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AlxGa1−xN nanowires are the key materials for next-generation ultraviolet (UV) detectors. However, such devices have a low quantum efficiency caused by the introduction of defects and impurities throughout the preparation process of nanowires. Herein, the effects of different interstitial defects and vacancy defects on the electronic structure of Al0.5Ga0.5N nanowires are investigated using density functional theory calculations. Our results successfully discovered that only the formation of an N interstitial defect is thermally stable. In addition, the introduction of different defects makes the different nanowires exhibit n-type or p-type characteristics. Additionally, different defects lead to a decrease in the conduction band minimum in band structures, which is the major cause for the decrease in work function and increase in electron affinity of Al0.5Ga0.5N nanowires. What is more, the calculation of the partial density of states also proved that the interstitial defects contribute to a re-hybridization of local electron orbitals and then cause more significant movement of the electron density. Our investigations provide theoretical guidance for the pursuit of higher-quantum-efficiency ultraviolet (UV) detectors. [ABSTRACT FROM AUTHOR]

The intrinsic point defect influence data for β –Si3N4 by far are incomplete and experimental clarification is not easy. In this contribution, the effects of vacancy ( V 2c , V 6h and V Si ) and interstitial ( I N and I Si ) defects on the electronic properties of H-passivated β –Si3N4 (0001) surface are explored based on density functional theory (DFT) calculation. The results show that it is easier to form N 6h vacancy defects in the surface layer under Si-rich conditions. The existence of N vacancies makes the bottom of conduction bands shift downwards, and the top of valance band is away from Fermi level. The presence of V Si makes the system have the characteristics of p-type semiconductor, and the closer to the inner layer, the narrower the range of additional energy bands and the greater the degree of localization of electrons. The closer the Si atom vacancy is to the surface, the smaller the photon energy corresponding to the maximum absorption coefficient is. Compared with the N vacancy system, the Si vacancy system has higher reflection ability in the low energy region. For the interstitial defect systems, I N is easy to form on the surface layer, and I Si is easy to produce in the inner layer. The I N system has a new additional energy level at the Fermi level, and as the I N is closer to the inner layer, the energy range of the additional energy level is also narrower. In the I Si system, the new additional energy levels appear at the Fermi level and the intermediate band. The results have positive significance for the design of this advanced structural and functional integrated ceramics. The absorption coefficient and reflection coefficient of I Si - 3 system are much higher than those of other systems when the energy is greater than 2.5 eV. [ABSTRACT FROM AUTHOR]

The beltline region of the reactor pressure vessel (RPV) is subject to an extreme radiation, temperature, and pressure environment over several decades of operation; therefore it is necessary to understand the mechanisms through which radiation damage occurs and how it affects the mechanical and chemical properties of the RPV steel. Chemical rate theory is a mean field rate theory simulation model which applies chemistry to the evaluation of irradiation-induced embrittlement. It presents one method of analysis that may be coupled to other distinct methods, in order to analyze defect formation, ultimately providing useful information on strength, ductility, toughness and dimensional stability changes for effects such as embrittlement, reduction in ductility and toughness, void swelling, hardening, irradiation creep, stress corrosion cracking, etc. over time as materials are subjected to reactor operational irradiation. This paper serves as a brief review of rate theory fundamentals and presents several examples of research that exemplify the application and importance of rate theory in examining the effects of radiation damage on RPV steel. [ABSTRACT FROM AUTHOR]

In current study molecular dynamics (MD) simulations are performed to reveal effects of pre-existing defects on nanoimprint of single crystal aluminum () thin films. Simulation results suggest that critical force required for plastic deformation initiation decreases with the increase of vacancy volume fraction, but increases with the interstitial volume fraction. It is found that adsorption phenomenon is affected by pre-existing defects, as adsorption phenomenon weakens with the increasing interstitial volume fraction. Pre-existing defects have significant influence on the deformation mechanisms and imprint forces during the nanoimprint processes. Simulation results also show that surface deformation is strongly affected by pre-existing defects. [ABSTRACT FROM AUTHOR]

The Ti-Ni-Sn half-Heusler compound exhibits a high power factor but relatively low figure of merit due to its high thermal conductivity. In this paper, we propose an effective and inexpensive way to reduce the thermal conductivity, and independently increase the power factor. To this end, we have systematically synthesized off-stoichiometric Ti-Ni-Sn half-Heusler compounds and introduced Y-Sb dilute co-doping at Ti-Sn sites. Excess Ni introduces interstitial defects in the half-Heusler crystal and results in significant reduction of the thermal conductivity, which drops below 3 W/mK at room temperature. In addition, the Y-Sb dilute co-doping at Ti-Sn sites improves the power factor while the thermal conductivity remains reasonably small. As a result, the figure of merit at room temperature is eight times larger than that of nondoped Ti-Ni-Sn. [ABSTRACT FROM AUTHOR]

The ability to incorporate high content of interstitial oxygen ions (Oi) in La1+xSr1‐xGa3O7+0.5x melilite owing to the good size match between La3+ and Sr2+ ions is well documented. Here, the complete substitution of Sr2+ by Pb2+ lone‐pair cations results in a significant loss of this ability, even though Sr2+ and Pb2+ have almost the same effective ionic radius. To explore the fundamental mechanism underlying this result, density functional theory (DFT) calculations are performed on both the LaSrGa3O7‐based and LaPbGa3O7‐based materials, revealing a new chemical bonding effect on the incorporation of mobile oxygen interstitial defects in melilites. For LaSrGa3O7‐based melilites, the interstitial oxygens have cooperatively weak antibonding interactions with the framework oxygen atoms (Of). This antibonding Oi‐Of interaction pushes Oi toward a 3‐linked Ga ion, enhancing the covalent bonding between this Ga ion and Oi. In addition, the antibonding Oi–Of interaction makes the oxygen interstitial defects and framework atoms highly active, benefiting the migration of defects. In contrast, for LaPbGa3O7‐based materials, the 6s2 electrons of Pb2+ point toward the c‐axis and form antibonding with framework O2−. This antibonding projects into the tunnel void, thereby directly hindering the entrance of interstitial oxygen atoms into the pentagonal rings. [ABSTRACT FROM AUTHOR]