Enhanced backscattering and transmission of light from random surfaces on semi-infinite substrates and thin films

Abstract

The enhanced backscattering of light from a random surface is manifested by a well defined peak in the retro-reflection direction in the angular distribution of the intensity of the incoherent component of the light scattered from such a surface. In this paper we present several new theoretical and experimental results bearing on the conditions under which enhanced backscattering occurs, and the way in which this phenomenon depends on the nature of the random surface roughness, both in the case that the random surface bounds a semi-infinite scattering medium and in the case that it bounds a film, either free-standing or on a reflecting substrate. In addition, we present new results on the transmission of light through thin metallic films bounded by random surfaces, which display the phenomenon of enhanced transmission, namely a well defined peak in the antispecular direction in the angular distribution of the intensity of the incoherent component of the light transmitted through such films.     

Enhanced and specular backscattering in random media

We study scalar waves probing a heterogeneous medium whose parameters are modeled in terms of a statistically isotropic random field. The medium is terminated by an oblique interface at one end (the bottom) and pressure release type boundary conditions at the other end (the top). The tilt of the bottom interface is relatively small so that the dominant contributions to the wave field are confined to a paraxial tube. This study generalizes the basic formulation in terms of Itô–Schrödinger equations in a one-dimensional deterministic background, describing the macrostructure, to one in which the background is more complicated. It provides the first step toward the analysis of scattered waves in general background media modulated by a random microstructure. We discuss in detail the enhanced backscattering phenomenon or weak localization in this setting, with a tilted interface imbedded in the random medium, and find that the backscattering cone does not depend on the tilt. We also find that the enhanced backscattering phenomenon is not affected by the replacement of a specular interface with a diffusive interface.     

Approximate calculation of coherent backscattering for semi-infinite discrete random media

We describe an approximate method for the calculation of all characteristics of coherent backscattering for a homogeneous, semi-infinite particulate medium. The method allows one to transform a system of integral equations describing coherent backscattering exactly into a system of linear algebraic equations affording an efficient numerical solution. Comparisons of approximate theoretical results with experimental data as well as with benchmark numerical results for a medium composed of nonabsorbing Rayleigh scatterers have shown that the method can be expected to give a good accuracy.     

High light transmission through thin absorptive corrugated films

The enhancement of light transmittance through periodically relief thin absorptive film at surface plasmon polariton excitation conditions, as a function of relief interrelation, was considered theoretically. Our calculation of transmittance-reflectance through periodically relief thin absorptive film was performed in the framework of differential formalism. There are two basic relief interrelation forms, namely, correlated and anticorrelated ones. The obtained spectral and angular dependencies demonstrate an essential increase of surface plasmon polariton peaks in the case of anticorrelated corrugation of film in comparison with the correlated ones.     

On the reflection and transmission of light through thin transparent films

A formula is deduced for the reflection and transmission of light through one thin film. The direction of the passing rays of light (right and left) is taken into account whereby a formula is obtained which is more general than that usually used. The former was used as the starting point for the deduction of formulae for the reflection and transmission of light through two and more thin films which were published by the author some years ago. An explanation is given of the complication of the formulae when the reflection of light from the upper film, adjacent to the air, is computed. The auxiliary phase deduced by the author in a previous paper is also explained as a necessary consequence.     

Enhanced backscattering and blazing effect from gratings, quasi-gratings and randomly rough surfaces

The blazing effect is probably the most important property of diffraction gratings used for spectroscopic purposes. On the other hand, the enhanced backscattering phenomenon has been generally studied in the framework of scattering from randomly rough surfaces. Using numerical results from rigorous theories, it will be shown that these phenomena, which have very different origins, should have more precise definitions. In a special case of a randomly rough surface formed by random corners, it will be shown that the effects of these phenomena are sometimes very difficult to distinguish.     

Enhanced backscattering and blazing effect from gratings,quasi-gratings and randomly rough surfaces

Abstract

The blazing effect is probably the most important property of diffraction gratings used for spectroscopic purposes. On the other hand, the enhanced backscattering phenomenon has been generally studied in the framework of scattering from randomly rough surfaces. Using numerical results from rigorous theories, it will be shown that these phenomena, which have very different origins, should have more precise definitions. In a special case of a randomly rough surface formed by random corners, it will be shown that the effects of these phenomena are sometimes very difficult to distinguish.     

Enhanced hardness in B-doped ZnO thin films on fused quartz substrates by pulsed-laser deposition

B-doped ZnO thin films have been fabricated on fused quartz substrates using boron-ZnO mosaic target by pulsed-laser deposition technique, and the mechanical properties have been studied by nanoindentation continuous stiffness measurement technique and transmission electron microscope (TEM). Nanoindentation measurement revealed that the hardness of B-doped ZnO films, 9.32 ± 0.90 to 12.10 ± 1.00 GPa, is much greater than that of undoped ZnO films and very close to that of traditional semiconductor Si. The mean transmittance (%) is larger than 81% in the visible range (380-780 nm) for all the films, and the Hall effect measurement showed that the carrier density is around 2 × 10²⁰ cm⁻³ and the resistivity lower than 3 × 10⁻³ Ω cm. TEM characteristics show undoped thin films have more amorphous area between grains while the B-doped ZnO films have thin grain boundaries. We suggest that the grain boundaries act as the strain compensation sites and the decrease in thickness of grain boundaries enhances the hardness of the B-doped ZnO films.     

Multicolor photon emission from organic thin films on different substrates

Thin films of 1-pentyl-2^/,3^/-difluoro-3^///-methyl-4^////-octyl-p-quinquephenyl and 9,10-Bis (4-pentylphenylethynyl)antracene organic molecules were grown on optical glass, silicon and porous silicon substrates. First optical and luminescent properties of such hybrid composites are thoroughly studied using spectroscopic techniques. The strong decrease of aggregation in thin films of 1-pentyl-2^/,3^/-difluoro-3^///-methyl-4^////-octyl-p-quinquephenyl on porous silicon was observed. The possibility of simultaneous red, green and blue tunable photon emission from organic film/porous silicon hybrid structure is demonstrated.     

Sputtering and backscattering of keV light ions bombarding random targets

The fission fragment fluence required to render CaUO₄, Na₂U₂O₄, MgUO₄, Sr₂U₃O₁₁ and u₃O₈ x-ray amorphous was deduced as ～5 × 10¹⁵ events cm³. Significant annealing of the structural damage occurred in the 300–-500°C range.     

Two-dimensional light diffraction from thin opal films

This paper reports on experimental and theoretical investigations of light diffraction from thin films of synthetic opal. The diffraction patterns have been studied visually and recorded in different scattering geometries with the films illuminated with white unpolarized light. The diffraction pattern obtained with the film illuminated with a light beam along the [111] axis, which is normal to the film surface, has C ₆ symmetry and consists of six strong reflections arranged symmetrically with respect to the incident beam. This pattern becomes substantially more complicated when the film is illuminated by white light at an arbitrary angle to the [111] axis. An experimental study of the spectral response and angular relations of the diffraction patterns has established a fairly full pattern of transformation of diffraction reflections obtained under variation of the angle of light incidence on an opal film. The remarkably good matching of experimental and calculated data provides compelling evidence for light diffraction from thin opal films being two-dimensional.     

Enhanced light transmission through cascaded metal films perforated with periodic hole arrays

We report experimental results on enhanced light transmission through two periodically perforated metal films separated by a layer of dielectric. A perforated metal film (single metallic structure) exhibits extraordinary optical transmission, and when two such perforated metal films are spaced by a dielectric layer (cascaded metallic structure), the transmission is further increased. The maximum transmission of the cascaded metallic structure, which depends on the distance between the two metal films, can be more than 400% greater than that of a corresponding single metallic structure. It is proposed that the coupling of surface plasmon polaritons between the two metal films is involved in the process.     

Elastic backscattering of electrons from surfaces

A Monte Carlo algorithm is proposed for calculating the elastic reflection coefficient, η_E, for elements. The algorithm accounts for the multiple elastic scattering of electrons in solids. The calculated values of η_E compare well with the literature data for elements with atomic number up to 47 and at primary energies above 2 keV. The proposed Monte Carlo method makes it possible to determine the functional relation between η_E and the inelastic mean free path, λ. This relation turned out to be non-linear, arid it deviates from a similar relation based on published earlier single elastic scattering model. The deviation is especially pronounced for elements with medium atomic numbers. The calculated function $\text{η}{}_{\mathrm{<mtext>E</mtext>}}\text{=}\text{f}\text{(λ)}$ offers a convenient method for determining the inelastic mean free path. The values of λ derived in the present work from published experimental values of η_E compare very well with the literature data.     

Tritium and helium analyses in thin films by enhancedproton backscattering

In order to study how to reliably perform quantitative tritium and helium analyses in thin film samples using enhanced proton backscattering (EPBS), several EPBS spectra for some samples consisting of non-RBS light elements (i.e., T, ⁴He, ¹²C, ¹⁶O, ^natSi), medium and heavy elements have been measured and analyzed using analytical SIMNRA and Monte Carlo-based CORTEO codes. The non-RBS cross sections needed in the CORTEO code are taken from the ENDF/B-Ⅶ.1 database and the calculations of SigmaCalc code and are incorporated into the CORTEO code. All non-RBS cross section data over the entire proton incident energy-scattering angle plane are obtained by interpolation. It is quantitatively observed that in EPBS analysis the multiple and plural scattering effects have little impact on the energy spectra for light elements and the RBS cross sections of light elements can be used in the SIMNRA code for dual scattering calculations. It is also observed that the results given by the CORTEO code are higher than the results of the SIMNRA code in the low energy part of EPBS spectra, and are in better agreement with the experimental data. Tritium and helium analyses in thin film samples using EPBS can be performed reliably when the multiple and plural scattering contributions are completely accounted.     

Stresses and deformation processes in thin films on substrates

The stresses that develop in thin films on substrates can be detrimental to the reliability of thin film electronic devices. In order to design these devices for improved mechanical reliability, an understanding of the origin of these stresses and the controlling deformation processes in thin films is needed. This review begins with a discussion of the basic techniques used for measuring stresses in thin films and for studying the mechanical properties of thin films. The proposed models for the origin of stresses in thin films are then reviewed. Finally, the effects of microstructure and substrate constraint on thin film deformation processes are discussed.     

Observation of phase conjugation of light arising from enhanced backscattering in a random medium

We measure the fundamental phase conjugation of a light field arising from enhanced backscattering in a multiple scattering medium. The measurements employ a two-window, time-resolved heterodyne method to suppress specularly reflected light and to determine the transverse Wigner function of the field, yielding joint amplitude and phase information. Using this method, a light field backscattered from an aqueous suspension of polystyrene spheres is found to reverse curvature relative to that of the incident field.     

Fabrication and characterization of indium sulfide thin films deposited on SAMs modified substrates surfaces by chemical bath deposition

In an effort to explore the optoelectronic properties of nanostructured indium sulfide (In₂S₃) thin films for a wide range of applications, the In₂S₃ thin films were successfully deposited on the APTS layers (-NH₂-terminated) modified ITO glass substrates using the chemical bath deposition technique. The surface morphology, structure and composition of the resultant In₂S₃ thin films were characterized by FESEM, XRD, and XPS, respectively. Also, the correlations between the optical properties, photocurrent response and the thickness of thin films were established. According to the different deposition mechanisms on the varying SAMs terminational groups, the positive and negative micropatterned In₂S₃ thin films were successfully fabricated on modified Si substrates surface combining with the ultraviolet lithography process. This offers an attractive opportunity to fabricate patterned In₂S₃ thin films for controlling the spatial positioning of functional materials in microsystems.