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1.
We report a systematic study of the structural, electronic, optical and elastic properties of the ternary ruthenium-based hydrides A2RuH6 (A = Mg, Ca, Sr and Ba) within two complementary first-principles approaches. We describe the properties of the A2RuH6 systems looking for trends on different properties as a function of the A sublattice. Our results are in agreement with experimental ones when the latter are available. In particular, our theoretical lattice parameters obtained using the GGA-PBEsol to include the exchange-correlation functional are in good agreement with experiment. Analysis of the calculated electronic band structure diagrams suggests that these hydrides are wide nearly direct band semiconductors, with a very slight deviation from the ideal direct-band gap behaviour and they are expected to have a poor hole-type electrical conductivity. The TB-mBJ potential has been used to correct the deficiency of the standard GGA for predicting the optoelectronic properties. The calculated TB-mBJ fundamental band gaps are about 3.53, 3.11, 2.99 and 2.68 eV for Mg2RuH6, Ca2RuH6, Sr2RuH6 and Ba2RuH6, respectively. Calculated density of states spectra demonstrates that the topmost valence bands consist of d orbitals of the Ru atoms, classifying these materials as d-type hydrides. Analysis of charge density maps tells that these systems can be classified as mixed ionic-covalent bonding materials. Optical spectra in a wide energy range from 0 to 30 eV have been provided and the origin of the observed peaks and structures has been assigned. Optical spectra in the visible range of solar spectrum suggest these hydrides for use as antireflection coatings. The single-crystal and polycrystalline elastic moduli and their related properties have been numerically estimated and analysed for the first time. 相似文献
2.
对SOI基片上的Si薄膜进行了一系列Si+自注入和热退火的改性实验,并利用低温光致发光(PL)光谱对这些Si薄膜样品的发光性能进行了测试. 在这些SOI样品的PL光谱中观察到了丰富的光学结构,包括D1,D2,D3,X以及异常尖锐的W线. 通过对比在同等光谱测试条件下的W线归一化强度,获得了针对SOI基片发射W线较为理想的自注入和热退火参数. 同时,还对D系列发光峰以及W线的缺陷起源和光学性质进行了很好的讨论.
关键词:
SOI结构
自离子注入
W线
近红外发光器件 相似文献
3.
The equilibrium structures and the electronic, spectroscopic and thermodynamic properties of small Pun (n=2-5) molecules are systematically investigated using the methods of general gradient approximation (GGA) of density functional theory (DFT). The results show that the bond length of the lowest-energy structure of Pu2 is 2.578 AA. The ground state structure of Pu3 is a triangle with D3h symmetry, whereas for Pu4, the ground state structure is a square (D4h) and the spin polarization of 16 for molecule Pu5 with square geometry (D4h) is the most stable structure. For the ground state structures, the vibrational spectra as well as thermodynamic parameters are worked out. In addition, the values for the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) along with the energy gap of all the Pu2-5 structures are presented. The relevant structural and chemical stabilities are predicted. 相似文献
4.
G. Baldacchini P. Chiacchiaretta V. Gupta V. Kalinov A. P. Voitovich 《Physics of the Solid State》2008,50(9):1747-1755
Thermoluminescence (TL) of nominally pure LiF crystals irradiated with gamma rays has been studied in connection with color
centers (CCs) generated during ionizing irradiation. A close analysis of the experimental TL spectra unveiled the existence
of 10 glow peaks (GPs) spanning from 100 to 450°C. The relatively well-resolved GPs up to 263°C are associated with F
3+, F
3, and F
2 CCs, while the remaining tangled ones are attributed to F and F-like CCs. A first-order kinetics approach is used to simulate the TL spectra, and the appropriate parameters of the carrier
traps are obtained. A critical analysis of their values showed, on the one side, the usefulness of using pure crystals to
understand their basic contributions to TL, and, on the other side, the possible existence of further weak GPs and the role
still played by the residual amount of impurities.
The text was submitted by the authors in English. 相似文献
5.
The crystal structures, band structures, elastic constants, hardness, and optical properties of pyrite-type dinitrides (CN2, SiN2, and GeN2) are obtained from the density functional theory using the plane-wave pseudopotential (PWP) method within the local density and generalized gradient approximations. The formation enthalpies for AN2 (A=C, Si, and Ge) compounds suggest the three structures that are stable. The calculated band structures show the indirect gaps (Γ−R) in CN2, SiN2, and GeN2. The intrinsic hardnesses of AN2 (A=C, Si, and Ge ) compounds are calculated. Our results show that the cubic CN2 and SiN2 are superhard materials. Furthermore, we studied the optical properties such as the complex dielectric function and the electron energy loss spectra. 相似文献
6.
In this paper the spectra of Gd3+ ions studied by electron spin resonance (ESR) in four types of tungstate crystals KY(WO4)2, CdWO4, CsLa(WO4)2 and La2(WO4)3 are discussed. The tungstate crystals were grown by the low-temperature gradient Czochralski technique with Gd2O3 addition in melt. The estimation of spin Hamiltonian (SH) parameters was realized using an original simulation program developed.
The parameters of crystalline field in oxide crystals are comparable with Zeeman interaction so the solution of the Schr?dinger
equation was realized numerically. We have estimated 36 SH parameters from ESR angular diagrams of Gd3+, including g
x
, g
y
, g
z
, g
i
(where i = 1, …, 6), B
m
n
, C
m
n
(where m = 2, …, 6, n = 0 (or 1 for C
m
n
), …, m), and the Euler angles. The positions of Gd3+ ions in the crystal structures, the charge compensation and the influence of lattice parameters on the SH parameters B
2
0 and B
2
2 are discussed in this paper as well.
Authors' address: Nikolay V. Cherney, Institute of Inorganic Chemistry, Russian Academy of Sciences, Lavrentyev av. 3, Novosibirsk
630090, Russian Federation 相似文献
7.
The luminescence spectra are obtained in the visible region for the high-T
c superconductors La2CuO4, YBA2Cu3O7−δ
, Bi2Sr2CaCu2O8±δ
, and YBa2Cu3O8±δ
and for the secondary phases BaCuO2±γ and Y2Cu2O5. The presence of a luminescence band with energy E
lum∼2.4 eV in the spectra of all the investigated compounds is established. The nature of the observed luminescence bands is
discussed on the basis of a comparative analysis of the crystal structures and luminescence spectra and on the basis of notions
as to the presence of bands in the spectra accompanied by photoinduced diffusion of weakly bound oxygen and photoinduced charge
transfer in the CuO2 planes.
Fiz. Tverd. Tela (St. Petersburg) 39, 1739–1746 (October 1997) 相似文献
8.
The optimized configurations, electronic structures, charge transfers, band gaps, total energies, cohesive energies, electron
density maps, infrared absorption spectra, Raman spectra, and relevant modes of natural acoustic vibrations for the semiconductor
clusters C24, B12N12, Si12C12, Zn12O12, and Ga12N12 are calculated using the ab initio Hartree-Fock method in the 6–31G basis set.
Original Russian Text ? V.V. Pokropivny, L.I. Ovsyannikova, 2007, published in Fizika Tverdogo Tela, 2007, Vol. 49, No. 3,
pp. 535–542. 相似文献
9.
María Eliana Defonsi Lestard María Eugenia Tuttolomondo Derek A. Wann Heather E. Robertson David W. H. Rankin Aida Ben Altabef 《Journal of Raman spectroscopy : JRS》2010,41(10):1357-1368
The molecular structure and conformational properties of ethyl trifluoroacetate, CF3CO2CH2CH3, were determined in the gas phase by electron diffraction, and vibrational spectroscopy (IR and Raman). The experimental investigations were supplemented by ab initio (MP2) and DFT quantum chemical calculations at different levels of theory. Experimental and theoretical methods result in two structures with Cs (anti–anti) and C1 (anti–gauche) symmetries, the former being slightly more stable than the latter. The electron‐diffraction data are best fitted with a mixture of 56% anti–gauche and 44% anti–anti conformers. The conformational preference was also studied using the total energy scheme, and the natural bond orbital scheme. Also, the infrared spectra of CF3CO2CH2CH3 are reported for the gas, liquid and solid states, as is the Raman spectrum of the liquid. The comparison of experimental averaged IR spectra of Cs and C1 conformers provides evidence for the predicted conformations in the IR spectra. Harmonic vibrational wavenumbers and scaled force fields have been calculated for both conformers. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
10.
S. E. Kulkova S. V. Eremeev A. V. Postnikov D. I. Bazhanov B. V. Potapkin 《Russian Physics Journal》2006,49(10):1088-1096
The atomic and electronic structures of α, β, β2, and ζ reconstructions for the Ga-terminated GaAs (001)-(4×2) surface are investigated in the framework of the pseudopotential approach. Total, surface, and local densities
of electron states, electron-energy spectra, and relative surface energies of the structures under consideration are calculated.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 44–52, October, 2006. 相似文献
11.
E. L. Ivchenko V. P. Kochereshko A. V. Platonov D. R. Yakovlev A. Waag W. Ossau G. Landwehr 《Physics of the Solid State》1997,39(11):1852-1858
Theory of specular light reflection from long-period quantum-well structures taking into account the exciton contribution
to dielectric polarization has been developed for an arbitrary relation between the background refractive index in the well,
n
a, and barrier-material refractive index nb. General expressions for the optical reflection and transmission coefficients for a structure with N equidistant quantum wells are derived with the use of the Green’s function and transfer matrix methods. Normal and oblique
light reflectance spectra from II-VI-based heterostructures were found to reveal a bright interference pattern caused by the
difference between n
a and n
b. A comparison of the theory with experiment has yielded the dispersion of n
a and n
b within a broad wavelength range and the parameters of the quasi-two-dimensional heavyhole exciton (e1-hh1), namely, the resonant frequency and the radiative and nonradiative damping rates. Reflectance spectra from resonant Bragg
and quasi-Bragg structures with real exciton parameters are calculated, and the effect on these spectra of the refractive-index
difference and the deviation from the Bragg condition is analyzed.
Fiz. Tverd. Tela (St. Petersburg) 39, 2072–2078 (November 1997) 相似文献
12.
WOLFGANG JABS MANFRED WINNEWISSER SERGEI P. BELOV FRANK LEWEN FRANK MAIWALD GISBERT WINNEWISSER 《Molecular physics》2013,111(1-2):213-238
An experimentally determined r s -type structure of HNCNH is reported: r NH = 1.0074 Å, r CN = 1.2242 Å, ∠HNC = 118.63°, ∠NCN = 170.63°, ∠HN ··· NH = 88.99°. The number of digits quoted allow for errors with two significant figures. In order to obtain these values we recorded rotational—torsional spectra of HN13CNH, H15NC15NH and DNCND, by using isotopically enriched cyanamide. A chemical equilibrium exists between carbodiimide, HNCNH, and the more stable isomer cyanamide, H2NCN, which strongly favours cyanamide (approximately 1:115 at 110 °C). The expensive C- and N-substituted isotopomers could only be investigated in the millimetre wave region, while for DNCND the far infrared spectrum between 10–350 cm?1 was also recorded. Rotational constants of the three isotopomers, as well as of the parent species, were determined by fitting the assigned spectral transitions to the Watson Hamiltonian in S reduction. Using fitting programs written by Schwendeman and Rudolph, r o, rs and rρ m structures of HNCNH were derived. The experimentally determined structural parameters are compared with an ab initio re structure. 相似文献
13.
Pioneering experiments on creating Cu(In)/p-ZnAs2 photosensitive Schottky barriers on monoclinic ZnAs2 single crystals grown by directional crystallization from a near-stoichiometric melt are described. Photosensitivity spectra
are taken from the structures in natural and linearly polarized radiations. The structures are found to be sensitive to polarization.
From the photoactive absorption spectra of the monoclinic ZnAs2, it follows that most minimal direct band-to-band transitions in these crystals are allowed in the E ∥ z axis polarization and can be used, specifically, in designing novel devices-polarization—controlled switches of spectral
ranges of incident radiation photorecording. 相似文献
14.
The electronic structure of the alkali-earth fluorides CaF2, BaF2, SrF2, and PbF2 with Frenkel defects is investigated in the tight-binding approximation by the LMTO method. The defect formation and migration
energies are calculated. The electronic structure and optical excitations of a H center in a defective fluorite structure are examined. It is shown on the basis of calculations of the binding energies that
CaF2, BaF2, and SrF2 are ionic compounds, while the chemical bond in PbF2 is partially covalent. Possible methods of displacement of interstitial fluorine atoms that lead to the observed optical
spectra of an H center are investigated.
Fiz. Tverd. Tela (St. Petersburg) 40, 2019–2025 (November 1998) 相似文献
15.
M. Maczka A. V. Knyazev N. Yu. Kuznetsova M. Ptak L. Macalik 《Journal of Raman spectroscopy : JRS》2011,42(3):529-533
Raman and infrared (IR) spectra of defect pyrochlores TaWO5.5, NH4SbWO6·H2O, HSbWO6·H2O, LiSbWO6·H2O, NaSbWO6·H2O, KSbWO6, RbSbWO6, CsSbWO6, and TlSbWO6 were measured. The obtained spectra are discussed using the factor group approach for the cubic Fd‐3m space group, and assignment of bands to respective motions of atoms is proposed. Our results show that the phonon properties of the pyrochlores are strongly affected by disorder, and therefore Raman and IR spectroscopies are very useful tools in studying disorder in this family of compounds. In particular, our studies have shown that in these ionic conductors disorder at sites occupied by NH , H+, or alkali‐metal ions decreases with increasing size and mass of these ions. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
16.
The Raman and FTIR spectra of three metal guanidinium sulfates, [C(NH2)3]2MII(H2O)4(SO4)2, (MII = Mn, Cd and VO), are recorded. The observed spectral bands are assigned in terms of the fundamental modes of vibration of the guanidinium ions, sulfate groups and water molecules. The appearance of the sulfate tetrahedra's ν1 and ν2 modes in the IR spectra and the partial lifting of the ν4 mode in the Raman spectra indicate the distortion of the SO42− tetrahedra in the structure, so that its symmetry is lowered from Td to C1. The geometry of the sulfate group in guanidinium vanadyl sulfate does not deviate much from that of the average sulfate group. The distortion of the SO4 tetrahedra is stronger in GuCds than in GuMnS. The CN3 group in the guanidinium ion is planar (D3h point group) in GuCdS and GuMnS, whereas it is lowered in the vanadyl compound. Furthermore, the spectral analyses show the presence of weak hydrogen bonds in the structures. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
17.
Structures and luminescence properties of Yb3+ in the double perovskites Ba2YB'O6 (B'=Ta5+, Nb5+) phosphors
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The Yb3+ doped Ba2YB'O6 (B'=Ta5+, Nb5+) were prepared by high temperature solid-state reaction method, their structures were determined by x-ray diffraction and refined by Rietveld method. The diffuse reflection absorption, excitation and emission spectra of Yb3+:Ba2YB'O6 (B'=,Ta5+, Nb5+) were measured at room temperature. Under the excitation of ultraviolet light, these phosphors exhibit broad charge transfer band emissions of TaO6 or NbO6 centre with large Stokes shift. The Yb3+ doped into these hosts are situated at Y3+ sites of cubic symmetry (Oh). The experimental energy levels of Yb3+ in Ba2YTaO6 and Ba2YNbO6 were determined by photoluminescence and diffuse reflection absorption spectra. Their wavefunctions and theoretical energy levels were obtained by diagonalising the Hamiltonian matrix. The experimental energy levels were fitted by Levenberg--Marquardt iteration algorithm to determine crystal field parameters. Then, the magnetic-pole transition line strengths of Yb3+:Ba2YB'O6(B'=Ta5+, Nb5+) from (2F5/2)Γ8- to the low-energy states were calculated. 相似文献
18.
基于密度泛函理论,采用第一性原理分子动力学模拟退火方法,对Li-n-1,Lin,Li+n+1 (n=20,40)的最低能量结构进行了全局搜索. 发现锂团簇的生长模式是以单个或多个嵌套的正多面体为核心,其余原子以五角锥为基本单元围绕核心生长. 基于最低能量结构的第一性原理电子结构计算得到锂团簇的分子轨道能级分布与无结构凝胶模型给出的电子壳层完全一致. 在总电
关键词:
团簇
电子结构
极化率
光吸收 相似文献
19.
用密度泛函理论的杂化密度泛函B3LYP方法在6-31G*基组水平上对[Mg(NH2)2]n(n=1—5)团簇各种可能的构型进行几何结构优化,预测了各团簇的最稳定结构.对最稳定结构的振动特性、成键特性、电荷特性等进行了理论研究.结果表明:团簇易形成链状结构,Mg—N键长为0.190—0.234 nm,N—H键长为0.101—0.103 nm,H—N—H键角为100.2°—107.5°;团簇中M
关键词:
2)2]n(n=1—5)团簇')" href="#">[Mg(NH2)2]n(n=1—5)团簇
密度泛函理论
结构与性质
储氢材料 相似文献
20.
The infrared and Raman spectra, heat of formation (HOF) and thermodynamic properties were investigated by B3LYP/6-31G** method for a new designed polynitro cage compound 1,3,5,7,9,11-hexo(N(CH3)NO2)-2,4,6,8,10,12-hexaazatetracyclo[5,5,0,0,0]dodecane. The detonation velocity (D) and pressure (P) were predicted by the Kamlet–Jacobs equations based on the theoretical density and condensed HOF. The bond dissociation energies and bond orders for the weakest bonds were analysed to investigate the thermal stability of the title compound. The computational result shows that the detonation velocity and pressure of the title compound are superior to those of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), but inferior to those of 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane (HMX) and hexanitrohexaazaisowurtzitane (HNIW). And the analysis of thermal stability shows that the first step of pyrolysis is the rupture of the N7–NO2 bond. The crystal structure obtained by molecular mechanics belongs to the P21 space group, with the lattice parameters Z = 2, a = 11.8246 Å, b = 10.4632 Å, c = 15.9713 Å, ρ = 1.98 g cm?3. 相似文献