A novel coupled quantum well structure and its excellent electro-optical properties

A novel InGaAs/InAlAs coupled quantum well structure is proposed for large field-induced refractive index change with low absorption loss. In the case of low applied electric field of 15 kV/cm and low absorption loss (±≤ 100 cm-1), a large field-induced refractive index change (for transverse electric (TE) mode, △n = 0.012; for transverse magnetic (TM) mode, △n = 0.0126) is obtained in the structure at the operation wavelength of 1.55 μm. The value is larger by over one order of magnitude than that in a rectangular quantum well. The result is very attractive for semiconductor optical switching devices.     

Electronic structure and optical properties of III–VI crystals

The polarized spectra of the full set of optical functions of GaS, GaSe, InSe, GaTe, InS, and TlSe crystals are determined in a wide range of fundamental-absorption energies. The ?₂ and -Im?^?1 spectra are decomposed into elementary components. The main parameters of the components were determined and the main features of the spectra and transition components are established. The results obtained are explained on the basis of the theoretical band calculations.     

Electronic structure,absorption spectra,and hyperpolarisabilities of some novel push–pull zinc porphyrins. A DFT/TDDFT study

DFT/TDDFT calculations have been performed on some novel push–pull zinc porphyrins (denoted ZnPor 1, ZnPor 2, and ZnPor 3). This theoretical work aims to investigate the electronic structure, absorption spectra, and hyperpolarisabilities of these molecules. To examine the effects of the peripheral substituents on the molecular properties, zinc porphine (ZnP) and zinc tetraphenylporphine (ZnTPP) were also included in the study. The orbital energy level patterns of the substituted zinc porphyrins are indeed rather different from those of ZnP and ZnTPP. The peripheral substitution breaks the molecular D_4h symmetry of the porphyrin, thereby leading to the splitting of the absorption Q band. On the other hand, the B band in the spectra may not arise only from a single excited state; instead, it could be made up of several states that are close in energy. The calculated hyperpolarisabilities (β _vec) increase strongly from ZnPor 1 to ZnPor 2 to ZnPor3. The latter two molecules were predicted to have a large β _vec value and thus may have potential application in the development of nonlinear optical (NLO) materials.     

Electronic structure and magnetic properties of metastable SmCo_7 compound

1 Introduction The rare-earth transition-metal intermetallic compounds have been widely investi-gated for many years, among them the Sm-Co series compounds with 1:5 and 2:17 crys-tal structures. These compounds have been used as sintered and bonded permanent magnets since the 1960s[1,2]. Interest recently has been focused on the TbCu7-type struc-ture Sm-Co intermetallic compounds with a strong uniaxial magnetocrytalline anisot-ropy and a low temperature coefficient (β = ?0.11%)[3―6] due t…     

Electronic properties of the SnSe–metal contacts:First-principles study

The geometries and electronic properties of Sn Se/metal contact have been investigated using first-principles calculation. It is found that the geometries of monolayer Sn Se were affected slightly when Sn Se adsorbs on M(M = Ag, Au, Ta)substrate. Compared with the corresponding free-standing monolayer Sn Se, the adsorbed Sn Se undergoes a semiconductorto-metal transition. The potential difference ?V indicates that Sn Se/Ta contact is the best candidate for the Schottky contact of the three Sn Se/M contacts. Two types of current-in-plane(CIP) structure, where a freestanding monolayer Sn Se is connected to Sn Se/M, are identified as the n-type CIP structure in Sn Se/Ag contact and p-type CIP structure in Sn Se/Au and Sn Se/Ta contact. The results can stimulate further investigation for the multifunctional Sn Se/metal contact.     

Electronic structure and energetics of tetragonal SrCuO? and its high-pressure superstructure phase

First-principles calculations have been used to investigate the electronic structure and energetics of the simple tetragonal SrCuO? (P4=mmm) and its high-pressure tetragonal superstructure (P4=mmm). Based on the calculations, the high-pressure phase is metastable as compared with the low pressure tetragonal phase, with an energy difference of 0.13 eV per SrCuO? formula unit. The energy barrier to the transition from the superstructure to the simple tetragonal structure is 0.24 eV at 7 GPa; thus, high temperatures are required to synthesize the latter. Among the possible structural configurations resulting from the partially occupied oxygen site in the superstructure phase, the most stable structure has a space group PN4m2, reduced from that of the simple tetragonal structure P4=mmm. The detailed analysis of the electronic band structures of the simple tetragonal and superstructure phases suggests that the out-of-plane buckling of the O atoms in the superstructure leads to significant decrease in the O p-Cu d orbital overlap, allowing the energy of the system to be lowered, which is necessary for the structural stability. An understanding of the electronic structure and energetics of the high-pressure superstructure phase and its relation to the simple tetragonal phase provides a basis for exploring the physical properties of the infinite layer, high-TC superconductor.     

DFT study on the structure and spectra of GasP5 cluster

In this paper, possible structures of GasP5 cluster were optimized by using density functional method with generalized gradient correction （B3LYP）. The electronic structure of the isomers with lower energy was studied. The most stable structure obtained for GasP5 is a distorted pentaprism. The Ga-P bond formed in the cluster is strongly ionic. Based on NBO analysis, an average value of 0.59 electron transfers from Gallium to Phosphorus. The bond length 2.33-2.43 is around the value in bulk GaP. The HOMO-LUMO gap is about 2.2 eV. The dipole moment and polarizability are calculated, and the IR and Raman spectra are also presented.     

Electronic structure and magnetic properties of （Mn,N）-codoped ZnO

The electronic structures and magnetic properties of（Mn, N）-codoped Zn O are investigated by using the firstprinciples calculations. In the ferromagnetic state, as N substitutes for the intermediate O atom of the nearest neighboring Mn ions, about 0.5 electron per Mn^2＋ion transfers to the N^2-ion, which leads to the high-state Mn ions（close to ＋2.5）and trivalent N3-ions. In an antiferromagnetic state, one electron transfers to the N2-ion from the downspin Mn2＋ion,while no electron transfer occurs for the upspin Mn^2＋ion. The（Mn, N）-codoped Zn O system shows ferromagnetism,which is attributed to the hybridization between Mn 3d and N 2p orbitals.     

Electronic structure and optical properties of In-doped SrTiO3 by density function theory

The effect of In doping on the electronic structure and optical properties of SrTiO3 is investigated by the first-principles calculation of plane wave ultra-soft pseudo-potential based on the density function theory （DFT）. The calculated results reveal that due to the hole doping, the Fermi level shifts into valence bands （VBs） for SrTi1-x InxO3 with x = 0.125 and the system exhibits p-type degenerate semiconductor features. It is suggested according to the density of states （DOS） of SrTi0.875In0.125O3 that the band structure of p-type SrTIO3 can be described by a rigid band model. At the same time, the DOS shifts towards high energies and the optical band gap is broadened. The wide band gap, small transition probability and weak absorption due to the low partial density of states （PDOS） of impurity in the Fermi level result in the optical transparency of the film. The optical transmittance of In doped SrTiO3 is higher than 85% in a visible region, and the transmittance improves greatly. And the cut-off wavelength shifts into a blue-light region with the increase of In doping concentration.     

Electronic structure and electrochemical properties of electrode material Li7−xMnN4

The electronic structure and the charge balance mechanism of the Li_7−xMnN₄ system were investigated by core-level electron energy loss spectroscopy. The spectra are strongly affected by configuration interactions and reveal the existence of a considerable amount of nitrogen 2p holes in the ground state. Based on the results, we conclude that the Li₇MnN₄ system can be classified into the charge transfer-type compounds. The systematic variation of the operating voltages versus Li/Li⁺ of the Li₇MnN₄ system and the other transition metal nitrides and oxides can be qualitatively explained by classification into the Mott–Hubbard and the charge transfer regimes.     

Electronic states and spectroscopic properties of MgH in absence and presence of spin–orbit coupling − a configuration interaction study

Electronic spectrum of astrophysically important molecule magnesium hydride (MgH) has been studied using configuration interaction methodology excluding and including spin–orbit coupling. Potential energy curves of several spin-independent (Λ?S) electronic states have been constructed and spectroscopic constants of low-lying bound Λ?S states within 8.2 eV of term energy are reported in the first stage of calculations. The X²Σ⁺ is identified as the ground state in the Λ?S level. In the subsequent stage, the spin–orbit interaction has been incorporated and its effects on the potential energy curves and spectroscopic features of different electronic states of the species have been investigated. The X²Σ⁺_1/2 is identified as the spin–orbit (Ω) ground state of the species. Transition moments of several dipole-allowed transitions are computed in both the stages and radiative lifetimes of the corresponding excited states are computed. Electric dipole moments (µ) for a number of low-lying bound Λ?S states as well as several low-lying Ω-states are also calculated in the present study.     

Electronic structure and magnetism of Co–Fe alloys with short-range order

Using a model which considers the localized and itinerant nature of the 3d electrons, and short-range order correlations, we obtain Co_xFe_1−x binary magnetic alloys electronic structure for different values of concentration x for subsequently finding the magnetic moment behaviour of each of the alloy components as function of the Co concentration x. In this way we are able to obtain results that agree with experiments of polarized neutrons diffraction.     

Electronic absorption spectra of ascorbic acid in water and water–dialkylsulfoxide mixtures

Gaussian analysis (LinkFit program) was used to deconvolute overlapping absorption bands due to neutral and anionic forms of ascorbic acid (AA). It has been shown that the neutral form of AA predominates in aqueous solutions of AA containing dialkylsulfoxides (DASO) because a hydrogen-bonded complex forms between DASO and AA molecules.     

Effect of thermal cycling on structure and properties of Ni–Mn–In-based alloys

Technical Physics - The results of investigations of the structure and properties of ternary alloys Ni47–x Mn42 + x In11 (0 ≤ x ≤ 2) after thermal cycling are presented. It has...     

Electronic structure and optical properties of boron-sulfur symmetric codoping in 4 × 4 graphene systems

The electronic structure and optical properties of boron-doped, sulfur-doped, andboron-sulfur-codoped graphene systems have been studied by using first-principlescalculations. Energy band structure and density of states are presented to describe theelectronic properties. The doping can open the band gap and change the optical propertiesof graphene. For all optical properties of doped graphene systems, parallel(E _∥) polarization and perpendicular(E _⊥) polarization are presented. Theoptical properties under two kinds of polarizations are reflected in the range of peakheight and the change of some extraordinary features.     

Electronic and optical properties of GaN–MoS_2 heterostructure from first-principles calculations

Heterostructures(HSs) have attracted significant attention because of their interlayer van der Waals interactions. The electronic structures and optical properties of stacked GaN–MoS_2 HSs under strain have been explored in this work using density functional theory. The results indicate that the direct band gap(1.95 e V) of the Ga N–MoS_2 HS is lower than the individual band gaps of both the GaN layer(3.48 e V) and the MoS_2 layer(2.03 eV) based on HSE06 hybrid functional calculations. Specifically, the GaN–MoS_2 HS is a typical type-II band HS semiconductor that provides an effective approach to enhance the charge separation efficiency for improved photocatalytic degradation activity and water splitting efficiency.Under tensile or compressive strain, the direct band gap of the GaN–MoS_2 HS undergoes redshifts. Additionally, the GaN–MoS_2 HS maintains its direct band gap semiconductor behavior even when the tensile or compressive strain reaches 5% or-5%. Therefore, the results reported above can be used to expand the application of Ga N–MoS_2 HSs to photovoltaic cells and photocatalysts.     

Electronic structure and magnetic and electromagnetic wave absorption properties of BaFe12-xCoxO19 M-type hexaferrites

Crystal, electronic structures and the magnetic and electromagnetic wave absorption properties of BaFe_12-xCo_xO₁₉ (x = 0–2) M-type hexaferrites prepared by a co-precipitation technique were studied. The analyses of X-ray diffraction patterns indicated that the samples mainly crystallized in the P6₃/mmc hexagonal structure, with the additional constitution of Y-type hexaferrite as x > 0. The replacement of Co²⁺ for Fe³⁺ in BaFe_12-xCo_xO₁₉ changed the lattice constants and caused lattice distortions. Particularly, Co²⁺ doping also reduced magnetization and hard magnetic property of BaFe_12-xCo_xO₁₉. This is ascribed to magnetic moment of Co²⁺ smaller than that of Fe³⁺ and to the decrease of magnetocrystalline anisotropy. Having studied electromagnetic wave absorption properties in the frequency range f = 0.1–18 GHz, we found BaFe_12-xCo_xO₁₉ showing high reflection loss (RL) values at frequencies of 0.1–15 GHz, but fairly low RL values at higher frequencies. These features suggest that BaFe_12-xCo_xO₁₉ can be suitable to electronic devices working at GHz frequencies.     

Calculation of the structure properties and P–T phase diagram of hafnium

Abstract

The full-potential linear muffin-tin orbitals (FP-LMTO) method is used to calculate the total energy and equilibrium lattice properties for the observed phases of Hf. The temperature and pressure dependences of the Gibbs energy are found for these structures within the Debye model. A quantitative agreement with the experimental points of the P-T phase diagram is obtained.     

The structures and electronic properties of ferrous nitride–fulminic acid clusters

The structures and electronic properties of ferrous nitride–fulminic acid (FeN–HCNO) clusters are investigated by using PW91 functional. The results reveal that the Fe atom of an FeN molecule prefers to be absorbed on the N–O of an HCNO molecule and it shows the highest kinetic stability. The Fe–N–C–N ring structure has the highest kinetic stability, while the FeN–HCNO chain configuration shows the highest kinetic activity. The N–Fe–ONCH chain structure displays the maximum dipole magnitude (DM) value (8.246 Debye). The Fe atom of the FeN molecule adsorbed on the C atom of the HCNO molecule has the minimum DM value (0.641 Debye). The linear FeN–HCNO configuration displays the largest total spin (2.945?μ_B/atom). The hybridization of sp orbital of the FeN–HCNO clusters is very important.