V. V. Sobolev

Chapter 5 – Optical Spectra of Arsenic Chalcogenides in a Wide Energy Range of Fundamental Absorption

This chapter presents new information on the spectra of complete sets of the fundamental optical functions of arsenic chalcogenide glasses in the range 0–35 eV, concerning their most intensive transitions and the main parameters of these transitions. Complete sets of the spectra of the fundamental optical functions of three glassy arsenic chalcogenides As 2 S 3 , As 2 Se 3 , As 2 Te 3 , and two phases of As x Se 1-x system in a wide energy range of intrinsic absorption are obtained. Their integral dielectric functions and characteristic bulk loss spectra are decomposed into the elementary transverse and longitudinal components. The main parameters of components are determined, including the transitions energies and probabilities. The schemes of interpretation of the components are proposed in the model of transitions occurring from the maximum densities of the occupied states to the unoccupied states. The obtained results substantially enlarge the amount of information about the optical spectra and electronic structure of As 2 X 3 glasses in a wide energy range of fundamental absorption. In addition, they lay a new principal foundation for the consideration of g-As 2 X 3 properties, and provide a basis for future theoretical calculations of their electronic structure and optical spectra.

Optical Properties and Electronic Structure of PdO

The complete set of optical spectra is calculated for the first time for crystalline PdO in the range 2–5.5 eV for the E ⊥ c and E || c polarizations using experimental dielectric permittivity data. The main features of the spectra are discussed. The origin of the strongest peaks in the spectra is inferred from comparison with band-structure calculations and polarized dielectric permittivity spectra.

Dielectric Permittivity of BiTeI

The dielectric permittivity and volume electron energy loss spectra of the ferroelectric semiconductor BiTeI are calculated for the E ⊥ c polarization in the range 0–12 eV. The spectra are decomposed into elementary components (13), and their principal parameters are evaluated. A correlation is found between the transverse and longitudinal components of interband transitions.

Optical Spectra of Palladium Oxide

The complete sets of spectra of the optical fundamental functions for porous films and single crystals of palladium oxide are determined in the range 1–6 eV. The main features of these functions and their dependences on the long-range order perfection of the structure are revealed.

Optical properties and electronic structure of fluorite and corundum

The complete sets of 12 fundamental optical functions for fluorite crystals in the range 5–39 eV and corundum crystals in the range 2–30 eV are determined from the experimental and theoretical spectra known for certain of these functions. The main features and generalities of these functions are revealed. A theoretical analysis of the optical spectra obtained is performed using the known theoretical band diagrams and the spectra of ɛ2.

Electron characteristic loss spectra of molybdenum dichalcogenides

The complete sets of the fundamental optical functions of molybdenum dichalcogenides have been considered for the first time. The energies of their bulk and surface plasmons of two types are determined. It is found that the energies of long-wavelength plasmons correlate with the energies of the deep minima in the reflectivity and ɛ2E2 spectra and the maxima in the reflectivity phase spectra.

Indirect interband transitions in graphite with a wide quasigap

Sets of fundamental optical functions in the energy range of 0–40 eV for longitudinal indirect interband transitions in graphite with a quasi-gap up to 2.6 eV have been determined for the first time. Their structure and parameters depend strongly on the electron wave vector transfer q. The nature of the peaks and shoulders of these functions is explained within the model of theoretical shifted bands for four electron wave vector transfers q in a volume characteristic electron-energy losses for the Γ-P direction in the Brillouin zone. The calculations were performed on the basis of the known experimental volume characteristic electron-energy loss spectra of graphite in the range of 0–40 eV for |q| = 0.00, 0.375, 0.625, and 1.00 Å−1 using a special software package.

Oscillator strengths and transition energies of diamond

The spectrum of the dielectric constant of three different samples of diamond in the 5–30-eV region is decomposed in thirteen elementary components. The main parameters of components are determined, and their nature is found on the basis of the band model.

Optical and electron energy loss spectra of cadmium dichloride and lead dichloride crystals

Experimental electron energy loss spectra of cadmium dichloride and reflection spectra of lead dichloride are used to calculate the complete sets of fundamental optical functions of the two highly ionic materials in a wide energy range (0–30 eV). Their cumulative permittivity and volume electron energy loss curves are decomposed into transverse and longitudinal elementary components of transitions, and their main parameters are evaluated. The effect of the nature of the cation on the key features of the optical spectra is examined.

Fundamental spectra of optical functions of ferroelectric sodium nitrite

Spectra of optical fundamental functions of ferroelectric sodium nitrite were determined in the range 4–24 eV at 77 K for the three polarizations: E ∥ a, E ∥ b, and E ∥ c. The calculations were based on the experimental R(E) reflection spectra and integral Kramers-Kronig relations. Using the method of Argand diagrams, the permittivity and bulk characteristic electron loss spectra were decomposed into the elementary transverse and longitudinal components. Their main parameters were determined. The obtained data were compared with the theoretical calculations of the permittivity spectra performed using the FPLAPW method. The main features of the permittivity spectra, the parameters of the transitions, and their theoretical nature were established.