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This paper reports the results of atomistic and ab initio simulation of several different tilt grain boundaries in silicon. The boundary structures obtained with genetic algorithm turned out to have no coordination defects, i.e., all silicon atoms restored their tetrahedral coordination during the structure optimisation. That concerns previously known symmetric Σ5 (130), Σ3 (211), and Σ29 (520) boundaries and previously unknown asymmetric Σ9 (̄255)/(̄211), Σ3 (̄255)/(̄211), and Σ13 (790)/(3 11 0) structures. An extensive study has been performed on defect segregation on the boundaries, including neutral vacancy and carbon, phosphorus, and boron impurities. A clear correlation has been revealed between the segregation energy of the defect and local geometry of the boundary site where the defect is segregated. The authors propose a simple purely geometric model for evaluating approximate segregation energies of the listed defects. [ABSTRACT FROM AUTHOR]

Hydrogenation is an effective approach to improve the performance of photocatalysts within defect engineering methods. The mechanism of hydrogenation and synergetic effects between hydrogen atoms and local electronic structures, however, remain unclear due to the limits of available photocatalytic systems and technical barriers to observation and measurement. Here, we utilize oxygen vacancies as residential sites to host hydrogen atoms in a layered bismuth oxychloride material containing defects. It is confirmed theoretically and experimentally that the hydrogen atoms interact with the vacancies and surrounding atoms, which promotes the separati30on and transfer processes of photo-generated carriers via the resulting band structure. The efficiency of catalytic activity and selectivity of defective bismuth oxychloride regarding nitric oxide oxidation has been improved. This work clearly reveals the role of hydrogen atoms in defective crystalline materials and provides a promising way to design catalytic materials with controllable defect engineering. Hydrogenated BiOCl shows high performance as a semiconductor photocatalyst, but the mechanism and synergetic effects of hydrogenation are hard to study. Here interactions of oxygen vacancies and hydrogen atoms in BiOCl nanosheets show a modulation of energy dispersion, which leads to both improvements in charge separation and photocatalytic activity. [ABSTRACT FROM AUTHOR]

The vacancy-type defects and their local chemical environment in different ODS alloys produced in the USA (14YWT), China (K5) and Russia (ODS EP-450) are studied. The Angular Correlation of Annihilation Radiation (ACAR), which is one of the positron annihilation spectroscopy method, was used. It was shown that in all alloys, except 14YWT, the dominant type of positron traps are vacancy-like defects, localised in matrix or associated with dislocations and/or interfaces of the incoherent particles. In the case of 14YWT alloy, which contains Y-Ti-O nanoclusters of a high density, the positrons confine and annihilate at O-vacancy pairs or complexes within nanoclusters. It is testified by enhanced electron density in annihilation sites and neighbourhood of Ti and Y atoms. These results, obtained by the ACAR method, indicate that the vacancies play an essential role in the formation of nanoclusters in ODS 14YWT alloy as it was theoretical predicted by first-principle calculations. [ABSTRACT FROM AUTHOR]

The detailed catalytic oxidation mechanisms of CO over Cr-embedded graphene have been investigated by means of M06-2X density functional. Both models with chromium atom embedded in single and double vacancy (Cr-SV and Cr-DV) in a graphene sheet were considered. It is found that the CO oxidation on Cr-SV-graphene prefers to Langmuir-Hinshelwood (LH) mechanism, while the Cr-DV-graphene shows good catalytic activity toward the CO oxidation via the Eley-Rideal (ER) mechanism. The present results imply that the low-cost Cr-embedded graphene is a prospective catalyst for CO oxidation at room temperature. [ABSTRACT FROM AUTHOR]

The composite β ′/ β ″ precipitates rather than well-defined β ′ phase form in trace-Sn containing Al-Mg-Si alloy peak-aged at 250 °C, leading to considerable morphological refinement. The preferential occupation of 2~6 adjacent Si sites of the tiny β ′ phase by Sn and typical β ″ substructure units covering the precipitates are frequently observed. The substructures grow upon further ageing into differently oriented β ″ with 2~3 complete structural unit cells. It is inferred that the β ′ (Mg 9 Si 5-x Sn x ) forms initially on the Sn/vacancy complexes and then acts as heterogeneous nucleus for β ″. These findings demonstrate Sn could fundamentally alter the pre−/precipitation behaviors in Al-Mg-Si alloys. [ABSTRACT FROM AUTHOR]

In the present work, pure CeO2, neodymium-doped CeO2, and neodymium and transition metal element (Cu, Zn, Cr)-codoped CeO2 nanoparticles were synthesized by an auto-combustion method and annealed at 700 ∘C. The X-ray diffraction (XRD) studies revealed that all the samples exhibited a single-phase cubic fluorite structure with the incorporation of respective dopant ions into the CeO2 lattice. The scanning electron microscopy (SEM) images displayed the prepared nanoparticles which had an irregular flaky structure with large agglomerations. The Fourier transform Raman (FT-Raman) spectroscopy analysis revealed the increased oxygen vacancy defects in CeO2 host after doping and codoping with neodymium and transition metal elements. Ultraviolet-diffuse reflectance spectroscopy (UV-DRS) studies revealed the decrease in bandgap values in doped and codoped samples compared to pure CeO2 sample. The Fourier transform infrared spectroscopy (FTIR) studies revealed the presence of functional groups in the prepared samples. Photoluminescence (PL) spectroscopy analysis reported the decreased luminescence intensities of Nd-doped and neodymium and transition metal-codoped CeO2 nanoparticles. The vibrating sample magnetometer (VSM) results depicted that all the samples exhibited room-temperature ferromagnetism. [ABSTRACT FROM AUTHOR]

The effects of Fe ion vacancy on structural and magnetic properties of NiFeO4 nanoparticles are investigated using X-ray diffraction, Fourier transform infrared, morphological, and magnetic measurements. The introduction of Fe ion vacancy leads to the increase of the lattice parameter and decrease of the particle size. Moreover, vibrating sample magnetometer measurement results revealed that the values of the magnetization decreased and that coercivity had no regular behavior with increasing Fe ion vacancy content. These behaviors could be explained by considering cation distribution in the spinel structure. The estimated cation distribution results show that the Fe ion vacancy mostly occurred at the B sites which is in good agreement with the theoretical calculations. [ABSTRACT FROM AUTHOR]

In this study, a first-principles study using the spin-polarized density functional theory approach within corrected functional was carried out to investigate the electronic features of manganese oxide surfaces under three situations of (a) cation vacancy, (b) intercalation of multi- and univalent ions, and (c) adsorption of a water molecule upon the surface as catalytic performance. The possibility of obtaining the significant absolute magnetic momentum phases from native defects in orthorhombic structures of Mn2O3 and Mn3O4 (001) surface is explored, whereas Mn vacancy provides a transition from the insulating phase into a metal-like nature and modifies the electronic transport. Moreover, bandgap engineering via impurity intercalation has been explored. Ca+2 and Al+3 intercalations have manifested substantial attributes and explain the experimental results as efficient conducting system and catalytic activity. Furthermore, the adsorption of one water molecule and the most stable configuration, adsorption energies and electronic properties were thoroughly discussed. Accordingly, it was explored that H2O: Mn2O3 and Mn3O4 exhibit suitable parameters as efficient catalytic synthesis. [ABSTRACT FROM AUTHOR]

The VH 1 defect in diamond (one hydrogen atom saturating one of the four dangling bonds of the carbon atoms surrounding a vacancy) is investigated at the quantum mechanical level by using the periodic supercell approach, an all electron Gaussian type basis set, “hybrid” functionals and two supercells. Both spin states, characterized by S z = 1/2 and S z = 3/2 and resulting from the unpaired electrons on the three unsaturated carbon atoms around the vacancy, have been investigated. The doublet state VH 1 d turns out to be more stable by 0.34 eV than the quadruplet VH 1 q . The band structure, charge and spin density distributions are analyzed. The two states present very different IR spectra, with peaks that can be used for their characterization. In particular the CH stretching peak can vary by as much as 400 cm −1 : from about 2800 cm −1 for VH 1 q to about 3200 cm −1 for VH 1 d in the harmonic approximation. Anharmonicity is quite important but very different in the two cases: for the C-H stretching, about 330 cm −1 for VH 1 q and only 190 cm −1 for VH 1 d , so that the final anharmonic wavenumbers differ by as much as 500 cm −1 . [ABSTRACT FROM AUTHOR]

The article focuses on a study which examines the potential of sodium or Na+/vacancy disordering in improving the cycling stability, kinetics and capability of Na-ion batteries (NIBs). The study involved methods including the synthesis of P2-NaNM and P2-NaNMT compounds, electrochemistry, and density functional theory (DFT) calculations. Results are provided with information on P2-NaNM and P2-NaNMT crystal structures, electrochemical performance and charge compensation mechanism.

The size of structural vacancies and structural vacancy density of 1/1-Al–Re–Si approximant crystals with different Re compositions were evaluated by positron annihilation lifetime and Doppler broadening measurements. Incident positrons were found to be trapped at the monovacancy-size open space surrounded by Al atoms. From a previous analysis using the maximum entropy method and Rietveld method, such an open space is shown to correspond to the centre of Al icosahedral clusters, which locates at the vertex and body centre. The structural vacancy density of non-metallic Al73Re17Si10was larger than that of metallic Al73Re15Si12. The observed difference in the structural vacancy density reflects that in bonding nature and may explain that in the physical properties of the two samples. [ABSTRACT FROM PUBLISHER]

Ab initio calculations of electronic, magnetic and optical properties of defected (beryllium (Be) doped or void induced) buckled free standing (FS) germanene have been explored. Concentrations of doping as well as vacancy (keeping a fixed low amount of Be) are increased thoroughly, in order to study the modifications of different physical properties critically. Our study reveals that, incorporation of doping and void destroy Dirac cone in band structure of germanene. Finite bandgap for the requirement of field effect transistor (FET) applications is obtained in case of semiconducting configuration with 15.62% doping concentration. Magnetism is also induced for doping of Be with high concentration only, which is supported from projected density of states (PDOS) and charge density analysis. Anisotropic effects are prominent in optical properties like dielectric functions, absorption spectra, reflectivity and its modulation and conductivity. Static real part of dielectric constant increases linearly with increase in doping concentration but decreases with increase in vacancy concentration considering parallel polarization of electro-magnetic (EM) wave. Predicted computational results of plasma frequencies are in well agreement with expected analytical data. Peak corresponding to maximum intensity of electron energy loss spectra (EELS) appears at the position of plasma frequency in case of every structure. We expect, this study may help for better understanding of next generation germanene based nano-technology. [ABSTRACT FROM AUTHOR]

Point defects, particularly vacancies, exist abundantly in the structure of a variety of clay minerals (e.g., kaolinite). Such defects significantly alter the physical/chemical characteristics of the minerals. Dissolution of kaolinite in an alkali medium is a critical step in the geopolymerization process and it determines the properties of the final product. In this work, a series of molecular dynamics (MD) simulations were carried out in the isothermal-isobaric (NPT) ensemble at 298 K and 1 atm to study the influence of structural vacancies (Al and Si vacancies in particular) on the interaction/dissolution of the two basal surfaces of kaolinite (partially deprotonated octahedral and tetrahedral surfaces) exposed to alkali media. Two different alkali media were used. One contained sodium cation (Na + ) only while the other potassium cation (K + ) and their concentrations were 3 M and 5 M. The MD results showed that regardless of the type of cation and cation concentration, Al vacancies on the octahedral surface promoted the dissolution of Al into the solution compared to the surface without Al vacancies. However, there existed a vacancy concentration (2 Al vacancies per 576 Al atoms) at which the dissolution amount was the maximum and above which the dissolution decreased with increasing Al vacancy concentration. The presence of Si vacancies in the tetrahedral surface did not show significant effect on the dissociation of Si. Radial distribution function (RDF) analyses indicated that the degree of crystallinity of the octahedral surface decreased as the number of Al vacancies increased but this was not the case for the tetrahedral surface. [ABSTRACT FROM AUTHOR]

The effects of defects on the fracture resistance of materials have attracted considerable attention recently. In the present work, the vacancy effects on the spallation in single-crystalline Ni are studied by nonequilibrium molecular dynamics simulations. The vacancy concentration ranges from 0% to 2.0%, and the spallation in shock wave loading along three low-index directions ([0 0 1], [1 1 0], and [1 1 1]) is investigated. We found that vacancies provide the sites of nucleation for compression-induce plasticity, and tension stress-induced plasticity plays the key role in void nucleation. Along the [0 0 1] direction, the degree of spall damage does not increase with the increase in vacancy concentration; however, along the [1 1 0] and [1 1 1] directions, it decreases with the increase in vacancy concentration when the vacancy concentration is higher than the threshold value. [ABSTRACT FROM AUTHOR]

The core structures and mobility of ⟨c⟩ dislocations in magnesium were predicted using both density functional theory and molecular dynamics simulations. The pure edge and screw cores are compact at 0 K. With increasing temperature up to 700 K, the edge dislocation dissociates into two ⟨c⟩/2 partials on the basal plane, but remains immobile. The screw dislocation remains compact and continuously cross-slips between the three prismatic planes. At room temperature, the screw dislocation only glides after emitting a vacancy at 420 MPa. The Peierls stress of the dislocation after vacancy emission is 50 MPa. [ABSTRACT FROM AUTHOR]

The hydrogen segregation at divacancies and impurity-vacancy clusters in nickel is studied using ab-initio calculations. Binding energy for up to 6 H atoms segregated at impurity-vacancy cluster and up to 10 atoms segregated at a divacancy is presented. The binding energy varies from −0.396 eV for H atom at the octahedral site “shared” by two vacancies to ≈ −0.27 eV for other sites. For clusters with more than 4 segregated H atoms the average binding energy is close to −0.3 eV. The effect of a soluble impurity on H segregation to a vacancy depends on the solute-vacancy interaction. The Mo atom is energetically repelled from vacancies, while Al and Li have weak binding energies. For the (Li, Al or Mo)-vacancy clusters the H segregation energy is increased for Li and decreased for Al and Mo. Li is predicted to have the largest effect on H segregation. The impurity effects and H binding correlate with variation of the defect formation volume. [ABSTRACT FROM AUTHOR]

In this report, we aimed to present our colleagues the phenomenon of dislocation of the os carpiradiale, which is rarely seen in dogs. A 10-year-old, spayed male Terrier was referred to the Animal Hospital of Near East Unıversity, TRNC, with the anamnesis of having lameness of the right front limb. Clinical examination of the right carpus showed soft-tissues welling, pain on motion of the carpal joint. Medio-lateral and dorso-palmar radiographs of the right carpus determined dorsopalmar luxation of the radiocarpal bone. Open reduction was performed under general anesthesia with Xylazine (1 mg/kg IM) and Ketamine (10 mg/kg IM). In 4 weeks after postoperative clinical examination, the carpal joints and walking was seen normal. Mediolateral and dorsopalmar radiographs of the os carpiradiale was determined to have occurred repositioning. [ABSTRACT FROM AUTHOR]

We performedin situobservation of one-dimensional (1D) migration of self-interstitial atom (SIA) clusters in iron under electron irradiation at 110–300 K using high-voltage electron microscopy. Most 1D migration was stepwise positional changes of SIA clusters at irregular time intervals at all temperatures. The frequency of 1D migration did not depend on the irradiation temperature. It was directly proportional to the damage rate, suggesting that 1D migration was induced by electron irradiation. In contrast, the 1D migration distance depended on the temperature: distribution of the distance ranged over 100 nm above 250 K, decreased steeply between 250 and 150 K and was less than 20 nm below 150 K. The distance was independent of the damage rate at all temperatures. Next, we examined fluctuation in the interaction energy between an SIA cluster and vacancies of random distribution at concentrations 10−4–10−2, using molecular statics simulations. The fluctuation was found to trap SIA clusters of 4 nm diameter at vacancy concentrations higher than 10−3. We proposed that 1D migration was interrupted by impurity atoms at temperatures higher than 250 K, and by vacancies accumulated at high concentration under electron irradiation at low temperatures where vacancies are not thermally mobile. [ABSTRACT FROM AUTHOR]

Thermal effects are important considerations at the initial stage in spark plasma sintering of non-conductive AlO powders. The generalized thermo-elastic theory is introduced to describe the influence of the heat transport and thermal focusing caused by thermal wave propagation within a constrained space and transient time. Simulations show that low sintering temperature can realize high local temperature because of the superposition effect of heat waves. Thus, vacancy concentration differences between the sink and the cross section of the particles increase relative to that observed during pressure-less and hot-pressure sintering. Results show that vacancy concentration differences are significantly improved during spark plasma sintering, thereby decreasing the time required for sintering. [ABSTRACT FROM AUTHOR]

The environment dependent interatomic potential (EDIP) including Ziegler–Biersack–Littermark (ZBL) interactions for close encounters is applied to cascades starting from a host atom and from an interstitial atom. We find the room temperature displacement threshold to be 25 eV, increasing to 30 eV at 900 K. The latter correlates well with the measured threshold for vacancy production. Additionally, divacancy production is found to occur, including interlayer divacancies from around 60 eV. The data suggest a new, continuous damage function applies, where the threshold region depends on the square root of the primary knock-on atom (PKA) energy in excess of the threshold, evolving to a linear dependence on PKA energy. [ABSTRACT FROM AUTHOR]

By using molecular dynamics and cluster dynamics simulations, we probed the role of hydrogen-vacancy complexes on nucleation and growth of proto nano-voids upon dislocation plasticity in α-Fe. Our atomistic simulations reveal that, unlike a lattice vacancy, a hydrogen-vacancy complex is not absorbed by dislocations sweeping through the lattice. Additionally, this complex has lower lattice diffusivity; therefore, it has a lower probability of encountering and being absorbed by various lattice sinks. Hence, it can exist metastably for a rather long time. Our large-scale molecular dynamics simulations show that when metals undergo plastic deformation in the presence of hydrogen at low homologous temperatures, the mechanically driven out-of-equilibrium dislocation processes can produce extremely high concentrations of hydrogen-vacancy complex (10 −5 ∼ 10 −3 ). Under such high concentrations, these complexes prefer to grow by absorbing additional vacancies and act as the embryos for the formation of proto nano-voids. The current work provides one possible route for the experimentally observed nano-void formation in hydrogen embrittlement of steels and bridges atomic-scale events and damage with macroscopic failure. [ABSTRACT FROM AUTHOR]

The nonzero thickness of single-layer (SL) MoS2 manifests in electron states forming classes of states that are even and odd with respect to reflections through the central plane. These states are energetically well separated: In particular, we show that pristine SL MoS2 exhibits two band gaps, Eg∥ = 1.9 eV and Eg⊥ = 3.2 eV, for the optical in-plane and out-of-plane susceptibilities χ∥ and χg⊥. respectively. Because of this, odd states are often neglected, which effectively reduces SL MoS2 to a perfect two-dimensional system. We study states bound to defects in SL MoS2 with three types of vacancy defects (VDs), (i) Mo vacancy, (ii) S2 vacancy, and (iii) 3 × MoS2 quantum antidot, and show that odd states play an equally important role as the even states. In particular, we show that odd states bound to VDs lead to resonances in χg⊥ inside Eg⊥ in SL MoS2 with VDs. Additionally, we demonstrate that the states bound to VDs are not necessarily confined to the band gap in the even subsystem, which necessitates extending the energy region affected by the bound states. [ABSTRACT FROM AUTHOR]

The behavior of atomic hydrogen in osmium dioxide and ruthenium dioxide is investigated through ab initio calculations using density functional theory. Interstitial hydrogen behaves as a donor in both metal oxides and only has one stable interstitial position, bonding with an O atom to form an OH O defect. The rates of diffusion parallel to the c -axis are estimated to be 3.95 × 10 − 7 exp(−0.793/ k B T ) m 2 /s and 3.64 × 10 − 7 exp(−0.659/ k B T ) m 2 /s in OsO 2 and RuO 2 , respectively. The rates of diffusion perpendicular to the c -axis are estimated to be 1.80 × 10 − 6 exp(−0.941/ k B T ) m 2 /s and 1.10 × 10 − 6 exp(−1.21/ k B T ) m 2 /s in OsO 2 and RuO 2 , respectively. Additionally, the binding energy of multiple H atoms in (O, Os, Ru) vacancies have been calculated. High binding energies of hydrogen in metal vacancies result in multiple H atoms associating with a single metal vacancy. In RuO 2 , the binding energy of multiple H atoms outweighs the formation energy of a single Ru vacancy as well as that of a Ru–O divacancy. [ABSTRACT FROM AUTHOR]

Vacancy depth profiles installed by rapid thermal annealing can be monitored either by Pt diffusion or through vacancy-assisted oxygen precipitation. The features of these profiles clearly show that the vacancy species manifested in these experiments is a 'slow vacancy', Vs. The evolution of Vs depth profiles is controlled by an exchange with another (mobile) kind of vacancy that is likely to be a 'Watkins vacancy', Vw, first observed at cryogenic temperatures. At low T the conversion of Vs into Vw is slow and practically irreversible. At higher T the two species coexist in an equilibrium ratio and diffuse as one entity with an averaged diffusivity. This model provides a good fit to the RTA-installed depth profiles of Vs. The total vacancy community includes, beside Vs and Vw, also a fast vacancy Vf that is responsible for the vacancy contribution into self-diffusion at high T. In RTA experiments, the Vf species seems to be completely annihilated by self-interstitials which leaves only two other vacancy species, Vs and Vw. [ABSTRACT FROM AUTHOR]

A theoretical model is suggested to determine the critical conditions for generation of circular prismatic misfit dislocation loops in hollow core–shell nanoparticles. Based on a strict solution of the linear elasticity boundary-value problem for a circular prismatic dislocation loop in a free-surface shell, we examine the loop formation energy in the nanoparticle and show a potential opportunity to fabricate hollow, coherently bonded, i.e. dislocation-free, core–shell nanoparticles by using thin-wall shells with inner-to-outer radii ratio >0.8 as supporting cores. [Copyright &y& Elsevier]

Vacancy clusters have been observed in ZnO by positron-annihilation spectroscopy (PAS), but detailed mechanisms are unclear. This is because the clustering happens in non-equilibrium conditions, for which theoretical method has not been well established. Combining first-principles calculation and kinetic Monte Carlo simulation, we determine the roles of non-equilibrium kinetics on the vacancies clustering. We find that clustering starts with the formation of Zn and O vacancy pairs (VZn-Vo), which further grow by attracting additional mono-vacancies. At this stage, vacancy diffusivity becomes crucial: due to the larger diffusivity of VZn compared to VO, more VZn-abundant clusters are formed than VO-abundant clusters. The large dissociation energy barriers, e.g., over 2.5 eV for (VZn-Vo), suggest that, once formed, it is difficult for the clusters to dissociate. By promoting mono-vacancy diffusion, thermal annealing will increase the size of the clusters. As the PAS is insensitive to VO donor defects, our results suggest an interpretation of the experimental data that could not have been made without the in-depth calculations. [ABSTRACT FROM AUTHOR]

We propose a phase field method to model consistently dislocation climb by vacancy absorption or emission. It automatically incorporates the exact balance between the vacancy flux and the phase field associated with the dislocation evolution, enforced by the conserved character of the total population of vacancies. One of its major advantage is the natural introduction of a dynamic coefficient controlling the kinetics of vacancy emission/absorption by the dislocation. We also derived a closed-form expression of the climb rate valid from the diffusion-limited to the attachment-limited regimes. [ABSTRACT FROM AUTHOR]

Abstract: Addition of trace amounts of Al, Si and Y into V–4Cr–4Ti alloy is beneficial for the mechanical properties under irradiation. It is thus important to investigate the influence of solute/trace elements on stabilities, energetics and diffusion behaviors of vacancy defects. We performed first-principles calculations to evaluate vacancy–solute/trace interaction inside dilute V–X (X =Ti, Cr, Al, Si, Y) and V–4Cr–4Ti–(Al, Si, Y) alloys. With addition of Si and Y, vacancy-based complexes tend to form near Ti–Si and Ti–Y pairs, while the effect of Al is negligible. Moreover, diffusion coefficients of solute/trace element in vanadium were derived using nine-frequency model. With high binding energy and low diffusion coefficient, Si atom is strongly attractive to vacancy in vanadium matrix. Our theoretical results suggest that the interactions between vacancy and solute/trace elements play some role in the evolution of microstructures inside vanadium alloys. [Copyright &y& Elsevier]

Highlights: [•] OVP site is the most stable site for CH3OH adsorption. [•] OVP site is not the most active site for CH3OH dissociation. [•] CH3OH on OVP vs. single OV is different from O2 on OVP vs. single OV. [•] Different 5-fold Ti sites show similar behaviors. [•] 5-Fold Ti sites are not suitable sites for CH3OH adsorption. [ABSTRACT FROM AUTHOR]

On the basis of a vacancy-squashing model for melting that we developed recently, a vacancy formed in the premelting liquid-like-layer is proposed to be squashed at the instance of its formation, which will significantly facilitate vacancy formation. Accordingly, the temperature for surface-induced melting and its size dependence are quantitatively calculated. By comparing the calculated data with the reported experimental results for metals, we show that the present approach may potentially predict the size-dependent melting point of other metals. [ABSTRACT FROM AUTHOR]

Electrolyte gating with ionic liquids is a powerful tool for inducing novel conducting phases in correlated insulators. An archetypal correlated material is vanadium dioxide (VO2), which is insulating only at temperatures below a characteristic phase transition temperature. We show that electrolyte gating of epitaxial thin films of VO2 suppresses the metal-to-insulator transition and stabilizes the metallic phase to temperatures below 5 kelvin, even after the ionic liquid is completely removed. We found that electrolyte gating of VO2 leads not to electrostatically induced carriers but instead to the electric field-induced creation of oxygen vacancies, with consequent migration of oxygen from the oxide film into the ionic liquid. This mechanism should be taken into account in the interpretation of ionic liquid gating experiments. [ABSTRACT FROM AUTHOR]

Random telegraph noise in resistive switching memory devices is governed by two distinct mechanisms—oxygen vacancy perturbations in the filament as well as the electron trapping–detrapping phenomenon. In this letter, we focus on the dominant role of vacancies in governing the stability of the filament in the high resistance state and characterize the dependence of the read disturb voltage (VDIST) on the depth of the reset level during switching. Our slow voltage ramp read disturb tests at different reset levels indicate the possibility of filamentary instability even for read voltages lower than the standard value of 0.10 V. These experimental trends can be well explained using the quantum point contact model for conduction in the filament, as deeper reset levels induce very steep potential gradients at the two ends of the constriction that make the filaments highly unstable and susceptible to structural modifications due to vacancy generation and/or transport during memory read operation. [ABSTRACT FROM PUBLISHER]

Over the past decade, the open frame ("cagey") structure of CoSb3 skutterudite has invited intensive filling studies with various rare-earth elements for delivering state-of-the-art midtemperature thermoelectric performance. To rationalize previously reported experimental results and provide new insight into the underexplored roles of La fillers and Sb vacancies, ab initio density functional theory studies, along with semiclassical Boltzmann transport theory calculations, are performed for pristine CoSb3 of different lattice settings and La-filled CoSb3 with and without Sb's mono- and divacancy defects. The effects of spin-orbit coupling (SOC), partial La filling, Sb vacancy defects, and spin polarization on the electronic and thermoelectric properties are systematically examined. The SOC shows minor effects on the electronic and thermoelectric properties of CoSb3. The peculiar quasi-Dirac band in the pristine CoSb3 largely survives La filling but not Sb vacancies, which instead introduce dispersive bands in the band gap region. The non-spin-polarized and spin-polarized solutions of La-filled CoSb3 are nearly degenerate. Importantly, the band structure, density of states, and Fermi surface of the latter are significantly spin polarized, giving rise to spin-dependent thermoelectric properties. Seebeck coefficients directly calculated as a function of chemical potential are interpreted in connection with the electronic structures. Temperature-dependent Seebeck coefficients derived for the experimentally studied materials agree well with available experimental data. Seebeck coefficients obtained as a function of charge carrier concentration corroborate the thermoelectrically favorable role at high filling fractions played by the Fermi electron pockets associated with the degenerate valleys in the conduction bands, and also point toward a similar role of the Fermi hole pockets associated with the degenerate hills in the valence bands. These results serve to advance the understanding of CoSb3 skutterudite, a class of materials with important fundamental and application implications for thermoelectrics and spintronics. [ABSTRACT FROM AUTHOR]

Suezawa et al. [Phys. Rev. B 90, 117201 (2014)] claim in their Comment that the data reported by Shimizu et al. [Phys. Rev. Lett. 98, 095901 (2007)] and Kube et al. [Phys. Rev. B 88, 085206 (2013)] on silicon selfdiffusion for temperatures between 900 and 735 °C are affected by carbon and vacancy clusters and, accordingly, do not reflect self-diffusion under thermal equilibrium conditions. We demonstrate in our Reply that an impact of carbon on self-diffusion can definitely be excluded. In addition it is rather unlikely that the self-diffusion data reported by Shimizu et al. [Phys. Rev. Lett. 98, 095901 (2007)] and Kube et al. [Phys. Rev. B 88.085206 (2013)] are affected by the dissolution of vacancy clusters since strong differences exist not only in the preparation of the samples used for the experiments, but also in the time of diffusion. Finally, the vacancy formation enthalpy deduced by Suezawa et al. [J. Appl. Phys. 110, 083531 (2011)] from quenching experiments is consistent with the value obtained from the temperature dependence of the vacancy formation enthalpy reported by Kube et al. [Phys. Rev. B 88, 085206 (2013)]. Overall we conclude that the quenching experiments of Suezawa et al. [J. Appl. Phys. 110, 083531 (2011)] cannot disprove the interpretation of the low-temperature self-diffusion data reported by Shimizu etal. [Phys. Rev. Lett. 98,095901 (2007)] and Kube et al. [Phys. Rev. B 88, 085206 (2013)]. [ABSTRACT FROM AUTHOR]

This paper presents the mono-vacancy formation and migration energies of each element Ti, Ga, and C in the MAX phase Ti2GaC, which are obtained by first principles calculations. We also calculate the formation energies of oxygen substituting for Ti, Ga, and C and two formation energies of oxygen interstitial in different sites. The results show that the formation energy of oxygen substituting for Ti is the highest, and the formation energies of the O substitution for Ga atoms decrease as the oxygen concentration increases. The two different formation energies of one oxygen interstitial show that the stable site for the oxygen interstitial is at the center of the triangle composed by three Ga atoms. The effects of vacancy, oxygen substitution, and the interstitial on the electronic properties of Ti2GaC are also discussed in light of the density of states and the electron charge density. [ABSTRACT FROM AUTHOR]

Phosphorene is receiving great research interests because of its peculiar physical properties. Nonetheless, no systematic studies on the transport properties modified due to defects have been performed. Here, we present the electronic band structure, defect formation energy and bias dependent transport property of various defective systems. We found that the defect formation energy is much less than that in graphene. The defect configuration strongly affects the electronic structure. The band gap vanishes in single vacancy layers, but the band gap reappears in divacancy layers. Interestingly, a single vacancy defect behaves like a p-type impurity for transport property. Unlike the common belief, we observe that the vacancy defect can contribute to greatly increasing the current. Along the zigzag direction, the current in the most stable single vacancy structure was significantly increased as compared with that found in the pristine layer. In addition, the current along the armchair direction was always greater than along the zigzag direction and we observed a strong anisotropic current ratio of armchair to zigzag direction. [ABSTRACT FROM AUTHOR]

We describe a one-step, deterministic and scalable scheme for creating macroscopic arbitrary entangled coherent states (ECSs) of separate nitrogen-vacancy center ensembles (NVEs) that couple to a superconducting flux qubit. We discuss how to generate the entangled states between the flux qubit and two NVEs by the resonant driving. Then the ECSs of the NVEs can be obtained by projecting the flux qubit, and the entanglement detection can be realized by transferring the quantum state from the NVEs to the flux qubit. Our numerical simulation shows that even under current experimental parameters the concurrence of the ECSs can approach unity. We emphasize that this method is straightforwardly extendable to the case of many NVEs. [ABSTRACT FROM AUTHOR]

GaAs1 − xBix alloys attract significant interest due to their potentiality for several applications, including solar cells. Recent experiments link the crucial optical properties of these alloys to Bi clustering at certain Bi compositions. Using ab initio calculations, we show that there is no thermodynamical driving force for the formation of small GaBi clusters incorporating As substitutional sites. However, the Ga vacancies should gather Bi atoms leading to small Bi clusters, and the Ga vacancies can act as nucleation centers for phase separation. The formation energy of the GaAs1 − xBix with respect to GaAs and GaBi shows a maximum at intermediate Bi concentrations. Thermodynamics and kinetics of the GaAs1 − xBix film growth is discussed. High Bi solubility is obtained, if the Bi atoms on the energetically favorable atom positions in the subsurface layer are relatively frozen. The Ga vacancy concentration may be increased by the incorporation of Bi. The Bi atoms can also prevent the out diffusion of Ga vacancies. [ABSTRACT FROM AUTHOR]