SURFACE EXCITATION PARAMETER IN QUANTITATIVE SURFACE ANALYSIS BY ELECTRON SPECTROSCOPY

The investigation of influence of surface effects on the energy spectra of electrons is essential for comprehensive understanding of electron-solid interactions as well as quantitative analysis. The accuracy of the analysis depends on the models for elastic and inelastic interactions. Electrons impinging on a solid or escaping from it suffer losses in the surface layer. The energy loss spectra therefore have contributions from surface excitations. The role of surface excitations is characterized by surface excitation parameter (SEP), which indicates the number of surface plasmons created by an electron crossing the surface. The imaginary part of complex self-energy of an electron is related to the energy.‘ loss cross section. SEP is numerically computed using self-energy formalism and compared with the results as described and calculated by different workers.     

表面等离子体激元增强薄膜太阳电池研究进展

表面等离子体激元共振是金属纳米结构非常独特的光学特性,对基于表面等离子体激元共振的纳米结构体系的研究已形成了一门新兴的学科,即表面等离子体光子学。可以利用金属纳米颗粒光散射、近场增强以及高度局域的表面等离子体极化激元增强薄膜太阳电池光吸收,提高电池转换效率。当前,表面等离子体光子学应用于太阳电池的设计已成为国际上光伏研究迅猛发展的一个热点。文章主要介绍表面等离子体激元增强薄膜太阳电池光吸收的原理及其在光伏器件中应用的最新研究进展。     

金属复合结构的反常透射增强效应的数值分析

利用全矢量的三维时域有限差分法,分析了一种金属银复合结构的反常透射增强效应.该结构是在一层打有六角排列的圆孔阵列的金属银层的上方放置一层六角排列的银圆环阵列构成.与普通的单层银打孔阵列相比,该结构明显具有更高的透射峰值和更窄的透射带宽.系统分析了结构的场强分布、坡印廷矢量能流分布图、透射峰的频率色散关系,结果表明该复合结构激发的更强的独特的表面等离激元模式主导了整个透射过程.     

角度指示型表面等离子共振传感器的研究

表面等离子体共振(SPR)技术被广泛应用于生物化学传感、药物分析和环境监测等领域。现基于表面等离子共振原理,在固定入射光波长为632.8nm的He-Ne激光入射下,采用镀有50nm银膜的Kretschmann棱镜型结构作为耦合器件,实现角度指示型SPR传感器对纯净水和酒精水溶液的检测。实验结果发现该SPR传感器具有较好的稳定性,其角度灵敏度达到219°/RIU。     

纯金膜表面等离子增强的旋光效应

为了研究棱镜的磁光特性对系统光学响应的影响,测试了单个BK7棱镜在全内反射条件下的旋光角度谱以及BK7棱镜与金膜组合构成Kretschmann结构的旋光角度谱,并根据传统光学理论分析了光谱的成因.理论分析结果表明:在单个BK7棱镜构成的全内反射结构中,棱镜底部对p波和s波产生的反射系数差异是导致系统进入全内反射临界角之前产生较强旋光效应的主要原因;在BK7棱镜与金膜组合构成的Kretschmann结构中,棱镜的磁光特性使得光波到达金膜表面之前产生了较小的s光分量,金膜表面等离子共振激发削弱了p光振幅,两种因素结合产生了一种新的表面等离子共振增强磁光效应的物理机制.实验结果表明:Kretschmann模式下,26 nm厚金膜的表面旋光角最大为1.7°,克服了传统磁光克尔效应响应较弱的缺点.     

Low energy electron induced characteristic losses in the Fe73.6Cu1Nb2.4Si15.8B7.2 (FINEMET) alloy surface

Electron Energy Loss Spectroscopy has been employed for investigation of the electronic states of amorphous and crystalline Fe_73.6Cu₁Nb_2.4Si_15.8B_7.2 (FINEMET) alloy surface and alloy components. Electron energy losses have been measured for primary electron beam energies E₀ from 150 to 650 eV. The characteristic energy loss spectra were composed of main peaks which we have interpreted due to surface and bulk plasmons, a combination of surface and bulk losses, high harmonics of plasma losses, inter-band transitions and ionization of core levels. The measured energies for the plasmon excitations were found not to agree with calculated values according to the classical theory for the collective oscillations in solids. Changes in the intensity lines of the surface and bulk plasmons were observed for all specimens depending on primary electron energy E₀. The present results are compared with characteristic energy loss data reported in the literature.     

Thermo-induced plasmon excitations in the near surface region of ternary Co-Cr-Mo alloy

Electron Energy Loss Spectroscopy has been employed for investigation of the surface and bulk plasmon excitations versus heating in the Co-Cr-Mo alloy surface for the primary electron beam energies Е₀ ranging from 150 to 800 eV. For the annealed alloy the experimental values of the plasmon energy are localized at more energies as compared to the non-annealed alloy. It was established that heating of the alloy promotes to insignificant deviations of the plasmon excitations. Damping of the intensity line of surface plasmon with a increase of heating was established. Physical processes which can influence on the energy displacements of long wavelength plasmon oscillations and damping of surface plasmon in the characteristic loss spectra at heating are considered.     

In situ optical spectroscopy during deposition of Ag:Si3N4 nanocomposite films by magnetron sputtering

In situ and real time surface differential reflectance (SDR) spectroscopy is employed to study the growth of metallic Ag and/or dielectric Si₃N₄ films during deposition by magnetron sputtering. The measurements during Si₃N₄ sputtering allow determining both the refractive index and the deposition rate. During Ag sputtering, the SDR presents a maximum in the visible range, typical of a surface plasmon resonance (SPR) indicating the 3D growth of silver nanoclusters. After a certain deposition thickness, the SDR change corresponds to a continuous layer growth and allows determining the Ag deposition rate. During Ag/Si₃N₄ alternate deposition, the SDR spectroscopy enables to follow the SPR modifications (position, amplitude and width) not only during the formation of the Ag nanoclusters but also during their capping by a Si₃N₄ matrix and during intermediate steps (holding time after the silver sputtering, Si₃N₄ target ignition and pre-sputtering before the Si₃N₄ deposition) where significant changes are detected. It suggests possible nanocluster reshaping or physicochemical processes occurring at the nanocluster interface during the different steps.     

金纳米颗粒在石英基片上的表面等离子激元效应研究

采用磁控溅射法制备了金纳米颗粒,分别用扫描电子显微镜(SEM)、X射线衍射仪(XRD)和紫外可见分光光度仪(UV-Vis)对其形貌、结构和光谱响应进行性能表征,研究其表面等离子激元效应。结果表明,直接在石英基片上溅射制备的金纳米颗粒并未产生表面等离子激元效应;在石英基片上组装单层排列均匀的Si O2微球后,溅射制备的金纳米颗粒结构产生了明显的表面等离子激元效应;溅射功率和时长对这一效应影响明显,40 W功率溅射2~3 min所得样品吸收峰较强。     

Directional emission of surface-enhanced Raman scattering based on a planar-film plasmonic antenna

A planar-film plasmonic antenna for surface-enhanced Raman scattering (SERS) with good emission directivity (divergence angle < 3°) was realized on a Kretschmann prism configuration with Raman-active analytes as emitters. The simulated results of finite-difference time-domain method show the emission efficiency, the directivity and the gain of the planar-film antenna were expected to be 50%, 300 and 22 dB, respectively. Angle-resolved spectroscopy was used to characterize its properties in SERS. The experimental results show that the SERS signal of analytes was remarkably enhanced when a laser excited this planar-film plasmonic antenna at the resonance angle. Meanwhile, the radiation of SERS was concentrated in a small region in space. The planar-film antenna with high gain coefficient can be a promising light harvesting and emitting device. The good emission directivity allows high collection efficiency. This advantage opens up interesting prospects in the applications for plasmon-enhanced spectroscopy and single-phonon detections.