Stoyan C. Russev

Instrument and methods for surface dilatational rheology measurements

We describe an instrument combining the advantages of two methods, axisymmetric drop shape analysis for well-deformed drops and capillary pressure tensiometry for spherical drops, both used for measuring the interfacial tension and interfacial rheological parameters. The rheological parameters are the complex interfacial elasticity, and the surface elasticity and viscosity of Kelvin-Voigt and Maxwell rheological models. The instrument is applicable for investigation of the effect of different types of surfactants (nonionic, ionic, proteins, and polymers) on the interfacial rheological properties both of air/water and oil/water interfaces, and of interfaces between liquids with equal mass densities. A piezodriven system and a specially designed interface unit, implemented in the instrument, ensure precise control for standard periodic waveforms of surface deformation (sine, square, triangle, and sawtooth) at a fixed frequency, or produce surface deformation at constant rate. The interface unit ensures accurate synchronization between the pressure measurement and the surface control, which is used for real-time data processing and feedback control of drop area in some of the applications.

β-Casein adsorption kinetics on air–water and oil–water interfaces studied by ellipsometry

In this work b-casein adsorption kinetics at air:water and oil:water surfaces is studied by ellipsometry. Double layer formation is observed; the process is not influenced by the type of the hydrophobic phase. A dense protein layer initially forms, and then the adsorption continues in a second more diffuse layer, which extends in the aqueous phase. The surface coverage (i.e. the adsorption, G) in the second layer approaches that in the first dense layer at long times, but the thickness and the refractive index of the second layer testify for lower volume density of protein there. The well known ellipsometric problem of correlating parameters in the case of measurement in a very thin layer (on a substrate which does not absorb light) has been overcome by using different upper phases (oil and air). This gives the opportunity to determine separately the refractive index and the thickness of the layer. The same procedure is applicable whenever a very thin layer structure with two unknown parameters is under investigation.

Plasmon-Enhanced Sub-Wavelength Laser Ablation: Plasmonic Nanojets

In response to the incident lights electric field, the electron density oscillates in the plasmonic hotspots producing an electric current. Associated Ohmic losses raise the temperature of the material within the plasmonic hotspot above the melting point. A nanojet and nanosphere ejection can then be observed precisely from the plasmonic hotspots.

Polynomial inversion of the single transparent layer problem in ellipsometry

It is shown that for a uniform transparent layer over a substrate the layer dielectric constant satisfies a fifth-degree polynomial. The problem of extracting the layer index and thickness from the ellipsometric measurement is then reduced to finding the roots of this polynomial. The coefficients of this polynomial are determined by the angle of incidence, the real incident-medium index, the complex substrate index, and the measured complex ellipsometric ratio ρ. This approach to the problem gives directly all the possible physical solutions without the need for initial guesses or ranges. Special cases are examined. Numerical analysis and error analysis are provided for the case of a silicon oxide layer over silicon.

Rotating analyzer–fixed analyzer ellipsometer based on null type ellipsometer

The theory and design of an inexpensive rotating analyzer unit is presented, which allows a conventional null type ellipsometer to work as rotating analyzer–fixed analyzer automatic ellipsometer, without sacrificing the possibility to work in null mode. The mode switching is performed simply by adding or removing the rotating analyzer from its holder. It is shown that the rotating analyzer phase shift in rotating analyzer–fixed analyzer mode can be run-time determined from the measured Fourier coefficients. This avoids any need of recalibration procedure after mode switching and makes unnecessary plane of incidence synchronization, which further simplifies the needed hardware and reduces the errors connected with the phase shift instability of the output signal. The run-time phase shift calibration procedure and subsequent ellipsometric angles determination do not involve normalization of the output signal Fourier coefficients to the zeroth harmonic, eliminating in this way the influence of the dc compone...

Conditions for Loss Compensation of Surface Plasmon Polaritons Propagation on a Metal/Gain Medium Boundary

One way to compensate for the surface plasmon polariton (SPP) propagation losses is to use a gain medium. However, simply ensuring high enough gain is not sufficient because it may violate the bounded character of the wave. Therefore, a detailed theoretical analysis is needed for the determination of the conditions for lossless or amplified SPP propagation. Here presented is an exact theoretical analysis of the SPP propagation in the case of an infinite metal/gain medium boundary. It is shown that the conditions for lossless/amplified SPP propagation can be conveniently examined and presented as a simply connected region in the complex plane of the gain medium dielectric function. Effective and minimum gain parameters are introduced, which facilitates the simultaneous analyses of different gain media/metals combinations. The practical application of these results is illustrated for several gain media/metal (silver, gold and aluminium) systems.

Note: Simple vacuum feedthrough for optical fiber with SubMiniature version A connectors at both ends

We present a simple way to insert an optical fiber, with existing standard SubMiniature version A connectors on both ends into a vacuum system. The fitting is tested in scanning electron microscope, at working pressures down to 2 × 10(-5) mbar for cathodoluminescent measurements. With slight modifications this fitting could be successfully adapted for optical fiber insertion into pressurized systems.

Representation of the transparent layer–arbitrary substrate system parameters through the Fourier coefficients of the ellipsometric function

A system of transparent layers on top of an arbitrary underlying subsystem is considered. It is shown that the layer refractive index and the subsystem generalized Fresnel coefficients can be expressed in a simple and explicit way by the Fourier coefficients of the ellipsometric function ρ with the layer thickness as an expansion parameter. Thus the inverse ellipsometric problem is reduced to a much simpler and well-defined problem of finding these Fourier coefficients. Analysis shows that the ellipsometric inverse task must be considered separately, depending on whether the modulus of the s-polarization Fresnel coefficient for the ambient–layer interface is smaller than, equal to, or greater than that for the layer–substrate system.

Exact polynomial inversion for top transparent layer parameters on an arbitrary substrate in ellipsometry

We consider the inverse ellipsometric problem for a transparent layer on top of an isotropic substrate, which may consist of an arbitrary number of plane parallel homogeneous layers with complex refractive indexes, or have an arbitrary depth profile variation of the complex refractive index. It is shown that the task of finding the top layer parameters can be split into two. First, the top layer dielectric constant is determined by the roots of a fifth degree polynomial and then the layer thickness is found. Error propagation analysis is provided on a sample system and the stability of the method is estimated.

Two dimensional polymerization of graphene oxide: Bottom-up approach

Abstract We demonstrate a bottom-up synthesis of structures similar to graphene oxide via a two dimensional polymerization. Experimental evidence and discussion are conveyed as well as a general framework for this two dimensional polymerization. The proposed morphologies and lattice structures of these graphene oxides are derived from aldol condensation of alternating three nucleophilic and three electrophilic centers of benzenetriol.