二维单原子斐波那契类准晶电子能谱特性研究

利用单电子、紧束缚、最近邻座模型,在重整化群的基础上,用分解-消元法分析了二维单原子斐波那契类准晶FC(n)的电子能谱分裂规律,数值计算了其电子能谱值,发现在一级近似下,该类二维准晶格中全部都只存在n×n,n×(n+1),(n+1)×(n+1)等三种原子簇分子,相应的能谱按Y_m-n-l方式分裂,得出了其电子能谱的能级数目通式,发现描述其能级数目的参量存在所谓的“斐波那契类数集合”,并且确定了该集合的前11个整数的稳定值,找出了有关斐波那契类数集合的经验公式.分析结果与数值计算值相符 关键词： 斐波那契类 准晶 电子能谱 重整化群     

Piecewise linear integrated optical device as an optical isolator using two-port nonlinear ring resonators

A nonlinear (piecewise linear) optical transfer function for optical applications generally and isolator especially is introduced and a realization method for the introduced block based on array of two-port nonlinear ring resonators is proposed. The effect of system parameters on the transfer function is studied. The characteristics of the introduced nonlinear device such as the threshold value and the slope of linear part can be controlled using the coupling coefficients and ring lengths. We show that using our proposed idea, easily more than 30-dB isolation well over 3 THz can be obtained only with similar two rings. Also, insertion loss less than 1 dB can be obtained using optical amplifier between rings. The proposed circuit is compact (0.2 mm²) and easily can be integrated with semiconductor lasers as well as other integrated devices and systems. Finally, the analytical result for approximation of the threshold and slope of linear part is presented.     

Splitting rules for the electronic energy spectra of 2D FC(n) with three kinds of atoms and one bond length

In this paper we study the splitting rules of energy spectra for two-dimensional Fibonacci-class quasilattices (FC(n)) with three kinds of atoms (A, B, and C) and one bond length by means of a decomposition-decimation method, and find that the sublattices of B atoms and C atoms are different from those of normal two-dimensional FC(n) and the corresponding splitting manners are new and interesting. B atom forms a kind of two-dimensional so-called FC(n)’, which structure is some different from that of normal FC(n-1) (n≥2), but the spectra lines are as the same as that of the latter. C atom forms two kinds of interesting one-dimensional periodic chains: n-atom chain and (n-1)-atom chain, which spectra will both tend to become continuous, respectively. The analytical results are confirmed by numerical simulations.     

光在按特殊准晶方式排列的媒质中的传播

简单介绍Fibonacci-class准晶(FC(n))的结构特性，利用电场理论和二阶单位模矩阵的特殊性质，研究了光在按FC(n)准晶链排列的多层介质膜中传播时的光透射性质，发现FC(2m)的透射系数具有开关性质，FC(2m+1)的透射系数具有六循环性质，它们的最大值在π(1/2±k)附近具有有趣的性质. 关键词：     

On the rotational intensity distribution in the a1Δg → X3Σg− magnetic dipole transition of oxygen molecule

The relative intensity distribution in the rotational structure of the a¹Δ_g → X³Σ_g⁻ magnetic dipole transition of molecular oxygen is examined. Use is made of experimental data obtained from the high-resolution (0.02 cm⁻¹) FTS recording of the 0-0 band published by C. Amiot and J. Verges (Canad. J. Phys. 59, 1391–1398 (1981)). Comparison of the experimental and theoretical intensities indicates that rotational linestrength formulas containing purely vibronic transition moments are inadequate and need to be supplemented by two additional parameters of rovibronic origin.     

Ab initio calculations study of the electronic, optical and thermodynamic properties of NaMgH3, for hydrogen storage

The structural stability, electronic structure, optical and thermodynamic properties of NaMgH₃ have been investigated using the density functional theory. Good agreement is obtained for the bulk crystal structure using both the local density approximation (LDA) and the generalized gradient approximation (GGA) for the exchange-correlation energy. It is found from the electronic density of states (DOS) that the valence band is dominated by the hydrogen atoms while the conduction band is dominated by Na and Mg empty states. Also, the DOS reveals that NaMgH₃ is a large gap insulator with direct band gap 3.4 eV. We have investigated the optical response of NaMgH₃ in partial band to band contributions and the theoretical optical spectrum is presented and discussed in this study. Optical response calculation suggests that the imaginary part of dielectric function spectra is assigned to be the interband transition. The formation energy for NaMgH₃ is investigated along different reaction pathways. We compare and discuss our result with the measured and calculated enthalpies of formation found in the literature.     

Investigations of the optical band positions,EPR parameters and defect structure for the trigonal Cr3+–Li+ centre in CsMgCl3 crystal

A unified calculation of optical band positions and electron paramagnetic resonance (EPR) (or spin-Hamiltonian) parameters for the trigonal Cr³⁺–Li⁺ centre in CsMgCl₃ crystal is made by using the complete diagonalisation (of energy matrix) method based on the two-spin–orbit-parameter model. In this model, the contributions from the spin–orbit parameter of central dⁿ ion and that of ligand ion are included. From the calculation, the 11 observed optical and EPR data (eight optical band positions and three EPR parameters g_//, g_⊥, D) are reasonably explained with five adjustable parameters and the defect structure of the Cr³⁺–Li⁺ centre (which is consistent with the expectation based on the electrostatic interaction) in CsMgCl₃ is acquired. The results are discussed.     

Unique optical traits of Sm3+ -doped magnesium borate glass

A series of Sm³⁺-doped magnesium borate glasses were prepared using the melt quenching and characterized to determine the effects of various Sm³⁺ contents on their optical traits. The absorption and luminescence spectra of the glasses revealed ten and four significant peaks, respectively. In addition, the experimental results on the optical properties were validated using the Judd-Ofelt (J−O) analyses. The obtained J−O intensity parameters (Ω_λ with λ = 2, 4, 6) confirmed the structural changes in the host network due to the Sm³⁺ doping. The value of Ω₂ for the studied glasses indicated the covalent and asymmetric nature of the Sm³⁺− O² linkages. The achieved J−O radiative parameters (quality factor, branching ratio and stimulated emission cross-section) were highest for the glass made with 0.5 mol% of Sm³⁺, demonstrating its lasing potency. The proposed glass compositions may be beneficial for the photonic devices.     

一种基于石墨烯的超宽带吸波器

隐身技术对降低飞行器目标的雷达散射截面、提高飞行器目标的生存能力具有重要的意义和价值, 而在飞行器目标上引入吸波器结构是一种重要的隐身手段. 然而, 目前已有吸波器的研究主要集中在单频或多频窄带方面. 为了拓展吸波器工作频带, 基于石墨烯材料提出了一种工作于S/C波段的新型超宽带吸波器模型单元, 其中包含一个用石墨烯材料设计的方圆形双环周期结构. 调节石墨烯的表面阻抗, 使得吸收率超过90%的频带范围为2.1-9.0 GHz, 相对带宽约为124%, 实现了超宽带的吸波特性; 鉴于模型的高度对称性, 提出的吸波器模型表现出对入射波极化不敏感的吸波特性; 在不改变模型结构情况下, 调节石墨烯的静态偏置电场, 亦可调控吸波器谐振在2.0-9.0 GHz频带范围内的任意频率点处, 且达到超过99%的吸收效果. 最后采用等效电路模型方法和波的干涉理论对其吸波机理进行深入研究与分析: 从等效电路角度来讲, 方形和圆形环分别引入高、低吸波谐振频率, 二者优化叠加拓展了吸波带宽; 从干涉理论方面来看, 吸波器表面处的首次反射波与透射波的多次出射波形成较强的干涉相消现象, 有效减少了吸波器的反射回波.     

Synthesis and characterization of conducting polypyrrole-containing iron complexes

Electrochemical or chemical oxidation of pyrrole-containing complex anions of iron cyanide or iron chloride results in the formation of films or powders of conducting polypyrroles. Freshly prepared films exhibit an additional IR band at ca 1630–1640 cm⁻¹, slowly disappearing in air and not observed in previously studies polypyrrole-based systems. It is possible that this new band is associated with the existence of a CN bond in dehydrogenated pyrrole rings which are transformed into regular pyrrole rings, probably due to the protonation reaction occurring in air and simultaneous bond rearrangement. The polypyrrole structure favours the presence of Fe(CN)₆⁴⁻ over Fe(CN)₆³⁻ since the former is the only iron species detected by Mössbauer spectroscopy in electrochemically prepared samples. It is also the dominant iron species in the samples oxidized chemically. The polypyrrole-containing Fe(CN)₆⁴⁻ is more ordered than those containing monovalent anions, as evidence by X-ray diffraction studies. High-spin eron complexes can be inserted into polypyrrole during electrochemical oxidation of pyrrole in non-aqueous solutions containing LiCl/FeCl₃. The inserted species exhibit Mössbauer parameters characteristic of slightly distorted FeCl₄⁻.     

OMNIDIRECTIONAL HIGH REFLECTOR FOR INFRARED WAVELENGTH

We have purposed the design of omnidirectional high reflectors with wide bandwidth (nearly 6300A⁰) for the infrared wavelength. Using translational matrix method for numerical calculation, it is found that a complete photonic band gap high reflector covering the wavelength region 11500A⁰ to 17800A⁰ is obtained for the quarter wave stack air / (n_L n_H)⁷ / air by using the tellurium (n=4.60) and TiO₂ (n=2.35) as material of high reflective index and SiO₂(n=1.45) low refractive index. Due to high refractive index of contrast of the structure i.e. SiO₂/tellurium, a large complete photonic band gap, omnidirectional high reflector, has been observed for the infrared wavelengths. This type of omnidirectional high reflector can be used in telecommunication. Besides this, we have studied the effective refractive indices (phase and group) of the proposed structures. It is observed that the effective refractive indices (phase and group) of the high omnidirectional reflector band are largely changed near the band edges due to the high refractive index of contrast, and the reflections from the internal interfaces of the structure.     

Optical and structural studies on Ba(Mg1/3Ta2/3)O3 thin films obtained by radiofrequency assisted pulsed plasma deposition

Single-phase Ba(Mg_1/3Ta_2/3)O₃ thin films were prepared by radiofrequency plasma beam assisted pulsed laser deposition (RF-PLD) starting from a bulk ceramic target synthesized by solid state reaction. Atomic force microscopy, X-ray diffraction and spectroscopic ellipsometry were used for morphological, structural and optical characterization of the BMT thin films. The X-ray diffraction spectra show that the films exhibit a polycrystalline cubic structure. From spectroscopic ellipsometry analysis, the refractive index varies with the thin films deposition parameters. By using the transmission spectra and assuming a direct band to band transition a band gap value of ≈4.72 eV has been obtained.     

Optical and electrical investigations on Cu2SnS3 layers prepared by two-stage process

Cu₂SnS₃ thin films were prepared using a simple and phase-controlled two-stage process. Initially, Cu-Sn precursors were deposited by DC sputtering, followed by sulfurization at different temperatures (T_s) that vary in the range, 150 - 500 °C. An exhaustive study of the optical properties in relation to sulfurization temperature was performed using transmission and reflectance measurements. The estimated optical absorption coefficient for all the layers was very high and found to be > 10⁴ cm⁻¹. The optical band gap was determined using Tauc plots and it varied in the range, 1.49–2.34 eV with an increase of T_s. The refractive index (n) and the extinction coefficient (k) were also obtained. The optical properties like dispersion parameters, dielectric constant, dissipation factor, optical conductivity, surface energy loss function, volume energy loss function and optical haze were also calculated. Further, analysis of electrical properties such as electrical resistivity, mobility and carrier density of the prepared films with sulfurization temperature was made in order to verify the suitability of synthesized CTS layers for solar cell application.     

按斐波那契类准周期序列排列的铁电畴超晶格二次谐波谱峰性质研究

在简介斐波那契类(Fibonacci-class)准晶(FC(n))的特征基础上,在小信号、平面波近似下详细地研究了通过N层按斐波那契类准周期系列排布的铁电畴超晶格的二次谐波光场的谱性质.发现其谱的极强峰在实空间,在不考虑介质色散效应的情况下,具有完美的自相似性;对于具有线性色散效应的铁电晶体,其谱在实空间也具有相同的结论;而对于具有非线性色散效应的铁电介质,极强峰的这种自相似性将被破坏.另外,二次谐波光的暗线处将存在缺级效应;亮线处则无缺级效应. 关键词：     

一维Fibonacci类准晶的衍射性质

利用傅里叶变换方法推导了一维Fibonacci类(FC(n))准晶衍射的结构因子方程,讨论了该系统的衍射峰和系统消光规则.在此基础上,计算了FC(1)和FC(3)准点阵的衍射谱.另外,把所得方程进行推广使之能用来研究FC(n)准周期超晶格的衍射性质.通过把FC(1)准周期超晶格衍射相对强度的计算结果与Merlin等人的实验结果进行比较,发现大多数衍射谱符合得较好,但有一条谱不一致.理论计算表明Merlin等人标定的谱(4,2)应该是一个次强峰.     

Structures,vibrational spectra,and relative energetics of FC(O)ONO and FC(O)NO2 isomers at DFT and ab initio levels

The structural and vibrational parameters of FC(O)ONO and FC(O)NO₂ isomers were examined theoretically using the B3LYP/6-311+G(3df) and CCSD(T)/6-311G(d) methods. Four conformers of FC(O)ONO isomer and one FC(O)NO₂ isomer are found here. Among them, the trans–cis and cis–cis FC(O)ONO configuration are new conformers. The energetics were refined with G3//B3LYP and CBS-QB3 calculations. The trans–trans conformer of the FC(O)ONO isomer is found to be the lowest energy structure, with an estimated heat of formation of ?104.9 kcal mol^?1 at 0 K as determined from CBS-QB3 theory. The next lowest structure is the cis–trans FC(O)ONO lying 1.7 kcal mol^?1 above the trans–trans structural form. The highest energy structure is the FC(O)NO₂ isomer with a predicted heat of formation of ?84.8 kcal mol^?1. A comparison of the relative stability of the FCNO₃ isomers with the isomers of ClCNO₃ shows that the Cl analogues follow the same pattern of stability, as do the F isomers. However, the chlorine isomers are unstable relative to their fluorine analogues.     

Analysis of reflectivity spectrum and band structure of Bi12GeO20

The fundamental reflectivity spectrum in the energy range 1.5–8.5 eV is reported for Bi₁₂GeO₂₀ (BGO) single crystals. From a Kramers-Kronig analysis the optical constants of BGO are computed. An energy level scheme for interband optical transitions is proposed. A value of 0.7 eV for the spin-orbit splitting of the valence band is suggested. Some features of the band structure are discussed, and the correlations between the band structures of BGO and A₂^VB₃^VI-compounds are indicated. The experimental premises for possible simplifications of a theoretical calculation of the band structure are given.     

Investigation of dispersion characteristic in MI- and MII-type single mode optical fibers

Dispersion characteristic of MI and MII type single mode optical fibers is analytically investigated. For this purpose modal analysis of these fibers to obtain possible wave vectors for given system parameters are done. Then using numerical evaluation of the presented analytical relations, chromatic and waveguide dispersions are calculated. The effects of geometrical and optical parameters of the fibers on dispersion characteristics are investigated. In this analysis, we show that with increase of Δ (optical parameter) for MI structure the slope of dispersion curve is decreased and the case is reversed for MII structure. Also, with rising of Q (geometric parameter) for MI structure the slope of dispersion curve is decreased and the situation is reversed for MII structure. Finally, we show that with boosting of R₂ for MII structure the slope of dispersion is increased. As a final result, our simulations show that small values for optical parameters are better in MII structure for multi-channel optical communications. In MI structure to obtain small dispersion slope, Q can be increased that is easy for fabrication in practice. Finally, Q and R₂ are suitable parameters for control of dispersion in the proposed structures.     

一维Fibonacci类准晶的衍射性质

利用傅里叶变换方法推导了一维Fibonacci类(FC(n))准晶衍射的结构因子方程,讨论了该系统的衍射峰和系统消光规则.在此基础上,计算了FC(1)和FC(3)准点阵的衍射谱.另外,把所得方程进行推广使之能用来研究FC(n)准周期超晶格的衍射性质.通过把FC(1)准周期超晶格衍射相对强度的计算结果与Merlin等人的实验结果进行比较,发现大多数衍射谱符合得较好,但有一条谱不一致.理论计算表明Merlin等人标定的谱(4,2)应该是一个次强峰.