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This study employs first-principles calculation to investigate the MoSi 2 N 4 /SiC heterojunction. It aims to determine the structure, electronic, and optical properties of the heterojunction and assess the impact of varying vertical electric fields and biaxial strains on these properties. The results show that the MoSi 2 N 4 /SiC heterojunction is a direct bandgap semiconductor, exhibiting a band gap of 0.31 eV. This heterojunction benefits from a built-in electric field originating from the SiC layer and extending to the MoSi 2 N 4 layer. The optical absorption peaks in the ultraviolet region are significantly more intense than those in MoSi 2 N 4 and SiC monolayers, particularly at a wavelength of 172 nm, where the intensity reaches 1.99 × 106 cm−1. The study also shows that an increasing positive vertical electric field leads to a rising band gap. On the other hand, increasing tensile or compressive strain causes a gradual decline in the band gap. Specifically, at a strain of −8 %, the absorption peak intensity reaches 3.4 × 106 cm−1 at 172 nm, and the absorption spectrum broadens to 722 nm at an 8 % strain. In conclusion, the MoSi 2 N 4 /SiC heterojunction shows promise for enhancing the optical properties of two-dimensional materials and offers valuable insights for the development of efficient new ultraviolet devices. [ABSTRACT FROM AUTHOR] more...

To comprehend the mechanical, electronic, and magnetic properties of chalcogenides HgSm2S/Se4, a DFT-oriented thorough investigation is carried out. The elastic constants and spin-dependent electrical characteristics are determined by using the PBEsol-GGA functional and (mBJ) potential correspondingly. Through optimization, a sufficient amount of energy is discharged by the FM state as compared to nonmagnetic states. By investigating Born stability criteria and formation energy, the structural stabilities of both spinels are verified. The calculated Poisson's and Pugh's ratios showed that both spinels are ductile. The estimation of Curie temperature has supported the existence of a ferromagnetic nature at room temperature. Moreover, the presence of ferromagnetism in both spinels is confirmed by spin-oriented electrical characteristics, owing to the coupling between component states associated with Sm and S/Se. [ABSTRACT FROM AUTHOR] more...

Bulk phosphorus oxynitride (PON), isoelectronic with SiO2, is confirmed to have many polymorphs as the latter. However, its 2D counterparts have not been studied. In this work, crystal structure exploration and property study are performed on 2D PON with the help of first‐principle calculation. Three 2D PON sheets are found with thermal, dynamical, and mechanical stability and all of them can be viewed as oxygen‐doped known 2D γ phosphorus nitride (γ‐PN). In the studies, it is indicated that they are indirect bandgap materials with gap values larger than 3 eV. The situations of orbital hybridization are discussed and their bonding properties are analyzed. Infrared vibrational spectra of these 2D materials are simulated and the vibrational modes at the Brillouin center are assigned by the factor group analysis. The reasons for the disappearance of some infrared peaks in the simulated spectra are revealed based on the calculated Born effective charges and vibrational eigenvectors. Their piezoelectric stress tensors are computed via density‐functional perturbation method and the piezoelectric strain tensors are also deduced via the calculated elastic constants. In the results, it is uncovered that these 2D PON sheets have considerably greater piezoelectric coefficients than the primitive 2D γ‐PN, which make them promising for nanopiezoelectric use. [ABSTRACT FROM AUTHOR] more...

Single-phase concentrated solid-solution alloys (CSAs) have exhibited excellent mechanical and radiation tolerance properties, making them potential candidate materials for nuclear applications. These excellent properties are closely related to dislocation movements, which depend on the stacking fault energies (SFEs). In CSAs, SFEs show large fluctuations due to variations in the local atomic environments in the vicinity of the stacking faults. In this work, first-principle calculations were performed to investigate the origin of the fluctuations in the SFEs of the widely studied CSA, NiCoCr, which show a very wide distribution from about −200 mJ/m2 to 60 mJ/m2. Compared to the common understanding that only atoms in close proximity to the stacking fault influence the SFEs in pure metals and dilute alloys, charge redistribution can be observed in several nearby planes of the stacking fault in NiCoCr, indicating that atoms several atomic layers away from stacking fault also contribute to the SFEs. Our analysis shows that Cr plays a major role in the large fluctuation in the SFEs of NiCoCr based on both electronic and magnetic responses. The flexible electronic structure of Cr facilitates easier charge transfer with Cr in several nearby atomic planes near the stacking fault, leading to significant changes in the d-electron number, orbital occupation number, and magnetic moments of Cr. [ABSTRACT FROM AUTHOR] more...

The fascinating realm of silicon quantum dots (Si QDs) has attracted considerable attention for their exceptional optical characteristics and potential applications in the optoelectronic industry. However, there remains a scarcity of research that directly compares the impacts of diverse surface modification methods on the electronic structure and charge transfer properties of Si QD nanomaterials. Considering this scientific challenge, we employ the first-principle calculations to conduct the following investigations. To begin, we have innovatively introduced the concept of the adjacent coordination number (ACN) to establish a quantitative correlation between the band gap (Eg) and the doping sites of boron (B) atoms across various sizes of Si QDs. Additionally, a combination of Total Density of States (TDOS), Partial Density of States (PDOS) and orbital component analysis reveals that the subtle dipole effect near the B-doping site significantly contributes to the reduction in the band gap, providing valuable insights into the complex impact of different doping sites on the electronic arrangement and structure of Si QDs. Ultimately, our absorption spectroscopy, charge transfer and Quantum Theory of Atoms in Molecules (QTAIM) analysis of organic molecule coupling Si QDs reveal the formation of dipoles on the surface and the correlation between charge migration direction and binding sites. This phenomenon not only amplifies the presence of conjugated coupling states but also significantly enhances the charge transfer capability of Si QDs. These valuable insights will provide significant advantages to scientists and researchers endeavoring to tailor the electronic structure and optical attributes of Si QDs using a diverse array of modification techniques to meet specific application requirements. The surface functionalization of Si QDs involves doping or coupling site selection and the establishment of charge transfer bridges is crucial for the formation of dipole–dipole interaction which may not only play a role in regulating band gap structures but also exert significant control over the charge transfer capacity of Si QDs. [ABSTRACT FROM AUTHOR] more...

We present a theoretical investigation on the wide-band-gap semiconductor WO   3 in its room-temperature monoclinic structure. We carried out density functional theory and GGA-1/2 calculations on the bulk phase and the most stable (001) surface of the material, either in their stoichiometric form or in the presence of oxygen vacancies at various concentrations. Concerning the bulk phase, our results show how the inclusion of these defects correctly reproduces the intrinsic n-type doping of the material. The system is also found to be magnetic at reasonably high defect concentrations. As for the surface, the presence of vacancies gives rise to a magnetic behavior, whose features depend on the relative arrangement of native point defects. Oxygen vacancies are also responsible for additional tungsten oxidation states in both bulk and surface. Based on these results, we provide a rationale for the interpretation of most experimental data of this material and, possibly, other widespread transition metal oxides with similar properties and applications such as ReO   3 , TiO   2 , and SnO   2 . [ABSTRACT FROM AUTHOR] more...

Novel semiconductor material with both high strength and ductility is urgently needed to meet the demands of increasing complex applications for electronic components. However, overcoming the inherent trade-off between strength and ductility has remained a longstanding challenge in materials science research. Herein, we proposed a three-dimensional carbon allotrope, oc-C24 with pure sp2 hybridization. This structure comprises arrays of carbon chains in an “8”-shape helix configuration, in between the C-chains which interlinked by the oriented ethylene with a planar π-conjugation. The distinctive structural unit imbues oc-C24 with remarkable tensile behavior, characterized by multi-stage chemical bond rearrangements and structural phase transitions along [010] crystallographic direction, displaying multi-level stress re-enhancement phenomena. A tensile strength of 104.2 GPa and a record strain of 1.05 are observed along [010] direction. Electronic band analysis reveals that oc-C24 is a semiconductor with an indirect band gap of 2.91 eV. The impressive tensile resistance and ductility of oc-C24 suggest its strong potential applications in electronic devices under extreme conditions. Our findings offer valuable insights and methodological strategies for designing novel carbon allotropes with unique mechanical responses. more...

Abstract The emergence of various topological semimetal states presents a novel opportunity for enhancing the efficiency of thermoelectric transport. This study introduces a recipe to improve the thermoelectric (TE) performance in topological materials containing single‐pair Weyl points (SP WPs) fermions and phonons. The recipe focuses on two key factors contributing to the enhancement of TE performance: the increase in the density of states to achieve a high power factor, and the introduction of additional phonon scattering to reduce the lattice thermal conductivity. The proposed recipe is confirmed in a half‐metallic SP WPs material BaNiIO6 through first‐principles methods. An enhanced density of states arises near the energy of the SP WPs in BaNiIO6, leading to a peak power factor connected to the complex Fermi surface due to the degeneracy of Weyl pockets in energy. Furthermore, it is shown that the SP WPs phonons in BaNiIO6 possess a high scattering rate and can likely contribute to the low lattice thermal conductivity, especially when two crossing points in SP WPs do not degenerate in frequency. The new recipe can be used for discovering high‐performance thermoelectric materials in the future by utilizing the transport advantages of degenerate‐in‐energy SP WPs fermions and non‐degenerate‐in‐frequency SP WPs phonons. more...

The effect of the Mn3+ ion on the local distortions of FeO6 octahedra in orthoferrite samples was investigated. Mössbauer spectroscopy measurements for a series of HoFe1−xMnxO3 (x = 0–0.7) orthoferrite samples with the space group Pnma were carried out at temperatures above the Néel point (700 K). The electric field gradient (EFG) tensor on Fe ions for these compounds was found using first-principle calculations. The concentration dependence of quadrupole splitting was obtained using experimental and theoretical data. Mn3+ cations were found to affect the Mössbauer spectra mainly due to distortions of the crystal lattice. Theoretical calculations show that the values of all electric field gradient components increase significantly with the manganese concentration in the system, and the eigenvectors exx and eyy of the electric field gradient tensor sharply change their direction at concentrations of x > 0.1. more...

Fe-containing intermetallic compounds (IMCs) are among the most detrimental second phases in aluminum alloys. One particularly harmful type is θ-Al13Fe4, which exhibits a needle- or plate-like morphology, leading to greater degradation of mechanical properties compared to other Fe-IMCs with more compact structures, such as α-Al15(Fe,Mn)3Si2. The addition of alloying elements is a crucial strategy for modifying the microstructure during the solidification process of aluminum alloys. This study investigates the effects of adding vanadium (V) and zirconium (Zr) on the morphology and crystal chemistry of θ-Al13Fe4 in an Al-4Fe alloy, employing a combination of experimental observations, first-principle calculations, and thermodynamic analysis. Our findings indicate that zirconium significantly refines both the primary θ-Al13Fe4 particles and the α-Al grains. Additionally, a small amount of vanadium can be incorporated into one of the Wyckoff 4i Al sites in θ-Al13Fe4, rather than occupying any Fe sites, under casting conditions, in addition to the formation of binary Al-V phases. more...

The past decade witnessed substantial attention toward metal‐organic frameworks (MOFs) for photocatalytic water splitting owing to their versatile structural and optoelectronic characteristics. However, MOFs capable of efficient photocatalytic overall water splitting (OWS) remain notably scarce. Although MOF‐based photocatalysts with OWS potential are highly promising due to their diverse building blocks and topological configurations, the vast number of possible MOFs renders traditional trial‐and‐error materials discovery approaches impractical. Herein, a data‐driven methodology that integrates machine learning with high‐throughput first‐principles computations to identify MOFs with OWS capability is presented. By systematically assessing factors including water stability, band gap, band positions, charge carrier transport, and optical absorption properties, 14 MOFs from the Quantum‐MOF (QMOF) database containing over 20,000 MOFs as promising candidates for visible‐light‐driven OWS are identified. Notably, five of them exhibit exceptional electronic and optical properties, outperforming previously reported MOF OWS photocatalysts, such as UIO66(Zr)‐NH2, MIL125(Ti)‐NH2, and MIL53(Al)‐NH2 is established. This work represents a large‐scale, data‐driven exploration of MOF‐based photocatalysts for water splitting, shedding light on the untapped potential of photocatalysis in MOFs. [ABSTRACT FROM AUTHOR] more...

We conducted a large set of ab initio density functional theory computations to model a variety of hammer-terminated graphene nanoflakes—finite counterparts of armchair graphene nanoribbons. We focused on the relationships among the length and width of the nanoflakes, the stoichiometry and the conformation of the hydrogen saturation of the caps, and the resulting electronic structure. The energetics and the thermodynamic stability of the nanoflakes were investigated as well. Based on this study, we provide a recipe for determining the most stable saturation of the dangling bonds at the caps, which is generally disregarded in theoretical studies, and we prove that this step is crucial for a reliable description of the electronic structure of these systems. Data analysis proved that flakes far from the most stable C–H pattern exhibited electronic properties that were typical of an unsaturated bonding structure. Based on thermodynamics, we also proved that, for any given flake, there was a well-defined hydrogen content and a conformation of H atoms at the caps, which were favored across a wide range of environmental conditions. [ABSTRACT FROM AUTHOR] more...

The rational design of metal single‐atom catalysts (SACs) for electrochemical nitrogen reduction reaction (NRR) is challenging. Two‐dimensional metal–organic frameworks (2DMOFs) is a unique class of promising SACs. Up to now, the roles of individual metals, coordination atoms, and their synergy effect on the electroanalytic performance remain unclear. Therefore, in this work, a series of 2DMOFs with different metals and coordinating atoms are systematically investigated as electrocatalysts for ammonia synthesis using density functional theory calculations. For a specific metal, a proper metal‐intermediate atoms p‐d orbital hybridization interaction strength is found to be a key indicator for their NRR catalytic activities. The hybridization interaction strength can be quantitatively described with the p−/d‐ band center energy difference (∆d‐p), which is found to be a sufficient descriptor for both the p‐d hybridization strength and the NRR performance. The maximum free energy change (ΔGmax) and ∆d‐p have a volcanic relationship with OsC4(Se)4 located at the apex of the volcanic curve, showing the best NRR performance. The asymmetrical coordination environment could regulate the band structure subtly in terms of band overlap and positions. This work may shed new light on the application of orbital engineering in electrocatalytic NRR activity and especially promotes the rational design for SACs. [ABSTRACT FROM AUTHOR] more...

The present review is aimed to understand the Rashba and Dresselhaus effects from the first-principle calculations. A brief overview of first-principle density functional theory (DFT) and its global acceptance have been discussed. The discussions of the Rashba–Dresselhaus splittings, spin textures and understanding the effects from first-principle DFT calculations have been highlighted. Rashba and Dresselhaus effects have gained much attention in recent era for their highly promising applications in spintronics. In the presence of spin-orbit coupling and inherent non-centrosymmetry, while BiTeCl, TiS2Se, rhombohedral CsPbF3 and BiCoO3 compounds show large values of Rashba parameter ( α R) of ∼ 1. 9 0 , 1.10, 1.05 and 0.74 eVÅ, respectively, the single-layered semiconductor nanostructure InSb, rhombohedral BiFeO3 and Ag2BiO3 systems however depict promising values of Dresselhaus parameter ( α D) of ∼ 2. 2 0 , 0.50 and 0.15 eVÅ, respectively. The future of Rashba–Dresselhaus effects and their advancements in spintronics have also been enlightened in this paper. We believe that this study will not only help to understand the Rashba–Dresselhaus effects from first-principle calculations, but can also augment their applications in next generation spintronic devices. [ABSTRACT FROM AUTHOR] more...

Borophene (B) is a promising two dimensional (2D) material because of the excellent carrier mobility, large specific surface area and very light mass. However, many problems (overactive borophene chemistry and difficulty) have limited it's further applications. To improve the catalytic hydrogen evolution reaction properties, here, we apply ab-initio calculations to study the structural stability of two defective borophene (χ 3 and β 12)/MoS 2 heterojunction as a hydrogen evolution reaction (HER) catalyst. In particular, we further explore the influence noble metals (Pt and Pd) on the catalytic properties of borophene(χ 3 and β 12)/MoS 2 heterojunction. The calculated results show that the involvement of MoS 2 not only improves the structural stability of the defective borophene@MoS 2 but also further improves the catalytic ability of the borophene@MoS 2. In particular, the calculated hydrogen adsorption Gibbs free energy (ΔG) of the χ 3 /MoS 2 -III heterojunction is only −0.0004 eV, which is an ideal catalyst for HER. Furthermore, the calculated Gibbs free energy (ΔG) of borophene (β 12)/Pd@MoS 2 -II is 0.0007 eV because of the strong localized hybridization between Pd and the borophene (β 12)/MoS 2 -II. Therefore, we believe that the Pd-doping can effectively improve the catalytic properties of the borophene (β 12)/Pd@MoS 2 as a hydrogen evolution reaction (HER) catalyst. [Display omitted] • The catalytic hydrogen evolution reaction of the defective borophene@Pt/Pd/MoS 2 heterojunctions is studied. • The involvement of MoS 2 improves the catalytic ability of the defective borophene@MoS 2 heterojunctions. • It is found that the χ 3 /MoS 2 -III heterojunction is an ideal catalyst for hydrogen evolution reaction. • The Pd-doping effectively optimizes the catalytic performance of the β 12 /Pd@MoS 2 heterojunction. [ABSTRACT FROM AUTHOR] more...

Superconductors with reduced dimensionality have been widely explored for their exotic superconducting behaviors. Especially, at the two-dimensional limit, two-monolayer Pb films with two types of structures provide an ideal platform to unveil the underlying superconducting mechanism [Science324, 1314 (2009)]. Here, by combining scanning tunneling microscopy (STM) with the first-principle calculations, we successfully identify that these two types have different atomic lattice structures with varying stacking phases, which further enables us to calculate the phonon spectrum and electron phonon coupling strength of each type. The theoretical calculations are in good agreement with tunneling spectroscopy measurements of the superconducting transition temperatures (Tc), which established a correlation between atomic structures and superconductivity. Moreover, it was observed that the higher Tc of these two types also possess higher out-of-plane upper critical magnetic fields (Hc2). These findings will provide important new insights into two-dimensional superconductivity at the atomic level. [ABSTRACT FROM AUTHOR] more...

L12-Al3X (X = Li, Sc, and Zr) precipitates are the main strengthened phases of high-strength aluminum alloys and are critical for aerospace structural materials. Point defects and substitutional ternary elements change the mechanical properties of Al3X. In this paper, the effect of point defects, including vacancy, antisite, and substitutional element addition defects on the elastic modulus of the off-stoichiometric Al3X (X = Li, Sc, and Zr) phase were investigated by using first-principle calculations. The formation enthalpies of the defective Al3X alloy and isolated point defects in Al3X were calculated, and the results showed that the defects have an effect on the structure and elasticity of the off-stoichiometric Al3X phases. The lattice distortion, elastic constants, and elastic moduli were further investigated. It was found that the point defects increased the Young's modulus for Al3Zr, and the doping of Er improved the Young's modulus for off-stoichiometric Al3Li and Al3Sc. Adjusting the position of vacancies can improve the elastic modulus. In addition, the doping of substitutional elements (especially Sc, Ti, Zr, Hf, Ta, Mn, Ir, and Cf) can greatly increase the Young's modulus of off-stoichiometric Al3Li. [ABSTRACT FROM AUTHOR] more...

Two-dimensional materials are widely used as a new generation of functional materials for photovoltaic, photocatalyst, and nano-power devices. Strain engineering is a popular method to tune the properties of two-dimensional materials so that performances can be improved or more applications can be obtained. In this work, a two-dimensional heterostructure is constructed from SiC and GaN monolayers. Using first-principle calculations, the SiC/GaN heterostructure is stacked by a van der Waals interaction, acting as a semiconductor with an indirect bandgap of 3.331 eV. Importantly, the SiC/GaN heterostructure possesses a type-II band structure. Thus, the photogenerated electron and hole can be separated in the heterostructure as a potential photocatalyst for water splitting. Then, the external biaxial strain can decrease the bandgap of the SiC/GaN heterostructure. From pressure to tension, the SiC/GaN heterostructure realizes a transformation from a type-II to a type-I semiconductor. The strained SiC/GaN heterostructure also shows suitable band alignment to promote the redox of water splitting at pH 0 and 7. Moreover, the enhanced light-absorption properties further explain the SiC/GaN heterostructure's potential as a photocatalyst and for nanoelectronics. [ABSTRACT FROM AUTHOR] more...

MBene with sufficient basal plane active sites exhibits excellent multifunctional HER/OER/ORR electrocatalytic activity. [Display omitted] • Six MBenes can maintain excellent HER catalytic activity under various H coverage. • Ni 2 B 2 and Co 3 B 4 MBenes can be promising multifunctional catalysts for HER/OER/ORR. • Different slopes of Δ G OOH* and Δ G O* versus Δ G OH* lead to low OER/ORR overpotentials. • The Δ G OH* is illuminated by the d-band center and charge transfer analysis. Exploring multifunctional electrocatalysts to realize efficient hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR) is urgently desired for developing novel renewable energy storage and conversion technologies. However, integrating these three merits in one single catalyst remains a big challenge due to the difficulty in balancing the adsorption strengths of multiple reaction intermediates. Herein, through first-principles calculations, we systematically investigated the electrocatalytic activity of M 2 B 2 , M 3 B 4 , and M 4 B 6 type MBenes (M = Cr, Mn, Fe, Co, and Ni) for multifunctional HER, OER, and ORR. The results indicate that most of the investigated MBenes show outstanding catalytic activity for HER with hydrogen adsorption Gibbs free energy close to the optimal value (0 eV). Thereinto, Ni 2 B 2 and Co 3 B 4 MBenes can be promising multifunctional HER/OER/ORR electrocatalysts, and Fe 3 B 4 MBene is expected to be a promising bifunctional electrocatalyst for HER/ORR. Especially, Ni 2 B 2 MBene is even better than the benchmark RuO 2 catalyst with ultralow low overpotentials of 0.26 and 0.30 V for OER and ORR, respectively. Then, we proposed that the overpotentials of OER/ORR can be well described by the varied Δ G OH* on MBene, which has been further illuminated through the d-band center and charge transfer analysis. Importantly, new scaling relations between the adsorption energies of OOH* and O* on MBenes have been established, where Δ G OOH* and Δ G O* possess different slopes versus Δ G OH* , allowing the significantly lower overpotentials of OER and ORR to be achieved. This work provides not only promising multifunctional HER/OER/ORR electrocatalysts but also new scaling relations to achieve the rational design of MBene-based electrocatalysts. [ABSTRACT FROM AUTHOR] more...

The research of nanocrystalline pyrochlores highlights the importance of the surface structure, composition and segregated point defect in their thermal, electrical, optical, magnetic, and catalytic performances. In order to provide a basic view on the surface‐related phenomena, thermodynamic stabilities of three low‐index (100), (110), and (111) surfaces for A2Sn2O7 (A = La, Ce, Pr, Nd, Pm, Sm, Eu, or Gd), together with their configurations, electronic structures and related oxygen vacancies are investigated using first‐principles calculations. The (111) surfaces with A3SnO8 and ASn3O6 terminations are predicted to be stable due to their low surface energies. Meanwhile, the (110) surfaces with A2Sn2O8 and A2Sn2O6 terminations are found to may also form. For these surface structures, the amount of broken bonds play the main role in their structural stability, and the local coordination environment variation also has minor contribution to it. Moreover, oxygen vacancies are observed to segregate on the surface layer, owing to lower energy of breaking bonds accompanying with oxygen vacancy formation and the larger relaxation space comparing to the counterpart in bulk. These results are expected to provide guidance on optimizing the performances of these compounds through surface engineering. [ABSTRACT FROM AUTHOR] more...

The atomic‐scale structure of cuprous selenide room temperature phase (α‐Cu2Se), which plays an important role in understanding the mechanism of its high thermoelectric performance, is still not fully determined. Here, direct observation with atomic‐scale resolution is realized to reveal the fine structure of α‐Cu2Se via spherical‐aberration‐corrected scanning transmission electron microscopy. It is observed to be an interesting self‐independent binary‐sublattice construction for Cu and Se in α‐Cu2Se, respectively, which shows a variety of ordered copper fluctuation structures are embedded in a rigid pseudo‐cubic Se sublattice. Ordering of Cu uses a variety of configurations with little energy difference, forming considerable amounts of "boundaries," which may lead to ultrastrong phonon scattering. Furthermore, density functional theory calculations indicate that the electronic structures are mainly determined by the rigid Se face‐centered cubic sublattice and not sensitive to the various copper fluctuations, which may guarantee the electron transfers with large carrier mobility. The self‐independent binary‐sublattice construction is speculated to enhance phonon scattering while still maintaining good electrical transport property. This study provides new critical information for further understanding the possible correlation between the specific structure and thermoelectric performance of α‐Cu2Se, as well as designing new thermoelectric materials. [ABSTRACT FROM AUTHOR] more...

In this article, the piezoelectric effects of the 2D semiconductors of IV group monochalcogenides (GeS, GeSe) are studied by methods of the density functional theory and first-principles pseudopotential based on own program code. The spatial distribution of valence electron density, density of states, and Coulomb potential along transverse direction are calculated. It was found that a more significant rearrangement of the electron density was observed during compression of both GeS and GeSe bi-layer films than mono-layer films, but more significant in GeS films. [ABSTRACT FROM AUTHOR] more...

To achieve the atomistic control of two-dimensional materials for emerging technological applications, such as valleytronics, spintronics, and single-photon emission, it is of paramount importance to gain an in-depth understanding of their structure–property relationships. In this work, we present a systematic analysis, carried out in the framework of density-functional theory, on the influence of uniaxial strain on the electronic and optical properties of monolayer MoTe2. By spanning a ±10% range of deformation along the armchair and zigzag direction of the two-dimensional sheet, we inspect how the fundamental gap, the dispersion of the bands, the frontier states, and the charge distribution are affected by strain. Under tensile strain, the system remains a semiconductor but a direct-to-indirect band gap transition occurs above 7%. Compressive strain, instead, is highly direction-selective. When it is applied along the armchair edge, the material remains a semiconductor, while along the zigzag direction a semiconductor-to-metal transition happens above 8%. The characteristics of the fundamental gap and wave function distribution are also largely dependent on the strain direction, as demonstrated by a thorough analysis of the band structure and of the charge density. Additional ab initio calculations based on many-body perturbation theory confirm the ability of strained MoTe2 to absorb radiation in the telecom range, thus suggesting the application of this material as a photon absorber upon suitable strain modulation. [ABSTRACT FROM AUTHOR] more...

In recent years, hydrogen (H 2) energy has been attracting extensive research attention as a clean resource as the energy shortage has become increasingly prominent. Two-dimensional (2D) materials exhibit superior physical and chemical properties compared to their conventional counterparts, hence demonstrating considerable advantages in the water-splitting photocatalyst application. Based on first principle calculations, in this work, monolayered ZnO and ZrXY (X, Y = Br, Cl and F) are combined to form vdW heterostructures and investigate their structural, optical and electronic properties for evaluating their ability to split water photocatalytically. Based on our calculations by two different models (model I and II), ZnO/ZrXY vdW heterostructures exhibit indirect band gaps with a type II band alignment, which benefits the effective spatial separation of photogenerated charge carriers. Bader charge, Charge density difference, and Planner-averaged electrostatic potential analysis suggest that photogenerated charges flow from ZrXY to the ZnO layer are effected by the dipole interface, which prevents the recombination of photogenerated charge carrier and promotes their separation and transfer. Moreover, calculations for optical properties in relation to the dielectric constant's imaginary part indicate that all primary excitation peaks are located in the visible light region, and a red-shift is also observed in ZnO/ZrXY vdW heterostructures. In addition, the band edges of ZnO/ZrXY vdW heterostructures span water redox potentials, which satisfy the requirement of overall photocatalytic water splitting. • We construct various vdW heterostructures by combining Janus ZnO and ZrXY (X, Y = Br, Cl and F) monolayers. • Two different stacking models due to the alternative position of chalcogen atoms in ZXY monolayers are designed. • ZnO/ZrXY (X, Y = Br, Cl and F) vdW heterostructures are indirect band gap semiconductors with type II band alignment. • Bader charge analysis, calculated charge density difference and also electrostatic potential confirm the charge transfer in these vdWH. • Photocatalytic response suggests that ZnO/ZrXY (X, Y = Br, Cl and F) can split water into O 2 / H 2 O and H + / H 2. [ABSTRACT FROM AUTHOR] more...

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The structure–performance mechanism provides new insights into performance modification and materials discovery. Herein, the electronic structure, Raman vibration, chemical bond factors and enhanced microwave dielectric properties of Zn 0.5 Zr 0.5 NbO 4 ceramics through oxygen-assisted reaction sintering were investigated by Raman spectroscopy, first-principle calculations, and complex P–V-L theory. Pure-phase Zn 0.5 Zr 0.5 NbO 4 ceramics were synthesized under oxygen-assisted reaction sintering, confirmed by XRD refinement and Raman analysis. Systematic vibration analysis was first introduced to provide complete mode assignments and Raman shift. Optimized microstructure with full density was obtained through morphology and EDS analysis. First-principle calculations indicated that the d orbit exerts the main contribution to Fermi energy with energy gap of 3.51 eV and Nb–O bonds may possess strong vibration, exhibiting a remarkable effect on dielectric loss. P–V-L results showed that Nb–O bonds have a significant influence on the dielectric constant and Q×f value while the Zn–O bonds dominate the τ f value. In addition, high-performance Zn 0.5 Zr 0.5 NbO 4 ceramics were fabricated through oxygen-assisted reaction sintering at 1250 °C, with ε r = 28.4, Q×f = 79,800 GHz, and τ f = −47.7 ppm/°C, exhibiting tremendous superiorities for commercial production. [ABSTRACT FROM AUTHOR] more...

A casting Mg–3Gd–0.6Zr alloy was designed to evaluate the effect of cuboid-shaped phase on its mechanical properties. The morphology of cuboid-shaped phase was correlated with the directional covalent bonding between Gd atoms and H atoms along <100 > directions. The cuboid-shaped phase can be eliminated by a designed annealing treatment, without grain coarsening simultaneously. The ductility of as-cast alloy is about 20% higher than that of the annealed one. The improvement of ductility was caused by cuboid-shaped phase in three aspects: first-principle calculations, hydrogen embrittlement and crystal imperfections. [ABSTRACT FROM AUTHOR] more...

Despite reports of 2D hexagon‐free carbon allotrope anode materials for Li‐ion batteries (LIBs), rate performance enhancement and the practical application of these materials are still major challenges. Here, a novel 2D hexagon‐free carbon allotrope C358X with a unique combination of triangular, pentagonal, octagonal, and decagonal rings is predicted to be a high‐performance anode material in LIBs. The special hexagon‐free configuration enables C358X to introduce many serviceable local strain regions and electron‐deficient regions on the surface. The formation of these regions is very important for enhancing the rate performance of C358X as an anode material for LIBs. C358X has rich adsorption active sites for lithium ions, a lower lithium‐ion diffusion energy barrier of 0.29 eV, a lower average open circuit voltage of 0.31 V, and a high theoretical capacity of 1116.7 mA h g−1. This work may facilitate the utilization of 2D carbon‐based anode materials for cost‐effective LIBs. [ABSTRACT FROM AUTHOR] more...

Two‐dimensional (2D) transition metal carbides and nitrides known as MXenes are a new family of 2D materials. Most of the previous studies mainly focus on the metallic MXenes, there are few studies on semiconducting MXenes. Based on first‐principles calculations within density functional theory, 480 ground‐state structures including 444 metals and 36 semiconductors have been screened from 2256 MXenes using the energy and electronic parameters as the descriptors. The bandgap, carrier mobility, and optical absorption of the semiconducting MXenes show a strong dependence on the surface functional groups. By tuning the surface functional groups, the bandgaps can be changed from 0.2 to 3 eV. Moreover, the semiconducting MXenes exhibit high carrier mobilities up to 104 cm2 v−1s−1 and high optical absorption coefficients (>105 cm−1). This work demonstrates that Sc‐based and Y‐based MXenes present high stability, moderate bandgaps, ultrahigh carrier mobility, and high optical absorption, which make them large potential for electronics, optoelectronics, and photocatalysts. [ABSTRACT FROM AUTHOR] more...

It is well known that element substitution is vital to an improvement of hydrogen storage capacity degraded by hydrogen-induced disproportionation of zirconium-cobalt (ZrCo) alloy. Contrary to other studies, this work is devoted to investigating the hydrogen desorption behavior of Zr 1- x Nb x Co 1- y Cr y H 3 (x = 0–0.25 and y = 0–0.125) systems formed by Nb substitution and Nb/Cr co-substitution in the ZrCoH 3 crystal using the first-principles calculations based on the density functional theory. Firstly, the preferred positions of Nb and Nb/Cr substitutions are determined through the minimum total energy. Lattice constants and the density of states are employed to characterize the bonding behavior between atoms. The thermodynamic properties of Zr 1- x Nb x Co 1- y Cr y H 3 are also assessed by the enthalpy of formation and equilibrium hydrogen pressure. It is shown that both the thermodynamic stability and dehydrogenation temperature of ZrCoH 3 decrease by increasing the Nb content, which is attributed to the fact that the Zr–H and Co–H binding capabilities are weakened by the presence of Nb. In addition, there are weaker thermal stability, lower dehydrogenation temperature, smaller volume of 8e site, and comparable volume of the hydride after ZrCoH 3 is co-substituted by Nb and Cr, thereby promoting the hydrogen release and enhancing the anti-disproportionation performance. Clearly, both Nb doping and Nb/Cr co-doping possess a positive effect on the hydrogen desorption ability of ZrCoH 3. More importantly, it is discoverable that compared to other substitution systems, the dehydrogenation temperature is the least for the Zr 0.75 Nb 0.25 Co 0.875 Cr 0.125 hydride, highlighting that Nb and Cr co-substitution is more beneficial to improving the dehydrogenation performance of ZrCo-based alloy. [Display omitted] • Effects of Nb doping and Nb/Cr co-doping on dehydrogenation properties of ZrCo–H systems are examined. • The dehydrogenation temperature is found to decrease by the Nb/Cr substitution. • The Zr–H and Co–H binding capabilities are weakened by the presence of Nb. • Co-substitution plays a more positive role on the thermodynamic performance. [ABSTRACT FROM AUTHOR] more...

In general, the transition elements, including Hafnium (Hf), have become the focus of researchers′ attention, as when they combine with chalcogens and halides, they turn into semiconductors with distinct energy gaps. Moreover, chalcogens and halides are desirable in scientific research when forming layers or membranes. The Janus monolayer is unique two‐faced material composed of two different chemical species on opposite sides of a single layer. Herein, we use first‐principles simulations to thoroughly investigate the electrical and optical properties of this material. Our calculations reveal that the Bromochlorohafnium (HfClBr) Janus monolayer is an indirect semiconductor at equilibrium, with an energy gap of 0.928 eV and changing from 0.532 eV to 1.233 eV after applying the biaxial strain, as determined by the Perdew‐Burke‐Ernzerhof (PBE) method. The results indicate that the Janus HfClBr monolayer has a competitive advantage over other materials for use in solar cells and energy storage devices due to its unique optical and electrical characteristics. Furthermore, our analysis showed that the optical and electrical characteristics of the Janus HfClBr monolayer are significantly impacted by biaxial strain, with the ability to absorb light in both the visible and ultraviolet spectral regions. Additionally, the first optical gap of the Janus HfClBr monolayer is found to be shiftable under the biaxial strain, suggesting potential applications in nano‐electronics, particularly in the field of solar cells. [ABSTRACT FROM AUTHOR] more...

In recent years, supercapacitors have been widely used in the fields of energy, transportation, and industry. Among them, electrical double-layer capacitors (EDLCs) have attracted attention because of their dramatically high power density. With the rapid development of computational methods, theoretical studies on the physical and chemical properties of electrode materials have provided important support for the preparation of EDLCs with higher performance. Besides the widely studied double-layer capacitance (CD), quantum capacitance (CQ), which has long been ignored, is another important factor to improve the total capacitance (CT) of an electrode. In this paper, we survey the recent theoretical progress on the CQ of two-dimensional (2D) electrode materials in EDLCs and classify the electrode materials mainly into graphene-like 2D main group elements and compounds, transition metal carbides/nitrides (MXenes), and transition metal dichalcogenides (TMDs). In addition, we summarize the influence of different modification routes (including doping, metal-adsorption, vacancy, and surface functionalization) on the CQ characteristics in the voltage range of ±0.6 V. Finally, we discuss the current difficulties in the theoretical study of supercapacitor electrode materials and provide our outlook on the future development of EDLCs in the field of energy storage. [ABSTRACT FROM AUTHOR] more...

Cu6Sn5-xAg alloys (x = 0, 3, 6; %, mass fraction) were synthesized using Ag as a dopant through a high-temperature melting technique. The microstructure of the alloy was analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), and other equipment, while the hardness of the alloy was measured to investigate the impact of Ag addition on the structure and microstructure of the Cu6Sn5 intermetallic compound. This study explored the influence of varying Ag contents on the properties of Cu6Sn5 intermetallic compounds, with calculations based on first principles revealing the mechanical properties and density of states of η′-Cu6Sn5 and its Ag-doped systems. The results indicated that Cu6Sn5-xAg alloys predominantly existed in three distinct forms, all exhibiting large masses without any impurities or precipitates. First-principle calculations demonstrated that Ag substitution in certain sites suppressed the anisotropy of the Young’s modulus of Cu6Sn5, particularly in the Cu1, Cu3, Sn1, and Sn3 positions, while the effect was less significant at the Cu2, Cu4, and Sn2 sites. The introduction of Ag through doping enhanced the covalent bonding within the η′-Cu6Sn5 structure, promoting the formation of a stable (Cu, Ag)6Sn5 structure. more...

Single-phase concentrated solid-solution alloys (CSAs) have exhibited excellent mechanical and radiation tolerance properties, making them potential candidate materials for nuclear applications. These excellent properties are closely related to dislocation movements, which depend on the stacking fault energies (SFEs). In CSAs, SFEs show large fluctuations due to variations in the local atomic environments in the vicinity of the stacking faults. In this work, first-principle calculations were performed to investigate the origin of the fluctuations in the SFEs of the widely studied CSA, NiCoCr, which show a very wide distribution from about −200 mJ/m2 to 60 mJ/m2. Compared to the common understanding that only atoms in close proximity to the stacking fault influence the SFEs in pure metals and dilute alloys, charge redistribution can be observed in several nearby planes of the stacking fault in NiCoCr, indicating that atoms several atomic layers away from stacking fault also contribute to the SFEs. Our analysis shows that Cr plays a major role in the large fluctuation in the SFEs of NiCoCr based on both electronic and magnetic responses. The flexible electronic structure of Cr facilitates easier charge transfer with Cr in several nearby atomic planes near the stacking fault, leading to significant changes in the d-electron number, orbital occupation number, and magnetic moments of Cr. more...

We present a theoretical investigation on the wide-band-gap semiconductor WO 3 in its room-temperature monoclinic structure. We carried out density functional theory and GGA-1/2 calculations on the bulk phase and the most stable (001) surface of the material, either in their stoichiometric form or in the presence of oxygen vacancies at various concentrations. Concerning the bulk phase, our results show how the inclusion of these defects correctly reproduces the intrinsic n-type doping of the material. The system is also found to be magnetic at reasonably high defect concentrations. As for the surface, the presence of vacancies gives rise to a magnetic behavior, whose features depend on the relative arrangement of native point defects. Oxygen vacancies are also responsible for additional tungsten oxidation states in both bulk and surface. Based on these results, we provide a rationale for the interpretation of most experimental data of this material and, possibly, other widespread transition metal oxides with similar properties and applications such as ReO 3, TiO 2, and SnO 2. more...

Researchers are interested in magnetic topological materials because they can integrate magnetic and topological properties. Using the first-principles calculations, we identify the P6322-type SrNiIO6 as a dynamically stable half-metallic candidate with a completely spin-polarized Weyl complex formed by two hourglass charge-3 and six charge-1 Weyl points. Furthermore, distinct surface arcs linked the projections of two spin-polarized charge-3 Weyl points and six spin-polarized charge-1 Weyl points, resulting in a fully spin-polarized sextuple-helicoid surface arc mode on the (001) surface of P6322-type SrNiIO6. P6322-type SrNiIO6 with fully spin-polarized charge-3 and charge-1 Weyl points and a fully spin-polarized sextuple-helicoid surface arc mode is, without a doubt, a promising candidate for applications in spintronic and topological physics. more...

Introduction: Ferroelectric substances, characterized by inherent spontaneous polarization, can boost photocatalytic efficiency by facilitating the separation of photogenerated carriers. However, conventional photocatalysts with perovskite-class ferroelectricity are generally constrained by their 3D arrangement, leading to less accessible active sites for catalysis and a smaller specific surface area compared to a 2D layout.Methods: In my research, I developed a 2D ferroelectric heterostructure consisting of C2N/α-In2Se3. I performed first-principle calculations on the 2D C2N/α-In2Se3 heterostructure, specifically varying the out-of-plane ferroelectric polarization directions. I primarily focused on C2N/α-In2Se3 (I) and C2N/α-In2Se3 (II) heterostructures.Results: My findings revealed that reversing the ferroelectric polarization of the 2D α-In2Se3 layer in the heterostructures led to a transition from the conventional type-II [C2N/α-In2Se3 (I)] to an S-scheme [C2N/α-In2Se3 (II)]. The S-scheme heterostructure [C2N/α-In2Se3 (II)] demonstrated a high optical absorption rate of 17% in visible light, marking it as a promising photocatalytic material.Discussion: This research underscores the significance of ferroelectric polarization in facilitating charge transfer within heterogeneous structures. It provides a theoretical perspective for developing enhanced S-scheme photocatalysts, highlighting the potential of 2D ferroelectric heterostructures in photocatalytic applications. more...

The adsorption behavior of atomic oxygen and molecular O2 on the 3C–SiC(1 1 0) surface is investigated by first‐principles calculations. The atomic O prefers to be adsorbed at the C top site (C–O) with adsorption energy of −1.95 eV after zero‐point energy correction, followed by the C–O–Si bridge site, Si–O–Si bridge site, and the Si top site (Si–O) with adsorption energies of −1.46, −1.36, and −1.13 eV, respectively. The molecular O2 separately trapped by the second nearest neighboring C and Si atoms (C–O–O–Si, M4 type) is the most stable configuration with the adsorption energy of −2.46 eV, which is followed by the Si–O–O–Si (M5 type), C–O–O–Si (M3 type), O–Si–O (M2 type), and Si–O=O (M1 type) configurations with the adsorption energies of −2.24, −1.87, −1.07, and −0.75 eV, respectively. All these molecular O2 adsorption configurations exhibit high tendency to dissociate with the dissociation barriers range of 0.09–0.19 eV. The adsorbed atomic O seems to be easily trapped at the C–O site due to the extremely low diffusion barrier. In addition, the infrared spectra of all the atomic O and molecular O2 adsorption configurations are predicted and compared with available experimental observations. [ABSTRACT FROM AUTHOR] more...

Graphene has been identified as a promising catalyst for improving the dehydrogenation performance of MgH 2 , however, an in-depth understanding of the mechanism is still lacking. Therefore, we constructed MgH 2 /graphene heterojunctions to deeply investigate the effect of graphene on the dehydrogenation performance of MgH 2 , and introduced noble metals (Pd and Pt) for further dehydrogenation performance enhancement. Our findings showed that graphene experienced difficulty in directly affecting the interaction on the MgH 2 (110) surface, and the enhanced dehydrogenation of MgH 2 /graphene heterojunction resulted from the weakened Mg–H interaction via the special charge distribution in the interaction region and narrowing of the band gap due to graphene introduction. In addition, Pd and Pt intercalation enhanced the structural stability and comprehensively improved the dehydrogenation performance indicators. In particular, the altered interfacial properties of intercalated heterojunctions induced a two-step dehydrogenation reaction, resulting in Pd- and Pt-intercalated MgH 2 /graphene heterojunctions with a superior dehydrogenation performance. [Display omitted] • The mechanism of graphene on MgH 2 is investigated in depth. • Noble metal intercalation stabilizes MgH 2 /graphene heterojunctions. • Noble metal intercalation comprehensively improves the dehydrogenation performance. • Improved dehydrogenation performance due to synergy of multiple effects. [ABSTRACT FROM AUTHOR] more...

Point defect-based single-photon emitters (SPEs) in GaN have aroused a great deal of interest due to their room-temperature operation, narrow line width and high emission rate. The room-temperature SPEs at the telecommunication bands have also been realized recently by localized defects in GaN in experiments, which are highly desired for the practical applications of SPEs in quantum communication with fiber compatibility. However, the origin and underlying mechanism of the SPEs remain unclear to date. Herein, our first-principle calculations predict and identify an intrinsic point defect NGa in GaN that owns a zero-phonon line (ZPL) at telecommunication windows. By tuning the triaxial compressive strain of the crystal structure, the ZPL of NGa can be modulated from 0.849 eV to 0.984 eV, covering the fiber telecommunication windows from the O band to the E band. Besides the ZPL, the formation energy, band structure, transition process and lifetime of the SPEs under different strains are investigated systematically. Our work gives insight into the emission mechanism of the defect SPEs in GaN and also provides effective guidance for achieving wavelength-tunable SPEs working in fiber telecommunication windows. [ABSTRACT FROM AUTHOR] more...

Two-dimensional van der Waals (vdW) heterostructures are potential candidates for clean energy conversion materials to address the global energy crisis and environmental issues. In this work, we have comprehensively studied the geometrical, electronic, and optical properties of M2CO2/MoX2 (M = Hf, Zr; X = S, Se, Te) vdW heterostructures, as well as their applications in the fields of photocatalytic and photovoltaic using density functional theory calculations. The lattice dynamic and thermal stabilities of designed M2CO2/MoX2 heterostructures are confirmed. Interestingly, all the M2CO2/MoX2 heterostructures exhibit intrinsic type-II band structure features, which effectively inhibit the electron-hole pair recombination and enhance the photocatalytic performance. Furthermore, the internal built-in electric field and high anisotropic carrier mobility can separate the photo-generated carriers efficiently. It is noted that M2CO2/MoX2 heterostructures exhibit suitable band gaps in comparison to the M2CO2 and MoX2 monolayers, which enhance the optical-harvesting abilities in the visible and ultraviolet light zones. Zr2CO2/MoSe2 and Hf2CO2/MoSe2 heterostructures possess suitable band edge positions to provide the competent driving force for water splitting as photocatalysts. In addition, Hf2CO2/MoS2 and Zr2CO2/MoS2 heterostructures deliver a power conversion efficiency of 19.75% and 17.13% for solar cell applications, respectively. These results pave the way for exploring efficient MXenes/TMDCs vdW heterostructures as photocatalytic and photovoltaic materials. [ABSTRACT FROM AUTHOR] more...

Electrocatalysts play key roles in improving the performance of lithium sulfur (Li‐S) batteries. Here, the electrocatalytic activity of different CoSe2 surfaces for the polysulfide redox reactions in Li‐S batteries, by means of first‐principle calculations is considered. The authors demonstrate that there are obvious differences in surface energy (0.7–2.34 J m−2), adsorption energy for lithium polysulfides (LiPSs) (1.2–3.5 eV), Gibbs free energy of sulfur reduction reaction (SRR) (0.37–1.16 eV), and Li2S decomposition barrier (0.15–0.94 eV) among different CoSe2 surfaces, and thus lead to the different electrocatalytic activity for different CoSe2 surface. The stoichiometric CoSe2 surface with high surface energy, such as the (001) surface, tends to have stronger adsorption energy and larger SRR Gibbs free energy for LiPSs. The surface electron states are mainly dominated by p–d hybridization orbitals and the p‐band center is vital for the surface electrocatalytic properties. Such surface‐dependent mechanism may shed light on the design of sulfur host materials for high‐performance Li‐S batteries. [ABSTRACT FROM AUTHOR] more...

The aim of present paper was to improve the anticorrosive properties of tantalum. Herein, the formation of tantalum oxide film via an argon ion etching pretreatment step and anodic oxidation is reported. The surface morphologies of etched tantalum investigated using scanning electron microscopy. The composition and corrosion resistance of the tantalum oxide film was characterized using X-ray photoelectron spectroscopy and an electrochemical workstation, respectively. The effects of vacancy defects and O atom adsorption on the on Ta (110), (200) and (211) surfaces have been investigated based on first-principles calculations to simulate the etched surface. The experimental results showed that the etched tantalum had a relatively clean surface with fine pores, which promoted the formation of an anodization film to 131.53 nm. The corrosion resistance of tantalum was obviously improved by etching followed by anodization, and the highest corrosion potential of 0.133 V and relatively low corrosion current density of 1.016 μA cm–2 were observed. Furthermore, first principle calculations revealed that vacancy defects increased the activity of the tantalum surface and enhanced the adsorption of oxygen, thereby promoting the formation of oxide film. Among all these defective surfaces, O atom adsorption on the (110) surface exhibited relatively a high adsorption energy of −519.66 kJ/mol and charge transfer of −1.310 e, followed by O atoms on the (200) and (211) surfaces showing an enhanced adsorption energy of −487.33 and −494.27 kJ/mol, and charge transfer of 1.255 and 1.194 |e |, respectively. This work demonstrated an effective argon ion etching pretreatment step to promote the formation of oxide film, which improved the corrosion behavior of tantalum. more...

This study utilizes DFT calculations to assess the effectiveness of Ti-TM (TM = W, Ru) alloys in obstructing copper diffusion, a pivotal factor for semiconductor device reliability. The calculated diffusion barriers for Cu in TiRu and Ti 4 W 12 alloys are found to be 0.48 eV and 0.34 eV, respectively, significantly surpassing the 0.25 eV barrier for Cu diffusion in Si. This comparative analysis highlights the enhanced diffusion resistance of these alloys, with TiRu displaying a barrier nearly twice that of Si. An in-depth examination of the electronic structure and microstructural attributes of the alloys indicates that atomic interactions at the Cu/Ti-TM interface play a crucial role in hindering Cu diffusion. The local density of states, charge density differences, and electron localization functions were scrutinized to clarify the nature of these interactions. The research uncovers that the combined action of Ru, W, Cu, and Ti atoms leads to a synergistic strengthening of the diffusion barrier, implying a robust interatomic repulsion that restricts Cu migration. The findings contribute to a deeper fundamental understanding of Cu diffusion mechanisms in Ti-TM alloys and offer a scientific basis for the judicious selection of materials for diffusion barrier layers. The study supports the further exploration and potential application of TiRu and Ti 4 W 12 alloys in the semiconductor industry. [ABSTRACT FROM AUTHOR] more...

We conducted a large set of ab initio density functional theory computations to model a variety of hammer-terminated graphene nanoflakes—finite counterparts of armchair graphene nanoribbons. We focused on the relationships among the length and width of the nanoflakes, the stoichiometry and the conformation of the hydrogen saturation of the caps, and the resulting electronic structure. The energetics and the thermodynamic stability of the nanoflakes were investigated as well. Based on this study, we provide a recipe for determining the most stable saturation of the dangling bonds at the caps, which is generally disregarded in theoretical studies, and we prove that this step is crucial for a reliable description of the electronic structure of these systems. Data analysis proved that flakes far from the most stable C–H pattern exhibited electronic properties that were typical of an unsaturated bonding structure. Based on thermodynamics, we also proved that, for any given flake, there was a well-defined hydrogen content and a conformation of H atoms at the caps, which were favored across a wide range of environmental conditions. more...

Van der Waals heterostructures with tunable band alignments are the promising candidates for the fabrication of high-performance multifunctional nano-optoelectronic devices. In this work, we investigate the band alignments and optical properties of two-dimensional MoSSe/C _3 N _4 and C _3 N _4 /MoSSe heterostructures using first-principles methods. The two most stable MoSSe/C _3 N _4 (C _3 N _4 -Se) and C _3 N _4 /MoSSe (C _3 N _4 -S) heterostructures (labeled as A2 and B2, respectively) out of the twelve possible heterostructures are selected for the corresponding properties research. It is found that the A2 exhibits type-I band alignment, making it suitable for light-emitting applications, while the B2 exhibits typical type-II band alignment, which is favorable for carrier separation. Moreover, the band alignment of the two heterostructures can be modulated by the external electric fields, that is, band alignment transition between type-I and type-II. In addition, the main absorption peaks of both heterostructures in their pristine state are located in the visible light region (approximately 2.9 eV), and the peak values of the absorption peaks can be enhanced (weaken) via applying positive (negative) external electric fields. Our findings demonstrate that the C _3 N _4 /C _3 N _4 and C _3 N _4 /MoSSe heterostructures hold significant potential for applications in multifunctional electronic devices including light-emitting, carrier separation, optical modulators, etc. more...

In this paper, the defect formation energies, the nature of chemical bonding, and electronic structures of Mn- and Mg-doped SnTe alloys were determined by first-principles calculations. The effects of substitutional atoms on thermoelectric parameters are analyzed by solving the Boltzmann equation. The solution solubility of Mg in SnTe alloy is higher than that of Mn, and the lattice distortion caused by Mn substituting Sn sites is more severe. In addition, the resonant level of Sn1-xMnxTe alloys possesses a flat trend of the valance band maximum, which improves the effective carrier mass and Seebeck coefficient. The Mg-doped alloys exhibit higher carrier mobility and electrical conductivity. The maximum value of the power factor is 5.78 mWm−1K−2 for the Sn0.97Mn0.03Te alloy. Corresponding directionally-solidified samples with the same composition were also prepared. The Sn0.97Mn0.03Te sample also achieves the highest ZT value of 1.28. These results provide theoretical reference for optimizing the thermoelectric performance of SnTe alloys by substituting atoms. more...