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Using first principles calculations, we have confirmed the electronic and optical properties of 2D kagomes graphene doped with IVA elements (Si, Ge, Sn, Pb). The results show that Si-doped system has higher structural stability. The doping system increases the band gap of single-layer kagomes graphene, with Sn doping system being the most pronounced, and therefore can be considered as an attractive material for optoelectronic devices. The difference charge density and bonding population verify that the covalence of doping atoms and C atoms decreases, and that the degree of covalence diminution increases with increasing atomic number. The undoped kagomes graphene exhibits a strong light absorption capacity in the ultraviolet region, and the absorption peaks value decreases after doping, indicating that the element doping has a great weakening effect on the light absorption capacity, which has a certain potential significance for this material to be used as the antireflection film and wave permeable material of solar cells. In addition, the Pb and Sn-doped models possess the highest and lowest static dielectric constants, respectively. The peak value of electron energy loss is lower in the range of ultraviolet and visible wavelengths. These characteristics demonstrate that kagomes graphene offers substantial potential in the areas of optoelectronic and microelectronic devices. [ABSTRACT FROM AUTHOR]

In this paper, the effects of rare earth elements on the bonding strength and stability of TiC/fcc-Fe interface are explored by using the first-principles method based on density functional theory. The results show that the Ti terminal is more stable than the C terminal in the process of forming the interface. The alloying elements tend to segregate at position 2 on the side of fcc-Fe. The segregation of Mo, Nb, Cr and Ce alloying elements increases the interatomic electron cloud enrichment and consumption between the interfaces and enhances the Fe–Ti interactions. The d orbitals of Mo, Nb, Cr and Ce and f orbitals of Ce have strong hybridization with Fe-d orbitals and Ti-d orbitals electrons near the Fermi energy level, indicating an increase in bonding strength and stability of the interfaces. When Fe atoms are replaced by W, Ni and Al atoms, the covalent bond strength between interfacial atoms is reduced, thus weakening the interfacial bonding strength. This provides solid theoretical foundation with regard to further application in austenitic heat-resistant steel fields. [ABSTRACT FROM AUTHOR]

In this paper, the adsorption behavior of Na atom on T-carbon (111) surface is investigated in detail by first principles calculations. The adsorption of Na atom on the T-carbon (111) surface is a chemical adsorption with excellent stability. The minor opening of the bandgap is present. The charges transfer from Na atom to C atom, which leads to a transition of the bonding properties from covalence to ionicity. For the H-site adsorption system, the adsorption energy is the lowest, indicating that the system is the most stable. At the same time, C-Na has the lowest bond population, indicating its strong ionic property. Additionally, the dielectric loss of the adsorbed system reduces, especially for the H-site adsorption, which is conducive to the improvement of the service life in electron material devices. In absorption spectrum, the peak values decrease and shift to the lower energy direction, resulting in the appearance of redshift phenomenon. The reflection peak and energy loss values are greatly reduced, in which the trend is most obvious for the H-site adsorption. The above analysis results provide a theoretical basis for the application of photosensitive devices and open a window on the design and control the micro-nano devices. [ABSTRACT FROM AUTHOR]

Exploring the next generation of invincible energy materials with fascinating properties is vital in the challenge of energy crisis. In this paper, we extract T-carbon as a potential candidate and have an insight into the electronic and optical properties by means of first principles. It is found that S1 position doping system is relatively more stable with the formation energy of 0.323 eV, and has the smallest bandgap value of 1.228 eV. Charge density difference maps show that the electron loss is obvious near the S atom and the covalent bond is weakened. The population analysis shows that the S atom will obtain electrons through competition, while the Se atom will lose electrons. Additionally, the peak values of 2 in the doped systems decrease significantly, especially for S2 doping system, indicating that S2 doping can effectively improve the service life in related devices. Compared with the instinct system, the absorption coefficient is lower in the UV region and greater in the visible region. The peak of energy loss spectrum reduces after doping, especially for Se1 doping. The results provide a theoretical basis for the industrial application of T-carbon in the energy microdevice fields. [ABSTRACT FROM AUTHOR]

We use a first-principles calculation to explore the effects of vacancies on structural, electronic and optical properties of β - Si 3 N 4 based on density functional theory (DFT). The results show that after optimization, the Si vacancy system of β - Si 3 N 4 is more difficult to produce than N vacancy system under the same thermodynamic conditions. The band gaps including N vacancy and Si vacancy systems are smaller than that of the perfect crystal. The charge density difference and population analysis show that the bonding near Si vacancy has stronger covalent property, whereas those near nitrogen vacancy have stronger ionic property. For Si vacancy system, the materials have much higher values of the imaginary part of the dielectric constant than those of N vacancies and perfect β - Si 3 N 4 . The maximum value of the Si vacancy system in absorption and reflection spectra is lower than those in different nitrogen vacancy systems. [ABSTRACT FROM AUTHOR]

The Nb 2 NT 2 /MoTe 2 heterojunction shows n -type Ohmic contacts in O terminal system, while p -type and n -type Schottky contacts are formed in F and OH terminal systems, respectively, which makes the system suitable for electron device in terms of bandgap engineering controlling. [Display omitted] • The Nb 2 NT 2 /MoTe 2 heterostructure is dominated by vdW interaction. • The equilibrium interlayer spacing is within the range of 3.061 Å to 3.328 Å. • 0.12 e per cell spontaneously transfer from MoTe 2 to Nb 2 NO 2 layer. • n -type Ohmic contacts are formed in O terminal system. • Schottky contacts are formed in F and OH terminal systems. In the current effort, a novel attempt to construct heterojunctions using Nb 2 N two-dimensional MXene materials with fascinating property and MoTe 2 transition metal disulfide compounds is proposed. The effect of vertical strain on the electronic structure and interfacial contact properties of the heterojunction is investigated by first principles calculations. The O, F, and OH functional groups prefer to be adsorbed on top of the N atoms of the Nb 2 N MXene material. The configuration III of heterojunction has the lowest energy and stable model, and the equilibrium layer spacing is within the range of 3.061 Å to 3.328 Å, indicating that they belong to typical vdW heterojunctions. The large work function difference between the two components induces the transfer and rearrangement of charge. 0.12 e per cell spontaneously transfer from MoTe 2 to Nb 2 NO 2 layer. In contrast, the Nb 2 NF 2 and Nb 2 N(OH) 2 layers transfer 0.01 e and 0.21 e to the MoTe 2 layer, respectively. n -type Ohmic contacts are formed in O terminal system, while p-type and n -type Schottky contacts are formed in F and OH terminal systems, respectively. Additionally, for vertical strain, with the decrease of the layer spacing, the p-type Schottky barrier height (SBH) decreases from 0.270 eV to 0.095 eV in former system, meanwhile the n -type Schottky barrier height in the latter system also decreases from 0.260 eV to 0.156 eV. These regulations of interest lays a theoretical foundation for bandgap engineering and Schottky junction preparation and opens a window into MXene-based heterojunction electron device. [ABSTRACT FROM AUTHOR]

Interfacial segregation engineering is widely used as a means of regulating the strength and toughness of materials. In this paper, the effect of alloying elements on the interfacial segregation and interfacial bonding properties of fcc-Fe/NbC is investigated with the precipitated phase NbC in austenitic heat-resistant steel. The results show that there are eighteen interfacial configurations between the fcc-Fe and NbC phase, and the stability of the interface with Nb terminal is better than that of C terminal according to the calculation results of separation work and interface energy. Al atom is easy to segregate on the surface of austenite, while the alloy elements Mo, Nb, Cr, Ti, Mn, Y and Zr tend to segregate in the austenite matrix. The segregation of alloy elements Mo, Nb, Cr and Ti can enhance the hybridization between the d orbits of Fe and Nb atoms at the interface, thus promoting the bonding strength of the interface, while the segregation of Mn, Al, Y and Zr reduces the covalent interaction of the interface atoms, which weakens the bond strength at the interface. The above results have important practical significance for improving and regulating the composition and interfacial properties of heat-resistant steels. • Six fcc-Fe(111)/NbC(111) interfaces with different interface terminations are studied by first-principles. • The work of separation of the Nb-terminated interface is greater than that of the C-terminated interface. • The interface of the C-terminal is unstable. • Alloying elements affect the bonding strength of interfacial atoms. [ABSTRACT FROM AUTHOR]

In this effort, the influence of alloying element doping on fcc-Fe (111)/NbN (111) interface property is investigated by means of first principles. The interface structure combined with 5-layer fcc-Fe and 7-layer NbN is selected for investigation, because they exhibit characteristic consistent with the bulk counterpart. By calculating the interface energy, separation work and phonon spectra, the results show that interface 6 is stable. The alloying elements are more easily segregated at position 2 in the interface and it is chosen as the object of study. After Co and V doping, the separation work of the interface increases and the interfacial energy decreases. The degree of charge density consumption around them is greater than that of the intrinsic interface, indicating that the covalent bonds between atoms have been enhanced. This indicates that doping with Co and V atoms can improve the stability of the interface, which is consistent with the results towards population analysis and density of states. On the contrary, after doping with Zr, Sc, Y, and Ti atoms, the interatomic covalence weakens and the interface stability decreases. Especially for Y doping, the lowest electron consumption and the smallest electron cloud enrichment in the middle layer can be observed, demonstrating the worst interface stability. This insight has important guiding significance for the interface segregation behavior of alloying elements, and provides a theoretical basis for the development of next generation austenitic stainless steel. • Studied the effect of segregation of alloying elements Ti, Co, Zr, Y, V, Sc on fcc-Fe (111)/NbN (111). • After doping with Co and V atoms, the covalence between atoms is enhanced. • After doping with Co and V atoms, the interface stability can be improved. [ABSTRACT FROM AUTHOR]

The electronic structure and photocatalytic properties of two-dimensional GaSe/MoS 2 heterostructure are systematically studied by first-principles calculation. It is found that it could be used as a potential visible light catalyst to decompose water into H 2 and O 2. The lattice mismatch rate is 3.55%, and the binding energy was −0.446 eV, indicating that it has a stable configuration. An indirect band gap of 2.255 eV with hybrid HSE06 functional is observed, which falls into a wide range of visible light absorption. It exhibits II-type band alignment and this can promote the spatial separation of photogenerated carriers. In addition, the band edge spans the redox potential of water, indicating that heterostructure can produce hydrogen by photocatalytic decomposition H 2 O. The electrons transfer from GaSe to MoS 2 layer, while the holes do the opposite, thus improving the photocatalytic efficiency. Therefore, GaSe/MoS 2 heterostructure has broad application prospects in photocatalysis. • The GaSe/MoS 2 heterostructure is a very promising photocatalyst. • Work function of a material plays a momentous role in the band alignments. • The density of state can show the mechanism behind the orbital reconfiguration. • Semiconductor photocatalysis is considered as an ideal way to convert solar energy into chemical energy. [ABSTRACT FROM AUTHOR]

[Display omitted] The effect of alloying element segregation on the interface properties of the fcc-Fe/Ni 3 Al was investigated using the first-principles approach based on density functional theory, revealing the element segregation mechanisms from the perspectives of atoms and electrons. The results show that the alloying elements tend to replace position 1 on the interface of fcc-Fe phase side, and the order of stability after replacement is Ti, Nb, Mo, Cr and Mn. The state density diagrams show that the 4d orbital electrons of Mo and Nb contribute to increase the peak of Al atom 2p orbital at −5 eV, while the 3d orbital electrons of Cr and Ti tend to weaken the peak of Fe atom 3d orbital at 1 eV. The degrees of electron cloud enrichment and consumption increase between interface atoms of the difference charge diagrams indicate that the bonding strength increases and the interface stability is improved. The result of bond population is consistent with the differential charge density diagram. The study has a certain guiding significance for interfacial segregation behavior of alloying elements in heat-resistant steels. [ABSTRACT FROM AUTHOR]

• The mh*/me* value of T-carbon is 0.107 indicating the better conductivity. • Doping improves the electron migration rate and conducive of T-carbon. • B doping causes the increasing of ionicity for the bonds 1 and 3. • The absorption and reflection values are reduced in the ultraviolet region for Al doping. The structure stability, electronic and optical properties of B and Al doped T-Carbon have been investigated by first-principles calculation under DFT framework. The calculated results show that the stability of B doping system is higher than that of the Al doping system and site 1 and 2 positions have equal contribution on the stability of systems. The mh*/me* value of T-carbon is 0.107 far away from 1, indicating that is conducive to the improvement of its conductivity. The doping of B and Al promotes the generation of impurity bands, and the disappearance of band gap, which is beneficial to the conductivity improvement of T-carbon. In Al doping systems, the absorption, reflection and loss peaks of light are reduced in the ultraviolet region, especially for the Al 2 system, which exhibits the application foundation and opens a window in the fields of photoelectron and microelectronics devices. [ABSTRACT FROM AUTHOR]

Electronic structure and optical properties of Cr-, Al- and Cr-Al co-doped 3C-SiC systems are investigated by the first principles method. The system presents the characteristics of n-type semiconductor materials A red-shift phenomenon after doping can be observed. The doped systems exhibit the "Transparent Type" characteristic in the visible region. Electronic structure and optical properties of Cr-, Al- and Cr-Al co-doped 3C-SiC systems are investigated by the first principles method. Al-, Cr- and Cr-Al co-doped systems present the characteristics of p-, n- and n-type semiconductor materials, respectively. Charge density difference results show that the covalency of bonding reduces after doping, which is verified by bond population values due to the fact that the values of single doped and Cr-Al co-doped systems are lower than that of un-doped 3C-SiC. The intrinsic 3C-SiC barely has microwave dielectric loss, however, it can be improved through Al or Cr doping, especially the effect of Al doping, indicating the enhanced ability of materials to absorb electromagnetic waves, which is helpful for SiC to be widely used in military and aerospace fields as absorbing materials. By analyzing the host peaks of the absorption coefficient and the loss function, it is found that there is a significant red shift after doping. SiC exhibits the "Transparent Type" characteristic based on the fact that it has a lower absorption coefficient and reflectance in the visible light region, which proves the foundation for optical property and opens a window for photoelectric devices. [ABSTRACT FROM AUTHOR]