129Xe NMR研究MCM-22分子筛中的Xe-Xe作用

¹²⁹Xe NMR 测量得到Xe-Xe碰撞产生的δ_Xe-Xe，该值要比自由 的Xe和在NaY、CaA分 子筛中的值小很多. 通过一定的理论分析，证明在MCM-22分子筛超笼中的Xe-Xe碰撞作用类似于一维气体碰撞，同时表明δ_Xe-Xe也和δ_S（由Xe与孔壁碰撞产生 的化学位移）一样与分子筛的孔道结构密切相关.      

Synthesis and characterization of highly textured Pt–Bi thin films

Pt–Bi films were synthesized on glass and thermally oxidized silicon substrates by e-beam evaporation and annealing. The structures were characterized using X-ray diffraction (XRD) and transmission electron microscopy/selected area electron diffraction (TEM/SAED) techniques. Single-phase PtBi was obtained at an annealing temperature of 300°C, whereas a higher annealing temperature of 400°C was required to obtain the highly textured γ-PtBi₂ phase. TEM/SAED analysis showed that the films annealed at 400°C contain a dominant γ-PtBi₂ phase with a small amount of β-PtBi₂ and α-PtBi₂ phases. Both the PtBi and γ-PtBi₂ phases are highly textured in these two kinds of film: the c-axis of the hexagonal PtBi phase is mostly in the film plane, whereas the c-axis of the trigonal γ-PtBi₂ phase is perpendicular to the film plane. The electrical resistivity of the film with the γ-PtBi₂ phase was smaller by one order of magnitude than that of the film with the PtBi phase.     

超极化129Xe磁共振分子影像学

磁共振分子影像学发展的主要瓶颈之一在于灵敏度的限制,基于激光光泵和自旋交换技术能获得增强4~5个量级的超极化¹²⁹Xe磁共振信号,因此超极化¹²⁹Xe磁共振分子影像学相对于传统MRI在灵敏度上表现出巨大的优势. 围绕提高灵敏度这一核心MRI问题及其在科学研究中的应用,该文介绍了目前基于超极化¹²⁹Xe的生物分子探针的基本结构和原理,阐述了与之相关的分子影像学方法和技术,同时评述了当前的最新研究进展和发展方向.     

激光极化129Xe的生物磁共振成像研究进展

激光光抽运自旋交换方法能够极大地增强＾１２９Ｘｅ核自旋极化,其获得的非平衡极化度远远高于在相同磁场里玻尔兹曼平衡值。     

Preferable solar cell absorber – Near stoichiometric or stoichiometric CBD CIAS thin films?

Near stoichiometric and stoichiometric [CuIn_(1 − x)Al_(x)Se₂] (CIAS) thin films are prepared by chemical bath deposition (CBD) technique. X-ray diffraction (XRD) analysis have been employed to estimate the structural properties of CBD CIAS thin films and also to identify the near stoichiometric in particular defect free Cu-poor CBD CIAS thin films as preferable solar cell absorber material.     

超极化129Xe自动收集-升华装置研究

因其较高的核自旋极化度所提供的探测灵敏度,超极化¹²⁹Xe气体已被成功应用于动物和人体磁共振成像（MRI）.但是,在超极化¹²⁹Xe的收集-升华过程中,多种因素会导致¹²⁹Xe核自旋弛豫,进而限制其应用范围.本文通过理论模型分析和实验测量,验证了温度、磁场、螺旋冷阱材质等对冷冻恢复过程中超极化¹²⁹Xe弛豫的影响;同时,测量了自动收集-升华装置的稳定性.研究结果表明,升华方式和冷阱材质对¹²⁹Xe极化度损耗的影响显著;自制收集-升华装置的自动化程度高、长时间稳定,¹²⁹Xe极化度的恢复率可达到85.6% ± 4.7%.本研究非常有助于提升超极化¹²⁹Xe在动物和人体MRI中的使用效率.     

The optical properties of MgxZnl-xO thin films

Mg_xZn_1-xO thin films have been prepared on silicon substrates by radio frequency magnetron sputtering at 60℃. The thin films have hexagonal wurtzite single-phase structure and a preferred orientation with the c-axis perpendicular to the substrates. The refractive indices of Mg_xZn_1-xO films are studied at room temperature by spectroscopic ellipsometry over the wavelength range of 400--760\,nm at the incident angle of 70℃. Both absorption coefficients and optical band gaps of Mg_xZn_1-xO films are determined by the transmittance spectra. While Mg content is increasing, the absorption edges of Mg_xZn_1-xO films shift to higher energies and band gaps linearly increase from 3.24.eV at x=0 to 3.90\,eV at x=0.30. These results provide important information for the design and modelling of ZnO/ Mg_xZn_1-xO heterostructure optoelectronic devices.     

Depolarization of backscattered linearly polarized light from ZnO thin film

The depolarization behavior of backscattered linearly polarized light from ZnO thin film was investigated experimentally.The results show that the characteristics are related to both the polarization orientation and wavelength of linearly polarized incident light.When the incident light is s-polarized,the depo- larization behaviors are different for different wavelengths.When the incident light is p-polarized,the depolarization behaviors,on the contrary,are similar for different wavelengths.In addition,there is an optimal incident angle for depolarization of linearly polarized light with different wavelengths,which is equal to their effective Brewster angles,respectively.     

激光极化129Xe核自旋弛豫率的测量

由弱磁场下光泵自旋交换、强磁场中核磁共振测量方法,获得激光极化低压同位素¹²⁹Xe气体的核自旋弛豫率1/T₁及其与N₂气压力、环境温度的关系.结果表明:在291K的室温下,对于0~11 333.05Pa的N₂气压力范围,1/T₁随着N₂气压力的增加而增大;N₂气压力为1 466.63Pa时,1/T₁随着样品温度从234K到292K增高而减小     

129Xe核自旋极化转移增强分子的核磁共振信号

激光极化的129Xe核具有极高的非平衡极化度和长的弛豫时间,这一特点使得它能够极化转移增强液体、固体或者固体表面分子中原子核自旋极化。因而,提高了它们的核磁共振探测灵敏度和扩展了在材料和表面科学研究中的应用。综述激光极化129Xe核与其它分子中原子核之间的极化转移研究与进展,介绍相关物理机制和参数的测量。     

Design of anisotropic reflector with birefringent thin films

A novel design for dielectric anisotropic mirrors with birefringent thin films for normal incidence is presented. This mirror consists of a stack of quarter-wave biaxial layers. The biaxial anisotropic layers can be fabricated by oblique deposition. The reflectance is different for two linear polarizations of light incidence on the mirrors. As a numerical example, the design is carried out on glass with TiO2 and ZrO2. These thin films could be applied to anisotropic reflective devices for lasers.     

Characterization of Fe–Nb sputtered thin films

Structure, composition and chemical behavior of co-sputtered Fe–Nb thin films are analyzed by different techniques, as conversion electron Mössbauer spectroscopy, x-ray photoelectron spectroscopy and x-ray diffraction. It is shown that oxygen is determinative in hindering the Fe–Nb alloy formation and, as a result, Fe_1−xO and Nb₂O₅ occur in significant amounts, even in vacuum. In spite of the oxygen role, a Fe–Nb alloy is formed in little amounts, which increase as the Nb content is increased. The increase of the Nb content is also related with the increase of Fe_1−xO and with a decreasing of the metallic Fe present. Mössbauer data indicate the Fe–Nb phase present is the Fe₂Nb Laves phase.     

Preparation and characterization of iron–molybdate thin films

Mixed Fe–Mo oxides are used in industrial catalytic processes of selective oxidation of methanol to formaldehyde. For better understanding of the structure-reactivity relationships of these catalysts we aim to prepare well-ordered iron–molybdate thin films as model catalysts. Here we have studied Mo deposition onto Fe₃O₄ (111) thin films produced on Pt(111) as a function of Mo coverage and annealing temperature using LEED, AES, STM and IRAS. At low temperatures, the iron oxide film is covered by Mo = O terminated molybdena nanoparticles. Upon oxidation at elevated temperatures (T > 900 K), Mo species migrate into the film and form new bonds with oxygen in the film. The resulting films maintain the crystal structure of Fe₃O₄, and the surface undergoes a (√3 × √3)R30° reconstruction. The structure is rationalized in terms of Fe substitution by Mo in the surface layers.     

Nanostructure and thermal-optical properties of vanadium dioxide thin films

A novel nanopolycrystalline structure of vanadium dioxide thin films is deposited on silicon or fused silica substrates by reactive ion sputtering and followed by an annealing. The characteristic analysis shows that the films have a columnar nanostructure with an average grain of 8 nm. The resistivities as a function of ambient temperatures tested by four-point probes for as-deposited films present that the transition temperature for nanostructure of vanadium dioxide films is near 35 ℃ which lowers about 33 ℃ in comparison with the transition temperature at 68 ℃ in its microstructure.     

Ferromagnetism in ZnCoO thin films deposited by PLD

Multilayer structures A–B–A⋅⋅⋅ consisting of alternating layers of a metal A and a semiconductor B can show large anisotropy in their transport properties. In tilted multilayer structures, where layer planes and sample surface include a nonzero tilt angle, nonvanishing off-diagonal elements in the sample’s transport tensors lead to transverse Seebeck and Peltier effects. Achievable temperature differences and figures of merit for transverse Peltier cooling are discussed and compared with experiments, coefficients of performance for transverse power generation are calculated.     

Superconductivity in amorphous thin films of tin–copper

The properties of the superconducting state in the amorphous Sn_1?xCu_x thin films were characterized. The concentration of copper changes in the range from 0.08 to 0.41. The calculations were conducted in the framework of the strong-coupling formalism, wherein the Eliashberg functions determined in the tunnel experiment were used. The value of the Coulomb pseudopotential equal to 0.1 was adopted. It will be shown that the critical temperature (T_C) decreases from 7 to 3.9 K. The ratio, R_Δ = 2Δ(0)/k_BT_C, differs from the BCS value: R_Δ ∈ <4.4, 3.95>, where Δ(0) represents the order parameter. Similarly behave the ratios: R_C = ΔC(T_C)/C^N(T_C) ∈ <2.2, 1.75> and R_H = T_CC^N(T_C)/H²_C(0) ∈ <0.141, 0.154>. The parameter ΔC(T_C) is the specific heat jump, C^N(T_C) denotes the specific heat of the normal state and H_C(0) is the thermodynamic critical field.     

Various properties of sputter-deposited Ta–Ru thin films

This paper discusses several structural, electrical and oxidation characteristics of co-sputtered Ta–Ru alloy films on oxidized Si-substrates. From X-ray examination, the Ta₁Ru₁ phase has formed and dominates in the compositions exceeding 54 at.% Ru content. The resistivity of the Ta–Ru thin films can reach a maximum of ∼320 μΩ cm in the composition range between 35 and 54 at.% Ru. After thermal treatment in air (600°C, 1 h), Ru-rich samples show a less increase in resistivity than Ta-rich ones. The observed preferential oxidation of Ta in the Ta–Ru samples can be further interpreted by thermodynamic calculations. The Ta-rich surface oxide is believed to be responsible for the passivating ability of the Ru atom toward oxidation at high temperatures. This results in the Ru of the metallic state though the oxidation of Ta occurs.     

All-optical switching effect based on azodye-doped polymer thin films

A simple all-optical switch based on photoinduced birefringence effect is demonstrated in azo dye (DR1) doped polymer (PMMA) thin films. The all-optical switching effect has been studied at different control beam power and different temperatures of the sample. With a control power of 30.7 mW and at 56 ℃, the response time of the switching is less than 5 ms, and the depth of the modulation reaches 80%.     

超极化129Xe磁共振波谱和成像及在生物医学中的应用

文章简要介绍了磁共振波谱和成像的基本原理和对限制其灵敏度的挑战,详细阐述了为增强磁共振信号而制备超极化129Xe的物理机制,论述了129Xe在生物组织中的溶解性以及化学位移的特异性,综述了当前超极化129Xe在肺部、脑部成像领域的研究进展和在临床方面应用所取得的有代表性的研究成果,并讨论了基于超极化129Xe分子生物探针的超灵敏磁共振技术的研究前景,最后对超极化129Xe在生物医学领域的应用与发展作了展望.