金属表面等离体子振荡

深入浅出地分析了金属表面等离体子振荡形成的机理，利用拉普拉斯方程得到了半无限金属、金属薄膜和球状纳米金属颗粒的表面等离体子振荡频率。     

Effect of interfacial alloying on the surface plasmon resonance of nanocrystalline Au-Ag multilayer thin films

Nanocrystalline Au and Ag in multilayer thin film form with Au/Ag/Au structure were prepared by high pressure (∼40 Pa) d.c. sputtering techniques. The Ag concentrations in Ag_xAu_1-x films were changed from x = 0 to 1. These multilayer films with varying Ag concentration showed significant changes in microstructures obtained from TEM and XRD analyses. The optical absorption spectra of these multilayer films showed a single plasmon band confirming the formation of Au-Ag alloy. We ascribe this alloying to the interfacial reactions in nanophase limited at the Au-Ag interface. The red-shift and broadening of the plasmon bands with the increase in silver concentration could be associated to the increase in size of the nanoparticles and its distribution. The observed red shift in the plasmon band may be associated with the change in electronic structure at the Au-Ag interface due to configuration mixing of the atomic energy levels of Au and Ag. Received 17 October 2002 / Received in final form 26 February 2003 Published online 23 May 2003 RID="a" ID="a"e-mail: msakp@mahendra.iacs.res.in     

Multipole surface plasmon resonance of an aluminium surface

The surface photoelectric effect and the surface plasmon resonances appear when a p/transverse magnetic polarized laser hits a gas-solid interface. We model this effect in the long wave length (LWL) domain (λ_vac > 10 nm, ?ω < 124 eV) by combining the Ampère-Maxwell equation, written in classical approximation, with the material equation for the susceptibility. The resulting model, called the vector potential from the electron density (VPED), calculates the susceptibility as a product of the bulk susceptibility and the electron density of the actual system. The bulk susceptibility is a sum of the bound electron scalar susceptibility taken from the experiment and of the conduction electron non-local isotropic susceptibility tensor in a jellium metal (Lindhard, 1954 [1]). The electron density is the square of the wave function solution of the Schrödinger equation. The analysis of observables, the reflectance R and the photoelectron yield Y as well as the induced charge density permits to identify and characterize the multipole surface plasmon resonance of Al(111) appearing at ω_m ∼ 0.8ω_p or 11-12 eV.     

Surface plasmon resonance biosensor modified with multilayer silver nanoparticles films

We alternately deposited negatively charged Ag-(3-mercaptopropionic acid) (Ag-MPA) sol and positively charged poly-(diallyldimethylammonium) (PDDA) on gold substrate modified with 4-aminothiophenol (4-ATP), through electrostatic layer-by-layer (LBL) self-assembly. We characterized the prepared three-dimensional Ag/PDDA multilayer films by surface plasmon resonance (SPR) and atomic force microscope (AFM). The thickness of each film in the multilayer films, the deposition effect of Ag nanoparticles, and the processing of DNA adsorption are characterized by SPR. AFM characterization shows that DNA/3(PDDA/Ag)/4-ATP composite is uniformly and firmly distributed on the surface of gold films. Compared with other sensors, gentamicin could be highly sensitively measured by DNA/3(PDDA/Ag)/4-ATP/Au sensor. There is a good linear relationship in the concentration range of 5 × 10⁻⁸ to 1 × 10⁻⁴ mol/L. The linear equation is found to be Δθ_SPR = 1.3521 × 10⁻⁵c + 0.08641 (the correlation coefficient is 0.9983) with detection limit of 1 × 10⁻⁹ mol/L. Since such LBL assembly film is simple to prepare, the work described here provides an effective method for studying small molecule drugs on SPR.     

表面等离子体共振技术的一些新应用

介绍了表面等离子体共振技术在表面等离子体共振传感器、扫描近场光学显微技术、薄膜光学和膜厚测量、全息成像技术、Q开关、精密角度测量等领域的新应用.     

Effect of surface roughness on surface plasmon resonance absorption

The absorption of light by surface plasmons has been studied using the method of attenuated total reflection. The reflectance from a quartz-Ag interface has been measured as a function of angle and surface structure for the wavelength region from 3600 to 6000 . It is shown that the reflectance minimum for a smooth Ag film is changed in both angular position and spectral half-width by roughening the Ag surface with CaF₂ underlayers. Dispersion curves are presented which show that the wave vector of a surface plasmon propagating on an irregular surface is greater than that of an equally energetic surface plasmon propagating on a planar surface.     

Polarization modulation spectroscopy of surface plasmon resonance

The features of surface plasmon resonance in gold nanofilms deposited on the surface of a total-internal-reflection prism have been investigated theoretically, using the Fresnel equation, and experimentally, with application of the polarization modulation technique. The angular characteristics of the polarization difference of the reflection coefficients for s-and p-polarized light, Δρ = R _s ² ? R _p ² , were measured in the wave-length range λ = 0.4–2.0 μm. It is shown that the characteristics of Δρ, in contrast to the results of standard measurements by the surface plasmon resonance method, have a resonance peak. Due to this, the characteristics of the polarization difference contain nonresonant components whose magnitudes are determined by the internal reflection coefficients for the metal and insulator; these parameters depend on the film thickness. The calculated and experimental data coincide when the model assumes exponential dependence of the refractive indices and extinction coefficients on the thickness of the metal film. It is established that the characteristic parameter of the exponential is a metal film thickness of 11.0 ± 0.5 nm, at which the film optical parameters correspond to the bulk characteristics.     

The surface ace plasmon resonance effect in holography

A hologram has been made using a surface plasmon resonance wave as the reference beam. The surface wave was stimulated on a 1200-line/mm aluminum reflection grating that was coated with a thin layer of high resolution photographic emulsion. Experimental results are presented.     

Evanescently coupled resonance in surface plasmon enhanced transmission

The optical transmission through subwavelength holes in metal films can be enhanced by several orders of magnitude by enabling interaction of the incident light with independent surface plasmon (SP) modes on either side of the film. Here, we show that this transmission is boosted by an additional factor of 10 when the energies of the SP modes on both sides are matched. These results, confirmed by a three-dimensional theoretical analysis, give a totally new understanding of the phenomenon of SP enhanced transmission. It is found that the holes behave like subwavelength cavities for the evanescent waves coupling the SPs on either side of the film. In this unusual device, the reflection at either end of the cavity is provided by the SP modes which act as frequency dependent mirrors.     

Humidity sensor based on localized surface plasmon resonance of multilayer thin films of gold nanoparticles linked with myoglobin

Layer-by-layer self-assembled multilayer thin films of gold nanoparticles (GNPs) linked with myoglobin (Mb) show substantial sensitivity to humidity at room temperature according to measurements of localized surface plasmon resonance (LSPR) absorption that relies on the interparticle interaction present in the film. The sensor response is reversible, with response and recovery times as low as 5 s. The sensing mechanism is as follows: as the ambient humidity changes, Mb molecules change their size, making the GNP-to-GNP spacing and thereby the interparticle interaction change; the change in the interparticle interaction causes a change in the LSPR absorption of the multilayer thin film. We found that the LSPR band of the multilayer thin film was almost insensitive to both the surrounding refractive index and the adlayer thickness, rendering the multilayer-film-based humidity sensor highly immune to ambient disturbances.     

Distributed optical fiber surface plasmon resonance sensors

The relationships of the resonant wavelength of optical fiber surface plasmon resonance (SPR) sensors to the modulation layer refractive index, thickness and the refractive index of the bulk medium are obtained by using theoretical calculation model of optical fiber SPR sensors under certain conditions, which indicates that resonant wavelength of the sensors is approximately linear with modulation layer thickness. Based on the linear relationship, multiple SPR sensors with different resonant wavelengths can be fabricated in a single optical fiber named as distributed optical fiber surface plasmon resonance sensors (DOFSPRSs).Experimental results are presented, showing that it is practical to fabricate more than one SPR sensors in a single optical fiber.     

准晶体结构光纤表面等离子体共振传感器特性研究

光纤表面等离子体共振传感器在高灵敏度传感和在线实时监测等领域具有重要意义. 设计了一种六重准晶体结构环形通道光纤表面等离子体共振传感器, 基于有限元法对该传感器的传感特性进行了数值模拟. 研究了光纤各结构参量对传感器特性的影响规律. 研究结果表明: 待测液折射率的有效监测范围为1.25–1.331, 最高灵敏度可达26400 nm·RIU^-1, 传感器具有损耗谱杂峰少、探测范围广、灵敏度高、设计灵活性高和光路可弯曲等特点, 在生化检测、公共安全、环境污染监测以及高灵敏度传感等领域具有广泛的应用前景.     

Thermal tuning of surface plasmon resonance: Ag gratings on barium strontium titanate thin films

Surface plasmon tuning via thermally induced refractive index changes in ferroelectrics is investigated. Epitaxial (Ba_0.7Sr_0.3)TiO₃ (BST) thin films were deposited on MgO (001) substrates by pulsed laser deposition. The refractive index of BST thin films measured by the prism-coupling technique was found to increase from 2.3932 (TE)/1.9945 (TM) at room temperature to 2.3949 (TE)/1.9965 (TM) at 66°C. Then 30-nm-Ag gratings with periodicity 750 nm and width 300 nm were fabricated on BST by soft ultraviolet nanoimprint lithography and subsequent lift-off process. The reflection spectra from 500 to 1000 nm with incident angle from 5° to 60° were measured at room temperature and 66°C, with a collimated and p-polarized light incident perpendicularly to the grating direction. Several modes were observed from the spectra. At 66°C, a red shift of a dip at about 850 nm by 2 nm was obtained at an incident angle of 15°. Calculations confirmed that the observed modes belong to the (−1), (2), (−2) and (3) surface plasmon modes from the Ag and BST interfaces and localized mode; the red shift by thermal tuning is also confirmed. The results indicate the feasibility of active modulation in surface plasmon resonance in solid-state structures.     

Surface plasmon resonance detection using amorphous carbon/Au multilayer structure

Surface plasmon resonance (SPR) can be used to detect the change in reflective index on a metal surface. In this report, we propose detection of the SPR can easily be applied to estimate the thickness of the amorphous carbon (a-C:H) films. To detect changes in film thickness using SPR, devices with an a-C:H/Au structure were fabricated. The a-C:H films were deposited by electron cyclotron resonance plasma chemical vapor deposition (ECR-CVD) and sputtering, and the obtained film densities were 1.4 and 1.6 g/cm³, respectively. By the deposition of an 11-nm thick a-C:H film on a Au layer by sputtering, the SPR angle changed from 44.90° to 47.05°. For a-C:H deposited by ECR-CVD, the SPR angle was shifted from 44.24° for Au without the a-C:H layer to 58.44° after deposition of 45 nm thick a-C:H film. In both systems of the SPR angle increased with increasing the film thickness. The rate at which the SPR angle shifted depended on the a-C:H film density. These results show that the thickness of an a-C:H film can be determined by the SPR angle shift on an a-C:H layer using a-C:H/Au device with an a-C:H film of the same density.     

The surface plasmon resonance of metal-film nanohole arrays

In this paper we investigated the enhanced transmission and surface plasmon resonance through a thin gold film with a periodic array of subwavelength nanoholes. Both freestanding gold-film nanohole arrays and gold-film nanohole arrays deposited on a gallium arsenide (GaAs) substrate are considered. Periodic arrays of nanoholes exhibit two different surface plasmon resonance features: localized waveguide resonance and the well-recognized photonic crystal resonance. The tangential electric field component $Ey$ is nonzero only in the hole region for a freestanding gold-film nanohole array, but it can exist in the hole region and in the metallic region for a gold-film nanohole array deposited on a GaAs substrate.     

半壳结构金纳米膜的局域表面等离子体共振效应

采用纳米模版印刷术和化学自组装技术制备了半壳结构的金粒子膜.利用场发射扫描电子显微镜和光谱仪等测试手段对样品的结构和光学性质进行了分析.研究发现，该结构的金膜所具有独特的局域表面等离子体共振效应取决于样品的粒子大小、间距等微观结构，且其峰值吸收波长对其周围环境介质的介电常数变化十分敏感.实验结果表明，粒子排列均匀的亚单层膜结构是控制光学性质稳定的关键. 关键词： 局域表面等离子体共振 半壳结构 纳米模版印刷术     

Real-time phase-shift detection of the surface plasmon resonance

We have investigated a method to directly measure the phase of a laser beam reflected from a metallic film after excitation of surface plasmon polaritons. This method permits real-time access to the phase information, it increases the possible speed of data acquisition, and it may thus prove useful for increasing the sensitivity of surface plasmon based sensors.     

Low-cost,high performance surface plasmon resonance-compatible films characterized by the surface plasmon resonance technique

A new analytical method based on the surface plasmon resonance (SPR) technique is presented, with which SPR curves for both wavelength and angular modulations can be obtained simultaneously via only a single scan of the incident angle. Using this method, the SPR responses of TiO2-coated Cu films are characterized in the wavelength range from 600 nm to 900 nm. For the first time, we determine the effective optical constants and the thicknesses of TiO2-coated Cu films using the SPR curves of wavelength modulation. The sensitivities of prism-based SPR refractive index sensors using TiO2-coated Cu films are investigated theoretically for both wavelength and angular modulations, the results show that in the case of sensitivity with wavelength modulation, TiO2-coated Cu films are not as good as the Au film, however, they are more suitable than the Au film for SPR refractive index sensors with angular modulation because a higher sensitivity can be achieved.     

Collective surface plasmon resonance coupling in silver nanoshell arrays

Collective surface plasmon resonance (SPR) excitations in an ordered array of silver nanoshells have been theoretically studied using generalized Mie theory. Near- and far-field radiative coupling between the nanoshells in the array result in a non-monotonic shift of the collective SPR band. When the distance between the shells in the array approaches that of the collective SPR wavelength, we observe narrowing of the collective SPR band due to constructive interference between the scattered electric field from the particles in the array. Further increase of the distance between the nanoshells in the array leads to destructive interference and broadening of the collective SPR band.     

Tunable local surface plasmon resonance in liquid-crystal-coated Ag nanoparticles

The far-field and near-field properties of a spherical nematic liquid crystal (NLC) coated metal nanoparticle (NPs) have been investigated in an external field, basing on the quasistatic theory. The resonant wavelength is tunable by varying metallic material of core, anisotropy extent and thickness of liquid crystals (LCs). The field enhancement is along the incident polarization near the outer surface of the shell. The direction of field is reverse in the inner surface comparing with the one if outer shell. In contrast to isotropy shell, the surface plasmon resonance (SPR) shows an obvious red shift and field enhancement near outer surface of the shell always is stronger.