利用发射光谱进行常压介质阻挡放电等离子体诊断及其在材料表面改性上的应用(英文)

使用介质阻挡放电光谱诊断装置,对常压介质阻挡放电在材料改性过程中的等离子体发射光谱进行测量,记录和比较了空气、氦气和氩气常压介质阻挡放电等离子体发射光谱,并运用氩元素谱线的相对强度来诊断电子温度等物理参量,以达到对材料表面改性过程的实时监控。工作的结果对常压介质阻挡放电及其在材料改性上的应用具有重要的意义     

Bulk Sn1−xMnxO2 magnetic semiconductors without room-temperature ferromagnetism

Polycrystalline Sn_1−xMn_xO₂ (0≤x≤0.05) diluted magnetic semiconductors were prepared by solid-state reaction method and their structural and magnetic properties had been investigated systematically. The three Mn-doped samples (x=0.01, 0.03, 0.05) undergo paramagnetic to ferromagnetic phase transitions upon cooling, but their Curie temperatures are far lower than room temperature. The magnetization cannot be attributed to any identified impurity phase. It is also found that the magnetization increases with increasing Mn doping, while the ratio of the Mn ions contributing to ferromagnetic ordering to the total Mn ions decreases.     

Preparation and characterization of ZnO nanorods from NaOH solutions with assisted electrical field

ZnO naorods on ZnO-coated seed substrates were fabricated by solution chemical method from Zn(NO₃)₂/NaOH under assisted electrical field. The working mechanism of electrical field was analyzed and the factors affecting the rod growth such as potential, precursor concentration and growth temperature were elucidated. The structural and optical properties are characterized by SEM, TEM, XRD, HRTEM and UV-vis. The results indicated that the nanorods have wurtzite structure without electrical field and are primarily of zincite structure under electrical field; when the electrical field is 1.1-1.3 V, not only the elevation of ion diffusion and adsorption lower the crystallite/solution interfacial energy and then the crystal nucleation barrier by increasing charge intensity, but also the production of H⁺ through oxidation of OH⁻ increases properly the degree of solution supersaturation near the substrate, and thus lowers the activation energy. Both the two processes do favor to rod growth. With increasing precursor concentration in this system, the average diameter and length of ZnO nanorods increase, leading to decreasing of optical transmittance. The maximum rod growth rate at given concentration of Zn²⁺ occurs at a specific temperature.     

Electric-field control of exchange bias in multiferroic epitaxial heterostructures

The magnetic exchange between epitaxial thin films of the multiferroic (antiferromagnetic and ferroelectric) hexagonal YMnO3 oxide and a soft ferromagnetic (FM) layer is used to couple the magnetic response of the FM layer to the magnetic state of the antiferromagnetic one. We will show that biasing the ferroelectric YMnO3 layer by an electric field allows control of the magnetic exchange bias and subsequently the magnetotransport properties of the FM layer. This finding may contribute to paving the way towards a new generation of electric-field controlled spintronic devices.     

薄膜法布里-珀罗滤光片中的超棱镜效应

基于薄膜法布里珀罗滤光片在其峰值波长处具有较大群延迟的特性,设计并从实验上验证了光束倾斜入射时这种结构中存在的超棱镜效应。根据光学薄膜理论中的特征矩阵法,数值模拟计算了器件的群延迟和空间色散曲线,镀制并对器件进行了测试。测试结果表明器件在透射峰值波长处因超棱镜效应引起的空间色散最大位移值达到65μm,与理论计算结果非常吻合;相对于传统的光栅和棱镜器件而言器件具有更高的空间角度色散,实际测试在784.5 nm至786.5 nm波长范围内器件的角色散达到30°/nm。     

The intruder orbitals in superdeformed bands and alignment additivity of odd–odd nuclei in the region

The particle-number conserving (PNC) method for treating the cranked shell model with monopole and quadrupole pairing correlations is used to study the superdeformed (SD) bands observed in odd–odd nuclei in the A190 mass region. Spins are assigned to the levels in these bands. The microscopic mechanism of the ω evolution of the dynamic moment of inertia J⁽²⁾ for these SD bands are analyzed. In particular, the major roles of the j_15/2 neutron and i_13/2 proton orbitals played in the SD bands are investigated in detail by contributions to J⁽²⁾ from each cranked orbital and interference terms between two cranked orbitals. Additivity in the A190 mass region is investigated. The experimental evidence for additivity of alignments in ¹⁹²Tl can be reproduced by our calculations.     

Spatial decorrelation in broad-area edge-emitting semiconductor amplifiers

We analyze experimentally the spatio-temporal dynamics of the transverse structures appearing in broad area edge-emitting semiconductor amplifiers under CW optical injection. We demonstrate that, in certain conditions, the light reflected by the system exhibits a multipeaked structure whose dependence on the parameters suggests an interpretation in terms of cavity solitons. These structures can exhibit self-pulsations with periods of the order of few milliseconds, which we explain in terms of regenerative thermal oscillations. In a particular device, we generate two single-peak structures which are spatially uncorrelated, as required for cavity solitons. A microscopic model shows good agreement with the main body of the experimental results.     

Structural characteristics of ultra-low k SiO<Subscript>2</Subscript> thin films prepared using a molecular template

Nanoporous SiO₂ thin films with ultra-low dielectric constants were synthesized using a molecular template method. Uniform films with pore size between 10 and 20 nm were obtained as observed by N₂ adsorption/desorption isotherms and transmission electron microscopy. Fourier transform infrared spectroscopy (FTIR) and differential thermal analysis were carried out to investigate the effect of n-hexane washing on structural properties before and after the surface modification process. The results showed that –OH bonds were substituted with –CH₃ bonds in the films as a result of modification of trimethylchlorosilane (TMCS)/n-hexane solution. Four kinds of model were used to analyze the relationship between porosity and dielectric constant of the films, where the dielectric constant was determined from capacitance-voltage measurements. The investigation indicated that the corresponding relationship was in accord with that estimated by the Rayleigh model.     

Barium ferrite (BaFe12O19) thin films prepared by pulsed laser deposition on MgO buffered Si substrates

Barium ferrite (BaFe₁₂O₁₉) thin films have been deposited by pulsed laser deposition (PLD) on Si substrates with MgO underlayers. The films were deposited in oxygen atmosphere by excimer laser (=248 nm, pulse duration=23 ns) in the temperature range 750–900 °C. The experiments showed that the substrate temperature has remarkable effect on the films magnetic and structural properties. The BaFe₁₂O₁₉ films deposited at 900 °C in 200 mTorr oxygen showed some perpendicular orientation, with a perpendicular squareness of 0.5 and an in-plane squareness of 0.3. Such thin BaFe₁₂O₁₉ films have platelet grains with a size of about 300 nm. The perpendicular saturation magnetization and coercivity are 185 emu/cm³ and 1.4 kOe, respectively. PACS 81.15.Fg.; 75.70.Ak; 75.50.Pp; 68.55.j     

Phase-resolved laser Raman scattering and laser Doppler velocimetry applied to periodic instabilities in a gas turbine model combustor

The understanding of periodic flame instabilities belongs to the major challenges in modern combustion research and technology and is of special importance for lean premixed gas turbine combustion. This paper presents experimental investigations in a gas turbine model combustor using laser diagnostic techniques. A partially premixed CH₄/air flame operated at a thermal power of 10 kW at atmospheric pressure and an overall equivalence ratio of 0.75, which exhibited thermoacoustic oscillations at a frequency of 290 Hz, was investigated. Phase-locked laser Raman scattering was applied in order to determine the major species concentrations, temperature, and mixture fraction. In addition, laser Doppler velocimetry (LDV) was used separately for the measurement of the axial and radial velocity components. The measurements revealed pronounced phase-dependent variations of the velocity and the temperature, species, and mixture fraction distributions. The combined Raman and LDV results also enabled the determination of molecular species fluxes which showed that the fuel and air supply rates both varied during an oscillation cycle by ±33% but with a phase shift of 80 between them. The correlations between temperature and mixture fraction revealed strong deviations from equilibrium composition and temperature, and their phase-dependent changes reflected the transport and mixing processes near the nozzle. The emphasis of the paper lies on the demonstration of the potential of phase-locked laser Raman scattering for the study of phenomena of periodic flame instabilities. PACS 33.20; 39.30; 47.27; 47.70; 82.33; 82.40