基于石墨烯Tamm等离子体激元的太赫兹强耦合效应

设计了一种全新的一维石墨烯-光子晶体(PhC)复合谐振结构,使用传输矩阵法(TMM)对其所支持的太赫兹Tamm等离子体激元(TPP)和腔体模式(CM)之间的强耦合效应进行理论研究。研究表明,用于表征耦合强度的Rabi分裂能随着光子晶体周期数的减小而增大;改变间隔层和腔体厚度以及石墨烯的费米能级时,也会影响Rabi分裂能。最后通过入射角度对耦合模式进行主动调控,当入射角处于0°~60°时,耦合模式的特性与偏振无关。本文的研究结果为太赫兹强耦合效应的研究和应用提供了新的思路。     

含Cu~(2+)云母的结构特性研究

含Cu~(2+)云母K_(1.66)Ba_(0.17)[Mg_5-_xCu_x][Si_8V_(20)]F_4(x=0～3)具有2M_1多型,在这种人工合成的新型云母中,CU—Mg类质同象取代对其晶体结构有影响。随着Cu含量的增加,晶胞参数b增大,β减小,反映在其粉晶衍射图上的d_(060)值增大。引起这些变化的原因是由于阳离子半径增大而导致了云母晶体结构中配位八面体的变形。     

Growth and characterization of dexterous nonlinear optical material: Dimethyl amino pyridinium 4-nitrophenolate 4-nitrophenol (DMAPNP)

The crystals (dimethyl amino pyridinium 4-nitrophenolate 4-nitrophenol [DMAPNP] suitable for NLO applications were grown by the slow cooling method. The solubility and metastable zone width measurement of DMAPNP specimen was studied. The material crystallizes in the orthorhombic crystal system with noncentrosymmetric space group of P2₁2₁2_1. The ocular precision in the intact visible region was found to be good for non-linear optical claim. Quality of the grown crystal is ascertained by the HRXRD and etching studies. Laser Damage Threshold and Photoluminescence studies designate that the grown crystal contains less imperfection. The mechanical behaviour of DMAPNP sample at different temperatures was investigated to determine the hardness stability of the grown specimen. The piezoelectric temperament and the relative Second Harmonic Generation (for diverse particle sizes) of the material were also studied. The third order nonlinear optical properties of DMAPNP crystals were premeditated by Z-scan method. Birefringence and optical homogeneity of the crystal were evaluated using modified channel spectrum method. The half wave voltage of the grown crystal deliberate from the elector optic experimentation. Photoconductivity measurement specified consummate of inducing dipoles owing to brawny incident radiation and also disclose the nonlinear activities of the grown specimen.     

An investigation of Eu-doped CaAlSiN3 fabricated by an alloy-nitridation method

We have synthesized CaAlSiN₃:Eu phosphors through an alloy-nitridation method with stable alloys as main starting materials, and investigated their crystal structures and photoluminescence properties in three aspects as below: (1) different Eu concentrations; (2) different Eu dopants; (3) different Al/Si molar ratios. The lattice volume calculated by using Rietveld refinement on the base of XRD analysis, decreases with oxygen incorporating, increases with the Al/Si ratios, and shows a limited expansion with the raise of Eu concentrations in CaAlSiN₃:Eu crystal lattice. The concentration quenching and the shifts of emission bands are investigated and discussed in details. The different lattice volumes deriving from corresponding compositions have an important effect on photoluminescence properties. This work provides some methods to tune the emission wavelengths of CaAlSiN₃:Eu phosphors.     

The effect of random grain distributions on fatigue crack initiation in a notched coarse grained superalloy specimen

Coarse grained superalloys are of large interest in high temperature applications, and can be found in e.g. gas turbine components, where great care must be given with respect to high temperature fatigue. Due to the large grain size, the material behaviour at e.g. sharp notches cannot be considered homogeneous. As a consequence, the fatigue behaviour is likely to expose a large variation. In order to numerically investigate this variation, a Monte Carlo analysis has been carried out by 100 FE-simulations of notched specimens, where placements and orientations of the grains were randomised. Furthermore, each grain was modelled as a unique single-crystal, displaying both anisotropic elastic and plastic behaviour and tension/compression asymmetry. The effect of randomness was investigated by the obtained dispersion in fatigue crack initiation life. It was concluded that the fatigue life behaviour of coarse grained nickel-base superalloys may show a considerable variation, which cannot be captured by one single deterministic analysis based on data for a homogenised material. Furthermore, the dispersion is of such a magnitude that it needs to be taken into account in industrial applications where highly stressed coarse grained materials are used.     

Crystal growth and characterization of Ho-doped Lu3Ga5O12 for 2 μm laser

Ho:LuGG single crystal was successfully grown by the Czochralski growth method, and its lattice parameter was found to be 12.2371 Å. Its thermal conductivity was measured to be 5.29 W mK⁻¹ at 300 K. Meanwhile, transmission spectra were recorded at room temperature, and then its absorption spectra were obtained combining with the transmission spectra of LuGG crystal. The transition intensity parameters Ω_t (t = 2, 4, 6), the oscillator strengths, fluorescence branching ratios, transition probabilities and the lifetimes of Ho³⁺ in LuGG crystal were all evaluated by the Judd–Ofelt theory. Furthermore, its emission spectra were also determined and analyzed.     

Grain-level statistical plasticity analysis on strain cycle fatigue of a FCC metal

The micromechanical strain cycle fatigue-life is systematically investigated by the micro-level numerical simulation, compared with symmetrical strain cycle experiments of copper, focusing on the characteristics of polycrystalline aggregation and the mechanism of microscale plastic deformation. A methodology to predict the low-cycle fatigue life by micro-level simulation along with statistical analysis is proposed through the following steps: (1) A crystal plasticity model is developed based on the nonlinear kinematic hardening mechanism of crystal slipping system. This model is applied to the calculations of crystal grain interior stresses and plastic strains. (2) A statistical representative volume element (SRVE) is constructed for a pure copper as a material model which features a polycrystalline Voronoi aggregation consisting of a number of crystal grains. This SRVE can be used for statistical analysis of the material inhomogeneous stresses and strains during cycle loading. (3) The simulations are performed to model the experimental cycle evolution of strain fatigue by using the SRVE under the symmetrical tensile–compressive loading. (4) Statistical and micromechanical analyses are carried out for the inhomogeneous interior stresses and strains of the SRVE of the polycrystalline copper in the low cycle regime. The resulting analysis can render the microscale interpretation and numerical simulation for the low-cycle fatigue evolution accordingly.     

Size effect on IMC growth induced by Cu concentration gradient and pinning of Ag3Sn particles during multiple reflows

Size effect on growth kinetics of interfacial intermetallic compound (IMC), induced by Cu concentration gradient and pinning effect of Ag₃Sn particles during multiple reflows, was investigated in this article. The simulation results, for Cu distributions in solder bulks of different volumes after a single reflow for 60 s at 250 °C, show that Cu concentration gradient in liquid increases with the growing size of solder bump. On the contrary, resistive pressure of nano particles decreases gradually with the increasing bump size. In conclusion, the pinning effect of Ag₃Sn particles on IMC grains plays a dominant role in small samples, whereas the inhibiting effect of Cu concentration gradient is mainly functional in big samples. Combining the two factors, solder bump in an intermediate diameter of 800 μm benefits most and has the largest IMC thickness during multiple reflows.     

Investigation of thermal and magnetic behaviour of mixed valence iron hydroxyphosphate from Fe3(PO4)2(OH)2 lipscombite systems

Iron hydroxyphosphates are promising candidates for applications as cathode materials for Li-ion batteries, for example and present low production cost and reduced toxicity. In this work, a new fast method is proposed for the synthesis of mixed valence iron hydroxyphosphate from Fe₃(PO₄)₂(OH)₂ lipscombite systems. The as-obtained products were characterized by X-ray diffraction, FT-IR spectroscopy, scanning electron microscopy, and magnetic measurements were carried out. Thermal treatment performed at 300 °C and 500 °C for 4 h indicate the formation of other lipscombite phases in accordance with thermogravimetric analysis where two weight loss steps were observed at ∼200 °C and ∼450 °C. A complex magnetic behaviour is observed with antiferromagnetic interactions at T_N ∼140 K for the pristine lipscombite Fe₃(PO₄)₂(OH)₂ compound related to the strong magnetic interactions in the 3D crystal structure with small values for Fe-Fe distances and super-exchange contribution through PO₄ tetrahedra.     

Determination of deuterium site occupancy in ZrCoD3 and its role in improved durability of Zr–Co–Ni deuterides against disproportionation

In the present study, we have for the first time reported the occupancy of deuterium in a new interstitial site of ZrCoD₃ which explain the hydrogen induced disproportionation behavior of ZrCo alloy. We have also reported the effect of Ni substitution on interstitial site occupancy of deuterium in ZrCo_1−xNi_xD₃, which in turn explains the improved durability of these Ni substituted deuterides against disproportionation. The crystal structure of the ZrCo_1−xNi_x (x = 0.0, 0.1, 0.2, 0.3) deuterides was investigated by X-ray powder diffraction and neutron diffraction methods. The XRD data reveals a single phase formation for all deuterides with varying Ni content (x). The neutron diffraction study shows that deuterium occupies a new site 8e in addition to 4c₂ and 8f₁. Additionally, the Zr–D distance in 8e site is shorter than that in ZrD₂. Therefore, increase in 8e site occupancy will in turn decreases the durability against disproportionation and vice-versa. Furthermore, the neutron diffraction reveals that occupancy of new 8e site decreases and its Zr–D distance increases with increase in Ni content, which explicate the higher durability against disproportionation for Ni rich compound.