间的电磁耦合效应，即LSP-SPP电磁耦合。 SERS在分子组装体方面的应用 首先通过SERS研究了硫醇类分子如4,4’-二巯基苯硫醚(4,4’-TBBT)在金表面的吸附，同时辅助其它表征手段如电化学、原子力等得出金属表面分子单层膜的吸附行为；通过SERS研究了该分子在银电极及银溶胶表面吸附行为的差异，得出该分子在银电极及银溶胶表面不同的吸附取向。 4. SERS在生物分析中的应用 利用SERS所具有的独特的特征，研究了染料分子在银纳米粒子上的SERS光谱及其作为光学探针在活体细胞中的应用；通过对纳米金进行适配子及Raman探针的标记构筑了对蛋白进行高灵敏度及选择性识别的SERS的适配子传感器。

基于二维表面等离子体激元的微结构

在介电常数符号相反的两个材料的界面处可激发出表面等离子体激元（Surface plasmon)。文中利用普通扫描电子显微镜中出现的电子束诱导沉积纳米碳基本现象，提出和发展了一种无需光刻胶和额外掩模的亚微米图形化技术。采用这一新方法，成功地在镀金的半导体InGaAlP量子阱表面制备了各种亚微米点阵结构，并得到基于二维表面等离子体激元的可见波段半导体发光的增强作用。

Spatial Mode Selection by the Phase Modulation of Subwavelength Plasmonic Grating

The extraordinary transmission of the subwavelength gold grating has been investigated by the rigorous coupled-wave analysis and verified by the metal-insulator-metal plasmonic waveguide method. The physical mechanisms of the extraordinary transmission are characterized as the excitation of the surface plasmon polariton modes. The subwavelength grating integrated with the distributed Bragg reflector is proposed to modulate the phase to realize spatial mode selection, which is prospected to be applied for transverse mode selection in the vertical cavity surface-emitting laser.

Terahertz Quantum Cascade Laser Operating at 2.94 THz

The development of quantum cascade laser at 2.94 THz is reported. The laser structure is based on a bound-to-continuum active region and a semi-insulating surface-plasmon waveguide. Lasing is observed up to a heat-sink temperature of 70 K in pulsed mode with light power of 4.75 mW at 10 K and 1 mW at 70 K. A threshold current density of 296.5 A/cm(2) and an internal quantum efficiency of 1.57 x 10(-2) per cascade period are also observed at 10 K. The characteristic temperature of this laser is extracted to be T-0 = 57.5 K.

One-pot synthesis of silver nanoplates and charge-transfer complex nanofibers

We describe a facile one-pot process to synthesize Ag nanoplates by reducing silver nitrate with 3,3',5,5'-tetramethylbenzidine (TMB) at room temperature. The silver nanoplates were highly oriented single crystals with (111) planes as the basal planes. TMB can be readily oxidized to charge-transfer (CT) complex between TMB, as a donor, and (TMB)(2+), as an acceptor. The pi-pi interaction of the neutral amine (TMB) and diiminium structure (dication, TMB2+) result in the formation of one-dimensional CT complex nanofiber.

Ethanol-induced formation of silver nanoparticle aggregates for highly active SERS substrates and application in DNA detection

A controllable silver nanoparticle aggregate system has been synthesized by adding different amounts of ethanol to cetyltrimethylammonium bromide (CTAB) capped silver nanoparticles (Ag-nps), which could be used as highly efficient surface-enhanced Raman scattering (SERS) active substrates. This ethanol-induced aggregation can be attributed to preferential dissolution of CTAB into ethanol, which leads a partial removal of the protective CTAB layer on Ag-nps. The optical and morphological properties of these aggregates under various volumes of ethanol were explored via UV-vis spectroscopy and atomic force microscopy.

Direct dissolution of Au nanoparticles induced by potassium ferricyanide

In this work, we studied the reaction between Au nanoparticles (Au NPs) and [Fe(CN)(6)](3-) by the UV-vis absorption spectroscopy, X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy. The absorption peak of Au NPs disappeared after adding [Fe(CN)(6)](3-) and the XPS data conformed the formation of [Au(CN)(2)](-). The results demonstrated that [Fe(CN)(6)](3-) could induce the dissolution of Au NPs, where the CN- from the dissociation of [Fe(CN)(6)](3-) played an important role.

Catalytic properties of silica/silver nanocomposites

The catalytic properties of silver nanoparticles supported on silica and the relation between catalytic activity of silver particles and the support (silica) size are investigated in the present article. The silver nanoparticles with 4 nm diameters were synthesized and were attached to silica spheres with sizes of 40, 78, 105 nm, respectively. The reduction of Rhodamine 6G (R6G) by NaBH4 was designed by using the SiO2/Ag core-shell nanocomposites as catalysts. The experimental results demonstrated that the catalytic activity of silica/silver nanoparticles depends on not only the concentration of catalysts (silver) but also the support silica size. Silver particles supported on small SiO2 spheres (similar to 40 nm) show high catalytic activity. Moreover, by making a comparison between the UV-vis spectra of the catalyst before and after the catalytic reaction, we found that the position of surface plasma resonance (SPR) peak of Ag nanoparticles changes little. The above results suggested that the size and morphology of silver particles were probably kept unchanged after the reduction of R6G and also implied that the catalytic activity of silver particles was hardly lost during the catalytic reaction.