Eugene G. Bortchagovsky

Surface plasmon mediated tip enhanced Raman scattering

The Raman signal can be strongly increased for molecules deposited on a thin metal film in a configuration where the emission of the Raman signal into a glass support of the film is mediated by leaky surface plasmons (SPs). Here we show that SP provides an efficient pathway to detect tip enhanced Raman scattering (TERS). Based on this result, we suggest a new edge plasmon mediated TERS configuration. Plasmon modes on metal covered edges of a dielectric tetrahedral tip couple to a highly directional beam of light into the dielectric body of the tip as a pathway for signal detection.

Ellipsometric method for investigation of the optical anisotropy of thin films: theory and calculations

Abstract Ellipsometry is known to be a powerful and convenient tool for investigations of the optical properties of thin films. However, in investigations of thin anisotropic films its usage is not as wide as it could be, due to a limitation in resolving the components of the dielectric tensor in the case of the transverse optical anisotropy of thin films. This problem may be solved by the immersion technique, but immersion in its standard variant of changing the ambient medium may add new uncertainties to the system under investigation. The changing of reflecting properties of a substrate is proposed in this work for the investigation of such anisotropy. To avoid the ambiguity connected to different chemical properties of different substrates, it is convenient to use the substrates from the same material, but with different thicknesses of an oxide film. Such systems have different optical properties, at the same time possessing identical chemical ones. It is shown here that the usage of such structure gives sensitivity to the transverse optical anisotropy. Calculations of the sensitivity and precision of the determination of film parameters by means of the proposed method, as well as the modeling determination of anisotropic optical parameters of a thin film, are presented.

On the modulation of optical transmission spectra of thin dye layers by a supporting medium

This work is devoted to the analysis of the shape of transmission spectra of composite systems including a thin adsorbed layer of absorbing dye molecules. It is demonstrated, that different from the often observed absorption characteristics in the transmission spectra as determined by the imaginary part of the layer’s dielectric function, the transmission spectra are in general determined by coherent light scattering of the molecules in the layer and an interference of this scattered light with the incident light. As a result, the shape of the dispersion of both, imaginary and real parts of the layer’s dielectric function, determines the transmission spectrum. Such spectra cannot be constructed from the transmission spectra of the initial system and the deposited film alone. It is shown that the shape of the transmission spectra of the composite films is described in general 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 re...

Possibilities of functionalized probes in optical near-field microscopy

Functionalization, bringing new functions to standard approaches, is used in different fields of science. Functionalized probes have found wide application in atomic force microscopy, especially in force spectroscopy and for the specific recognition of single molecules. At the same time they have found only minor application in scanning near-field optical microscopy in spite of the possibility to obtain new information. This article considers examples of the use of functionalized tips in near-field optics and emphasizes the new approach based on tip-enhanced Raman scattering (TERS) with functionalized tips. The concept of Raman probe is described considering some possible perspectives as well as the demonstration of an internal standard in TERS based on a functionalized tip.

The concept of a near-field Raman probe

This article considers the possibility to use tips, which are functionalised by Raman active molecules, as new Raman probes for near-field optics in such a way that the Raman spectrum can be recorded of such a tip. If the Raman spectrum of the probe molecules is sensitive to their immediate environment, the probe can be used to map a surface by its local influence on the Raman spectrum of the probe. This new concept may be very promising for the investigation of specific interactions at the nanoscale by an optical response. Examples of the sensitivity of such a probe to the local environment are presented as a basis for further development of such a probe.

Spectroscopic ellipsometry of fullerene embedded Langmuir–Blodgett films with surface plasmon excitation

Abstract This work presents the first results of an ellipsometric investigation of fullerene embedded Langmuir–Blodgett films with surface plasmon excitation. In contrast to standard ellipsometry, the angle Δ obtained in this way has pronounced features observed at the C60 transitions.

Model for the effective medium approximation of nanostructured layers with the account of interparticle interactions

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.

Ellipsometric method in near‐field recording

This article is devoted to the demonstration of the capability of an ellipsometric detection method for near-field optical measurements. By numerical calculations different combinations of illumination and detection applicable in near-field optics were analyzed. The obtained results show that the change in the state of polarization of scattered light due to tip-protrusion interaction is sufficient for detection in the most of the analyzed cases, even without resonant enhancement. This suggests that ellipsometry of scattered light may be used in near-field optics for the investigation of relevant systems of interest.

The shape of transmission spectra of thin films deposited on a substrate.

On the basis of the previous considerations [E. G. Bortchagovsky and U. C. Fischer, J. Chem. Phys. 117, 5384 (2002)] we analyze here the shape of the spectral lines created in transmission spectra by thin films deposited on a substrate. We demonstrate that such lines have as a rule the shape of an asymmetrical Fano line with the minimum shifted from the resonance position. Thus we present the additional argument that the popular visual estimation of the parameters of resonances from the shape of those lines should be made with care.

Internal Reflection of the Surface of a Plasmonic Substrate Covered by Active Nanoparticles

Self-consistent analytical approach was developed to describe the optical properties of an assembly of evenly distributed nanoparticles on a plasmonic substrate. The approach is based on the effective susceptibility concept in the frame of the Green function method with the account of the local-field effects in the system. The analytical expressions for the effective susceptibility (polarizability) of a single cylinder-like particle as well as for an ensemble of such particles on plasmonic substrate were derived. In the frame of developed approach, the analytical expressions for reflection coefficients were obtained. On the base of these coefficients, the influence of geometrical parameters of the particle and their surface concentration on reflectance spectrum of p-polarized electromagnetic radiation in the Kretschmann configuration was studied. The strong coupling of surface and localized modes with their hybridization and Rabi splitting at high nanoparticle concentrations was demonstrated.