Excitation and propagation of shear-horizontal-type surface and bulk acoustic waves

This paper reviews the basic properties of shear-horizontal (SH)-type surface acoustic waves (SAWs) and bulk acoustic waves (BAWs). As one of the simplest cases, the structure supporting Bleustein-Gulyaev-Shimizu waves is considered, and their excitation and propagation are discussed from various view points. First, the formalism based on the complex integral theory is presented, where the surface is assumed to be covered with an infinitesimally thin metallic film, and it is shown how the excitation and propagation of SH-type waves are affected by the surface perturbation. Then, the analysis is extended to a periodic grating structure, and the behavior of SH-type SAWs under the grating structure is discussed. Finally, the origin of the leaky nature is explained     

Analysis of accuracy in prism coupling methods and a proposal of two simple ways for coupling to guided waves and/or for exciting surface plasmon resonance

The stationarity of the coupling spot in relation with different shapes of couplers is discussed. The accuracy in measuring the effective index by various couplers is analyzed. Two simple methods are proposed to couple light into guided waves and/or to excite surface plasmon resonance (SPR). One uses an optical block as a coupler and the incident beam falls onto it in two perpendicular directions. This method is particularly useful for exciting SPR at an interface between metal and anisotropic dielectric media, but also can be used to couple light into guided waves. Another method does not need any coupler. The incident beam is directly launched into the sample from the sustrate side. When a thin metal film is deposited on the substrate and covered either by air or another dielectric layer, SPR can be excited at the interface of metal/air of metal/dielectric. This method can be viewed as an alternative of Kretschmann configuration.     

Probing molecular junctions using surface plasmon resonance spectroscopy

The optical absorption spectra of nanometer-thick organic films and molecular monolayers sandwiched between two metal contacts have been measured successfully using surface plasmon resonance spectroscopy (SPRS). The electric field within metal-insulator (organic)-metal (MIM) cross-bar junctions created by surface plasmon-polaritons excited on the metal surface allows sensitive measurement of molecular optical properties. Specifically, this spectroscopic technique extracts the real and imaginary indices of the organic layer for each wavelength of interest. The SPRS sensitivity was calculated for several device architectures, metals, and layer thicknesses to optimize the organic film absorptivity measurements. Distinct optical absorption features were clearly observed for R6G layers as thin as a single molecular monolayer between two metal electrodes. This method also enables dynamic measurement of molecular conformation inside metallic junctions, as shown by following the optical switching of a thin spiropyran/polymer film upon exposure to UV light. Finally, optical and electrical measurements can be made simultaneously to study the effect of electrical bias and current on molecular conformation, which may have significant impact in areas such as molecular and organic electronics.     

Electrical Excitation of Long-Range Surface Plasmons in PC/OLED Structure with Two Metal Nanolayers

A current-driven source of long-range surface plasmons(LRSPs)on a duplex metal nanolayer is reported.Electrical excitation of LRSPs was experimentally observed in a planar structure,where an organic light-emitting film was sandwiched between two metal nanolayers that served as electrodes.To achieve the LRSP propagation in these metal nanolayers at the interface with air,the light-emitting structure was bordered by a one-dimensional photonic crystal(PC)on the other side.The dispersion of the light emitted by such a hybrid PC/organic-light-emitting-diode structure(PC/OLED)comprising two thin metal electrodes was obtained,with a clearly identified LRSP resonance peak.     

Propagation properties of longitudinal leaky surface waves on lithium tetraborate

Theoretical and experimental results of longitudinal leaky surface waves with a higher phase velocity than that of ordinary leaky surface waves and a low propagation loss on lithium tetraborate (LBO) are investigated in detail. They propagate along the surface with a phase velocity close to that of longitudinal bulk wave, slightly radiating two kinds of shear bulk waves (or one shear bulk wave in the case that one of two shear wave terms is uncoupled) into the solid. Most surface components of the mode consist of a longitudinal wave term and an electromagnetic wave term. The detailed propagation properties of the longitudinal leaky surface waves on LBO with the Euler angles (phi, theta, 90 degrees ) are investigated theoretically and experimentally. The (011) cut of LBO was found to be desirable for higher frequency SAW devices. One of the reasons why that mode on LBO has a low propagation loss is also discussed.     

Photoluminescence emission through thin metal films via coupled surface plasmon–polaritons

We present experimental results showing the variation in photoluminescence from an organic material emitted through a thin metal film as successive dielectric overlayers are added to the far side of the metal. The intensity of the emission from the structure is examined as the surface plasmon–polariton (SPP) modes associated with the two metal surfaces evolve with increasing overlayer thickness from individual to coupled SPP modes. The SPP modes are scattered to produce light by the addition to the metal film of wavelength-scale periodic microstructure. We show that the addition of a dielectric overlayer of an appropriate thickness to the metal film is accompanied by an increase in the intensity of the emission by a factor of 3 over a similar structure with no dielectric overlayer, and by a factor of 50 over a similar planar structure. We show that this increase in emission is mediated via coupled SPP modes.     

金属光子晶体薄膜可见光和微波波段传输性能

一维金属光子晶体薄膜是由金属-介质多层结构组成的等效均匀的各向异性超构材料。相比单层金属膜层,该结构在色散调控方面具有更多的自由度。在该结构中由于表面等离子体激元(SPP)的存在,可实现倏逝波的定向传输。在本文中,等效介质理论、时域有限元差分法(FDTD)的计算结果和实验结果都表明,传输倏逝波的波长、频宽和强度可通过金属光子晶体结构调整实现主动设计。金属膜厚比例越小,传输波长的中心和截止波长越长,频带越宽。当金属膜层厚度小于SPP穿透深度时,可获得宽频段的倏逝波的传输。同时,对金属光子晶体在微波波段的传输性能也进行了研究,发现其在微波波段等效介电常数为负,具有良好的反射性能。该结构的屏蔽效能远大于厚度相近的ITO薄膜的电磁屏蔽效能。在厚度只有几百纳米时,该结构即可实现良好的电磁屏蔽效能。通过金属光子晶体薄膜可实现电磁屏蔽材料的薄膜化、轻质化和可视化。     

Optical configuration for unpolarized ultra-long-range surface-plasmon-polariton waves

Multilayered structures were designed on both sides of a thin silver film to let both transverse-magnetic- and transverse-electric-polarized electromagnetic waves propagate along a thin metal film simultaneously in the same configuration, as so-called long-range surface-plasmon-polariton (LRSPP) waves. Based on the admittance analysis and design, the propagation length of an unpolarized LRSPP wave can be extended by more than 1 order of magnitude compared with previous results.     

Role of surface profiles in surface plasmon-polariton-mediated emission of light through a thin metal film

We show that the emission of light mediated by surface plasmon-polaritons through a thin metal film depends sensitively on the profile of the grating structure used to couple the surface plasmon-polariton modes to light. In particular, we show that when the emission of light takes place through a metal film, a non-conformal geometry for the two surfaces of the metal film is to be preferred. Our results may be important in the design of devices such as organic light-emitting diodes.     

Explosive collapse of vapor film under conditions of intensive heat fluxes

The stability is investigated (linear and nonlinear analysis) of the interface between a thin vapor film and a layer of liquid in the presence of a steady heat flux from a metal surface heated to a high temperature to the vapor film and then from vapor to subcooled liquid. In view of thermal disequilibrium which takes into account the temperature dependence of saturation pressure, boundary conditions on the vapor-liquid interface are derived, which generalize the known correlations on the free surface of liquid in the gravity field. A number of new effects arise in the problem under consideration, as distinct from the classical problem. The thermal processes, which occur on the phase boundary and are possible in the absence of the force of gravity as well, lead to the generation of weakly decaying periodic waves of low amplitude, whose velocity may exceed significantly that of gravity waves. The heat flux through the interface may cause on this surface periodic waves of small length (ripple) which are not capillary. The processes of phase transition on the interface are capable of providing for the stability of vapor film under the layer of liquid in the gravity field. Along with periodic waves and solitons, the mode of explosive instability may arise in the nonlinear stage because of a weak variation of the film thickness, where the amplitude of an initially low-amplitude plane wave rises to infinity during a finite period of time.     

Simple recurrence matrix relations for multilayer anisotropic thin films

Generalized Abelès relations for one anisotropic thin film [E. Cojocaru, Appl. Opt. 36, 2825-2829 (1997)] are developed for light propagation from an isotropic medium of incidence (with refractive index n(0)) within a multilayer anisotropic thin film coated onto an anisotropic substrate. An immersion model is used for which it is assumed that each layer is imaginatively embedded between isotropic gaps of zero thickness and refractive index n(0). This model leads to simple expressions for the resultant transmitted and reflected electric field amplitudes at interfaces. They parallel the Abelès recurrence relations for layered isotropic media. These matrix relations include multiple reflections while they deal with total fields. They can be applied directly to complex stacks of isotropic and anisotropic thin films.     

陷光结构在GaAs薄膜太阳电池中的应用

陷光结构由于其独特的光学特性,在光伏器件中发挥的作用越来越重要。目前硅基太阳电池中陷光结构的应用很常见,然而在GaAs薄膜太阳电池中陷光结构的报道并不多。详细介绍了陷光结构的原理及其在GaAs薄膜电池中的研究现状和应用情况。综述了GaAs薄膜太阳能电池中常用的三类陷光结构:正面陷光结构(包括纳米颗粒、纳米线、纳米锥等)、背面陷光结构(如镜面背反射层)以及混合陷光结构。大量研究表明,陷光结构的使用可以进一步提高GaAs薄膜电池的光电转换效率,一定程度上达到降低电池生产成本的目的。     

Propagation of longitudinal leaky surface waves under periodic SiO (2)/Al structure on Li(2)B(4)O(7) substrate

The properties of longitudinal leaky surface waves (LLSW) under a periodic SiO(2)/Al structure on Li(2)B(4)O (7) (LBO) substrate, were investigated theoretically and experimentally, in order to improve the high propagation losses of LLSWs under a periodic Al grating with the normalized thickness over 2%. In the theoretical analysis, the previously presented method based on the boundary integral equations for the periodic metal grating structure on the substrate was extended to include the dielectric layer. In the experiments, devices with Al electrodes recessed into a SiO(2) groove on LBO were fabricated, and the propagation losses of them were estimated. As a result, it was shown that, when the surface of the structure was flattened, the propagation losses were sufficiently low and the first Bragg stopband width decreased.     

纳米多孔光波导漏模共振传感器的折射率灵敏度分析(英文)

在玻璃基片上射频溅射50 nm厚的金膜,然后利用TiO2胶体溶液在金膜表面制备了厚度约为320 nm的TiO2纳米多孔薄膜.以此双层膜为漏模光波导芯片,构建了基于Kretschmann结构的波长调制型光波导漏模共振(LMR)传感器.利用扫描电子显微镜(SEM)观测了TiO2纳米多孔薄膜的表面和横截面形貌.实验研究了在纳米多孔光波导中给定漏模的共振波长及折射率灵敏度与入射角的依赖关系.结果表明,随着入射角的增大,共振波长逐渐蓝移,折射率灵敏度随之下降.此外,与传统的表面等离子体共振(SPR)传感器进行了对比,结果表明在相同的共振波长下,纳米多孔光波导LMR传感器折射率灵敏度大于SPR传感器.     

Characteristic parameters of surface acoustic waves in a periodic metal grating on a piezoelectric substrate

The coupling problem between electrodes due to the propagation of acoustic waves in a periodic metal grating on a piezoelectric substrate is theoretically studied. A method for the determination of the mutual admittance between the grating electrodes is presented, and an analytical expression for the contribution of surface acoustic waves (SAWs) is proposed. The SAW characteristic parameters are determined with a numerical technique that is able to deal with a leaky SAW as well as a true SAW (conventional Rayleigh type or Bleustein-Gulyaev type). Using this technique, the SAWs' contribution to the mutual admittance can be removed, and the analysis of other contributions becomes possible. In particular, the amplitude decay rate of the residual mutual admittance with electrode separation gives information about the propagation of the surface skimming bulk waves (SSBWs). The method presented is applied to several currently used material-cut configurations.     

Acoustic microscopy measurement of elastic constants and massdensity

A method is presented to determine the elastic constants and the mass density of isotropic and anisotropic solids and anisotropic thin films. The velocity and attenuation of leaky surface acoustic waves (SAWs) have been obtained for specified propagation directions from V(z) curves measured by line-focus acoustic microscopy (LFAM). The experimentally obtained velocities have been compared to velocities obtained from a measurement model for the V(z) curve which simulates the experiment. Since the measured and simulated V(z) curves have the same systemic errors, the material constants are free of such errors. For an isotropic solid, Young's modulus E, the shear modulus G and the mass density ρ have been determined from the leaky Rayleigh wave velocity and attenuation, measured by LFAM, and a longitudinal wave velocity measured by a pulse-echo transit-time technique. For a cubic-crystalline solid, the ratios of the elastic constants to the mass density (c₁₁ /ρ, c₁₂/ρ, c₄₄/ρ) have been determined from the directional variation of measured SAW velocities, using a preliminary estimate of ρ. The mass density ρ has subsequently been determined by additionally using the attenuation of leaky SAWs in crystal symmetry directions. For a cubic-crystalline thin film deposited on a substrate, the elastic constants and the mass density (c₁₁, c₁₂, c₄₄, ρ) of the film have been determined from the directional variation of the measured SAW velocities, and a comparison of the corresponding attenuation coefficient with the measured attenuation coefficient has been used to verify the results     

Acoustic waves in bounded anisotropic media: theorems, estimations, and computations

This paper discusses some basic achievements in theoretical studies on acoustic wave propagation along boundaries in anisotropic solids. In particular, the following issues are reviewed: existence theorems for subsonic surface and interface waves, leaky surface acoustic waves (SAW) and their relation to "supersonic" SAWs and fast exceptional bulk waves, the resonance reflection of bulk waves in the vicinity of leaky wave branches. General conclusions are illustrated by numerical examples.     

Substrate-assisted laser desorption of neutral peptide molecules.

The ultraviolet (248-nm) laser desorption of neutral peptide molecules is found to be greatly enhanced by applying a thin layer of the sample (500 monolayers) on top of an ultraviolet-absorbing organic substrate, sinapinic acid. With this sample preparation, peptides as large as gramicidin S are desorbed as intact neutral molecules. The samples are examined with laser desorption/chemical ionization (LD/CI) Fourier transform mass spectrometry. The neutrals desorbed by this method have approximately 1 eV less internal energy than those desorbed directly from a metal film surface. The organic substrate aids the desorption of neutrals when the laser wavelength is not strongly absorbed by the peptide sample (248 nm), but is not effective in aiding the desorption of neutrals when the laser wavelength is strongly absorbed by the sample (193 nm).     

光信息存储量与真空技术

任何一种ＤＶＤ光盘都是由信息记录层、介质保护层、金属反射层．．．．．．等薄膜组成的二层、三层或多层光匹配的薄膜体系。不同膜系要用不同的真空淀积技术制备,各制备单元最终连成完整的光盘生产线。本文着重讨论各类光盘薄膜材料的真空淀积技术和相应的生产线,旨在探讨光盘生产线国产化的前景。     

Transverse surface waves in a piezoelectric material carrying a gradient metal layer of finite thickness

The existence and propagation behavior of transverse surface waves in a layered structure concerning a piezoelectric substrate and a gradient metal layer are theoretically investigated in this paper. The Wentzel-Kramers-Brillouin (WKB) method is applied to obtain the analytical solutions in the gradient metal layer. The dispersion equation for transverse surface waves in such structure is obtained in a quite simple mathematical form, where the material gradient of the metal layer assumes arbitrary functions. Effects of material gradient on three types of dispersion behavior are discussed in detail based on a proper classification. Numerical results show that the material gradient in the metal layer evidently affects the fundamental mode shape of the transverse surface waves but has negligible effects on the higher order modes.