Importance of considering all the degrees of freedom in analyzing the deformations of a polymer chain

The problem of the elastic variation of all the degrees of freedom of a plane zigzag chain of the composition (-CR₂-)_n in axial tension is formulated in the homogeneous deformation approximation. The deformations of the internal coordinates and the modulus of elasticity of the polyethylene chain are the subject of a numerical calculation.     

Toward a theory of light absorption by excitons in quantum-well structures

A theory of light absorption by excitons in periodic structures with an arbitrary number of quantum wells is constructed. It is shown that the temperature dependence of the frequency-integrated absorption characteristics is due to a competition between the processes of dissipative decay of quasi-two-dimensional excitons and the light-exciton interaction. Fiz. Tverd. Tela (St. Petersburg) 40, 824–826 (May 1998)     

Theory of nonlinear vibrations of free and loaded polymer molecules

The contributions of three- and four-phonon processes to the halfwidth of the valence vibration band of the linear chain are numerically estimated. It is concluded that the experimentally observed halfwidths of the skeletal vibration bands of polymers are attributable to anharmonic phonon interactions. The effect of chain loading on the halfwidth is also investigated.Ioffe Physicotechnical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 4, pp. 579–585, July–August, 1971.     

Local field effects in magneto-optics of two-dimensional arrays of ferromagnetic nanoparticles

A theory of the polar magneto-optical Kerr effect in a layer of small ferromagnetic particles has been developed in the framework of the Green’s function method of electrodynamics. The manifestation in magneto-optics of the local field effect, which is initiated by the contribution to the effective field of dipole moments induced in particles, has been studied in terms of the model of a square lattice of ferromagnetic ellipsoids. The magneto-optical Kerr effect stimulated under normal incidence of a linearly polarized electromagnetic wave on a layer of particles magnetized perpendicular to the layer plane has been analyzed. The dependence of the Kerr rotation angle in an array of ellipsoidal Co particles embedded in the transparent dielectric CaF₂ on the light frequency, the parameters of the ellipsoidal particles, and the lattice period (concentration of the magnet in the layer) has been studied numerically. It has been shown that, within a broad (2.0–4.5 eV) spectral range, the local field effect studied as a function of increasing concentration of Co particles in the layer manifests itself in the reversal of the sign of the Kerr rotation compared to that observed in a single ellipsoid or a solid Co film.     

Spectroscopy of the photonic stop band in synthetic opals

The photonic band gap of opals has been studied experimentally from their optical transmission spectra as a function of the incident beam orientation in the opal crystal lattice. The measurements were carried out for all high-symmetry points on the surface of the Brillouin zone of an fcc lattice. The experimental dependence of the energy position of the photonic band gap on the light wave vector direction is well described by the set of theoretical relations developed for the stop bands originating from the Bragg diffraction of light on {111}-type planes of the twinned fcc lattice of synthetic opals.     

Effect of certain factors on the vibrations of polymers

The authors' work on the effect of various factors on the vibrations of the polymer chain is reviewed. A method of calculating chain vibrations is briefly described, an expression is given for the strain energy of a polymer molecule in the nonlinear approximation, the frequency shift of the vibrations of a molecule under load is calculated and discussed, the effect of intermolecular interaction in the polymer crystal and the disorder of the chain on the vibration spectrum is taken into account, and the change in the intensity of the normal vibrations when the chain is loaded and the effect of anharmonicity on the band width are investigated. In conclusion, the stress distribution over the interatomic bonds is estimated.A. F. Ioffe Physico-Technical Institute, Academy of Sciences of the USSR, Leningrad. Translated from Mekhanika Polimerov, No. 1, pp. 33–46, January–February, 1975.     

Spontaneous emission and elastic scattering of light from quantum-well excitons in a Fabry-Perot microcavity

A theory of spontaneous emission and elastic light scattering by quasi-two-dimensional excitons in a quantum well placed in a Fabry-Perot microcavity is developed. The problem is solved by means of electrodynamic Green’s functions with inclusion of fluctuations of the quantum-well width and cavity wall shape treated as a perturbation. General expressions are found in a zero approximation of perturbation theory (plane interfaces) for the radiative decay rates of quasi-two-dimensional excitons and for their energy shifts in the cavity. The boundary conditions for the electromagnetic field are taken into account through the coefficients of inward light reflection from the cavity walls. Resonance contributions to the scattering cross sections, which differ in the polarizations (p or s) of the incident and scattered waves, are derived in the lowest (Born) approximation in quantum-well width fluctuations. The spectral and angular dependences of elastic light scattering are studied numerically for Gaussian and exponential correlation functions. It is shown that the contribution from quantum-well width fluctuations to light scattering exceeds that due to single interfaces (surfaces) of a heterostructure by two orders of magnitude.     

Two-Dimensional Coulomb Plasmon-Excitons: Relaxation of Excitations

Physics of the Solid State - A theory is developed for the relaxation of two-dimensional non-radiative (Coulomb) plasmon-excitons in closely located thin layers of a metal and a semiconductor. In...     

Anisotropic local-field effects of nanoparticles in plasmonic optics and magneto-optics

A theory of anisotropic optical local-field effects caused by resonantly polarizable small particles in multilayer polarizable media is developed. Considered is the model of a rectangular lattice of ellipsoidal nanoparticles with taking account of “image forces” at an interface in a layered medium. The lattice sums for anisotropic dipolar interactions are found using the Green’s function method in the quasi-point dipole approximation, and the effective polarizabilities of particles in a layer located near an interface are calculated self-consistently. The manifestation of an anisotropic local field of nanoparticles in optical radiation and propagation of evanescent waves responsible for optical near-field effects is investigated. Applications of the obtained results in the polar magneto-optical Kerr effect and reflectance anisotropy spectroscopy in propagating the polarized light along the normal to layers are considered. The resonant features in the spectra due to enhancement of the optical effects under excitation of surface (local) plasmons in nanoparticles of a noble metal are studied.