Papers by Keyword: Energy Levels

Abstract: It is argued in this work that a DLTS signal associated with hole emission from a radiation-induced defect with an energy level at E_v + 0.09 eV is related to a complex of silicon di-interstitial with an oxygen atom (I₂O). This signal has been observed in the DLTS spectra of p-type Si:O samples irradiated with either 4-6 MeV electrons or alpha particles. Isochronal and isothermal annealing studies of the samples have shown that the defect responsible for the DLTS signal from the E_v + 0.09 eV level disappears upon heat-treatments in the temperature range 75-100 °C and its formation and annealing behavior is similar to that of a center giving rise to the infrared absorption band at 936 cm^-1 previously assigned to a local vibrational mode (LVM) due to the I₂O complex. Possible configurations of the I₂O complex have been found by ab-initio modeling and analyzed. Formation and binding energies, energy levels and LVMs for different configurations have been determined. It has been found that the minimum energy configuration of the I₂O complex consists of the compact I₂ to which a divalent interstitial oxygen atom is attached. Calculated values of the strongest LVM (ν = 971 см^-1 ) and position of the donor level {E_v + (0.11-0.13) eV} for the minimum energy configuration are very close to those assigned to the I₂O defect in the infrared absorption and DLTS experiments.

Abstract: Early transition metals (TMs) of the 3d and 4d rows are undesired contaminants in solarandelectronic-grade Si. From the theoretical standpoint, understanding the properties of these TMs insilicon still remains a challenging problem owing to the strong correlations among the TM d-electrons.The present study proposes a first-principles Hubbard-corrected DFT+U approach, with on-site parametersaccounting separately for electron Coulomb (U) and exchange (J) effects. We use this approachtogether with conventional DFT to determine electrical levels and migration barriers of early3d (Ti, V and Cr) and 4d (Zr, Nb and Mo) TMs in Si. Comparisons with experimental data allowedus to uniquely assign the deep levels in the gap appraising also the effect of on-site correlation. Ourresults also resolve existing controversies in the literature concerning the type and origin of the donorlevels of Cr and Mo. For all the metals, with the exception of Cr, high barriers of interstitial diffusionare obtained, thus confirming that most of these TMs are slow diffusers in silicon.

Abstract: The effects of thickness and impact energy on the impact damage of CFRP laminates were studied in this paper. Impact tests for the CFRP laminates with the size of 600 mm×700 mm with five different thicknesses were subjected to impact fatigue loading at different energy levels from 5 J to 65 J. The crater depth and matrix length were investigated according to different energy levels and different thicknesses. The impact damage was evaluated by visual inspection, three-dimensional microscope. The experimental results reveal that the crater depth and the crack length increase with the increasing impact energy. For the same impact energy, the crater depth and the crack length decreased with the increasing thickness of specimens.

Abstract: The effects of the impact energy on the impact damage of CFRP laminates were studied in this paper. Impact tests for the CFRP laminates with the size of 600 mm×700 mm were subjected to different the impact energy levels from 5 J to 50 J. The matrix length was investigated according to different energy levels. The experimental results reveal that the crack length increases linearly with the increasing impact energy. The impact damage of CFRP laminates tends to be more severe as impact energy increases, and the impact area and crater depth increases with increasing impact energy. The surface of impact dent of specimen looks like W shape.

Abstract: The data obtained recently from combined deep-level-transient spectroscopy (DLTS), local vibrational mode (LVM) spectroscopy and ab-initio modeling studies on structure, electronic properties, local vibrational modes, reconfiguration and diffusion paths and barriers for trivacancy (V₃) and trivacancy-oxygen (V₃O) defects in silicon are summarized. New experimental results on the introduction rates of the divacancy (V₂) and trivacancy upon 4 MeV electron irradiation and on the transformation of V₃ from the fourfold coordinated configuration to the (110) planar one upon minority carrier injection are reported. Possible mechanisms of the transformation are considered and discussed.

Abstract: Tungsten-phosphate glasses doped with trivalent europium ion are synthesized and their spectroscopic properties are analyzed. Following the evolution of the 5D0 → 7F1 electronic transition in a series of various glass compositions via two rank crystal field parameters (cfp’s), a slight modification of the local symmetry is evidenced in the series. Decay lifetimes of 5D1 and 5D0 levels are also analyzed. Optical properties clearly correspond to Eu3+ in the glassy phase. At room as well as at liquid nitrogen temperatures, the emission spectra display comparable features with prominent 5D0 → 7F2 transition. However, at 77 K, the maximum 7F1 splitting exhibits an increase of ≈ 20-23 % for all compounds. This increase is directly connected to a change in local environment around the rare earth ion. The optical properties and the crystal field variation could be correlated with the shortness of the metal-oxygen distances produced by the pressure when cooling.

Abstract: Interaction of boron and aluminum with interstitial carbon is studied using first principles calculations. It is shown that carbon can form very stable complexes with Al and B, forming a family of negative-U bistable defects with deep levels. The influence of this effect on the activation rate of p-type implants is discussed.