Indirect Band Gap Semiconductor Research Articles

Geometrical, elastic, electronic, phonon, and optical properties of Na3AgO2 from first-principles calculation

In this paper, the geometrical, elastic, electronic, phonon, and optical properties of Na3AgO2 have been systematically studied by first-principles calculation. The results show that Na3AgO2 is mechanically stable and has small compressibility. Na3AgO2 is an indirect band-gap semiconductor with weak interatomic interaction. The bandgap calculated by HSE06 is 2.314 eV, and that calculated by GGA is 1.261 eV. For Na3AgO2, in the valence band near the Fermi level, the curve peaks of TDOS at −2.11 eV and −0.885 eV are primarily composed of O 2p states, which hybridize the 4 d and 4p states of Ag. The conduction band mainly consists of the 4p, 4 d, and 5s states of Ag, while hybridizing a few 2p states of O and a few 2p and 3s states of Na. As can be seen from the phonon dispersion spectrum there is no negative phonon frequency in the whole Brillouin region, indicating the structure is stable. Mulliken bond population of Na3AgO2 shows that O–Ag bonds have strong covalency, O–Na bonds have strong ionic properties, Na–Na bonds and Na–Ag bonds are antibonding. Na3AgO2 has a small reflectivity and a small absorption coefficient in the direction of (100) and (010) and has good transparency. The transparency of blue-violet light in the (001) direction is not as good as that of low-energy visible light. The obtained results lead to the conclusion that Na3AgO2 is a promising p-type transparent conducting material and is expected to be applied in practice.

Physical properties of novel double perovskite oxides Ba2XSbO6(X = P, As) by first-principle calculations

In this article, the structural, mechanical, electronic, optical, thermal, and thermodynamic properties of Ba2XSbO6 (X=P, As) double perovskite oxides were investigated by using first-principles calculations. The results show that the Goldsmith’s tolerance factor and octahedral factor of the two perovskites are in a stable range, the binding energy and formation energy are negative, and the elastic constants meet the Born-Huang stability criterion. These results suggest the stability of the two perovskite oxides. The mechanical property study indicates that Ba2XSbO6 (X=P, As) exhibits high bulk modulus and shear modulus. Poisson’s ratio (ν) and the elastic anisotropy index (A) suggest that they are anisotropic ductile materials. The electronic properties show that Ba2PSbO6 and Ba2AsSbO6 are indirect bandgap semiconductors with bandgap values of 2.130 eV and 1.596 eV, respectively. The optical properties show that Ba2XSbO6 (X=P, As) has excellent light absorption capacity in the range of 2.5–30 eV. Specifically, Ba2AsSbO6 has a higher absorption capacity for visible light compared to Ba2PSbO6. Thermodynamic properties show that the Debye temperature of the two perovskites is higher than 420 K, the melting points is higher than 1700 K, the minimum lattice thermal conductivities is close to 1, and the specific heat reaches the Dulong-Petit limit at about 700 K. This study shows that the double perovskite oxide Ba2XSbO6 (X=P, As) has important potential in the field of thermoelectricity and optoelectronics.

Effect of biaxial strain on the electronic structure and optical properties of two-dimensional Bi2Te2S

In this work, the effects of biaxial strain on the electronic structure and optical properties of monolayer Bi2Te2S are studied by the first-principles methods. The calculated results show that the monolayer Bi2Te2S is an indirect band gap semiconductor with a band gap of 1.0 eV. The absence of imaginary frequency in the phonon spectrum indicates that the structure can exist stably. With the increase of tensile strain, the band gap value decreases approximately quasi-linearly. When 10 % tensile strain is applied, the band gap value is reduced to 0 eV, achieving the transition from an indirect bandgap semiconductor to a direct bandgap semiconductor. With the increase of compressive strain, the band gap value increases first and then decreases, and the band gap value reaches a maximum of 1.28 eV at −4 % strain. Combined with the density of states analysis, the reason for this change in the band structure is that the contribution of Bi 6p, Te 5p and S 3p state electrons to the conduction band and valence band changes under different strains. The effect of strain on the optical properties shows that when different strains are applied, the monolayer Bi2Te2S has a high absorption coefficient in the entire visible region. The single-layer Bi2Te2S material has a smaller refractive index under tensile strain. The static dielectric function value increases with the increase of tensile strain, and the peak value of the dielectric function decreases and moves to the low energy direction. This indicates that the tensile strain will enhance the migration of photogenerated electron-hole pairs, which is beneficial to improving the utilization of light. This work will provide a theoretical reference for the subsequent study of the electronic and optical properties of monolayer Bi2Te2S.

A first-principles prediction of novel Janus ZrGeZ3H (Z = N, P, and As) monolayers: Raman active modes, piezoelectric responses, electronic properties, and carrier mobility.

In this article, an attempt is made to explore new materials for applications in piezoelectric and electronic devices. Based on density functional theory calculation, we construct three Janus ZrGeZ3H (Z = N, P, and As) monolayers and study their stability, piezoelectricity, Raman response, and carrier mobility. The results from phonon dispersion spectra, ab initio molecular dynamics simulation, and elastic coefficients confirm the structural, thermal, and mechanical stability of these proposed structures. The ZrGeZ3H monolayers are indirect band gap semiconductors with favourable band gap energy of 1.15 and 1.00 eV for the ZrGeP3H and ZrGeAs3H, respectively, from Heyd-Scuseria-Ernzerhof functional method. It is found that the Janus ZrGeZ3H monolayers possess both in-plane and out-of-plane piezoelectric coefficients, revealing that they are potential piezoelectric candidates. In addition, the carrier mobilities of electrons and holes along transport directions are anisotropic. Notably, the ZrGeP3H and ZrGeAs3H monolayers have high electron mobility of 3639.20 and 3408.37 cm2 V-1 s-1, respectively. Our findings suggest the potential application of the Janus ZrGeZ3H monolayers in the piezoelectric and electronic fields.

Unveiling the electronic, optical, thermoelectric, and magnetic properties of novel Ba2GdMO6 (M = Pa, Ta) via DFT calculation

The optoelectronic, thermoelectric, and magnetic properties of novel Ba2GdMO6 (M = Pa, Ta) double perovskites have been computed with the spin-polarized density functional investigation. The calculations are performed using the FP-LAPW method in Wein2K code, by employing the GGA + U approximations. The band structures and density of states analysis show that Ba2GdPaO6 is an indirect band gap semiconductor with band gap values of 3.0 eV and 3.1 eV in the up and down spin channels, respectively. The Ba2GdTaO6 is also predicted as a semiconducting material with a direct band gap of 2.9 eV and 3.0 eV in up and down spin channels. The optical characteristics of the materials, such as the dielectric constants, absorption coefficient, reflectivity, loss function, and refractive index are computed. The optical results reflect that the materials are excellent choices for high-energy absorbent. The Seebeck coefficient increases beyond the temperature of 300 K for Ba2GdPaO6 and 400 K for Ba2GdTaO6. The increase in the Seebeck coefficient values suggests that these materials are p-type semiconducting. The ferromagnetic nature of the materials has been confirmed by predicting the ferromagnetic phase to be the most stable state. The total magnetic moments of the materials are found equal to 7 µB.

2D Janus TeMoZAZ’ (A = Si,Ge; Z,Z’ = N, P, As; Z ≠ Z'): First‐Principles Insight into the Electronics, and Piezoelectric Properties

AbstractJanus materials possess a diverse array of properties resulting from the breaking of mirror and inversion symmetries, holding significant potential for nanodevices. This study explores the novel TeMoZAZ' (A = Si,Ge; Z,Z' = N, P, As; Z ≠ Z') monolayers derived from the MoA2Z4 monolayer. Utilizing first‐principles calculations, the stability, electronic, transport, mechanical, and piezoelectric properties of the TeMoZAZ' monolayers are investigated. Among the 12 investigated structures, only five‐ TeMoNSiP, TeMoNSiAs, TeMoPSiAs, TeMoAsSiP and TeMoAsGeP monolayers‐ are found to be stable. The electronic properties analysis reveals metallic behavior in the TeMoNSiAs monolayer, while the remaining structures exhibit indirect or direct band gap semiconductor properties. Futher examination of the semiconducting monolayers indentifies the TeMoAsSiP monolayer with notably high hole carrier mobility along the y‐direction, reaching up to 3622.33 cm2 s−1 V−1. Moreover, investigation into the piezoelectric properties of these four semiconductor structures suggests their suitability for diverse applications in piezoelectric devices. Additionally, the effects of biaxial strain on the electronic and piezoelectric properties of these four semiconductor structures are explored. These findings propose a novel approach for designing 2D Janus materials, expanding the repertoire of 2D MA2Z4‐based Janus family and offering promising candidates for optoelectronic devices, wearable devices, and electromechanical systems.

Large valley splitting induced by spin-orbit coupling effects in monolayer Hf3N2O2

Valleytronics is an emerging field of electronics that aims to utilize valley degrees of freedom in materials for information processing and storage. Nowadays, the valley splitting of 2D materials is not particularly large, therefore, the search for large valley splitting materials is very important for the development of valleytronics. This work theoretically predicts that MXene Hf3N2O2 is a 2D material with large valley splitting. It is an indirect bandgap semiconductor with a bandgap of 0.32 eV at the PBE level and increases to 0.55 eV at the HSE06 level. Since Hf3N2O2 breaks the symmetry of spatial inversion, when we consider spin–orbit coupling (SOC), there is a valley splitting at K/K′ of the valence band with a valley splitting value of 98.76 meV. The valley splitting value slightly decreases to 88.96 meV at the HSE06 level. In addition, The phonon spectrum and elastic constants indicate that it is both dynamically and mechanically stable. According to the maximum localization of the Wannier function, it is obtained that the Berry curvature is not zero at K/K′. When a biaxial strain is applied, Hf3N2O2 transitions from metal to semiconductor. With increasing biaxial strain, the valley splitting value increased from 70.13 meV to 109.11 meV. Our research shows that Hf3N2O2 is a promising material for valleytronics.

Comparative Study of the Mechanical, Electronic Structure, and Optical Properties of Cubic Lithium‐Based Perovskite LiMgX3 (X = Cl, Br, I) under Pressure Effects: First‐Principles Calculations

The mechanical, electronic structure, and optical properties of lithium‐based perovskite LiMgX3 (X = Cl, Br, I) are investigated for the first time at 0–20 GPa using density‐functional theory. The Born stability criteria reveal that the phase transition points of LiMgCl3, LiMgBr3, and LiMgI3 are 20.7, 20.9, and 23.4 GPa, respectively. At 0 GPa, studies on the electronic properties using the Heyd‐Scuseria‐Ernzerhof (HSE06) functional show that LiMgCl3 and LiMgBr3 are indirect bandgap insulators with values of 5.336 and 4.113 eV, whereas LiMgI3 is an indirect bandgap semiconductor with a value of 2.055 eV. In addition, the bandgap calculated using both the PBEsol and HSE06 functionals decreases with increasing pressure, and the bandgap trends with pressure are consistent. Both functionals are also used to study the optical properties of LiMgX3 compounds, which show that they have potential for use in vacuum ultraviolet and photovoltaic applications. The mechanical and optical characteristics of the materials are significantly enhanced under pressure.

Physical performances for six novel Si allotropes in hexagonal 15 and 18 stacking orders

Elevating visible light absorption and carrier transport capacity of diamond silicon is a terrifying challenge for improving photoelectric conversion efficiency. Here, six new crystals with similar stacking patterns but various arrangement orders to Si–I are predicated by the random approach combined with group and graph theories. Considering potential applications in the photovoltaic field, we have conducted a detailed study on the stability and physical properties of these structures by first-principles calculations. As a result, these new structures meet mechanical, dynamic, and thermodynamic stabilities, and they are all indirect band gap semiconductor. In particular, among these materials, the effective mass of the smallest hole is only 0.11m0, which is smaller than that of diamond silicon. This result indicates that these structures have better carrier transport capabilities than diamond. In addition, XRD patterns of these six structures were studied for shedding more light for developing these structures in the experiment.

Modulated bandgap and gas adsorption behavior on two-dimensional SrAl2S4 monolayer: Potential applications for photovoltaic and energy storage

The structure of a novel two-dimensional layered material SrAl2S4 monolayer has been proposed, and its kinetic and thermodynamic stability has been confirmed. Researches have shown that SrAl2S4 monolayer is a semiconductor material with a bandgap of 1.630 eV for PBE and 2.798 eV for HSE06 at the ground state. Under biaxial strain, SrAl2S4 monolayer can complete the transition from a direct bandgap semiconductor to an indirect bandgap semiconductor, and its bandgap can vary between 0.187 eV and 1.712 eV. In addition, We have considered the adsorption behavior of SrAl2S4 monolayer for hydrogen and oxygen molecules, and the results show that SrAl2S4 monolayer adsorbed H2 molecules remains a direct bandgap semiconductor, whereas SrAl2S4 monolayer adsorbed O2 molecules show indirect bandgap semiconductor properties. At the same time, the adsorption of O2 molecules causes a flat band near the Fermi level, which increases the electrical conductivity. The few charges transfer observed between the SrAl2S4 monolayer and gas molecules confirms that the adsorption process of gas molecules on SrAl2S4 monolayer is physical adsorption. The tunable bandgap characteristics and good adsorption behavior of hydrogen and oxygen exhibited by SrAl2S4 monolayer make it a promising candidate material in the fields of photovoltaics and energy storage.

Deep insights into the optoelectronic properties of AgCdF3-based perovskite solar cell using the combination of DFT and SCAPS-1D simulation

The main focus of this research is to explore the properties and photovoltaic application of AgCdF3, and hence, initially, the CASTEP software was used in this study to assess the structural, optical, mechanical, and electrical characteristics of the AgCdF3 perovskite absorber layer within the context of the density functional theory (DFT) method. AgCdF3 resulting from the structural research is confirmed to be chemically and thermodynamically stable by the estimated tolerance factor and formation enthalpy. According to the band structure analysis, AgCdF3 is an indirect band gap semiconductor with a band gap of 1.106 eV, where the electrons of Cd-4d and F-2s dominate the band edges of this semiconductor. Analysis of mechanical properties revealed that the AgCdF3 cubic perovskite has a stable structure and enhanced ductility, indicating superior machinability. After completing the DFT analysis, a one-dimensional solar cell capacitance simulator 1D (SCAPS-1D) was used with three popular electron transport layers (ETLs), including ZnO, PCBM, and C60, to examine the photovoltaic (PV) performance of various AgCdF3-based solar cell heterostructures. Based on simulation findings, the device design with ITO/ZnO/AgCdF3/CuI/Au showed the highest photoconversion efficiency compared to the other configurations. A detailed analysis was conducted for the aforementioned configurations to determine the impact of variations in the absorber and ETL thickness on PV performance. Moreover, the effects of the three designs were assessed in terms of function, generation and recombination rate, capacitance, operating temperature, series and shunt resistance, and Mott-Schottky. Thus, this comprehensive simulation with validation results demonstrated the true potential of AgCdF3 absorber with appropriate ETLs such as ZnO, PCBM, and C60; on the other hand, the CuI as hole transport layer (HTL), paving the way for promising studies to develop high-efficiency AgCdF3 PSCs for the photovoltaic industry.

First-principles study on the effect of torsional deformation on WSe2 as an anode material for calcium ion batteries.

In this paper, the effects of torsional deformation on the electronic properties of intrinsic WSe2 system and Ca-adsorbed WSe2 system were systematically studied by first-principles method. The results show that Ca can be stably adsorbed on the vacancy (H site) of WSe2 surface in all deformation systems, and the adsorption energy of the system without deformation is the highest. Intrinsic WSe2 is a semiconductor with a direct band gap of 1.53 eV. The torsional deformation makes WSe2 change from a direct band gap semiconductor to an indirect band gap semiconductor and finally to a metal property. The adsorption of Ca makes the conduction band of WSe2 move down and increases the number of peaks in the conduction band region. The new density of state peaks are mainly derived from the contribution of W-d, Se-p, and d orbitals of adsorbed atoms in each adsorption system. Mulliken charge analysis shows that Ca transfers most of the valence electrons to the substrate, and the torsional deformation changes the amount of transferred charge. The twist deformation reduces the diffusion barrier of Ca on WSe2 surface from 0.20 to 0.14 eV. The above results provide a basis for the improved application of WSe2 in ion batteries. In this study, all the first-principles calculations are based on Materials Studio 8.0 software package. The generalized gradient approximation (GGA) functional Perdew-Burke-Ernzerhof (PBE) is used for the electron exchange correlation interactions in all systems. The optimization algorithm uses Broyden-Fletcher-Goldfarb-Shanno (BFGS) to optimize the model structure and calculate the energy. The measured cutoff energy is optimized to 450 eV, and the radius of the vacuum layer in the Z-axis direction is 20 Å. The K-point of 7 × 7 × 1 is selected by Monkhorst-Pack method. The structural optimization criterion is selected, the convergence radius of the force is 0.01 eV/Å, and the displacement radius between atoms is within 0.001 Å distance. The energy convergence radius of each atom is less than 1.0 × 10-6 eV/atom.

Theoretical analysis of magnetic, optoelectronic, and thermoelectric properties of Cs2CuCrX6 (X = Cl and Br) double perovskites for spintronic and data storage devices

Spintronics is an emerging field that has the potential to replace conventional electronics due to their comparatively high speed, low power consumption, and infinite endurance. The phenomena of ferromagnetism with high spin polarization in double perovskites make them the desired materials for spintronics. In the present work, the structure of Cs2CuCrX6 (X = Cl and Br) and their magnetic and optoelectronic properties were studied by utilizing density functional theory (DFT). For the calculations of exchange-correlation potential, PBE-sol approximation was utilized while for the accurate measurement of electronic band structure and density of states (DOS), we employed mBJ potential. Both materials exhibit cubic structure and are thermodynamically stable as confirmed by volume optimization and negative formation energy respectively. Spin-based energy-volume optimization and values of exchange constants reveal the ferromagnetic nature of materials. It has been observed that 3-d states of Cr are responsible for ferromagnetism and have the major contribution to the net magnetic moment caused by exchange splitting. Furthermore, investigations of band structure and electronic density of states showed that both Cs2CuCrCl6 and Cs2CuCrBr6 were indirect bandgap (Eg) semiconductors with the Eg values of 1.2 eV and 0.33 eV respectively. The optical spectra of materials showed strong absorption in the ultraviolet region. Lastly, the transport and thermoelectric properties (TE) of materials were investigated in the range of temperature 300 K–800 K by using the BoltzTrap code. The transport parameter which included the electrical conductivity (σ/τ) and thermal conductivity (κe/τ) of the materials showed a decreasing trend with temperature whereas the Seebeck coefficient (S) and Power factor (P.F) showed an increasing trend for Cs2CuCrCl6 while decreases in case of Cs2CuCrBr6. Furthermore, a high figure of merit (ZT) with values of 0.75 and 0.64 was obtained for Cs2CuCrCl6 and Cs2CuCrBr6 respectively. The results of this work are encouraging and show the capabilities of the discussed materials in the fields of spintronics, thermoelectric, and optoelectronics.

Structural Preferences of Metal Chalcogenide based Nanothreads (MX; M=Au, Ag; X=S, Se): A Computational Study

AbstractThis study investigates the structural stability and electronic properties of α‐MX nanothreads and β‐MX nanosheets (M=Au, Ag; X=S, Se) using density functional theory. Our findings confirm the thermal and dynamic stability of all nanostructures, with β‐MX phases being more stable than α‐MX, albeit with minimal energy differences between the two phases. Electron localization analysis reveals predominantly ionic bonding character between M (Ag and Au) and X (S and Se) atoms. All the phase exhibits metallophilic interactions (Argentophilic and Aurophilic), with α‐MX nanothreads demonstrating a higher level of interaction compared to β‐MX nanosheets, attributed to the curvature inherent in the nanothreads. Significantly, these interactions are effectively small and do not compromise the relative stability between the α‐MX and β‐MX phases. Additionally, both α‐MX and β‐MX structures exhibit characteristics of indirect bandgap semiconductor behaviour. The band gap values do not significantly differ between α‐MX and β‐MX phases. Fermi analysis reveals that α‐MX phases exhibit small effective electron masses and large hole mobility along the uniaxial direction. These findings suggest promising prospects for α‐MX nanothreads as 1D semiconductors in nano‐electronics and nano‐optoelectronics applications in the future.

TaF4: A Novel Two-Dimensional Antiferromagnetic Material with a High Néel Temperature Investigated Using First-Principles Calculations.

The structural, electronic, and magnetic properties of a novel two-dimensional monolayer material, TaF4, are investigated using first-principles calculations. The dynamical and thermal stabilities of two-dimensional monolayer TaF4 were confirmed using its phonon dispersion spectrum and molecular dynamics calculations. The band structure obtained via the high-accuracy HSE06 (Heyd-Scuseria-Ernzerhof 2006) functional theory revealed that monolayer two-dimensional TaF4 is an indirect bandgap semiconductor with a bandgap width of 2.58 eV. By extracting the exchange interaction intensities and magnetocrystalline anisotropy energy in a J1-J2-J3-K Heisenberg model, it was found that two-dimensional monolayer TaF4 possesses a Néel-type antiferromagnetic ground state and has a relatively high Néel temperature (208 K) and strong magnetocrystalline anisotropy energy (2.06 meV). These results are verified via the magnon spectrum.

Optoelectronic properties of mechanically stable cubic Niobate compounds under hydrostatic pressure: A systematic DFT investigation

Perovskite oxides, particularly cubic Niobate compounds, have been studied for their potential application in the development of optoelectronic devices. The mechanical stability of these compounds has been verified by determining their elastic constants. Based on an analysis of their electronic band structures and densities of states, it has been found that both compounds exhibit non-magnetic behavior and possess properties typical of indirect bandgap semiconductors. The bandgap energies of the compounds are 1.524 eV and 1.392 eV, respectively. The optical properties of the compounds are analyzed under varying hydrostatic pressure conditions. Bandgap modulation results in a shift in absorption spectra from ultraviolet to visible wavelengths, rendering the materials appropriate for use in optoelectronic devices. Perovskites with (K,Rb)NbO3 exhibit potential as non-magnetic indirect bandgap semiconductors for the advancement of optoelectronic devices.

The structural, stability, electronic, optical and thermodynamic properties of Ba2AsXO6（X = V, Nb, Ta）double perovskite oxides: A First-Principles study

In this paper, the structural, mechanical, electronic, optical and thermodynamic properties of Ba2AsXO6 (X = V, Nb, Ta) double perovskite oxides have been studied based on the first principles of density functional theory. By calculating some parameters such as Goldsmith’s tolerance factor (tG), octahedral factor (µ), Bartel’s tolerance factor (τ), formation energy, binding energy and elastic constants, it is found that these double perovskite oxides have the potential for stable existence. In addition, Ba2AsXO6 (X = V, Nb, Ta) is an anisotropic material, in which Ba2AsVO6 is brittle, Ba2AsNbO6 and Ba2AsTaO6 are ductile. The electronic properties of the materials show that Ba2AsVO6 and Ba2AsNbO6 are indirect bandgap semiconductors with a band gap of 1.676 eV and 2.654 eV respectively, while Ba2AsTaO6 is direct bandgap semiconductor with a band gap of 3.252 eV. The optical properties revealed that these perovskites exhibit favorable far-ultraviolet light absorption characteristics. The thermodynamic properties show that the specific heat capacity of these double perovskite oxides reaches the Dulong-Petit limit at around 800 K. These results indicate that Ba2AsXO6 (X = V, Nb, Ta) double perovskite oxides have broad application prospects in the fields of thermoelectricity and optoelectronics. Furthermore, these results also provide a valuable theoretical basis for their future experimental synthesis.

Strain engineering of electronic, mechanical, and optical properties of orthorhombic III–V group monolayers by first principles calculations

Using first principles calculations, we systematically investigated the effects of strain engineering on the electronic, mechanical, and optical properties of two-dimensional (2D) orthorhombic III–V group materials, including BN, BP, BAs, AlN, AlP, and GaN. It is shown that all the III–V orthorhombic monolayers exhibit excellent mechanical anisotropy for Young’s modulus, Shear modulus, and Poisson’s ratio, especially for the AlN and GaN monolayers. AlN, AlP, and GaN are predicted to be indirect bandgap semiconductors, with their bandgap of 0.70, 0.15, and 0.53 eV, respectively. And BN is demonstrated to be a direct bandgap semiconductor (0.63 eV). Under uniaxial tensile strains, their electronic structures have non-monotonic anisotropic variations and these monolayers can be effectively modulated from metal to semiconductor, experiencing indirect–direct bandgap transitions. In addition, all the orthorhombic III–V materials exhibit highly anisotropic light-harvesting performances and the optical absorbance can be efficiently tailored with tensile strains applied along a- and b-directions. The strong optical absorptions in the visible light regions suggested that AlN, BN, and GaN may be optically tunable 2D materials for component absorbance layers for solar cell applications. The excellent anisotropic and tunable electronic, mechanical, and optical performances indicate that the orthorhombic III–V monolayers are promising candidates for potential applications of optoelectronics and photovoltaics.

Ultrahigh tunneling magnetoresistance ratios in the sandwich-structured full MXene Cr2NO2/Ti2CO2/Cr2NO2 van der Waals heterojunction

In this study, the structure, magnetism, energy-band, and spin-dependent electron transport properties of the Cr2NO2/Ti2CO2/Cr2NO2 magnetic tunnel junction (MTJ) were investigated using a combination of density functional theory and non-equilibrium Green’s function methods. The calculation band structures indicate that Cr2NO2 MXene is an “ideal” half-metal with a magnetic moment of 5.00 μB. Ti2CO2 MXene is an indirect band-gap semiconductor, and the Cr2NO2/Ti2CO2-stacked heterojunction reserve 100 % spin polarization because of the weak Van der Waals interface interaction. For the equilibrium state of the most stable Cr2NO2/Ti2CO2/Cr2NO2 MTJ, the total transmission coefficient for parallel configuration is about eleven orders of magnitude larger than that for anti-parallel configuration. An ultrahigh tunneling magnetoresistance (TMR) ratio of 1.92×1013% can be detected. For the non-equilibrium state, our calculation results show that the Cr2NO2/Ti2CO2/Cr2NO2 MTJ has a good transport performance when bias voltage ranges from 0 V to 0.1 V. The minimum TMR ratio of 7.51×1012% is detected at the bias voltage of 0.09 V, which can be considered as an excellent TMR ratio. Therefore, the Cr2NO2/Ti2CO2/Cr2NO2 MTJ is an excellent candidate for spintronic device application.

Theoretical Study of the Ternary Compound Monolayer CuP2Se for Photocatalytic Water Splitting with Efficient Optical Absorption.

Utilizing photocatalytic method to produce hydrogen by splitting water is an efficient strategy to solve the hotspot issues of energy crisis and environmental pollution. Herein, we systematically investigate the corresponding properties of the reported Cu-bearing ternary compound monolayer CuP2Se by using the first-principle calculations. The monolayer CuP2Se has quite small cleavage energy of 0.51 J/m2, indicating it can be easily produced by the mechanical exfoliation method experimentally. In addition, it is an indirect bandgap semiconductor material which has a moderate value of 1.91 eV. The conduction band minimum (CBM) and valence band maximum (VBM) can perfectly straddle the redox potentials of water when a biaxial strain of -4% to 4% is applied, unveiling the high photocatalytic thermodynamic stability of monolayer CuP2Se in response to the effect of solvent tension. Remarkably, the monolayer CuP2Se also demonstrates significant sunlight capturing ability in the visible region. The outstanding electronic and optical properties suggest that the monolayer CuP2Se is undoubtedly a viable material for photocatalytic water splitting.