Charge transfer mechanism in high-purity silicon-basedn +-π-p + structures

Results of experimental investigations into current-voltage characteristics of n⁺-π-p⁺ structures based on high-purity silicon doped with boron are presented. It is shown that the I–V characteristic at high injection levels is described by Stafeev's theory, when the thickness d of the π-region is smaller than or close to three ambipolar diffusion lengths L_a. For a current density J above (3–50) A/cm² at varying temperatures, the I–V characteristic obeys a relation usually occurring in the case where charge-carrier recombination in the n⁺ and p⁺-regions dominates that found in the π-region. The effect of mutual electron-hole scattering on the behavior of the I–V characteristic is evident at J>630 A/cm³. For d/L_a=9, the I–V characteristic at high injection levels is treated by the theory of double carrier injection into a semiconductor with consideration for diffusion corrections. In the temperature range below 200–276 K, the I–V curve for all samples studied exhibits a linear dependence on J followed by a portion corresponding to a maximum occupancy of recombination levels by injected electrons. Here the Fe or Au donor levels presumably act as recombination levels. The electron and hole capture areas (cross sections) by recombination centers are roughly estimated. Siberian Physicotechnical Institute at Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 35–45, July 2000.     

Electron impact excitation of high-lying states in the tungsten atom

The extended crossed-beam method has been used to study excitation of high-lying levels in the tungsten atom. 40 excitation cross sections of WI spectral lines have been measured for exciting electron energy 50 eV. Two optical excitation functions were recorded in the electron energy range 0–200 eV. The results obtained were used to calculate the total excitation cross sections of 24 odd WI energy levels. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 3, pp. 283–288, May–June, 2007.     

Features of particle excitation in high-frequency capacitive discharge

The efficiencies of excitation of different atomic and molecular levels of a gaseous medium by a low-current high-frequency capacitive discharge (HFCD) and a dc discharge are compared theoretically. It is shown that for transitions between lower vibrational levels of molecules an increase in spectral line intensity by a factor of 1.2–1.6 is observed, and for neon transitions from high-lying levels, by a factor of 1.5–3.0. The stability of low-current HFCD is experimentally investigated for different configurations of gas-discharge gaps. The results of these investigations are used in developing compact planar and coaxial HFCD lasers. B. I. Spepanov Institute of Physics, Academy of Sciences of Belarus, 70, F. Skorina Ave., Minsk, 220071. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 3, pp. 291–296, May–June, 1997.     

Investigation of Saha-Boltzmann equilibrium in the analyte zone of a two-jet plasma generator

Relative populations of the excited levels for Cr(I), Cr(II), Fe(I) and Fe(II) in the argon plasma flow of an arc two-jet plasma generator used in spectrochemical analysis were measured. The range of the total energy E of excitation and ionization was 4.5–8.0 and 12.5–16.0 eV, respectively. It is shown that the populations of atom and ion levels are linear with respect to energy lower than E∼15 eV. For ionic lines with energy close to 15.5–16.0 eV the line intensities behave anomalously against equilibrium values. This can be associated with charge transfer between the analyte and argon ions. Deviation of I from LTE values increases in the plasma zones below and above the site of jet confluence, where the plasma temperature decreases. A. P. Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, 1a Favorskii St., Irkutsk, 664033, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 5, pp. 575–581, September–October, 1997.     

Energies,Landé <Emphasis Type="Italic">g</Emphasis>-factors,and lifetimes for some excited levels of doubly ionized lanthanum

Using the relativistic Hartree-Fock (HFR) method developed by Cowan, we calculated the energy levels, Landé g-factors, and lifetimes for nd (n = 5–25), ns (n = 6–24), ng (n = 5–25), nf (n = 4–22), and np (n = 6–25) excited levels of doubly ionized lanthanum (La III, Z = 57). We compared the results with previously reported calculations and experiments.     

Defect formation in thin films of the semiconductor compound Cu(In,Ga)Se2 when bombarded by protons

We have used low-temperature (4.2–78 K) photoluminescence to study defect formation processes in Cu(In,Ga)Se₂ films when bombarded by protons with energy 380 keV. We have observed formation of luminescence centers with deep levels at ∼410 meV and 470 meV. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 6, pp. 828–830, November–December, 2006.     

Electric-field-dependent energy structure of quasi-one-dimensional conductor <Emphasis Type="Italic">p</Emphasis>-TaS<Subscript>3</Subscript>

Energy structure of the Peierls gap in orthorhombic TaS₃ is examined by spectral study of photoconduction. The gap edge and energy levels inside the Peierls gap are observed. The amplitude of the energy levels is found to depend on both the temperature and the electric field. The electric field of the order of 1–10 V/cm affects the energy levels and leads to the redistribution of intensity between peaks. The small value of the electric field indicates participation of the collective state in formation of the energy levels inside the Peierls gap. Published in Russian in Pis’ma v Zhurnal éksperimental’noĭ i Teoreticheskoĭ Fiziki, 2009, Vol. 89, No. 10, pp. 607–611. The article was translated by the authors.     

Thermally stimulated currents in semi-insulating GaAs Schottky diodes and their simulation

We report the investigation of the non-irradiated and irradiated-with-pions Schottky diodes made on semi-insulating GaAs. Thermally stimulated currents have been measured experimentally and modeled numerically. To reveal the influence of the single levels, we used the thermal emptying of the traps by fractional heating. Attention is paid to the comparative analysis of the distribution of the parameters of different samples produced and processed by the same technique, contrary to the usual approach of the analysis of a few different samples. The following main conclusions are drawn. First of all, many different levels (from 8 to 12) have been found in the temperature range from 90 K to 300 K in all samples. Their activation energies range from 0.07 up to 0.55 eV, their capture cross-sections are 10^-22–10^-14 cm², and initial occupation is 2×10¹¹–5×10¹⁴ cm^-3. The irradiation with pions does not influence the density of most levels significantly. On the other hand, levels with activation energies of about 0.07–0.11 eV, 0.33–0.36 eV, 0.4–0.42 eV, and 0.48–0.55 eV have been found only in the irradiated samples. Irradiation also increases the inhomogeneity of the crystals, which causes the scattering of the activation energies obtained by fractional heating technique. Received: 13 November 1998 / Accepted: 16 April 1999 / Published online: 4 August 1999     

Nuclear structure investigations in the region of superheavy nuclei

Radioactive decay from the ground state or isomeric states has been investigated for a series of nuclei in the region of Z = 100–106 by means of α–γ—or evaporation residue-(γ, conversion electron)—measurements in prompt and delayed coincidence. Systematic trends in single-particle level energies in N = 145–151 odd-even isotones could be extended up to Z = 104, while an energy systematics of lowlying Nilsson levels in odd-mass einsteinium isotopes was established. Information on nuclear levels at E* > 500 keV was obtained from the decay study of isomeric states in ^251−255No. The text was submitted by the author in English.     

Spectroscopic characteristics of erbiumand ytterbium-activated laser media

Judd–Ofelt parameters (Ω₂ = 5.09∙10^–20, Ω₄ = 0.92∙10^–20, and Ω₆ = 0.63∙10^–20 cm²) and oscillator strengths of fundamental optical transitions involved in lasing at wavelength 1.54 μm have been calculated for borosilicophosphate glass co-activated with Er³⁺ and Tb³⁺ ions based on experimental luminescence and absorption spectra and refractive indices. The results were used to determine the emission (6∙10^–23 cm²) and absorption (5∙10^–21 cm²) cross sections for λ = 1.54 μm and the gain cross section as a function of inverse population levels.     

Propagation of higher order Bessel–Gaussian beams in turbulence

The propagation characteristics of higher order Bessel–Gaussian beams travelling in turbulent atmosphere are investigated. Using extended Huygens–Fresnel principle, I formulated receiver plane intensity and solved it down to a double integral stage. Source beam plots are made illustrating the variation of intensity against order and width parameter. From the examination of receiver intensity graphs, it is seen that Bessel–Gaussian beam are converted into modified Bessel–Gaussian beams at intermediate propagation ranges eventually ending up as Gaussian profiles. The impacts of order and turbulence levels on beam profile are analysed. Focusing effects and beam size change along the propagation axis are studied. PACS 41.85.Ew; 42.68.Bz     

On the biphoton excitation of the fluorescence of the bacteriochlorophyll molecules of purple photosynthetic bacteria by powerful near IR femto-picosecond pulses

The authors of a number of experimental works detected nonresonance biphoton excitation of bacteriochlorophyll molecules, which represent the main pigment in the light-absorbing natural “antenna” complexes of photosynthesizing purple bacteria, by femtosecond IR pulses (1250–1500 nm). They believe that IR quanta excite hypothetic forbidden levels of the pigments of these bacteria in the double frequency range 625–750 nm. We propose and ground an alternative triplet mechanism to describe this phenomenon. According to our hypothesis, the mechanism of biphoton excitation of molecules by IR quanta can manifest itself specifically, through high triplet levels of molecules in the high fields induced by femtosecond-picosecond laser pulses.     

Topological Berry phase and semiclassical quantization of cyclotron orbits for two dimensional electrons in coupled band models

The semiclassical quantization of cyclotron orbits for two-dimensional Bloch electrons in a coupled two band model with a particle-hole symmetric spectrum is considered. As concrete examples, we study graphene (both mono and bilayer) and boron nitride. The main focus is on wave effects – such as Berry phase and Maslov index – occurring at order (^h/_2p)\hbar in the semiclassical quantization and producing non-trivial shifts in the resulting Landau levels. Specifically, we show that the index shift appearing in the Landau levels is related to a topological part of the Berry phase – which is basically a winding number of the direction of the pseudo-spin 1/2 associated to the coupled bands – acquired by an electron during a cyclotron orbit and not to the complete Berry phase, as commonly stated. As a consequence, the Landau levels of a coupled band insulator are shifted as compared to a usual band insulator. We also study in detail the Berry curvature in the whole Brillouin zone on a specific example (boron nitride) and show that its computation requires care in defining the “k-dependent Hamiltonian” H(k), where k is the Bloch wavevector.     

New insights into nanocomposite adsorbents for water treatment: A case study of polystyrene-supported zirconium phosphate nanoparticles for lead removal

By encapsulating zirconium phosphate (ZrP) nanoparticles into three macroporous polystyrene resins with various surface groups, i.e., −CH₂Cl, −SO₃ ⁻, and −CH₂N⁺(CH₃)₃ three nanocomposite adsorbents (denoted as ZrP–Cl, ZrP–S, and ZrP–N) were fabricated, respectively for lead removal from water. Effect of the functional groups on nano-ZrP dispersion and effect of ZrP immobilization on the mechanical strength of the resulting nanocomposites were investigated. The presence of the charged functional groups (−SO₃ ⁻ and −CH₂N⁺(CH₃)₃) are more favorable than the neutral −CH₂Cl group to improve nano-ZrP dispersion (i.e., to achieve smaller ZrP nanoparticles). ZrP–N and ZrP–S had higher capacity than ZrP–Cl for lead removal. As compared to ZrP–N, ZrP–S exhibits higher preference toward lead ion at high calcium levels as a result of the potential Donnan membrane effect. On the other hand, nano-ZrP immobilization would simultaneously reinforce both the compressive strength and the wear performance of the resulting nanocomposites with the ZrP loadings up to 5 wt%. The results reported herein would shed some light on the generation of environmental nanocomposites with high capacity and excellent mechanical strength.     

Optico-Mechanical Analogy: an Axiomatic Approach

An axiomatic characterization of a ‘two-level Hamiltonian structure’ is proposed, which expresses the optico-mechanical analogy by representing optics and mechanics as (disjoint) classes of models satisfying the axioms. There is the ‘Hamilton–Jacobi level’, which involves a differential manifold on which the characteristic function satisfying the Hamilton–Jacobi equation is defined; and the ‘symplectic level’, involving the Hamiltonian, defined on the cotangent bundle of the manifold. The two levels, with the (analogous) structures on them, concern both optics and mechanics.     

A Mathematical Theory for Vibrational Levels Associated with Hydrogen Bonds I: The Symmetric Case

We propose an alternative to the usual time–independentBorn–Oppenheimer approximation that is specifically designed todescribe molecules with symmetrical Hydrogen bonds. In our approach,the masses of the Hydrogen nuclei are scaled differently from thoseof the heavier nuclei, and we employ a specialized form for theelectron energy level surface. Consequently, anharmonic effects playa role in the leading order calculations of vibrational levels. Although we develop a general theory, our analysis is motivated byan examination of symmetric bihalide ions, such as FHF ⁻ orClHCl ⁻. We describe our approach for the FHF ⁻ ion in detail. Partially Supported by National Science Foundation Grants DMS–0303586 andDMS–0600944.     

Luminescence studies of porphyrin exchange in pregnant females

Results of investigations of the level of proto- and coporphyrins in erythrocytes and excretion of coproto- and uroporphyrins from the organism for two control groups are presented. The first group consisted of healthy males and females 20–33 years of age; the second group was consisted of females with nonpathological pregnancy. Levels of proto- and coporphyrins in erythrocytes and copro- and uroporphyrins in urine are investigated. A reliable (P<0.03) increase in the protoporphyrin concentration in erythrocytes of pregnant females compared to the first control group is found. The average protoporphyrin levels in the first and second groups are 344±18 and 488±20 μg/liter, respectively. Coporphyrin levels in these groups differ insignificantly. Coporphyrin excretion from the organism of pregnant females has shown a tendency to increase for pregnancy terms of up to eight weeks and decrease for long terms (more than 32 weeks). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 5, pp. 633–636, September–October, 1997.     

Chern–Simons particles with nonstandard gravitational interaction

The model of nonrelativistic particles coupled to nonstandard (2+1)-gravity is extended to include Abelian or non-Abelian charges coupled to Chern–Simons gauge fields. Equivalently, the model may be viewed as describing the (Abelian or non-Abelian) anyonic dynamics of Chern–Simons particles coupled, in a reparameterization invariant way, to a translational Chern–Simons action. The quantum 2-body problem is described by a nonstandard Schr?dinger equation with a noninteger angular momentum depending on energy as well as particle charges. Some numerical results describing the modification of the energy levels by these charges in the confined regime are presented. The modification involves a shift as well as splitting of the levels. Received: 16 March 2001 / Published online: 13 June 2001     

Effects of energy-spectrum broadening in alloyed semiconductor superlattices

The density of energy states is calculated for alloyed semiconductor superlattices for different excitation levels with cllowance for the effects of screening and fluctuations of impurity concentrations. The influence of the state density tails on spontaneous-emission spectra is investigated for cross-over transitions and in a model without a selection rule for the electron wave vector. Account for the state density tails allows one to describe the longwave wing and shape of spontaneous-emission spectra in accordance with experimental data. Reported at the Second International Scientific and Technical Conference on Quantum Electronics, Minsk, November 23–25, 1998. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 5, pp. 711–715, September–October, 1999.     

Thermal ionization of impurity centers in Fe-doped Bi12SiO20 and Bi12GeO20 crystals

The spectral and temperature dependence of the optical absorption and thermally stimulated depolarization currents in Fe-doped Bi₁₂SiO₂₀ and Bi₁₂GeO₂₀ crystals are investigated in the photon energy range 1.36–3.46 eV and temperature 85–750 K. The results show thermally induced electron redistribution between donor and acceptor levels and defect association-dissociation processes and are discussed using the configuration-coordinate model. Fiz. Tverd. Tela (St. Petersburg) 41, 1006–1011 (June 1999)