On the dielectric approximation in the additional light waves theory: an historical rehabilitation (recovery)

After the basic Pekar papers on crystal optics with spatial dispersion (CSD) among a lot of others there was the “dielectric approximation” (DA) method. But soon it has been fully rejected because, as it was recognized by the main group of authors on the theme, it came in conflict with the law of conservation of energy flux through the ideal vacuum-crystal interface. The objective of this paper is to advance a way for rehabilitation of DA method by using indispensable broadening and essential generalization of the expression just for the energy flux density vector (EFDV) at the vacuum-medium interface (the so-called Poynting-Pekar vector in the additional light waves (ALW) theory)

Resonance generation of sum harmonic in static electric field

Using the group theory considerations, we investigate the nonlinear effect tensor (NET) for a crystal in a static electric field when a harmonic or the initial emission frequency approaches that of the excitonic absorption band. The dependence of additional terms in NET (resulting from the electric field applied) on the electric field components is found. Their form is shown to differ from that of usual NET. The results obtained are illustrated by considering the case of the D₂d crystal symmetry

Analysis of the fundamental absorption edge of the films obtained from the C₆₀ fullerene molecular beam in vacuum and effect of internal mechanical stresses on it

Nanostructures with fullerene C₆₀ were obtained using vacuum sublimation thermal C₆₀ fullerene powder onto unheated substrates made of silicon, mica, silica and coverslip glass. The effect of the structure, composition and mechanical stresses in the films on fundamental absorption, density-of-states tails in them were investigated by Ramаn spectroscopy, atomic force microscopy, light absorption, electroreflectance modulation spectroscopy and measuring the bend of heterosystems. Ascertained in this work has been the origin of variation observed in literature data concerning the width of the band gap Eg between 1.48 to 2.35 eV and the nature of the fundamental absorption edge in solid C₆₀. This variation is related with decomposition of fullerene molecules caused by the increase in temperature of sublimation. It has been found that C₆₀ in the crystalline state is direct band-gap semiconductor with Eg close to 1.6 eV in the singular point X of the Brillouin zone. The electroreflectance spectra of films and heterosystems bending were used to calculate the Eg dependence on the internal mechanical stresses. The respective coefficient value is equal to –2.8 10⁻¹⁰ eV/Pa

Effect of oxidation of catalytically active silicon-based electrodes on water decomposition

In this work, we continue to study the revealed phenomenon of current creation in the electrochemical system with distilled water during its decomposition without any applied external voltage. Investigated are catalytically active (to decompose water) electrodes based on silicon with modified surface (due to lapping, texturing, doping with palladium, creation of silicides) before and after thermooxidizing for 1 hour in dry oxygen at 850 ºC. Also performed are investigations of time dependences for the current between silicon electrodes and counter-electrodes made of Al, Pt, Yb when using the circuit with the external voltage V₀ = ± 9.7 V. Analyzed are the results obtained and prospects for a further study

Investigation of ZnO single crystals subjected to a high uniform magnetic field in the IR spectral range

Based on the experimental data obtained, we performed the theoretical investigation of the external reflectance coefficients of uniaxial optically anisotropic polar ZnO single crystals subjected to the action of a high uniform magnetic field that is parallel to the crystal axis С and the surface under the condition that E⊥B (the Voigt configuration, Fig. 1). For the first time, we have found the regions in the external reflection spectra of ZnO single crystals, where new oscillations appear which are due to the effect of a high uniform magnetic field. A possibility of solving the direct and inverse problems in such a case is demonstrated

Effect of strong magnetic field on surface polaritons in ZnO

Using the attenuated total reflectance technique, we studied the effect of strong uniform magnetic field H on the main properties of surface polaritons in ZnO single crystals. The used orientations were C || y , k ⊥ C , xy || C , H ⊥k , H || y , k x =k , ky,z =0; the free charge carrier concentration varied from 9.3×10¹⁶ up to 2.0 × 10¹⁸ cm⁻³. It has been shown that three dispersion curves exist in the zinc oxide single crystals for the above orientation. The possibility of excitation of an additional dispersion branch in optically anisotropic semiconductors placed into magnetic field is found using ZnO single crystals as an example. The damping coefficients for surface phonon and plasmon-phonon polaritons have been determined

Spectra of the photo-electric phenomena physically differentiated on the light absorption factor

The pleochroism phenomena in photoconductivity of Ge samples and gate photoelectomotive force (photo-emf) of Si samples were experimentally investigated by a polarization modulation method. Anisotropy of dielectric properties was created by uniaxial compression. The spectral characteristics of the polarization difference describing above effects were measured. We found that: а) the pleochroism spectrum of photoconductivity is a derivative with respect to the absorption factor of a photocurrent function; b) the pleochroism spectrum of the gate photo-emf contains dichroic components, determined by the sample thickness, diffusion length of majority carriers, and layer thickness of a spatial charge

Ge/GaAs(100) Thin Films: Large Effect of Film Growth Rate and Thicknesses on Surface Morphology, Intrinsic Stresses and Electrical Properties

We found out and studied a profound effect of film growth rate on the electrical properties, intrinsic stresses and surface morphology of thin Ge films grown on GaAs(100). This effect is essential and has to be accounted for when developing and producing devices based on the Ge/GaAs heterostructure. All the Ge films under investigation were single-crystalline and epitaxially-grown on the GaAs(100) substrates. However, the transport phenomena in Ge films grown at low and high deposition rate differed drastically. Those obtained at low deposition rate were p-type and high resistant. They had a low concentration of free charge carriers and thermally activated conductivity, which is characteristic of heavily doped and strongly (in the limiting case, fully) compensated semiconductors. Although such films were single-crystalline, their conductivity was percolation-type. The Ge films obtained at high deposition rate were n-type and low resistant. They had high concentration of free charge carriers. The temperature dependence of conductivity in such films was weak or practically absent, which is characteristic of degenerate heavily doped semiconductors. Besides, the surface morphology cardinally differed for films obtained at low and high deposition rate. At low film growth rates, surfaces with developed relief were observed whose valleys and ridges formed grains of irregular shape with pronounced substructure. As the film thickness grew, the surface relief became essentially pronounced. At rather high film deposition rates, contrary to the above, the Ge film surface was fine-grained and smooth; the surface relief practically did not depend on the film thickness. As the deposition rate went down, the intrinsic stresses in films essentially decreased. The results obtained were analyzed from the viewpoint of formation of compositional and morphological inhomogeneities, and fluctuations of electrostatic potential at low growth rates. Such potential fluctuations modulate Ge energy bands leading to appearance of potential relief and deep tails of density of states in the Ge bandgap. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3506

Surface polariton excitation in ZnO films deposited using ALD

The conductive ZnO films deposited using atomic layer deposition (ALD) on the optical glass substrates were studied using the modified method of the disturbed total internal reflection within the range 400…1400 cm⁻¹ for the first time. The frequency “windows” with the obtained excited surface phonon and plasmon-phonon polaritons have been found in the measured infrared reflectance spectra. The dispersion response of high and low frequency branches of the IR spectra have been presented

Influence of some physico-chemical factors on properties of electrodes that decompose water catalytically

We have investigated the current creation accompanied by the water decomposition H₂O → OH + H caused by various catalytically active electrodes with different electrochemical potentials, both without external electric voltage on these electrodes and with the applied voltage V₀ = ±9.7 V. It is found that the current value and its time dependence are essentially influenced by such factors as thermal and natural (in ambient atmosphere) oxidation of electrodes (made of Al, Si, Yb, Ni, Ti, Cr₃Si, and Ni₃Si), changing their relief (texturing, polishing), and the electrolytic deposition of palladium as an impurity on the surface (Ti, Cr₃Si). Changes in the current caused by the above factors are realized as a consequence of changes in both the electron work function inherent to these electrodes and their catalytical activity concerning the water decomposition both in the absence and the presence of the external voltage V₀