This work considers the application of Effective-Medium Approximation to the case of thin inhomogeneous layer like a
layer of nanoparticles on a surface. It is shown that Effective-Medium Approximation models built for the case of bulk
composites are not able to describe the optical properties on thin layers. Another approach based on the Green function
formalism and accounted all interparticle interactions is proposed to construct the effective polarizability of such a layer,
which can be considered as two-dimensional analogue of standard Effective-Medium Approximation for bulk media.
On the base of the developed formalism for the determination of the optical response of a layer of nanoparticles with the
account of interparticle interactions we calculated transmission spectra of such a layer in the dependence on the particle
size, shape and concentration on the surface. These spectra were modeled versus the thickness of an additional layer
covering the particles what allowed to determine the sensitivity of such kind of optical sensor. Such an analysis allows to
find optimal parameters of the layer of particles to obtain maximal sensitivity of such kind of sensor.
This work is devoted to the analysis of the shape of transmission spectra of stratified systems with a deposited thin adsorbed layer. It is demonstrated, that the transmission spectra are in general determined by coherent light scattering of the molecules in the deposited layer and interference of this scattered light with the incident one. As a result, the shape of the dispersion of both imaginary and real parts of the layer's dielectric function determines the transmission spectrum instead of only the imaginary part as in the case of transmission spectra of adsorbed layers on a transparent bulk substrate. The fact that such spectra can not be constructed from the absorption spectra of the stratified system and the deposited film alone was often the reason for seeking of new interactions in such systems. We demonstrate that this non additive property of the spectra has to be expected for such systems in general also in the absence of such interactions and that the position of the minimal transmission in a normalized spectrum does not correspond to the position of an absorption line. It is shown that the shape of such spectra is described by an asymmetrical line like a Fano line and that the origin of such a shape can be associated with the physics underlying a Fano resonance. A new approach for the determination of the dielectric function of deposited films is proposed on the basis of the presented analysis. It is demonstrated experimentally and theoretically that the deposition of a thin absorbing layer can give rise to an increase in transmission of an initial system. Conditions of such an increase are presented.
This talk is devoted to the analysis of different ellipsometric methods for their ability to get separately thickness and refractive index of thin films. Such analysis is necessary for unambiguous determination of all thin film parameters, not only its 'optical thickness.' Analysis and comparison of different approaches for solving of this problem is made both on the base of the theoretical consideration of methods background and on the calculation of correlation matrix for parameters of interest.
The article gives a new approach for the consideration of the precision reachable by rotating-analyzer ellipsometers. Presented results approve all qualitative conclusions of the previous article on this topic, but the general equations and numerical results are different. Additionally this article treats the problem of optimizing the measurements of ellipsometric angles separately. It is shown, measured (Psi) and (Delta) are correlated for such type of ellipsometers. For most real in practice short-noise-limited case a good rule of thumb is proposed, which gives the compromise for suboptimize measurements as (rho) , so (Psi) and (Delta) at the same time. It is proved, as all sources of noise work simultaneously, as well as for null-ellipsometry it is impossible to make measurements at the Brewster angle with rotating-analyzer ellipsometers.
This work presents the first results of ellipsometric investigation of fullerene embedded Langmuir-Blodgett films on gold with surface plasmon excitation. In contrast to the standard ellipsometry, the spectrum of the delta angle obtained in such way has pronounced peculiarities at the C60 optical transitions. Obtained data unambiguous exhibit dependence of electromagnetic response of the system of interest on the proximity of fullerene to the gold surface.
Comparison of the precision of measurements by means of null-ellipsometer with rotating analyzer is made here on the base of the developed formalism. The dependence of measurement's errors on the reflectivity of an investigated system is taken into account and is the base of the presented comparison.
This article is devoted to the comparison of possibilities of ellipsometry, surface plasmon spectroscopy and their combination in the investigation of thin films. The problem of separation of the thickness and refractive index of the film of interest is considered as well as the possibility to find the transverse optical anisotropy of such film. The special attention to the way for comparison of different methods is paid. It is proved the only such way can show which method gives more information about an investigated systems and allows to inspect the surface treatment more exactly. Such comparison is made for different kinds of substrate in the case of standard ellipsometry, as well as for separated surface plasmon spectroscopy and ellipsometry with surface electromagnetic waves excitation.
Ellipsometry is well known to be a very powerful technique for investigation of films, surfaces, interfaces and so on. Thanks to its principals and high quality of standard polarization prisms, ellipsometry has a sensitivity about one hundred's part of monolayer or some hundred's parts of angstrom if this sensitivity is recalculated for the thickness measurements. This very convenient and sensitive method of investigations also is very simple in realization. Unfortunately, ellipsometry is an indirect method. It may be the best method for investigations of little changes in well defined systems, but obtaining the optical parameters of an investigated system from the measured ellipsometrical angles (psi) and (delta) can be very difficult. Thus all results of ellipsometrical measurements have to be interpreted on the basis of some physical model and obtained optical parameters are only the parameters of the concrete chosen model. Difficulties in investigations of thin films and sub-monolayer coverings are: the nonuniformity of a substrate, the choice of an appropriate model for having the meaningful physical description, and a selection of measurement conditions for obtaining all parameters of this model. This article does not pretend to review all of the problems of the thin films ellipsometry and does not have a somehow full list of references; it is only a short look over some aspects of the ellipsometry of thin films.
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