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We investigate systematically the electronic properties of fully hydrogenated GaN (HGaNH) monolayer under effects of the biaxial strain and external electric field. Results assert that the pristine GaN monolayer is an indirect semiconductor with a band gap of 1.933 eV. Band structures indicate that the N-p and Ga-p states are the main contributors to the valence and conduction bands near Fermi level, respectively. The full hydrogenation can induce an increase of this parameter to 3.019 eV, with H-s state being present in both valence and conduction bands. Interestingly, the HGaNH monolayer transforms from indirect to direct gap as a consequence of GaN hydrogenation. Based on results, the electronic band gap of HGaNH monolayer shows sensitivity to the biaxial strain and external electric field. Therefore, these factors can be used to effectively tune the electronic properties of HGaNH monolayer in order to make it more suitable for optoelectronic applications. • GaN monolayer has a planar graphene-like structure and the hydrogenation generates a buckling height of 0.705 Å. • GaN monolayer is a semiconductor with a band gap of 1.933 eV and the hydrogenated has a band gap of 3.019 eV. • Biaxial strain and external electric field effect on the electronic properties of the hydrogenated GaN monolayer is studied in details. • The hydrogenated GaN monolayer band gap is sensitive to biaxial strain and external electric field. [ABSTRACT FROM AUTHOR]

• The electronic structure of Mg 2 Si 1-x Sn x compounds is studied in detail from first principles. • The transport parameters (S, σ, κ e) of Mg 2 Si 1-x Sn x were elucidated. • The energy band gaps decrease with increasing Sn content in Mg 2 Si 1-x Sn x. • Heavy conduction band, CB H , and light conduction band, CB L , are formed in Mg 2 Si 1-x Sn x. • n -type Mg 2 Si 1-x Sn x compounds are found to be excellent TE materials for practical use. Mg 2 X (X = Si, Sn, and Ge) based compounds have attracted great attention due to their numerous advantages in thermoelectric (TE) applications. In particular, to date, ternary Mg 2 X based alloys have been recognized the most extensively explored thermoelectric systems, because these compounds exhibit excellent TE properties. Using the first-principles methods, we accomplished mutual alloying of Mg 2 X (Si, Sn) compounds in order to develop their efficiency in expanding the range of TE applications. The electrical, structural, and thermoelectric properties of Mg 2 Si 1-x Sn x were studied. With increasing Sn content in Mg 2 Si 1-x Sn x compounds, our calculations reveal a linear increase of the unit-cell constant and a decrease of the bulk modulus. Besides, this Sn content increase also leads to a decrease in the energy gap values. Moreover, taking into account the carrier concentration impact on the TE properties, we can state that the n -type Mg 2 Si 1-x Sn x alloys reveal higher TE behavior resulting from the large effective mass m * (in terms of electron mass m 0) and higher DOS at the Fermi level. In particular, the supreme ZT value is about 1.4 for n -type Mg 2 Si 0.375 Sn 0.625 at 700 K with n = 4x1020 cm−3, where the combination of elevated power factor and small thermal conductivity values play a key role. The supreme value of ZT is 0.9 for p-type Mg 2 Si at 700 K. These results suggest that Mg 2 Si 1-x Sn x alloys could be considered exceptional TE materials for practical use due to their fair TE performance. [ABSTRACT FROM AUTHOR]

Surface modification has been widely employed to modify fundamental properties of two-dimensional (2D) materials and create new multifunctional candidates for practical applications. In this work, the effects of chemical functionalization on silicon germanide (SiGe) monolayer have been investigated using first-principles calculations. Pristine monolayer exhibits good dynamical stability and a Dirac cone at K point in the band structure. The nearly semimetallic nature and absence of magnetic properties represent great challenge for SiGe monolayer applications. Our results show that these deficiencies can be overcome with oxygenation and hydrogenation processes. Oxygen (O) and hydrogen (H) atoms prefer to be adsorbed on-top of bridge and Si atom, respectively. The non magnetic nature is preserved under oxygenation, however a significant band gap up to 1.35 eV can be introduced depending on the O concentration. Meanwhile, the ferromagnetic semiconducting is induced by hydrogenation, where magnetic properties are produced mainly by Ge atoms, regardless the H coverage. In fact, efficient methods have been introduced to make SiGe monolayer promising 2D material for optoelectronic and spintronic applications through adsorbing O and H atoms. [ABSTRACT FROM AUTHOR]

Investigations of stable lead-free perovskites have ignited an increasing interest in overcoming lead-based perovskites' instability and toxicity problems. This study thoroughly investigated the transport, nature of electronic, stability, and optical properties of inorganic halide double perovskites', namely Na 2 CuMCl 6 (M = Bi, Sb), to better understand their possible applications. The theory of density function was applied to determine the physical characteristics of these materials. This cubic material's stability was validated by optimizing the mechanical stability test, tolerance factor, and structure. Small bandgap semiconductors with outstanding optoelectronic performance caused by low reflectivity, high conductivity, and optical absorption, as well as a high potential for optoelectronic application, were used. Due to the small bandgap, we also identified multiple transport parameters with chemical potential (μ). Based on this study, our findings revealed that the figure of merit (ZT) was near to unity due to the semiconducting nature of the materials, implying that it will be effective in thermoelectric technology. [ABSTRACT FROM AUTHOR]

[Display omitted] • Calcium modified 10Co/Al 2 O 3 catalysts were synthesized for simulated biogas dry reforming. • Basicity of catalyst is proportional to the calcium loading. • Metal dispersibility and catalyst reducibility can be enhanced with a proper addition of calcium. • A sufficient dosage of calcium boosts both methane and carbon dioxide conversions. • Allotrope of deposited carbon was changed in the presence of calcium toward amorphous type. The upgrading of simulated biogas with an equal mole ratio of methane and carbon dioxide through dry reforming over calcium promoted on cobalt-based catalysts was investigated in this work. Catalysts with different loading of calcium oxide were synthesized and used to explore that the calcium loading is critical in the performance of catalysts. At low calcium dosages in a range of 0.1–0.2 wt%, the average Co 3 O 4 crystalline size decreased from 8.15 nm to 6.01–7.43 nm, suggesting well-dispersed cobalt on the surface. In addition, the reducibility and basicity of catalysts were also enhanced with a sufficient addition of promoters. The optimal catalyst, 0.2Ca-10Co/Al 2 O 3 , exhibited the best performance with roughly 84% and 89% of CH 4 and CO 2 conversions, respectively. Moreover, the coke formation was suppressed by 78.72%, enabling higher activity and long-lasting stability. The findings offer new opportunities to enhance the dry reforming of simulated biogas performance using earth-abundant catalysts. [ABSTRACT FROM AUTHOR]

On the basis of first-principles projector augmented wave method, the effects of point defects and doping on the MgO monolayer electronic and magnetic properties are studied. Pristine monolayer is an insulator two-dimensional (2D) material with a band gap of 3.37 eV. Various defect types including single vacancy of Mg (V M g) and O (V O), Mg+O divacancy (V M g O), and antisites formed by replacing one Mg atom by one O atom (O M g), one O atom by one Mg atom (M g O ) and exchanging position of one Mg-O pair (M g ↔ O) have been considered. Material becomes ferromagnetic semiconductor upon creating a Mg single vacancy, whose magnetic properties are produced mainly by O atoms closest to the defect site. Meanwhile, the non-magnetic nature is preserved in other cases with a significant variation of the electronic band gap. Similarly, non-magnetic features are obtained when substituting one Mg atom by one Si or Ge atom (S i M g and G e M g ). In contrast, the feature-rich half-metallicity (semiconductor spin-up state and metallic spin-down state) is induced when doping at O site (S i O and G e O ). In these cases, magnetism is generated mainly by dopants with a small contribution from their neighbor O atoms. This work provides important insights on the MgO monolayer purposing efficient approaches to widen its working region for optoelectronic applications, as well as make it prospective to be applied as spin-filter and generate spin current in spintronic devices. [ABSTRACT FROM AUTHOR]

The main objective of this article is to deal with and establish a new type of transparent conducting material by doping Gallium Nitride (GaN) with rare-earth RE (Gd, Sm) elements. A theoretical study was performed by using the density functional theory (DFT) implemented in WIEN2k code and BoltzTraP package based on semi-classical Boltzmann transport equation (BTE) within constant relaxation time and rigid band approximation (RBA). The application of the modified Becke–Johnson (TB-mBJ) potential has improved the electronic structure, especially the electronic bandgap. Our simulation result matches with other computational results as well. We have compared the total energy of ferromagnetic (FM) and Anti-ferromagnetic (AFM) configurations for the doped system to analyze the magnetic ground state stability. Preferentially the most stable magnetic configuration is found to be ferromagnetic. The low value of formation energy indicates the possibility of the preparation of these materials in the lab. To further compare the results, we have also used the VNL-ATK quantumwise code based on the Linear Combination of Atomic Orbital (LCAO) approach. VNL-ATK incorporate a new functional DFT-1/2 to correct the Kohn–Sham KS eigenvalues around the minima and maxima of the conduction band, and the valence band, respectively, which enhances the bandgap. It shows the high optical absorption and the high electrical conductivity. These characteristics offer that GaN doped with rare earth elements are potential candidates for optoelectronic, solar cell, and spin-based magnetic devices. [ABSTRACT FROM AUTHOR]

The investigations on the physical properties of the Ba 2 NaIO 6 double perovskite, in this work, are presented. These investigations are carried out using WIEN2k computational code realized within the density functional theory (DFT) approach and at the level of the generalized gradient approximation (GGA) of exchange correlational functional as parameterized by Perdew Burke and Erenzerhof (PBE) beside employing modified Becke-Johnson (mBJ) as well as hybrid Heyd-Scuseria-Ernzehof (HSE) potentials. The results obtained for structural parameters have been found well-matching to the available literature. The obtained results of the electronic structure indicate the Ba 2 NaIO 6 has a direct bandgap semiconductor at the center of the Brillouin zone (T). We also presented a detailed study on its optical properties. Concerning its mechanical properties, the results of the bulk, Young, and shear modulus (G), the anisotropic factor (A), and Poisson's ratio (ν) are obtained using the first-principles results for the elastic constants. The sound velocities and Debye temperature are also determined for this compound. Furthermore, calculations of its transport properties demonstrate its p-type semiconductor nature. The results of the reported parameters show that Ba 2 NaIO 6 double perovskite is a suitable base material for optoelectronic devices particularly working for the infrared region as well as for thermoelectric applications. • Ba 2 NaIO 6 is elastically stable, anisotropic and brittle compound. • Ba 2 NaIO 6 is a non-central force solid and the atomic bonding is a mix of both (metallic and covalent) bondings. • Ba 2 NaIO 6 double perovskite is a direct and narrow bandgap semiconductor. • Ba 2 NaIO 6 is a suitable base material for optoelectronics and thermoelectric applications. [ABSTRACT FROM AUTHOR]

In this paper, we study theoretically the structural, electronic, optical, elastic and thermoelectric properties of MgSc 2 X 4 (X ​= ​S; Se) compounds using first-principles calculations. The calculated band structure reveals that MgSc 2 S 4 and MgSc 2 Se 4 are direct-gap semiconductors. The optical features of MgSc 2 S 4 and MgSc 2 Se 4 as functions of photon energy were calculated for energy range of 0–20 ​eV. MgSc 2 X 4 (X ​= ​S; Se) are promising optoelectronic, and thermoelectric compounds whose absorption rates can reach 4 orders of magnitude in the visible range, and 6 orders of magnitude in ultraviolet range. Both chalcogenides possess high brittleness with the Pugh's ratio (B / G), and Cauchy pressure C 12 − C 44 of 1.60 and − 4.485 GPa (for MgSc 2 Se 4); 1.61 and − 3.655 GPa (for MgSc 2 S 4). MgSc 2 S 4 and MgSc 2 Se 4 reveal similar Z T e values. The obtained properties of MgSc 2 X 4 (X ​= ​S; Se) are well confirmed by experimental results. Weighted band structures of MgSc 2 S 4 and MgSc 2 Se 4 as obtained by TB-mBJ. Image 1 • Structural, and electronic properties of MgSc 2 X 4 (X ​= ​S; Se) spinel compounds. • The distribution of the conduction bands depends on the hybridization S/Se- p orbitals and Sc- d orbitals. • High absorption rate in the visible and ultraviolet ranges. • High brittleness of MgSc 2 S 4 , and MgSc 2 Se 4. • Good thermoelectric and optoelectronic properties. [ABSTRACT FROM AUTHOR]

Transparent conducting oxides (TCOs) of semiconductor family gained significant attention due to increasing trends in the optoelectronic and thermo-physical applications. In current work, we reported electronic, optical, transport and thermodynamical properties of spinel oxides ZnGaO 2 , [ZnGaO 2 :Mn3+ and [ZnGaO 2 :Rh3+ compounds. Based on DFT, we employed first-principles calculations implemented in Wien 2k using the modified-Becke-Johnson (mBJ) on parent spinel and generalized-gradient-approximation plus Hubbard potential U (GGA + U) on doped materials, respectively. The calculated band structure shows insulating nature of parent compound, while doped material observed semiconducting nature contains direct band gap for both spin channels with band gaps of [ZnGaO 2 :Mn3+ (0.59 up, 2.4 eV dn) and [ZnGaO 2 :Rh3+ (2.1 eV up/dn) respectively. The electronic and optical results reveal that hybridization occurred mainly due to O-p/Zn, Mn-d, Rh-d and Ga-s orbitals. It is analyzed that Mn-doped material shows good absorption in the visible region while other are good in UV region. The effective masses of spinel oxides are also computed at high symmetry directions hence varied nonlinearly with the doping. The stability of materials is checked by calculating formation energies which indicate Mn-doped spinel oxide is most stable as that of others. The thermoelectric properties of spinel oxides were carried out by Post-DFT (Boltztrap) calculations. Large values of Seebeck coefficient and power factor of Mn-doped spinel oxide indicate that this material can be used for thermoelectric devices. The thermodynamical properties are calculated by quasi-harmonic Debye model implemented in GIBBS 2 code. Moreover, the pressure and temperature dependence of all (TD) parameters of investigated spinel oxides are analyzed using quasi-harmonic Debye model. Image 1 • We investigated structral, optoelectronic and tranport properties of spinel oxides Fe 3 BO 6 and Rh 0.08 Fe 0.92 BO 6 compounds. • The approximation used for these calculations was generalized gradient plus Hubbard potential (GGA+U). • The band structure of parent compound for spin up shows insulating nature while other channel is semiconducting nature (4.181 eV Up/2.41 eV Dn). • The optical dispersion exhibits strong absorption in the UV region, for both materials. • The transport parameters are computed by Post-DFT approximations based on rigid band approach in Boltzmann code. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) materials design for nanoscience and nanotechnology has attracted continuously the researchers' attention because of the important role in the next generation of optoelectronics. In this paper, we report results concerning the prediction of a new 2D material, Lithium Chloride LiCl, using first-principles calculations. This material is proposed for the detection and absorption of ultraviolet (UV) radiation. Our calculations assert that the pristine LiCl monolayer, which crystallizes in the D 3 h symmetry (space group P 6 ‾ 2 m) is dynamically stable. The monolayer at hand is an indirect gap insulator with a band gap of 6.048(7.212) eV predicted by WC(HSE06) functional. The external strains effect on the electronic structure of LiCl monolayer is also investigated. Optical absorption calculations show a wide absorption band in the UV region and high absorption coefficients. Results suggest that the LiCl monolayer may be a promising candidate for optoelectronic applications in the UV-detection and absorption. We believe that results presented in this work should pave a solid way for the applications of alkaline halides monolayers with a wide electronic band gap in optoelectronic devices. • h-LiCl monolayer is dynamically stable. • The monolayer has an indirect band gap of 6.048 eV. • External strain effect on the electronic structure is examined. • The single layer has wide absorption and high absorption coefficient in the UV spectrum. • h-LiCl monolayer may be promising candidate for UV detection and absorption. [ABSTRACT FROM AUTHOR]

Electronic structure, optical and thermoelectric properties of the HfSSe Janus monolayer have been comprehensively investigated using first-principles calculations based on the full-potential linearized augmented plane-wave (FP-LAPW) method. Results show that the HfSSe Janus monolayer is dynamically stable. Electronic properties features indicate that the two-dimensional (2D) material at hand is an indirect gap semiconductor with a band gap of 0.756 eV calculated by the Wu-Cohen scheme within generalized gradient approximation (GGA-WC). The spin-orbit coupling (SOC) inclusion in the calculations breaks the degeneracy in both valence and conduction bands, and gives a smaller band gap of 0.653 eV. Additionally, the external strain effect on the electronic structure is also examined. The metallization can be achieved when a compressive strain of −8% is applied. Optical properties results suggest that the studied 2D monolayer may be a promising candidate to be applied in nano-optoelectronic devices provided that it displays a wide absorption band from visible to ultraviolet with high absorption coefficient of the order of 103/cm. Finally, the thermoelectric properties including electrical conductivity, Seebeck coefficient, electronic thermal conductivity and power factor are calculated using the semi-classical Boltzmann transport theory. Results indicate that the electron doping may be favorable for the thermoelectric performance of the HfSSe Janus monolayer due to large power factor values as compared with those of the hole doping. • HfSSe monolayer is dynamically stable. • HfSSe is an indirect gap semiconductor with a band gap of 0.756 eV. • Spin-orbit coupling removes the energy degeneracy and decreases slightly the band gap. • HfSSe shows good optical absorption from visible to ultraviolet regime. • HfSSe possesses high thermopower and power factor, and the hole doping is favorable. [ABSTRACT FROM AUTHOR]

Combining different two-dimensional materials into layered van der Waals heterostructures are recently considered as an effective route to enhance the electronic properties of the constituent materials and to extend the application range in next-generation nanodevices. Here, the GeC/GaSe heterostructure and its electronic properties controlled by electric field have been constructed and systematically investigated using first-principles calculations. Five different stacking patterns of the GeC/GaSe heterostructure are constructed to consider the stacking effects on the electronic properties. We find that the GeC/GaSe heterostructure is mainly characterized by the weak van der Waals forces, dominating between GeC and GaSe layers, preserving their intrinsic properties in GeC/GaSe heterostructure. The GeC/GaSe heterostructure exhibits the type-II band alignment, where the electron–hole pairs are separated, making it suitable for fabricating next-generation optoelectronic nanodevices. Moreover, the stacking configurations have little affect the structural and electronic properties of the GeC/GaSe heterostructures. The pattern-I stacking configuration has the lowest binding energy and shortest interlayer distance as compared with other stacking patterns of the GeC/GaSe heterostructure. Furthermore, our results demonstrate that the electric field is considered as an effective route to modulate the electronic properties of GeC/GaSe heterostructure from semiconductor to metal. This finding makes the GeC/GaSe heterostructure promising material for optoelectronic nanodevices. • GeC/GaSe heterostructure is mainly characterized by the weak van der Waals forces. • GeC/GaSe heterostructure exhibits the type-II band alignment. • Stacking configurations have little affect electronic properties of heterostructures. • Electric field is an effective way to tune the electronic properties of heterostructure from semiconductor to metal. [ABSTRACT FROM AUTHOR]

• The PbI2/SnSe2 heterostructure possesses an indirect band gap semiconductor and exhibits a type-I band alignment. • The optical absorption of the PbI2/SnSe2 heterostructure in both the visible light and ultra-violet regions is enhanced. • Type-I to type-II band alignment and the semiconductor to metal transitions are also observed in the PbI2/SnSe2 heterostructure when the electric field is applied. Constructing van der Waals heterostructures can be considered as an effective strategy for generating new physical phenomena that merit for high-efficiency nanodevices. Here, we construct the PbI 2 / SnSe 2 heterostructure using first-principles calculations and explore its electronic structure and optical performance as well as the effects of electric fields. The PbI 2 / SnSe 2 heterostructure owns an indirect band gap and exhibits type-I band alignment, making it promising candidate for light emission applications. Furthermore, the optical absorption of the PbI 2 / SnSe 2 heterostructure in both the visible light and ultra-violet regions is enhanced as compared with that of the PbI 2 and SnSe 2 monolayers. Furthermore, in the PbI 2 / SnSe 2 heterostructure, the electric fields can convert the type-I to type-II band alignment and tune the transition from semiconductor to metal. Our results provide useful guidance for practical application in high-efficiency nanodevices. [ABSTRACT FROM AUTHOR]

The characteristics of defective ZrS 2 monolayers containing S-vacancies adsorbed various gases (NO, NO 2 , CO, SO 2 , N 2 , H 2 , O 2 , CO 2) were studied using a theoretical approach based on the density functional theory calculations. A favorable configuration for each gas adsorption was also found. The structural properties of defected ZrS 2 monolayers with S-vacancies adsorbed the given gas contents were elucidated. The obtained results show that the defected ZrS 2 monolayers with S-vacancies enhance the capacity of the gas adsorption in respect of the perfect ZrS 2 structures. Among those gases, the CO 2 , CO and N 2 molecules are physically adsorbed on S-vacancies of the defected ZrS 2 monolayers, whilst the O 2 , NO, SO 2 molecules are chemically adsorbed in the areas closed to S-vacancies of the ZrS 2 monolayers. Moreover, a NO 2 molecule can be separated by a S-vacancy of the defected ZrS 2 monolayer. The results of this work suggest that defective ZrS 2 monolayers with S-vacancies can be used as an adsorbent using in gas sensors to detect CO 2 , CO and N 2 gas contents. Therein, the highest sensitivity in detecting N 2 molecules is observed. • The S-vacancy on the ZrS 2 monolayer enhances the gas adsorption properties compared to the perfect ZrS 2 monolayer. • The molecules of CO 2 , CO and N 2 are physically adsorbed on the S-vacancies of defected ZrS 2 monolayers. • The molecules of O 2 , NO and SO 2 are chemically adsorbed on the areas closed to the S-vacancies of the defected ZrS 2 monolayers. • NO 2 molecule can be separated by a S-vacancy on a ZrS 2 monolayer. • The defected ZrS 2 monolayers can be used in gas sensors to detect CO 2 , CO and N 2 contents. [ABSTRACT FROM AUTHOR]

In this work, the electronic and optical properties of monolayer GaTe under biaxial strain and external electric field were investigated by density functional theory. Our calculated results indicate that the monolayer GaTe is an indirect-semiconductor with an energy gap of 1.41eV at equilibrium. Electronic properties of monolayer GaTe, especially the energy gap, depend greatly on the biaxial strain and external electric field. While the compressive strain slightly increases the energy gap, the tensile strain reduces quite rapidly the energy gap of the monolayer GaTe. In particular, semiconductor–metal phase transition can be observed when the external electric field was introduced. The GaTe monolayer strongly absorbs light in the ultraviolet region and the biaxial strain greatly changes its optical characteristics, especially the compression strain significantly increasing the absorption coefficient of the monolayer. Our results can provide more useful information for the prospect of application of the GaTe monolayer in next-generation optoelectronic devices. • Monolayer GaTe is an indirect-semiconductor with a moderate gap of 1.41eV at equilibrium. • Band gap of monolayer GaTe depends strongly on the biaxial strain. • Semiconductor–metal phase transition can be occurred in monolayer GaTe due to electric field. • Monolayer GaTe strongly absorbs light in the ultraviolet region. • Biaxial strain causes a significant shift in the first optical peaks of the GaTe monolayer. [ABSTRACT FROM AUTHOR]

The transition metals (TM = V, Cr and Mn) doping effects on the structural, electronic and magnetic properties of boron arsenide (BAs) monolayer have been comprehensively investigated using pseudopotential calculations within the framework of density functional theory (DFT). Calculations show that the pristine BAs monolayer has a graphene-like structure and its chemical bond is a mixture of covalent and ionic nature. Electronic properties results indicate that the BAs monolayer is a paramagnetic semiconductor with a direct band gap of 0.682 eV. The possibility of V-, Cr- and Mn-doping is determined by positive binding energy of 1.592, 1.668 and 1.876 eV, respectively. The incorporation of V and Cr generates the half-metallicity in the BAs monolayer with a spin-down band gap of 0.873 and 0.897 eV, respectively, while the one doped with Mn is nearly half-metallic. The doping also induces the magnetism and it is produced mainly from the 3 d orbital of the TMs with a small contribution from the nearest neighbor As atoms. Results presented in this work may be useful for the design of the magnetic nano-materials. • BAs monolayer adopts a honeycomb planar arrangement. • Transition metals doping induces local structural distortion. • Pristine BAs monolayer is a direct semiconductor. • V- and Cr-doped BAs monolayer show half-metallicity, while Mn-doped system is nearly half-metallic. • Magnetism is produced mainly from transition metal spin-up and small contribution from As spin-down. [ABSTRACT FROM AUTHOR]

Boron nitride (BN) monolayer (ML) has been the subject of many investigations, however, its large electronic band gap has limited so much its applications. Therefore, the band gap engineering is a necessary step at the time of designing practical uses of the BN ML to extend its applicability to nano-optoelectronic devices. In this work, we investigate systematically the impact of P- and As-doping as well as an external electric field on the electronic structure of BN ML using first-principles calculations based on the pseudopotential density functional theory. Results indicate that the pristine BN ML has an indirect K − Γ band gap of 4.589 eV. The N-substitution by P and As induces a band gap reduction of the order of 19.50% and 22.29%, respectively. Additionally, the external electric fields with strength in the range of −0.5 to 0.5 (eV/Å/e) are applied along the z-axis perpendicular to the MLs for both upward and downward directions. Under a weak electric field ± 0.1 (eV/Å/e), the electronic band gap of all three considered monolayers does not show a significant change. However, a stronger electric field will decrease considerably this parameter. Our results confirm that the coexistence of doping and external electric field can be a quite efficient approach to fine-tune the electronic structure of BN ML. • BN monolayer has a graphene-like honeycomb planar structure. • P- and As-doping induces a local structural distortion. • Pristine BN monolayer is an indirect semiconductor with band gap of 4.589 eV. • The electronic band gap decreases considerably under both doping and external electric field presence effect. [ABSTRACT FROM AUTHOR]

• h -BP monolayer with vacancy, antisite and Stone–Wales defects were investigated. • Pristine and most defected h -BP are semiconductor, metallic and non-magnetic. • Boron vacancy induced ferromagnetic ordering in the host lattice. • Formation energy indicate that B P antisite is the most predominant defect type. Using density functional theory (DFT), we systemically studied the impact of various point defects on the structural, magnetic and electronic properties of graphene-like boron phosphide (h -BP) monolayer. The results showed that the defect-free monolayer structure retained semiconductor-like the respective bulk compound, but the band gap modifies its character from indirect to direct. The band gaps of h -BP sheet varied from 0.142/0.46 to 0.75/1.26 eV using PBE/HSE06 schemes due to the existence of Stone-Wales (SW) and antisites defects. Also, it should be noted that the defect-free monolayer showed metallic behavior with a noticeable ferromagnetism, by hosting a boron vacancy, and becomes an indirect semiconductor through single (P) and double (P–B) vacancies. Additionally, the stability of the favorable point defects has been predicted based on the cohesive and formation energies. We have collected STM images of the SW defect structure for upcoming experimental observations. This study may be useful when designing novel optoelectronic and magnetic devices that employ defective h -BP monolayers. [ABSTRACT FROM AUTHOR]

Two-dimensional materials and their combined heterostructures have paved the way for numerous next-generation electronic and optoelectronic applications. Herein, we performed first principles calculations to computationally design the MoSe 2 /WS 2 heterostructure and consider its geometric structure, electronic properties and contact behavior, as well as the effects of the electric fields and strain. Our results show that the MoSe 2 /WS 2 heterostructure is energetically, thermodynamically and mechanically stable. Depending on the stacking configurations, the MoSe 2 /WS 2 heterostructure could form type-I or type-II band alignment. The versatility in contact behavior makes the MoSe 2 /WS 2 heterostructure attractive in electronics and optoelectronics. The combination of the MoSe 2 /WS 2 heterostructure also leads to an enhancement in the adsorption efficiency and the carrier mobility compared with the constituent components. More interestingly, our findings demonstrate that the electric field can induce the transition between type-I and type-II band alignments, as evident by the experimental measurement [J. Kistner-Morris, A. Shi, E. Liu, T. Arp, F. Farahmand, T. Taniguchi, K. Watanabe, V. Aji, C. H. Lui and N. Gabor, Nat. Commun. , 2024, 15 , 4075]. Additionally, we also find that strain can also induce the transition between type-I and type-II band alignments and lead to the transition from semiconductor to metal in the MoSe 2 /WS 2 heterostructure. Our findings prove that the MoSe 2 /WS 2 heterostructure holds significant potential for developing next-generation electronics.

In the present work, we propose GaGeX 2 (X = N, P, As) monolayers and explore their structural, vibrational, piezoelectric, electronic, and transport characteristics for multifunctional applications based on first-principles simulations. Our analyses of cohesive energy, phonon dispersion spectra, and ab initio molecular dynamics simulations indicate that the three proposed structures have good energetic, dynamic, and thermodynamic stabilities. The GaGeX 2 are found as piezoelectric materials with high piezoelectric coefficient d of -1.23 pm V 11 of -1.23 pm V -1 for the GaGeAs 2 monolayer. Furthermore, the results from electronic band structures show that the GaGeX 2 have semiconductor behaviours with moderate bandgap energies. At the Heyd-Scuseria-Ernzerhof level, the GaGeP 2 and GaGeAs 2 exhibit optimal bandgaps for photovoltaic applications of 1.75 and 1.15 eV, respectively. Moreover, to examine the transport features of the GaGeX 2 monolayers, we calculate their carrier mobility. All three investigated GaGeX 2 systems have anisotropic carrier mobility in the two in-plane directions for both electrons and holes. Among them, the GaGeAs 2 V 2 V -1 s -1 in the x and y directions, respectively. With high electron mobility, large piezoelectric coefficient, and moderate bandgap energy, the GaGeAs 2 material holds potential applicability for electronic, optoelectronic, piezoelectric, and photovoltaic applications. Thus, our findings not only predict stable GaGeX 2 structures but also provide promising materials to apply for multifunctional devices., Competing Interests: There are no conflicts of interest to declare., (This journal is © The Royal Society of Chemistry.)

Recently, searching for a metal-semiconductor junction (MSJ) that exhibits low-contact resistance has received tremendous consideration, as they are essential components in next-generation field-effect transistors. In this work, we design a MSJ by integrating two-dimensional (2D) graphene as the metallic electrode and 2D Janus γ-Ge 2 SSe as the semiconducting channel using first-principles simulations. All the graphene/γ-Ge 2 SSe MSJs are predicted to be energetically, mechanically, and thermodynamically stable, characterized by the weak van der Waals (vdW) interactions. The graphene/γ-SGe 2 Se MSJ-vdWH form the n -type Schottky contact (SC), while the graphene/γ-SeGe 2 S MSJ-vdWH form the p -type one, suggesting that the switching between p -type and n -type SC in the graphene/γ-Ge 2 SSe MSJ-vdWHs can occur spontaneously by simply altering the stacking patterns, without requiring any external conditions. Notably, the contact features, including contact types and barriers of the graphene/γ-Ge 2 SSe MSJs are significant in versatility and can be altered by applying electric gating and adjusting interlayer spacing. Both the applied electric gating and strain engineering induce switchability between p - and n -type and SC to OC in the graphene/γ-Ge 2 SSE MSJs. This versatility underscores the potential of the graphene/γ-Ge 2 SSe MSJ for next-generation applications that require low-contact resistance and high performance.

First principles calculation was performed to study the Sn 2 Te 2 X 4 (X = P, As) monolayers. Structural investigation confirms the stability of the two monolayers with Young's modulus in the range of 30.34-33.65 N m -1 and a Poisson's ratio of 0.18-0.21. The two monolayers are semiconductors with a direct band gap of 1.52-1.66 eV. The light absorption rate of the two monolayers is rather high 10 4 -10 5 cm -1 . Both monolayers have high charge carrier mobility and suitable VBM and CBM positions for the redox reaction. The η STH efficiency of both materials (15.76-17.12%) is close to the theoretical limit of 18%. Moreover, moderate strains can improve the light absorption rate, while the suitable VBM and CBM positions are preserved. These characteristics suggest that Sn 2 Te 2 X 4 (X = P, As) monolayers are good candidates for being applied in flexible devices and for the conversion of solar energy to other types of energy., Competing Interests: There are no conflicts of interest to declare., (This journal is © The Royal Society of Chemistry.)

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 ZrGeZ 3 H (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 ZrGeZ 3 H monolayers are indirect band gap semiconductors with favourable band gap energy of 1.15 and 1.00 eV for the ZrGeP 3 H and ZrGeAs 3 H, respectively, from Heyd-Scuseria-Ernzerhof functional method. It is found that the Janus ZrGeZ 3 H 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 ZrGeP 3 H and ZrGeAs 3 H monolayers have high electron mobility of 3639.20 and 3408.37 cm 2 V -1 s -1 , respectively. Our findings suggest the potential application of the Janus ZrGeZ 3 H monolayers in the piezoelectric and electronic fields., Competing Interests: There are no conflicts of interest to declare., (This journal is © The Royal Society of Chemistry.)

Breaking structural symmetry in two-dimensional layered Janus materials can result in enhanced new phenomena and create additional degrees of piezoelectric responses. In this study, we theoretically design a series of Janus monolayers HfGeZ 3 H (Z = N, P, As) and investigate their structural characteristics, crystal stability, piezoelectric responses, electronic features, and carrier mobility using first-principles calculations. Phonon dispersion analysis confirms that HfGeZ 3 H monolayers are dynamically stable and their mechanical stability is also confirmed through the Born-Huang criteria. It is demonstrated that while HfGeN 3 H is a semiconductor with a large bandgap of 3.50 eV, HfGeP 3 H and HfGeAs 3 H monolayers have narrower bandgaps being 1.07 and 0.92 eV, respectively. When the spin-orbit coupling is included, large spin-splitting energy is found in the electronic bands of HfGeZ 3 H. Janus HfGeZ 3 H monolayers can be treated as piezoelectric semiconductors with the coexistence of both in-plane and out-of-plane piezoelectric responses. In particular, HfGeZ 3 H monolayers exhibit ultra-high electron mobilities up to 6.40 × 10 3 cm 2 V -1 s -1 (HfGeAs 3 H), indicating that they have potential for various applications in nanoelectronics., Competing Interests: There are no conflicts of interest to declare., (This journal is © The Royal Society of Chemistry.)

Currently, tremendous efforts have been made to explore efficient glucose oxidation electrocatalysts for enzymeless glucose sensors to meet the urgent demands for accurate and fast detection of glucose in the fields of health care and environmental monitoring. In this work, an advanced nanostructured material based on the well-aligned CuO/Cu 2 S heteronanorods incorporated with P atoms is successfully synthesized on a copper substrate. The as-synthesized material shows high catalytic behavior accompanied by outstanding electrical conductivity. This, combined with the unique morphology of unstacked nanorod arrays, which endow the entire material with a greater number of exposed active sites, make the proposed material act as a highly efficient electrocatalyst for the glucose oxidation reaction. Density functional theory calculations demonstrate that P doping endows P-doped CuO/Cu 2 S with excellent electrical conductivity and glucose adsorption capability, significantly improving its catalytic performance. As a result, a non-enzymatic glucose sensor fabricated based on our proposed material exhibits a broad linear detection range (0.02-8.2 mM) and a low detection limit (0.95 μM) with a high sensitivity of 2.68 mA mM -1 cm -2 and excellent selectivity.

Using compressive mechanical forces, such as pressure, to induce crystallographic phase transitions and mesostructural changes while modulating material properties in nanoparticles (NPs) is a unique way to discover new phase behaviors, create novel nanostructures, and study emerging properties that are difficult to achieve under conventional conditions. In recent decades, NPs of a plethora of chemical compositions, sizes, shapes, surface ligands, and self-assembled mesostructures have been studied under pressure by in-situ scattering and/or spectroscopy techniques. As a result, the fundamental knowledge of pressure-structure-property relationships has been significantly improved, leading to a better understanding of the design guidelines for nanomaterial synthesis. In the present review, we discuss experimental progress in NP high-pressure research conducted primarily over roughly the past four years on semiconductor NPs, metal and metal oxide NPs, and perovskite NPs. We focus on the pressure-induced behaviors of NPs at both the atomic- and mesoscales, inorganic NP property changes upon compression, and the structural and property transitions of perovskite NPs under pressure. We further discuss in depth progress on molecular modeling, including simulations of ligand behavior, phase-change chalcogenides, layered transition metal dichalcogenides, boron nitride, and inorganic and hybrid organic-inorganic perovskites NPs. These models now provide both mechanistic explanations of experimental observations and predictive guidelines for future experimental design. We conclude with a summary and our insights on future directions for exploration of nanomaterial phase transition, coupling, growth, and nanoelectronic and photonic properties.

The electronic and optical properties of an AgGaGeS 4 crystal were studied by first-principles calculations, where the full-potential augmented plane-wave plus local orbital (APW+lo) method was used together with exchange-correlation pseudopotential described by PBE, PBE+ U , and TB-mBJ+ U approaches. To verify the correctness of the present theoretical calculations, we have measured for the AgGaGeS 4 crystal the XPS valence-band spectrum and the X-ray emission bands representing the energy distribution of the electronic states with the biggest contributions in the valence-band region and compared them on a general energy scale with the theoretical results. Such a comparison indicates that, the calculations within the TB-mBJ+ U approach reproduce the electron-band structure peculiarities (density of states - DOS) of the AgGaGeS 4 crystal which are in fairly good agreement with the experimental data based on measurements of XPS and appropriate X-ray emission spectra. In particular, the DOS of the AgGaGeS 4 crystal is characterized by the existence of well-separated peaks/features in the vicinity of -18.6 eV (Ga-d states) and around -12.5 eV and -7.5 eV, which are mainly composed by hybridized Ge(Ga)-s/p and S-p state. We gained good agreement between the experimental and theoretical data with respect to the main peculiarities of the energy distribution of the electronic S 3p, Ag 4d, Ga 4p and Ge 4p states, the main contributors to the valence band of AgGaGeS 4 . The bottom of the conduction band is mostly donated by unoccupied Ge-s states, with smaller contributions of unoccupied Ga-s, Ag-s and S-p states, too. The AgGaGeS 4 crystal is almost transparent for visible light, but it strongly absorbs ultra-violet light where the significant polarization also occurs., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The MXene SnSiGeN 4 monolayer as a new member of the MoSi 2 N 4 family was proposed for the first time, and its structural and electronic properties were explored by applying first-principles calculations with both PBE and hybrid HSE06 approaches. The layered hexagonal honeycomb structure of SnSiGeN 4 was determined to be stable under dynamical effects or at room temperature of 300 K, with a rather high cohesive energy of 7.0 eV. The layered SnSiGeN 4 has a Young's modulus of 365.699 N m -1 and a Poisson's ratio of 0.295. The HSE06 approach predicted an indirect band gap of around 2.4 eV for the layered SnSiGeN 4 . While the major donation from the N-p orbitals to the band structure makes SnSiGeN 4 's band gap close to those of similar 2D MXenes, the smaller distributions from the other orbitals of Sn, Si, and Ge slightly vary this band gap. The work functions of the GeN and SiN surfaces are 6.367 eV and 5.903 eV, respectively. The band gap of the layered SnSiGeN 4 can be easily tuned by strain and an external electric field. A semiconductor-metal transition can occur at certain values of strain, and with an electric field higher than 5 V nm -1 . The electron mobility of the layered SnSiGeN 4 can reach up to 677.4 cm 2 V -1 s -1 , which is much higher than the hole mobility of about 52 cm 2 V -1 s -1 . The mentioned characteristics make the layered SnSiGeN 4 a very promising material for use in electronic and photoelectronic devices, and for solar energy conversion., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

We discuss and examine the stability, electronic properties, and transport characteristics of asymmetric monolayers XWGeN 2 (X = O, S, Se, Te) using ab initio density functional theory. All four monolayers of quintuple-layer atomic Janus XWGeN 2 are predicted to be stable and they are all indirect semiconductors in the ground state. When the spin-orbit coupling (SOC) is included, a large spin splitting at the K point is found in XWGeN 2 monolayers, particularly, a giant Rashba-type spin splitting is observed around the Γ point in three structures SWGeN 2 , SeWGeN 2 , and TeWGeN 2 . The Rashba parameters in these structures are directionally isotropic along the high-symmetry directions Γ - K and Γ - M and the Rashba constant α R increases as the X element moves from S to Te. TeWGeN 2 has the largest Rashba energy up to 37.4 meV (36.6 meV) in the Γ - K ( Γ - M ) direction. Via the deformation potential method, we calculate the carrier mobility of all four XWGeN 2 monolayers. It is found that the electron mobilities of OWGeN 2 and SWGeN 2 V 2 V -1 s -1 , which are suitable for applications in nanoelectronic devices.

In this work, we systematically examine the electronic features and contact types of van der Waals heterostructures (vdWHs) combining single-layer boron phosphide (BP) and Janus Ga 2 SSe using first-principles calculations. Owing to the out-of-plane symmetry being broken, the BP/Ga 2 SSe vdWHs are divided into two different stacking patterns, which are BP/SGa 2 Se and BP/SeGa 2 S. Our results demonstrate that these stacking patterns are structurally and mechanically stable. The combination of single-layer BP and Janus Ga 2 SSe gives rise to an enhancement in the Young's modulus compared to the constituent monolayers. Furthermore, at the ground state, the BP/Ga 2 SSe vdWHs possess a type-I (straddling) band alignment, which is desired for next-generation optoelectronic applications. The interlayer separation and electric field are effectively used to tune the electronic features of the BP/Ga 2 SSe vdWH from the type-I to type-II band alignment, and from semiconductor to metal. Our findings show that the BP/Ga 2 SSe vdWH would be appropriate for next-generation multifunctional optoelectronic and photovoltaic devices., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

In this work, the effects of transition metal (TM = V and Cr) adsorption on AlN monolayer electronic and magnetic properties are investigated using first-principles density functional theory (DFT) calculations. TMs prefer to be adsorbed on-top of a bridge position as indicated by the calculated adsorption energy. V adatoms induce half-metallicity, while Cr adatoms metallize the monolayer. The magnetic properties are produced mainly by the V and Cr adatoms with magnetic moments of 3.72 and 4.53 μ , respectively. Further investigation indicates that antiferromagnetic (AFM) ordering is energetically more favorable than ferromagnetic (FM) ordering. In both cases, the AFM state is stabilized upon increasing adatom coverage. The AlN monolayer becomes an AFM semiconductor with 0.5 ML of V adatom, and metallic nature is induced with 1.0 ML. Meanwhile, the degree of metallicity increases with increasing Cr adatoms. Results reported herein may provide a feasible new approach to functionalize AlN monolayers for spintronic applications.B , respectively. Further investigation indicates that antiferromagnetic (AFM) ordering is energetically more favorable than ferromagnetic (FM) ordering. In both cases, the AFM state is stabilized upon increasing adatom coverage. The AlN monolayer becomes an AFM semiconductor with 0.5 ML of V adatom, and metallic nature is induced with 1.0 ML. Meanwhile, the degree of metallicity increases with increasing Cr adatoms. Results reported herein may provide a feasible new approach to functionalize AlN monolayers for spintronic applications., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (This journal is © The Royal Society of Chemistry.)

First-principles calculations were performed to study a novel layered SnGe 2 N 4 compound, which was found to be dynamically and thermally stable in the 2H phase, with the space group P 6̄ m 2 and lattice constant a = 3.143 Å. Due to its hexagonal structure, SnGe 2 N 4 exhibits isotropic mechanical properties on the x-y plane, where the Young's modulus is 335.49 N m -1 and the Poisson's ratio is 0.862. The layered 2H SnGe 2 N 4 is a semiconductor with a direct band gap of 1.832 eV, allowing the absorption of infrared and visible light at a rate of about 10 4 cm -1 . The DOS is characterized by multiple high peaks in the valence and conduction bands, making it possible for this semiconductor to absorb light in the ultraviolet region with an even higher rate of 10 5 cm -1 . The band structure, with a strongly concave downward conduction band and rather flat valence band, leads to a high electron mobility of 1061.66 cm 2 V -1 s -1 , which is substantially greater than the hole mobility of 28.35 cm 2 V -1 s -1 . This difference in mobility is favorable for electron-hole separation. These advantages make layered 2H SnGe 2 N 4 a very promising photoelectric material. Furthermore, the electronic structure of 2H SnGe 2 N 4 responds well to strain and an external electric field due to the specificity of the p-d hybridization, which predominantly constructs the valence bands. As a result, strain and external electric fields can efficiently tune the band gap value of 2H SnGe 2 N 4 , where compressive strain widens the band gap, meanwhile tensile strain and external electric fields cause band gap reduction. In particular, the band gap is decreased by about 0.25 eV when the electric field strength increases by 0.1 V Å -1 , making a semiconductor-metal transition possible for the layered SnGe 2 N 4 ., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

In this paper, the structural, electronic, and transport properties of Janus GaInX 3 (X = S, Se, Te) single-layers are investigated by a first-principles calculations. All three structures of GaInX 3 are examined to be stable based on the analysis of their phonon dispersions, cohesive energy, and Born's criteria for mechanical stability. At the ground state, The Janus GaInX 3 is a semiconductor in which its bandgap decreases as the chalcogen element X moves from S to Te. Due to the vertical asymmetric structure, a difference in the vacuum level between the two surfaces of GaInX 3 is found, leading to work functions on the two sides being different. The Janus GaInX 3 exhibit high directional isotropic transport characteristics. Particularly, GaInX 3 single-layers have high electron mobility, which could make them potential materials for applications in electronic nanodevices., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Hypothesis: Janus particles (JPs) and surfactants express different behaviors at the oil-water interface under compression. When both are present at the interface, their synergies result in a different collapse mechanism than when present individually depending on the concentration of the JPs and surfactants., Experiments: Coarse-grained modeling methods were used to probe the synergies between Janus nanoparticles and nonionic surfactants on the stability of an oil-water interface under compression. When both JPs and surfactants were present, the interface was covered at 0-55% area by JPs and contained surfactants at 0-40% of the interfacial surfactant concentration corresponding to the critical micelle concentration (CMC)., Findings: Compression of the interface with only surfactants resulted in the expulsion of surfactant molecules to the water phase once the interfacial concentration of surfactant molecules reached the CMC value. Compression of a Janus particle-laden interface past the closed-packing point led to a buckled interface, so that the total interfacial area remained constant upon further compression. When both surfactants and JPs were present on the interface, JPs still caused buckling, which helped retain the surfactant molecules on the interface. The interface exhibited a higher level of deformation in presence of surfactants. When the surfactant concentration was high, under compression, the surfactants partitioned into the water phase, but the buckling of the interface persisted., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Motivated by the recent successful synthesis of 2D quintuple-layer atomic materials, for the first time, we design and investigate the electronic and transport properties of Janus Al 2 XY 2 (X/Y = S, Se, Te; X ≠ Y) monolayers by using the density functional theory. Our calculations demonstrate that most of the models of Al 2 XY 2 (except for Al 2 STe 2 monolayer) are dynamically and mechanically stable. By using the hybrid functional, all models of Al 2 XY 2 are semiconductors with an indirect bandgap. Meanwhile, Al 2 TeS 2 monolayer is found to be metal at the Perdew-Burke-Ernzerhof level. Due to the vertical asymmetry structure, an intrinsic built-in electric field exists in the Al 2 XY 2 and leads to a difference in the vacuum levels between the two sides of the monolayers. Carrier mobilities of Al 2 XY 2 monolayers are high directional anisotropic due to the anisotropy of their deformation potential constant. Al 2 XY 2 monolayers exhibit high electron mobility, particularly, the electron mobility of Al 2 SeS 2 exceeds 1 × 10 4 cm 2 V -1  s -1 , suggesting that they are suitable for applications in nanometer-sized electronic devices., (© 2021 IOP Publishing Ltd.)

Two-dimensional Janus monolayers have outstanding electronic and transport properties due to their asymmetric atomic structures. In the present work, we systematically study the structural, electronic, and transport properties of the Janus GaIn X 2 ( X = S, Se, Te) monolayers by using the first-principles calculations. The stability of the investigated monolayers is confirmed via the analysis of vibrational spectrum and molecular dynamics simulations. Our calculations demonstrate that while GaInS 2 and GaInSe 2 monolayers are direct semiconductors, GaInTe 2 monolayer exhibits the characteristics of an indirect semiconductor. The band gap of GaIn X 2 decreases when the chalcogen element X varies from S to Te. Obtained results reveal that small spin-orbit splitting energy in the valence band is found around the Γ point of the Brillouin zone when the spin-orbit coupling is included. Interestingly, GaInS 2 and GaInSe 2 have high and directional isotropic electron mobility meanwhile the directional anisotropy of the electron mobility is found in the Janus GaInTe 2 monolayer. Our findings not only present superior physical properties of GaIn X 2 monolayers but also show promising potential applications of these materials in nanoelectronic devices., (© 2021 IOP Publishing Ltd.)

This work aims to test the effectiveness of newly developed DFT-1/2 functional in calculating the electronic and optical properties of inorganic lead halide perovskites CsPbBr 3 . Herein, from DFT-1/2 we have obtained the direct band gap of 2.36 eV and 3.82 eV for orthorhombic bulk and 001-surface, respectively. The calculated energy band gap is in qualitative agreement with the experimental findings. The bandgap of ultra-thin film of CsPbBr 3 is found to be 3.82 eV, which is more than the expected range 1.23-3.10 eV. However, we have found that the bandgap can be reduced by increasing the surface thickness. Thus, the system under investigation looks promising for optoelectronic and photocatalysis applications, due to the bandgap matching and high optical absorption in UV-Vis (Ultra violet and visible spectrum) range of electro-magnetic(em) radiation., (© 2021. The Author(s).)

Motivated by very recent successful experimental transformation of AB-stacking bilayer graphene into fluorinated single-layer diamond (namely fluorinated diamane C 4 F 2 ) [P. V. Bakharev, M. Huang, M. Saxena, S. W. Lee, S. H. Joo, S. O. Park, J. Dong, D. C. Camacho-Mojica, S. Jin, Y. Kwon, M. Biswal, F. Ding, S. K. Kwak, Z. Lee and R. S. Ruoff, Nat. Nanotechnol. , 2020, 15 , 59-66], we systematically investigate the structural, elastic, electronic, transport, and optical properties of fluorinated diamane C 4 F 2 by using density functional theory. Our obtained results demonstrate that at the ground state, the lattice constant of C 4 F 2 is 2.56 Å with chemical bonding between the C-C interlayer and intralayer bond lengths of about 1.5 Å which are close to the C-C bonding in the bulk diamond. Based on calculations for the phonon spectrum and ab initio molecular dynamics simulations, the structure of C 4 F 2 is confirmed to be dynamically and thermally stable. C 4 F 2 exhibits superior mechanical properties with a very high Young's modulus of 493.19 N m -1 . Upon fluorination, the formation of C-C bonding between graphene layers has resulted in a comprehensive alteration of electronic properties of C 4 F 2 . C 4 F 2 is a direct semiconductor with a large band gap and phase transitions are found when a biaxial strain or external electric field is applied. Interestingly, C 4 F 2 has very high electron mobility, up to 3.03 × 10 3 cm 2 V -1 s -1 , much higher than other semiconductor compounds. Our findings not only provide a comprehensive insight into the physical properties of C 4 F 2 but also open up its applicability in nanoelectromechanical and optoelectronic devices., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Two-dimensional MoSi 2 N 4 is an emerging class of 2D MA 2 N 4 family, which has recently been synthesized in experiment. Herein, we construct ultrathin van der Waals heterostructures between graphene and a new 2D Janus MoGeSiN 4 material and investigate their interfacial electronic properties and tunable Schottky barriers and contact types using first-principles calculations. The GR/MoGeSiN 4 vdWHs are expected to be energetically favorable and stable. The high carrier mobility in graphene/MoGeSiN 4 vdWHs makes them suitable for high-speed nanoelectronic devices. Furthermore, depending on the stacking patterns, either an n-type or a p-type Schottky contact is formed at the GR/MoGeSiN 4 interface. The strain engineering and electric field can lead to the transformation from an n-type to a p-type Schottky contact or from Schottky to Ohmic contact in graphene/MoGeSiN 4 heterostructure. These findings provide useful guidance for designing controllable Schottky nanodevices based on graphene/MoGeSiN 4 heterostructures with high-performance.

Epidemiological studies have consistently linked exposure to PM 2.5 with adverse health effects. The oxidative potential (OP) of aerosol particles has been widely suggested as a measure of their potential toxicity. Several acellular chemical assays are now readily employed to measure OP; however, uncertainty remains regarding the atmospheric conditions and specific chemical components of PM 2.5 that drive OP. A limited number of studies have simultaneously utilised multiple OP assays with a wide range of concurrent measurements and investigated the seasonality of PM 2.5 OP. In this work, filter samples were collected in winter 2016 and summer 2017 during the atmospheric pollution and human health in a Chinese megacity campaign (APHH-Beijing), and PM 2.5 OP was analysed using four acellular methods: ascorbic acid (AA), dithiothreitol (DTT), 2,7-dichlorofluorescin/hydrogen peroxidase (DCFH) and electron paramagnetic resonance spectroscopy (EPR). Each assay reflects different oxidising properties of PM 2.5 , including particle-bound reactive oxygen species (DCFH), superoxide radical production (EPR) and catalytic redox chemistry (DTT/AA), and a combination of these four assays provided a detailed overall picture of the oxidising properties of PM 2.5 at a central site in Beijing. Positive correlations of OP (normalised per volume of air) of all four assays with overall PM 2.5 mass were observed, with stronger correlations in winter compared to summer. In contrast, when OP assay values were normalised for particle mass, days with higher PM 2.5 mass concentrations (μgm -3 ) were found to have lower mass-normalised OP values as measured by AA and DTT. This finding supports that total PM 2.5 mass concentrations alone may not always be the best indicator for particle toxicity. Univariate analysis of OP values and an extensive range of additional measurements, 107 in total, including PM 2.5 composition, gas-phase composition and meteorological data, provided detailed insight into the chemical components and atmospheric processes that determine PM 2.5 OP variability. Multivariate statistical analyses highlighted associations of OP assay responses with varying chemical components in PM 2.5 for both mass- and volume-normalised data. AA and DTT assays were well predicted by a small set of measurements in multiple linear regression (MLR) models and indicated fossil fuel combustion, vehicle emissions and biogenic secondary organic aerosol (SOA) as influential particle sources in the assay response. Mass MLR models of OP associated with compositional source profiles predicted OP almost as well as volume MLR models, illustrating the influence of mass composition on both particle-level OP and total volume OP. Univariate and multivariate analysis showed that different assays cover different chemical spaces, and through comparison of mass- and volume-normalised data we demonstrate that mass-normalised OP provides a more nuanced picture of compositional drivers and sources of OP compared to volume-normalised analysis. This study constitutes one of the most extensive and comprehensive composition datasets currently available and provides a unique opportunity to explore chemical variations in PM 2.5 and how they affect both PM 2.5 OP and the concentrations of particle-bound reactive oxygen species., Competing Interests: Competing interests. The authors declare that they have no conflict of interest.

This study aims to critically evaluate the source apportionment of fine particles by multiple receptor modelling approaches, including carbon mass balance modelling of filter-based radiocarbon ( 14 C) data, Chemical Mass Balance (CMB) and Positive Matrix Factorization (PMF) analysis on filter-based chemical speciation data, and PMF analysis on Aerosol Mass Spectrometer (AMS-PMF) or Aerosol Chemical Speciation Monitor (ACSM-PMF) data. These data were collected as part of the APHH-Beijing (Atmospheric Pollution and Human Health in a Chinese Megacity) field observation campaigns from 10 th November to 12 th December in winter 2016 and from 22 nd May to 24 th June in summer 2017. 14 C analysis revealed the predominant contribution of fossil fuel combustion to carbonaceous aerosols in winter compared with non-fossil fuel sources, which is supported by the results from other methods. An extended Gelencsér (EG) method incorporating 14 C data, as well as the CMB and AMS/ACSM-PMF methods, generated a consistent source apportionment for fossil fuel related primary organic carbon. Coal combustion, traffic and biomass burning POC were comparable for CMB and AMS/ACSM-PMF. There are uncertainties in the EG method when estimating biomass burning and cooking OC. The POC from cooking estimated by different methods was poorly correlated, suggesting a large uncertainty when differentiating this source type. The PM 2.5 source apportionment results varied between different methods. Through a comparison and correlation analysis of CMB, PMF and AMS/ACSM-PMF, the CMB method appears to give the most complete and representative source apportionment of Beijing aerosols. Based upon the CMB results, fine aerosols in Beijing were mainly secondary inorganic ion formation, secondary organic aerosol formation, primary coal combustion and from biomass burning emissions.

We report the relation between the optical properties and electronic structure of lithium thiogallate (LiGaS 2 ) by performing XPS and XES measurements and theoretical calculations. According to the XPS measurements, the LiGaS 2 crystals grown by the Bridgman-Stockbarger method possess promising optical qualities, low hygroscopicity and high stability upon middle-energy Ar + -ion irradiation. The difference in the LiGaS 2 band gaps obtained by theoretical calculations and experimental measurements was, for the first time, reduced down to 0.27 eV by applying the Tran-Blaha modified Becke-Johnson (TB-mBJ) potential where the Coulomb repulsion was considered by introducing Hubbard parameter, U . The TB-mBJ+ U method also reproduces the XPS spectrum well. The TB-mBJ+ U band-structure calculations of LiGaS 2 are found to be in good agreement with the XPS and XES experimental data. The accurate electronic structure of LiGaS 2 allows further investigation of the optical properties. The relation between the photoluminescence of LiGaS 2 and its electronic structure was revealed. Moreover, the theoretical results show the possibility of emissions at higher energy levels in LiGaS 2 , that has not been measured in experiments yet. Good phase-matching of LiGaS 2 was expected to occur at energy levels of 5, 6, 6.2, 7, 7.2, and 8 eV., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

This paper focuses on the electronic and thermoelectric properties of monolayer MoS 2 . Here, we have examined the structure of MoS 2 , in which the hole in the center of the hexagonal cage is considered as a void atom, termed 1H-MoS 2 . Density functional theory (DFT) employing the generalized gradient approximation (GGA) and spin-orbit coupling (SOC) has been used for all calculations. Incorporation of SOC resulted in a significant change in the profile of the band energy, specifically the splitting of the valence band maximum (VBM) into two sub-bands. The "split-off" energy is found to be ∼20.6 meV. The reduction of the band gap with SOC is a prominent feature at the K-K location in the Brillouin zone. The band gap calculated with the GGA is ∼1.75 eV. However, on implementation of SOC, the GGA band gap was reduced to ∼1.68 eV. The frequency-dependent phonon dispersion curve was obtained to analyse the thermodynamical stability. 1H-MoS 2 is found to be thermodynamically stable with no imaginary frequency. We report a low value of lattice thermal conductivity ( κ l ) and low electron effective masses, which are desirable for potential applications in thermoelectric devices., Competing Interests: All authors declare that there are no conflicts of interest., (This journal is © The Royal Society of Chemistry.)

The unique physical and chemical properties of β 12 -borophene stem from the coexistence of the Dirac and triplet fermions. The metallic phase of β 12 -borophene transitions to the semiconducting one when it is subjected to a perpendicular electric field or bias voltage. In this work, with the aid of a five-band tight-binding Hamiltonian, the Green's function approach and the Kubo-Greenwood formalism, the electronic thermal conductivity (ETC) of the semiconducting phase of β 12 -borophene is studied. Two homogeneous (H) and inversion symmetric (IS) models are considered depending on the interaction of the substrate and boron atoms. In addition, due to the anisotropic structure of β 12 -borophene, the swapping effect of bias poles is addressed. First of all, we find the pristine ETC IS < ETC H independent of the temperature. Furthermore, a decrease of 74.45% (80.62%) is observed for ETC H (ETC IS ) when strong positive bias voltages are applied, while this is 25.2% (47.48%) when applying strong negative bias voltages. Moreover, the shoulder temperature of both models increases (fluctuates) with the positive (negative) bias voltage. Our numerical results pave the way for setting up future experimental thermoelectric devices in order to achieve the highest performance.

The data on the electronic structure and optical properties of bromide K 0.5 Rb 0.5 Pb 2 Br 5 achieved by first-principle calculations and verified by X-ray spectroscopy measurements are reported. The kinetic energy, the Coulomb potential induced by the exchange hole, spin-orbital effects, and Coulomb repulsion were taken into account by applying the Tran and Blaha modified Becke-Johnson function (TB-mBJ), Hubbard U parameter, and spin-orbital coupling effect (SOC) in the TB-mBJ + U + SOC technique. The band gap was for the first time defined to be 3.23 eV. The partial density of state (PDOS) curves of K 0.5 Rb 0.5 Pb 2 Br 5 agree well with XES K Ll and Br Kβ 2 , and XPS spectra. The valence band (VB) is characterized by the Pb-5d 3/2 and Pb-5d 5/2 sub-states locating in the vicinities of -20 eV and -18 eV, respectively. The VB middle part is mainly formed by K-3p, Rb-4p and Br-4s states, in which the separation of Rb-4p 3/2 and Rb-4p 1/2 was also observed. The strong hybridization of Br-p and Pb-s/p states near -6.5 eV reveals a major covalent part in the Br-Pb bonding. With a large band gap of 3.23 eV, and the remarkably high possibility of inter-band transition in energy ranges of 4-7 eV, and 10-12 eV, the bromide K 0.5 Rb 0.5 Pb 2 Br 5 is expected to be a very promising active host material for core valence luminescence and mid-infrared rare-earth doped laser materials. The anisotropy of optical properties in K 0.5 Rb 0.5 Pb 2 Br 5 is not significant, and it occurs at the extrema in the optical spectra. The absorption coefficient α ( ω ) is in the order of magnitude of 10 6 cm -1 for an energy range of 5-25 eV., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Vertical heterostructures from two or more than two two-dimensional materials are recently considered as an effective tool for tuning the electronic properties of materials and for designing future high-performance nanodevices. Here, using first principles calculations, we propose a GeC/C 2 N van der Waals heterostructure and investigate its electronic and optical properties. We demonstrate that the intrinsic electronic properties of both GeC and C 2 N monolayers are quite preserved in GeC/C 2 N HTS owing to the weak forces. At the equilibrium configuration, GeC/C 2 N HTS forms the type-II band alignment with an indirect band gap of 0.42 eV, which can be considered to improve the effective separation of electrons and holes. Besides, GeC/C 2 N vdW-HTS exhibits strong absorption in both visible and near ultra-violet regions with an intensity of 10 5 cm -1 . The electronic properties of GeC/C 2 N HTS can be tuned by applying an electric field and vertical strains. The semiconductor to metal transition can be achieved in GeC/C 2 N HTS in the case when the positive electric field of +0.3 V Å -1 or the tensile vertical strain of -0.9 Å is applied. These findings demonstrate that GeC/C 2 N HTS can be used to design future high-performance multifunctional devices., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)