Single Vacancy Research Articles

8-Pmmn borophene: edge states in competition with Landau levels and local vacancy states.

The tight-binding method is used to investigate the electronic and magnetic properties of borophene nano-ribbons (BNRs) in the presence of a perpendicular magnetic field. Most BNRs exhibit metallic characteristics due to edge bands. Additionally, the appearance of Landau levels (LLs) is strongly influenced by the edge states, contrasting with the sheet platform which produces distinct LLs. We also investigated single atomic vacancy disorders in BNRs and observed localized vacancy states (LVSs) resulting from atomic disorder. Both LVSs and LLs are influenced by the edge states, underscoring that the electronic and magnetic properties of BNRs are strongly edge-dependent. This aspect is crucial for consideration in experimental, theoretical, and computational studies.

Modifying the electronic and magnetic properties of the scandium nitride semiconductor monolayer via vacancies and doping.

In this work, the effects of vacancies and doping on the electronic and magnetic properties of the stable scandium nitride (ScN) monolayer are investigated using first-principles calculations. The pristine monolayer is a two-dimensional (2D) indirect-gap semiconductor material with an energy gap of 1.59(2.84) eV as calculated using the GGA-PBE (HSE06) functional. The projected density of states, charge distribution, and electron localization function assert its ionic character generated by the charge transfer from the Sc atoms to the N atoms. The monolayer is magnetized by a single Sc vacancy with a total magnetic moment of 3.00μB, while a single N vacancy causes a weaker magnetization with a total magnetic moment of 0.52μB. In both cases, the magnetism originates mainly from the atoms closest to the defect site. Significant magnetization is also reached by doping with acceptor impurities. Specifically, a total magnetic moment of 2.00μB is obtained by doping with alkali metals (Li and Na) in the Sc sublattice and with B in the N sublattice. Doping with alkaline earth metals (Be and Mg) in the Sc sublattice and with C in the N sublattice induces a value of 1.00μB. In these cases, either magnetic semiconducting or half-metallicity characteristics arise in the ScN monolayer, making it a prospective 2D spintronic material. In contrast, no magnetism is induced by doping with donor impurities (O and F atoms) in the N sublattice. An O impurity metallizes the monolayer; meanwhile, F doping leads to a large band-gap reduction of the order of 82%, widening the working regime of the monolayer in optoelectronic devices. The results presented herein may introduce efficient methods to functionalize the ScN monolayer for optoelectronic and spintronic applications.

Electronic and magnetic properties of GeS monolayer effected by point defects and doping.

In this work, defect engineering and doping are proposed to effectively functionalize a germanium sulfide (GeS) mononolayer. With a buckled hexagonal structure, the good dynamical and thermal stability of the GeS monolayer is confirmed. PBE(HSE06)-based calculations assert the indirect gap semiconductor nature of this two-dimensional (2D) material with a relatively large band gap of 2.48(3.28) eV. The creation of a single Ge vacancy magnetizes the monolayer with a total magnetic moment of 1.99 μB, creating a the feature-rich half-metallic nature. VaS vacancy, VaGeS divacancy, SGe and GeS antisites preserve the non-magnetic nature; however, they induce considerable band gap reduction of the order 47.98%, 89.11%, 29.84%, and 62.5%, respectively. By doping with transition metals (TMs), large total magnetic moments of 3.00, 4.00, and 5.00 μB are obtained with V, Cr-Fe, and Mn impurities, respectively. The 3d orbital of TM dopants mainly regulates the electronic and magnetic properties, which induces either the half-metallic or diluted magnetic semiconductor nature. It is found that the doping site plays a determinant role in the case of doping with VA-group atoms (P and As). The GeS monolayer can be metallized by doping the Ge sublattice, meanwhile both spin states exhibit semiconductor character with strong spin polarization upon doping the S sublattice to obtain a diluted magnetic semiconductor nature with a total magnetic moment of 1.00 μB. In these cases, the magnetism originates mainly from P and As impurities. The obtained results suggest an efficient approach to functionalize the GeS monolayer for optoelectronic and spintronic applications.

Realizing new 2D spintronic materials from the non-magnetic 1T-PdO2 monolayer through vacancy defects and doping.

In this work, vacancy- and doping-based magnetism engineering in a non-magnetic 1T-PdO2 monolayer is explored in order to realize new two-dimensional (2D) spintronic materials. The pristine monolayer is an indirect gap semiconductor with a band gap of 1.45 (3.20) eV obtained using the PBE (HSE06) functional. Half-metallicity with a total magnetic moment of 3.95 μB is induced by creating a single Pd vacancy, where the magnetic properties are produced mainly by O atoms around the vacancy site. In contrast, the non-magnetic nature is preserved under the effects of a single O vacancy, however a band gap reduction in the order of 37.93% is achieved. Further doping with transition metals (TMs = V, Cr, Mn, and Fe) in the Pd sublattice and with non-metals (B, C, N, and F) in the O sublattice is investigated. TM impurities lead to the emergence of a diluted magnetic semiconductor nature, where total magnetic moments of 1.00, 2.00, and 3.00 μB are obtained in the V-, Cr(Fe)-, and Mn-doped systems, respectively. In these cases, the TMs' 3d electrons mainly originate the system's magnetism. Significant magnetization of the PdO2 monolayer is also achieved by doping with B, N, and F atoms, where either half-metallic or diluted magnetic semiconductor natures are induced. Herein, electronic and magnetic properties are regulated mainly by the interactions between the 2p orbital of the dopant, 4d orbital of the first neighbor Pd atoms, and 2p orbital of the second neighbor O atoms. Meanwhile, C impurity induces no magnetism in the PdO2 monolayer because of the strong electronic hybridization with their neighbor atoms. Results presented herein may introduce efficient approaches to engineer magnetism in a non-magnetic PdO2 monolayer, such that the functionalized systems are further recommended for prospective spintronic applications.

Influence of defects induced by plasma-bombarded monolayer WS<sub>2 </sub>on optical properties of bound excitons

<sec>Monolayer transition metal dichalcogenides (TMDCs) exhibit exceptional properties including atomic-scale thickness, direct bandgap, and strong spin-orbit coupling, which make them have great potential applications in spintronics, optoelectronics, and other fields. Usually, materials contain various structural defects, which are either formed during preparation and growth or induced by subsequent treatments. These defects can significantly change their physicochemical properties. Consequently, controlling and comprehending defects is an important approach to adjusting the properties of these materials.</sec><sec>Herein, we use Ar<sup>+</sup> plasma to bombard monolayer WS<sub>2,</sub> which is exfoliated mechanically, thereby introducing defects whose density is controlled by changing the bombardment duration. The photoluminescence (PL) and Raman spectroscopic measurements at different temperatures and power values are utilized to investigate the optical properties of the defects. Furthermore, time-resolved photoluminescence is employed to unveil the dynamic behaviors of free and trapped excitons.</sec><sec>The bombardment can introduce different types of defects into typical two-dimensional (2D) TMDCs such as MoS<sub>2</sub> and WS<sub>2</sub>. Single sulfur vacancies are frequently generated, while other defects like double sulfur vacancies or metal atom vacancies can also occur. Exciton effects dominate the optical properties of monolayer TMDCs due to reduced screening and large effective mass. At low temperatures, bound exciton emissions arise from trapped states. Our measurements reveal two types of defect-bound excitons from the PL spectra at around 1.85 eV (X<sup>B1</sup>) and 1.55 eV (X<sup>B2</sup>). Meanwhile, the Raman peaks of the samples before and after treatment exhibit no obvious changes, indicating that the lattice structure remaines unchanged. After the Ar<sup>+</sup> bombardment, the intensity of the free neutral exciton significantly decreases to 1/6 of untreated WS<sub>2</sub>, owing to the free exciton population and the increased non-radiative centers. The dynamic processes of these two bound excitons are considerably slower than the neutral exciton’s, showing the typical dynamic behavior of defect-bound excitons. Furthermore, comparison between the PL under vacuum condition and the PL under atmospheric condition shows that the intensities of the two bound excitons exhibit opposing behaviors. In an atmospheric environment, neutral excitons and bound exciton X<sup>B1</sup> possess higher intensities. In the vacuum, the strength of neutral exciton and X<sup>B1</sup> decrease quickly, while the intensity of deep-level bound exciton X<sup>B2</sup> increases.</sec><sec>In summary, we observe two bound exciton states arising from specific vacancy states in monolayer WS<sub>2</sub> after Ar<sup>+</sup> bombardment. Their energy values are 200 meV and 500 meV lower than those of the neutral exciton, with a splitting energy value being about 300 meV. The detailed evolution of the relative spectral weight with temperature and excitation power are presented. This work provides insights into the generation, control, and characteristic spectra of defects in 2D materials.</sec>

Controlling the electronic and magnetic properties of the GeAs monolayer by generating Ge vacancies and doping with transition-metal atoms.

Controlling the electronic and magnetic properties of two-dimensional (2D) materials is a key step to make new multifunctional candidates for practical applications. In this work, defects and doping with transition metals (TMs = V, Cr, Mn, and Fe) at Ge sublattices are proposed in order to develop novel features in the hexagonal germanium arsenide (GeAs) monolayer. The pristine GeAs monolayer is a non-magnetic indirect gap semiconductor with an energy gap of 1.20(1.82) eV as provided by PBE(HSE06)-based calculations. A single Ge vacancy metallizes the monolayer, preserving its non-magnetic nature. In contrast, significant magnetization with a total magnetic moment of 1.96 μ B is achieved by a pair of Ge vacancies. Herein, the computed band structures assert the half-metallic behavior of the defective system. Similarly, half-metallicity is also obtained by V, Mn, and Fe doping. Meanwhile, the Cr-doped GeAs monolayer is classified as a diluted magnetic semiconductor 2D system. In these cases, magnetic properties are produced mainly by TM-3d electrons with total magnetic moments between 2.00 and 4.00 μ B. Further, the effects of substituting a pair of Ge atoms with a pair of TM atoms (pTMGe systems) are also investigated. Results indicate the ferromagnetic half-metallicity of the pVGe system, meanwhile antiferromagnetic ordering is stable in the remaining cases. In all cases, TM impurities transfer charge to the host GeAs monolayer since they are surrounded by As atoms, which are more electronegative than dopant atoms. Results presented herein may introduce new 2D systems - made from the non-magnetic GeAs monolayer - for spintronic applications with suitable electronic and magnetic features controlled mainly by transition metals.

Effect of single vacancy defects on two-dimensional <i>δ</i>-InSe stability

The two-dimensional (2D) semiconductor material of InSe has received much attention due to its excellent electrical properties and moderate adjustable bandgap. The vacancy defects in the material affect not only the optical and electrical properties, but also the environmental stability. Compared with other phases in InSe materials, <i>δ</i>-InSe has superior material properties, however, the effect of environment on this material stabilityhas not been reported. In this work, we systematically investigate the stability of 2D <i>δ</i>-InSe material under oxygen environment based on density functional theory. The results are shown below. Firstly, in an oxygen environment, the perfect <i>δ</i>-InSe surface exhibits good inertness and stability, for O<sub>2</sub> molecules need to overcome an exceptionally high energy barrier of 1.827 eV from physical adsorption to chemical adsorption on its surface. Secondly, the presence of Se vacancies (V<sub>Se</sub>) promotes the oxidation reaction of <i>δ</i>-InSe, which only requires overcoming a low energy barrier of 0.044 eV. This suggests that the stability of <i>δ</i>-InSe in an oxygen environment is significantly reduced because of the presence of V<sub>Se</sub>. The O<sub>2</sub> molecules oxidized <i>δ</i>-InSe monolayer is beneficial to the dissociation and adsorption of H<sub>2</sub>O molecules. Finally, the oxidation rate of <i>δ</i>-InSe with In vacancies (V<sub>In</sub>) is slower, with the adsorption energy and charge transfer involved in the physical adsorption of O<sub>2</sub> molecules on the V<sub>In</sub> surface being similar to those on a perfect surface. The oxidation process needs to overcome a higher energy barrier of 1.234 eV. The findings of this study will provide theoretical guidance for better understanding the oxidation behavior of single vacancy defects in monolayer <i>δ</i>-InSe, and reference for experimental preparation of high-reliability 2D <i>δ</i>-InSe devices.

Theoretical strength of austenite in the presence of a pore or vacancies in the crystal: Molecular dynamics study

The molecular dynamics method was used to study the influence of pores of different diameters, as well as the corresponding concentration of individual vacancies, on the theoretical strength of austenite at different temperatures. The deformation in the model was carried out by shear at a cons­tant rate of 20 m/s. We considered a shear along two directions: [ \(\bar 1\ \bar 1\) 2] and [111]. The computational austenite cell had the shape of a rectangular parallelepiped 14.0 nm long, 14.0 nm high, and 5.1 nm wide. To describe interatomic interactions, the Lau EAM potential was used, which reproduces well the structural, energy, and elastic characteristics of austenite. The stress-strain curves obtained for both considered shear directions had a similar form. In the absence of dislocation sources, plastic deformation was carried out by the formation of dislocation dipoles (dislocations with opposite Burgers vectors). The presence of a pore significantly reduced the yield strength of austenite. In this case, it was found that single vacancies randomly scattered over the volume of the computational cell also lead to a decrease in the yield strength, but, of course, not as much as the pore. The emission of dislocations during deformation occurred by the formation of dislocation loops, as a rule, in two slip planes at once. The effect of pores and vacancies on the yield strength was stronger at low temperatures. As the temperature increased, the effect of defects on the critical stress at which dislocations were formed decreased. With an increase in the pore size, as well as the concentration of vacancies, the yield strength decreased. In this case, the strongest dependence was observed for pores up to 1 nm in diameter. The influence of the concentration of vacancies in the considered range on the yield strength turned out to be comparatively smoother and almost linear.

Peculiarities of interaction between oxygen and solute/vacancy in commercial-type zirconium-based alloys: A first-principles study

Unveiling the interaction between dissolved oxygen and solutes/vacancies during the initial stages of oxide layer formation at microscale is significant for the peculiarities of Zr-based alloys oxidation exposed in PWRs or LWRs. We perform ab-initio calculations of the diluted zirconium-based alloys with dissolved Nb and Sn solutes, vacancy and oxygen atom and discuss the solute-oxygen and vacancy-oxygen binding. Our analysis shows that with increasing content of Nb solutes the attractive interaction between niobium and oxygen becomes much stronger, which results in a decrease in corrosion rate of these alloys at the bre-breakaway regime caused by diffusion of oxygen. An increase in content of Sn in an alloy results in enforce of the repulsive interaction between Sn atom and oxygen, which causing tin-enriched alloys are characterized by an increased corrosion rate. We conclude that the dissolved oxygen can be localized near Nb atom rather than near Sn atom if both impurities are second-nearest neighbors, the dissolved oxygen can capture single vacancy and small vacancy clusters in zirconium matrix. This study provides a deep insight into the details of oxygen segregation in zirconium-based alloys exploited in nuclear-power plants.

Structural, Electronic and Magnetic Properties of Silicene Functionalized with 4d TM Atoms

The experimental realization of silicene has ignited a great deal of interest in researching its properties for utilization in device applications. Silicene is composed of a lattice of silicon. As a result, it can be integrated with contemporary circuitry structures, which are predominantly silicon-based. Therefore, investigating its characteristics, especially those of the bandgap, is pivotal. In the present work, the density functional theory approach is employed to examine the structural, electronic and magnetic characteristics of free-standing silicene doped with 4d Transition Metal (TM) atoms. Modelling is done for a 4x4 silicene supercell with a single vacancy. The resulting structure is, thus, doped with 4d transition metal atoms. Doping results in lattice distortion, as evidenced by the variance in Si-TM bond length relative to Si-Si bond length. The shortest bond length is noticed in the instance of Ru doping, thus demonstrating its strongest bonding with Si atoms. Doping causes the structure to become increasingly deformed, as proved by the elevation in buckling height as well. Except for Zr, Ru and Pd, which exhibit semiconductor behaviour, the 4d TM doping in silicene results in metallic characteristics as the bands cross the Fermi level in the majority of the configurations discussed here. A narrow band gap with a range of 2.1 to 252 meV is produced by doping silicene with Zr, Ru, and Pd. Magnetism is demonstrated by Nb, Mo, Tc, and Rh-doped structures, whereas the other structures are nonmagnetic. The presence of magnetism in these structures is primarily due to contributions from Si-3p, TM- 4d/5s orbitals, and their hybridization.

Monte Carlo Simulation of Energy Dissipation during the Cascade Decay of Inner-Shell Vacancies in an Iron Atom Placed in Water

We have performed the Monte Carlo simulation of the processes of secondary ionization of water induced by cascade decays of inner-shell vacancies in an iron atom placed in water. We have obtained the spectra of electrons and photons emitted during the decay of vacancies in the K and L shells of the iron atom. The dependences of the number of secondary ionization events and the energy absorbed as a result of these processes on the radius of the sphere in which such processes occur have been calculated. The decay of a single 1s vacancy in an iron atom generates on the average 232 events of secondary ionization induced by an electron impact, in which the energy of 3274 eV is absorbed, as well as 18 secondary photoionization events, in which the energy of 256 eV is absorbed. The dependences of the dose absorbed in water on the distance from the iron atom have been calculated.

Improvement quantum capacitance in supercapacitors using vacancy-defected BC3 monolayer

In present research, we aimed to assess effectiveness of employing defected BC3 monolayer in supercapacitors as an electrode through DFT computations. Our focus was on single and double-vacancy BC3 monolayer. We studied stored charge diagrams, integrated quantum capacitance (CQ), and density of state (DOS) for both pristine and vacancy-modified defected BC3 monolayer structures. According to findings, applying vacancy-modified defected structures between −0.80 and 0.80 V leads to greater CQ value in comparison to pristine BC3 monolayer. Single and double vacancies may be employed as positive and negative electrodes, and are considered as a semiconductor. Computations reveal that stored charge in vacancy-modified defected structures is more than pristine BC3 monolayer between 0 and 0.8 V. Moreover, DV-modified defected structure stores more charge than both SV structures and BC3 monolayer. Our findings suggest that DV BC3 monolayer shows potential as a material for high-performance supercapacitors.

HTHP treatment of diamonds containing N1 centers. Neutral state of the N1 center as a limiting step in the aggregation of substitutional nitrogen into A form

The step-by-step annealing of natural plastically deformed type IaAB diamond revealed new information on the N1 center, which is two nitrogen atoms separated by one carbon in an ionized state (S = 1/2). A slight increase in the intensity of the N1 electron paramagnetic resonance (EPR) spectrum after annealing at 1000 °C (10h) was observed, and the complete disappearance was detected at a temperature of 1300 °C (4 h). This behavior of the N1 paramagnetic center was associated with the annealing of electron acceptors, and we analyzed the conditions for the formation of complex vacancy defects. The temperature of 1000 °C corresponds to the formation of three vacancy chains from single vacancies and 1300 °C corresponds to their disappearance. We experimented with electron irradiation of the crystals (energy of 3 MeV and a fluence of 1018 e/cm2) followed by annealing at 1000 °C (for 10 h) and the N1 EPR spectrum appeared back with an intensity five times higher than in the initial crystal. The next heat treatment at 1400 °C (2 h) resulted in the expected vanish of the N1 EPR spectrum. In this case, electron irradiation followed by annealing at 1000 °C led to the restoration of a very weak EPR spectrum. The presence of the “EPR-silent” N1 centers in a neutral state in plastically deformed diamond prompted us to investigate their existence in crystals that were not subjected to plastic deformation. We generated acceptor centers in different diamonds by the above method and found N1 centers in the type IaAB natural and type IaA synthetic diamonds. The results obtained can suggest that the rate-limiting step in the aggregation of two impurity nitrogen atoms into close pair is the neutral N1 defect. In the ionized state of N1, the Coulomb repulsion between the unpaired extra electrons of nitrogen is eliminated, reducing the energy barrier in the final stage of transformation into the A center.

Effect of temperature, pressure, crystal defect types, and densities on the mechanical behavior of tungsten under tensile deformation: A molecular dynamics simulation study

The mechanical behavior of tungsten under tensile deformation was investigated using molecular dynamics simulations, with a focus on the effects of temperature, pressure, crystal defect types, and densities. Single vacancies, spherical voids, and self-interstitials were studied at concentrations ranging from 0.1% to 2%. The Common neighbor analysis reveals that the crystal structure underwent a phase transition from the body-centered cubic to the face-centered cubic structure at increasing levels of applied strain, followed by the formation of a disordered phase. Increasing temperature reduced the mechanical properties of tungsten, including yield strength, yield strain, modulus of elasticity, and ultimate tensile stress, possibly due to the activation of dislocation nucleation and propagation, resulting in the formation of dislocation loops. Increasing pressure enhanced the mechanical properties of tungsten, with the formation of dislocation loops occurring at much lower strains at higher pressures. All mechanical parameters decreased with increasing defect density, with self-interstitial defects having a more severe effect than single vacancies and spherical voids. The number and length of dislocation loops also increased with increasing defect density. Temperature and pressure had varying effects on the stress–strain curve of tungsten with different defect types and densities, with increasing pressure generally enhancing its mechanical behavior and increasing temperature decreasing it. These findings provide valuable insights into the design and development of tungsten-based materials with enhanced mechanical properties.

Effect of vacancy and pyridinic-like X-atom (X = Mg, B, C, and N) doping on the electronic and magnetic properties of antimonene: First-principles insights

We have explored the effect of vacancy and pyridinic-like X-atom (X = Mg, B, C, and N) doping on the geometries, electronic structure, and magnetism of antimonene (Sb) by means of first-principles calculations. The results showed that Sb with a single vacancy (SV-Sb) becomes a ferromagnetic metal with a moment of 0.33 µB. The X-atoms were doped at the edge site of the SV-Sb to form SV-nX-Sb (n = 1, 2, 3). All doped atoms except Mg form strong bonds with neighboring Sb-atoms. The stability of the designed structures was verified from formation energy (Efor). It was found that the SV-1X-Sb system is energetically more favorable (i.e. has the lowest Efor) for X = Mg, B, and C, while SV-3N-Sb is found more stable than SV-1N-Sb and SV-2N-Sb. Unlike metallic SV-Sb, the SV-1Mg-Sb, SV-1B-Sb, SV-1 C-Sb, and SV-3N-Sb structures exhibit semiconducting properties with a small band gap (of less than 0.5 eV). The ferromagnetism of SV-Sb is retained for X = B, and N doping, whereas Mg and C doping turned SV-Sb to non-magnetic, caused by the reconstruction of the edge Sb/X atoms. In addition, selective doping significantly altered the work function of the host material. These findings suggest the potential use of non-magnetic elements for tuning the electronic and magnetic properties of the monolayer antimonene for extended applications.

Determining the defect type in a graphene lattice

We consider four common defects that appear in an infinite single-layer graphene lattice, i.e. single vacancy V 1 ( 5 − 9 ) , Stone-Wales SW ( 55 − 77 ) , and double vacancies V 2 ( 5 − 8 − 5 ) and V 2 ( 555 − 777 ) . Investigating the honeycomb pattern of the graphene, we make use of the concept of shortest closed paths (periodic orbits) in the underlying topological structure. Using properties of the shortest closed paths of odd length we present and prove mathematically an algorithm that classifies which one of these defects occurs.

A study on mechanical properties of 1H-type crystalline nickel ditelluride

We used the molecular dynamic finite element method with Stillinger-Weber potential to study the mechanical behavior of monolayer 1H-type nickel ditelluride (1H-NiTe2) sheets under uniaxial tension. As the size of the pristine 1H-NiTe2 sheet increases, the Young’s modulus in the armchair direction increases by 6.2 %, while that in the zigzag one decreases by 6.0 %. Both tend to be size-independent in larger sheets and approach the same value at around 54 N/m. The ultimate stress in the armchair direction remains almost unchanged but that in the zigzag one reduces by about 9.5 % as the size inclines. Besides the influence of size, our results show that single vacancy defects strongly affect the ultimate stress and strain while having no effect on Young’s modulus and Poisson’s ratio. When a Te atom is missing at the sheet’s center, the ultimate stress in the armchair direction is reduced by 11.7 %, while a decrease of 16.0 % is caused by a Ni atom vacancy

Investigating the Effect of Structural Modifications on Mechanical Properties of Carbon Nanotubes under Tensile Loading Using Molecular Dynamics Simulations

The discovery of Carbon Nanotubes (CNT) has opened the doors for revolutionary applications in the mechanical, aerospace, and electrical sectors. However, to fully utilize the potential of carbon nanotubes, there is a persisting need to identify all sorts of structural modifications that can be observed in any type of manufacturing procedure for CNTs. Thus, the presented study investigates the mechanical properties of CNTs with variable waviness and defect density. Furthermore, the study is performed using classical Molecular Dynamics simulations (MD). The structures are then characterized with single or multiple vacancy defects along the axis of the nanotube structure, which is modeled as wavy structures to replicate their natural structure. After the simulation results were analyzed, it was observed that the increase in the surrounding temperature from 300K to 1500K reduces the overall tensile strength of the CNT sample from 89-47 GPa. However, introducing a single vacancy defect to the same structures was shown to reduce the tensile strength to 41 GPa at 1500K and 62 GPa at 300K.

Multiple channelling single-photon emission with scattering holography designed metasurfaces

Channelling single-photon emission in multiple well-defined directions and simultaneously controlling its polarization characteristics is highly desirable for numerous quantum technology applications. We show that this can be achieved by using quantum emitters (QEs) nonradiatively coupled to surface plasmon polaritons (SPPs), which are scattered into outgoing free-propagating waves by appropriately designed metasurfaces. The QE-coupled metasurface design is based on the scattering holography approach with radially diverging SPPs as reference waves. Using holographic metasurfaces fabricated around nanodiamonds with single Ge vacancy centres, we experimentally demonstrate on-chip integrated efficient generation of two well-collimated single-photon beams propagating along different 15° off-normal directions with orthogonal linear polarizations.

High-Level Multireference Investigations on the Electronic States in Single-Vacancy (SV) Graphene Defects Using a Pyrene-SV Model.

The nonplanar character of graphene with a single carbon vacancy (SV) defect is investigated utilizing a pyrene-SV model system by way of complete-active-space self-consistent field theory (CASSCF) and multireference configuration interaction singles and doubles (MR-CISD) calculations. Planar structures were optimized with both methods, showing the 3B1 state to be the ground state with three energetically close states within an energy range of 1 eV. These planar structures constitute saddle points. However, following the out-of-plane imaginary frequency yields more stable (by 0.22 to 0.53 eV) but nonplanar structures of Cs symmetry. Of these, the 1A' structure is the lowest in energy and is strongly deformed into an L shape. Following a further out-of-plane imaginary frequency in the nonplanar structures leads to the most stable but most deformed singlet structure of C1 symmetry. In this structure, a bond is formed between the carbon atom with the dangling bond and a carbon of the cyclopentadienyl ring. This bond stabilizes the structure by more than 3 eV compared to the planar 3B1 structure. Higher excited states were calculated at the MR-CISD level, showing a grouping of four states low in energy and higher states starting around 3 eV.