表面等离子共振效应中传统近似理论与薄膜光学理论

指出Kretschmann模型的传统表面等离子共振公式在求解金属薄膜的参量时存在近似性,采用更为严密的薄膜光学理论,通过薄膜膜系的特征矩阵,得出表面等离子体共振衰减曲线.结果表明,表面等离子体共振近似理论与薄膜光学理论得到的共振角及反射率幅度存在差别;采用等高线图,给出了共振角差随着金属介电常量的变化规律.进一步的实验表明,薄膜光学理论所得模拟结果较表面等离子体共振近似理论与实验值吻合地更好,证明薄膜光学理论应用在表面等离子体共振效应要优于常用的近似理论.最后,采用两种理论对表面等离子体共振传感器进行优化设计,结果表明,两种理论所获得的高灵敏度分布区域差异较大,必须采用薄膜光学理论提供更精确的薄膜参量,来优化设计高灵敏度表面等离子体共振传感器.     

Characterization of gold films by surface plasmon spectroscopy: Large errors and small consequences

Evaporated gold films have a smooth interface with their substrate and a rougher top surface. We investigate the optical response of such a film by excitation of surface plasmons both on the rough and on the smooth side. The smooth side, although polycrystalline, has an optical response that is very similar to a monocrystalline surface. The film can be modeled as two-layers with significantly different optical constants. For investigations on thin dielectric films though, this heterogeneity introduces only a negligible error.     

膜层厚度对金属薄膜光学常数的影响

从麦克斯韦方程出发,可以得到超薄金属膜层光学常数n、k与其厚度有关系的理论依据。采用电阻热蒸发和电子束热蒸发的方法在K9玻璃基底上分别沉积了不同厚度的Cu膜、Cr膜、Ag膜,由椭偏法检测、Drude模型拟合,获得了不同厚度Cu膜、Cr膜、Ag膜光学常数n、k随波长λ的变化规律。超薄金属薄膜与块状金属的光学常数相差较大,随着薄膜厚度的增加,n、k值趋近于块状金属。通过对样品膜层吸收、色散特性的分析,发现连续金属薄膜在可见光波段对长波的吸收较大,而且相比于介质薄膜平均色散率高10mn～102nm量级。     

Thermally tunable optical constants of vanadium dioxide thin films measured by spectroscopic ellipsometry

Smart materials with reversible tunable optical constants from visible to near-infrared wavelengths could enable excellent control over the resonant response in metamaterials, tunable plasmonic nanostructures, optical memory based on phase transition and thermally tunable optical devices. Vanadium dioxide (VO₂) is a promising candidate that exhibits a dramatic change in its complex refraction index or complex dielectric function arising from a structural phase transition from semiconductor to metal at a critical temperature of 70 °C. We demonstrated the thermal controllable reversible tunability of optical constants of VO₂ thin films. The optical/dielectric constants showed an abrupt thermal hysteresis which confirms clearly the electronic structural changes. Temperature dependence of dielectric constants as well as optical conductivity of sputtered VO₂ thin films was also reported and compared to previous theoretical and experimental reports.     

Investigation of interface roughness cross-correlation properties of optical thin films from total scattering losses

The interface roughness and interface roughness cross-correlation properties affect the scattering losses of high-quality optical thin films. In this paper, the theoretical models of light scattering induced by surface and interface roughness of optical thin films are concisely presented. Furthermore, influence of interface roughness cross-correlation properties to light scattering is analyzed by total scattering losses. Moreover, single-layer TiO₂ thin film thickness, substrate roughness of K9 glass and ion beam assisted deposition (IBAD) technique effect on interface roughness cross-correlation properties are studied by experiments, respectively. A 17-layer dielectric quarter-wave high reflection multilayer is analyzed by total scattering losses. The results show that the interface roughness cross-correlation properties depend on TiO₂ thin film thickness, substrate roughness and deposition technique. The interface roughness cross-correlation properties decrease with the increase of film thickness or the decrease of substrates roughness. Furthermore, ion beam assisted deposition technique can increase the interface roughness cross-correlation properties of optical thin films. The measured total scattering losses of 17-layer dielectric quarter-wave high reflection multilayer deposited with IBAD indicate that completely correlated interface model can be observed, when substrate roughness is about 2.84 nm.     

介质/金属结构太赫兹空芯光纤的传输特性

理论分析了金属、介质/金属结构空芯光纤在THz波段的模式结构和传输特性.金属空芯光纤支持TE11模式,介质/金属空芯光纤的介质膜厚在取最优值时支持HE11模式.对于波长为200μm的太赫兹波,内径为1 mm的两种空芯光纤,TE11和HE11模式的损耗分别为8.4 dB/m和2 dB/m.为优化介质/金属结构宅芯光纤的传输性能,分析了金属和介质材料的光学常数对衰减系数的影响.基于几种已发表的金属在太赫兹波段的光学常数,计算结果表明铝是最好的选择;初步测量结果显示,在各种树脂材料中聚乙烯在THz波段吸收较小,并且其折射率接近介质膜的最优值1.41,为太赫兹波空芯光纤中介质膜材料的理想选择.     

用衰减全反射(ATR)及拟合法对固体表面物理性质的研究

提出了一种利用光学中全反射衰减特性及拟合法对介质上蒸镀的金属薄膜物理性质进行研究的方法,并运用该方法对金属薄膜的厚度和复介电常量进行了精确测定,该方法是研究固体表面物理的一种有效的方法和技术.     

Detection of nano-interfacial space charge field at metal–organic film interface by SHG and surface potential

At the metal–organic film nano-interface, surface polarization phenomena are observed, due to the displacement of excess charges from metal to the films as well as alignment of polar dipoles. Surface potential method has been employed to examine these surface polarization phenomena, and the distribution of space charges and distribution of electronic density of states have been determined. However, for further understanding of the nanometric interface phenomena, it is very helpful to develop an experimental method that can detect electrical and optical phenomena induced by the space charge formation. In this paper, it is shown that optical second harmonic generation measurement is effective through our experiment on phthalocyanine films deposited on Al and Au electrodes.     

The determination of the thickness and the optical dispersion property of gold film using spectroscopy of a surface plasmon in the frequency domain

We propose to use wavelength modulation approach,i.e.,the spectroscopy of a surface plasmon in the frequency domain,to characterize the optical dispersion property of gold film.Using this method,we determine the dispersion relationship of gold film in a wavelength range from 537.12 nm to 905.52 nm,and our results accord well with the reported results by other authors.This method is particularly suited for studying the optical dispersion properties of thin metal films,because a series of dielectric constants over a wide spectral range can be determined simultaneously via only a single scan of the incident angle,thereby avoiding the repeated measurements required when using the angular modulation approach.     

Optical properties of composite thin films containing silver nanoparticles

Absorption and reflection of electromagnetic radiation by a composite thin film consisting of a transparent dielectric matrix with inclusions of metal nanoparticles of radius much less than the wavelength were theoretically investigated based on the Maxwell–Garnett model. The absorption, reflection, and transmission of optical radiation in such a dielectric composite film were analyzed using effective optical parameters for the refractive index and absorption coefficient that depended on the nanoparticle size.     

Enhanced dielectric constant resolution of thin insulating films by electrostatic force microscopy

Electrostatic force microscopy has been shown to be a useful tool to determine the dielectric constant of insulating films of nanometer thicknesses that play a key role in many electrical, optical and biological phenomena. Previous approaches have made use of simple analytical formulas to analyze the experimental data for thin insulating films deposited directly on a metallic substrate. Here we show that the sensitivity of the EFM signal to changes in the dielectric constant of the thin film can be enhanced by using dielectric substrates with low dielectric constants. We present detailed numerical calculations of the tip-sample electrostatic interaction in the following setup: an insulating thin film, a dielectric substrate (or spacing layer) of known low dielectric constant and a metallic electrode. The EFM sensitivity to the dielectric constant increases with the thickness of the spacing layer and saturates for thicknesses above 100-300 nm, when it is close to that of an infinite medium.     

Charge interaction in layered systems with spatial dispersion

The potential electrostatic energy of a charge near the surface of a metal with a metal or a dielectric coating (adsorbate), on the interface between metal (semimetal) and insulator (electrolyte) and in layered thin-film sandwich-type systems (MIS structures) has been calculated. The influence of the metal and the dielectric epitaxial coatings of the metal surface upon the interaction of charges is investigated. Taking into account the spatial dispersion effects, it is shown that in thin films surrounded by a medium with a large dielectric constant, the Coulomb repulsion between electrons decreases.     

A study of the thin metal film/fluid interface using surface plasmon-polaritons

Surface plasmon-polaritons have been used as the probe to study the interface between a thin polycrystalline gold film and a series of aliphatic alcohols. It is found that fitting the reflectivity data to theoretical predictions from Fresnel's equations for layered structures produces variations in both the apparent thickness and the dielectric constants of the gold film which depend on the adjacent alcohol. These variations are far greater than the experimental error and lead to the conclusion that a very thin (<0.5 nm) surface roughness layer has a significant influence on the results from this type of experiment.     

氧化铟锡薄膜的椭偏光谱研究

用溅射法在Si片上制备了厚度为140nm的氧化铟锡(ITO)薄膜。X射线衍射研究表明所制备的薄膜为多晶结构。在1.5~4.5eV范围内对ITO薄膜进行了椭偏测量。分别用德鲁德-洛伦茨谐振子(Drude Lorenz oscillators)模型、层进模型结合有效介质近似模型对椭偏参量ψ、Δ进行了拟合,得到ITO薄膜的折射指数n的变化范围在1.8~2.6之间,可见光范围内消光系数k接近于零,在350nm波长附近开始明显变化,且随着波长的减小k迅速增加。计算得到直接和间接光学带隙分别是3.8eV和4.2eV。并在1.5~4.5eV段给出一套较为可靠的、具有实用价值的ITO介电常量和光学常量。     

Nonlinear s-polarized surface plasmon polaritons

We have examined the dispersion relations for s-polarized surface plasmon polaritons, guided by (a) the interface between a semi-infinite metal and dielectric medium, and (b) a metal film bounded by semi-infinite dielectric media for situations in which one or more of the dielectric media are characterized by an intensity-dependent refractive index. We found that s-polarized waves satisfy the dispersion relations for very thin metal films bounded by nonlinear dielectric media. These waves exist only for power levels above a threshold that depends on the material parameters. We also comment on the experimental feasibility of observing these waves.     

Role of annealing on morphological,linear and nonlinear properties of nanoparticle of Tris [2-phenylpyridinato-C2, N] Iridium III films prepared by electron beam evaporator

Tris(2-phenylpyridinato-C₂, N] Iridium III, Ir(ppy)₃, is experimentally investigated as a novel deposited thin film. Ir(ppy)₃ thin films were fabricated by the electron beam evaporator technique. X-ray diffraction (XRD) of Ir(ppy)₃ powder is investigated to be polycrystalline with triclinic crystal. XRD pattern of Ir(ppy)₃ film and the annealed film is analyzed, and the average of crystallite size slightly increases with thermal annealing from 14 to 40 nm. The linear optical parameters were estimated and found that the annealing effect on lattice dielectric constants, dispersion energy, oscillator energy, and the ratio of carrier concentration to its effective mass. The Urbach energy and optical energy gap are estimated at different thermal annealing. On the other hand, dielectric constants and optical conductivity were estimated and found that the annealing plays a remarkable role in the increasing of their values. The calculated values of third-order susceptibility were increased by thermal annealing. Thus, the thermal annealing can be utilized as a tool to modify the optical properties of Ir(ppy)₃ films, which can be used in many important applications such as high capacity communication network.     

Sensitivity enhancement of guided-wave surface-plasmon resonance sensors

It is demonstrated theoretically and experimentally that, by using the guided-wave surface-plasmon sensor configuration with a top layer of dielectric thin film (10-15 nm) having a high value of the real part of the dielectric function, it is possible to improve the sensitivity of the sensor up to 1 order of magnitude. The stability is improved because the thin nanolayer acts as a protection layer for the metal. The enhancement is due to the increase in the interaction volume and the evanescent field enhancement near the top layer-analyte interface.     

Effective dielectric constant model of electromagnetic backscattering from stratified air–sea surface film–sea water medium

Studies of surface film medium on the sea surface are carried out in this paper for developing the technology to automatically detect and classify sea surface films, and an effective dielectric constant model of electromagnetic backscattering from a stratified air–ocean interface. Numerical results of the new model show the characteristics of effective dielectric constants for the air–sea surface film–sea water medium as follows. The effective dielectric constants decrease with increasing relative dielectric constants of the sea surface films. The effective dielectric constants decrease in horizontal polarization(abbr. HH polarization) and increase in VV vertical polarization(abbr. VV polarization) with increasing radar incident angle. Effective dielectric constants vary with relative sea surface film thickness as a cosinusoidal function of sea surface film thickness. Effective dielectric constant of VV polarization is larger than that of HH polarization. Two potential applications are found with our model, i.e., the retrieval of dielectric constants from the sea surface film, and the film thickness retrieval with our model. Our model has a highly significant influence on improving the technology related to the remote sensing of sea surface films.     

New interferometric method for determining the refractive index of thin dielectric film,its thickness,the phase shift,and the order of interference

A new interferometric method is proposed, using white light fringes of equal chromatic order to determine simultaneously the following paramcters:

1. The refractive index of a thin dielectric film, and hence its dispersion.
2. The film thickness.
3. The correct value of the order of interference.
4. The phase shift occuring due to reflection at the dielectric/metal interface. In the present work, doubly silvered zinc sulphide (ZnS) thin dielectric film was used as an example in applying the proposed method.

     

Sodium beta-alumina thin films as gate dielectrics for A1GaN/GaN metal-insulator-semiconductor high-electron-mobility transistors

<正>Sodium beta-alumina（SBA） is deposited on AlGaN/GaN by using a co-deposition process with sodium and Al₂O₃ as the precursors.The X-ray diffraction（XRD） spectrum reveals that the deposited thin film is amorphous.The binding energy and composition of the deposited thin film,obtained from the X-ray photoelectron spectroscopy（XPS） measurement,are consistent with those of SBA.The dielectric constant of the SBA thin film is about 50.Each of the capacitance-voltage characteristics obtained at five different frequencies shows a high-quality interface between SBA and AlGaN.The interface trap density of metal-insulator-semiconductor high-electron-mobility transistor（MISHEMT） is measured to be（3.5～9.5）×10¹⁰ cm^-2·eV^-1 by the conductance method.The fixed charge density of SBA dielectric is on the order of 2.7×10¹² cm^-2.Compared with the AlGaN/GaN metal-semiconductor heterostructure high-electronmobility transistor（MESHEMT）,the AlGaN/GaN MISHEMT usually has a threshold voltage that shifts negatively. However,the threshold voltage of the AlGaN/GaN MISHEMT using SBA as the gate dielectric shifts positively from—5.5 V to—3.5 V.From XPS results,the surface valence-band maximum（VBM-E_F） of AlGaN is found to decrease from 2.56 eV to 2.25 eV after the SBA thin film deposition.The possible reasons why the threshold voltage of AlGaN/GaN MISHEMT with the SBA gate dielectric shifts positively are the influence of SBA on surface valence-band maximum （VBM-E_F）,the reduction of interface traps and the effects of sodium ions,and/or the fixed charges in SBA on the two-dimensional electron gas（2DEG）.