Simulation of near-infrared photodiode detectors based on β-FeSi2/4H-SiC heterojunction

In this paper, we propose the near-infrared p-type β-FeSi₂/n-type 4H-SiC heterojunction photodetector with semiconducting silicide (β-FeSi₂) as the active region for the first time. Optoelectronic characteristics of the photodetector are simulated using a commercial simulator at room temperature. The results show that the photodetector has a good rectifying character and a good response to the near-infrared light. Interface states should be minimized to obtain a lower reverse leakage current. The response spectrum of the β-FeSi₂/4H-SiC detector, which consists of a p-type β-FeSi₂ absorption layer with a doping concentration of 1×10¹⁵ cm^-3 and a thickness of 2.5 μm, has a peak of 755 mA/W at 1.42 μm. The illumination of the SiC side obtains a higher responsivity than that of the β-FeSi₂ side. The results illustrate that the β-FeSi₂/4H-SiC heterojunction can be used as a near-infrared photodetector compatible with near-infrared optically-activated SiC-based power switching devices.     

The first high-resolution infrared study of diazirinone, N2CO: Analysis of the Fermi-coupled ν1 and 2ν5 bands

The first validated detection of the elusive diazirinone molecule (N₂CO) in the gas phase was performed using high-resolution infrared spectra recorded in the 1810–2100 cm⁻¹ region. The ν₁ and 2ν₅ bands were identified at 2043.8 and 1863.3 cm⁻¹ close to the ab initio prediction [X.Q. Zeng, H. Beckers, H. Willner, J.F. Stanton, Angew. Chem. Int. Ed. 50 (2011) 1720–1723]. For these two bands, the individual lines exhibit a (2:1) intensity alternation, confirming a three membered ring structure (C_2V symmetry) for N₂CO. The major output of the ν₁ and 2ν₅ bands analysis is the first experimental determination of the ground-state rotational constants of cyclic N₂CO. The observed intensity pattern of the ν₁ and 2ν₅ bands is in agreement with the existence of a strong Fermi resonance coupling the 1¹ and 5² energy levels.     

Structure and photoluminescence of β-Ga2O3:Eu nanofibers prepared by electrospinning

Eu³⁺-doped β-Ga₂O₃ nanofibers were fabricated by electrospinning. The influence of Eu³⁺ concentration on the photoluminescence properties of the obtained nanofibers was investigated. The morphology and structure of β-Ga₂O₃:Eu³⁺ were characterized by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) and Raman spectra. The diameter of the Eu³⁺-doped β-Ga₂O₃ nanofibers was in the range of 180-300 nm. When the β-Ga₂O₃:Eu³⁺ nanofibers were excited by 325 nm wavelength, the main emission peak of the samples was 620 nm (⁵D₀→⁷F₂), which corresponded to a typical red emission (⁵D₀→⁷F_j (j = 1, 2, 3, 4) intra-4f transitions of Eu³⁺ ions). In addition, the concentration quench effect and energy transfer mechanism in β-Ga₂O₃:Eu³⁺ were also discussed.     

Luminescence of silicon Dioxide — silica glass, α-quartz and stishovite

This paper compares the luminescence of different modifications of silicon dioxide — silica glass, α-quartz crystal and dense octahedron structured stishovite crystal. Under x-ray irradiation of pure silica glass and pure α-quartz crystal, only the luminescence of self-trapped exciton (STE) is detected, excitable only in the range of intrinsic absorption. No STE luminescence was detected in stishovite since, even though its luminescence is excitable below the optical gap, it could not be ascribed to a self-trapped exciton. Under ArF laser excitation of pure α-quartz crystal, luminescence of a self-trapped exciton was detected under two-photon excitation. In silica glass and stishovite mono crystal, we spectrally detected mutually similar luminescences under single-photon excitation of ArF laser. In silica glass, the luminescence of an oxygen deficient center is presented by the so-called twofold coordinated silicon center (L.N. Skuja et al., Solid State Commun. 50, 1069 (1984)). This center is modified with an unknown surrounding or localized states of silica glass (A.N. Trukhin et al., J. Non-Cryst. Solids 248, 40 (1999)). In stishovite, that same luminescence was ascribed to some defect existing after crystal growth. For α-quartz crystal, similar to silica and stishovite, luminescence could be obtained only by irradiation with a lattice damaging source such as a dense electron beam at a temperature below 80 K, as well as by neutron or -irradiation at 290 K.     

Rare decays of Λ b → Λ γ and Λ b → Λ l + l ? in universal extra-dimension model

The exclusive weak decay of Λ _b →Λ γ and Λ _b →Λ l ⁺ l ⁻ are investigated in the Appelquist–Cheng–Dobrescu model, which is an extension of the standard model in the presence of universal extra dimensions. Employing the transition form factors obtained in the light-cone sum rules, we analyze how the invariant-mass distribution, the forward–backward asymmetry and the polarization asymmetry of the Λ baryon of these decay modes can be used to constrain the only additional free parameter with respect to the standard model, namely, the radius, R, of the extra dimension. Our results indicate that the Kaluza–Klein modes can lead to approximately 25% suppression of the branching ratio of Λ _b →Λ γ; however, their contributions can bring about 10% enhancement to the decay rate of Λ _b →Λ l ⁺ l ⁻. It is shown that in the present scenario the zero position of the forward–backward asymmetry of Λ _b →Λ μ ⁺ μ ⁻ is sensitive to the compactification parameter R, while the measurement of polarizations of Λ baryon in the Λ _b decays are not a useful tool to provide any valuable information for the universal extra-dimension model.     

Radiative scalar-meson decays f0(980) → ρ(ω)γ and a0(980) → ρ(ω)γ within the local Nambu-Jona-Lasinio model

The widths with respect to the radiative decays f ₀(980) → ργ and a ₀(980) → ωγ were calculated within the local Nambu-Jona-Lasinio model. The contributions of both quark and meson loops were taken into account. The latter and the former play a dominant role for the radiative decays of, respectively, the f ₀(980) and the a ₀(980) meson.     

The 2ν1, 2ν2 and 2ν3 overtones of FClO3

The infrared spectra of the 2ν₁, 2ν₂ and 2ν₃ overtones of perchloryl fluoride, FClO₃, have been recorded at high resolution using monoisotopic pure samples. Four symmetric top species have been investigated: F³⁵Cl¹⁶O₃, F³⁷Cl¹⁶O₃, F³⁵Cl¹⁸O₃ and F³⁷Cl¹⁸O₃. The v_i = 2, i = 1, 2, 3 vibrationally excited states are totally symmetric, so these overtones correspond to parallel bands of medium/weak intensity, centered from 2010 to 2120 cm⁻¹ (2ν₁), from 1390 to 1430 cm⁻¹ (2ν₂) and from 1070 to 1100 cm⁻¹ (2ν₃). Most of the bands are unperturbed and their analysis was straightforward. The band origins, the rotational and centrifugal molecular constants in the v₁ = 2, v₂ = 2 and v₃ = 2 states have been determined, with standard deviations of the fits from 0.00024 to 0.00067 cm⁻¹. The 2ν₁ overtones of F³⁵Cl¹⁶O₃ and F³⁷Cl¹⁶O₃ are perturbed by an A₁/E Coriolis resonance between the v₁ = 2 state and one E component of the v₄ = 1, v₆ = 2 manifold. The 2ν₂ of F³⁷Cl¹⁸O₃ is perturbed by the same kind of interaction involving the v₁ = v₆ = 1 (E) state, at about 1396 cm⁻¹. In these bands the resonance is localized on rotational levels with specific J and K values. As a consequence, a few transitions of the perpendicular bands involving the interacting levels could be identified in the spectra. A simultaneous fit of the transitions assigned to the dyads has been performed and the parameters of the excited states have been determined, including the high order Coriolis interaction coefficient . The anharmonic constants x₁₁, x₂₂, x₃₃ of all the studied isotopologues of FClO₃, x₄₆ of F³⁵Cl¹⁶O₃, x₄₆ + g₄₆ of F³⁷Cl¹⁶O₃ and x₁₆ of F³⁷Cl¹⁸O₃, have been derived.     

单壁手性碳纳米管Γ点E1和E2振动模式

在卷曲法计算得到的单壁碳纳米管12个非简并的本征频率与手性和管径关系的基础上，继续讨论了简并的本征频率中E₁和E₂的振动模式，以及其频率与手性和管径的关系. 关键词： 单壁碳纳米管 手性管 振动模式.     

N2 and O2 pressure broadening and pressure shift in the 4ν2 band of OCS

To measure accurately OCS concentrations in planetary atmospheres, it is important to know precisely nitrogen and oxygen pressure broadening and pressure-induced shift coefficients for the lines used in the retrievals. We present in this study the corresponding coefficients for lines of the P and R branches of the 4ν₂ band of the primary isotopologue of carbonyl sulfide (¹⁶O¹²C³²S).For this purpose, infrared absorption spectra of a natural carbonyl sulfide (OCS) gas sample were recorded at an unapodized resolution of 0.004 cm⁻¹, at room temperature for different pressures of N₂ and O₂, using a Bruker IFS125HR spectrometer at the LISA Laboratory in France. The line parameters were derived using the multispectrum fitting method applied to the measured shapes of the lines, including the interference effects caused by the line overlaps.The results are compared with earlier measurements and with values calculated using a semi-classical model based upon the Robert and Bonamy formalism that reproduces rather well the experimental m (m=−J for P(J) lines and m=J+1 for R(J) lines) quantum number dependence of the N₂ and O₂ broadening coefficients. On the other hand most of the lines studied here have positive shift coefficients, which do not show any systematic dependence on m. However, in previous studies of the ν₃, 2ν₃ and ν₂ bands, these coefficients were negative for all lines.     

Biomolecule-assisted hydrothermal synthesis of Sb2S3 and Bi2S3 nanocrystals and their elevated-temperature oxidation behavior for conversion into α-Sb2O4 and Bi2O3

We have developed a novel biomolecule-assisted hydrothermal method to prepare Sb₂S₃ and Bi₂S₃ nanocrystals with various sizes and shapes, in which cysteine combined with other sulfur source can exert the synergistic effect on products. The samples were characterized XRPD, TEM, HRTEM, FESEM, and PL techniques. First, we prepared a series of Sb₂S₃ and Bi₂S₃ nanocrystals by simply adjusting the composition of sulfur sources under hydrothermal conditions. Then, we studied the elevated-temperature oxidation behavior of these sulfides in air, which can lead to the formation of α-Sb₂O₄ and Bi₂O₃ samples at 600 °C for 3 h. The optical properties of the α-Sb₂O₄ and Bi₂O₃ samples were also discussed.     

Surface reconstruction on stishovite SiO2,HfO2 and rutile TiO2 （001）

This paper systematically investigates the surface reconstruction processes and patterns on stishovite SiO 2,HfO 2 and rutile TiO 2 (001) by using classical molecular dynamics.It is found that these three surfaces relax instead of reconstruction at 0 K,and have little possibility to reconstruct below 40 K.Above 40 K,surface reconstructions take place as collective atomic motion which can be speeded by higher temperature or compressed strain.Several reconstruction patterns with approximate surface energies are found,and electrostatic potentials on them are also provided in comparison with possible microscopic results.     

Line shifts in the ν2, 2ν2, and ν4 bands of NH3 perturbed by O2

Pressure-induced line shift coefficients have been measured for more than 200 rovibrational lines of NH₃ perturbed by O₂ at room temperature (T = 295 K) in some branches of the ν₂, 2ν₂, and ν₄ bands. These lines with J values ranging from 1 to 13 are located in the spectral range 800-1800 cm⁻¹. Experiments were made with a high-resolution Fourier transform spectrometer. The treatment of vibration-rotation lines includes interference effects caused by the overlapping of lines. The O₂ pressure-induced shift coefficients have been derived from the non-linear least-squares multi-pressure fitting technique. The results illustrate a vibrational dependence of line shifts with vibrational quantum number. Most of the measured shifts are negative in the ν₄ band. They are positive for the ν₂ and 2ν₂ bands. The measured shift coefficients are compared with previous measurements and with those calculated from a semiclassical theory based upon the Robert-Bonamy formalism extended to the case of symmetric top molecule with inversion motion. The predictions are generally in satisfactory agreement with the experimental data. Analyses of measured and predicted results illustrate that these shifts mainly originate from the isotropic part of the intermolecular potential.     

H掺杂α-Fe2O3的第一性原理研究

α-Fe₂O₃是一种重要的磁性半导体材料, 在电子器件中应用广泛, 具有重要的研究意义. 本文基于密度泛函理论, 采用GGA+U方法, 应用第一性原理对间隙H掺杂前后的六方相α-Fe₂O₃的晶格常数、态密度、Bader 电荷分布进行了计算分析. 研究了U值对结果的影响, 发现U=6 eV时, 体相α-Fe₂O₃的晶胞平衡体积、Fe原子磁矩、带隙值与实验值最符合. 在选取合适U值后, 第一性原理计算结果表明, H掺杂后, 间隙H部分被氧化, 其最近邻的Fe 和O部分被还原, H和O有一定程度的成键. 在费米面附近, 出现了新的杂化能级, 杂化能级扩展了价带顶的宽度, 同时导带底下移, 引起带隙减小, 表明H掺杂是一种有效的能带结构调控方法.     

Varistor and dielectric properties of Cr2O3 doped SnO2–Zn2SnO4 composite ceramics

Cr₂O₃ doped SnO₂–Zn₂SnO₄ composite ceramics were prepared by traditional ceramic processing and the varistor, dielectric properties were investigated. With increasing Cr₂O₃ content, the breakdown electrical field E_B increases from 11 to 92 V/mm and the relative dielectric constant ε_r measured at 1 kHz, 50 °C decreases from 11,028 to 3412, respectively. The barrier height ?_B about 0.8–0.84 eV and the decreasing of SnO₂ grain size suggest that the varistor behavior with high ε_r is originated from SnO₂–SnO₂ or SnO₂–Zn₂SnO₄ grain boundary. In the dielectric spectra lower than 1 kHz, a dielectric peak is presented and depressed with increasing bias voltage. Similarly, at high temperature, the dielectric constant also presents a dielectric peak in the temperature spectra and the peak becomes faint with increasing frequency. The exhibition of the dielectric peak is thought to be attributed to the conduction of grain boundary since it is accompanied by the sharp increase of dielectric loss. In addition, a dielectric relaxation with the activation energy about 0.4–0.5 eV was observed in the temperature range of 20–100 °C. Based on the results, the formation mechanism of Schottky barriers at grain boundaries and the varistor behavior with high dielectric constant are well understood.     

Black Cr/α-Cr2O3 nanoparticles based solar absorbers

Monodisperse spherical core–shell particles of Cr/α-Cr₂O₃ with high adhesion were successfully coated on rough copper substrates by a simple self-assembly-like method for the use in solar thermal absorbers. The structure and morphology of the core-shell particles of Cr/α-Cr₂O₃ were effectively controlled by deposition temperature and the pH of the initial precursor solution. Their characterizations were carried out with X-ray diffraction, scanning electron microscopy, energy dispersive spectrometry and attenuated total reflection, as well as UV–vis diffuse reflectance spectroscopy. The samples aged for more than 40 h at 75 °C exhibit the targeted high absorbing optical characteristic “Black chrome” while those aged for ≤40 h show a significant high UV–vis diffuse reflectance “green color”.     

Study of B c → J / ψ π , η c π decays with?perturbative?QCD?approach

The B _c →J/ψ π, η _c π decays are studied with the perturbative QCD approach. It is found that the form factors and for the B _c →J/ψ, η _c transitions and the branching ratios are sensitive to the parameters ω, v, f _J/ψ and , where ω and v are the parameters of the charmonium wave functions for a Coulomb potential and the harmonic-oscillator potential, respectively, and f _J/ψ and are the decay constants of the J/ψ and η _c mesons, respectively. The large branching ratios and the clear signals of the final states make the B _c →J/ψ π, η _c π decays the prospective channels for measurements at the hadron colliders.     

外电场辅助化学气相沉积方法制备网格状β-Ga2O3纳米线及其特性研究

利用外电场辅助化学气相沉积（CVD）方法,在蓝宝石衬底上制备出了由三组生长方向构成的网格状β-Ga₂O₃纳米线.研究了不同外加电压大小对β-Ga₂O₃纳米线表面形貌、晶体结构以及光学特性的影响.结果表明：外加电压的大小对样品的表面形貌有着非常大的影响,有外加电场作用时生长的β-Ga₂O₃纳米线取向性开始变好,只出现了由三组不同生长方向构成的网格状β-Ga₂O₃纳米线;并且随着外加电压的增加,纳米线分布变得更加密集、长度明显增长.此外,采用这种外电场辅助的CVD方法可以明显改善样品的结晶和光学质量.     

Ni/α-Al2O3催化剂作用下苯甲醚的加氢脱氧

Ni-based catalysts supported on di erent supports (α-Al₂O₃,γ-Al₂O₃, SiO2, TiO₂, and ZrO₂) were prepared by impregnation. Effects of supports on catalytic performance were tested using hydrodeoxygenation reaction (HDO) of anisole as model reaction. Ni/α-Al₂O₃ was found to be the highest active catalyst for HDO of anisole. Under the optimal conditions, the anisole conversion is 93.25% and the hydrocarbon yield is 90.47%. Catalyst characteriza-tion using H₂-TPD method demonstrates that Ni/α-Al₂O₃ catalyst possesses more amount of active metal Ni than those of other investigated catalysts, which can enhance the cat-alytic activity for hydrogenation. Furthermore, it is found that the Ni/α-Al₂O₃ catalyst has excellent repeatability, and the carbon deposited on the surface of catalyst is negligible.