Vacancy Type Research Articles

A DFT study of CH4 adsorption on OMS-2 (1 1 0) surface with different types of oxygen vacancies

Cryptomelane-type octahedral molecular sieves (OMS-2) is considered as a promising non-precious metal catalyst, and its catalytic activity is largely related to oxygen vacancies (OVs). Hence, the effects of two types of OVs on CH4 adsorption on the surface of OMS-2 (110) were investigated based on density function theory (DFT). The cohesive energy, OVs formation energy, adsorption energy, density of states and Bader charge were calculated. The results show that OVs will preferentially form at sp3 oxygen sites on the surface. Methane tends to adsorb at the K site with three H atoms facing the surface. When the O-sp3 vacancy is introduced, the adsorption capacity of (110) surface for methane is enhanced, the electron transfer is increased, and the degree of CH activation is higher. Moreover, the adsorption capacity is further strengthened with increasing the number of O-sp3 defects. Conversely, the introduction of sp2 oxygen defect hinders the adsorption of methane by the catalyst due to the rearrangement of surface atoms. These conclusions can provide theoretical guidance for the development of efficient methane catalysts.

Anisotropic Li diffusion in pristine and defective ZnO bulk and (10[formula omitted]0) surface

We study the Li interstitial diffusion in pristine and defective ZnO bulk and (101¯0) surface by means of first-principles density functional theory (DFT) coupled with the Nudged Elastic Band (NEB) calculations. We consider three types of point defects, i.e., oxygen vacancy (Ovac), Zn vacancy (Znvac) and ZnO vacancy pair (ZnOvac-pair) and investigate their individual effect on the energy barrier of Li interstitial diffusion. Our results predict that Ovac and Znvac lower the Li diffusion energy barrier as compared to the pristine ZnO case. However, we further find that Li interstitial, on the other hand, may possibly be trapped inside the Znvac subsequently forming the LiZn substitutional type of defect. The similar behavior also observed for Li interstitial in the vicinity of Zn-Ovac_pair though with less change of Li diffusion barriers as compared to the other two cases. For Li diffusion on the ZnO surface, our results indicate that Ovac imposes similar effect as in the bulk case; it lowers the energy barriers for Li to diffuse outward (inward) from (to) ZnO sub-surface lattice. Our results indicate that among the three considered defects only Ovac shows possible enhancement of the kinetics of Li diffusion inside the bulk and on the surface of ZnO.

Simulation of diffusion with non-equilibrium vacancies, Kirkendall shift and porosity in single-phase alloys

In an alloy subject to vacancy-mediated diffusion, differences in intrinsic diffusivities tend to produce vacancy excess and deficit. These are accommodated by mechanisms such as dislocation climb and pore formation. This is of concern in high temperature alloy-coating systems used in industrial applications, as pores may develop at the interface between the alloy and the coating, which is undesired. This paper presents a multicomponent diffusion model with two types of vacancy sinks/sources: one is associated with dislocation climb and generates lattice shift, the other one is associated with porosity increase/decrease. The model is designed toward a 1D implementation, and porosity is described with a local average volume fraction. Thermodynamic properties and mobility are modeled according to the Calphad method to allow future application to engineering materials. Finite-difference simulations run on two binary systems, NiCr and NiSi, illustrate the role of the two types of sinks in interdiffusion and pore development. Diffusion is found to be more sensitive to the sink strengths in the NiSi system, where intrinsic diffusivities have a stronger composition dependence. This work provides a basis for the evaluation of the parameters involved in vacancy generation/annihilation (e.g. dislocation density) from experimental data, such as concentration profiles obtained from diffusion couple experiments, and for the prediction of porosity in engineering materials.

Regulating the Electronic Configuration of Spinel Zinc Manganate Derived from Metal-Organic Frameworks: Controlled Synthesis and Application in Anode Materials for Lithium-Ion Batteries.

In recent years, transition metal oxides have been considered as the most promising anode materials due to their high theoretical capacity, low price, and abundant natural reserves. Among them, zinc manganate is used as an electrode material for anodes, whose application is mostly hindered due to its poor ionic/electronic conductivity. In this work, a series of ZnMn2O4 (ZMO) are synthesized by a hydrothermal technique coordinated with a metal-organic framework-based high-temperature calcination process for their application as an anode in lithium-ion batteries (LIBs). Meanwhile, this study systematically explores the influence of carbon doping and the types of organic ligands and oxygen vacancies on the electrochemical properties of the synthesized ZMO. Density functional theory (DFT) calculations and experimental investigations reveal that the introduction of carbon and oxygen vacancies can enhance electronic conductivity, more active sites and faster Li+ adsorption, resulting in better electrochemical performances. As expected, all ZMOs with carbon doping (PMA-ZMO, MI-ZMO, and BDC-ZMO) derived from 1,2,4,5-benzenetetracarboxylic acid, 2-methylimidazole, and 1,4-dicarboxybenzene achieve outstanding electrochemical performance. Meanwhile, the introduction of oxygen vacancies can enhance the electronic conductivity and can significantly reduce the activation energy of Li+ transport, thereby accelerating the Li+ diffusion kinetics in the lithiation/delithiation process. Furthermore, an optimal ZMO anode material synthesized by 2-methylimidazole delivers a high reversible capacity of 1174.7 mA h g-1 after 300 cycles at 0.1 A g-1 and 600 mA h g-1 at 0.5 A g-1 after 300 cycles. After high-rate charge and discharge cycles, the specific capacity rapidly recovers to a value greater than the initial value, which proves the unusual activation and thereby an excellent rate property of the electrode. Hence, we conclude that ZMO provides potential application prospects as an anode electrode material for LIBs.

Role of Sr doping and external strain on relieving bottleneck of oxygen diffusion in La2−xSrxCuO4−δ

In many complex oxides, the oxygen vacancy formation is a promising route to modify the material properties such as a superconductivity and an oxygen diffusivity. Cation substitutions and external strain have been utilized to control the concentration and diffusion of oxygen vacancies, but the mechanisms behind the controls are not fully understood. Using first-principles calculations, we find how Sr doping and external strain greatly enhances the diffusivity of oxygen vacancies in La2−xSrxCuO4−δ (LSCO) in the atomic level. In hole-doped case (2x > δ), the formation energy of an apical vacancy in the LaO layer is larger than its equatorial counterpart by 0.2 eV that the bottleneck of diffusion process is for oxygen vacancies to escape equatorial sites. Such an energy difference can be reduced and even reversed by either small strain (< 1.5%) or short-range attraction between Sr and oxygen vacancy, and in turn, the oxygen diffusivity is greatly enhanced. For fully compensated hole case (2x ≦ δ), the formation energy of an apical vacancy becomes too high that most oxygen vacancies cannot move but would be trapped at equatorial sites. From our electronic structure analysis, we found that the contrasting change in the formation energy by Sr doping and external strain is originated from the different localization natures of electron carrier from both types of oxygen vacancies.

TEM characterization of irradiation-induced dislocation loops and voids in ion-irradiated pure chromium

Chromium (Cr) based coatings have been proposed for Zircaloy fuel rods to enhance the accident tolerance in water-cooled reactors. However, the response of Cr to irradiation has received limited attention in prior studies. To get a better understanding of radiation damage in Cr for future nuclear applications, in the present study, the irradiation-induced microstructure evolution of dislocation loops and voids was studied in pure Cr subjected to 2.8 MeV iron ions irradiation at 550 °C (belonging to stage III, intermediate-temperature). TEM observation results show that the distribution of dislocation loops extends the SRIM simulated irradiation depth to 3.5 µm, while voids were only formed in the irradiated region up to a depth of 1.3 µm. A rigorous method with combined consideration of edge-on view and inside-outside analysis was proposed to determine the habit plane. With this method, what has normally considered as an unsafe zone becomes a favored zone for determining the nature of dislocation loops. The nature of dislocation loops was determined including both interstitial and vacancy types with ½<111> Burgers vector in all regions. Within the irradiation region, the loops are approaching half interstitial and half vacancy, while beyond the irradiated region interstitial loops became dominant. The irradiation-induced swelling was quantified by the void size and density. The swellings are mostly corresponding well with the irradiation dose distribution which is simulated by SRIM. The swelling rate close to the peak region is around 0.3%/dpa. Results demonstrate that Cr tends to experience some similarities in irradiation loop evolution to W-based, Mo-based materials, as they are in the same group in the periodic table, despite the discrepancy in the characteristic of loops such as the irradiation temperature-dependent dislocation loop formation was observed as well. The present study is significant not only for supplementing the fundamental knowledge of irradiation damage in Cr but also for the application of Cr coating to the accident tolerant fuel claddings or other nuclear structure materials.

Effect of vacancy modification on the quantum capacitance of silicene- based electrode in efficient supercapacitors

In this study, we tried to evaluate the application of defected silicene as an electrode in supercapacitors using density functional theory calculations. Researchers have focused on single and double-vacancy silicene. In this work, we investigated six types of vacancies, namely the structures of mono vacancy (MV), double vacancy (DV), triple vacancy (TV), quadruple vacancy (QV), five vacancy (FV) and six vacancy (SV). The density of state, the integrated quantum capacitance, and stored charge plots for the pristine and the vacancy-modified defected silicene structures were investigated. Our results showed that using the vacancy-modified defected structures in the voltage range of -0.50 to 0.50 V provides more quantum capacities than using the pristine silicene. The vacancies MV, TV, QV, FV, and SV can be used as negative and positive electrodes, and they are p-type semiconductors. According to our calculations, the charge stored in at the vacancy-modified defected structures is higher than the charge stored in the pristine silicene at 0 to 0.5 V. The values of the charge stored in all of the vacancy-modified defected structures are similar to those in the pristine silicene. According to our results, the defected silicene is considered as a promising material in high-efficiency supercapacitors.

Vacancy-engineered half-metallicity and magnetic anisotropy in CrSI semiconductor monolayer

By virtue of their complete spin polarization at the Fermi level, two-dimensional (2D) magnetic half-metallic materials are emerging as one of the latest wonder building blocks for spintronic applications. Using first-principles calculations, we explored how vacancy defects affect the electronic structure and magnetic properties of CrSI semiconductor monolayer. Our results indicate that the magnetic semiconductor monolayer becomes metallic with the presence of single Cr vacancies, VCr, or paired vacancies made up of Cr and nearby S atoms, VCr-S, while by introducing VS, VI, VCr-I and VS-I vacancies, the monolayer becomes a half-metallic ferromagnet with Curie temperature TC above room temperature. Compared with the pristine case that exhibits an intrinsic in-plane magnetic anisotropy with an easy axis along the [100] direction, the six types of vacancies considered in this study either enhance the in-plane anisotropy or switch it to out-of-plane. Our work implies that vacancy engineering could be a viable approach for achieving both half-metallicity and perpendicular magnetic anisotropy in structurally similar magnetic semiconductor monolayers as well as in relevant designer van der Waals heterostructures for 2D spintronic applications.

Temperature-dependent luminescence of intrinsic defects and excitons in nanocrystalline monoclinic Y2O3 films

This work presents a comprehensive study of the optical properties of Y2O3 film with a monoclinic structure obtained by magnetron sputtering on a silica glass substrate. The parameters of band energy structure and emission characteristics of the film were determined by absorption, transmission, and photoluminescence spectroscopy. The dispersion of refractive index was established and the values of transparency gaps for direct and indirect interband transitions were determined. Optically active intrinsic centers were identified as vacancy (F - centers) and interstitial type (Oi - centers) defects, which are characterized by distribution of radiative states over activation energy of emission quenching. Luminescence in the UV and visible spectral ranges is interpreted as triplet-singlet radiative transitions in self-trapped and bound excitons. The values of thermally activated barriers for flare up and quenching of exciton luminescence are determined, and the configuration-coordinate diagram is proposed.

Electron-donating N−–Ti3+–Ov interfacial sites with high selectivity for the oxidation of primary C–H bonds

Element doping can fabricate different types of oxygen vacancies (O v ) on TiO 2 , but the effects of O v coordination and configuration on the oxidation reaction remain unclear. Here, we modify the local geometric ligand environment of O v by doping N and B into anatase TiO 2 (N-TiO 2 and B-TiO 2 ). N − –Ti 3+ –O v is induced in N-TiO 2 by substituting O with N, which has similar ionic size and electronegativity, and Ti 3+ –O v is found in TiO 2 and B-TiO 2 . Density functional theory calculations indicate that N − –Ti 3+ –O v is more reactive than Ti 3+ –O v toward O 2 activation. The resultant N-TiO 2 -0.25 enriched in N − –Ti 3+ –O v contributes to a rapid formation of superoxygen species (•O 2 − ), which increase the oxidation rate of primary C–H bonds in toluene, and thus exhibits much higher selectivity and yield. The fabrication of N − –Ti 3+ –O v develops doped catalysts with improved O v reactivity and enhanced primary C–H bond oxidation selectivity. • N − –Ti 3+ –O v is more reactive than Ti 3+ –O v toward O 2 activation to generate ⋅O 2 − • The generation of ⋅O 2 − is the rate-determining step in selective oxidation of toluene • The introduced photo energy does not change the thermal selective oxidation process • A higher yield of products is attributed to the increased selective oxidation rate Oxygen vacancies in TiO 2 influence catalytic activity differently depending on their coordination environment. Chen et al. explore N and B doping and show that N − –Ti 3+ –O v is more reactive than Ti 3+ –O v toward O 2 activation, enhancing the primary C–H bond oxidation of toluene.

Interaction of primary precipitates in reduced -activation ferritic/martensitic steel F82H with hydrogen atoms: Atomistic calculation based on the density functional theory

• We used DFT to perform first-principles calculations to understand the fundamental aspects of the interactions between hydrogen isotopes and VC and Cr 23 C 6 crystals in F82H steel. • The single H atom in the carbon vacancy in VC crystal is situated at the center of the vacancy, and the trapping energy is 1.99 eV. • Each H atom and C atom are bound to each other with strong covalent forces, and up to six H atoms can be trapped in the vanadium vacancy in VC crystal. • The trapping energy of H atom in the Cr(8c) vacancy is the strongest among the five types of vacancies in Cr 23 C 6 crystal. To understand the interaction of hydrogen isotopes with VC and Cr 23 C 6 precipitates, in reduced-activation ferritic/martensitic steel (F82H), we have performed first-principles calculations based on density functional theory. Energy calculations and electron density analysis were performed with a focus on the hydrogen retention by vacancies in precipitates. The H atoms in the C vacancy in the VC crystal are bound to the surrounding Cr atoms by relatively weak covalent forces and Coulombic attraction, and up to four H atoms are trapped. In the case of a Cr vacancy, H atoms are strongly covalently bonded to neighboring C atoms as well as to an interstitial H atom, capturing up to six H atoms. H atoms in vacancies in Cr 23 C 6 have a weak bonding force with the Cr atom but a strong repulsive force with the C atom. As a result, H atom is not trapped in the Cr(4a) vacancy, and H atoms are trapped only at a distance from the C atom in the Cr(48H) and Cr(32f) vacancies. The Cr(8c) and C vacancies are relatively far from the C atoms and have higher hydrogen trapping energies. The Cr 23 C 6 precipitate containing vacancies may be a dominant trapping site in the temperature range when H atoms immediately dissociate from vacancies. In addition, the VC precipitate may be the only trapping site for hydrogen isotopes at higher temperatures when Cr 23 C 6 precipitates cannot trap them.

Interfacial characterization in defective graphene/PET substrate structure through traction separation models: A molecular dynamics study

Among various graphene-based flexible electronic devices, the graphene/polymer substrate is one of the most common microstructures. Its interfacial mechanical properties directly determine the performance and reliability of these devices. Accordingly, the interaction between single-layer two-dimensional material such as graphene and polymer substrate has become an urgent research field in the manufacture and application of flexible electronic devices. In this study, traction-separation (T–S) models are established to study the interfacial mechanical behaviors of graphene/polyethylene terephthalate (PET) substrate structures using molecular dynamics (MD) simulations. The calculated interface parameters are verified by simulating the blister test with MD simulation and finite element analysis (FEA). Two common types of defects (Stone-Wales (S–W) and single vacancy (S–V)) are considered. By monitoring the aromatic ring distribution (order parameter and concentration) in PET substrate, the results reveal that under the normal loading, the S-W defect in graphene enhances the interfacial strength, while the separation energy is not sensitive to the existence of the S–W defect. The S–V defect in graphene degrades both the normal interfacial strength and separation energy owing to the loss of carbon atoms. Under the shear loading, it is found that the surface roughness of graphene caused by defects is an essential factor affecting the interfacial shear properties at the nanoscale. In addition, the results indicate that a low-concentration S–V defect can increase the surface roughness of graphene to obtain stronger mechanical interlocking, thereby enhancing the interfacial shear properties.

Radiation-induced segregation on dislocation loops in austenitic Fe-Cr-Ni alloys

Radiation-induced segregation of alloying elements to crystallographic defects is commonly observed in irradiated austenitic stainless steels. The interaction between solutes and radiation-induced defects changes the physical distribution of solutes and thus affects the formation and growth of defects. The change of the microstructure consequently affects the mechanical properties of the material. A qualitative and quantitative understanding of the interaction between solutes and defects is desirable to better predict the service lifetime of nuclear materials. We used atom probe tomography to measure the distribution of solutes at dislocation loops in 304L stainless steel, irradiated with 2 MeV protons up to 1.5 displacements per atom at 373 and 633 K. No segregation at dislocation loops was found in samples irradiated at 373 K, whereas Ni and Si enrichment and Cr depletion were detected at dislocation loops irradiated at 633 K. The experimentally observed perfect and faulted dislocation loops in vacancy and interstitial types were reproduced by molecular dynamics (MD). A hybrid MD/Monte Carlo method was used to predict the redistribution of alloying atoms at all possible types of dislocation loops in face-centered cubic Fe-Cr-Ni alloys at the same irradiated temperatures (373 and 633 K). The simulations show that, at both temperatures, Cr clusters were formed and distributed randomly, and Ni atoms enriched or depleted at interstitial or vacancy dislocation loops, respectively. The change of solute concentration reaches the highest at the edge of the loop. Ni profiles exhibit characteristic behavior in terms of the stress field of the loops: tension inside of vacancy loops showing depletion of Ni atoms compared with compression inside of interstitial loops showing enrichment of Ni atoms. In addition, the stress field is reduced after solute redistribution. The absence of alloying segregation observed in experiments at a lower temperature (373 K) is explained by a rate theory model: Low-temperature irradiation requires significantly longer irradiation time to see the same amount of segregation as at high temperatures because of the extremely low diffusion of vacancies at low temperatures.

Growth and characterization of GeSnO thin films for thermoelectric power generation applications

In this paper, we have demonstrated the thermoelectric properties of GeSnO thin films grown by physical vapor deposition technique. The GeSn pellets were prepared by mixing of germanium (Ge) and tin (Sn) powders with 1:1 ratio using a hydraulic press. Hard pellet was evaporated in a vacuum tube furnace on glass substrate. The grown sample was cut into pieces and subjected to the annealing process at different temperatures ranging from 350 to 500 0C in an oxygen environment. XRD data confirmed the formation of GeSnO crystal structure and it was found to be improved up to annealing temperature 350 °C due to the compensation of oxygen vacancy type defects. But further annealing temperature degrades the crystal quality because oxygen atoms get additional thermal energy and it may generate interstitial defects. Raman and SEM data further supported our argument. Seebeck data confirmed the enhancement in the values of Seebeck coefficient, power factor and electrical conductivity with annealing temperature. The enhancement of thermo power with annealing temperature is due the fact that it degrades the crystal quality which resulted in the generation of secondary phases. These secondary phases are the major contributors of Seebeck coefficient and electrical conductivity.

Influence of vacancy on the mechanical and thermodynamic properties of PtAl2 from the first-principles investigation

ABSTRACT The point defect plays an important role in high-temperature materials. Although PtAl2 is a promising high-temperature alloy, the mechanism of point defect in PtAl2 is entirely unknown. By using the first-principles calculations, here, we study the influence of vacancy on the structural stability, mechanical and thermodynamic properties of PtAl2. Two vacancy types – Al vacancy and Pt vacancy – are considered. The calculated result shows that PtAl2 prefers to form the Al vacancy in comparison to the Pt vacancy. The calculated elastic modulus of Al vacancy is larger than the Pt vacancy. Essentially, the low elastic modulus is that the removed atom changes the localised hybridisation between Pt and Al. PtAl2 with these vacancies also shows ductility behaviour. Finally, it is found that the calculated Debye temperature of Al vacancy is lower than the perfect PtAl2. However, the calculated Debye temperature of Pt vacancy is higher than the perfect PtAl2. Therefore, this work theoretical reveals the vacancy mechanism of PtAl2 alloy and provides a new path to improve the mechanical and thermodynamic properties of PtAl2 high-temperature alloy.

Multiple synergistic losses in the absorption of electromagnetic waves by three-dimensional cross-linked carbon fiber

Carbon fiber with a three-dimensional (3D) cross-linked structure was prepared by electrostatic spinning and heat treatment. The HRTEM images of carbon fiber were used as the basis for determining the types of graphite defects in carbon fiber by combining the intensity ratios of the D and D′ peaks in the Raman spectra, and the contribution of different graphite defects types in carbon fiber to electromagnetic wave absorption was analyzed. Among the three types of graphite defects, sp3 type, vacancy type, and boundary type, the carbon fiber with predominantly boundary type graphite defects showed excellent electromagnetic wave absorption performance. The heat treatment temperature has a significant effect on the conductivity and electromagnetic properties. The broadest effective absorption bandwidth (EAB) is 5.44 GHz at 2.07 mm when the thermal treatment temperature is 650 °C. In carbon fiber with a carbonization temperature of 850°, graphite nanocrystals and large graphite areas coexist and graphite defects are predominantly of the boundary type. Interfacial polarization of amorphous carbon and graphite nanocrystals under the action of electromagnetic waves produces dielectric losses; large graphite areas produce conductive losses and eddy current losses. The dielectric loss, conductive loss, and eddy current loss synergistically achieve a strong absorption of the electromagnetic wave multi-spectrum at 5.08 GHz, −40.55 dB, −43.35 dB, and −44.44 dB at 5.08 GHz, 7.46 GHz, and 14.94 GHz respectively. Without the addition of magnetic materials, the carbon fiber in this study achieves the ability of a dielectric loss type electromagnetic wave absorbing material to possess magnetic loss.

Investigating the potential of AgZnO thin film composites for waste heat recovery using Seebeck data

In this paper, we have demonstrated the thermoelectric properties of Silver Zinc oxide (AgZnO) composite grown by thermal evaporation method. A mixture of Silver and Zinc powders with 1:4 ratio was evaporated on silicon substrate using a vacuum tube furnace. The grown composites were subjected to post growth annealing process at various temperatures ranging from 500 to 800 °C in a programmable muffle furnace. XRD data proved that the crystallinity of the annealed samples was improved because more and more oxygen atoms were able to fill the oxygen vacancy type defects in the host crystal of AgZnO. The observed structural behavior was also verified by Raman spectroscopy measurements. Seebeck measurements revealed a remarkable enhancement in the values of Seebeck coefficient (303–711 μV/°C) and electrical conductivity (17–176 S/cm) with annealing temperature. The high annealing temperature may cause an enhancement in the mobility of Ag atoms which resulted in the increase of Seebeck coefficient and electrical conductivity simultaneously.

Giant Stokes shift for charged vacancies in monolayer SnS

We perform first-principles density-functional theory calculations to determine the equilibrium defect structures, formation energies, charge transition levels, and electronic structures of Sn and S vacancies in monolayer SnS. Both Sn and S vacancies exhibit multiple charge transition levels and in-gap defect states, indicating that they may be stable in different charge states depending on the Fermi level in the system. Depending on the charge state of the vacancy, the easily distorted SnS lattice undergoes different relaxations, and in some cases, symmetry-breaking reconstructions, creating defect states within the gap that electrons can occupy at a lower energetic cost. Due to significant atomic relaxations between the equilibrium defect structures in different charge states, optical charge transitions involving both types of vacancies exhibit significant Stokes shifts of over 1 eV, which may provide opportunities for increased efficiency in light emission diode, solar cell, and solar concentrator applications.

Multi-photon multi-quantum transitions in the spin- 32 silicon-vacancy centers of SiC

Silicon vacancy centers in silicon carbide are promising candidates for storing and manipulating quantum information. Implementation of fast quantum gates is an essential requirement for quantum information processing. In a low magnetic field, the resonance frequencies of silicon vacancy spins are in the range of a few MHz, the same order of magnitude as the Rabi frequencies of typical control fields. As a consequence, the rotating wave approximation becomes invalid and nonlinear processes like the absorption and emission of multiple photons become relevant. This work focuses on multi-photon transitions of negatively charged silicon vacancies driven by a strong RF field. We present continuous-wave optically detected magnetic resonance (ODMR) spectra measured at different RF powers to identify the 1-, 2-, and 3-RF photon transitions of different types of the silicon vacancy in the 6$H$-SIC polytype. Time-resolved experiments of Rabi oscillations and free induction decays of these multiple RF photon transitions were observed for the first time. Apart from zero-field data, we also present spectra in magnetic fields with different strength and orientation with respect to the system's symmetry axis.

Defect modulated electronic structure and magnetism in the 1T′ phase of Janus MoSSe

By means of first-principles calculations, we systematically investigate the stable geometry, formation energy, and magnetic and electronic properties modulated by the vacancy, antisite, and complex defects in the 1T′ phase of monolayer (ML) Janus MoSSe. The formation energies for different positions of vacancy defects shows that the metallic and semiconductive phases can be produced for the vacancy defect with inequivalent atoms. Furthermore, the magnetism could be induced in ML Janus 1T′-MoSSe by the Mo-Se(A) and Mo-S(A) antisite defects. For the complex defects case, we found that the magnetism can be induced and is widespread for different types of vacancy in the 1T′-MoSSe substrate. The band gap of the original ML Janus 1T′-MoSSe can be efficiently modified by introducing defects and vacancies. Our investigation indicates that the 1T′ phase of ML Janus MoSSe with defects and vacancy has a potential application for spintronics and optoelectronics.