Electronic structure of the Si-C-N amorphous films

The results of the investigation of amorphous a-SiC _x N _y films of various compositions by the ultra-soft X-ray emission spectroscopy are presented. The Si L _{2, 3}, C K _α, and N K _α emission spectra, which reflect the partial densities of states Si 3s3d, C 2p, and N 2p, respectively, have been measured and analyzed. It has been established that the Si-N chemical bond is similar in type to the Si-C chemical bond and completely substitutes for the Si-C bonds in thin a-SiC _x N _y films as the oxygen concentration increases. A similar effect is associated with the local agglomeration and subsequent clusterization of carbon atoms in the SiN-enriched regions of the internal volume of the film. A high ability of the a-SiC _x N _y films to oxidation in air has been established. This has been confirmed by a satisfactory approximation of the Si L _{2, 3} X-ray emission spectra of a-SiCN with the use of the superposition of the spectra of γ-Si₃N₄ and Si₂N₂O. The relative weight coefficients of the spectra of γ-Si₃N₄, which have been used to approximate the spectra of thin a-SiC _x N _y films, are proportional to the values of the Young’s modulus for different values of compositions (different values of x and y).     

Vibronic structure and the anisotropy of excitons in cubic LiH single crystals

The shape of one-phonon sidebands of exciton in LiH is studied both in reflection and edge luminescence spectra. The main structure of the shape is found to reflect the phonon density of states. This fact is interpreted as a result of a high anisotropy of the exciton band.     

Effect of high doses on the Si <Emphasis Type="Italic">L</Emphasis><Subscript>2,3</Subscript> x-ray emission spectra of silicon implanted with iron ions under steady-state conditions

The effect of high doses on p-and n-type silicon samples implanted with Fe⁺ ions under steady-state conditions (implantation energy, 100 keV; ion current density, 0.6–0.8 μA/cm²; irradiation dose, 10¹⁴–10¹⁶ ions/cm²) is investigated using Si L _{2, 3} x-ray emission spectroscopy (the 3d3s → 2p electronic transition). An analysis of the Si L x-ray emission spectra of the silicon samples is performed by comparison with the spectra of reference materials and the spectra of silicon samples implanted with Fe⁺ ions in a pulsed mode. The Si L x-ray emission spectra are simulated by the molecular dynamics and full-potential linearized augmented-plane-wave (FLAPW) methods. It is revealed that the effect of high doses under steady-state conditions of Fe⁺ ion implantation into the semiconductor crystal matrix exhibits specific features: the disordering of the structure and partial amorphization of the sample from the surface deep into the bulk are more pronounced than those observed under conditions of pulsed ion implantation, although virtually no recrystallization of the sample at the threshold dose occurs. The most probable origins and mechanisms of the effect of high doses on the samples under investigation are discussed.     

On Independence of the Thermal-Spike Temperature in Pure Metals of the Implanted Ion Energy and Atomic Mass

Russian Physics Journal - The optical emission spectra of pure metals Fe, Zr, Ta and W are measured during their irradiation with Ar+, Kr+ and Xe+ ions (5, 10, 15 and 20 keV). It is found out that...     

Computer simulation of the energy gap in ZnO- and TiO2-based semiconductor photocatalysts

Ab initio calculations of the electronic structures of binary ZnO- and TiO₂-based oxides are performed to search for optimum dopants for efficient absorption of the visible part of solar radiation. Light elements B, C, and N are chosen for anion substitution. Cation substitution is simulated by 3d elements (Cr, Mn, Fe, Co) and heavy metals (Sn, Sb, Pb, Bi). The electronic structures are calculated by the full-potential linearized augmented plane wave method using the modified Becke-Johnson exchange-correlation potential. Doping is simulated by calculating supercells Zn₁₅D₁O₁₆, Zn₁₆O₁₅D₁, Ti₁₅D₁O₃₂, and Ti₈O₁₅D₁, where one-sixteenth of the metal (Ti, Zn) or oxygen atoms is replaced by dopant atoms. Carbon and antimony are found to be most effective dopants for ZnO: they form an energy gap ΔE = 1.78 and 1.67 eV, respectively. For TiO₂, nitrogen is the most effective dopant (ΔE = 1.76 eV).     

Study of breakdown in yttrium aluminum garnet at subnanosecond times of increasing voltage

Crystallographically oriented channels with bottlenecks in the regions of reflection of the pulses have been obtained in aluminum yttrium garnet during multipulsed nanosecond breakdown from the anode under voltages of 100–140 kV, and the propagation rate of the fronts of the phase transition in this voltage range has been determined. It has been shown that the character of the observed pattern of the sequential formation of separate chains of the complete breakdown structure indicates that the channel is formed only locally and immediately at the point of time of passing the breakdown front since the maximal field strength, the magnitude of which determines the diameter of the breakdown channel, is observed in the vicinity of the breakdown front.     

Resistance of a pulsed electrical breakdown channel in ionic crystals

A technique for estimating the resistance of the electrical breakdown channel in ionic crystals is proposed. This technique is based on measuring the channel velocity in a sample when a ballast resistor is connected to the circuit of a needle anode and on using the theoretical dependence of the channel velocity on the channel conductivity. The breakdown channel resistance at a voltage of 140 kV is about 6.5 kΩ in KCl and about 6.1 kΩ in KBr. These resistances are shown to characterize a gas phase. The gas-phase resistance is found to be nonuniform along the breakdown channel. The head part ～1 mm long has the maximum resistance. This head region is concluded to contain dielectric substance clusters, which then decompose into metal and halogen ions. The cluster lifetime is ～10^?9 s.     

Simulation of the electronic structure of simple oxides BeO and SiO2 and complex oxides Be2SiO4 and Be2SixGe1 ? xO4 with the phenacite structure

The ab initio numerical calculations of the electronic structure of simple oxides BeO and SiO₂ and complex oxides Be₂SiO₄ and Be₂Si _x Ge_{1 − x} O₄ with the phenacite structure have been performed using the electron density functional theory. The calculations indicate that the main feature of the systems under investigation is the presence of oxygen states in both the valence and conduction bands. The splitting of the bottom of the conduction band has been revealed in the electronic structure of the Be₂Si _x Ge_{1 − x} O₄ system. The splitting width is about 1.5 eV. The main contribution to the formation of a narrow subband of the conduction band comes from the 2s and 2p states of oxygen and the 4d state of germanium. Microscopic models of the spatial localization of the electron density on lower energy states of the conduction band of oxide crystals have been developed using the Wannier function technique. The reflection spectra of BeO, SiO₂, and Be₂SiO₄ have been analyzed. The reported calculations of the electronic structure imply the exciton nature of the 9.7-eV reflection peak in the Be₂SiO₄ crystal.     

The effect of high iron-ion implantation doses on the X-ray emission spectra of silicon

X-ray emission spectroscopy (Si L _{2, 3} spectra, 3d3s → 2p electronic transition) was employed to study p-and n-type silicon samples implanted with Fe⁺ ions in a pulse mode (the implantation energy was 30 keV, the pulse current was varied up to 0.5 A, the pulse duration was 400 μs, and the ion irradiation doses ranged from 10¹⁴ to 10¹⁷ cm⁻²). The x-ray emission spectra were found to be dependent on the ion irradiation dose and the electron-accelerating voltage that was used in the x-ray studies. By comparing the Si L spectra with the spectra of reference materials and by modeling the former spectra, it was revealed that, as the ion-irradiation dose increases, there occur disordering of the structure, partial amorphization of the sample in a surface layer approximately 7200-? thick, and its subsequent recrystallization (under high irradiation doses). It was shown that this effect is most pronounced in a layer at a depth of ∼1000 ? and is not associated with the formation of iron silicide FeSi in the bulk of the sample but rather is due to the breakage of Si-Si bonds caused by ion implantation under the irradiation doses used. Original Russian Text ? D.A. Zatsepin, E.S. Yanenkova, é.Z. Kurmaev, V.M. Cherkashenko, S.N. Shamin, S.O. Cholakh, 2006, published in Fizika Tverdogo Tela, 2006, Vol. 48, No. 2, pp. 204–209.