Enhanced scattering from a thin film with one-dimensional disorder

This paper deals with a TE plane wave scattering from a thin film with one-dimensional disorder by means of the stochastic functional approach. The thin film is one-dimensionally inhomogeneous in the horizontal direction with infinite extent, and is homogeneous in the vertical direction with finite thickness. Based on an approximate wavefield representation in terms of a Wiener-Hermite expansion in a preceding paper (Tamura et al., 2004, Waves in Random Media, 14, 435-465), the first- and second-order incoherent scattering cross-sections are presented in explicit forms and scattering properties are discussed. The scattering properties vary entirely with the film thickness. In a case where the thickness is smaller than a few wavelengths in the thin film, enhanced scattering and associated enhanced scattering may appear as sharp peaks or dips on the second-order incoherent scattering distribution if the thin film has guided wave modes. When the thickness becomes sufficiently larger than the wavelength inside the film, a new enhanced scattering phenomenon appears as gentle peaks on the second-order incoherent scattering distribution in four special directions. Such four directions are the directions of forward scattering, specular reflection, backscattering, and the symmetrical direction of forward scattering with respect to the normal of the film surface.The first-order incoherent scattering occurs distinctly in four such directions. Such enhanced scattering is independent of the existence of the guided wave modes inside the thin film, and deeply relates to the structure of the thin film with one-dimensional disorder that has infinite correlation in the vertical direction. For SiC and glass thin films having one-dimensional disorder with a Gaussian correlation and three types of exponential correlation, the first- and second-order incoherent scattering cross-sections are illustrated in figures. The narrow enhanced scattering peaks appear for the glass film in a thin case. The gentle enhanced peaks turn up for both the SiC and glass films in a thick case. Furthermore, the optical theorem is calculated for several cases. It is then found that the error of the optical theorem decreases and the performance of the wavefield is improved by taking into account the second-order incoherent scattering.     

Wave reflection and transmission from a thin film with one-dimensional disorder

This paper deals with a TE plane wave reflection and transmission from a thin film with one-dimensional disorder by means of the stochastic functional approach. The relative permittivity of the thin film is written by a Gaussian random field in the horizontal direction with infinite extent, and is uniform in the vertical direction with finite thickness. Arandomwavefield is obtained in terms of a Wiener-Hermite expansion representation with approximate expansion coefficients (Wiener kernels) under a small fluctuation case. For a SiC thin film and a glass thin film having one-dimensional disorder with Gaussian correlation or an exponential correlation, numerical examples of the first-order incoherent scattering cross section and the optical theorem are illustrated in the figures. It is then found that ripples and four major peaks appear in angular distributions of the incoherent scattering. Such four peaks may occur in the directions of forward scattering, specular reflection, backscattering and in the symmetrical direction of forward scattering with respect to the normal to surface of the thin film. Physical processes that yield such ripples and peaks are discussed.     

Scalar plane wave scattering from a thin film with two-dimensional fluctuation

This paper deals with a scalar plane wave scattering from a thin film with two-dimensional fluctuation by means of the stochastic functional approach. The refractive index of the thin film is written as a Gaussian random field in the transverse directions with infinite extent, and is invariant in the longitudinal direction with finite thickness. An explicit form of the random wavefield involving effects of multiple scattering is obtained in terms of a Wiener-Hermite expansion under small fluctuation. The first- and second-order incoherent scattering cross-sections are calculated numerically and illustrated in figures. In the incoherent scattering, scattering ring, quasi-anomalous scattering, enhanced scattering and gentle enhanced scattering may occur.     

Electron scattering at one-dimensional chain with composition disorder

A new method is proposed for determining average kinetic parameters of one-dimensional disordered systems. Electron scattering at a one-dimensional chain with structural and composition disorders is considered. The solution of a finite-difference equation derived for the average resistance shows that the dependence of the average resistance on the number of scatterers (sample length) for all states of the one-electron spectrum is a sum of three exponential functions irrespective of the type of random field in the system. It is proved that, in the case of a mixed disorder, all one-electron states are localized in a chain of δ potentials.     

Conductance of a perfect thin film with diffuse surface scattering

The conductance of thin films with diffusive surface scattering was solved semiclassically by Fuchs and Sondheimer. However, when the intrinsic electron mean free path is very large or infinite their conductance diverges. In this Letter a simple diffraction picture is presented. It yields a conductance which corresponds to a limiting mean free path of a(2)/lambda(F), where a is the film thickness.     

Electron-ripplon scattering for a thin film of liquid helium

The mobility of electrons governed by an electron-ripplon scattering is calculated for finite thickness of He films.     

Resonant optical transmission through a one-dimensional photonic crystal adjacent to a thin metal film

We theoretically and experimentally reveal that the large resonant optical transmission (ROT) can be realized through a one-dimensional photonic crystal adjacent to a thin metal film, at a frequency in the original band-gap of the photonic crystal (PC). The influence of periodic number of PC and the thickness of the adjacent metal on the transmission frequency and intensity is studied in detail. An optimum design is given to reach the maximum transmission efficiency, meanwhile a mechanism underlining the ROT phenomenon is proposed. An effective admittance-matching theory is proposed to understand this effect and quantitatively determine the operating frequency, which matches very well with the simulated and measured results. The effects might be very useful to realize some optical filters and sensor devices since the structure is easy for mass production and is matured technically to be prepared in industry.     

Enhanced ultraviolet emission from ZnO thin film covered by TiO_2 nanoparticles

A ZnO thin film covered by TiO2 nanoparticles is prepared by electron beam evaporation. The structure and surface morphology of the sample are analyzed by X-ray diffraction （XRD） and atomic force microscopy （AFM）, respectively. Photoluminescence is used to investigate the fluorescent property of the ample. The results show that the ultraviolet （UV） emission of the ZnO thin film is greatly enhanced after it is covered by TiO2 nanoparticles while the green emission is suppressed. The enhanced UV emission mainly results from the fluorescence resonance energy transfer （FRET） between ZnO thin film and TiO： nanoparticles. This TiO2-ZnO composite thin film can be used to fabricate high-efficiency UV emitters.     

Enhanced polarization conversion for an anisotropic thin film

This work presents an explicit expression for the reflection and transmission coefficients of an anisotropic thin film in the general case in which the optical axis and the incident ray are arbitrarily directed in three dimensions. The polarization conversion quantities for reflected light from an anisotropic thin film are calculated and analyzed for two three-layered systems. With light incident from a dense medium, polarization conversion will be enhanced at a particular incident angle that exceeds the critical angle.     

Raman scattering for lead telluride-based thin film structures

For single-crystal epitaxial lead telluride films, Raman spectra obtained under conditions in which the intensity of incident radiation is minimized in order to suppress photo-initiated oxidative process are presented. The spectra were measured with an InVia Renishaw spectrometer at an exciting radiation wavelength of 514.5 nm and in-line focusing of a 20-μW beam. These measuring conditions allowed us for the first time to experimentally observe a large set of peaks for lead telluride, the positions of which were in line with the theoretical values of harmonics and combinatorial PbTe phonon modes. In order to demonstrate the possibilities of the methodology used, the picture of phonon modes for single-crystal and polycrystalline films of the Pb_{1 ? x} Eu _x Te (0.05 ? x ? 0.10) solution was additionally considered.     

Raman scattering from one-dimensional carbon systems

Although the Raman effect was discovered nearly 80 years ago, it is only recently that the special characteristics of Raman scattering for one-dimensional systems have been seriously considered. This review focuses on the special interest of the Raman effect for one-dimensional systems that is of particular relevance to carbon nanostructures. Two examples of Raman scattering in one-dimensional systems are given. The first illustrates the use of Raman spectroscopy to reveal the remarkable structure and properties of carbon nanotubes arising from their one-dimensionality. Some of the recent advances in using Raman spectroscopy to study doping and intercalation to modify nanotube properties are reviewed, in the context of a one-dimensional system. The second example is the Raman spectra of a linear chain of carbon atoms and the special properties of this interesting system. New approaches toward applying Raman spectroscopy to carbon nanostructures are also emphasized.     

Enhanced backward scattering by surface plasmons on silver film

Surface plasmon and its potential application in nanotechnology have attracted a remarkable amount of attention recently due to their novel properties. In this work we present an angularly resolved surface plasmon scattering study on a primitive metal surface. Using a reversed attenuated total reflection (RATR) setup in the experiment, we obtained a double-crescent shaped and enhanced scattering pattern at far field. The scattering pattern as a function on the variation of angle and polarization of incident beam are studied. Both theoretical and experimental results reveal an enhanced backward scattering by surface plasmon excitation. Consequently, it is shown that this angularly resolved surface plasmon scattering measurement can be employed for resolving a richness of nanoscale surface textures. PACS 42.79.-e; 42.30.Wb; 78.20.Ci     

Long-range propagation of plasmon polaritons in a thin metal film on a one-dimensional photonic crystal surface

We present experimental results on ultralong-range surface plasmon polaritons, propagating in a thin metal film on a one-dimensional (1D) photonic crystal surface over a distance of several millimeters. This propagation length is about 2 orders of magnitude higher than the one in the ordinary Kretschmann configuration at the same optical frequency. We show that a long-range surface plasmon polaritons propagation may take place not only in a (quasi)symmetrical scheme, where a thin metal film is located between two media with (approximately) the same refraction index, but also in a scheme where the thin metal film is located between an appropriate 1D photonic crystal and an arbitrary (air, water, etc.) medium. The ultralong-range surface plasmon polaritons are potentially important for biosensors, plasmonics, and other applications.     

Total-reflection inelastic X-ray scattering from a 10-nm thick La0.6Sr0.4CoO3 thin film

To study equilibrium changes in composition, valence, and electronic structure near the surface and into the bulk, we demonstrate the use of a new approach, total-reflection inelastic x-ray scattering, as a sub-keV spectroscopy capable of depth profiling chemical changes in thin films with nanometer resolution. By comparing data acquired under total x-ray reflection and penetrating conditions, we are able to separate the O K-edge spectra from a 10 nm La0.6Sr0.4CoO3 thin film from that of the underlying SrTiO3 substrate. With a smaller wavelength probe than comparable soft x-ray absorption measurements, we also describe the ability to easily access dipole-forbidden final states, using the dramatic evolution of the La N4,5 edge with momentum transfer as an example.     

Enhanced optical absorption by Ag nanoparticles in a thin film Si solar cell

Thin film solar cells have the potential to significantly reduce the cost of photovoltaics. Light trapping is crucial to such a thin film silicon solar cell because of a low absorption coefficient due to its indirect band gap. In this paper, we investigate the suitability of surface plasmon resonance Ag nanoparticles for enhancing optical absorption in the thin film solar cell. For evaluating the transmittance capability of Ag nanoparticles and the conventional antireflection film, an enhanced transmittance factor is introduced. We find that under the solar spectrum AM1.5, the transmittance of Ag nanoparticles with radius over 160 nm is equivalent to that of conventional textured antireflection film, and its effect is better than that of the planar antireflection film. The influence of the surrounding medium is also discussed.     

碳氮薄膜的制备及其拉曼光谱研究

使用自行设计的真空系统 ,采用弧光放电等离子体的方法 ,成功制备了表面光滑致密的碳氮薄膜 .牛顿环干涉图样进一步验证了薄膜厚度的均匀性 .拉曼光谱显示了 3个主要的散射峰和几个相对较弱的峰 ,拉曼光谱分析表明 ,膜的结构是一种无定形非晶碳氮膜 ,碳原子与氮原子在薄膜中以各种不同的键态存在 .通过比较样品不同区域的拉曼光谱图发现 ,谱图几乎没有变化 ,说明制备的碳氮薄膜结构是均匀的     

Mobility in a one-dimensional disorder potential

In this article the one-dimensional, overdamped motion of a classical particle is considered, which is coupled to a thermal bath and is drifting in a quenched disorder potential. The mobility of the particle is examined as a function of temperature and driving force acting on the particle. A framework is presented, which reveals the dependence of mobility on spatial correlations of the disorder potential. Mobility is then calculated explicitly for new models of disorder, in particular with spatial correlations. It exhibits interesting dynamical phenomena. Most markedly, the temperature dependence of mobility may deviate qualitatively from Arrhenius formula and a localization transition from zero to finite mobility may occur at finite temperature. Examples show a suppression of this transition by disorder correlations.Dedicated to Professor H. Wagner on the occasion of his 60th birthday     

Enhanced photocatalytic activity of TiO2 nano-structured thin film with a silver hierarchical configuration

TiO₂ sol-gels with various Ag/TiO₂ molar ratios from 0 to 0.9% were used to fabricate silver-modified nano-structured TiO₂ thin films using a layer-by-layer dip-coating (LLDC) technique. This technique allows obtaining TiO₂ nano-structured thin films with a silver hierarchical configuration. The coating of pure TiO₂ sol-gel and Ag-modified sol-gel was marked as T and A, respectively. According to the coating order and the nature of the TiO₂ sol-gel, four types of the TiO₂ thin films were constructed, and marked as AT (bottom layer was Ag modified, surface layer was pure TiO₂), TA (bottom layer was pure TiO₂, surface layer was Ag modified), TT (pure TiO₂ thin film) and AA (TiO₂ thin film was uniformly Ag modified). These thin films were characterized by means of linear sweep voltammetry (LSV), X-ray diffraction (XRD), scanning electron microscopy (SEM), electrochemical impedance spectroscopy and transient photocurrent (I_ph). LSV confirmed the existence of Ag⁰ state in the TiO₂ thin film. SEM and XRD experiments indicated that the sizes of the TiO₂ nanoparticles of the resulting films were in the order of TT > AT > TA > AA, suggesting the gradient Ag distribution in the films. The SEM and XRD results also confirmed that Ag had an inhibition effect on the size growth of anatase nanoparticles. Photocatalytic activities of the resulting thin films were also evaluated in the photocatalytic degradation process of methyl orange. The preliminary results demonstrated the sequence of the photocatalytic activity of the resulting films was AT > TA > AA > TT. This suggested that the silver hierarchical configuration can be used to improve the photocatalytic activity of TiO₂ thin film.