Surface and interface phonon-polaritons in freestanding quantum well wire systems of polar ternary mixed crystals

The surface and interface phonon-polaritons in freestanding rectangular quantum well wire systems consisting of polar ternary mixed crystals are investigated in the modified random-element-isodisplacement model and the Born–Huang approximation, based on the Maxwell's equations with the boundary conditions. The numerical results of the surface and interface phonon-polariton frequencies as functions of the wave-vector, geometric structure, and the composition of the ternary mixed crystals in GaAs/Al_xGa_1−xAs and Zn_xCd_1−xSe/ZnSe quantum well wire systems are obtained and discussed. It is shown that there are 10 and 8 branches of surface and interface phonon-polaritons in the two quantum well wire systems respectively. The effects of the “two-mode” and “one-mode” behaviors of the ternary mixed crystals on the surface and interface phonon-polariton modes are shown in the dispersion curves.     

Absorption in the final state in reactions and decays in the medium

The role of strong absorption of particles in intermediate and final states has been considered. The range of applicability of phenomenological models of absorption has been studied. This model is nonuniversal. Its applicability depends on the type of interaction Hamiltonian and matrix element used. We also demonstrate that the violation of the unitarity condition can produce a qualitative error in the results. The absorption (decay) in the final state does not tend to suppress the total process probability as well as the probability of the channel corresponding to absorption. This is true for the reactions, decays and nˉ conversion in the medium.     

Laser-induced crystallization of β′-RE2(MoO4)3 ferroelectrics (RE: Sm, Gd, Dy) in glasses and their surface morphologies

The glasses with the compositions of 21.25RE₂O₃-63.75MoO₃-15B₂O₃ (RE: Sm, Gd, Dy) were prepared and the formation of β′-RE₂(MoO₄)₃ ferroelectrics was confirmed in the crystallized glasses obtained through a conventional crystallization in an electric furnace. The features of the glass structure and crystallization behavior were clarified from measurements of Raman scattering spectra. Continuous-wave Nd:YAG laser with a wavelength of 1064 nm (laser power: 0.6-0.9 W, laser scanning speed: S = 1-16 μm/s) was irradiated to 10.625Sm₂O₃-10.625Gd₂O₃ (or Dy₂O₃)-63.75MoO₃-15B₂O₃ glasses, and the structural modification was induced at the glass surface. At the scanning speed of S = 10 μm/s, crystal lines consisting of β′-Gd_2−xSm_x(MoO₄)₃ or β′-Dy_2−xSm_x(MoO₄)₃ crystals were patterned on the glass surface. It was found that those crystal lines have the surface morphology with periodic bumps. At S = 1 μm/s, it was found that crystal lines consist of the mixture of paraelectric α-Gd_2−xSm_x(MoO₄)₃ and ferroelectric β′-Gd_2−xSm_x(MoO₄)₃ crystals, indicating the phase transformation from the β′ phase to the α phase during laser irradiation. Homogeneous crystal lines with β′-RE₂(MoO₄)₃ ferroelectrics have not been written in this study, but further research is continuing.     

杭州市冬季大气气溶胶PM2.5中二恶英和多氯联苯的污染特征

2014年1月在杭州市选择5个点位采集大气颗粒物PM_2.5样品,采用同位素稀释高分辨气相色谱/高分辨质谱测定PM_2.5中的二恶英（PCDD/Fs）和多氯联苯（PCBs）,对PM_2.5的污染状况以及PM_2.5中PCDD/Fs和PCBs的污染水平及分布特征进行了研究。PM_2.5的质量浓度范围为85~168 μg/m³,PM_2.5污染较重,但与2004年同期相比明显降低。PM_2.5中PCDD/Fs的毒性当量（TEQ）为0.277~0.488 pg I-TEQ/m³,明显高于2004年同期采集样品。颗粒物中PCDD/Fs以八氯代二苯并-对-二恶英（OCDD）为主,毒性当量主要贡献者为2,3,4,7,8-五氯代二苯并呋喃（2,3,4,7,8-PeCDF）。PM_2.5中PCBs的质量浓度范围为2.9~8.1 pg/m³,二恶英类多氯联苯（DL-PCBs）的毒性当量范围为2.6~6.1 fg WHO-TEQ/m³,污染较低。PCBs在颗粒物中分布以PCB-28为主,但对毒性当量贡献最大的为PCB-126。PCDD/Fs和PCBs的气-固分配特征表现为PCDD/Fs主要分布于颗粒物中,而PCBs主要分布于气相中。     

Possible origin of room-temperature ferromagnetism in undoped GaN epilayers implanted with Mn ions

Manganese ions were implanted into unintentionally doped GaN epilayers grown by metal organic chemical vapor deposition (MOCVD). The (Ga,Mn)N and Ga_xMn_y phases were formed after Mn-implanted undoped GaN epilayers annealed at 700 and 800 °C. The samples showed ferromagnetic behavior at room temperature with the highest magnetization obtained in the sample annealed at 800 °C. Ferromagnetic signal reduces as annealing temperature increased above 900 °C. It is believed that the room-temperature ferromagnetic property of Mn-implanted undoped GaN epilayers are mainly from (Ga_,Mn)N. The Ga_xMn_y phases play a critical role in providing holes and also contribute to increasing the ferromagnetic property.     

Local atomic structures in Zr-Ni metallic glasses

Local atomic structures of Zr100−xNix (x=33.3, 36, 50 at%) binary metallic glasses were investigated by means of extended X-ray absorption fine structure (EXAFS) probe. Structural parameters show that the Zr-Ni bond length, RZr-Ni, keeps a constant value of 2.62 Å, regardless of alloy compositions. This result implies that there is a strongly chemical interaction between Zr and Ni atoms, leading to significant chemical short-range orders (CSROs) in the present metallic glasses. Further analysis indicates that the SRO structures in these metallic glasses are extremely similar with those in their crystalline counterparts. It is interesting to note that the CSROs in the eutectic Zr₆₄Ni₃₆ metallic glass consist of Zr₂Ni-like and ZrNi-like CSROs.     

The effect of Al doping on the morphology and optical property of ZnO nanostructures prepared by hydrothermal process

The undoped and Al-doped ZnO nanostructures were fabricated on the ITO substrates pre-coated with ZnO seed layers using the hydrothermal method. The undoped well-aligned ZnO nanorods were synthesized. When introducing the Al dopant, ZnO shows various morphologies. The morphology of ZnO changes from aligned nanorods, tilted nanorods, nanotubes/nanorods to the nanosheets when the Al doping concentrations increase. The ZnO nanostructures were characterized by X-ray diffraction, field emission scanning electron microscopy, X-ray photoelectron spectroscopy, photoluminescence and Raman technology. The Al doping concentrations play an important role on the morphology and optical properties of ZnO nanostructures. The possible growth mechanism of the ZnO nanostructures was discussed.     

Optical characteristics of highly ordered gallium oxide nano-islands on GaAs

A periodic array of Ga oxide islands was obtained by annealing the highly ordered Ga nano-droplets on GaAs surface at 400°C under an oxygen atmosphere for 7 hours. These Ga oxides are a mixture of α-Ga₂O₃ and β-Ga₂O₃ confirmed by Raman spectroscopy study. Enhanced optical transmission of GaAs with such ordered Ga oxide nano-islands was obtained. Both dielectric and dimensional confinement effects were considered in analysis of the electromagnetic characteristics of the nanostructured materials. Finite-difference time-domain method was used to numerically study the light transmission through the patterned Ga oxide on GaAs surface. Based on the calculated results, the light transmission enhancement is attributed to the formation of the ordered nano Ga oxides.     

ZnO-based film bulk acoustic resonator devices on a specially designed Bragg reflector

In this paper, we studied ZnO-based film bulk acoustic resonator (FBAR) device fabricated on a specially designed multilayered Bragg reflector part. Very thin chromium adhesion layers (0.03 μm thick) were additionally deposited to improve the quality of the Bragg reflector and some thermal treatments were performed to improve the resonant characteristics of the FBAR device. At the operating frequency of ∼2.7 GHz, excellent resonant characteristics were observed in terms of return loss and quality factor, and effective electromechanical coupling coefficient.     

Various transmission electron microscopic techniques to characterize phase separation - illustrated using a LaF3 containing aluminosilicate glass

Various transmission electron microscopy techniques which are useful for the characterization of phase-separation phenomena in glass materials are exemplarily demonstrated at a 40 SiO₂-30 Al₂O₃-18 Na₂O-12 LaF₃ glass. It is shown that direct imaging of phase-separated regions possesses manifold advantages over the traditional replica technique, particular if the feature size approaches the nano-scale. Although surface replica can be accomplished effortless and made a great leap in glass structure research possible, the method is indirect, i.e. requires a deep understanding of the chemical attack leading to the surface topography eventually imaged. Moreover, surface replicas reach their limits for nanosized features due to the inherent structure of the deposited replica film.