Search

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 microscopic electronic structure and related optical properties of the 4H-SiC (111) surface doped with B, Al, Ga elements are explored by first principles calculation methods. Compared with Al- and Ga-doped systems, the formation energy of B-doped system is found to be very small, showing excellent stability. The bandgaps of doped system decrease obviously, and an indirect bandgap is observed in all the systems. Charge density difference maps show that the covalency is increased after B doping and the iconicity is increased after Al and Ga doping. Moreover, due to the sharp increase in static dielectric constant and dielectric loss, the B-doped system can be used as the candidate for absorbing materials. In addition, the increase in the peak value of the absorption and reflectivity makes the doped systems more promising in the development of solar cells. [ABSTRACT FROM AUTHOR]

An insight into electronic structure and optical feature of S-adsorbed 3C–SiC (111) surface is carried out employing first-principles calculation. It is found that the T o and B position systems with adsorption energies of 3.880 and 3.895, respectively, are relatively stable compared to the T w and C systems. Impurity energy levels are present near Fermi level in C and T w position adsorption systems and the band-gap decreases obviously in the two systems. A raindrop-like electron cloud of S atom can be observed in T w adsorption system and the order of the chemical bond strength in the adsorption system is (B , T o ) > T w > C. The B and T o adsorption systems have good light permeability in the visible and infrared regions, while the C and T w adsorption systems are relatively suitable as dielectric materials and have high service life when they as devices in the ultraviolet region. [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]

Electronic structures and optical properties of IV A elements (Ge, Sn and Pb)-doped 3C-SiC are investigated by means of the first-principles calculation. The results reveal that the structure of Ge-doped system is more stable with a lower formation energy of 1.249 eV compared with those of Sn- and Pb-doped 3C-SiC systems of 3.360 eV and 5.476 eV, respectively. Doping of the IV A elements can increase the band gap, and there is an obvious transition from an indirect band gap to a direct band gap. Furthermore, charge difference density analysis proves that the covalent order of bonding between the doping atoms and the C atoms is Ge–C > Sn–C > Pb–C, which is fully verified by population values. Due to the lower static dielectric constant, the service life of 3C-SiC dramatically improved in production practice. Moreover, the lower reflectivity and absorption peak in the visible region, implying its wide application foreground in photoelectric devices. [ABSTRACT FROM AUTHOR]

Based on first‐principles with the generalized gradient approximation (GGA) of the Perdew–Burke–Ernzerhof (PBE) form, the authors carry out systematic investigations regarding the electronic structures and optical properties of zinc‐blende (ZB) ZnS doped with six types of transition metals. The Cd‐doped system has greater structural stability with a lower formation energy of 0.526 eV compared to other systems. Additionally, the band structures of systems are employed to show the superior semiconductor capacity of Mo‐ and Pt‐doped systems with decreased band gaps (EG) of 0.978 eV and 0.843 eV, which are smaller than those of the pure system and others. Moreover, charge difference density maps show that the covalent properties of MoS and PtS bonds are enhanced by exposing the electron‐deficient region. Meantime, optical properties, including absorption and reflectivity spectra, dielectric constant, and loss function, are introduced to reveal that the absorption spectra curves reach the lowest absorption peak of 2.375 × 105 cm−1 at 7.227 eV for the Mo‐doped system, in which the system exhibits a relatively negative reflectivity spectrum and dielectric loss that is expected in the solar cell industry, predicting its broad scope of application prospects in the photoelectric and microelectronic device fields. [ABSTRACT FROM AUTHOR]

Electronic structures and optical properties of zinc-blende aluminum nitride doped with transition metals are investigated. Lu-doped system possesses the most considerate stability with the lowest formation energy of −9.033 eV compared to others. Band structures of systems are introduced to investigate a more excellent semiconductor capacity for Re-doped system with a band gap (EG) of 0.689 eV, with others having band gaps of 2.120, 2.159, 1.806, 1.837 and 0.879 eV, respectively, much smaller than that of pristine one, 3.113 eV. Moreover, absorption spectra curve reaches the lowest peak of 2.558×105cm−1 for Os-doped system; simultaneously, the system exhibits a relatively negative reflectivity spectra and dielectric loss of 5.620 eV that are extensively expected in solar cell industry, predicting its broad scope of application prospects in photoelectric and microelectronic devices. [ABSTRACT FROM AUTHOR]

In the present research, we use a first principles calculation to investigate the electronic structure and optical properties of Mo-, Pt- and Rh-doped rutile TiO2. The results indicate that the band gap of the Mo-, Pt-, and Rh-doped systems decreases to 1.758, 0.906, and 0.971 eV, respectively, compared with the 1.968 eV band gap of intrinsic TiO2, which is due to the hybridization of the doped atom d and O p orbital electrons, resulting in the formation of an impurity level and enhanced conductivity. The charge-difference density maps show that the covalence is enhanced in the region around Ti atoms for Mo- and Pt-doped systems, whereas Rh doping has little effect on the covalence. Based on these results, the bond population is 0.42, 0.28, and 0.27 for Mo–O, Pt–O, and Rh–O bonds, respectively. In the absorption spectrum, the peaks of the doped systems decrease significantly and redshift. Compared with the Mo-doped system, the Rh- and Pt-doped systems have lower static dielectric constant and dielectric loss in the low-energy region, which is promising for fascinating applications in microelectronic components. [ABSTRACT FROM AUTHOR]

Based on first-principles simulations with the generalized gradient approximation (GGA) of the Perdew-Burke-Ernzerhof (PBE) functional, we studied the electronic structures and optical properties of hexagonal silicon nitride (β-Si3N4) doped with IV A elements, C, Ge, Sn and Pb. It was found that the Ge-doped system is characterized by a more stable structure with a lower formation energy of 2.584 eV compared with those of the C-, Sn- and Pb-doped systems of 3.877 eV, 5.249 eV and 7.672 eV, respectively. The band gap (EG) of the Pb-doped system was the lowest at 1.6 eV, displaying semiconducting characteristics. Additionally, there was a transition from a direct band gap to an indirect band gap in the C-doped system. Charge difference density analysis showed that the covalent property of the C-N bonds was enhanced by expansion of the electron-free region and the larger Mulliken population values of 0.71 and 0.86. Furthermore, lower absorption and reflectivity peaks at 11.30 eV were observed for the C-doped system, demonstrating its broader potential for application in photoelectric and microelectronic devices. [ABSTRACT FROM AUTHOR]

We use first-principles calculations in this contribution to study electronic structures and optical properties, especially absorption and reflectivity spectra, dielectric constant and loss function of Li, Na, K, Be, Mg, Ca and Al adsorption behaviors on (2 0 0) surface of hexagonal silicon nitride (β-Si 3 N 4 ). The lower adsorption energy of −3.931 eV for Ca-adsorbed surface indicates that it has more excellent structural stability. The seven kinds of adsorptions are all featured by chemisorption with commonly negative value of adsorption energy, implying relatively abated capacity of defending the chemical corrosion formed by metals mentioned above. Band gaps of surfaces with different adsorptions are 0.113 eV, 0.099 eV, 0.113 eV, 0.147 eV, 0.154 eV, 0.151 eV and 0.111 eV for Li-, Na-, K-, Be-, Mg-, Ca- and Al-adsorbed surface structure, respectively, along with 0.143 eV for clean surface of β-Si 3 N 4 , which leads more efficient measures of potential for obtaining outstanding semiconductor properties for materials. Moreover, absorption spectra curve of surface drops to a lower peak value of 5.46 × 10 4  cm −1 , 4.94 × 10 4  cm −1 and 3.53 × 10 4  cm −1 for Na-, Mg- and Ca-adsorption, decreasing by 10.0%, 18.6% and 41.8% in contrast to clean surface, 6.07 × 10 4  cm −1 , respectively, in which the surface carries decreased reflectivity spectra and dielectric loss that are greatly valued and expected in solar cell industry, indicating its broader application potential in photoelectric and microelectronics devices fields. [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]

Using DFT-GGA-PW91 calculations we investigate the electronic structures and optical properties of doped GaP. It is found that the lattice constants and volume increase slightly for Al, In, As and Sb doped systems and E G distinctly decrease after doping. The formation energies are 0.587 and 0.273 eV for As and Sb doped systems, respectively, and lower remarkably than those in other systems, indicating that the stability of the two systems is higher. The direct band gap transition occurs when doped with In, As and Sb elements. The charge density difference images reveal that electron loss near Al atom is observed accompanying the enhancement of covalent bond feature, and then electron enrichment is present around N atom demonstrating that the ionic bond characteristic is obvious. The Sb-doped system has the higher static dielectric constant illustrating the applications in semiconductor devices. The absorption peak value is located at 194.7 nm for Al-doped system and this shows that the system can absorb a large amount of light and displays “Barrier-type” characteristics in UV region. In the visible region, the doped systems have lower reflectivity coefficient, indicating that the systems all have “clear-type” properties. This is conducive to fundamentally insights to a tunable band gap semiconductor with enormous potential in device fields. [ABSTRACT FROM AUTHOR]

Based on the first-principles calculation method of quantum mechanics, we systematically studied the geometric structure and electronic properties of graphene/CdSe heterojunction, and considered the influence of vertical strain on its performance. The calculated results show that the model II has the smallest binding energy of −1.09 eV when the interlayer distance is 3.4 Å. Graphene opens a small band gap of 3 meV, which indicates that it has a good application prospect in future micro-nano devices. Differential charge density found that the electrons and holes at the interface gathered on the surface of CdSe and graphene, respectively. When the interlayer distance increases from 2.6 Å to 4.0 Å, the band gap decreases from 19 meV to 1 meV. In addition, the most stable heterojunction has n- and p -type Schottky barrier heights of 0.224 eV and 1.324 eV, respectively, thus the system forms n -type Schottky contact. As the interlayer distance increases, the n - and p -type Schottky barrier heights continuously decrease and increase, respectively. When the interlayer distance increases from 2.6 Å to 2.8 Å, the heterojunction changes from p -type Schottky contact to n -type Schottky contact, and when the interlayer distance reaches 4.2 Å, the heterojunction can realize the transformation from n -type Schottky contact to n -type Ohmic contact. These findings may have potential guiding significance for the design and preparation of graphene/CdSe heterojunction nanodevices. [ABSTRACT FROM AUTHOR]

• The graphene/GaP heterostructure is dominated by vdW interaction. • The equilibrium interlayer spacing is 3.40 Å and the binding energy is −39.35 meV. • A tiny bandgap of 20 meV has opened at the Dirac point. • The interlayer distance and biaxial strain may change the contact mode. • A conversion from p-type Schottky to p-type Ohmic contact is present. Establishing the desired heterostructures by assembling suitable semiconductor materials has shown significant potential for applications in next-generation micro-nano electronic devices. In this present contribution, we demonstrate the geometric structure and electronic properties of graphene/GaP heterostructure by first-principles calculations. It is found that the heterostructure is characterized by weak interlayer coupling accompanying the stable layer spacing of 3.40 Å and binding energy of −39.35 meV, meaning that the interlayer is dominated by van der Waals (vdW) force. The electronic band structure of free-standing graphene and GaP monolayers are preserved well. Meanwhile, a tiny bandgap of approximatively 20 meV at the Dirac point of graphene is opened, which is attributed to the breakdown of sublattice symmetry. In the ground state, the Schottky contact of p -type is present with the n -type and p -type SBH of 1.71 eV and 0.10 eV, respectively, which can be effectively induced by imposing interlayer coupling as well as in-plane strains. Especially, the transition of p -Schottky contact to p -Ohmic contact occurs when the layer spacing decreases to 3.20 Å or the strain increases to +2 %. These theoretical results may offer potential guiding principle in future electronic devices. [ABSTRACT FROM AUTHOR]

The thermodynamic stability and mechanical strength of grain boundaries (GBs) govern many key properties of nanocrystalline or polycrystalline metals. In order to design novel Cu-based alloys with extraordinary properties and broaden the application scopes of Cu alloys, it is essential to clarify the effects of GB structure and composition on the stability and cohesion of Cu GBs. Firstly, the GB energies and works of separation of 12 Cu symmetrical tilt GBs with various GB orientations were figured out by using first-principles calculations, to link the GB properties with structures. Our results shown that the GB energies and works of separation of 12 Cu GBs are notably anisotropic. The GB energies for these GBs have an inverted and linear relationship with their works of separation. As to GB composition, the segregation tendencies of 8 alloying elements (Mg, Ca, Cr, Ni, Zn, Zr, Ag and Sn) in the Cu Σ5 [001](210) symmetrical tilt GB and their cohesive and embrittling effects on the GB were studied. It was found that all considered solutes excluding the element Ni can segregate to the Cu GB and thus play stabilizing roles into the Cu GB. Among 8 solutes, only the Zr and Cr segregations can improve the thermodynamic stability and fracture strength of Cu GB simultaneously. The GB strengthening effects of Zr and Cr segregations was attributed to their significant chemical contributions to the embrittling potencies, i.e., the presence of covalent-like bonding features in newly-formed Cu–Zr/Cr bonds. The reduction/increase of anti-bonding/bonding states below the Fermi level in Cu–Zr/Cr atomic pairs should be responsible for the GB stabilizing effects of Zr and Cr segregations. [Display omitted] • Zr and Cr segregation can strengthen Cu Σ5 [001](210) symmetrical tilt grain boundary. • Zr and Cr segregation can stabilize Cu Σ5 [001](210) symmetrical tilt grain boundary. • Grain boundary energy present inverted linear relationship with work of separation. [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]